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Contents
Acknowledgements i-ii
List of Figures iii-vii
List of Tables viii
Chapter 1– Introduction 1-7
1.1 Background information 1-2
1.2 Problem delineation 2-3
1.3 Present status and scope of work 3-5
1.4 Objectives 5
1.5 Implication of work
1.6 Organization of thesis
6
7
Chapter 2– Geology and Stratigraphy of the Marwar Supergroup 8-14
2.1 Introduction 8-9
2.2 Geology and Classification of the Marwar Supergroup 9-11
2.3 Study area: Jodhpur and surrounding areas 11-12
2.4 Marwar Supergroup: age assessment 13-14
Chapter 3 – Methodology 15-22
3.1 (a) Field work 15
(b) Laboratory work 15-16
3.2 Petrography 16
3.2.1 Sandstone section 17-18
3.2.2 Giant Nodule
18-20
3.2.3 Carbonate Investigation 20-21
3.2.4 Nagaur Sandstone 21-22
Chapter 4 – Systematic Palaeontology 23-95
4.1 Palaeontology 23
4.1.1 Animal body fossil from the Jodhpur Group 23-36
a. Five-armed body fossil 23-26
b. Marsonia artiyansis 27-33
c. Hiemalora 34
d. Aspidella 34-35
4.1.2 Plant fossils 37-51
4.1.3 Microbial Mats 52-69
4.1.4 Stromatolites from the Bilara Group 70-72
4.1.5 Trace fossils from the Nagaur Group 73-95
Chapter 5 – Biozonation and Correlation 96-109
5.1 Biozonation 96
A. Body fossils 96-98
B. Organo-sedimentary Structures 99-101
C. Trace fossils 101-103
D. Microfossils 103-104
5.1.1 Discussions 104-105
5.2 Correlation 106-109
Chapter 6- Conclusions 110-114
References 115-126
i
ACKNOWLEDGEMENTS The thesis is the end of journey for obtaining my Ph.D. but heralds the beginning of a new era in the field of research. It is the thesis that builds a passion for getting updated in the field of research and creates enthusiasm for keeping us on track. However, the completion of thesis seems to be partial without the support and encouragement of numerous people including mentor, well-wishers, friends, colleagues and family. So most humbly, I would like to thank all those people who made this thesis possible and an unforgettable experience for me. It is a pleasant task to express my thanks to all those who contributed in many ways to the successful completion of this study and made it an unforgettable moment.
At this moment of accomplishment, I pay respect to Dr. S. Kumar whose guidance, tremendous support, critical analysis of my work, depth of views and continuous encouragement. Due to his incredible guidance and valuable suggestions, I have successfully overcome many hurdles of the thesis work and learned a lot.
I am also extremely indebted to my mentor and supervisor Dr. A.K. Jauhri, to accomplish my research work. I owe his greatness for selecting me as a student at the critical stage of my Ph.D. I warmly thank, for his valuable advice, constructive criticism and his extensive discussions regarding my work.
It feel privileged in acknowledging Dr. Sunil Bajpai, Director, Birbal Sahni Institute of Palaeobotany, Lucknow for his kind support and motivation for my thesis with new and better directions.
It is my humble submission to give regards to Dr. Mukund Sharma, Scientist F, Birbal Sahni Institute of Palaeobotany, Lucknow for his continuous and sincere encouragement and inspiration for my research work and boosting me with proper guidance for research completion.
I pay respectful thanks to Prof. K.K. Agarwal, Head, CAS in Geology, University of Lucknow, Lucknow, for providing me with adequate facility and soothing environment in the department.
I gratefully acknowledge the suggestion and the help received from Dr. Adolf Seilacher, Tübengen University, Germany and Dr. Nigel Hughes, University of California, during the field work.
My sincere thanks are due to Prof. I.B. Singh, Prof. Ashok Sahni and Prof. M.P.Singh for their understanding, encouragement and personal attention for providing valuable ideas for my thesis work. I express my gratitude to Prof. A.R. Bhattacharya, Prof. N.L. Chhabra, Prof D.D. Awasthi, Prof. Vibhuti Rai, Prof. R. Bali, Dr. Ajai Mishra, Dr. D.S. Singh, Dr. S. Sensarma, Dr. Munendra Singh, Dr. A.K. Kulshrestha and Mr. Ajay Arya for their help and cooperation.
I express deep sense of gratitude to Dr. D.M. Banerjee, Delhi University, for valuable guidance in the field. I am also thankful to Dr. Purnima Srivastava, Department of Geology, University of Lucknow for her constant support and valuable suggestion.
I would also like to thank my seniors and colleagues specially Dr. Naval K. Tewari, Dr. Atal B. Shukla, Dr. Ajay P. Singh, Dr. Alok Thakur, Dr. Yogendra Bhadauria, Mrs. Akansha Bhadauria, Dr. Anju Verma, Dr. Biswajeet Thakur, Dr. Anju Saxena, Dr. Amit K. Singh, Dr. Santosh Kumar Pandey, Dr. Vikram Bhardwaj, Dr. S. Nawaz Ali, Dr. Kamlesh K. Verma, Dr. Krishna Gopal Mishra, Dr. Pankaj Sharma, Mr. Sushant Singh, Dr. Amit Awasthi, Mr. Saurabh Rastogi, Mr. Kalyan Krishna, Mr. Ashish Sharma, Mrs. Nivedita Sarkar and Mr. Ankur
ii
Kashyap for help and discussion in compilation of this work. Late Mr. P.K. Joshi who of great help in finalizing the figures during the early days of my research work is thankfully acknowledged.
I would like to express my particular appreciation of Dr. Pranay Vikram Singh for his useful suggestions and constant motivation towards completion of this work. His critical remarks on findings of research work have helped me to improve my work. I am indebted to my friends Mr. Dheerendra Kumar, Mr. Chandra Prakash, Mr. Amit Singh, Mr. Dharmendra Kumar Jigyasu, Mr. Shailendra Kumar Prajapati, Mrs. Droupti Yadav, Ms. Nigar Jahan, Ms. Purnima Sharma, Ms. Shasi Verma, Mr. Rohit Kuvar, Mr. Parijat Mishra, Mr. Gaurav Joshi and Mr. Shakti Yadav for providing stimulating and congenial environment. My warm appreciation is due to Dr. Pawan Govil, Mr. Veeru Kant Singh, Dr. Arjun Singh Rathore, Ms. Bandana Dimri and Mr. Keshav Ram for providing me hospitable research environment. My sincere thanks goes to Mr. Ashok Verma and Mr. Anuj Saxena for his technical support in times of urgent need and requirements.
I take this opportunity to say heartfelt thanks to Late Mr. B.B. Singh and Late Mrs. Sheela Singh for blessings and source of inspiration. Thanks are also due to Mr. Anand Singh Chauhan and Mrs. Mandavi Singh Mr. Vishwajeet Singh for their moral support.
I feel highly indebted to Ms. Arunabha Singh for their unconditional moral support and help me in finalizing my thesis work.
I also wish to thanks all the non-teaching staff of Geology Department for their constant support.
Words fail me to express my gratitude towards my father Late Mr. Abdul Salim who gave me freedom to choose my path and always encouraged me to achieve my goal. He was always beside me during the happy and hard moments to push me and motivate me. This thesis is dream of my father and is fulfilled with the grace of God.
It’s my fortune to gratefully acknowledge the support of my family members My mother Mrs. Afrooz Khatoon, My elder brothers Mr. Javed Ahmad, Mr. Suhail Ahmad and my sisters Ms. Zarina Parveen, Ms. Shahnaaz for their moral support, encouragement all through my work. I owe everything to them.
I take this opportunity to sincerely acknowledge the Department of Science and Technology (DST)(vide letter no SR/S4/ES-348/2008), Government of India, New Delhi, for providing financial assistance in the form of Junior Research Fellowship which buttressed me to perform my work comfortably and later on SRF fellowship awarded by CSIR, New Delhi (Fellowship no. 09/528(0019)/2013 EMR-I).
Besides this, several people have knowingly and unknowingly helped me in the successful completion of this project.
(Shamim Ahmad)
iii
List of Figures
Page No.
Fig. 1.1 : Generalized geological map of the Marwar Supergroup (redrawn and modified after Pareek, 1981).
3
Fig. 3.1 : Well developed Salt Pseudomorphs of various shapes in shale on the
road side on Bhopalgarh - Dhanapa road. 17
Fig 3.2 : Photomicrograph of Quartz arenite of Jodhpur Sandstone; a and b)
Showing the compact arrangement of quartz grain in cross nicol and PPL respectively; c and d) Quartz grain showing subrounded to rounded in cross nicols.
18
Fig. 3.3 : Giant nodules seen in the Jodhpur Sandstone. There is no lithologic
difference between the host rock and the lithology of the nodule, except the hardness. a. The host rock is seen both at the base as well as at the back of the nodule, in which the nodule is embedded, b. The host rock is also seen associated with the nodule, c. Outer margin of the giant nodule showing parallel differential markings in the sandstone, d. Transverse section of the giant nodule showing clearly marked circular margin and lack of any internal structure; the entire surface looks homogenous, e. and f. Photomicrographs of sandstone forming the nodule and host rock. The sandstones are made up of subangular to subrounded detrital quartz grains cemented together by silica (under crossed nicols). e. Sandstone of the nodule; f. Sandstone of the host rock.
19
Fig. 3.4 : Photomicrograph of Limestone of Bilara Group. a-b) Gotan limestone
showing microcrystalline calcite in cross nicol and PPL respectively. Quartz vein is also observed in the thin section.
21
Fig. 3.5 : Photomicrograph of Quartz arenite of Nagaur Sandstone; a and b)
Showing the compact arrangement of quartz grain in cross nicol and PPL respectively.
21
Fig. 4.1 : Geological and location map of the Marwar Supergroup, western
Rajasthan, showing study area (after Pareek, 1984). 24
Fig. 4.2 : Litholog of the fossil-bearing horizon, Jodhpur Sandstone, Sursagar
mine, western Rajasthan. 25
Fig. 4.3
: Five-armed body fossil on the bedding surface of the Jodhpur Sandstone. A and C) Five-armed body fossil; B) Line diagram of the fossil seen in A and B) Enlarged view of (C) showing a disc-like structure at the centre of the body fossil.
25
Fig. 4.4 : A, Location map of the Jodhpur area, western Rajasthan. B, Geological
map of the Jodhpur area, showing fossil locality, (Redrawn after Raghav et al., 2005).
27
Fig. 4.5 : Detailed geological map of the Artiya Kalan area, Jodhpur District,
Rajasthan showing fossil locality (Redrawn after Raghav et al., 2005). 28
iv
Fig. 4.6 : Litholog of the fossil-bearing horizon, Jodhpur Sandstone, Artiya Kalan
area, western Rajasthan. 28
Fig. 4.7 : A) Field photograph of the Jodhpur Sandstone; arrow marks the position
of the fossil-bearing horizon; B) Section of the Jodhpur Sandstone (Sonia Sandstone) exposed in a pit near the Artiya Kalan area, district Jodhpur. The lower part is made up of sandstone and the upper part is made up of shale and siltstone which has yielded the fossils; C) Marsonia artiyansis shows wrinkled margin at the outer bell with four radial arms originating from the central part of the medusa, Sample no. SK/AK-1; D) Specimen showing smooth outer margin with elevated central disc up to 2mm in height, Sample no. SK/AK-2 and E) (i) Upper surface of the poorly preserved medusa showing wrinkled outer margin. When sample in E (i) was chipped it yielded a sample E (ii) which on its sole shows marks of the radial arms with negative relief and E (iii) is its counterpart which shows arms in positive relief.
31
Fig. 4.8 : Marsonia artiyansis shows variation in size as well as in the outer
margin from smooth to wrinkled. A) (sample no. SK/AK-21) and B) (sample no. SK/AK-23), Smooth outer margin with dislocated radial arms; C) “a” and “b” are the counter parts of the same specimen; “a” shows raised central part showing central disc with four radial arms; outer margin smooth, sample no. SK/AK-22 a and b. Specimen “b” shows depressed radial arms, D) Specimens “b” is the chipped off part of specimens “a”, showing additional circle in the middle and minute central pit at the central part (specimen “b”), sample no. SK/AK-32 a and b; E) Bead-like structure is seen in photograph marked by arrow, sample no. SK/AK-3 and F) Specimen showing preservation of many wrinkle layers, sample no. SK/AK-16.
32
Fig. 4.9 : Simplified sketch of Marsonia artiyansis. A) Longitudinal section of the
umbrella or bell and B) Oral view of the animal showing gonads and oral arms. The shaded area represents the thinner part of the bell.
33
Fig. 4.10 : Field photographs of Hiemalora from Sursagar mine, Jodhpur
Sandstone. a) Showing the specimen deposited over the ripple marks. b) Radiating arms originating from the centre of the specimen.
34
Fig.4.11 : Field photographs of Aspidella from Sursagar mine, Jodhpur Sandstone.
A) Showing well preserved Aspidella with solid outer rim (marked by an arrow); b) Close up photograph of Aspidella showing the circular morphology.
35
Fig. 4.12 : Field photograph of fossil bearing locality. (1) Showing the horizon
from where the fossils have been collected. (2) Trail marks in fine grain sandstone. (3 and 4) Showing well preserved network of burrows.
36
Fig. 4.13 : Geological and location map of the Jodhpur area, western Rajasthan (after Pareek, 1984).
38
Fig. 4.14 : Litholog of the fossil-bearing horizon, Sursagar mine area, Jodhpur, 39
v
western Rajasthan. Fig. 4.15 : Plant fossils of the Jodhpur Sandstone, Sursagar area, Jodhpur, western
Rajasthan. A) The holotype of Vendophycus rajasthanensis showing thallus with swollen tips referred as beads; arrow marks the beads; B) Close-up view of (A) showing the swollen part at the tip. C) Development of microbial mat over the thallus of plant fossil on the bedding surface; D) Vendophycus rajasthanensis showing thallus with smooth wall preserved on the top of the rippled surface of the medium grain sandstone. E) Thallus preserved as hollow tube; F, Development of thallus showing fertile structures at their tips as beads. G, Branching pattern of Vendophycus rajasthanensis seen on the bedding surface; H) Figure shows overlapping of thallus as well as splitting tendency of thallus; I) Magnified view of (D) showing well developed fertile structure (oogonia); J) Close up view of (K) showing cf developing synzoospore and K) Figure shows well developed thallus with antheridia and oogonia, marked by arrows “a” and “b” respectively.
42
Fig. 4.16 : Vendophycus sursagarensis reported from the Jodhpur Sandstone,
Sursagar area, Jodhpur, western Rajasthan. A) Photomicrograph showing the contact of the host rock and the thallus of the plant fossil. The dotted line marks the contact; B) Well developed branching pattern in the thallus; C) View of the thallus showing regular pattern of branching; D) Swollen structures at the tip of the thallus; preserved as negative hyporelief; E) Swollen structure seen at the tip of the thallus; F) Elliptical size of the thallus in cross sectional view, preserved in sandstone and G-H) Typical characteristic feature of splitting of the thallus at middle observed in Vendophycus sursagarensis.
45
Fig 4.17 : Plant fossil Indophycus marwarensis reported from the Jodhpur
Sandstone, Sursagar area, Jodhpur, western Rajasthan. A) Indophycus marwarensis showing shrub-like profuse branching with abundance of bead like structure on the thallus preserved on the top of the bedding plane; B) Figure shows hollow depressions in the middle of the thallus, marked by the arrow; C) Excellent preservation of fertile structures (oogonia) closely attached with the thallus; D) Closely attached bead like structure at the wall of thallus with bulbous tip; E) Close up view of the thallus showing closely attached beads making the outer wall serrated which is marked by the arrow; F) Photograph showing development of thallus with well preserved beads as fertile structures. Arrow marks the structures and G, Magnified view of fertile parts of plant; antheridia and oogonia are marked by the arrows “a” and “b” respectively.
47
Fig. 4.18 : Schematic diagrams of Jodhpur plant. A, Vendophycus sursagarensis, B,
Vendophycus rajasthanensis C, Indophycus marwarensis. D, Schematic diagram depicts the mode of occurrence of the Jodhpur plant. The plant is embedded within the microbial mat in the Jodhpur Sandstone.
51
Fig. 4.19 : Geological and location map of the Marwar Supergroup western
Rajasthan, showing study area (after Pareek, 1984). 53
Fig. 4.20 : Litholog of the MISS (Microbially Induced Sedimentary Structures) 54
vi
bearing horizon of the Jodhpur Group. Fig. 4.21 : Field photograph of Microbially Induced Sedimentary Structures (MISS)
reported from the Jodhpur Sandstone, western Rajasthan. A) Incomplete ripples over microbially flat laminated surface (coin diameter = 2.4 cm); B, C and D) Various types of well preserved sinusoidal, curved and straight wrinkle marks on the bedding surface (coin diameter = 2.4 cm and lens cap diameter = 5.7 cm); E and F) “Bun shaped” microbial structures with positive relief (maximum elevation from the bedding plane = 3.5 cm), the growth of the “bun shaped” structure not effected the ripples (lens cap diameter = 5.7 cm).
57
Fig. 4.22 : A) Well developed cracks in the sandstone (scale = 12cm); B) Cracks
along the ripple crests bounded by sharp ridges (marked by arrows) by both sides of the crack (coin diameter = 2.3cm); C) Inverted flute structure in sandstone illustrates surface pavement in which sand has accumulated forming small drumlin shaped inverted flute cast (coin diameter = 2.4cm); D) Magnified view of Inverted flute Structure (scale bar = 2cm); E) Well preserved Aristophycus around a large sandstone clast showing primary, secondary and tertiary bifurcations (coin diameter = 2.4cm) and F) Close up of Aristophycus: an inorganically formed structure showing well developed bifurcations which is possibly formed by action of water current and microbial mat (coin diameter = 2.4cm).
61
Fig 4.23 : A) Arumberia banski showing presence of small ridges on bedding
surface separated by concave furrows (coin diameter = 2.4cm); B and C) Rameshia rampurensis showing very small mounds or blisters making the entire bedding surface granular (coin diameter = 2.4cm); D) and E) Blisters are arranged in a linear fashion (coin diameter = 2.4cm) and F) Transitional form exhibiting characteristics both Arumberia and Rameshia, (coin diameter = 2.4cm).
65
Fig. 4.24 : A) Rameshia anastomose showing small mound like structure forming
anastomose pattern (coin diameter = 2.3cm); B) Jodhpuria circularis showing ridges forming circular to concentric pattern in the central part while in the outer part it forms petal like arrangement of ridges (marked by arrows), (coin diameter = 2.4cm); C) Close up view of Jodhpuria circularis; D) Old Elephant Skin (OES) textured surface (coin diameter = 2.3cm); E and F) Poorly developed microbial structures on rippled surface (coin diameter = 2.3cm).
69
Fig. 4.25 : Stromatolites of the Bilara Group. A, D and E- Colonnella columnaris;
B- Transverse section of Colonnella. C and F- Coniform stromatolites. 71
Fig. 4.26 : Stromatolites of the Bilara Group. A- Colonnella columnaris B-
Coniform stromatolite C-Transitional form D- Pseudocolumnar form, E and F- New form A (Scale bar = 2 cm).
72
Fig. 4.27 : Geological and location map of the Dulmera area, District Bikaner,
Rajasthan (after Pareek, 1984). 73
Fig. 4.28 : Litholog of the Nagaur Sandstone showing the position of trace fossils, 74
vii
Dulmera area, Bikaner district, Rajasthan. Fig. 4.29 : Trace fossils reported from the Nagaur sandstone, Dulmera area,
Rajasthan. A) Rusophycus carbonarious; B) Close up view of Rusophycus carbonarious; C and D) Rusophycus didymus; E and F) Cruziana fasiculata (diameter of coin = 2.3cm).
81
Fig. 4.30 : Trace fossils reported from the Nagaur sandstone, Dulmera area,
Rajasthan. A) Cruziana cf salomonis; B) Isopodichnus isp; C) Tasmanadia cachii; D and E) Diplichnites; F) Merostomichnites isp; G) Planolites beverleyensis.
82
Fig. 4.31 : Trace fossils reported from the Nagaur sandstone, Dulmera area,
Rajasthan. A, B and C) Bergaueria aff. Perata; D) Dimorphichnus cf. obliquus; E and F) Monocraterion isp.
85
Fig. 4.32 : Trace fossils reported from the Nagaur sandstone, Dulmera area,
Rajasthan. A) Planolites annularis; B, C, D and E) Scratch marks of arthropods.
87
Fig. 4.33 : Trace fossils reported from the Nagaur sandstone, Dulmera area,
Rajasthan. A) Treptichnus pedum; B) Monomorphichnus isp; C) Small knob like Burrow; D) Chondrites isp. E) Animal escape structure; F) Horizontal burrow.
91
Fig. 4.34 : Trace fossils reported from the Nagaur sandstone, Dulmera area,
Rajasthan. A) Needle like burrow; B) Tubular burrow; C and D) Palaeophycus tubularis; E) Small burrows reported from Tunkliyan; F) Scratch marks reported from Tunkliyan.
95
Fig. 5.1 : The schematic diagram showing the different biozones present in the
various stratigraphic horizons of Marwar Supergroup. The biozone are constructed on the basis of megafossils, microbial mat, trace fossils, stromatolites and microfossils.
99
Fig. 5.2 : Map shows the geographical distribution of Biozones based on the
palaeontological remains of the Marwar Supergroup. 106
Fig. 5.3 : Schematic diagram showing the correlation between the Bhander section of the Vindhyan Basin and Jodhpur section of Marwar Basin. (after Kumar, 2012).
108
Fig. 5.4 : Comparative stratigraphy (idealized) and proposed correlations between
the Marwar Supergroup, the Salt Range (Pakistan), the Krol-Tal (Himalayas) and the Huqf Supergroup of Oman (modified after Davis et al., 2013).
109
viii
List of Tables
Page No.
Table 1.1 Stratigraphic Succession of the Marwar Supergroup (modified after Pareek, 1984 and Chauhan et al., 2004).
4
Table 2.1 Lithostratigraphic succession of the Marwar Supergroup, western Rajasthan (after Pareek, 1984).
10
Table 5.1 Behavioural pattern of the Ichnofossil from Nagaur Group 102
1
Introduction
1.1 Background information
The intracratonic Marwar Supergroup is exposed in Rajasthan in the western of
part of the Peninsular India. Earlier, it was believed that the Marwar Supergroup was the
extension of the Vindhyan Supergroup; hence it was also called the “Trans-Aravalli
Vindhyans” in the older literature. Now the studies have shown that there are many
differences in the lithological facies as well as in the fossil content. The Marwar
Supergroup (MSG) occupies a large area of about ~51,000 km2 in the Jodhpur-Khatu-
Nagaur-Bikaner areas of western Rajasthan (Paliwal, 2007) (Fig. 1.1). It attains a
thickness of about 1000 m (Pareek, 1984). It unconformably overlies the Malani Igneous
Suite which has been dated as 779 to 681 Ma (Roy and Jakhar, 2002). Later on, it was
revised by Gregory et al. (2009) as 771±5 (U-Pb dating). The Marwar Supergroup is
overlain by the Permo-Carboniferous Bap Beds. It is believed that the sedimentation
either ended before the onset of Cambrian or during Lower Cambrian. As stated earlier,
the Marwar Supergroup was considered as unfossiliferous as no body fossil had been
discovered except a report of a brachiopod from the Jodhpur Sandstone published in the
form of an abstract by Khan (1973) which could not be replicated by any other person
since then and hence, it is now ignored. Stromatolites have been recorded from the Bilara
Group (Khilnani, 1964; Barman 1980; 1987) but they were not helpful in suggesting any
age. Recently, the Ediacaran fossils have also been discovered from the Jodhpur
Sandstone (Raghav et al., 2005), but the morphology of the reported fossils is not clearly
discernible and the taxonomic assignment of the reported fossils is somewhat doubtful.
More recently, microfossils have also been discovered from the Bilara Group (Babu et
al., 2009; Mehrotra et al., 2008). The presence of Precambrian-Cambrian boundary
within the middle part of the Marwar Supergroup is speculative as it is based on the
chemical signatures of carbon, strontium and sulfur isotopes of the carbonates of the
Bilara Group (Pandit et al., 2001; Maheshwari et al., 2002; Mazumdar and Strauss,
2006). Recently, Kumar and Pandey (2008) for the first time have discovered the trilobite
trace fossils from the Nagaur Sandstone which constitutes the upper part of the Marwar
2
Supergroup, and confirmed its Cambrian age. However, it has also been correlated with
the Purple Sandstone of the Salt Range of Pakistan which has been considered Cambrian
in age (Kumar and Pandey, 2010). Kumar et al. (2009) have also noted some possible
Ediacaran forms and a megaplant fossil in the Jodhpur Sandstone. In recent years, much
attention is also given to the algal mat structures in the siliciclastic sediments and their
utility in correlation is now being accepted. Recently, Sarkar et al. (2008) have described
a number of algal mat structures from the Jodhpur Sandstone. Kumar and Pandey, (2009)
also recorded Arumberia banksi from the Jodhpur Sandstone (the Sonia Formation of
Pareek, 1984) which is a characteristic form of Ediacaran age (Kumar and Pandey, 2008;
2009).
The present study envisages establishing a high resolution biozonation based on
megafossils, trace fossils, stromatolites and algal mat structures for the Marwar
Supergroup. Pattern and distribution of the Ediacaran biota are helpful establish
palaeobiogeography and evolution of the earliest multicellular life within the basin. The
present study will be helpful in the correlation and in assigning ages to different
lithostratigraphic units on the basis of biogenic signatures. With the lower group of the
Marwar Supergroup representing Ediacaran age and the younger group representing
Cambrian age, the biozonation will help in establishing Precambrian-Cambrian boundary.
Biozonation will also help in its correlation with homotaxial stratigraphic units of both
the peninsular and the Himalayan regions of India.
1.2 Problem delineation The Marwar Supergroup attains a huge thickness of about 1000 m and was earlier
considered unfossiliferous. It overlies the Malani Igneous Suite which has been dated as
771±5 (U-Pb dating) by Gregory et al. (2009) and is overlain by the Permo-
Carboniferous Bap Beds. Pareek (1981) subdivided the MSG into three groups’ viz., the
Jodhpur Group, the Bilara Group and the Nagaur Group (Table 1.1). Only in the Bilara
Group, the carbonates are developed, while the Jodhpur and the Nagaur Groups show
siliciclastic sediments dominantly represented by sandstones. In the absence of
3
radiometric dates, the age of these groups is basically speculative. Presence of fossils and
biogenic structures help to establish the biozones which in turn will help in suggesting
precise age. With age assignment it will be much easier to establish interbasinal
correlation.
Fig 1.1: Generalized geological map of the Marwar Supergroup (redrawn and modified after Pareek, 1981). 1.3 Present status and scope of work:
Recently, much attention has been drawn towards the presence of hydrocarbons in
the Precambrian basins. In the light of this, the Nagaur Basin (the Marwar Supergroup)
has been identified as a potential basin for the presence of hydrocarbon (Banerjee et al.,
4
1999). For the source of hydrocarbons, there has to be established the presence of organic
matter vis-a-vis the presence of life at the time of deposition of the sediments in a basin
unless the hydrocarbons are migrated from other younger source. Thus, the presence of
fossils or any signature of their presence is very crucial for deciding the potentiality of
the basin for the presence of hydrocarbons.
Table 1.1: Stratigraphic Succession of the Marwar Supergroup (modified after Pareek, 1984 and Chauhan et al., 2004).
Presence of Precambrian-Cambrian (Pc-C) boundary has a global significance as
very important and significant changes in evolution, ocean chemistry and possibly in
composition of atmosphere have taken place during this transition. The Pc-C boundary
has been used with confidence for correlation as well as in suggesting the age. There are
5
definite chemical signatures for the presence of this boundary within the Bilara Group
(Maheshwari et al., 2002; Mazumdar and Bhattacharya, 2004; Mazumdar and Strauss,
2006) but no fossil evidence has so been far presented. The Ediacaran deposits
underlying Pc-C boundary should also contain Ediacaran assemblages as reported from
most of the coeval deposits of the world. Ediacaran biota has not yet been discovered
from the Marwar sediments.
The Ediacaran fossils in the Jodhpur Sandstone may have a distinctly unique
assemblage because of biogeographic provinciality and may differ from the other known
occurrences such as Ediacara Hill (Australia), Avalon (Newfoundland) and Nama
(Namibia). They may also constitute a different biofacies. There are reports of the
Ediacaran fossils from the Marwar Supergroup (Raghav et al., 2005; Paliwal, 2007) but
both the reports show a very poor quality of material and the biogenicity of the reported
fossils and their taxonomic assignment could not generate a fair degree of confidence
(Kumar and Pandey, 2008). However, there is an excellent preservation of microbial mats
in the siliciclastic sediments of the Jodhpur Group which is of Ediacaran age and in
general the Ediacaran fossils are preserved where microbial mats are developed. The
Ediacaran fossils are unique in nature and their status in the overall evolution of
megascopic life is still not well understood. Any record of these fossils will definitely
give better understanding of the evolution of early life.
1.4 Objectives
The main objectives of the work are as follows:
1. Search and identification of megafossils and trace fossils.
2. Search and description of algal mat structures in the arenaceous facies.
3. Establish a relationship of microbial mat structures and associated Ediacaran
fossils in light of ecological and sedimentological setting.
4. Identification of biozones in the Marwar Supergroup.
5. Correlation of the Marwar Supergroup with other successions of Indian
subcontinent.
6
1.5 Implication of work
The present work shall have implications with respect to the following points:
A. To establish a high resolution biozones representing megafossils, microbiota
and algal mat textures f and their correlation for the Marwar Supergroup.
B. Detailed field work in Jodhpur, Nagaur, Gotan and the Dulmera areas and
preparation of different lithologs of different fossil-bearing horizons would
enhance the detailed prospective view for biostratigraphy of the basin.
C. Sampling and detailed taxonomic description and petrographical studies of
different stromatolites, megafossils and algal mat structures will help to
understand palaeoecology and depositional environment during the deposition of
sediments through time and space.
D. Detailed biozones could help to establish and describe the different biogenic
facies with in the basin.
E. Interbasinal correlation of the Marwar Basin with the Vindhyan Basin will
help to understand the evolutionary history of two Neoproterozoic basins of
India and adjoining areas.
F. If glacial events are identified in the Jodhpur Group, it will of considerable help in
intrabasinal correlation, age assignment and will give a much better understanding
of the all global events during the Neoproterozoic.
7
1.6 Organization of thesis
The work has been subdivided into six chapters.
Chapter-1 deals with the outlines of the background information, problem delineation,
present status and scope of work, objectives, implication of work and
organization of thesis.
Chapter-2 focuses on the geology and stratigraphy of the Marwar Supergroup and also
deals with the age assessment of the study area.
Chapter-3 illustrates the present work for which samples of fossils and sedimentary rocks
have been collected and analyzed in laboratory as well as in the field.
Chapter-4 concerned with the systematic palaeontology of the fossils reported from the
study area.
Chapter-5 deals with the biozonation of the Marwar Supergroup and its correlation with
the Vindhyan Supergroup and other coeval succession from other parts of the
world.
Chapter-6 comprises the conclusions of the present study.
A complete list of the various references cited in the text is given at the end of the thesis.
8
Geology and Stratigraphy of the Marwar Supergroup
2.1 Introduction
The rocks of the Marwar Supergroup are exposed in NNW-SSE trending shallow
intracratonic sag basin. The Marwar Basin extends from near Jodhpur to further
northwestward to the Salt Range, Pakistan (Chauhan et al., 2004). The Jodhpur
Sandstone has been considered by earlier workers, namely Blandford (1887) Oldham
(1886) and La Touché (1902) as equivalent to the Vindhyans of Son Valley
(Neoproterozoic to Early Cambrian). Earlier, the workers correlated the Jodhpur
Sandstone with the Purple Sandstone of the Cambrian of Salt Range on the basis of gross
lithology. The association of salt pseudomorphs (Halite casts) and limestone lent support
to the Jodhpur Sandstone as being its equivalent to Cambrian of Salt Range. Heron
(1932) considered the Marwar Supergroup of rocks as the Trans-Aravalli Vindhyans.
According to Barman (1980), the Marwar Basin does not show any link to the Vindhyan
Basin but may possibly represent southerly extension of the Cambrian Basin of Salt
Range. Shrivastava (1971, 1992) proposed rock-stratigraphic nomenclature for the
sediments of western Rajasthan and made studies related to palaeogeography. Virendra
Kumar (1995, 1999) correlated sandstones of the Nagaur Group with the Purple
Sandstone of Salt Range.
The first major attempt to reconstruct the stratigraphy in the study area was
attempted by Pareek (1981, 1984) who drew conclusions on the palaeogeographic set-up
of the western part of this sub-continent. Gupta et al. (1981) have renamed the erstwhile
Trans-Aravalli Vindhyans as the Marwar Supergroup (MSG). The MSG with an
estimated thickness of about 1000m lies unconformably over the basement rocks
comprising either Malani Igneous Suite and/or Delhi metamorphites. Pareek (1984)
divided the Marwar Supergroup into three parts: lower arenaceous (Jodhpur Group),
middle calcareous (Bilara Group) and upper argillaceous/arenaceous (Nagaur Group).
The earlier palaeontological studies made on the sediments of the Marwar Supergroup
revealed that over most part is unfossiliferous except for the stromatolites. Khilnani
(1964, 1968) first drew attention towards the occurrence of the stromatolites in the Bilara
9
Limestone. Srivastava (1971) mentioned about the occurrence of the algal remains in the
Bilara Limestone. Barman (1980, 1987) also reported stromatolites from other parts of
the Marwar Supergroup. Shrivastava (1971, 1992) worked in Marwar and also in the
Phalodi-Khichan area. The contact of the Igneous Basement and the Marwar Supergroup
(Jodhpur sandstone) is noticed at Mehrangarh Fort. At Jodhpur Fort, the Jodhpur
Sandstone directly overlies the rhyolites, where the contact is sharp and is heterolithic in
nature. 2.2 Geology and Classification of Marwar Supergroup
Pareek (1984) has divided the Marwar Supergroup into the Jodhpur Group, the
Bilara Group and the Nagaur Group. These groups are further subdivided into formations.
In the study area, the Jodhpur Group was subdivided into three units viz. Pokaran Boulder
Bed (lower unit), Sonia Sandstone (middle unit), and Girbhakar Sandstone (upper unit).
The Pokaran boulder bed is dominated by the boulder and overlain by calcrete and
coarse-grained sandstone. The next lithounit is the Sonia Sandstone. The facies of this
lithounit consists of maroon siltstone and shale, creamish sandstone with abundant
sedimentary structures such as salt pseudomorphs, ripple marks, cross-bedding, etc. The
Sonia Sandstone is overlain by the Girbhakar Sandstone. The facies association in this
unit is characterized by the brick-red sandstone, siltstone; sandstone is gritty to pebbly
near the top. The classification of MSG is summarized in table 2.1. Later, Chauhan et al.
(2004) clubbed the Sonia Sandstone and Girbhakar Sandstone into the Jodhpur Sandstone
as they did not find marked variations in the lithological attributes. The MSG
classification given by Chauhan et al. (2004) has been followed in the present work. The
Jodhpur Group is overlain by the carbonate rocks of the Bilara Group. The Bilara Group
(250 to 300 m thick) is subdivided into three units namely Dhanapa, Gotan and Pondlo
formations in ascending order. The Bilara Group conformably overlies the Jodhpur
Group with gradational contact. The contact can be seen at Pichak village near Bilara
town. The Bilara Group shows good development of stromatolites. The Dhanapa
Formation exposed in Dhanapa village is represented by chert beds at the base, followed
upwards by well-bedded and laminated cherty dolomite and massive dolomite. The
dolomites at places contain stromatolites. The stromatolites and biohermal limestone
10
attain a thickness of about 15 m near Dhanapa village. This formation is also exposed
near Khoaspura, Borunda and Gorawat villages. The Gotan Formation is composed of
dark grayish laminated limestone interbedded with variegated clay beds. Unlike Dhanapa
Formation, the stromatolites are less pronounced in this unit. A good section (5 m to 10 m
thick) of this unit is exposed near Gotan village.
Table 2.1. Lithostratigraphic succession of the Marwar Supergroup, western Rajasthan (after Pareek, 1984).
11
The Pondlo Formation is composed of dolomite, cherty dolomite, claystone,
siltstone and reddish sandstone. The dolomite is stromatolitic in nature. The section is
best exposed near Pondlo village. The Nagaur Group overlies unconformably the Pondlo
Formation. The Nagaur Group is subdivided into the lower Nagaur and upper Tunklian
formations. The Nagaur Formation is composed of reddish to brownish, coarse to
medium grained sandstone, siltstone and maroon shale. The shale is intercalated with
siltstone and sandstone. The sandstone of the Nagaur Formation is typically ferruginous
and contains clay balls. The sandstone shows profuse development of ripple marks, mud
cracks and cross beddings. The sections are well exposed near Dulmera area in Bikaner
District, Rajasthan. The Tunklian Formation is gritty to pebbly, containing brick red
sandstone, siltstone, pebbles of granite, rhyolite, dolomite, quartzite, etc. as observed near
the Tunklian hill. It is best exposed at the base of Tunklian hill; it comprises reddish to
purplish shale followed upwards by ferruginous gritty to pebbly sandstone beds.
2.3 Study area Jodhpur and surrounding areas
The Marwar Supergroup unconformably rests over the Malani Igneous Suite. The
Malani Igneous Suite is a broad term used to denote Neoproterozoic granites and felsic
volcanics exposed over an area of 54,000 km2 in Rajasthan, India (Gregory et al., 2009).
Magmatic activity associated with the Malani Igneous Suite is constrained to at least
three distinct phases. The initial phase of igneous activity was characterized by major
felsic and minor mafic flows. This was followed by the emplacement of granitic bodies
into the region. The intrusion of volumetrically minor felsic and mafic dykes represent
the final phase of Malani Igneous activity. The Malani Igneous Suite rests unconformably
over Paleo to Mesoproterozoic metasediments, and basement granitic gneisses and
granodiorite. The Pokaran Boulder Bed is 4 m thick and is developed only in the western
part of the basin around Pokaran where it unconformably overlies the Malani Igneous
Suite. In rest of the area, the Jodhpur Sandstone directly overlies the Malani Igneous
Suite (Pareek, 1981, 1984; Chauhan et al., 2004).The Jodhpur Group holds the important
place in the Marwar stratigraphy; it represents the oldest litho sequence along with
12
significant age deciphering fossils such as Aspidella, Hiemalora, and Arumberia. It
consists mainly of fine to medium grained, ripple marked sandstone, gritty coarse-grained
sandstone, siltstone and shale. The uneven gritty sandstone is deposited under fluvial
conditions. In the Jodhpur Sandstone, the repetitions of fine to medium grained sandstone
and the coarse-grained gritty/pebbly/conglomeratic sandstone has been observed in the
entire basin. In thin section, fine-grained sandstone of the Jodhpur Group comprises
subangular to subrounded grains of quartz, in good amount, few grains of feldspar, mica,
calcite and opaque iron minerals are present as accessory minerals and the cementing
material is siliceous. The calcareous sandstone contains some amount of micritic calcite.
The outcrops of the Bilara Group are scanty and can be seen only in the southern
part (Kumar, 2012). It contains mostly carbonate rocks. The Bilara Group exhibits
excellent development of biohermal stromatolites. Well-preserved sections can be seen
near Sojat in the south to Phalodi in the west through Rundhia, Bilara, Hariadhana,
Gorawat, Dhanapa, Gotan, Pondlo, etc. The beds are horizontal to subhorizontal. The
Bilara Group has a maximum thickness of 300 m pinching out in the eastern and western
extensions. In the western part of the Marwar Basin, the exposures are absent but the
rocks are present in the subsurface region, as inferred on the basis of the borehole data.
This subsurface deposit is named as the Hanseran Group. It attains a maximum thickness
of 652 m as found in the borehole data near Hanseran (Rastogi et al., 2005). It is
considered to be a facies variation of the Bilara Group developed in the southern part.
The Nagaur Group consists of predominantly red coloured rocks and these
sediments were deposited under very shallow marine conditions and had a very
prolonged aerial exposure for intensive oxidation (Rastogi et al., 2005). The ripple marks
and cross bedding can be seen in the Dulmera area. These sediment associations indicate
a periodical high energy environment within predominant low energy environment of
deposition (Dey, 1991). The younger Tunkliyan Sandstone is developed in Tunkliyan hill
near Gudralli area. It is characterized by brick red claystone, calcareous clay to gritty and
pebbly sandstone. The nature of this Tunkliyan Formation is indicative of somewhat
humid climatic conditions as compared to the arid climatic conditions of the Nagaur
Formation (Dey, 1991).
13
2.4 Marwar Supergroup
Age assessment
In the present scenario, the Marwar Basin is considered as the repository of
various fossils of different ages ranging from the Ediacaran to the Lower Cambrian. The
Marwar Supergroup was historically classified as Neoproterozoic based upon the
relatively undeformed stratigraphy and the absence of index fossils within the sequence.
The Malani Igneous Suite is well dated to between 750-800 Ma (Torsvik et al., 2001;
Gregory et al. 2009; Van Lente et al., 2009; Pradhan et al., 2010) and therefore provides
a maximum age for the unconformably overlying Marwar sediments. Assuming that the
Neoproterozoic Snowball Earth event was globally distributed, the absence of glacial
deposits within the Marwar Supergroup suggests a post-Marinoan age for the deposits
(i.e. <650 Ma). The Ediacaran fossils collected from the Jodhpur Group, including
Arumberia, Beltanelliformis, Aspidella, and Hiemalora, support a late-Neoproterozoic
age assignment (< ~570 Ma; Kumar and Pandey, 2009; Kumar et al., 2009). Previously,
the Marwar Supergroup was considered as an unfossiliferous basin but Khan (1973)
reported brachiopod, which could not be replicated again. Malone et al. (2008) recently
studied detrital zircon populations from the Jodhpur Sandstones of the Jodhpur Group.
The results yielded a peak detrital zircon age range between 800-900 Ma along with a
smaller subset of 780 Ma zircons. The carbonates of the Bilara Group were the focus of
several chemostratigraphic attempts to constrain the age of the Marwar Supergroup. The
presence of stromatolite assemblage in the carbonate rocks of Marwar Supergroup was
first reported by Khilnani (1964) giving evidence of early life. Later on, Khan (1971) and
Hashimi and Gauri (1972) also reported a few other fossils from the Marwar Supergroup
but the facts are still debatable. A major detailed study was carried out by Barman
(1975), who highlighted the presence of a numerous stromatolite beds associated with the
marked lithofacies changes in a sedimentary sequence adjacent to the western margin of
the Aravalli range. The stromatolitic assemblage completely lacks the typical Riphean
and Vendian forms (Preiss, 1976) such as Conophyton, Baicalia, and Kussiella which are
confined to the eastern side of the Aravalli Range. The stromatolites of the Bilara Group
do not indicate any significant age; however, the form genus Colleniella would point to
14
the terminal Riphean-Cambrian age (Semikhatov, 1976). Carbon isotope studies suggest
that the Precambrian-Cambrian boundary lies within the Bilara Group based upon
negative δ13C anomalies (<-4.3% PBD and <-6.5% PBD) that correlate with the Nemakit-
Daldynian-Tommotian carbon isotopic evolution curve (Mazumdar and Bhatacharya,
2004). Mazumdar and Strauss (2006) analyzed the δ34S concentrations within trace
sulfates from the Bilara Group carbonates and calcium sulfates from the Hanseran
evaporites and concluded that the data (33.8±3.1% and 32.4±3%) closely matched the
sulfate enrichment patterns from the end-Neoproterozoic. Mazumdar and Strauss (2006)
also examined the Strontium isotopic composition from the Bilara carbonates and
Hanseran Evaporites and found that the results (87Sr/86Sr= 0.70832±0.000354) were
comparable to Post-Varangerian 87Sr/86Sr global seawater curves. The Nagaur Group, the
uppermost unit of the Marwar, yielded trace fossils e.g. Rusophycus, Dimophichnus, and
Cruziana, suggesting an Early Cambrian age for the unit (Kumar and Pandey, 2008,
2010). Recently, McKenzie et al. (2011) studied detrital zircon populations from the
Nagaur Sandstones. The results of this study demonstrate a large concentration of grains
between 700 Ma and 1000 Ma and a small population of young grains with a peak at 540
Ma.
15
Methodology
Methodology is the mainstay of the present work in order to achieve the objectives of the study. In the present work, the methodology has been divided into two parts: the first part deals with the field observations, data and sample collections and preparation of detailed lithologs while the second part deals with the laboratory work including the study of fossils, trace fossils, microbial mat structures and the thin section study of rock samples. Schematic diagrams have been prepared wherever needed. Based on the above criteria, the chapter has been divided into two parts:
a) Field work
b) Laboratory work
3.1 a) Field work
The field work has been carried out in different localities of the Marwar Supergroup viz. Sursagar (Jodhpur district), Artiya Kalan (Jodhpur district), Khatu (Nagaur district), Pokaran (Jaisalmer district), along Jodhpur-Jaisalmer highway, Bilara district, Dhanapa-Gotan-Pondlo (Bilara district) and Dulmera village (Bikaner district). The Survey of India (SOI) toposheets no. 45E/12, 45F/3, 45F/6, 45F/12, 45F/14, 45F/10, 44H/11, and 40N/13 based on scale 1:50,000 were used for the study. In the field investigation the different sections were identified and detailed lithologs were prepared. During the field work, the non-carbonaceous megaplant fossils, animal body fossils, MISS (Microbially Induced Sedimentary Structures), trace fossils and stromatolites were searched and studied in the siliciclastic rocks. The geological data as well as samples were collected for the detailed study in the laboratory.
3.1 b) Laboratory work In the laboratory, animal and plant fossils were studied for their biogenic
characters. The thin sections of non-carbonaceous megafossils were studied with the help
of Wild Stereomicroscope. Carbonate thin sections were stained by Alzarine Red S
16
solution for the identification of calcite and dolomite. Photomicrographs were prepared
with the help of Wild, Leitz Orthoplan and Leica DMRXP microscopes. The thin sections
of the chert have been scanned for the study of microbiota with the help of Leitz
Orthoplan microscope. On the basis of field and laboratory study along with literature
review, the biozones of the Marwar Supergroup have been established. The plant and
animal body fossils, organo-sedimentary structures including MISS and stromatolites,
trace fossils and microfossils were used for biozonation. This chapter also delineates the
sedimentological aspect of the present study based on thin sections.
3.2 Petrography
The petrographical study of sandstone and carbonate rocks has been done. The
grain size analysis of sandstone was carried out to decipher the depositional history. For
the ease of the study, this chapter is further subdivided into sandstone section and
carbonate section, and giant nodules. Sedimentary structures such as medium to large
scale cross bedding and ripple marks are generally associated with the sandstones. The
salt pseudomorphs (Fig. 3.1) with GPS value 26o33.846″ N and 73o44.930″ E are also
found at the upper horizon of the Jodhpur Sandstone on way to Dhanapa village.
17
Fig 3.1: Well-developed Salt Pseudomorphs of various shapes in shale on the road side on Bhopalgarh-Dhanapa road. 3.2.1 Sandstone Section
For petrographic analysis of the Jodhpur Sandstone, in all, 35 thin sections have been
studied. The rock is mainly constituted of equidimensional, medium sized quartz grains
which constitute more than 95% while the matrix is less than 5% of the rock (Fig. 3.2).
The grains are more compact and closely in contact with each other binded by cementing
material which is made up of silica. The quartz is well sorted and subrounded to rounded.
A few grains of orthoclase and microcline also noted. The authigenic enlargement or
overgrowth on quartz grains is commonly seen. The typical accessory minerals include
only the stable minerals such as zircon, tourmaline and rutile. Texturally, most quartz
sandstone is characterized by thorough sorting. They are usually clean, well washed
sandstone comprising quartz and devoid of silt and clay. Presumably, they are deposited
18
in stable environments either continental or marine, where deposition was relatively slow
and particles were so winnowed by currents before final burial that the argillaceous
material washed away. At least, few of them are the result of more than one cycle of
erosion and deposition. Under these conditions, the quartz grains tend to become sub-
rounded to well-rounded. It can be classified as quartz arenite.
Fig 3.2: Photomicrograph of Quartz arenite of Jodhpur Sandstone; a and b) Showing the compact arrangement of quartz grain in cross nicol and PPL respectively; c and d) Quartz grain showing subrounded to rounded in cross nicols. 3.2.2 Giant Nodule
In the mines of the Sursagar, Jodhpur district (26˚ 19.70� N and 73˚ 0.12� E), a
number of giant nodules of sandstone are seen within the sandstone beds (Fig. 3.3 A-D).
About 10-20 m thick succession of the middle part of the Jodhpur Sandstone is exposed
in the Sursagar mines and the nodules are mainly exposed approximate 10 m from the
base level of mines.
19
Fig 3.3: Giant nodules seen in the Jodhpur Sandstone. There is no lithologic difference between the host rock and the lithology of the nodule, except the hardness. a. The host rock is seen both at the base as well as at the back of the nodule, in which the nodule is embedded, b. The host rock is also seen associated with the nodule, c. Outer margin of the giant nodule showing parallel differential markings in the sandstone, d. Transverse section of the giant nodule showing clearly marked circular margin and lack of any internal structure; the entire surface looks homogenous, e. and f. Photomicrographs of sandstone forming the nodule and host rock. The sandstones are made up of subangular to subrounded detrital quartz grains cemented together by silica (under crossed nicols). e. Sandstone of the nodule; f. Sandstone of the host rock.
20
It appears that the nodules are restricted at a specific stratigraphic horizon. The nodules are spherical whose diameter ranges from 2.0m to 6.0m. The nodules are spherical to slightly distorted. At places two nodules are seen merging with each other. The outer surface is smooth with horizontal parallel marking (Fig. 3.3 C).
Any internal structure including concentric banding is completely lacking as the
cross section of the nodules are homogenous (Fig. 3.3 D). Along with this, no colour
marking or mineralogical differences is noticed. In comparison to the host rock, the
nodules do not show any marked colour difference and nodules are formed due to relative
hardness. The nodules are light reddish brown to light whitish brown in colour with
resemblance to the host rock. The sandstone has been identified as quartz arenite with
silica as the cementing material. There is no marked petrographic difference between the
sandstone of the nodules and the host rock (Fig. 3.3 E and F). It appears that the silica
cement plays an important role in the formation of the nodules and higher concentration
of silica may be responsible for genesis of the same.
3.2.3 Carbonate investigation The carbonate investigation has been carried out for the middle part of the
Marwar Supergroup, i.e. Bilara Group. The contact between the Bilara and Nagaur
Groups is also conformable and is marked by a distinct transitional lithology. The
lithounits of Bilara Group are calcareous in most parts and is represented by limestone,
dolomitic limestone, dolomite and cherty limestone. The observed chert content is
significant in the basal part (Dhanapa Dolomite) but increases in the upper part (Pondlo
Dolomite). The stromatolitic composition is highest in lower, negligible in the middle and
moderate in the upper parts. In field, it is difficult to demarcate the lithological boundary
between Dhanapa, Gotan and Pondlo Formations as they laterally grade into each other.
These three formations are found only in their respective type localities and their
persistence is not discernible. In all 18 thin sections of the carbonate rocks have been
studied. In the petrographic study, it is observed that no microfossils were encountered in
carbonate rocks as well as in the cherts. In thin sections, the rock is essentially fine-
grained calcite (micrite). Infirmly lithified limestones, such aggregates consist of
interlocking anhedral calcite crystals typically less than 20 µm in diameter and they are
21
generally considered to represent original carbonate mud. In thin section quartz vein is
observed which may be representing the post-depositional event. The quartz vein may be
observed as nearly vertical to the lamina. The thin sections (Fig. 3.4 a and b) show the
laminated nature of limestone. The lamina is being demarcated by the colour variation
and change in textural arrangement. The dark colour band seen at the top of the
photomicrograph is composed entirely of clay-sized material which may be the cemented
material comprising of limestone. Presumably, the carbonate material was deposited
initially as an impalpable mud composed of minute crystals of calcite, which by
cementation and partial recrystallization, was converted to microcrystalline calcite.
Fig 3.4: Photomicrograph of Limestone of Bilara Group. a-b) Gotan limestone showing microcrystalline calcite in cross nicol and PPL respectively. Quartz vein is also observed in the thin section. 3.2.4 Nagaur Sandstone
Fig 3.5: Photomicrograph of Quartz arenite of Nagaur Sandstone; a and b) Showing the compact arrangement of quartz grain in cross nicol and PPL respectively.
22
For petrography of Nagaur sandstone, the 20 thin sections have been studied. The
rock is mainly comprised of equidimensional, medium sized quartz which constitutes
more than 90% of the host rock with matrix and cementing material less than 10% (Fig.
3.5). Therefore, the rock is classified as quartz arenite. The grains are very compact in
nature and closely in contact amongst themselves. The cementing material is usually
silica but at some instances the presence of iron oxides is also noticed which is indicated
by the reddish-brown colour in thin section. The grains are rounded to sub rounded
indicating the mature stage of the rock in depositional environment. In terms of accessory
minerals hematite, zircon, tourmaline, etc. are also noticed.
23
Systematic Palaeontology
4.1 Palaeontology
The palaeontological investigation has been carried out on the Jodhpur Group, the
Bilara Group and the Nagaur Group of rocks exposed in the different localities of
Jodhpur, Khatu, Barna Mine near Bilara, Dhanapa, Gotan, Pondlo, Bikaner, Nagaur and
Tunkliyan. The lowermost Jodhpur Group yields the fossils of the Late Neoproterozoic
era comprising body fossils, trace fossils, burrows, trail marks, fourteen types of well-
preserved microbial mats and non-vascular megaplant fossils from the Jodhpur
Sandstone. Stromatolites from the carbonate section have been studied. The Nagaur
Group of the Early Cambrian age consists the Nagaur Sandstone and the Tunkliyan
Sandstone. From the Nagaur sandstone, a number of trace fossils, burrows and scratch
marks of arthropods have been studied. The Tunkliyan Sandstone has also yielded some
sort of organic activity in the forms of scratch marks of arthropods and poorly preserved
burrows in the fine-to medium-grained sandstone. The fossils are described in
stratigraphic order.
4.1.1 Animal body fossils from the Jodhpur Group
There are four body fossils recorded from the Jodhpur Sandstone along with one
burrow structure and a few trail marks from the Tunkliyan Sandstone.
a) Five-armed body fossil b) Marsonia artiyansis c) Hiemalora d) Aspidella
a) Five-armed body fossil
The five-armed body fossil has been found on the bedding surface of the light
brown coloured, fine-grained Jodhpur sandstone in a mine at Sursagar with GPS value
26°15.77′N and 73°0.14′E, which is about 7 km NW of Jodhpur city (Figs. 4.1 and 4.2).
The fossil-bearing sandstone is quartz arenite with mean grain size of 0.23 mm. The
fossil is preserved as an epirelief and is characterized by the presence of five unequal,
wavy arms arising from a central circular disc of 1 cm in diameter (Fig. 4.3). Arms are
24
found radiating away from the disc (Fig. 4.3 D). The angle between the different arms
varies between 30° and 90°, and their length ranges from 12.5 to 22.5 cm, and mean
length is 17 cm. The maximum width of the arms varies from 0.4 to 0.7 cm with mean as
0.56 cm. The margins of these arms are smooth and their distal ends are pointed.
However, no other surface feature could be observed.
Fig 4.1: Geological and location map of the Marwar Supergroup, western Rajasthan, showing study area (after Pareek, 1984).
25
Fig 4.3: Five-armed body fossil on the bedding surface of the Jodhpur Sandstone. A and C) Five-armed body fossil; B) Line diagram of the fossil seen in A and B) Enlarged view of (C) showing a disc-like structure at the centre of the body fossil.
Fig 4.2: Litholog of the fossil-bearing horizon, Jodhpur Sandstone, Sursagar mine, western Rajasthan.
26
The morphology of the structure under description cannot be produced by any
inorganic process, including microbial mat-related sedimentary structures such as
Aristophycus (Häntzschel, 1975) which is characterized by a regular, anastomosing,
raised pattern of branching structures. It is not comparable with Hiemalora stellaris
(Fedonkin, 1982) also; as Hiemalora is characterized by the presence of appendages
(rays) outwardly radiating from a disc generally of the order of disc diameter and rarely
reaching double the diameter of the disc. The appendages are densely packed to
moderately spaced, narrow rays. In the present specimen, there are only five arms and the
ratio of the dimensions of the arms and the disc is between 12.5 and 22.5 cm, whereas it
is never more than 2 cm in Hiemalora. The morphology of the phylum Echinodermata
shows five arms with a central disc and has been known from the Cambrian Period.
Living echinoderms are characterized by extensive water vascular structure and are
pentamerous. Fossil evidence shows that stereon evolved before pentamery, but both
were acquired during the Lower Cambrian. The tests of echinoderms are made up of
calcium carbonate though the present fossil shows no preservation of the nature of the
soft tissues.
Body Fossil from Artiya Kalan
The medusoid form Marsonia artiyansis reported by Raghav et al. (2005) from
the Sonia Sandstone (Jodhpur Sandstone) of the Marwar Supergroup is restudied. For
this, a fresh collection was made in the abandoned mines near Artiya Kalan, about 66 km
northeast from Jodhpur on Jodhpur-Gotan motor road from where Raghav et al. (2005)
had originally described the fossil. The Marwar Supergroup occupies a large area in the
western Rajasthan forming small hillocks in a desert setting (Figs. 4.4 A, B and 4.5). The
sampling for the collection of Marsonia artiyansis has been done from the type locality
which is near Artiya Kalan village in the Jodhpur district, Rajasthan. About seven meters
thick succession is exposed in the pits which are about 1 km east of the village (Fig. 4.7
A and B).
27
Fig 4.4: A, Location map of the Jodhpur area, western Rajasthan. B, Geological map of the Jodhpur area, showing fossil locality, (Redrawn after Raghav et al., 2005).
b) Marsonia artiyansis The Marsonia has been first evaluated as biogenic structure before attempting its
taxonomic assignment. It occurs as a simple impression on the bedding surfaces of the
shales. It is marked by a circular, disc-shaped structure with well-preserved wrinkle
marks. Occasional presence of beads and arm-like structures within the disc-shaped
structure is very common.
28
Fig 4.5: Detailed geological map of the Artiya Kalan area, Jodhpur District, Rajasthan showing fossil locality (Redrawn after Raghav et al., 2005).
Fig 4.6: Litholog of the fossil-bearing horizon, Jodhpur Sandstone, Artiya Kalan area, western Rajasthan.
29
Phylum Cnidaria
Class Scyphozoa
Family Incertae sedis
Genus Marsonia Raghav et al. 2005
(Fig. 4.7 C- E i-iii; Fig. 4.8 A-F)
Type species: Marsonia artiyansis Raghav et al. 2005
Holotype: Raghav et al. (2005) have identified 4 holotypes for the genus Marsonia which
is not legitimate according to the rules of biological nomenclature. We have selected the
best photograph shown in Fig. 3C of his published paper as Holotype whose sample
number is not available.
Paratype: SK/AK-1, 16, 21, 23, 29, 30, 32.
Diagnosis: It is disc shaped, generally circular to elliptical in outline, marked by
impression on the top of the bed (Fig. 4.7). The diameter ranges from 0.5 to 5.5 cm. The
outer peripheral margin of the disc is smooth (Fig. 4.7 D and Fig. 4.8 A, B, C, D) or
marked by complex wrinkles (Fig. 4.7 C and Fig. 4.8 E, F). Wrinkled margins are slightly
irregular and individual wrinkle could not be traced around the circular outer margin. The
width of wrinkled part of the disc varies from 2 mm to 4 mm. Non-wrinkled part is
marked by uneven surface and also shows small, straight to slightly curved ridges or
arms, which are symmetrically or asymmetrically placed. They taper at the outer margin
of the disc. The arms are originating from the centre but do not continue up to the outer
margin. The maximum length of the arm has been measured as 2 cm. In a few forms, the
arms are placed in such a way as to divide the disc into four more or less symmetrical
parts. In the central part of the disc, a circular mark is preserved both as positive or
negative epirelief with diameter ranging from 1 to 2 mm (Fig. 4.8 C “a” and “b”). The
central part of the disc also shows bead-like structures (Fig. 4.8 E); otherwise it is
uneven. The outer margin of the bell is completely devoid of tentacles.
Remarks: A large variation is seen in the morphology of Marsonia. In some, the central
part is uneven, while in others few arms are missing. In the larger forms, the wrinkle
marks are prominent. The quality of preservation in the smaller forms is relatively better.
It appears that the effect of compression or overloading was less in smaller forms in
30
comparison to the larger forms. A few forms are embedded in the bed and have three
dimensional preservation. It can be confirmed when small chips of shale is removed from
the top surface of the fossils and some preservation could still be seen on the under
surface suggesting continuity of the fossil body (Fig. 4.7 E i- iii). Differences in the
morphology of the fossil may also be due to the fact that whether the preservation is from
the oral or aboral side of the medusoid.
Discussion: In morphology, the present form resembles Marsonia reported by Raghav et
al. (2005). In their collection, they had only four samples and all were erroneously
described as holotypes (see page 24, Raghav et al., 2005). In the published photographs
of Raghav et al. (2005), the morphology of the fossil can be observed only in fig. 3-A, B,
C, F and G, out of which B, C, F and G are the photographs of the same sample. All the
forms have a diameter of about 1cm. In none of the photographs, the wrinkles are seen
but their presence has been mentioned in the description. Though the diameter is shown
to be ranging from 0.4 to 1 cm, no photograph is given for the smaller range. In fig. 3-A
nothing is visible in the areas marked as ‘b’, ‘c’ and‘d’. In our collection, we could
observe the morphology in the forms with more than 0.5 cm diameter. Hence, the
minimum diameter is taken as 0.5 cm and the maximum diameter is recorded as 5.5 cm,
whereas Raghav et al. (2005) have given this range as from 0.4 to 1 cm. The form is soft
bodied. The presence of arm-like structure, beads, opening in the centre, circular body,
wrinkle marks in the outer margin and absence of hard parts point towards the medusoid
of Scyphozoan affinity. Raghav et al. (2005) have placed Marsonia under phylum
Cnidaria, class Scyphozoa and family Incertae sedis.
Marsonia artiyansis Raghav et al. 2005, emended
(Fig. 4.7 C to F; Fig. 4.8 A to F)
Paratypes: SK/AK-1, 16, 21, 23, 29, 30, 32 a and b
Description: As for the genus.
Discussion: Specimens are characterized by circular to slightly elliptical shape and it is
termed the bell which is an outer body in a jelly fish. The quality of preservation in
smaller form is relatively better in comparison to the larger forms. A notable character is
the smooth outer margin of the bell in the smaller forms and wrinkled in the larger ones.
31
Concentric rings are discontinuous and none of them make a complete circle around the
disc. This suggests that the outer part of the bell was very soft and thin.
Fig 4.7: A) Field photograph of the Jodhpur Sandstone; arrow marks the position of the fossil-bearing horizon; B) Section of the Jodhpur Sandstone (Sonia Sandstone) exposed in a pit near the Artiya Kalan area, district Jodhpur. The lower part is made up of sandstone and the upper part is made up of shale and siltstone which has yielded the fossils; C) Marsonia artiyansis shows wrinkled margin at the outer bell with four radial arms originating from the central part of the medusa, Sample no. SK/AK-1; D) Specimen showing smooth outer margin with elevated central disc up to 2 mm in height, Sample no. SK/AK-2 and E) (i) Upper surface of the poorly preserved medusa showing wrinkled outer margin. When sample in E (i) was chipped it yielded a sample E (ii) which on its sole shows marks of the radial arms with negative relief and E (iii) is its counterpart which shows arms in positive relief.
32
Fig 4.8: Marsonia artiyansis shows variation in size as well as in the outer margin from smooth to wrinkled. A) (sample no. SK/AK-21) and B) (sample no. SK/AK-23), Smooth outer margin with dislocated radial arms; C) “a” and “b” are the counter parts of the same specimen; “a” shows raised central part showing central disc with four radial arms; outer margin smooth, sample no. SK/AK-22 a and b. Specimen “b” shows depressed radial arms, D) Specimens “b” is the chipped off part of specimens “a”, showing additional circle in the middle and minute central pit at the central part (specimen “b”), sample no. SK/AK-32 a and b; E) Bead-like structure is seen in photograph marked by arrow, sample no. SK/AK-3 and F) Specimen showing preservation of many wrinkle layers, sample no. SK/AK-16.
33
The smooth margin in the smaller forms and better preservation may be due to the
fact that central part of the bell-shaped animal was thicker as depicted in the schematic
diagram in fig. 4.9, where the transverse and oral sections of the animal are shown. It
explains the preservation of complete body of the animal in the larger form and only the
nonstippled part in the smaller form. Outer margin of the bell is devoid of tentacles. The
radial arms originating from the central disc may act as gastrovascular system in the
animal (Raghav et al., 2005). A schematic diagram is made to show the transverse
section and oral section of the animal.
Fig 4.9: Simplified sketch of Marsonia artiyansis. A) Longitudinal section of the umbrella or bell and B) Oral view of the animal showing gonads and oral arms. The shaded area represents the thinner part of the bell.
34
c) Hiemalora
Genus Hiemalora Fedonkin, 1982
(Type Species: Hiemalora stellaris Fedonkin, 1980)
cf. Hiemalora sp.
(Fig. 4.10 a, b)
Sample no: JD-036, 54
Locality: Sursagar Mine, Jodhpur area, Rajasthan
Description: Circular, disc shaped, with numerous radiating, moderately packed rays or
appendages of variable length seen on the bedding surface of sandstone. The diameter of
disc is about 7.5 cm. No internal structure is visible. The appendages are rectilinear to
slightly sinuous with maximum length of 6.5 cm. Generally unbranched but bifid
branching occasionally seen. Tapering is common. The maximum width of the
appendages is 1.5 mm. In all, 42 appendages are counted.
Fig 4.10: Field photographs of Hiemalora from Sursagar mine, Jodhpur Sandstone. a) Showing the specimen deposited over the ripple marks. b) Radiating arms originating from the centre of the specimen.
d) Aspidella
Genus Aspidella Billings, 1872
(Type Species: Aspidella terranovica Billings, 1872)
Aspidella sp.
(Fig. 4.11 a, b)
35
Sample no: JD-405,406
Locality: Sursagar Mine, Jodhpur area, Rajasthan
Description: Small circular discs on bedding surface with slightly concave to flat relief
showing that varied morphotypes are preserved. In some forms, raised rim is clearly seen
but in others two to several concentric rings are preserved with very low relief. The
diameter ranges 1.5 cm to 2.5 cm. Maximum relief of the ridges is up to 2 mm. (14
samples traced)
Remarks: Aspidella sp. is considered by Hofmann et al. (2008) as taphonomically quite
variable fossil remain and Gehling et al. (2000) have interpreted the discs as casts of the
basal impression of collapsible or hollow bulb-shaped organism.
Fig 4.11: Field photographs of Aspidella from Sursagar mine, Jodhpur Sandstone. a) Showing well preserved Aspidella with solid outer rim (marked by an arrow); b) Close up photograph of Aspidella showing the circular morphology.
Burrow
(Fig. 4.12-3, 4)
Sample no. AK/SK-21/2011 Burrows are unbranched, horizontal to vertical, present on the top of the bedding
plane, preserved as full relief. Burrows are circular in outline depressed at few places,
forming mess-like network and overlapping each other in a few instances. These are
composed of medium grained sandstone. The maximum to minimum length of burrows
are 0.4 to 11 cm with up to 2 mm in diameter.
36
These burrows show deposition either at beach or nearshore regime of marine
environment with well oxygenated conditions. The presence of biological activity like
trail mark support in interpreting these structures as burrows.
Fig 4.12: Field photograph of fossil bearing locality. (1) Showing the horizon from where the fossils have been collected. (2) Trail marks in fine grain sandstone. (3 and 4) Showing well preserved network of burrows.
Trail marks (Fig.4.12-2)
Sample no. AK/SK-22/2011 11 cm long and 2 mm wide trail mark running parallel on the bedding plane,
branched and shows sigmoidal movement. In lateral view, it shows “U” shape. Specimen
preserved on top of the bedding plane with medium sand.
37
4.1.2 Plant fossils Kumar et al. (2009) have reported noncarbonaceous, filamentous megaplant
fossils from the Jodhpur Sandstone and compared them with the extant Vaucheria of
Xanthophycean affinity. The only difference between the fossils and Vaucheria is the
size which is 140 times larger in the fossil record. The morphology of these filamentous
structures is evaluated again for their biogenic nature. These structures are preserved on
the bedding planes of the sandstones as epirelief marked by colour difference with the
host rock. They occur as cast and mould and show more or less similar lithology as that
of the host rock which is a quartz arenite but there is a difference in grain size of the plant
fossils and the host rock. In thin section, the plant fossil is made up fine-grained
sandstone, whereas the host rock is made up of medium grained sandstone (Fig. 4.16 A).
It has been argued that if these structures were of inorganic origin, they should either
represent sandstone dykes or some diagenetic structures. In the Sursagar mines, the
transverse sections to the bedding planes can be studied in detail as there are many
available areas and sections for such scrutiny, but nowhere has any evidence for the
presence of sandstone dykes and sills has been noticed. Moreover, the interwoven nature
of the tube like structures at many places rules out the possibility of these structures being
sandstone dykes. These structures are synsedimentary with the formation of the sandstone
and it is inferred from the fact that a thin microbial mat in the form of small blisters
referred to as a microbial mat Rameshia rampurensis (see Kumar and Pandey, 2008) has
also engulfed the tubular structures. This is possible only when the plant already existed
before the development of the microbial mat. Thus, the chances of it is being a primary
inorganic sedimentary structure as well as a diagenetic structure are ruled out. If
biogenic, it has also been evaluated as to whether these structures belong to a plant
kingdom or they represent the body fossils or trace fossils. It is not comparable to any
animal body fossil or trace fossil and its morphology is also not comparable to any
microbial mat induced sedimentary structures (MISS) (see Schieber et al., 2007). But it
has a pattern and consistency comparable to the thallus of nonvascular plants. In support
of its nonvascular plant origin the following points can be cited:
38
Fig. 4.13: Geological and location map of the Jodhpur area, western Rajasthan (after Pareek, 1984).
I. The structure is represented by a filamentous tube which is comparable to a
thallus of a nonvascular plant. It is nonseptate with smooth margins. In cross
section the thallus is circular, elliptical or compressed. At a few places, it is
preserved as a hollow tube with thin walls.
II. It has tapering ends but the thallus maintains its width for a considerable length.
39
III. Branching is prominently seen in the thallus.
IV. In the middle part of the thallus, a swelling is seen which looks like an intercalary
sporangia as seen in the living Vaucheria (Fig. 4.15 K).
V. Presence of swelling at the end of the thallus as well as on the thallus is a
prominent feature. It can be compared with oogonium (sporangia) of a living
Vaucheriacean plant.
VI. The hook-shaped structures present at the margins of the thallus can be compared
with the antheridium. The antheridia are curved, sickle-shaped cylindrical tube
generally found along with oogonia in modern-day Vaucherian algae (Robin
South and Whittick, 1987).
All these features support the conclusion that these structures show morphologies
comparable to the nonvascular plants and, hence, it seems that the Jodhpur filamentous
bodies can be assigned to plant kingdom with affinity to the nonvascular plants. The
consistency in the morphology observed at different places also supports this conclusion.
Taxonomy
Two genera and three species of the megaplant fossils have been identified in the
Jodhpur Sandstone. All the species have been assigned to family Incertae sedis as their
true nature could not be deciphered. Their morphology is comparable to the morphology
Fig. 4.14: Litholog of the fossil-bearing horizon,
Sursagar mine area, Jodhpur, western Rajasthan.
40
of the Vaucheria plant in shape, branching, presence of beads and antheridium but the
dimensions are so dissimilar that it is not possible to compare them. They are megascopic
and Vaucheria is microscopic. The plant fossils are recorded only in the Sursagar area,
near Jodhpur which is about 8 km NNE of Jodhpur city (Fig. 4.13). The fossils can be
studied in the different mine pits where about up to ca. 15 m thick section of the middle
part of the Jodhpur Sandstone is exposed. The GPS value of the fossil-bearing horizon is
N26o20.007' and E72o59.76'. Since the rocks are more or less horizontal, cross bedding
(Fig. 4.14), the bedding planes can be searched for the plant fossils in different mines.
These are preserved as mould and cast on the bedding planes of the light brown coloured,
fine to medium-grained sandstones. The fossils are marked by the relatively darker colour
in comparison to the host rock on the exposed bedding surfaces (Fig. 4.16 D) and the
grain size marking the structure is relatively less in comparison to the host rock. But in
the fresh section they are also of lighter colour. All the samples have been deposited in
the Museum of the Department of Geology, University of Lucknow, Lucknow.
Family: Incertae sedis
Genus: Vendophycus gen. nov.
(Figure. 4.15)
Type Species: Vendophycus rajasthanensis gen. & sp. nov.
Holotype: Sample no. SK-15
Paratype: Sample no. SS/SK-10, 11, 12, 14
Locality: Sursagar mines, Jodhpur area, Rajasthan.
Lithology: Fine to medium grained sandstone.
Stratigraphic horizon: Middle part of the Jodhpur Sandstone (Sonia Sandstone of Pareek,
1984).
Nomenclature: Genus is named after the ‘Vendian’ stage denoting the age of the Jodhpur
Sandstone.
Diagnosis: The plant is generally preserved as cast on the bedding surface. It is
occasionally preserved as mould also. It is represented by filamentous form which is
large in size and made up of nonseptate cylindrical and tubular body, straight to sinuous
41
with smooth margins (Fig. 4.15 D, G and 4.18 B). It is freely branched with tapering ends
(Fig. 4.15 A, B). Branching generally occurs at acute angles but the branching at obtuse
angle is also noted (Fig. 4.15 F). Interwoven nature of the filaments is also seen. The
width of the filament varies from 0.3 to 5 cm. If the tubular filament is thin, it shows
smooth upper surface and is circular to elliptical in cross-section (Fig. 4.16 F), but in
thicker filaments striations are seen on the surface of the filament wall and it is
compressed or flattened (Fig. 4.15 C). The filaments appear to be hollow with a thin wall
(Fig. 4.15 E). It shows a tendency to break or split with smooth margin in the middle part
of the thallus (Fig. 4.15 D). Overlapping of filament is also observed (Fig. 4.15 H). Tip of
the filaments is either tapering or becomes swollen forming a circular, globular or
elliptical body (Fig. 4.15 I, J). Small, curved bodies noted on the filament can be
compared to the antheridia of a living Vaucheria plant of Xanthophycean affinity (Fig.
4.15 J).
Remarks: The structure under consideration is preserved as mould and cast in which no
trace of organic matter could be recovered. Thus there is no way to confirm the organic
nature of the structure. It is the morphology of the structure which can help in assigning
its affinity. The morphology is comparable to vegetative thallus and the swollen ends as
sporangia of living Vaucheria only in shape. Hence, the structure appears to be closest to
the family Vaucheriaceae under the class Xanthophyceae, order Vaucheriales and
division Xynthophyta. But since the dimensions are so different it is kept under the
family Incertae sedis. The filament is described as thallus, and the swellings beads as
sporangia. The curved structure attached to the thallus has been diagnosed as
antheridium. The present form is megascopic with width as large as 5 cm while in
Vaucheria it is less than 1 mm. Vaucheria like fossils are known since Mesoproterozoic
(see Butterfield, 2004). Figure 4.15 C depicts the development of microbial mat over the
thallus on the rippled bedding surface confirming to the synsedimentary nature of the
thallus.
42
Fig 4.15: Plant fossils of the Jodhpur Sandstone, Sursagar area, Jodhpur, western Rajasthan. A) The holotype of Vendophycus rajasthanensis showing thallus with swollen tips referred as beads; arrow marks the beads; B) Close-up view of (A) showing the swollen part at the tip. C) Development of microbial mat over the thallus of plant fossil on the bedding surface; D) Vendophycus rajasthanensis showing thallus with smooth wall preserved on the top of the rippled surface of the medium grain sandstone. E) Thallus preserved as hollow tube; F, Development of thallus showing fertile structures at their tips as beads. G, Branching pattern of Vendophycus rajasthanensis seen on the bedding surface; H) Figure shows overlapping of thallus as well as splitting tendency of thallus; I) Magnified view of (D) showing well developed fertile structure (oogonia); J) Close up view of (K) showing cf. developing synzoospore and K) Figure shows well developed thallus with antheridia and oogonia, marked by arrows “a” and “b” respectively.
43
Vendophycus rajasthanensis gen. & sp. nov.
(Figure. 4.15, 4.18 B)
Holotype: Sample no. SK-15 Paratypes: Sample no. SS/SK-10, 11, 12, 13 Locality: Sursagar mines, Jodhpur. Lithology: Fine grained to medium grained sandstone. Nomenclature: The species is named after the “Rajasthan” state in western India from
where it is being reported for the first time.
Diagnosis: The plant is generally preserved as cast on the bedding surface. It is
occasionally preserved as mould also. It is represented by filamentous form which is
large in size and made up of nonseptate cylindrical and tubular body, straight to sinuous
with smooth margins (Fig. 4.15 D, G and 4.18 B). It is freely branched with tapering
ends. Branching generally makes at obtuse angles also (Fig. 4.15 F). Interwoven nature of
the filaments is also seen. The width of the filament varies from 0.3 to 3.5 cm. If the
tubular filament is thin, it shows smooth upper surface and is circular to elliptical in
cross-section, but in thicker filaments striations are seen on the surface of the filament
wall and it is compressed or flattened (Fig. 4.15 C). The filaments appear to be hollow
with a thin wall (Fig. 4.15 E). It shows a tendency to break or split with smooth margin in
the middle part of the thallus (Fig. 4.15 D). Overlapping of filament is also observed (Fig.
4.15 H). Tip of the filaments is either tapering or swollen forming a circular, globular or
elliptical body (Fig. 4.15 I, J). The mean diameter of the globular bodies is 1.6 cm. Small,
curved bodies noted on the filament are comparable to the antheridia of living Vaucheria
(Fig. 4.15 J).
Remarks: It is characterised by many swellings at the end of the filament tips, whereas
they are very few in V. sursagarensis and swellings are smaller in size.
44
Vendophycus sursagarensis gen. and sp. nov.
(Figure. 4.16, 4.18 A)
Holotype: Sample no-SS/SK-16 Paratypes: Sample no-VS/C 1-4 Locality: Sursagar mines, Jodhpur. Lithology: Fine to medium grained sandstone. Nomenclature: The species is named after the locality Sursagar, near Jodhpur Township
from where it is reported for the first time. Diagnosis: The plant is generally preserved as cast on the bedding surface. It is
represented by filamentous tube, large in size made up of nonseptate cylindrical and
tubular body, straight to sinuous with smooth margins. It is freely branched (Fig. 4.16 B
and C) with tapering ends. Interwoven nature of the filaments is also seen. The maximum
width of the filament is up to 5 cm. The maximum length recorded is 167 cm. The
filament bifurcates at a mean angle of 56o (N=8). The maximum elevation of the filament
from the bedding surface is 1.4 cm (N=10). Bifurcation on an average is after a length of
35 cm (N=15). If the tubular filament is thin, it shows smooth upper surface and is
circular to elliptical in cross-section (Fig. 4.16 F), but in the thicker thallus it is
compressed or flattened with striation on the surface. The thallus is curved and smooth
walled (Fig. 4.16 F). It shows a tendency to break or split in the middle (Fig. 4.16 G and
H). Very few swollen tips are seen with diameter ranging from 2 to 3 mm (Fig. 4.16 E).
45
Fig 4.16: Vendophycus sursagarensis reported from the Jodhpur Sandstone, Sursagar area, Jodhpur, western Rajasthan. A) Photomicrograph showing the contact of the host rock and the thallus of the plant fossil. The dotted line marks the contact; B) Well developed branching pattern in the thallus; C) View of the thallus showing regular pattern of branching; D) Swollen structures at the tip of the thallus; preserved as negative hyporelief; E) Swollen structure seen at the tip of the thallus; F) Elliptical size of the thallus in cross sectional view, preserved in sandstone and G-H) Typical characteristic feature of splitting of the thallus at middle observed in Vendophycus sursagarensis.
46
Remarks: The difference between the two species of the genus Vendophycus is that in the
V. sursagarensis the swollen tips are very few and rare, while in the V. rajasthanensis
they are common and the swellings are relatively larger in size. The frequency of
branching is more in Vendophycus sursagarensis than in V. rajasthanensis.
Family: Incertae sedis
Genus Indophycus gen. nov.
(Type Species: Indophycus marwarensis gen. and sp. nov.)
(Figure. 4.17)
Holotype: Sample no.SS/SK-1 Paratypes: Sample no. SS/SK-2, 3, 4, 6 Locality: Sursagar mines, Jodhpur area. Lithology: Fine to medium grained sandstone. Stratigraphic horizon: Middle part of the Jodhpur Sandstone (Sonia Sandstone of Pareek,
1984). Nomenclature: Genus is named after India from where it is being reported for the first
time.
Diagnosis: The plant is preserved as cast and rarely as mould on the bedding surface. It is
represented by filamentous tubes with profuse branching (Fig. 4.17 A and B). It is made
up of nonseptate cylindrical and tubular body, straight to sinuous, with smooth to uneven
margins (Fig. 4.17 E). It is freely branched with a tapering end. Interwoven nature of the
filaments is also seen (Fig. 4.17 A). The maximum length recorded is up to 72 cm. The
width of the filament varies from 0.5 to 3 cm. In a few forms, the thallus is marked by a
depression in the middle (Fig. 4.17 B). Tip of some filaments becomes swollen and forms
a circular or elliptical body which is comparable to sporangia of living Vaucheria (Fig.
4.17 F). Size of swollen bodies varies from 0.4 to 1.4 cm. The filaments also show
abundance of bead like bodies attached at the margin of the thallus (Fig. 4.17 D). Even
serrated or cracked margin is quite common (Fig. 4.17 E). Presence of small, curved
bodies or antheridia (male sex organs) (Fig. 4.17 G) on the filament is also noted. The
antheridia are about 1 cm in length and 0.5 cm in width.
47
Fig 4.17: Plant fossil Indophycus marwarensis reported from the Jodhpur Sandstone, Sursagar area, Jodhpur, western Rajasthan. A) Indophycus marwarensis showing shrub-like profuse branching with abundance of bead like structure on the thallus preserved on the top of the bedding plane; B) Figure shows hollow depressions in the middle of the thallus, marked by the arrow; C) Excellent preservation of fertile structures (oogonia) closely attached with the thallus; D) Closely attached bead like structure at the wall of thallus with bulbous tip; E) Close up view of the thallus showing closely attached beads making the outer wall serrated which is marked by the arrow; F) Photograph showing development of thallus with well preserved beads as fertile structures. Arrow marks the structures and G, Magnified view of fertile parts of plant; antheridia and oogonia are marked by the arrows “a” and “b” respectively.
48
Remarks: Indophycus differs from Vendophycus in having smaller dimensions, more
profuse branching pattern and abundance of bead-like bodies on the tubular/cylinderical
thallus. The thallus never breaks or splits in the middle as is commonly seen in
Vendophycus. Size is smaller in comparison to Vendophycus and the branching is more
common in Indophycus giving a shrub-like appearance.
Indophycus marwarensis gen. and sp. nov.
(Figure. 4.17, 4.18 C)
Holotype: Sample no.SS/SK-1 Paratypes: Sample no. SS/SK-2, 3, 4, 6 Locality: Sursagar mines, Jodhpur. Lithology: Fine to medium grained sandstone. Stratigraphic horizon: Jodhpur Sandstone (Sonia Sandstone). Nomenclature: The species is named after the Marwar region of the western Rajasthan. Diagnosis: As for the genus. Remarks: As for the genus.
• Proposed model for the development of Jodhpur plants The present plant fossils have been recorded from that part of the Jodhpur
Sandstone where the microbial mat or biomat-related structures are abundantly
developed. The make-up of the microbial community is unknown as they did not leave
any record in the sediment. On the basis of the available information on the modern
microbial mats, it is inferred that it must have been made up of cyanobacterial, bacterial
and algal forms (see Noffke, 2010). Most mats in marine or hypersaline environment are
principally cyanobacterial mats built predominantly by eukaryotic microorganisms and
are cosmopolitan in shallow marine, lacustrine and flowing waters (Ward et al., 1992). It
can be presumed that within the microbial community there must have been competition
both for the nutrients and space for growth. The nutrient supply was through surface
membrane. A few microbial forms started to increase their size for occupying larger
space but retained the physiological characters of the original microscopic size.
49
Ultimately, some plants could increase their size to the megascopic level. The microbial
community played the most significant role in stabilizing the sand at the sediment-water
interface up to a depth of few millimeters to possibly several tens of centimeters. This
inference can be drawn on the basis of the abundance of microbial related sedimentary
structures which are conspicuously common in the middle part of the Jodhpur Sandstone
(Sarkar et al., 2008), the firm sandy bottom layer is possible only when the sand is made
firm by the development of microbial mat. The microbial mats that developed at the
water/sand interface offered resistance to erosion. In addition, the absence of benthic
animal population which could have produced burrows for living and were sediment
feeders, the microbial mats were not bioturbated and remained stable. Thus, a stabilized
and firm ground was available in sandy substrate for the growth of megaplants. During
the Ediacaran period, the plants were not growing vertically but developed a creeping
mode of growth which followed the sediment/water interface partially embedded within
the microbial mat. The following conditions can be suggested for this change:
i. The Jodhpur plants developed at the microbial mat-water interface partly
embedded within the microbial mat in a shallow water marine setting where sand was
being dominantly deposited in a moderate energy condition. The microbial mat could
develop in the upper few centimeters of sandy substrate.
ii. The increase of the plant size was triggered because of the competition between
the various communities of algae and cyanobacteria and it was facilitated by the
availability of space for the growth on the upper surface of the mat and ambient water.
iii. The embedded nature of the plant within the microbial mat gave stability to the
plant.
iv. Holdfast, if present, could not be preserved or destroyed early.
v. This plant assemblage did not survive in the Cambrian because of the appearance
of animal life which started bioturbating the sediments. It also affected the stability of the
microbial mats. The animals also nourished on the mega plants. With the loss of mats, the
50
plants lost their habitat. With the loss of habitat and sudden growth of benthic animal life
in the Cambrian the mega plants became extinct.
vi. Fig. 4.18 (A-C) gives the line sketch of the three plant species to highlight the
morphological difference between them. Fig. 4.18 D shows the schematic diagram
showing the development of the Jodhpur plants on the microbial mat. The mat has
stabilized the sand and the plant is embedded within the mat.
51
Fig 4.18: Schematic diagrams of Jodhpur plant. A, Vendophycus sursagarensis, B, Vendophycus rajasthanensis C, Indophycus marwarensis. D, Schematic diagram depicts the mode of occurrence of the Jodhpur plant. The plant is embedded within the microbial mat in the Jodhpur Sandstone.
52
4.1.3 Microbial Mats
Description of Microbially Induced Sedimentary Structures
(MISS)
Sarkar et al. (2008) have described a number of mat related morphologies which are
preserved in the Jodhpur Sandstone and considered them simply as the mat-influenced
sedimentary structures. But in the present work, these structures are described under three
headings:
A. Those microbially induced structures which could be compared with the structures
also produced by the inorganic processes.
B. Those structures which have unique morphologies and could not have been produced
by inorganic processes alone.
C. Those structures which could not acquire specific morphologies and can be referred to
as ‘textured morphological surfaces’ in the sense of Gehling and Droser (2009).
Six structures have been described by using binomial nomenclature. These are
described as ‘group’ and ‘form’ as used for the stromatolites instead of ‘genus’ and
‘species’. It is done for the ease of communication, conceding the fact that these
morphologies are not true fossils but are the product of a collective interaction of a
community of micro-organisms with the sediments. It is emphasized that the form and
group are not species and genus in the true sense of palaeontology; for example the
nomenclature is used for describing siliciclastic mat structure Arumberia banksi from the
Arumbera Sandstone, Australia reported originally by Glaessner and Walter (1975) but is
now considered a mat structure (McIlroy and Walter, 1997) and it is not a species but a
‘form’. In all, 12 microbial forms and 2 types of textured morphological surfaces have
been described from the Jodhpur Sandstone which owes their origin to the microbial
activity at the time of the formation of the sandstones. These have been reported from
two areas; one is the Sursagar area near Jodhpur and the other is the Khatu area, about 60
km from Nagaur Township in the western Rajasthan. The samples have been deposited in
the museum of the Centre of Advanced Study in Geology, University of Lucknow,
Lucknow, Uttar Pradesh.
53
Fig 4.19: Geological and location map of the Marwar Supergroup western Rajasthan, showing study area (after Pareek, 1984).
54
A. Microbially Induced Sedimentary Structures which also show similarity with the inorganically produced sedimentary structures:
(i) Microbial Flat Laminated Beds (Fig. 4.21 A)
In the Sursagar area, there are many sandstone beds in the Jodhpur Sandstone on
whose bedding surfaces incomplete or isolated ripples are preserved. The thickness of
such beds varies from a few centimeters to tens of centimeters and they are massive
looking. The height of the ripple crest is up to about 4 mm and the distance between the
two crests varies from 1.4 to 3 cm. In most of the cases, the ripples are wave ripples. The
two ripple crests are separated by plane or flat surface. A number of horizons are noted in
the middle part of the Jodhpur Sandstone in the Sursagar mines. Formation of incomplete ripples or isolated ripples over a sandstone bed is
suggestive of a fact the structure is formed only when the basement for the incomplete
ripples was made firm and stable before the formation of these ripples. The incomplete
ripples are formed when there is insufficient supply of sand to cover the entire surface on
the firm bottom and the wave motion or the current action tends to heap the grains or
Fig 4.20: Litholog of the MISS (Microbially Induced Sedimentary Structures) bearing horizon of the Jodhpur Group.
55
particles into isolated small symmetrical or asymmetrical lenticular bodies (Reineck and
Singh, 1980). Sand being non-cohesive requires presence of microbial community to
make a firm substrate.
In the modern sediments, flat laminated microbial mats rarely form relief above
the horizon but they may extend to some depth below the surface from a few mm to
several meters (Franks and Stolz, 2009). As such, it is very difficult to distinguish these
beds in absence of the preservation of microbial community in siliciclastic sandy
sediments from the beds produced by purely inorganic processes. However, any evidence
which can give clue about the stability and firmness of non-cohesive sandy beds may
help in the identification of microbially formed flat beds.
(ii) Microbial Wrinkle Marks
(Fig. 4.21 B, C and D)
These are represented by small ridges developed on the bedding surface which
vary in height from 1 mm to 17 mm. They are straight to curved, sinuous to irregular. The
ridges can be traced up to 40 cm or more. The ridges are separated by flat to slightly
concave surfaces. They also bifurcate. At few places the ridges are arranged in such a
way to form more or less semicircular pattern. It appears that depending upon the level of
cohesiveness and the available hydrodynamic conditions a variety of morphologies
representing wrinkle marks are produced in the fine to medium grained sandstone. Sarkar
et al. (2008) have described similar structures from these sandstones as mat-layer
wrinkled structures (mlw).
These wrinkle marks are comparable to the wrinkles marks produced in the mud
by inorganic processes. However, in the sandstones their presence is possible only when
the sand is made cohesive by the development of microbial mats due to the presence of
EPS (Extracellular Polymeric Substance). In literature, these are also described as
Runzelmarken and Kinneyia ripples (Reineck and Singh, 1980). There are many places in
the different mine sections around Jodhpur where wrinkle structures are well preserved in
the sandstones.
56
(iii) Microbial Buns and Mounds
(Fig. 4.21 E and F)
On the bedding surface of the sandstone, the bun or small mound shaped domal
structures are seen on the ripples and non-rippled surfaces which vary in diameter from 4
cm to 20 cm with an average of 8.6 cm (N=10). The maximum height recorded is 3.5 cm.
The surfaces as well as the margins of the buns are smooth. Generally these are circular
but elliptical outline also noted. In cross section no cavity filling or any other internal
structure is seen. These structures have not affected the ripple crests and their continuity
can be traced on these mounds suggesting that these structures were formed after the
formation of the ripples. Noffke (2010) has suggested that the decay of organic matter in
the microbial mat will produce gases which may accumulate under the sediments sealing
the mat. With increasing pressure the gas will lift the microbial mat which may lose
contact with the under lying substrate. It will produce a hallow cavern. But in the present
case no hallow gap is noted which rules out the role of gases in producing the domal
structures. There is also no evidence of the presence of escaping water jet to produce
domal structures. Thus, the chances are fair that these domes are formed by localized
microbial growth.
57
Fig 4.21: Field photograph of Microbially Induced Sedimentary Structures (MISS) reported from the Jodhpur Sandstone, western Rajasthan. A) Incomplete ripples over microbially flat laminated surface (coin diameter = 2.4 cm); B, C and D) Various types of well preserved sinusoidal, curved and straight wrinkle marks on the bedding surface (coin diameter = 2.4 cm and lens cap diameter = 5.7 cm); E and F) “Bun shaped” microbial structures with positive relief (maximum elevation from the bedding plane = 3.5 cm), the growth of the “bun shaped” structure not effected the ripples (lens cap diameter = 5.7 cm).
58
(iv) Cracks in Sandstones
(Fig. 4.22 A) At a number of places, the sandstone shows cracks which compare well with the
mud cracks/synaeresis cracks of the argillaceous rocks. The cracks are irregular. The
width varies from 1-2 mm. These cracks join each other and form the polygon whose size
(longest axes) ranges from 0.4 cm to 2.5 cm. The cracks have depth up to several mm.
From the same horizon Sarkar et al. (2008) have described cracks in the sandstone as mat
induced surface cracks (misc).
These cracks in the sandstones are possible only when the sand becomes cohesive
just after its deposition; on drying the mat cracks to form the structure. In the absence of
lithification, the only possible way by which the sand can be made cohesive is by
invoking the role of microbial mats which developed either immediately or shortly after
the deposition at the sand-water interface involving up to few mm or few cm thick
organically produced layer. This layer under drying conditions developed cracks. Some
of these cracks may have subsurface synaeresis origin. The presence of cracks in the
sandstones simply confirms the role of microbial mats.
(v) Cracks along the Ripple Crests
(Fig. 4.22 B)
Some of the ripple crests show cracks which run parallel to the strike of the crests.
Generally, the cracks are not seen at right angle to the crests or in the troughs. The cracks
are 2.4 cm wide and up to 0.6 cm deep. If the ripples are formed and then partly eroded
then the crest should have a planar surface. However, the crests show cracks all along the
strike marked by a depression. It is envisaged that a thin microbial layer was formed after
the formation of the ripple marks which stabilized the ripples. The ripples were
subsequently eroded but instead of producing flat surface at the ripple crest, the crests
show cracks which depict somewhat deeper and marked erosion with preserved thin
margins. Sarkar et al. (2008) have described them as mat-induced cracks along ripple
crests (micr).
59
(vi) Microbially produced Inverted Flute Cast
(Figs. 4.22 C and D)
These structures look like inverted flute casts arranged parallel to each other on
the top of the sandstone beds. They are steep at one end and flare out at the other. The
maximum recorded length is 2.8 cm and the width is 1.4 cm. They have a positive relief
and are oriented in one direction. The structure is described from both modern beaches
and ancient sediments (Friedman and Sanders, 1974; Sarkar et al. 2008; Chakraborty et
al. 2013). For preservation of this structure, Sarkar et al. (2011) have suggested the role
of microbial mat. For its genesis they have envisaged the role of trapping of wind
deflated sands on the lee sides of moist obstructions of sections in the littoral-supralittoral
depositional setup. These obstructions must have been formed by the even growth on the
microbial mat surface. Sarkar et al. (2008) have reported them as mat protected setulf and
referred to them as mpsf.
B. Microbial Structures which could not have been produced by
inorganic processes alone: Under this heading all such structures are grouped which could not have been
produced by inorganic processes alone and the role of the microbial mat is essential for
their genesis. The structures described in the previous section can be produced by the
inorganic processes in the cohesive sediments but the structures described in this section
cannot be produced without the participation of microbial mats. All the structures have
been given binomial nomenclature for the ease of communication conceding the fact that
they are not true species and genera in the traditional sense of palaeontology. Instead they
are referred to as ‘form’ and ‘group’ as have been done in describing the stromatolites.
60
(vii) Aristophycus Miller and Dyer 1878 (in Häntzschel, 1975)
(Type form: Aristophycus ramosum Miller and Dyer 1878; in Häntzschel, 1975)
Aristophycus sp.
(Figs. 4.22 E and F)
Sample no: SK/ARI-12/09.
Locality: Khatu area, Nagaur district, Rajasthan; GPS value N27º 8.837’, E74º 19.596’. Lithology: Fine grained sandstone. Stratigraphic horizon: Middle part of the Jodhpur Sandstone. Description: It is a branching form characterized by anastomizing raised ridges seen on
the top of the sandstone bed. It shows main branch, generally straight to slightly curved
in which secondary, tertiary and quaternary branches develop forming anatomizing raised
structure. The main branch shows maximum width as 1.8 cm. For secondary and tertiary
branches it decreases gradually. The height of the raised structure is 5 mm. Tapering is
quite prominent and it starts from the side of maximum width. The maximum width in
the main branch is seen at the raised part of the bedding plane. The secondary and tertiary
branches bifurcate and rarely trifurcate. The raised ridges show flat or slightly convex
surface. Branches make an angle which ranges from 30o-60o. Area between ridges is
concave to smooth. The margins of the ridges are smooth. The ridges taper off and
merges with the bedding plane at the distal part. The structure is developed around a
raised part made up of sandstone clasts.
Remarks: Aristophycus is a branching structure well developed in the Khatu area in the
northern side of the main hillock at western side of the Khatu Township. It is recorded in
the fine grained light whitish coloured sandstone showing large scale cross bedding. It is
developed around large sized sandstone clasts. The clast shows slightly higher position
with respect to the bedding and there is a slope around the clasts. The structure is
developed with large stem or main branch near the clast and as one moves away from
clast the width decreases. Originally the structure was considered as of inorganic origin
and Häntzschel (1975) included it under the heading ‘Pseudofossils’. Seilacher (2007)
suggested the origin of this structure. He considered Aristophycus as a dewatering
structure. It is formed when water escapes during compaction from the sand and it is
61
stopped by the overlying biomat. Since the water fails to escape, it dissipates below the
biomat eroding its sole producing a structure resembling a distributary river system.
Subsequently the sand below the mat occupied the eroded space to produce the structure.
Fig 4.22: A) Well developed cracks in the sandstone (scale = 12cm); B) Cracks along the ripple crests bounded by sharp ridges (marked by arrows) by both sides of the crack (coin diameter = 2.3cm); C) Inverted flute structure in sandstone illustrates surface pavement in which sand has accumulated forming small drumlin shaped inverted flute cast (coin diameter = 2.4cm); D) Magnified view of Inverted flute Structure (scale bar = 2cm); E) Well preserved Aristophycus around a large sandstone clast showing primary, secondary and tertiary bifurcations (coin diameter = 2.4cm) and F) Close up of Aristophycus: an inorganically formed structure showing well developed bifurcations which is possibly formed by action of water current and microbial mat (coin diameter = 2.4cm).
62
(viii) Arumberia banksi Glaessner and Walter 1975
Group: Arumberia Glaessner and Walter 1975 (Type form: Arumberia banksi Glaessner and Walter 1975)
(Fig. 4.23 A) Sample no: Kh0608. Locality: Khatu area, Nagaur district, Rajasthan; GPS value N27º 8.837’, E74º 19.596’. Lithology: Fine-grained sandstone. Stratigraphic horizon: Upper part of the Jodhpur Sandstone. Description: It is marked by the presence of small ridges seen on top of the bedding plane
separated by flat to concave furrows. These are parallel, straight, gently curved and
between 1 to 3 mm wide separated by flat to gently concave furrows of 1 to 4 mm in
width. The relief of the ridges is less than 1 mm and maximum recorded length is 14 cm.
Generally the ridges are parallel but they also bifurcate. It is seen on plane as well as
rippled surface. Remarks: This form was originally described by Kumar and Pandey (2009) from the
same locality. It compares well with Arumberia banksi described by Glaessner and
Walter (1975) from the Arumbera Sandstone, Australia. It also compares with the form
described by Kumar and Pandey (2008) from the Maihar Sandstone, the uppermost
lithostratigraphic unit of the Bhander Group of the Vindhyan Supergroup of the Son
Valley Section. It grades to Rameshia rampurensis with the development of small
mounds/blisters or pustules interspersed and superimposed on the Arumberia banksi (Fig.
4.15-F).
(ix) Rameshia rampurensis (Kumar and Pandey, 2008)
Group: Rameshia Kumar and Pandey, 2008
Type form: Rameshia rampurensis Kumar and Pandey, 2008
(Figs. 4.23 B and C)
63
Sample no: Kh0808. Locality: Two localities; one is in Khatu area, Nagaur district with GPS value N
27°08.168′; E 74° 18.871′ and the second is in the Sursagar area, Jodhpur district with
GPS value as 26°15.774′ N ; 73°00.148′ E.
Lithology: Fine-grained sandstone. Stratigraphic horizon: Upper part of the Jodhpur Sandstone. Description: It is made up of rounded to elliptical very small mounds/blisters making the
entire surface granular. The size of the blisters ranges from 1 mm to 4 mm. Generally it is
circular to elliptical. It gives a mat texture to the bedding plane. It is seen both on the
rippled surface as well as on the plane bed.
Remarks: Kumar and Pandey (2009) were the first to describe it from the Khatu area. It
compares well with form described from the Maihar Sandstone of the Vindhyan
Supergroup by Kumar and Pandey (2008). In the Sursagar area, there are many horizons
where this structure is seen.
(x) Rameshia linearis New form
(Figs. 4.23 D and E) Sample no: SK/JD08/12. Locality: Two localities; one is in Khatu area, Nagaur district with GPS value N
27°08.168′ ; E 74° 18.871′ and the second is in Sursagar area, Jodhpur district with GPS
value as N 26°15.774′ ; E73°00.148′. Lithology: Fine-grained sandstone. Stratigraphic horizon: Middle part of the Jodhpur Sandstone. Diagnosis: It is made up of rounded to elliptical very small mounds/blisters arranged in
rows. At places rows are made up of two or more blisters. Diameter of the blisters ranges
from 1 mm to 5 mm. Generally the blisters are circular to elliptical. The rows are straight
to slightly curved. The rows can be traced up to 26 cm. The distance between the two
64
rows varies from 8 mm to 10 mm. It is seen both on the rippled surface as well as on the
plane bed. Description: As above. Derivation of name: The form is named because the blisters are arranged in rows.
Remarks: In Rameshia rampurensis the blisters cover the entire surface of the bedding
plane, whereas in R. linearis the blisters are linearly arranged in rows. Gerdes (2007) has
suggested the role of gases which are formed by the decay of microbial mats in producing
the structure.
65
Fig 4.23: A) Arumberia banski showing presence of small ridges on bedding surface separated by concave furrows (coin diameter = 2.4cm); B and C) Rameshia rampurensis showing very small mounds or blisters making the entire bedding surface granular (coin diameter = 2.4cm); D) and E) Blisters are arranged in a linear fashion (coin diameter = 2.4cm) and F) Transitional form exhibiting characteristics both Arumberia and Rameshia, (coin diameter = 2.4cm).
(xi) Rameshia anastomose (New form)
(Fig. 4.24 A)
Sample no: SK/JD09/12. Locality: Sursagar area, Jodhpur district with GPS value as N 26°15.774′; E73°00.148′.
66
Lithology: Fine grained sandstone. Stratigraphic horizon: Middle part of the Jodhpur Sandstone. Diagnosis: It is made up of rounded to elliptical very small mounds/blisters arranged in
rows which form irregular pattern. Diameter of the blisters ranges from 1 mm to 4 mm.
Generally the blisters are circular to elliptical. The rows are curved and form different
enclosed patterns. The diameter of the enclosed area varies from 2 cm to 5 cm. Description: As above. Derivation of name: The form is named after the nature of the rows of the blisters which
form irregular enclosed patterns. Remarks: In Rameshia rampurensis the blisters cover the entire surface of the bedding
plane, whereas in R. linearis the blisters are linearly arranged more or less in straight
rows. In the present form the linearly arranged blisters form irregular enclosed patterns.
(xii) Jodhpuria new group
(Type species: Jodhpuria circularis)
(Fig. 4.24 B and C)
Sample no: SK/1108. Locality: Sursagar area, Jodhpur district with GPS value as N 26°15.774′; E73°00.148′. Lithology: Fine-grained sandstone. Stratigraphic horizon: Middle part of the Jodhpur Sandstone.
Diagnosis: It is made up of very thin ridges forming complex colonies in which the
individual colony is formed by a circular flower like pattern. It is made up of a central
body with expanding circular ridges which subsequently interfere with adjacent colonies.
The individual circular outline in general is not continuous but broken to form somewhat
irregular pattern which collectively form expanding flower like pattern. Length of the
ridges varies from 10 cm to 25 cm. Top of the ridge smooth and rounded. Height of the
67
ridges is less than 1 mm. It is seen both on the rippled surface as well as on the plane
beds.
Derivation of name: The form is named after the town Jodhpur from where it is reported
for the first time.
Remarks: Sarkar et al. (2008) have described it as mat related structures and referred it as
mld (mat-layer discoidal) structure. Banerjee et al. (2010) have compared this structure
with Palaeopascichnus though in no way it is related to this trace fossil.
Jodhpuria circularis new group and form
Jodhpuria circularis
(Fig. 4.24 B and C)
Description: It is made up of very thin ridges forming a pattern of rose petals or flower
like pattern arranged in a circular or concentric manner around a rim which is more or
less circular in outline or having a distorted shape. The expanding pattern of ridges
overlaps the previous ridges and creates a unique pattern. The expanding ridges
subsequently interfere with the adjoining units. The size of the central sub-circular rim is
ca 4.2 cm and the maximum size of the circular pattern is 34 cm (excluding outer petal
like structure marked in Fig. 4.16 B). The width of the ridges varies from 1 mm to 2.4
mm. The entire structure covers an area of about 1 meter. The area between the ridges is
smooth. The concentric rims quite often produce spindle shaped bodies. Sarkar et al.
(2008) have called these patterns as mat-layer discoidal structures (mld).
Remarks: As for the group.
Derivation of name: It is named because of the circular nature of the ridges.
C. Structures which could not acquire specific morphologies and can be referred to
as ‘Textured Morphological Surfaces’:
Textured Organic Surfaces (TOS) are defined as a diverse assemblage of
structures that may have discrete morphological characters but do not have a defined
shape or size that might enable taxonomic description (Gehling and Droser, 2009). On
68
many bedding surfaces of sandstones, there are features which cannot be given any name
as the morphology of the structures could not attain any specific shape. Though Gehling
and Droser (2009) have identified 9 different forms, only two patterns have been
identified here under this heading. These are:
(I) Old elephant skin weathering pattern
(II) Poorly developed patterns
(I) Old elephant skin weathering pattern
(Fig. 4.24 D)
“Elephant skin” texture occurs as network of reticulate ridges that grade laterally
into more irregular pattern (Gehling, 1999). It is developed in grayish black silty
sandstone. According to Seilacher (2007), the elephant skin texture represents a kind of
load casts on a rather smaller scale. The structure is characterized by reticulate ridges on
the upper bedding surface, or respective impression on lower bedding surface. They also
form polygonal network with a width of 5 to 10 mm. Old elephant skin weathering
pattern is geometrically distinguishable forms other mat-forming structures and easily
recognized by its textured surface.
(II) Poorly developed patterns
(Fig. 4.24 E and F)
Under this heading, all such patterns are included which could not be defined on
the basis of morphology. Such forms could not have formed by only inorganic processes.
There are many records of mat induced structures in the Jodhpur Sandstone which do not
have a specific shape, geometry and pattern which could be given a name but in spite of
that they provide good proxy records of the presence of biomat (microorganisms) in a
shallow marine to sub-tidal environment of the Jodhpur Sandstone.
69
Fig 4.24: A) Rameshia anastomose showing small mound like structure forming anastomose pattern (coin diameter = 2.3cm); B) Jodhpuria circularis showing ridges forming circular to concentric pattern in the central part while in the outer part it forms petal like arrangement of ridges (marked by arrows), (coin diameter = 2.4cm); C) Close up view of Jodhpuria circularis; D) Old Elephant Skin (OES) textured surface (coin diameter = 2.3cm); E and F) Poorly developed microbial structures on rippled surface (coin diameter = 2.3cm).
70
4.1.4 Stromatolites from the Bilara Group Only stromatolites have been reported from the Bilara Group. Though the
microbiota has been reported from the black chert by Babu et al. (2009), in the present
work none of the thin section of the chert has yielded any microfossil. Prasad (2010) have
reported fossils from the Bilara Group by using maceration methods. The stromatolites
are restricted to the carbonate rocks of Bilara Group only. The carbonate rocks are
exposed in all the three formation of the group i.e. the Dhanapa Formation, the Gotan
Formation and Pondlo Formation (from lower unit to upper unit). Khilnani (1964) was
the first to notice them in the Bilara Group. The stromatolites exhibit diverse
morphologies from domal to columnar forms but most of them are stratiforms sheets of
low relief. Some of these stromatolites are identified by Barman (1987) as Collenia
pseudocolumnaris Maslov, Colleniella Koroyak. Cryptozoon occidentale Dawson and
Stratifera Korolyuk with occasional Oncolites pia (Barman 1980, Verma and Barman,
1980). According to Barman (1987), these stromatolites are generally stunted in growth
as compared to stromatolites of Aravalli, Delhi, Vindhyan Supergroup. The stromatolites
of the Marwar Supergroup do not have well defined margins. Such stromatolites with ill
formed column margin may be termed the colloform mat structures conforming to
subtidal conditions (Hoffman, 1974). Most of the stromatolites of the Bilara Group show
development of asymmetrical laminations with thicker laminae developed on one side.
The stromatolites assemblage, from the carbonaceous Bilara Group (Marwar Supergroup)
has no form which is distinctive for age determination of the host rocks. However, it is
certain that the Late Riphean and the Vendian forms of stromatolites (Preiss 1976 p, 361)
are not present in the Bilara Group of rocks.
71
Fig 4.25. Stromatolites of the Bilara Group. A, D and E- Colonnella columnaris; B- Transverse section of Colonnella. C and F- Coniform stromatolites.
72
Fig 4.26: Stromatolites of the Bilara Group. A- Colonnella columnaris B- Coniform stromatolite C-Transitional form D- Pseudocolumnar form, E and F-New form A (Scale bar = 2 cm).
73
4.1.5 Trace Fossils from the Nagaur Group Only one body fossil has so far been described by Singh et al. (2013). However,
well-preserved trace fossils are abundantly recorded. Kumar and Pandey (2010) were the
first to describe the trace fossils from the Nagaur Group. In the present study, numerous
trace fossils were identified, out of which six forms are new. Most of these fossils are
seen on the sole of the bedding plane as well as on top of the bedding surface. Lithology
is represented by fine-grained sandstone, siltstone and shale.
Fig 4.27: Geological and location map of the Dulmera area, District Bikaner, Rajasthan (after Pareek, 1984).
74
Fig 4.28: Litholog of the Nagaur Sandstone showing the position of trace fossils, Dulmera area, Bikaner district, Rajasthan.
Ichnogenus Rusophycus Hall, 1852
Rusophycus carbonarius Dawson, 1864
(Figs. 4.29 A and B)
Repository ref. NG/SK13/1
Material: A single slab of fine grained sandstone showing 35 specimens preserved as
hyporelief on the sole of the bedding plane.
Description: Convex, coffee-bean-shaped hypichnia, 0.5 to 1.5 cm long with mean value
as 1.03 cm (N=35) and 0.4 to 0.9 cm wide with mean value as 0.6 cm (N=35). The
individual lobe is 0.2 to 0.7 cm wide. The two symmetrical lobes are separated by a
distinct furrow. The furrow is 0.1 to 0.2 cm wide. Lobes are parallel, rarely oblique and
0.3 to 0.5 cm in height from the bedding surface. The median furrow runs for through full
length of hypichnion.
75
Discussion: The specimens do not display the stripes on the lobes which is typical
characteristic of Rusophycus carbonarius (Schlirf et al., 2001). However, Kieghley and
Pickerill (1996) interpreted such specimen as taxonomic variants of R. carbonarius. The
Early Cambrian R. carbonarius was possibly produced by small or juvenile trilobite
(Stachacz, M. 2012). R. carbonarius is believed as a resting trace of tiny arthropod
(Hofmann et al., 2012). Present form is slightly larger in size and closely resembles
ichnospecies R. carbonarius reported from the Holycross Mountain, Poland (Stachacz,
M., 2012).
Rusophycus didymus, Salter 1856
(Figs. 4.29 C and D)
Repository ref. D-108/08
Material: One slab of fine grained sandstone showing two well preserved specimens on
top and nine on the sole of the bedding plane.
Description: Short bilobate, smooth, elliptical in outline, resembling coffee bean,
posteriorly tapering lobes preserved as epirelief on the other side (anterior) making acute
angle (40-45o). The lobes are 0.9 to 3 cm long with mean value as 1.8 cm (N=11) and 0.8
to 2.1 cm wide with mean value as 1.6 cm (N=11), whereas, the individual width of the
lobe varies from 0.4 to 0.9 cm with mean value as 0.6 cm (N=11). The gap between the
lobes varies from 0.2 to 0.7 mm (mean=0.3 cm; N=11). Normally both lobes are parallel
but sometime making an acute angle and median furrow rarely seen. The traces are 2 to 3
mm in height from the bedding surface.
Remarks: Both lobes are smooth devoid of any stripes. Specimen closely resembles
Rusophycus didymus Salter, 1856. This ichnogenus has worldwide occurrence such as
Europe, North America, North Africa, Asia, and the Lower Cambrian of Pakistan
(Moore, 1962). Rusophycus is first described by Salter (1856) and later on by Seilacher
(1953) who interpreted it as a trilobite resting excavation. The specimen is also described
by Kumar and Pandey (2008, 2010) from the same horizon simply as Rusophycus isp.
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Ichnogenus Cruziana d’ Orbigny, 1852
Cruziana fasiculata Seilacher, 1970 (Figs. 4.29 E and F)
Repository ref. DL-45, 47, 51, 52, 56, 60, 102, 124, NS-12 and NS-24 Material: Ten slabs of fine-grained sandstone containing more than fifty two specimens
oriented broadly in particular direction or randomly arranged on the sole of the bedding
plane, while four specimens are preserved on the top of the bed. Description: Elongate furrow, herringbone-shaped ridges with sub-equal scratches.
Median furrow runs parallel and divides the structure into two lobes and continues
uninterrupted. The specimens taper at posterior end and broader at anterior end. Genal
spine absent in all specimens. Width varies from 1 to 3 cm with mean value as 1.6 cm
(N=56), length ranges from 1.4 to 30 cm with mean value as 5.8 cm (N=56). The traces
are 0.5 to 1 mm in height. The gap between the two consecutive scratch marks is 1 to 2
mm. The furrow width ranges upto 0.2 cm. Length of median furrow is as per the size of
the specimen. The podial marks on the lobes meet centrally at a furrow making V-shaped
structure with varying angle ranges from 50-60o. Remarks: Scratch marks present on both the lobes are not identical. Each lobe showing
scratch marks in bundles which is comparatively unequal in 1 cm length. The podial
marks are counted as 8 to 10 lines/cm, which indicates the movement of the animal,
faster or slower. Present specimen is very close to ichnogenus Cruziana fasiculata
Seilacher in terms of podial marks. Cruziana is considered a burrow produced by
trilobites (Seilacher 1970). Cruziana fasiculata is also described by Kumar and Pandey,
(2010) from the same horizon simply as Cruziana isp.
Cruziana cf. salomonis Seilacher, 1990
(Fig. 4.30 A)
Repository ref. NG/SK-13/4&5
77
Material: Two slabs of fine grained sandstone comprising 5 specimens collected from the
Dulmera mine preserved as hyporelief on the sole of the bedding surface.
Description: The form is having typical morphology of Cruziana species. The endopodal
scratches are prominent in the frontal part of furrow. The median furrow has constituent
width all along the trace. The traces are 1.4 to 2.8 cm long with mean value as 3.8 cm
(N=5) and is 2.4 cm wide with mean value as 1.1 cm (N=5). The individual widths of
lobes are 0.9 to 1.3 cm. Both lobes are more or less symmetrical in shape. The continuous
length of furrow up to 1.7 cm is noticed with mean value as 1.5 cm (N=5) along with 0.1
to 0.3 cm wide. The striation joins at the furrow at about 150o to 170o making an obtuse
angle. 10 podial marks are counted in 1 cm length.
Discussion: The present form has close resemblance with the form reported from the
eastern desert of Egypt (Seilacher, 1970) in furrow morphology and obtuse angle
relationship between two sets of podal markings. C. salomonis endorsed to the activities
of small to medium trilobite mostly digging activity within the sand (Hofmann et al.,
2012). The specimen is close to C. salomonis only in terms of angular relationship of
podial marks with respect to median furrow, but differs in lacking 3 to 4 podial marks in
groups.
Ichnogenus Isopodichnus Bornemann 1889
Isopodichnus isp.
(Fig. 4.30 B)
Repository ref. DL-108/106/ 115 and 202 Material: Four slabs of muddy to fine grained sandstone with three specimens preserved
on the top and three on the sole.
Description: Paired ribbon like trail, smooth walls, straight to curved, separated by fine
prominent furrow. There is no marking observed on the wall of track. Trails are 3.4 to 9
cm long and 0.9 to 1.5 cm wide. The furrow runs parallel to the structure and ranges from
0.1 to 0.4 cm in width.
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Remarks: Specimen is comparable to Cruziana as far as the morphology and the outline
the trail is concerned but it lacks any type of scratch marks (sensu Fürich, 1974). The
specimen is closely resembles Isopodichnus described by Kumar and Pandey, (2010).
Ichnogenus Tasmanadia, Chapman, 1929
Tasmanadia cachii Durand and Aceñolaza, 1990 (Fig. 4.30 C)
Repository ref. NG/SK-13/21
Material: One slab containing two specimens preserved as positive relief on fine grained
sandstone on the top of the bedding plane. Description: Double rows of prominent ridges forming “bracket”-shaped structure. The
trace is 2.8 cm long and 1.3 cm wide containing total 14 ridges, seven at both sides. The
space between two contiguous ridges is 0.6 cm. Discussion: Morphologically, the present specimen shows close resemblance with the
Tasmanadia cachii Durand and Aceñolaza (1990) and the trace is interpreted as the
trackway produced by an arthropod. The bracket-shaped outline of the trackway indicates
the shape of the body of the animal; it means that animal moves in jumps rather than
walking continuously (Seilacher, et al., 2005). This ichnospecies is being reported for the
first time from the Nagaur Sandstone.
Ichnogenus Diplichnites, Dawson, 1873
Diplichnites gouldi (Bradshaw, 1981)
(Fig. 4.30 D) Repository ref. NG/SK-13/18 Material: Two specimens preserved hyporelief in fine grained sandstone. Description: Trackway consisting two parallel series of fine ridges, oriented
perpendicular to the track axis. Width of the trackway 1.7 cm and length measured up to
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5.2 cm. Individual ridge elongate, 0.4 to 0.6 cm in length. Both rows of are 0.6 cm apart.
The gap between the two contiguous ridges is 0.3 cm. Both series are well preserved. Remarks: Specimen shows close resemblance with ichnogenus Diplichnites aenigma
Dawson (1873), which is interpreted as a walking trace of trilobite (Seilacher, 1955;
Radwanski and Roniewicz, 1963; Crimes 1970). Specimen quite differs from
Dimorphicnus in respect of lacking prominent ridges. During the movement, the width of
the trace will depend on the size of the animal and how far its limbs extend outside
(Crimes and Harper, 1970). The specimen shows fine imprints oriented perpendicular to
the midline of the trackway which is similar in Diplichnites gouldi Bradshaw, 1981(see
Minter and Lucas, 2009). Diplichnites are abundantly reported from Cambrian rocks
(Seilacher, 1955). The specimen is comparable with the form described by Kumar and
Pandey (2010).
Ichnogenus Merostomichnites Packard, 1900b
(Type ichnospecies Merostomichnites beecheri Häntzschel, 1962)
Merostomichnites isp. (Figs. 4.30 E and F) Repository ref. NG/SK-12/102 Material: Specimens preserved as epirelief in fine-grained sandstone. Description: Sickle-shaped, prominent and parallel rows of ridges arranged in a pair,
obliquely to midline of trackway. Width of the trackway is 1.5 cm and length varying
from 2.4 to 5.3 cm, individual ridge varies from 2 to 5 mm in width and 8 mm in length
while gap between two consistent ridges is 3 to 4 mm. The series of ridges is 6 mm apart
from each other and gap between the two consistent ridges is 2 mm. The ridges are
crescent in outline. Remarks: The specimen is comparable with the ichnogenus Merostomichnites described
by Häntzschel, 1975. It also shows resemblance with the specimen described by Parcha
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and Pandey (2011). Merostomichnites differs from ichnogenus Diplichnites Dawson
(1873) in lacking median grooves and morphology of making podial marks. This
ichnogenus is formed by resting activity of the animal.
Ichnogenus Planolites Nicholson 1873
Planolites beverleyensis, Billings 1862
(Fig. 4.30 G)
Repository ref. NG/SK-13/23 Material: Four specimens preserved as positive hyporelief in fine-grained sandstone. Description: Full relief, unbranched, horizontal to the bedding surface, straight to slightly
curved burrow, partly infilled with host sediments. Individual burrow is 2.0 to 8.5 cm
long and 1 to 3 mm wide.
Remarks: The specimens closely resemble Planolites beverleyensis, Crimes and
Anderson (1985), in unbranched nature of burrows. It is often difficult to distinguish
between Planolites and Palaeophycus Hall, except in non branching nature of burrow.
Planolites beverleyensis has a broad range from Precambrian to Recent.
81
Fig 4.29: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A) Rusophycus carbonarious; B) Close up view of Rusophycus carbonarious; C and D) Rusophycus didymus; E and F) Cruziana fasiculata (diameter of coin = 2.3cm).
82
Fig 4.30: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A) Cruziana cf. salomonis; B) Isopodichnus isp; C) Tasmanadia cachii; D and E) Diplichnites; F) Merostomichnites isp; G) Planolites beverleyensis.
83
Ichnogenus Bergaueria Prantl 1945
Bergaueria aff. perata Prantl 1945 (Fig.4. 31 A, B and C)
Repository ref. NG/SK-13/24
Material: Total four specimens preserved in fine-grained sandstone as positive
hyporelief.
Description: Cup-shaped protrusion with smooth walls, wider than deeper, perpendicular
to bedding plane. Circular to sub-circular in outline 2 to 4 cm in diameter and 0.4 to 1.0
cm deep. Lower end rounded, with shallow depression. Outer wall smooth, devoid of any
striations.
Discussion: Bergaueria is interpreted as a domichion or cubichion produced by actinarian
and ceriantharian coelenterates (Fillion and Pickerill, 1990; Bromley, 1996). Bergaueria
is regarded as a dwelling structure, and present specimen shows close resemblance with
Bergaueria perata Prantl (1945). The specimen has global occurrences from Cambrian to
Ordovician strata (Häntzschel, 1975) but most common in Lower Cambrian (Mc Kee,
1945; Seilacher, 1956; Crimes and Anderson, 1985; Gàmez vintaned et al., 2006).
Ichnogenus Dimorphicnus Seilacher, 1955
Dimorphicnus cf. obliquus Seilacher, 1955 (Fig. 4.31 D)
Repository ref. NG/SK-13/29
Material: one slab of fine grained sandstone with two specimens preserved as positive
hyporelief.
Description: A pair of symmetrical trails horizontal to the bedding plane, the length of
the structure is up to 1 cm and width 1mm, and is less than 1 mm apart from each other.
Remarks: The specimen described herein resembles Dimorphicnus cf. obliquus Seilacher
(1955). According to Seilacher (1955), Dimorphicnus is a grazing trace formed by
trilobites while scratching the sea bottom with appendages in search for food. This
ichnogenus also known from the Lower Cambrian succession of Wales (Crimes, 1970),
Lesser Himalaya (Tewari and Parcha, 2006), Zanskar (Parcha and Singh, 2010), western
84
Rajasthan (Kumar and Pandey, 2008 and 2010), Krol-Tal succession of Lesser Himalaya
(Singh and Rai, 1983).
Ichnogenus: Monocraterion Torell 1870,
Monocraterion isp. (Figs. 4.31 E and F)
Repository ref. NG/SK-13/44
Material: Two specimens collected in situ with full relief within fine-grained sandstone.
Description: Knob-like circular structure projecting downward, perpendicular to the
bedding plane, never branched. The centre of burrow is deep and unornamented; two
circular rings are present; one central and other making the outline of the body. The
diameter of outer ring is 3 to 4.5 cm and up to 1.5 cm deep, while inner circle is 1.8 to 2.3
cm in diameter and up to 0.5 cm deep.
Discussion: The specimen shows close resemblance with the ichnogenus Monocraterion
in terms of its cylindrical burrow and concordant funnel at the top. But present specimen
is not so much deep and it also lacks the well-developed, funnel-like structure, which is a
diagnostic feature of Monocraterion (Häntzschel, 1975). The specimen is also
comparable with the ichnogenus Bergaueria but the presence of circular rings and
absence of any concentric structure on the body completely rules out this idea.
85
Fig 4.31: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A, B and C) Bergaueria aff. Perata; D) Dimorphichnus cf. obliquus; E and F) Monocraterion isp.
86
Ichnogenus Planolites Nicholson, 1873
Planolites annularis Walcott, 1890 (Fig. 4.32 A)
Repository ref. NG/SK-13/39
Material: One slab of fine-grained sandstone having ten specimens preserved as positive
hyporelief on the sole of the bedding plane.
Description: Transversely annulated, horizontal burrow, generally straight, slightly
curved, arranged in a back to back pattern. Single scratch varies from 1.0 to 3.9 cm long
and width 2 to 4 mm. The gap between the annulations is normally 1mm. There are 6 to
8 transverse annulations counted per cm.
Discussion: This specimen shows resemblance with Planolites annularis Walcott,
1890.The specimen also shows some resemblance with the Priapulid-like worm reported
from the Nagaur Group (Srivastava, 2012b) only in transverse annulations, but differs in
overall morphology (shape and size).
Scratch marks/Dig marks
(Figs. 4.32; B, C, D and E)
Repository ref. NG/SK-13/42, 42, 44 and 45
Material: Ten specimens of fine grained sandstone collected as positive relief from the
sole of bedding plane.
Description: Even spaced deep imprints, comb shaped, generally straight, sometime
curved with very prominent ridges from 2.0 to 3.5 cm long and 1 mm in width. The
distance between the two consecutive imprints is 2 mm. The finger print like imprints
(Fig. C and E) possessing 4 to 5 division/cm.
Discussion: The structures shown in fig. 4.32 B show close resemblance with the scratch
marks possibly produced by arthropod. These structures are formed by digging activity of
the animal. On the other hand the structures shown in fig. 4.32 C, D and E are termed
here the trilobite fingerprints rather than scratch marks. These structures have been also
described as trilobite finger prints by Seilacher (2007). Possibly, the fingerprints are left
by the tips of the endopodites displaying groupings of claws or setae. These specimens
87
also show similarity with the dig mark of one lobe produced by trilobite (Crimes and
Harper, 1976).
Fig 4.32: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A) Planolites annularis; B, C, D and E) Scratch marks of arthropods.
88
Ichnogenus Treptichnus Miller, 1889
Treptichnus pedum Seilacher, 1955 (Fig. 4.33, A)
Repository ref. NG/SK-12/05
Material: The specimen preserved in situ as positive hyporelief in fine-grained sandstone.
Two slabs having four specimens were collected.
Description: Burrow system with oblique to curved row of segments, arranged alternately
left and right, or in a zig-zag feather-stitch pattern (Häntzschel, 1975), comparable to
ramification of plants. Individual segments are slightly displaced in relation to each other.
Segments are simple or elongated. Length of individual segments is 0.5 to 2 cm and
width up to 4 mm with 3 mm in height. The complete stretch of structure is 13 cm.
Remarks: On the basis of the diagniostic characteristic of feather-stitch like arrangement
of segments the present specimen appears close to ichnogenus Treptichnus Miller, 1889.
The present burrow system Treptichnus is interpreted as fodichnion made by vermiform
animals (Buatois et al., 1998). Parcha and Pandey (2011) considered Treptichnus in
Phylum Annelida. The present form is similar to the ichnogenus Treptichnus pedum
reported from the Nagaur Sandstone (Srivastava, 2012a).
Ichnogenus: Monomorphicnus Dawson, 1873
Monomorphicnus isp.
(Fig. 4.33; B)
Repository ref. NG/SK-13/28
Material: Two specimens preserved as hyporelief in fine-grained sandstone.
Description: Gently curved ridges arranged in a row. The ridge is 5.4 cm long and is 3
mm in width. Ridges are 1 cm apart from each other. The specimen comprises of 4 to 6
curved ridges.
Discussion: The specimen is morphologically close to the Monomorphicnus Crimes,
1970. Monomorphicnus lineatus reported from Paseky Shale of Czech Republic by
Mikulas, R (1995). It is suggested that the structure was formed by the sideways
propagation of the animal.
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Small Knob-shaped burrow Form A (Fig. 4.33 C)
Repository ref. NG/SK-13/32
Material: One single slab containing more than 5 specimens preserved as positive relief
in fine-grained sandstone.
Description: Small-knob like burrow, horizontal to the bedding plane. The length is 2 to
4.5 cm and width 0.5 to 0.8 cm, with poorly preserved transverse markings on the wall of
burrow.
Remarks: The burrow and its ornamentation on wall is slightly different from all the
reported burrow forms from the Lower Cambrian.
Ichnogenus Chondrites von Sternberg, 1833
Chondrites isp.
(Fig. 4.33 D)
Repository ref. CH/SK-13/34
Material: Single slab of fine grain sandstone. Specimen preserved on the top of bed.
Description: Dendritic pattern, small tunnel like structure lying parallel to the bedding
plane, asymmetrical traces of biogenic origin. Specimen is 1.0 mm wide while length
varying from 0.4 to 2.0 cm. Width constant throughout the length. The angle of branching
may also be variable between 35º - 40º.
Discussion: The present form of Chondrites resembles in all respect Chondrites von
Sternberg. Chondrites undoubtly belongs to the fodinichnia and is to be regarded as a
feeding structure of animals (Seilacher, 1955; Osgood, 1970) and not a dwelling burrow
of filter feeding annelids (Osgood, 1970).
Animal escape structure Form B
(Fig. 4.33 E)
Repository ref. NG/SK-13/33
Material: Two specimens preserved in fine grained sandstone.
Description: Vertically perpendicular to the bedding plane depicting “U”-shaped
morphology. The burrow structures are 3.8 cm in depth and 1.7 cm in width. There are 7
90
to 8 concentric “U”-shaped lines in 1 cm. Both limbs of burrow are parallel. Distance
between the limbs at surface is less than 1 cm.
Discussion: The present structure is formed by hideaway activity of the animal during its
life span. The specimen resembles Diplocraterion Torell (1870); but a typical “U” shaped
burrow without any opening structure at the bedding plane, completely rules out the idea
of structure being Diplocraterion. Although the specimen is a “U” shaped burrow, it fails
to show openings at the surface of the bedding plane. It closely resembles the structure
known as animal escape structure reported by Hofmann et al. (2012).
Horizontal Burrow Form C
(Fig. 4.33 F)
Repository ref. NG/SK-13/34
Material: Three slabs with randomly oriented specimens preserved as positive relief in
fine-grained sandstone.
Description: Randomly arranged, horizontal to the bedding plane, varying in size. Length
3 to 4 cm, width up to 0.4 to 0.8 cm. These structures tapering at both ends.
Remarks: The present specimen closely resembles the burrow morphology shown by
Crimes and Harper (1970);( see page for fig. 29 b).
91
Fig 4.33: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A) Treptichnus pedum; B) Monomorphichnus isp; C) Small knob like Burrow; D) Chondrites isp. E) Animal escape structure; F) Horizontal burrow.
92
Needle-like burrow Form D (Fig. 4.34 A)
Repository ref. NG/SK-13/35
Material: The twenty six specimens preserved as hyporelief in fine grained sandstone.
Description: Small, needle-like, uniform, epichinial cast ranging from 0.3 mm to 1.0 cm
in length; 1 mm in width. These structures are randomly arranged.
Discussion: These structures show resemblance with forms reported as exichnial and
hypichnial cast of horizontal burrows by Crimes and Harper (1970); (see page 25 for
Plate I D). These needle-like burrows are very small in shape and size and indicate the
morphology of the animal as well. Present specimen is being reported for the first time
from the Nagaur Sandstone.
Tubular burrow Form E
(Fig. 4.34 B)
Repository ref. NG/SK-13/36
Material: A single slab containing around 60 forms are counted, preserved as positive
relief in fine grained sandstone on the sole of the bedding plane.
Description: Randomly distributed, medium to small worm-like burrow, length ranges
between 0.2 to 1.9 cm, while width varies from 1 to 3 mm; the specimens are 2 mm in
height. Both ends of the structure are curved and rounded. Out of sixty specimens, twenty
five forms are medium while the rest are small.
Discussion: Possibly, this structure could be a burrow formed by worm-like animals.
There are two sets of structures, one large and one small. Both forms are preserved in an
isolated patch. Another possibility is that this structure could be faecal remains of
existing animals as far as the morphology is concerned. However, the size and shape
completely rules out the idea of its being a fecal remain.
93
Ichnogenus: Palaeophycus Hall, 1847
Palaeophycus tubularis Hall, 1847 (Figs. 4.34 C and D)
Repository ref. NG/SK-13/40
Material: One specimen in situ preserved as full relief on the bedding surface in fine-
grained sandstone.
Description: Horizontal to the bedding plane, cylindrical in outline, solid, infilled with
host rock. Straight to slightly curved, unbranched and smooth body wall. The dimensions
of the structure are 1.6 cm (longer axes) in diameter, 12.5 cm in length. Width varies
from one end to other end, maximum width recorded at the middle part (2.6 cm) and
tapering at posterior end.
Remarks: Morphologically, it resembles with the Palaeophycus Hall, 1847. The structure
is interpreted as the result of dwelling activity of the animal. The present form is quite
larger, bulbous in outline and different from the Palaeophycus Hall, 1847. It is also
similar with the form reported from the Tethys Himalaya by Parcha and Pandey (2011).
Small burrows reported from Tunkliyan
(Fig. 4.34 E)
Material: Six slabs of sandstone comprising twelve specimens preserved as hyporelief on
the sole of bedding plane.
Description: Small tubular burrow, horizontal to the bedding plane, spindle shaped,
smooth wall. Specimens randomly preserved. Burrow width maximum at the middle part
varying from less than 1to 2 mm; 0.4 to 1 cm in length.
Remarks: The present structure depicts the burrow morphology which is similar to forms
reported from the Nagaur Sandstone; however, the only difference is that these forms are
small and straight, whereas the burrow forms reported earlier from the Nagaur Sandstone
are slightly larger and curved in nature.
94
Scratch marks from Tunkliyan (Fig. 4.34 F)
Repository ref. TNK/SK-12/16
Material: Four specimens collected from Tunkliyan preserved as positive hyporelief.
Description: Specimen shows a large numbers of scratch marks which are randomly
preserved. The width of the scratch mark is 0.4 to 0.7 cm, while individually it is up to 2
mm and length of scratch marks is 2.5 cm. The consecutive gap between the podial marks
is 1 mm.
Discussion: Morphologically, the specimens are close to scratch mark produced by
trilobite. The podial markings are in ascending order. The present specimen is similar to
the scratch marks reported from the Nagaur Group by Kumar and Pandey (2010). The
present specimen is being reported for the first time from the Tunkliyan Sandstone.
95
Fig 4.34: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A) Needle like burrow; B) Tubular burrow; C and D) Palaeophycus tubularis; E) Small burrows reported from Tunkliyan; F) Scratch marks reported from Tunkliyan.
96
Biozonation and Correlation
In the Marwar Supergroup, the fossils are recorded from the Late Neoproterozoic
Jodhpur Sandstone to the Early Cambrian Nagaur Group. Though there are limited
parameters available for defining biozones, the fossil pattern obeys the chronological
order as the lower part of MSG (Marwar Supergroup) consists of fossils of the Ediacaran
age; followed by the middle part, i.e. the Bilara Group comprising stromatolites which
possibly characterized the Pc-C, and the upper part, i.e. the Nagaur Group having fossils
of Early Cambrian age.
5.1 Biozonation The Biozonation of the Marwar Supergroup has been proposed on the basis of the
available fossil records. In all, XIII biozones (fig 5.1) have been recognized in the
Marwar Supergroup on the basis of mega as well as microfossils. The biozones are
categorized under the following headings:
A. Body fossils
B. Organo-sedimentary structures
C. Trace fossils
D. Microfossils
A. BODY FOSSILS: This category includes the plant and animal body fossil
which further subdivides into five respective biozones namely Aspidella-Hiemalora zone,
Marsonia zone, Priapulid zone, Articulated Arthropod Tergites zone and Vendophycus
zone,
Aspidella-Hiemalora zone
This biozone includes the soft bodied ediacaran body fossils viz. Aspidella,
Hiemalora, etc. which have been reported from the Sursagar mine, Golasni mine of the
Jodhpur Group. Aspidella is a circular Ediacaran body fossil which is of worldwide
occurrence during the Ediacaran period and potentially represents a biozone. The other
Ediacaran fossil is a Cnidarian identified as Hiemalora with radiating arms/rays from the
97
centre portion of the body. It is also reported from the Bhander Group of the Vindhyan
Supergroup, Flinders Ranges South Australia, Newfoundland Canada by Hofmann
(2008), etc.
Marsonia zone
This biozone is located near Artiya Kalan village in Jodhpur district, Rajasthan.
This zone is named after Marsonia artiyansis reported by Raghav et al. (2005) and later
restudied by Kumar and Ahmad (2012). Marsonia is the first known medusoid body
fossil reported from middle part of the Jodhpur Group. The fossil is circular to slightly
elliptical disc, preserved in shale. M. artiyansis comes under the class Scyphozoa. In this
class all the animals are marine, free swimming and have a well developed gastrovascular
cavity with large medusa. The medusoids known from different countries across the
globe including USSR, Canada, New Zealand and Australia (Sokolov and Ivonowski,
1985) represent the phylum Cnidaria. Thus, the Marsonia artiyansis unfolds the
evolutionary facts about the Ediacaran fossils.
Priapulid zone
This biozone includes Priapulid worm like fossil reported by Srivastava (2012b)
from the Nagaur Sandstone which is a body fossil and can constitute a biozone.
Articulated arthropod tergites zone
This biozone is located in the Nagaur Group. The body fossil is reported by Singh
et al. 2013. The fossil is not very convincing as a body fossil of trilobite. The authors
named as “articulated arthropod tergites or trilobite” similar to the fossils reported from
lesser Himalayan region of India. Except the present body fossil, no other body fossil has
been reported from this horizon; although, the horizon is rich in trace fossils.
Vendophycus zone
This biozone includes non-carbonaceous mega plant fossils. This zone exclusively
located in the Sursagar mine of Jodhpur district and stratigraphically comes under the
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Jodhpur Group. The plant fossils are preserved as mould and cast on the bedding surfaces
in a shallow marine setting. The plant fossils are divided into two genera and three
species viz., Vendophycus rajasthanensis, Vendophycus sursagarensis and Indophycus
marwarensis and are described with many morphological features comparable to the
extant Vaucheriaceae family with tube like nonseptate thallus, branching pattern,
presence of swellings at the ends of tubes and on the tubes and also within the tubes; but
the dimensions of the present forms are megascopic. The plants acquired megascopic size
because of competition with other plant communities, availability of space and nutrients
and stability of the habitat. These plants lost their existence in the Cambrian with the loss
of their habitat because of the appearance of the faunal life which bioturbated the
substrate and browsed upon the microbial mats as well as the mega plants. Hence, the
occurrence of this giant sized plant fossil has a great significance in the stratigraphy of
the Marwar Supergroup.
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Fig 5.1: The schematic diagram showing the different biozones present in the various stratigraphic horizons of Marwar Supergroup. The biozone are constructed on the basis of megafossils, microbial mat, trace fossils, stromatolites and microfossils.
B. ORGANO-SEDIMENTARY STRUCTURES: This category is divided into
the following subcategories such as Stromatolites, and Microbially Induced Sedimentary
Structure (MISS). The MISS is further subdivided into Arumberia zone and Ediacaran
Disc zone.
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Collenia-Conophyton zone
The biozone is the assemblage of Stromatolites located in the Bilara Group. The
Stromatolites are predominantly found in the Dhanapa Dolomite, Gotan Limestone and in
few parts of Pondlu Dolomite. The Stromatolites assemblage includes viz. Collenia
columnaris, Conophyton, Collenia pseudocolumnaris, Oncolites, etc. The Collenia
cololumnaris is a columnar form well exposed in the Dhanapa dolomite near Dhanapa
village. The Conophyton is exposed in the block section of Barna mine near Bilara
village. The Oncolites are exposed mainly in the Dhanapa Dolomite and dolomite in the
Moriya locality in Phalodi district. The assemblage is comparable with the stromatolites
of the Chambal valley section of the Vindhyan Supergroup.
Arumberia zone
This biozone is well exposed in the middle (Sursagar mine) and upper parts
(Khatu area) of the Jodhpur Sandstone. It includes different kinds of microbial mats. The
microbial mats include Arumberia banski, Rameshia rampurensis and Aristophycus
exposed in the Khatu section of the Jodhpur Group. Aristophycus is a branching structure
well developed in the Khatu area in the northern side of the main hillock at western side
of the Khatu Township. Seilacher (2007) considers its genesis as due to dewatering. The
middle part of the Jodhpur Sandstone exposed in the Sursagar area, exhibits 12 different
types of microbial mats with 2 poorly preserved structures. Out of these Arumberia
banski and Aristophycus are exposed in the Khatu section. There are three new forms viz.
Rameshia linearis, Rameshia anastamose and Jodhpuria circularis exposed in the fine
grained Jodhpur sandstone. The microbial mats are of value in the intrabasinal and
interbasinal correlations when age marker fossils are absent. The microbial mat provides
base for the preservation of different types of body fossils and other biological signatures.
Without microbial mat, the preservation of soft bodied Ediacaran fossils is not possible in
quartz arenite facies of MSG. These microbial mats are the main source of food for the
metazoans and the animals that may have existed during the Ediacaran period.
Ediacaran Disc zone
This biozone is located in the Sursagar mine of Jodhpur district, which is the
middle part of the Jodhpur sandstone. They are restricted to the Jodhpur Group only as
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they are absent in the Bilara and Nagaur Group. Their size ranges up to a few mm to 75
cm (Srivastava, 2013). Their genesis is under debate. According to Srivastava (2013), it
is a disc of Ediacaran age as its name reveals. These discs are thought to have Cnidarians
affinity in terms of origin. These discoidal discs are similar to the Ediacaran body fossil
Aspidella but they (Ediacaran disc) are bigger in shape and size. The other feature that
differentiates the Ediacaran disc from Aspidella is that in case of Aspidella, there is a
prominent outer rim and elevated inner disc which differs from the Ediacaran disc.
Therefore, it seems reasonable to put this type of structure in separate biozone.
C. TRACE FOSSILS The trace fossils are sub-categorized as trace which further
divided into 3 biozones which are as follows:
Cruziana-Rusophycus zone
It is categorized as a biozone, which includes traces of arthropods, exclusively the
trilobite. The zone falls under the Nagaur Group and it is exposed in the Dulmera village
which is about 65 km from Bikaner district on Bikaner-Sri Ganganagar Highway. In 18
m thick sequence of maroon colour sandstone, shale and siltstone, there are number of
traces of Rusophycus carbonarious, Rusophycus didymus, Cruziana fasiculata, Cruziana
solomonis, Isopodichnus isp and Tasmanadia cachii. This zone is helpful in demarcating
the age of the Nagaur Group as the Lower Cambrian (upper part of Marwar Supergroup).
The general behavioural trend of the trace fossils are shown in the table 5.1. It is based on
the work of Kumar and Pandey (2009) and present findings.
Treptichnus zone
This biozone also exists in the Nagaur Group. It is an important biozone as it
defines the Pc-C boundary in the Marwar Supergroup. The T. pedum is an index fossil of
Lower Cambrian. The lithology is the fine grained sandstone. The dimension of
Treptichnus pedum is 0.5 to 2 cm long and width up to 4 mm with 3 mm in height. The
complete stretch of structure is 13 cm. In the same quarry there is another fossil named
as Priapulid which is a segmented worm. The priapulid-like worm is responsible for
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creating the Treptichnus pedum burrows (Srivastava, 2012a). The present biozone
includes the work of Srivastava, (2012a) and present work.
Trail and burrows
The biozone represents the biogenic activity during the course of the life cycle.
This zone includes the scratch marks, tracks and trail marks, animal escape structure and
well preserved burrows of different dimensions. The scratch marks are possibly produced
by Monomorphicnus linearus which indicates the movement activity of the animal. The
tracks and trail marks are produced by the Diplichnites aenigma, Dimorphichnus
obliquus, Chondrites isp and other arthropods. The animal escape structure is unique
feature as it shows similarity with the “U” shaped burrow. Another important content of
this zone is the burrows. The Bergaueria perata, Palnolites vulgaris, Palaeophycus
tubularis, Merostomichnites isp, Monocraterion isp and some unknown burrows which
are not related with the known burrow forming genera, are named as Form “A”, Form
“B”, Form “C”, Form “D” and Form “E”.
Table 5.1: Behavioural pattern of the Ichnofossil from Nagaur Group
S. No. Ichnogenera Behavioural activity
1 Rusophycus Carbonarious Cubichnia (Resting trace of trilobites)
2 Rusophycus didymus Cubichnia (Resting trace of trilobites)
3 Merostomichnites isp. Cubichnia (Resting trace of trilobites)
4 Tasmanadia cachii Cubichnia (Resting trace of trilobites)
5 Cruziana fasiculata Repichnia (Crawling trace)
6 Cruziana solomonis Repichnia (Crawling trace)
7 Diplichnites aenigma Repichnia (Crawling trace)
8 Isopodichnus isp. Walking trace of trilobites
9 Planolites vulgaris Fodinichnia (Feeding structure)
10 Treptichnus pedum Fodinichnia (Feeding structure)
11 Chondrites isp Fodinichnia (Feeding structure)
12 Planolites annularis Fodinichnia (Feeding structure)
13 Burrows Fodinichnia (Feeding structure)
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14 Bergaueria perata Domichnia (Dwelling Structure)
15 Monocraterion isp. Domichnia (Dwelling Structure)
16 Palaeophycus tubularis Domichnia (Dwelling Structure)
17 Dimorphicnus obliquus Pascichnia (Grazing Trace)
18 Monomorphicnus isp. Pascichnia (Grazing Trace)
19 Scratch marks Pascichnia (Grazing Trace)
The Tunkliyan Sandstone, stratigraphically, the topmost part of the Marwar
Supergroup has also yielded some poorly preserved scratch marks and small burrows.
Before the present study, the particular horizon was untouched and no fossils have been
reported from it.
D. MICROFOSSILS: This category includes the two biozone i.e. Obruchevella zone
and Acritarch zone.
Obruchevella zone
This biozone is recorded with in the Gotan Limestone is based on the thin section
study of black chert lenses by Babu et al. (2009). This microfossil zone includes the
assemblage of various microfossils viz. Obruchevella valdaica Yankauskas et al.;
Polythrichoides lineatus Hermann, Siphonophycus septatum Schopf; Leiosphaeridia
jacutica (Timofeev) Yankauskas et al.; Octosphaeridium truncatum Rudavaskaja;
Echinosphaeridium maximum Yin; Gloeocapsamorpha karauliensis Maithy and Mandal;
Stictosphaeridium, sinapticuliferum Timofeev; Trachysphaeridium laminaritum
(Timofeev) Vidal; Synsphaeridium sorediforme, (Timofeev) Eisenack and
Cymatiosphaera wenlokia Downie.
Acritarch zone
This biozone is reported from the different horizons of the Marwar Supergroup. It
is based on subsurface samples and the fossils are recovered through standard
palynological technique by Prasad et al. (2010). The assemblage includes
Lophosphaeridium spp, along with various species of Leiosphaeridia, suggesting Late
Ediacaran age. Occurrence of small micrhystrids (Asteridium spp.) and appearance of
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Dictyotidium birvetense, Pterospermella solida and Annulum squamaceum in the lower
part of the Bilara Group, suggests Latest Ediacaran to Early Cambrian age. The recorded
acritarch assemblages suggest demarcation of Precambrian-Cambrian boundary within
the lower part of Bilara Group, Marwar Supergroup. The succeeding Upper Carbonate
Sequence of Bilara Group (727-481m) shows abundant Cristallinium randomense,
Cymatiosphaera crameri and Asteridium spp., along with other species of
Cymatiosphaera and Cristallinium, and also includes the Late Cambrian marker forms,
such as Striatotheca loculifera and Dorsenidium (Veryhachium) minutum, suggest Middle
Cambrian to Late Cambrian age. This assemblage also makes a potential biozone in the
Marwar Supergroup. This biozone not only emphasizes the age but has also helped to
understand the palaeoenvironment of the Marwar Supergroup based micropalaeontology.
The age implication based on acritarchs gives somewhat younger age in comparison to
the age inferred on the basis of trace fossils.
5.1.4 Discussions The different assemblages from the Jodhpur Group, Bilara Group and Nagaur Group are
shown in fig 5.4 and categorized under the body fossil, organosedimentary structures,
trace fossils and microfossils. The Aspidella-Hiemalora biozone is a well known
Ichnofossil reported from the Ediacaran period with worldwide occurrences such as
Ediacara Hills (South Australia), Ukraine, Mistaken Point in Newfoundland etc. On the
basis of this zone, the oldest unit i.e. the Jodhpur Group is assigned the Ediacaran age.
Another important biozone is Marsonia artiyansis, a typical medusoid form. The
medusoid forms are global in occurrence during the Ediacaran period. The “Articulated
Arthropod Tergites” zone which is supposed to be a body fossil of trilobite. Opens an
opportunity for searching a more relevant body fossil in the Nagaur Sandstone where
only trace fossils are in abundance. The Vendophycus biozone includes two genera and
three species viz. Vendophycus rajasthanensis, Vendophycus sursagarensis and
Indophycus marwarensis, which are preserved as mould and cast on the bedding surfaces
in a shallow marine setting. The basic concept behind this zone is that they exist in the
Ediacaran period and become extinct near the Cambrian with the loss of their habitat
105
because of the appearance of the animal life which bioturbated the substrate and browsed
upon microbial mats as well as the mega plants.
The stromatolite assemblage consists of Colleniella Korolyuk (1960), Collenia
Pseudocolumnaris Maslov (1960), Oncolites Pia, (1927). The stromatolites present in the
Marwar basin completely lack the typical Riphean and Vendian forms (Priess, 1976) such
as Baicalia, Kussiella which are confined to eastern side of Aravalli range. The form
genus Colleniella would point to terminal Riphean-Cambrian age (Semikhatov, 1976).
Arumberia zone is very important component in the present study as it has relevance in
terms of time framed occurrences in the Latest Neoproterozoic Era. Ediacaran Disc zone
is well marked in the Jodhpur Sandstone.
The Cruziana-Rusophycus biozone is important because on the basis of this zone
the age of Nagaur Group is bracketed as the Lower Cambrian. Treptichnus pedum is
crucial in delineating the Ediacaran-Cambrian boundary. The Treptichnus pedum is
essential to evaluate the reliability of the Ediacaran-Cambrian (Buatois et al., 2013). The
next important biozone is based on the microfossil Obruchevella zone, which is assigned
the Vendian age. The Acritarchs (Prasad et al., 2010) is also used in establishing the
biozone in the Marwar Supergroup. The geographical distribution of biozones in the
Marwar Supergroup is shown in the figure 5.2.
106
Fig 5.2: Map shows the geographical distribution of Biozones based on the palaeontological remains of the Marwar Supergroup. 5.2 Correlation
Regional Correlation The Marwar Supergroup was traditionally considered to be a westward extension
of the upper part of the adjacent Vindhyan sedimentary basin (Heron, 1932; Pandey and
Bahadur, 2009). It was originally referred to as the ‘Trans-Aravalli Vindhyans’. In the
absence of radiometric dates in the Marwar Supergroup, the interbasinal correlation is
possible only with help of biogenic signatures and megafossils. The dating has been done
only in the part of the Bilara Group with the help of Rb/Sr dating (Mazumdar et al.,
2004) and δ13C studies (Pandit et al., 2001) and recently in the Nagaur Sandstone of the
Nagaur Group by McKenzie et al., 2011 (540Ma DZ; LAICPMS). The Marwar
107
Supergroup has a vast range of fossil assemblages varying from the soft-bodied to the
invertebrate fossils. In this group, the interbasinal correlation is attempted with following
parameters such as microbial mats, stromatolites, body fossils, etc. Here the lower part of
Marwar Supergroup i.e. Jodhpur Group is correlated with the Bhander Group which is
the upper part of the Vindhyan Supergroup (Fig. 5.3). The Jodhpur Group has been
assigned an Ediacaran age on the basis of the presence of Arumberia, Aristophycus,
Rameshia rampurensis, Rameshia linearis, Beltanelliformis, Marsonia artiyansis,
Aspidella and cf. Hiemelora. It unconformably overlies the Malani Igneous suite which
has been dated as 779 ± 5 Ma by U-Pb method (Gregory et al., 2009). The stromatolites
reported in the Marwar Supergroup are different from the assemblages of the Vindhyan
Supergroup at generic level. The Nagaur Sandstone has yielded trilobite trace fossils and
has been assigned the Lower Cambrian age, hence the Bilara Group possibly straddles the
Precambrian-Cambrian boundary. But it is inferred after the discovery of Treptichnus
pedum (Srivastava et al., 2012a) from the Nagaur Group that the possibilities of the
presence of Pc-C boundary below the Nagaur Group or within the Nagaur cannot be ruled
out. Since, no Cambrian fossils are present in the Vindhyan Basin, the youngest horizon
of the Vindhyan Basin, the Maihar Sandstone, which is Ediacaran in age, can be
correlated with the Jodhpur Sandstone of the Marwar Supergroup.
Intercontinental Correlation
The Marwar Basin is located in proximity to basins in Oman, Pakistan, Madagascar
and northern India (Krol-Tal region). Many of these sedimentary sequences show
remarkable similarities and there exist possible correlations between these basins. The
Marwar Supergroup has also been correlated with the other parts of the world such as the
Salt Range, Pakistan, Krol-Tal of Lesser Himalaya, Huqf Supergroup of Oman. The
correlation is based on U-Pb dating and hence, it is concluded that the Marwar
Supergroup developed near the close of the Ediacaran Period and is a part of a larger
group of sedimentary basins which includes the Huqf Supergroup (Oman), the Salt Range
(Pakistan), the Krol-Tal belt (Himalayas) and perhaps the Molo Supergroup
(Madagascar) (Davis et al., 2013). Many of these sedimentary sequences show
108
remarkable similarities and are here attempted to show possible correlations between
these basins (Fig 5.4).
Fig. 5.3: Schematic diagram showing the correlation between the Bhander section of the Vindhyan Basin and Jodhpur section of Marwar Basin. (after Kumar, 2012).
109
Fig.
5.4
: C
ompa
rativ
e st
ratig
raph
y (id
ealiz
ed)
and
prop
osed
cor
rela
tions
bet
wee
n th
e M
arw
ar S
uper
grou
p, t
he S
alt
Ran
ge
(Pak
ista
n), t
he K
rol-T
al (H
imal
ayas
) and
the
Huq
f Sup
ergr
oup
of O
man
(mod
ified
afte
r Dav
is e
t al .
, 201
3).
110
Conclusions
Based on the available information and present study, the following conclusions have been
drawn and summarized:
1. Marsonia artiyansis, a medusoid by Raghav et al. (2005) reported from the Jodhpur
Sandstone of Ediacaran age has been restudied for its taxonomic affinity. The
conclusions drawn by Raghav et al. (2005) concerning its affinity with a medusoid of
Class Scyphozoa can be accepted on the basis of morphology. It is characterized by a
circular disc-shaped structure with smooth to wrinkled margin and mode of preservation
in a very shallow water lagoonal setting. The animal must have been a planktic soft
body. The major variations in morphology possibly appear to be due to taphonomy and
load-effect of the overlying sediments.
2. The burrows and trail marks in the lower part of the Jodhpur Sandstone from the Artiya
Kalan locality suggest presence of benthic community during deposition of the Jodhpur
Sandstone.
3. One of the important findings of the present study is the record of MISS (Microbially
Induced Sedimentary Structures) in the Jodhpur Sandstone, where there is a complete
range of such structures (MISS) from two poorly defined morphologies to twelve well-
defined structures. The dominance of microbial structures with varied morphologies in
the Jodhpur Sandstone is its unique feature which requires explanation. Near absence of
animal life allowed the microbial community to flourish in a shallow marine setting with
abundance of sunlight and nutrients. The quartz-dominated sand and moderate to high
energy environment allowed growth of the microbial community due to removal of mud
which made the water less turbid. Quartz sand allowed the light to penetrate deeper in
the sediment at sediment-water interface which helped the microbial community to grow
to greater depths, and also to produce varied morphologies on the bedding surfaces. In
the present study, of the reported fourteen microbial mat structures some appear to have
been restricted within a specific time period near the Precambrian-Cambrian boundary
111
(i.e. the Ediacaran Period). It appears that the different mat morphologies were shaped
by a combination of the microbial community, physical parameters, mineralogy and
textural composition of the sediments. If the physical parameters and the mineralogy of
the sediments of the different stratigraphic horizons are compared, the morphological
variation in the microbial mats can be attributed to the differences in the composition of
the microbial community. Thus, the morphological variations in the microbial mats in a
similar environment may represent the dominance of differing microbial community.
Hence, such morphologies can be identified by their specific characters. The microbial
mats may often leave a proxy record of the microbial community bearing specific
morphologies produced in the sandstones. These are Arumberia banksi, Rameshia
rampurensis and Jodhpuria circularis which have not been reported from the modern
sediments. The origin of Aristophycus is also linked to mats. Its origin is explained by
Seilacher (2007) who suggested that the plant like appearance is linked to water escape
under a strong microbial mat. The water jet could not break the mat but eroded the
underside of the mat which might have later been filled with the sand.
4. The Ediacaran Jodhpur Sandstone shows profuse development of noncarbonaceous
megaplant fossils which are preserved as mould and cast on the bedding surfaces in a
shallow marine environment. The plant fossils have been studied for their taxonomic
assignment and genesis. Two genera and three species viz., Vendophycus rajasthanensis,
Vendophycus sursagarensis and Indophycus marwarensis are described whose
morphological features are compared to the extant Vaucheriaceae family characterized
by tube-like nonseptate thallus, branching pattern, presence of swellings at end of tubes
and on the tubes and also within the tubes but the dimensions of the present forms are
megascopic. The plants acquired megascopic size because of competition with other
plant communities, availability of space and nutrients and stability of the habitat. These
plants lost their existence in the Cambrian when their habitats disappeared with the
appearance of the animals, which bioturbated the substrate and browsed upon the
microbial mats and the mega plants.
112
5. The presence of stromatolites is noted in the Bilara Group. In the present study,
Colonnella columnaris, Coniform stromatolites, domal stromatolites, stratified forms;
pseudocolumnar forms and a new form simply referred to as Form A have been
reported. The assemblage differs from the stromatolite assemblage of the Bhander
Group of the Vindhyan Basin. No age can be assigned to the stromatolite assemblage.
6. The Marwar Supergroup has yielded twenty five ichnogenera. These are Rusophycus
carbonarious, Cruziana fasiculata, Cruziana solomonis, Isopodichnus isp, Tasmanadia
cachii, Diplichnites aenigma, Bergaueria perata, Monomorphicnus isp, Monocraterion
isp, Planolites vulgaris, Planolites annularis, Merostomichnites isp, Treptichnus pedum,
Dimorphicnus obliquus, Palaeophycus tubularis, Chondrites isp, scratch marks, burrow
forms from the Nagaur Group. These trace fossils in the MSG (Marwar Supergroup)
provide a robust database to throw light on the evolving life in the Precambrian-
Cambrian (Pc-C) time span in the global level.
7. The biogenic proxies in the present study help to establish the detailed biozones in the
studied successions of the study area as well as the entire basin (Marwar Supergroup).
These provide diagnostic age brackets for the Ediacaran to Early Cambrian successions.
The age assignment helps to establish inter-and intra-basinal correlation. The animal
body fossils include the Aspidella, Hiemalora, Marsonia, etc which are helpful in age
determination and in suggesting the age of the Jodhpur Group as the Ediacaran.
8. The evidence of multicellular animal origin on the basis of the five-armed body fossil
can simply be considered to represent a pre-biomineralization stage in the evolution of
echinoiderms during the Ediacaran Period. Along with the participation of biological
systems in the environment of deposition, the sedimentological role was equally
significant in shaping the basinal morphology and for better understanding of the
palaeogeographic evolution and stratigraphic sections in both the Marwar Supergroup
and the Bhander Group (Vindhyan Supergroup). An attempt has been made in respect of
biogenic correlation. The Jodhpur Group of the Marwar Supergroup have been assigned
113
Ediacaran age on the basis of the presence of Arumberia, Ediacaran body fossils
Marsonia, Aspidella and cf. Hiemalora. The correlation of the lithounits of the Marwar
Supergroup has also been established with the sequences from the other parts of the
world, such as the Salt Range (Pakistan), Krol-Tal of the Lesser Himalaya, Huqf
Supergroup of Oman, this correlation also supports the present findings.
9. The present work has identified 13 biozones in the Marwar Supergroup based on the
biological records. These are categorized under the body fossils, organosedimentary
structures, trace fossils and microfossils. The first category (i.e. body fossil) has been
further subdivided into five biozones. The first biozone is Aspidella-Hiemalora zone
from the study area of the Jodhpur Sandstone which is of global significance in the
Ediacaran period. This biozone is also important as it suggests a definite Ediacaran age
to the oldest group (Jodhpur Group). The second biozone is also from the same group
and it carries the name as Marsonia zone. This biozone is named after the medusoid
fossil called Marsonia artiyansis. The medusoids have worldwide distribution and
provide strong data-base in exploring the evolutionary trends of the Ediacaran life.
Hence, this biozone also supports the Ediacaran age to the Jodhpur Group. The third
biozone is referred to as Priapulid worm biozone. This work is supposed to build the
Treptichnus pedum burrows and is from the Nagaur Group. The fourth biozone is the
body fossil from the Nagaur Group which is suggested by Nigel Hughes to be
“Articulated arthropod tergites”. Therefore, this biozone justifies the age of the Nagaur
Group as Early Cambrian. The fifth biozone represents non-carbonaceous plant
megafossils preserved in the middle part of Jodhpur Sandstone. These plant fossils are
megascopic up to metric level and are interrelated with the modern-day Vaucherian
algae in morphology and its fertile structures and bear much similarity.
10. The next category of biozones is the organo-sedimentary structures which comprise
stromatolites and microbially induced sedimentary structures. In this category, the sixth
biozone is based on stromatolites from the Bilara Group. The important stromatolites are
Colonnella coloumnaris, Conophyton and pseudocolumnar forms including one new
unknown form. This assemblage differs from the stromatolites of the Bhander Group.
114
Hence, they are not comparable. No definite age can be given to the stromatolite
assemblage.
11. The next subcategory is made up of MISS (Microbially induced sedimentary structures)
which is further sub-classed into two biozones. The seventh biozone is named as
Arumberia zone which belongs to the Jodhpur Group. Arumberia is a typical Ediacaran
microbial mat and its presence indicates the Ediacaran age. In the same manner, the
eighth biozone includes the Ediacaran discs abundantly reported from the Jodhpur
Sandstone and hence it has also been assigned the status of a biozone.
12. The next category for biozonation includes the trace fossils and constitutes ninth, tenth
and eleventh biozones respectively. The ninth biozone includes trace fossils belonging to
the trilobites from the Nagaur Group. This biozone has been assigned the Early
Cambrian age for the Nagaur Group. The tenth biozone described as Treptichnus zone is
the index fossil of the Lower Cambrian age. The demarcation of Pc-C boundary has
been suggested on the basis of Treptichnus pedum. The eleventh biozone has been
established on behalf of the behavioural activity of the arthropods indicating the mode of
life during early phase of evolution.
115
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