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SYNTHESIS AND REVIEW ON FAUNAL RECORDS FROM THE SURMA BASIN
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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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