Evolution of Vaigai Delta, Tamilnadu, India (East Coast ... · Nadu, India 2 – Principal, Dept. of Geology, National College, Tiruchirappalli, Tamil Nadu, India ABSTRACT The present

INTERNATIONAL JOURNAL OF GEOMATICS AND GEOSCIENCES Volume 1, No 2, 2010

© Copyright 2010 All rights reserved Integrated Publishing services Research article ISSN 0976 – 4380

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Evolution of Vaigai Delta, Tamilnadu, India (East Coast) During Quaternary

Prabakaran.K 1 , Anbarasu.K 2

1 – Research Scholar, Dept. of Geology, National College, Tiruchirappalli, Tamil Nadu, India

2 – Principal, Dept. of Geology, National College, Tiruchirappalli, Tamil Nadu, India

ABSTRACT

The present study aims to study the geomorphology, sea level changes and evolution of landforms and sedimentary plains of the Vaigai Delta, Tamilnadu, India. Remote sensing, sedimentological and Geographical Information Systems (GIS) techniques were employed to achieve the objectives of the study. Aerial photos in the scale 1:50,000 and IRS 1D LISS III satellite images were interpreted to study the landforms. A detailed field survey was conducted for observing the interrelation between landforms and for morphometric analysis. The synthesis of the landforms of the delta suggests that the delta development has been influenced mainly by the fluvial and tectonic processes along with the Quaternary sea level oscillation. The occurrence of paleo deltas of Vaigai observed both in the North and south of the present river course indicates both the switching process of the delta and avulsion process of the river. The results of the study indicate that the sea had transgressed over the delta twice in Quaternary, the first around 125,000 years BP and the second around 6000years BP. These sea level changes had induced the fluvial system to change it regime of sedimentation causing switching of delta building. Neotectonic processes have also induced the shifting of riverine process at several time during the Quaternary.

Keywords: Vaigai, Quaternary, Sea level, Neotectonism, Delta.

1. Introduction

Vaigai, an ephemeral stream originates from the Kodaikanal hill ranges of Western Ghats, flows for about 240 km in the southeast direction and debouches into the Palk Bay (Bay of Bengal) near Mandapam. The Vaigai river delta covering an area of 2,500 sq.km. has the apex at Manamadurai. Ancient Sangam Tamil literatures (300BC) have described and paid tribute to the river as if it brings water when one touches it by hands (etymologically Vai = put, gai = hand) though the river is dry in major periods of the year nowadays. The large delta developed by the river attests the observations of the ancient literature. The occurrence of several hundreds of lakes, though filled with water during rainy season only, in the delta region and the surroundings is yet another proof that Vaigai river had once received enormous water. The present inactive sedimentation of the



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river is also evidenced by the occurrence of coral reefs fringing the coastal boundaries of the delta. The synthesis of the landforms of the delta suggests that the delta development has been influenced by the fluvial and tectonic processes along with the Quaternary sea level oscillation. The occurrence of paleo deltas of Vaigai observed both in the North and south of the present river course indicates the switching process of the delta and avulsion process of the river.

The shoreline of the delta is dynamic as the longshore currents bring varied amount of sediments seasonally from south and deposit here (Thanikachalam and Ramachandran 2003). Rameshwaram Island, an extension of Vaigai Delta, has a basal dead coral beds overlain by Aeolian red sands and beach ridges. The beach ridges are often intervened by swales with marshy black clay deposits. Marine calcareous hardpan occurs as low terraces and platforms with admixture of quartz, limonite, and garnet concentrations in the northeastern part (Ramachandramoorthy et.al 2009). Tertiary sandstone with intercalation of clays occur under the dead coral beds (Sivasankar and Ramachandramoorthy 2009). Holocene beach rocks occur in patches in several parts of Rameshwaram (Dajkumar sahayam et.al 2010). The relative sealevel curve of the east coast of India for MidLate Holocene period, proves that the sea level stood approximately at 3 m above the present LTL around 7300±130110 yrs BP and at about 2 m above the present LTL around 5500 yrs BP. The radiocarbon dates of coral colonies along the adjacent Rameshwaram Island also range from 7300 to 5660 yrs BP (Gaitan Vaz et.al 2008). Secondary changes of relative sea level by a few metres after the mid Holocene transgressive maximum are not unique to the east coast of India (Banerjee 2000)

Beach ridges, swales, spits and bars, abandoned channels, dunes, wave cut terraces, lagoons and alluvial delta plains are the landforms observed in the area. Most of the coastal landforms are those that were inherited from the Quaternary sea level oscillation. The synthesis of the landforms has revealed great deal of information on the Quaternary trans – and regressive events which in turn help in determining the evolution of delta. These sea level episodes have interrupted and modified the regimes of fluvial sedimentation from time to time switching the delta building from place to place. These marine and fluvial processes have also been influenced by the tectonic crustal flexure in the form of up warping whose effects are observed in the occurrence of features of emergence and submergence adjacently. Hence the evolution of the delta could well be understood by analyzing the impact of these three factors namely fluvial sedimentation, sea level oscillation and tectonism.



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Figure 1: Location map of the study area



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2. Study Area

The study area forms a part of East Coast of India in Tamilnadu region from latitude 9 o 10’ N. to 9 o 45’ N. and longitude from 78 o 30’ E to 79 o 30’ E (fig. 1). The climate is subtropical dry and generally receives moderate to poor rainfall. The Survey of India topo sheets No.58K/10, 11, 12, 13, 14, 15 and 16 cover the area. The area is well connected with rail and road and an important town of this region is Ramanathapuram.

3. Materials and Method

Aerial photos in the scale 1:50,000 and IRS 1D LISS III satellite images were interpreted to study the landforms of the region using Arc.View 3.2a and Arc GIS 9.1 softwares. A detailed field survey was conducted involving morphometric analysis, sediment sample collection, observing the interrelation between landforms and collecting samples for dating. This work is a part of the CSIR sponsored project entitled “Exploration for buried placer and silica sand deposits in the Quaternary sediments of the Vaigai and Tambrabarani Delta” conducted between May 2007 and March 2010 in the Department of Geology, National College, Tiruchirappalli.

Figure 2: Geomorphology of Vaigai Delta



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3.1 Coastal landforms

Deltaic alluvial plain, beach ridges and intervening swales form about 75 % of the deltaic area. The dominant wave action with large amount of sediments derived through long shore currents make the beaches as the most dynamic landforms of the area. The beach ridges plain is bordered in the west by deltaic alluvial plains (fig. 2).

Beach ridges are prominently well developed around Mandapam and ten beach ridge series are observed. During the late Quaternary and Holocene periods the delta building has been facilitated mainly by marine processes as indicated by the series of beach ridges of late Pliestocene and Holocene age. This jettied type of bar observed in the immediate vicinity of the river mouth suggests that the inertial forces are dominant (Coleman 1981). River mouth is deep and hence the estuary extends 5 km into the river channel. The delta can broadly be classified into three segments namely abandoned, active and receiving delta regions. Abandoned delta forms the region from apex of the delta to region where the curvilinear line connecting the places Sayalkudi, Ramanathapuram and Salaigramam and the region is covered by deltaic alluvial plain. Active portion of the delta covers the area that is inclosed in the line connecting Valinokam, Mandapam and Tiruvettiyur. The beach ridge underlain by deltaic plain are observed in the active portion of the delta. The delta front area abutting the shoreline is the receiving basin which is covered by active corals today indicating the absence of sedimentation in the recent past.

The grain size study of the sediments of the delta indicates the progradational decreases in grain size from abandoned region to the receiving basin. The underground lithology shows the repeated alternate occurrence of deep and shallow water sediments. Rameshwarm island is considered to be the extension of delta though it is underlain by dead corals. Sandy barrier beaches and beach ridges observed in Ramehwaram are considered to be the delta building sediments. Palkstrait occurring in between mainland and the island is fully covered by active corals. It is peculiar to note that corals thrive in an environment where river debouches the sediments into the sea, but it is suggestive of absence of suspended mass in the sediments. A raised dead coral bed of the region has been dated to 125,000 years BP and another coral terrace has been dated to 6000 years BP (Rajamanickam and Loveson 1990). The occurrence of dead corals of varied ages sandwiched between sediments and the presence of active corals in the region indicate that the area has experienced alternate periods of sedimentation and non deposition. The turbid free environment formed during the period of non deposition has favored the growth of corals and the period of sedimentation has hindered the growth. These alternate phenomena are found to have occurred since 125,000 years BP.

The occurrence of lakes in hundreds and their distribution in radial pattern in the abandoned portion of the delta attracts a special attention of the geomorphologists. These lakes have trapped most of the sediments supply and it is the reason assigned for the absence of suspended sediments in the active portion of the delta facilitating the growth of corals today in the receiving basin environs. The pattern of distribution of these lakes



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not only points the direction of river flow during the past but also suggest the lobes of the paleo delta.

3.2 Tectonic setting

The sediments ranging in age from Tertiary to recent are found to occur in the basin upto 8000m thick. The underlying basement rocks exhibit horst and graben structure as observed in other deltas of Tamilnadu. These ridges and basins have been active through the geologic time and accelerated the sedimentation process of the basin (Sastri and Raiverman1968, Sastri et al., 1977, Sastri et al., 1981). Neotectonic movements involving East West displacements have also been noted along the Vaigai river course. The occurrence of paleo deltas in the north (around Mimisal and Jegatha patnam ) and south (Tuticorin) of the present Vaigai river signify the switching process of the delta and the reason for this type of switching is assigned to the tectonic effects (Angusamy 1996, Anbarasu and Rajamanickam 2002). A cymatogenic upwarping noted in the region is presumed to have been responsible for the avulsion phenomenon of the river and for the switching the delta building from place to place.

3.3 Fluvial process

The influence of marine and tectonic process on the fluvial sedimentation is prominently observed in the region. The TL and C14 dates of the samples collected from varied landforms (Bruckner 1988 and 1989, Rajamanickam and Loveson, 1990, Stoddart and Gopinatha Pillai 1972 ) suggest that the delta building commenced initially around Tuticorin where a paleo delta is observed today. Then the regime of fluvial sedimentation shifted from Tuticorin to Ramanathapuram region and further north to Mimisal as a sequel to the avulsion of the river by the effect of warping and repeated episodes of sea level oscillations. The present river course resumed the delta building following the avulsion of the river from Mimisal. These changes in the regime of sedimentation were not only caused by the effects of warping but also influenced by the Quaternary sea level oscillation.

3.4 Marine process

The prominent longshore currents are responsible for the occurrence of series of islands around palk bay region and the beach ridges occurring along entire length of the coast of the study area especially around Mandapam. The stranded deposits on land around Ramanathapuram imply the transgression that took place during last interglacial (125,000 years BP) and Holocene (6000years BP) periods. The landforms and a coral terrace of Rameshwaram have also indicated the transgressive events ( Bruckner1989 . Rajamanickam and Loveson, 1990). These transgressive events exerted pressure in the riverine process and as a result of disharmony between the river and marine process the river tend to shift its domain of sedimentation.



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Table 1: Radiometric dates of Coastal Quaternary deposits of Tamilnadu

Sl. No.

Reference Site Specifications Lab. No.

Age Remarks

1 Bruckner (1988)

Cape Comorin

Beach deposits up to +2m above HTL, at some places upto +5m above HTL

112 ka (230 Th/234 U)

Last interglacial maximum

2 Bruckner (1988)

Rameshwara m

Coral reef, noth side of the Island, Porites.sp. upto +2.5m above

112 ka (ESR)


3 Bruckner (1988)

Chetticulam Lagoonal loam, upto +8m above HTL with Veneridae of Circe (closed)

139.5ka (230 Th/ 234U)


4 Bruckner (1988)

Manappad Beach deposits upto +3m above HTL with insitu Balanus.sp at +1.25m above HTL

139.5ka (230 Th/ 234U)

Last interglacial maximum, Glacial

5 Stoddart and Gopinadha Pillai (1972)

Rameshwara m

Porites.sp from the raised coral reef at Pamban

GAK 3187

4020+/160 yr. BP. (14C age)

6 Bruckner (1989)

Cape Comorin

Shells in conglomerate bed at 30 cm above HTL

Cape C HD 1064

112 ka (230 Th/234 U)

Last interglacial deposits

7 Bruckner (1989)

Mouth of Nambiar river

Shells in the marine terrace at 2.5 to 3m above HTL

Vija 52HD 1061

112 ka (230 Th/234 U)

Last interglacial deposits

8 Bruckner (1989)

Between Kulasekarap attinam and Tiruchendur

Shells in the fossil beach ridge at 7m above sealevel

Tuti 5A HD 1061

6240+/50 yr. BP. (14C age)

Holocene transgression maximum

9 Bruckner (1989)

4km weat of Mandapam

Cardium.sp in lagoonal loam upto 1m above HTL

Man M (K1 2338 001)

2740+/60 yr. BP. (14C age)

Late Holocene regression

10 Loveson (1993)

Ariyankund u

Coral +0.55 m above MSL 30/248 /C5

5440+/ 60 yr. BP. (14C age)

Middle Holocene transgression

11 Gardner (1981)

Ramanathap uram

Landsnail in aeolinite deposit +30m above MSL

BM 1670

21000+/ 400 yr. BP. (14C age)

Last glacial regression

12 Sarma (1991)

Kaveripatna m

WoodArchaeological sample TF 207

2316+/103 yr. BP. (14C age)


13 Tissot (1987)

Pichavaram Mangrovesroot tip 2000 yr. BP. (14C age)




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Figure 3: Stages of Development of Vaigai Delta

4. Evolution

The C14 and other dating carried by various authors (table 1) in the delta region were assigned as relative age of the coastal landforms that helps to surmise the stages of evolution of the delta. Based on the study it has inferred four stages in the development of delta during Quaternary.

4.1. Stage 1

This stage coincides with the last interglacial transgressive event. The sea had reached west of Ramanathapuram and the stranded deposits observed around the region were formed as a sequel to this event. Vaigai river was flowing through the channels observed south of the present course and debouched into the sea around Tuticorin. The paleo delta observed here were formed prior to this stage (fig.3). The avulsion of the river channel to the north and the switching of delta was associated with stage.



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4.2. Stage 2

The regression that took place following the last interglacial transgression maximum receded the sea beyond the present shore line and the reclaimed shelf exposed the coral masses and formed the present raised coral terraces in Rameshwaram. The delta building was active around Ramanathpuram and the river Vaigai was flowing with the rejuvenated force while the sea was receding (fig.3).

4.3. Stage 3

This stage coincides with the Holocene transgression that took place by 6000 years BP. The transgression forced Vaigai river to shift its course further north and the river was flowing through the channel observed north of the present course and debouched into the sea around Mimisal. This facilitated the delta building processes around the region. The transgression also created favorable environment for the growth of coral around Rameshwarm and this is evidenced by corals masses dated to 6000years BP. This transgressive event has also developed beach ridges observed around Mandapam (fig.3).

4.4. Stage 4

The regression that took place following the Holocene transgression maximum again facilitated the reclamation of the shelf and the river resumed its present course (fig.3). The delta building also resumed around Ramanathapuram. But there were intermittent transgressive events during the larger regressive phase of the sea. One of such transgression favoured the development of a ancient port named Korkai. This place is observed about 5 km onland today. Ancient Tanil literature has described the place as one of the important port of Pandiya kingdom ie. around 300BC. But the regression following this made this place unsuitable for port activity as it has been reclaimed. Coral terraces at different elevation in Rameshwarm also corroborate the events. The submergence of Danuskodi and exposure of beach rocks around Mandapam indicate the transgressive phase of the sea today.

5. Results and Discussion

The study indicates that the sea has transgressed over the region two times first during inter glacial event (1,25,000 years BP) and the next during Middle Holocene event (6000 years BP). The two series of beach ridges – older and younger – denotes the formation of ridges during the two transgressive events. Banerjee (2000) has also recorded these late Pleistocene and Holocene transgressive events. These transgressive events played a major role in the evolution of coastal landforms and alluvial plains associate with the Vaigai river delta. Theses transgressive events have also induced the shifting of the Vaigai river course and there by facilitated the river to change the regime of sedimentation. The occurrence of paleo deltas one in the north and the other in the south corroborates such changes in the regime of sedimentation.



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Though a large delta is observed, the river involves little delta building activity currently. The occurrence of living corals around Rameshwaram, where the mouth of the Vaigai river occurs, indicates the absence of sediments in the region. Thanikachalam (2003) while estimating the erosion and accretion along the coast of the resgion using Remotsensing and GIS technique has also observed the absence of sedimentation in the region. The study of sedimentary characteristic of the region by Angusamy and Victor Rajamanickam (2006) has also revealed the sedimentation free environment here.

It is also inferred that though the shifting of river courses have been intiated by the transgressive force of the sea, the avulsion phenomenon of the river is attributed to the ongoing neo tectonic activity. Angusamy and Victor Rajamanickam (2000) while studying heavy minerals around Mandapam have inferred such neotectonic activity in the concentration process. Gaitan Vaz et.al (2008) has inferred that the sea – level fluctuations all along the east coast of India have been caused by a combination of neotectonic movements and glacioeustatic sea – level changes. The recorded levels of occurrence of high strandline positions with reference to the present sea level vary from one coastal segment to other, possibly due to postformational tectonism. Evidences of vertical neotectonic movements in the Palk Bay and the Gulf of Mannar coastal segments and around Dhanushkodi in Rameshwaram Island are established. Similarly subsidence and submergence of the southern part of erstwhile Dhanushkodi township nearly 57 years ago along WNWESE trending fault has been established. The above observation indicate that the coastal segments of the Palk Bay and the Gulf of Mannar have undergone neotectonic movements.

6. Conclusion

The sea had transgressed over the delta twice in Quaternary, the first around 125,000 years BP and the second around 6000years BP. These sea level changes pressurized the fluvial system to change it regime of sedimentation and to switch the delta building. Neotectonic processes have also added to the cause of the shifting of riverine process at several times during the Quaternary.



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Evolution of Vaigai Delta, Tamilnadu, India (East Coast ... · Nadu, India 2 – Principal, Dept. of Geology, National College, Tiruchirappalli, Tamil Nadu, India ABSTRACT The present