RECORDS OF THE GSI Vol. 112 Part IV 1982, p 31- 38

SYNTHESIS AND REVIEW ON FAUNAL RECORDS FROM THE SURMA BASIN

BY

SUJIT DASGUPTA

Geological Survey of India

(With Plate 7.1)

ABSTRACT

Faunal records from different parts of the Surma Basin have been summarized and reviewed. This

indicates that the ‘Surma Series’ of Evans may transgress the Palaeogene-Neogene boundary and

the Lower Bhuban Formation may be of Upper Oligocene age. More systematic palaeontological

study is suggested for biostratigraphjc correlation and zonation. Similarities in invertebrate

megafossil content between the Surma and Central Burma Basin indicate close connection during

the Neogene times.

The name ‘Surma Series’ first coined by Evans

(1932) is after the name of river Surma, a

distributary of the Barak river, in the Sylhet

District of Bangladesh, for a thick (>6000m)

group of Oligo- Miocene argillaceous and

arenaceous sediments. Originally, these rocks

were studied and described from the Cachar

Valley of Assam and further west bordering the

Shillong Plateau. Subsequently these rocks have

been found to occur in Tripura and Mizo hills,

beneath the alluvial plains and Chittagong hill

tracts of Bangladesh and further south in Coastal

Burma. Evans (1932), from his study in the Surrna

and Cachar Valley classified these rocks as Surma

Series and subdivided into younger Boka Bil and

older Bhuban Stage. Evans’ classification is based

entirely on lithology and at best it can be

designated as local stratigraphy not being co-

relatable lithologically with other areas.

Subsequent mapping in this area (Surma Basin)

within India has been undertaken by the

Geological Survey of India and ONGC; and in

Bangladesh (formerly East Pakistan) by the Oil

Companies. Unfortunately, no standard

stratigraphic nomenclature and subdivision

evolved for the Surma Group of rocks mainly due

to some inherent inconsistencies of the sediments.

The first to mention is the rocks are notoriously

devoid of faunal content, which is the major key

in subdividing monotonous sediments of huge

thickness, limiting the scope of biostratigraphic

subdivision and correlation. Lithostiatigraphic

classification is possible as has been done by

Evans, but correlation from one part to the other is

difficult, if not impossible, due to wide spread

litho-facies variation, absence of marker horizon

and the monotonous nature of the sediments.

Structural complexity has added to the difficulty.

Attempts have been made to classify and

subdivide the sediments by sand/shale ratio

(Holtrop and Kaizer, 1969) for the rocks below

the Bangladesh alluvial plains and by heavy

mineral analysis (Sinha and Sastri, 1973) for the

exposed rocks of Cachar and Tripura hills. Such

attempts, though partially successful, need further

work for a complete stratigraphic picture to

emerge.

Though faunal records are scanty, some studies

have been undertaken from different samples

collected earlier by the geologists from G.S.I. and

B.O.C. and recently by the author and others

working in Tripura-Mizoram area. In this

compilation an attempt has been made to present

an exhaustive summary of available data on fossil

occurrences in the Surma Basin (Plate 7.1). It will

help to understand our present status of

knowledge about the age of the sediments from its

faunal content and will also throw light on future

lines of work that may contribute to evolve a

stratigraphic hierarchy.

To systematize the description of faunal

remnants, the area has been divided into six

regions, namely— (1) Surma sediments bordering

the Garo hills, (2) Cachar Valley, (3) Sediments

below the alluvium of Sylhet and Comilla

Districts of Bangladesh, (4) Fossil localities in

Tripura, (5) Fossil localities in Mizoram and (6)

The Chittagong hill tracts. Fossil localities in

Coastal Burma have not been included in this

account. This has been summarized recently by,

A.B. Dasgupta (1977) in his Presidential Address

delivered before the fifty-second annual general

meeting of the Geological, Mining and

Metallurgical Society of India.

Surma sediments bordering the Garo hills

First fossil collection from this area was by

Scott and Colebrooke (1822, quoted from

Mukherjee, 1939) from the Karaibari hills (not

shown in Plate 7.1) lying between the western

extremity of the Garo hills and the Brahmaputra

river. From this collection, Mukherjee (1939)

identified the following species:

GASTROPOD: Turritella (Torculoidella) angulata

Sow. Calyptraea rugosa Noet.

LAMELLIBRANCH: Anadara submultiformis Vred.

Ostrea latimarginata Vred. Ostrea cf. digitata Eich.

ANTHOZOA: Paracyathus sp.

ARTHROPODA: Balanus (Chirona) sublaevis Sow.

MAMMALIA: Anthracotherium silistrense Pentland.

Choeromery silistrensis Pentland.

The mammalian remains are closely related or

identified with similar mammalian fauna from the

Gaj (Burdigalian) of Sind. Turritella angulata

Sow. has been recorded from Upper Gaj of

Kirthar region having allies in the estuaries of the

present day. The general faunal assemblage in the

Karaibari exposure indicates approximately a

Lower Miocene age equivalent to Aquitanian-

Burdigalian and in all probability identical in age

with the Bagmara- Dalu fossil horizons discussed

below.

Pinfold (l919) discovered two fossil localities

from the southern Garo hills and the organic

remains were described by Vredenburg (1921). Of

the two 1ocalilies, the more easterly one is near

the banks of the Someswari river, 2.4 Km. south-

west of the village Bagmara (25°11′: 90°40′) and

the westerly one is 6.4 Km north of the town Dalu

(25°14′: 89°15′). The two localities are separated

by a distance of about 48 Km and the fossil

horizons occur under similar conditions.

The organic remains are mostly those of

mollusca with delicate shells, a few sharks’ teeth

and Otoliths. The shells are mostly fragmentary

and include specifically indeterminable specimens

of Conus, Oliva, Murex, Natica, Solerium,

Calyptarea, Arca, Pecten, Ostrea, Lucina,

Dosinia, Venus and Tellina. Nine gastropod forms

that have been specifically identified are: (1)

Terebra protomyuros Noet. (2) Surcula promensis

var. silistrensis Vred. (3) Drillia proto cincta

Noet (4) D. tjemoroensis Mart. (5) Mitra chinesis

Gray var. subscrobiculata d’ Orbigny (6)

Siphonalia subspedicea Vred. (7) Turritella

pinfoldi Vred. (8) T. angulata Sow and (9)

Calliostoma promense Vred. This specific

determination was of great palaeontological

interest and importance because some precise age

connotation could be assigned for the first time to

some late Tertiary formation of Assam. Amongst

these nine species, Species No. 3 occurs in the

Kama beds (Aquitanian) of Burma and in the

Pliocene Soude’ Series of Java. No. 4 also

characterizes the Kama stage of Burma; No. 7

occurs in beds of Burma along with Ostrea

latimarginata which must be referable to the

Pyalo stage (Burdigalian). No. 8 occurs in the

Singu (Chattian), Kama and the Pyalo beds of

Burma. No. 5 is the only undoubted living species

recognized in the fauna of the Garo hills where it

is represented by the variety subscrobiculata, also

present in the Gaj Series of Cutch. This

assemblage suggests an age approximately

coinciding with the Pyalo stage of Burma and

with the Upper Gaj Stage of Cutch.

Another small collection by C. A. Phillips

(quoted from Mukherjee, 1939) of B.O.C. from

Bagmara was studied by Coggin Brown and the

species identifled include 7 gastropods, of which 3

are common to Pinfolds’ collection, 2

lamellibranchs and 1scaphopod:

(1) Drillia protocincta Noet. (2) Turritella pinfoldi

Vred. (3) T. angulata Sow. (4) Terebra (Myurlla) cf

intermedia Vred. 5) Terebra (Duplicaria)

woodwardiana Mart, var. mindegyiensis Vred. (6)

Sigaretus loevgaus Lam. (7) Clavetula (Perrona)

birmanica Vred. (8) Arca (Anamolocardia) yawensis

Noet. (9) Arca (Anamolocardia burnesi d’ Arch and

Haime. and (10) Dentalium junghuhni Mart.

More attention was paid to these two fossil

localities and Mukherjee (1924, see Mukherjee,

1939) collected a large number of fossils. This

new collection, besides including almost all the

forms already recorded by Vredenburg (1921) and

Brown (see Mukherjee, 1939), comprises a very

large number of well preserved forms which are

known to occur in beds ranging from Oligocene to

Pliocene from different parts of the world. This

collection of Mukherjee inc1udes mostly

mollusca, in which thirty-eight species of

lamellibranchs and seventy-four species of

gastropods have been described (Mukherjee,

1939). Besides these, the following forms have

also been noticed:

Foraminifera: Rotalia becearii (Linn)

Anthozoa: Paracyathus cf. coeruleus Duncan.

Scaphopoda: Dentalium junghuhni Mart.

Arthropoda: Balanus (Chirona) sublaevis Sow.

Calianassa birmanica Noet.

Pisces: Carcharias sp. Mylicbatis sp.

Reptilia: Garialis sp.

The following species (eleven lamellibranchs

and nine gastropods) described from the Garo

hills have been considered by many workers to be

of great value as time indices and characteristic of

Lower Miocene.

(1)Taras incerta d’ Arch (2) Aplometis (Tellina)

grimesi Noet. (3) Cardium minbuense Noet.

(4) Antigona garnosa Sow. (5) Timoclea

subspedicea Cossm. (6) Macrocalista erycina

Linn. (7) Clementia papyracea Gray. (8) Trisidos

semitorta Lam. (9) Anadara craticulata Nyst.

(10) Chlamys senatoria Gmel. (11) Ostrea

latimarginata Vred. (12) Turritella angulata Sow.

(13) T. pinfoldi Vred. (14) Rimella subrimosa

d’Orbg. (15) Siphonalia subspadicea Vred.

(16) Melongena ponderosa Vred. (17) Marginella

birmanica Vred. (18) Terebra protomyuros Noet.

(19) T. reticulata Sow. and (20) Cancellaria

dertonesis Bell.

That the fauna of the Garo hills is not younger

than Lower Miocene is further evidenced by the

presence of a nautiloid species, definitely

referable to the characteristic Mediterranean

Miocene form Aturia aturi (Basterot): The faunal

assemblage indicates an age close to the Lower

Miocene approximately equivalent to the

quitanian-Burdigalian and is therefore equivalent

to the Gaj of Northwest India.

Cachar Valley

Owing to the rarity of fossils in the Upper

Tertiaries of the Surma Basin a special interest is

attached to the fossil bed at Kanchanpur (24°39′ :

92°31′) of Cachar valley. In this locality a

comparatively rich marine fauna of Lower

Miocene age occur in a thin fossiliferous bed

which is placed stratigraphically in the uppermost

part of the Bhuban Stage. Dr. CS. Fox visited the

piace with Mr. H.M. Sale of B.O.C. and collected

the specimens from northwest of Kanchanpur,

about 6.4 kms west-south-west of Hailakandi.

Amongst the collection, Mukherjee (1928) found

only two which admitted specific determination.

These are two species of Meiocardia of which one

is closely related to Meiocardia metavulgaris

Noet., while the other was new. Noetling recorded

the species M. metavulgaris from his zone of

Mytilus nicobaricus Reeve., from the Singu Stage

of Burma. Vredenburg correlated the Singu stage

with the Upper Nari of northwest India and,

therefore regarded it as Chattian (Upper

Oligocene).

The collection was enriched afterwards by Sale

of B.O.C. and the following specific

determination was made by Mukherjee (1929)

besides the above two species of Isocardia

(Meiocardia):

Gastropod: Drillia (Crassispira) cf. delabeensis

Vred. Drillia cf. protointerrupta Noet. Pyrula

dissumieri Valenc.

Lamellibranch: Nucula alcockij Noet. Mactra

protoreevesi Noet.. Ledo virgo Mart.

Anthozoa: Flabellum distinctum Noet.

Dendrophyllia sp.

Arthopoda: Balanus(Chirona)cf.birmanicus With.

Hipponyx sp.

Echinoidea: Cidaris sp.

Drillia cf. delabeensis Vred. closely resemble

D. harpularia Desm. from the Miocene of

Australia. D. terebra Bast. and D. fratercula Bell.

from the Miocene of Europe also resemble the

Kanchanpur fossil. Pyrula dissumieri is very

closely related to P. ficus Linn. from the Makran

beds of Baluchistan and the Mio-Pliocene of Java.

The above assemblage shows that the age of the

Kanchanpur fossil bed is not Upper Oligocene but

more likely of Miocene (Gaj) age.

Sediments below the Alluvium of Sylhet and

Comilla District, Bangladesh

In the Surma Valley of Bangladesh several wells

have been sunk in connection with oil exploration.

Nine anticlinal structures have been penetrated

starting from Cachar-Bangladesh border in the

northeast to Tripura-Bangladesh border in the

southwest. Palaeontological and stratigraphical

data from these drillings have been summarised

by Holtrop and Kaizer (1969). Faunal

development has been found to be discontinuous,

and these are (a) Bulimina 2, (b) Rotalia 2, (c)

Globigerinoides 1and (d) Bulimina 3. The

individuals constituting the assemblage zone are

numerous and only the important ones are

mentioned below:

Bulimina 2: Bulimina, Bolivina, Eponides,

Haplophragmoides, Rotalia, Buliminella,

Cassidulina, Anommlina, Cibicides and Nonion.

Rotalia 2: Rotalia, Uvigerina Elphidium,

Bolivina, Cibicides and GIobgerinoides.

Globigerinoides 1: Globigerinoides,

Cassigerinella, Globigerina, Rotalia, Bolivina,

Cibicides, Cassidulina, Haplophragmoides,

Porticulasphaero, Globorotalia and

Globoquadrina.

Bulimina 3: Bulirnina, Rotalia, Bolivina,

Clavuluioides, Trochamnina, Gyroidina,

Cristellaria, Bathysiphon and Globigerina.

Specific identification of some of the above

genera include Globigerinoldes triloba, G.triloba

immatura, G. triloba disphaerica, Globigerina

ouachitaensis varsenites, G. ciperoensis,

Globorotalia foshi borisanensis, Globoquadrina

cf. altispira, Cassigerinella chipolensis and

Proticulasphaera glomerosa.

Assemblage zone Bulimina 2 has been found to

be associated with the Upper BokaBil marine

shales and the age is assumed to be lower

Miocene and/or younger. This zone has been

encountered in wells Chhatak l (between 527m-

519m), Sylhet 2 (1286m-1329m), Kailash Tila l

(2206m-2286m), Fenchuganj 1 (1231m-1365m),

Rasidpur l and 2 (1250m-1408m), Habiganj 1

(1250m-1436m), Titas 1 (853m-957m) and

Lalmai l and 2 (1103m-1250m).

Rotalia 2 assemblage zone corresponds roughly

with the major part of the BokaBil Formation and

the age is Lower Miocene and/or younger. In the

Chhatak structure this zone has been encountered

between 1433m-1530m depth; between 1950m-

2112m in Rashidpur 1 and 2; between 1716m-

1950m depth in Habiganj structure; from l347m to

l458m in Titas-l and between 1469m and 1685 in

Lalmai l and 2.

Globigerinoides 1 represents grossly the

Bhuban Formation with a Lower Miocene age and

has been encountered in Kailash Tila-1 (3761m-

3770m); Rashidpur 1 and 2 (3737m-4133m);

Habiganj 1 (2963 m- to the bottom of the well,

3505m); Titas l and 2 (2445 m to more than 3237

m probably up to the bottom of the well, 3758m)

and Bakhrabad 1 (2396m to bottom, 2838m).

Bulimina 3 assemblage zone has been

encountered only in Rashidpur 2 drillings at a

depth of 4163m. This zone is thought to represent

the Barail and is probably of Oligocene age.

Fossil Localities in Tripura

First collection of fossils from this area, was by

K.L. Das (1938, see Vachell, 1942), State

Geologist to His Highness, the Maharaja of

Tripura. F.E. Eames identified the organic

remains which include remains of mollusca and

pisces. Das collected the fossil from the Jarnpui

range of Tripura from localities southwest and

east of village Manpui (24°2.5′: 92°17′), east and

west of village Tlangsang (23°54.5′ 92°17.5′) and

in the Deo river section. Specifically determined

fauna include (1) Polinices (Euspira) globosus

Chemn. (2) Turritella (Zaria) angulata Sow. (3)

Paphia (Protapes) galius Gmel. (4) Arca

(Larkinia) submultiformis Vred. (5) Arca

craticulata burnesi Nyst. (6) Carcharias

(Prionodon) gengeticus Muller and Henle and (7)

Carcharon megalodon Ag.

This assemblage indicates an Oligocene-Lower

Miocene age of the sediments. From the same

area, west of the village Manpui, two bands of

shell limestone have recently been discovered by

Dasgupta and Bhattacharyya (1977). Samples

were sent to the Palaeontological Laboratory, GSI

at Calcutta and Shillong and the following faunal

remnants were identified by R.S. Misra,

B.P. Chatterjee and A. Bhattacharyya.

R.S. Misra identified the following forms:

(1) Miogypsina sp. (2) Globorotalia sp.

(3) Globigerina sp. (4) Operculina sp. and (5)

Rotalids. Along with these foraminifera occur

broken and unidentifiable fragments of coral, fish

remains, gastropods and shark teeth.

B.P. Chatterjee identified the following forms:

(1) Miogypsina (?Miolepidocyclina) sp. and (2)

Rotalids. Identification of A. Bhattacharyya

includes (1) Rotalia sp. (2) Nonion sp. (3)

Eponides sp. (4) Sigmoilopsis sp. and Ostracods

include (1) Acutioythercis sp. (2) Bairdia sp. and

(3) Leguminocythereis sp.

The above faunal assemblage also indicates an

Upper Oligocene-Lower Miocene age of the

limestone, stratigraphically located on the upper

part of the Bhuban Formation. From a shale

pebble conglomerate within the BokaBil shales,

western flank of Gajalia anticline, upstream of

Hichha Chara, south Tripura, B. P. Chatterjee

described larger foraminifera Miogypsina

(Miolepidocyclina) sp. indicating an Upper

Oligocene- Lower Miocene age.

Sar (1968) collected some samples of calcareous

sandstones and shell limestones from Lalkung and

Lawan Chara in North Tripura, western flank of

Sakhan range. The samples were studied by Oil

India Limited and they reported:

(1) Rotalia sp. (2) Cibicides sp. (3) Anomalina sp.

and (4) Valvulineria sp. All the forms are ill

preserved but Rotalia sp. from these samples is

comparable to the type species (Oil India) number

4. This Rotalia 4 in Assam has been recorded

from the Middle Bhubans of Masimpur wells,

Damchara area and Kikar shales (Middle

Bhuban). Since these are benthonic forms not

much reliance can be placed for age

determination.

North of the above locality on the Assam-

Agartala Road, in between two tributaries of

Chidang Chara, Dasgupta (1974) collected some

vertebrate fossils from a conglomerate horizon

within the BokaBil shales. These organic remains

have been studied by P. K. Basu of

Palaeontological Laboratory, Calcutta and

identified the following species:

Pisces (Shark tooth): Carcarias gangeticus Muller

and Henle., Isurus (Oxyrhina) spallanzani Bonap.

Reptilia (Crocodilian tooth): Gavialis sp.

Mammalia: Gomphotherium cf. pandionis Falc.

Pachyportax nagrii Pilg.

Basu and Dasgupta (1977) summarised that

Gomphotherium cf. pandionis Falc. is a Middle

Miocene elephantoid form described earlier from

the Lower Manchar Stage of Sind and Kamlial

Zone of Salt range. Pachyportax nagrii is an

Upper Miocene primitive bovid and has been

described from the Nagri Zone of Salt range. Thus

the age of the intraformational conglomerate is

probably not older than Upper Miocene.

Trivedy (1966) reported the occurrence of the

vertebrate fossils from a conglomerate horizon

within the BokaBil shale from (1) about 9 km.

west of Teliamura (23°50′20″ : 91°38′30″) and

(2) NarengBari (23°47′15″ : 91°033′45″) in the

Baramura Range, Tripura. The following fossils

have been identified by Trivedy:

Pisces: (1) Oxyrhina spallanzanii Bonap. (2)

Oxyrhina sp. (3) Oxyrhina cf. pagoda Noet.

(4) Prinodon gangeticus Muller and Henle.

(5) Siluroid gen. (bony fish)

Reptilia: (1) Crocodilus palustris Less.

(2) Gharialis gangeticus Gmel.

(3) Gharialis cf. gangeticus Gmel.

(4) Gharialis sp.

Mammalia: (I) Trilophodon angustidens Lyd.

(2) Dorcatherium sp.

This assemblage reveals an Upper Miocene age

for the BokaBil stage. Trilophodon angustidens

found in the Manchar Series of northwest India

and Dorcatherium found in the Chingi Stage of

Siwalik, indicate a Tortonian age for the

conglomerate bed in which these fossils have been

found.

Fossil Localities in Mizoram

Organic remains from the Lushai hills were first

discovered by La Touche (1891) at Lungleh, south

Mizoram and a species of Schizaster has been

reported. Nandy and Mukheree (1972) collected a

few samples from about 4.5 km. west of Aizawl

on the Aizawl-Sirang road presumably from the

Upper Bhuban Formation. These samples yielded

sorne ill preserved micro- fossils and B. P.

Chatterjee identified them as different species of

foraminifera and ostracoda. These include (1)

Ammonia cf. beccarii (2) A. cf. pappillosa (3)

Globigerina sp. (4) Leguminocythereis sp. The

forms are long ranging but ostracod-foraminiferal

assemblage is indicative of Miocene age.

Mukherjee and Saxena (1973) mapped a few

bands of shell conglomerate within Upper and

Middle Bhuban rocks on the Lungleh-Demagiri

road in between villages Pachang and Rothlang.

About thirty samples were studied and yielded

fragments of Mollusca, Echinoid, Shark tooth and

Carbonised wood pieces. The invertebrates

include specifically indeterminable specimens of

Pecten, Crassatella, Spondvlus, Rimella, Lunalia,

Volutospira and Opissaster.

Banerjee, Sarkar and Dasgupta (1977) collected

a few samples of calcareous sandstone and shell

limestone from boulders of huge dimensions

occurring in the narrow gorge of Ngharum Lui

and Suibal Lui, tributaries of Sonai river just

south of the Bridge on Sonai river on the Aizawl-

Seling road. From their collection R. S. Misra

identified foraminifera up to genus level that

include Archeis, Austrotillina, Eponides,

Globorotalia, ?Lepidocyclina, Rotaliids and

Miliolids, A. Bhattacharyya identified some

molluscs that include Venus, Barbatia, Cardium

and Tellins. This assemblage is indicative of

Oligocene-Miocene age.

Dasgupta (1977) collected two samples of shell

limestone from the Kolodyne river bed, south of

Kalchaw (22°23′50″: 92°58′) that yielded

mollusca and foraminiferal remains. A.

Bhattacharyya identified the followings:

Venericardia, Venus, Cardium,

Solen and Unio; Ammonia sp., Textularia sp.,

Globigerina sp., Quinqueloculina sp. and

Sigmoilopsis sp.

Recently Banerjee and Dasgupta (1978)

discovered three fossil localities (? Lower Bhuban

rocks) from a remote corner of the country, in the

Mizo hills, in and around Tuipang (22°19′:

93°01′40″). A large number of mollusca,

foraminifera and ostracoda have been identified

by the Palaeontolgical Laboratory, Calcutta.

A. Bhattacharyya studied the megafossils while

M. Sen studied the microfossils.

MEGAFOSSILS

Lamiellibranch: (1) Lima protosquimosa Noet.

(2) Cardium sp. (3) Tellina sp. (4) Tellina grimesi

Noet. (5) Venreicardia sp. (6) Batissa sp. (7)

Tellina indifferns Noet. (8) Nucula aleocki Noet.

(9) Septifer sp. (10) Meretrix sp. (11) Meratrix

protophilippinarum Noet. (12) Corbula socialis

Mart. (13) Unio sp. (14) Trachycardium

minbuense Noet. (15) Chlamys sp. (16) Pecten sp.

(17) Chlamys senatorius Gmel. (18) Corbula sp.

(19) Venericardia noetlingi Cott. (20) Nucula sp.

(21) Siliqua sp. (22) Vericorbula sp. (23)

Pectuncalina sp.

Gastropods: (1) Turritella noetlingi Vred. (2)

Carithium sp. (3) Conus decollatus Linne′ (4)

Terabra sp. and (6) Conus sp.

MICROFOSSILS

Foraminifera: (1) Textularia sp. (2) Cibicides sp

(3) Ammonia sp. (4) Globigerina sp. (5)

Sigmoilopsis sp. (6) Eponides sp. (7) Rotalia sp.

(8) Nonion sp.(9) Quinqueloculina sp. (10)

Textularia agglutinans (11) T. akminei,

(12) Quinqueloculina seminulum (13) Q. oblique

camerata (14) Q. seminulangulata and (15)

Opeiculina sp.

Ostracoda : (1) Bairdia sp. (2) Krithe sp. (3)

Acuticythereis sp. 4) Leguminocytheris sp. and (5)

Neomonoceratina sp.

In general the state of preservation is very poor.

Microfossils are rarely present in the samples and

most of the megafossils are either casts or

impressions. Megafossil assemblages contain

fossils indicating Eocene to Miocene age and

microfossil assemblage indicates a Miocene age.

Most of the megafossils mentioned above have

been described from the Pegu Series of Burma.

Among the lamellibranchs Lima protosquimosa

(No.1) have been described from the Singu

(Chattian) and Kama (Aquitanian) Stage of

Burma. No. 4 reported from Singu and Kama

Stage of Burma and from Bagmara and Dalu area

of Garo hills. No. 7 has been reported from the

Padaung (Lower Nari) and Kama Stage of Burma,

and from the Bagmara area of Garo hills. No. 8

occurs in Padaung, Singu and Kama Stage of

Burma, in the Upper Bhubans of Kanchanpur and

Bagrnara area. No. 11 is present in all the stages

of Pegu Series and in the Garo hill sediments. No.

12 occurs within Miocene Quilon beds of Kerala,

Garo hills of Assam and in the Kama Stage of

Burma. No. 14 is present in the Garo hills and in

Singu and Kama sediments. No. 17 has been

reported from the Gaj Series of Sind and Surma

Series of Garo hill. No. 19 occurs in all the stages

of Pegu Series. Among the Gastropods, No. 1 and

3 is present in the Upper Tertiary of Garo hills and

in Kama Stage of Burma.

Analysis of the invertebrate fauna present in the

Tuipang area of Mizo hills indicates a faunal

resemblance with that of Burma and the

assemblage indicates an age equivalent to the

Kama Stage of Burma.

Chittagang Hill Tract

The Gajalia anticline of Tripura continues

further south in the Chittagong hills of

Bangladesh with a slight knee bend near the

Tripura-Bangladesh border. From the western

flank to this structure, south of Sitakund, Pascoe

(1914) reported rocks containing moluscan

fragments and correlated it with the Pegu Series of

Burma. Some fossils were also collected by C. M.

P. Wright from this area. Among them was an

Oyster which has been identified as Ostrea

digitalina Eich. (Syn.O.prymansis Noet.). Pascoe

found several fragments of this Ostrea, the hinge

area of a thick Ostrea (O. grypoides Schi. syn.

with O. crassissima, Lam.), many plates of

Balanus, a broken Shark’s tooth and

indeterminable fragments of Arca, Pecten,

Trochus, Oliva, and Corals. These fossils occur

‘within hard conglomerate and shell limestone.

Conclusion

Faunal development in the Surma sediments is

poor and discontinuous. Planktonic foraminifera

are rare or absent from all the samples that have

been studied and this restricts giving precise age

connotation for a sequence of sediments. Even

when present they do not admit specific

determination due to ill preservation. However,

systematic sampling from within an uninterrupted

sedimentary sequence and faunal study there from

has also not been undertaken. More study of

microfauna is necessary towards building up a

unified stratigraphy for the basin.

From our present knowledge on fossil

occurrences it seems that the ‘Surma Series’ of

Evans may extend downwards up to the Upper

Oligocene. Most of the localities from where

fossils have been studied are either from the so-

called Boka Bil or the Upper Bhuban Stage

(Formation) and the fossil assemblage indicate

mostly a Lower Miocene age approximately

equivalent to the Aquitanian-Burdigalian age. The

Bagmara and Dalu fossil horizon of Garo hills

occur within, what has been considered by Evans

as BokaBil Stage indicating a Lower Miocene

age. The fossil bed of Kanchanpur,

stratigraphically occurs at the top of the Bhuban

Formation and indicate a Miocene age. In Tripura,

the Jampui and Sakhan shell limestone occur

within the Upper Bhuban rocks and has yielded

foraminifera belonging to Upper Oligocene-

Lower Miocene age. Thus the Upper Bhuban and

BokaBil Formation which constitute the Upper

part of Surma Group, indicate a Middle-Lower

Miocene age. In that case, what has been

described as Middle and Lower Bhuban will

possibly enter into the Paleogene.

Specific identification of Jampui limestone

foraminifer assemblage may help

biostratigraphical correlation. Fossil occurrences

in Tuipang area is probably from an older horizon

and demands critical study.

Almost all the invertebrate megafossils reported

from different parts of the Surma basin have also

been recorded from the Upper Tertiaries of

Central Burma. This indicates a close connection

between the paired Neogene basins on either side

of the Chin hills-Arakan Yoma Orogen.

Acknowledgements

Without the help of a large of personnel in

Geological Survey of India, it would not have

been possible for the author to prepare this

account. D. R. Nandy, Geologist (Sr.), inspired to

write this account and helped in collecting the

data. K. V. Krishnamurthy, Director, Mrinal Sen

and J. Bhattacharyya, Geologists (Jr.), GSI kindly

went through the manuscript and offered

suggestions for its modification.

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Note from the author: There are spelling

mistakes both in the original printed document

and also added during running the OCR after

scanning. Sorry but can’t help. The author is not a

serious paleontologist and cannot correct them

now in August 2010.

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