CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY OF THE JAISALMER BASIN
Journal of the Palaeontological Society of India
Volume 59(1), June 2014: 29-44
29
ISSN 0522-9630
BARTONIAN AGE CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY OF
TANOT WELL-1, JAISALMER BASIN AND ITS IMPLICATIONS
JYOTSANA RAI1, ABHA SINGH1 and DIVYAM GULATI2
1
BIRBAL SAHNI INSTITUTE OF PALAEOBOTANY, 53-UNIVERSITY ROAD, LUCKNOW-226007
2
UNIVERSITY OF PETROLEUM AND ENERGY STUDIES, DEHRADUN-248007
E-mail: Jyotsana_rai@yahoo.com
ABSTRACT
A fairly rich and moderately diversiied nannofossil assemblage comprising thirty-eight species belonging to eighteen genera and one calcareous
dinolagellate species are described from subsurface samples of Tanot #1 well (Oil India Limited) representing the Bandah Formation of the Jaisalmer Basin.
The assemblage though contains little overgrowth in delicate forms, yet displays exceptional preservation at some levels. The assemblage is dominated
by reticulofenestrids specially Cribrocentrum reticulatum. The assemblage is typically indicative of low-latitude, near-shore, shallow and warm water
environment and can be assigned to zone NP17 Discoaster saipanensis Zone. This is correlatable with parts of both P13 Orbulinoides beckmanni and P14
Truncorotaloides rohri planktonic foraminiferal Zones and a part of D11 dinolagellate Zone of Bartonian age. This nannofossil data from subsurface of
Jaisalmer is coeval with more diversiied nannofossil assemblage from Kachchh and less diversiied assemblages from the Dilni River section, Meghalaya.
Though the entire Bartonian spans (41.3-37.my) ca. four million years, it appears that the nannofossil assemblages in both western and eastern sectors of
India pertain only to 1.5 my. time slice (39.5-38.0 my) of global eustatic rise. The late Eocene (Priabonian) is hiatus both in the Kachchh and Jaisalmer basins
of western India, whereas the sedimentation continued in Meghalaya in the eastern sector and the sea encroached on the Cambay Basin in western India in
late Eocene.
Keywords: Nannofossils, Bartonian, Biostratigraphy, Jaisalmer Basin
INTRODUCTION
Calcareous nannofossils are ideal for high-resolution
biostratigraphy and palaeoenvironmental interpretations of
shallow marine and deep sea deposits (Siesser and Haq, 1987).
Jaisalmer Basin, situated in the north-western part of Rajasthan,
western India displays a nearly lat topography covered with
recent desertic alluvium. Marine Mesozoic-Tertiary rocks
crop out in a few prominent hillocks. The occurrence of
marine Tertiary rocks in the Jaisalmer Basin was irst noted
by Blanford (1876). The outcropping marine Cenozoic rocks
on surface in the Jaisalmer Basin overlying Deccan traps are
classiied as the Sanu, Khuiala, Bandah and continental Shumar
formations in ascending order. The Khuiala and Bandah
formations of the Jaisalmer Sub-basin are dated on the basis of
ostracod assemblages as lower and middle Eocene respectively
(Khosla, 1972). The age of echinoid-bearing horizon of the
Khuiala Formation (calcareous sandy marl) is constrained
by the presence of index larger foraminifer Assilina lacunata
Cizancourt (Srivastava et al., 2008) which indicates an Early
Eocene (Ypresian) age. The ostracode, bivalve and other biotic
elements previously described from the Khuiala and Bandah
formations (Khosla, 1972; Das Gupta, 1974; Pareek, 1984;
Ghosh, 1987; Bhandari, 1995; Singh, 1996; Singh, 1997; Singh,
2003) are also consistent with these age assignments. The surface
samples from the Khuiala and Bandah formations proved barren
of nannofossils. In order to examine the basinal continuity and
better preserved datable microfossils, the samples from bore
well material of Oil India Limited have been studied. Study of
calcareous nannofossils from Paleocene-Eocene succession of
the Jaisalmer Basin has been carried out by Singh (1998) and
from the Cambay Basin by Samanta et al. (2013a, 2013b).
In the present paper, a systematic study of nannofossil
assemblage (under light and scanning electron microscope) is
presented along with their application in age determination,
biozonation and palaeoenvironmental interpretation of the
subsurface Bandah Formation of Tanot #1. A comparison of
the recorded nannofossil assemblages is made with known
assemblages from coeval succession in other Indian sedimentary
basins of Kachchh (Rai, 1988, 1997, 2007; Jafar and Rai, 1994)
and Dilni River Section, Meghalaya (Rai and Garg, 2009).
Khartar well-C from the Jaisalmer Basin has yielded poorly
preserved undatable calcareous nannofossils from the Khuiala
Formation and datable nannofossil assemblage belonging to
CP14 Reticulofenestra umblica/NP17 Discoaster saipanensis
zone from the Bandah Formation (Singh, 1998). The present
inding of nannofossil from Tanot #1 is actually lateral coeval
extension of same deposits in another well. The assemblage in
Tanot #1 is more diversiied and in Khartar well-C several forms
remained unidentiied (Singh, 1998 Pl. 3, p. 168-169).
GEOLOGICAL SETTING
Rajasthan is endowed with a continuous geological
sequence of rocks from the oldest Archaean metamorphic
to sub-recent, alluvium and wind- blown sand (Fig.1). The
sedimentary sequences include the rocks of Aravalli Super
group, Delhi Super group, Upper Precambrian Vindhyan Super
group and of Cambrian to Jurassic, Cretaceous and Tertiary
ages. The southeastern extremity of the State is occupied by a
pile of basaltic lows of Deccan Traps of Late Cretaceous age.
Rajasthan Basin forms the eastern lank of Indus geo-syncline
and comprises the sedimentary tract to the west and northwest
of Aravallis up to Indo-Pakistan border. Encroachment of
an arm of the sea from the south-westerly direction into
western Rajasthan during the Jurassic period laid down thick
fossiliferous marine sequence. During ?Paleocene-Eocene
times, fresh marine transgression seems to have inundated
a large part of western Rajasthan with the deposition of thick
beds of fossilliferous limestone. To the North of Jaisalmer, the
30
JYOTSANA RAI, ABHA SINGH AND DIVYAM GULATI
Fig. 1. Location map of the Jaisalmer Basin showing location of study area.
CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY OF THE JAISALMER BASIN
Jurassics are overlapped by Tertiary age nummulitic limestone.
In view of exploration of hydrocarbons the Jaisalmer Basin is
kept under essentially unexplored basins of India (Raghavendra
Rao, 1972; JaiKrishna, 1987).
PREVIOUS WORK
Earlier work on the stratigraphy of the Jaisalmer Basin
was done by several workers (Blanford, 1876; Oldham, 1886;
Raghavendra Rao, 1972; Das Gupta, 1973, 1975). Das Gupta
(1975) revised the Mesozoic-Tertiary stratigraphy of the
Jaisalmer Basin on the basis of detailed surface and subsurface
geological investigations of the area. Pareek (1981, 1984) gave
an account of the basin coniguration and stratigraphy of western
Rajasthan. Singh et al. (2005) gave an overview of structural
elements and stratigraphy while working for hydrocarbons in
the Jaisalmer Basin.
Narayanan (1959) identiied Kirthar foraminifera in the
Bandah Formation, west of Ramgarh in Jaisalmer district.
Khosla (1972) provided ostracode assemblage based ages from
the Khuiala and Bandah formations of Bikaner and Jaisalmer
districts. Kalia and Kintso (2006) described planktonic
foraminifera of the Paleocene/Eocene boundary in the Jaisalmer
Basin. Singh (1998) provided calcareous nannoplankton and
foraminiferal biostratigraphy of Paleocene and middle Eocene
(Bartonian) age nannofossils from Khartar well-C of the
Jaisalmer Basin from Parh, Sanu and Bandah formations. The
Khuiala Formation showed absence of calcareous nannofossils.
LITHOSTRATIGRAPHY
FORMATION
OF
THE
help of a clean dropper. Two slides, one containing iner and
the other comparatively coarser fraction were prepared and
allowed to dry on a hot plate. Two drops of mounting medium
(Canada Balsam) was poured with the help of a glass rod and
a cover slip of appropriate dimension (22 X 40mm) to cover
the slide containing dry suspension ilm. The air bubbles were
allowed to escape. The slide was cooled and the coverslip was
evenly pressed so that permanent slide of uniform thickness
was prepared. Nannofossils were observed with a Leitz make
polarizing Microscope with X10 or X12.5 occulars and X100
objective, the latter requiring oil immersion. Polarization and /
or phase contrast equipments are necessary for the study of most
of the forms. The use of gypsum plate helps in the identiication
of some critical forms.
Scanning Electron Microscopy (SEM)
For the scanning electron microscopy two samples (14544
and 14562) bearing sample number 528 and 615 (which
showed best preservation amongst all the samples under light
microscope) were selected and used short centrifugation
method (Bown, 1998) for the preparation of the suspension. The
suspension were spread over numbered coverslips and allowed
to dry up. Coverslips were then mounted on aluminium stubs
with both sided sticking tape. The side containing suspension
was masked by quick silver, coated with gold-palladium and
examined under SEM LEO 430 model microscope.
BANDAH
The formation is named after the Bandah village (Narayanan,
1959). The formation consists of argillaceous limestones
and clay. Khosla (1973) recognized two larger foraminiferal
assemblage zones namely lower Discocyclina sella and upper
Discocyclina dispansa assemblage zones, within the Bandah
Formation of the Jaisalmer Basin, based on which the middle
Eocene age has been assigned to the Bandah formation. Singh
(1998) recorded only one Nummulites acutus zone from Bandah
Formation of Kharatar well-C of the Jaisalmer Basin. Besides
this, the planktonic foraminiferal assemblage containing
Truncorotaloides rohri indicates top of middle Eocene. The
nannofossil assemblage recorded from the Bandah Formation
also provides precise Bartonian age (NP17=CP14b) zone
(Singh, 1998).
MATERIAL AND METHODS
In the Jaisalmer Basin Oil India Limited had drilled a number
of exploratory wells in search of hydrocarbons at Bakhri-Tibba,
Ghotaru, Manhera Tibba, Dandewala and Tanot area. Twenty
two well cuttings samples were studied from Tanot Bore Well-1
(27° 46’ N and 70° 17’ E) at different intervals (between 528m
to 627m depths) (Fig.2).
The studied succession represents Bandah Formation
from which well to moderately preserved, highly diversiied
nannofossils have been recorded.
Light Microscopy (LM)
Smear-slides were prepared for nannofossil studies. 1gm
(dry weight) of material is taken and kept in the covered
crucible. 10ml of distilled water was poured to make an even
suspension by stirring it. A thin ilm of sediment on the slide
was made by pouring few drops of the suspension with the
31
Fig. 2. Litholog of Tanot well #1.
AGE
BARTONIAN
EUROPEAN STAGE/AGE
NANNOFOSSIL ZONE/SUBZONE
MARTINI 1971 EMENDED RAI, 1988
LITHOSTRATIGRAPHY
DISCOASTER SAIPANENSIS ZONE NP-17
BANDAH FORMATION
528
534
538
543
552
555
558
561
564
570
573
579
585
591
594
600
603
609
615
618
624
627
SAMPLE
M
G
G
G
G
G
G
M
G
G
M
M
P
P
M
M
M
G
G
G
G
G
PRESERVATION
A
A
A
A
A
A
A
A
A
C
C
C
F
R
R
F
F
C
A
C
C
A
ABUNDANCE
R
R
R
Braarudosphaera bigelowii
Braarudosphaera discula
R
R
Campylosphaera dela
F
R
R
A
F
F
F
F
R
F
R
Coccolithus eopelagicus
F
F
Coccolithus subpertusus
R
R
R
R
R
F
R
R
R
R
R
A
F
A
A
A
A
F
F
C
C
R
R
R
F
R
R
R
R
R
F
C
R
R
R
R
R
F
R
R
C
F
A
A
A
C
F
R
R
F
F
R
F
F
F
Cyclococcolithus formosus
Cyclococcolithus kingii
Cyclicargolithus loridanus
C
F
C
R
R
F
C
C
F
C
R
R
R
R
R
C
Cribocentrum reticulatum
A
C
C
C
C
A
F
F
C
F
F
F
R
Dictycoccites stavensis
F
R
F
R
Discoaster saipanenesis
F
R
R
R
R
R
R
R
R
R
F
R
R
R
R
C
R
R
R
R
C
Discoaster barbadiensis
R
R
F
R
R
R
R
R
Discoaster tanii
Discoaster distinctus
R
R
R
R
R
Discoaster binodosus
R
R
R
R
R
F
Helicosphaera euphratis/parallela
Helicosphaera compacta
R
R
R
R
R
R
F
R
R
Helicosphaera bramletti
R
R
R
R
R
R
R
R
Helicosphaera lophota
R
R
R
Helicosphaera heezenii
R
R
R
R
F
R
R
R
F
R
R
R
R
R
Lanternithus minutus
Micrantholithus crenulatus
R
R
R
F
R
R
C
Pemma basquensis
R
Pemma papillatum
F
R
R
R
F
R
R
R
Pontosphaera vesca
R
R
F
F
F
F
R
R
R
Pontosphaera pectinata
A
R
F
F
R
R
R
R
R
R
C
R
R
R
Reticulofenestra pseudoumbilica
R
R
R
R
R
F
C
R
R
R
Reticulofenestra sp.
R
F
R
R
R
R
F
F
R
F
R
R
R
R
R
R
F
R
Reticulofenestra minuta
R
F
F
F
R
F
Reticulofenestra hillae
F
C
C
C
F
R
R
R
F
F
R
R
R
R
F
R
F
C
Sphenolithus moriformis
R
R
R
R
R
R
R
R
R
R
JYOTSANA RAI, ABHA SINGH AND DIVYAM GULATI
R
R
R
F
R
Sphenolithus predistentus
32
R
C
Fig. 3. Distribution chart of nannofossil assemblage recorded from Tanot well #1.
LATE MIDDLE EOCENE
CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY OF THE JAISALMER BASIN
SYSTEMATIC PALAEONOTLOGY
The classiication adopted herein is based on some
morphological features of living coccolithophores (Young,
1987) and employed for fossil material as well:
Kingdom Protista
Division Haptophyta
Class Prymnesiophyceae Hibberd, 1976
Systematic treatment of calcareous nannoplankton is after
Perch-Nielsen (1971). Families and genera contained herein are
arranged in alphabetical sequence.
Genus Braarudosphaera Delandre, 1947
Braarudosphaera bigelowii (Gran and Braarud, 1935)
Delandre, 1947
(Pl. I, igs. 1a-b)
Remarks: It is originally described from plankton of
Atlantic Ocean as Pontosphaera bigelowi (Gran and Braarud,
1935). Later Delandre (1947) based on trapezoidal shape of
the morphology, proposed new genus and transferred it under
Braarudosphaera bigelowii. It is characterized by having
trapezoidal shaped elements making regular pentaliths. 60 of
these units form complete pentagonal dodecahedral cyst cell.
The sutures between the adjacent regular pentaliths are weak
and contain slit like openings corresponding to 30 edges of
the pentagonal dodecahedron with hollow interior. They are
characteristically conined to nearshore, shallow and warm
water areas. It is reported from Cretaceous to recent marine
sediments all over the world. In the study material B. bigelowii
is rare in Bandah Formation.
Occurrence in India: Known from Bartonian of Kachchh
and Jaisalmer.
Braarudosphaera discula Bramlette and Riedel, 1954
Remarks: Pentaliths nearly round, tending to be more or
less pentagonal in shape, with sutures between the ive segments
reaching the margin at or very near the angles of the pentagon.
Diameter is usually 6-9 microns. Its stratigraphic range has not
been established but it seems to be common only in the Eocene
and particularly in the Lower-Middle Eocene.
Occurrence in India: Known from Bartonian of Jaisalmer.
Genus Micrantholithus Delandre, 1950
Micrantholithus crenulatus Bramlette and Sullivan, 1961
Remarks: Small to medium sized pentaliths displaying
poreless triangular segments with crenulated peripheral margin
and an overall regular pentagonal outline. Rare in the studied
samples.
Occurrence in India: Known from Bartonian of Kachchh,
Jaisalmer and Meghalaya.
Genus Pemma Klumpp, 1953
Pemma basquense (Martini, 1959) Báldi-Beke, 1971
(Pl. II, ig. 5a-5c; Pl. IV, ig.2,3)
Remarks: Fairly characteristic species of Pemma with
protruding elements along radial sutures, small to large
openings, one in each segment of the pentalith are included in
this species with no differentiation of sub-species as done by
several authors. Reported from Middle Eocene to Oligocene age
shallow marine sediments of several regions.
Occurrence in India: Known from Bartonian of Kachchh,
Jaisalmer and Meghalaya.
Pemma papillatum Martini, 1959
Remarks: Pemma papillatum is fairly large pentalith
characterised by typically club shaped protuberances on
peripheral margin. Even fragmented specimens can be easily
identiied under LM. P. papillatum is known to range from
33
middle to late Eocene shallow marine sediments and was used as
a zonal marker for middle Eocene of Alabama (Gartner, 1971).
Occurrence in India: Known from Bartonian of
Kachchh and Jaisalmer.
Genus Lanternithus Stradner, 1962
Lanternithus minutus Stradner, 1962
(Pl. II, ig. 4a-4b)
Remarks: It is common constituent of nannolora of Middle
Eocene to early Oligocene shallow marine deposits of several
regions of the world. Detailed morphology both under LM and
EM of this interesting holococcolith can be found in Gartner
and Bukry (1969). It is a rectangular holococcolith with distinct
lateral and rim blocks with a large central pore. In side view it
has a box-like appearance that tapers slightly to one end where
it is capped by a cover.
Occurrence in India: Known from Bartonian of Kachchh,
Jaisalmer and Meghalaya.
Genus Campylosphaera Kamptner, 1963
Campylosphaera dela (Bramlette and Sullivan, 1961)
Hay and Mohler, 1967
(Pl. III, ig. 4)
Remarks: It is a large species (5-6µm) with a delicate cross,
the bars being aligned to the major and minor axes of the coccolith.
Typical rectangular outline and distinct proximal and lateral
curving of the shields differentiate it from Cruciplacolithus. It
is documented only under SEM in the present material. It ranges
from early to late Middle Eocene Zone NP10 to base of NP17
(Perch- Nielsen, 1985).
Occurrence in India: Known from Bartonian of Kachchh
and Jaisalmer.
Genus Coccolithus Scwarz, 1894
Coccolithus eopelagicus Bramlette and Riedel, 1961
(Pl. I, ig. 2a-2c; Pl. IV, ig. 2,3,5)
Remarks: C. eopelagicus has been widely reported from
Middle Eocene to Late Eocene of several regions. Morphology
is very similar to that of living C. pelagicus, except for large
sizes of Paleogene specimens. Possible relationships between
Ericsonia and Coccolithus are discussed by Perch-Nielsen
(1985).
Occurrence in India: Known from Bartonian of Kachchh,
Jaisalmer and Meghalaya.
Coccolithus subpertusus (Hay and Mohler, 1967) van
Heck and Prins, 1987
(Pl. I, ig. 3a-3c)
Remarks: Circular to subcircular species having large central
opening. The complex distal shield is formed of four cycles. The
proximal shield is more than half as wide as the distal shield,
and sutures are inclined clock wise in proximal view. The central
opening appears plugged under normal light.
Occurrence in India: Recorded from Bartonian of
Jaisalmer Basin.
Genus Discoaster Tan Sin Hok, 1927
Discoaster barbadiensis Tan Sin Hok, 1927
(Pl. I, ig. 9-11; Pl. III, ig. 9-11)
Remarks: It is the most characteristic Eocene discoaster.
These are rosette shaped asteroliths containing 7-14 rays
joined along most of their length with blunt to pointed tips. The
asteroliths display proximal curvature with characteristic stem,
best observed in side views. In India D. barbadiensis is reported
from Bartonian equivalent sediments of Kachchh Basin (Singh
et al., 1980) and late Eocene of western India (Jafar et al., 1985).
34
JYOTSANA RAI, ABHA SINGH AND DIVYAM GULATI
Fig. 4. Correlation chart showing nannofossil zones and events in present study along with the nannofossil studies in same age bracket from Kachchh,
Meghalaya and the Jaisalmer Basin with sea-level luctuations.
Occurrence in India: Known from Bartonian of Kachchh
and Meghalaya.
Discoaster binododsus Martini, 1958
(Pl. I, ig. 12)
Remarks: They are characterized by the presence of notch
on the ray tips, diameter of central area, thickness and number of
arms (5-8) which are variable. More than one pair of nodes may
be seen on each ray with short free length in 8-rayed asteroliths.
It may look very similar to D. mirus (Stradner and Papp, 1961)
but the suture lines in wide central area are more prominent in
D. mirus which differ it from D. binododsus.
Occurrence in India: Known from Bartonian of Kachchh.
Discoaster distinctus Martini, 1958
(Pl. I, ig. 14)
Remarks: D. distinctus was originally described from Early
Late Eocene. Six (sometimes 5) rayed stellate discoasters with
heavily noded, bifurcate ray-tips that resemble spanners. In
overgrown specimens, it is often dificult to recognize.
Occurrence in India: Known from Bartonian of
Kachchh and Meghalaya.
Discoaster saipanensis Bramlette and Riedel, 1954
(Pl. I, ig. 15-17; Pl. III, ig. 12; Pl. IV, ig. 1)
Remarks: It was originally reported from the Late Eocene of
Saipan islands (Bramlette and Riedel, 1954; Bramlette, 1959).
These are discoasters with 5-8 straight or curved rays joined
through half their length and which then taper to a point. A
central stem and distinct radial sutural ridges and depressions
are visible in some specimens. D. saipanensis is extremely
useful for biostratigraphy. Extinction of D. saipanenesis along
with D. barbadiensis deines Eocene-Oligocene boundary.
Occurrence in India: Known from Bartonian of Kachchh.
Discoaster cf. D. saipanensis Bramlette and Riedel, 1954
(Pl. I, ig. 13)
Remarks: It is a seven-rayed asterolith which shows
curvature and termination of rays resembling D. saipanensis
however, the rays are slightly blunt in termination.
Occurrence in India: Known from Bartonian of Jaisalmer.
Discoaster tanii Bramlette and Riedel, 1954
(Pl. I, ig. 18)
Remarks: Originally described from Late Eocene (Bramlette
and Riedel, 1954). 5-6 rayed stellate discoaster with long free
rays of uniform width terminating in a lat or slightly notched
ray-end. They may show poorly developed unpaired lateral
nodes on some rays.
Occurrence in India: Known from Bartonian of Kachchh.
Genus Helicosphaera Kamptner, 1954 ex Jafar and
Martini, 1975
Helicosphaera bramletti (Müller, 1970) Jafar and Martini, 1975
(Pl. I, ig. 19a-19b)
Remarks: H. bramletti was originally described from
Late Middle Oligocene of borehole material of Southern
Germany. Under LM observation, diagnostic for H. bramletti,
is the characteristic bridge in the form of thick “I” with oblique
orientation and spanning a comparatively small central area.
Occurrence in India: Known from Bartonian of Kachchh.
Helicosphaera compacta Bramlette and Wilcoxon, 1967
Remarks: H. compacta was originally described from
Oligocene of Cipero section (Bramlette and Wilcoxon, 1967)
and indicated to range from Late Eocene to Late Oligocene.
These are elliptical Helicosphaera with well deined birefringent
blanket in XPL and narrow central area spanned by a conjunct
bar. Under crossed nicols, large part of the helicolith remains
dark, while bright small central area shows characteristic and
tiny pair of openings separated by a thin birefringent bar.
Occurrence in India: Known from Bartonian of Kachchh.
Helicosphaera lophota (Bramlette and Sullivan, 1961)
Jafar and Martini, 1975
(Pl. II, ig. 2a-2c)
Remarks: Elliptical, oblong or reniform Helicosphaera with
wide lange and central area spanned by a broad, near-longitudinal
CALCAREOUS
NANNOFOSSIL BIOSTRATIGRAPHY OF THE
Journal of the Palaeontological
Society of India
Volume 59(1), June 2014
JAISALMER BASIN
35
Plate I
RAI, SINGH AND GULATI
36
JYOTSANA RAI, ABHA SINGH AND DIVYAM GULATI
disjunct bar with distinct median suture. Helicoliths of H.
lophota with oval outline are similar to that of H. seminulum,
but distinguished by a sturdy bar aligned nearly parallel to the
major axis of the helicolith.
Occurrence in India: Known from Bartonian of Kachchh
and Meghalaya.
Helicosphaera parallela Bramlette and Wilcoxon, 1967
(Pl. II, ig. 3a-3c)
Remarks: A typical Helicosphaera but not an easily
differentiated species. Central area occupied by a parallel sided
bar with little or no central opening apparent even between
crossed nicols although not in optical continuity with the shield,
and bar nearly parallel to the long axis of specimen.
Occurrence in India: Known from Bartonian of Kachchh.
Genus Cribrocentrum Perch-Nielsen, 1971
Cribrocentrum reticulatum (Gartner and Smith, 1967)
Perch- Nielsen, 1971
(Pl. I, ig. 4a-4c; Pl. IV, ig. 6)
Remarks: Circular placoliths displaying characteristic
squarish central area which is traversed by dark extinction lines.
It is an extremely important middle Eocene stratigraphic marker
and palaeoceanographic indicator. It ranges from NP17 – NP20
(Saunders et al., 1984). Perch- Nielsen reported its FAD from
Zones NP16/ NP17 boundary. Aubry (1988) recorded its FAD
in the Upper part of NP16 to recognize Lutetian/Bartonian
boundary. The size ranges from small, medium to large. The
small forms are typical of near-shore whereas large forms are
usually found in open ocean setting. In the present assemblage
both medium and large forms are recorded, but it appears that
the larger size may be due to overgrowth.
Occurrence in India: Known from Bartonian of Kachchh
and Meghalaya.
Genus Dictyococcites Black, 1967
Dictyococcites stavensis (Levin and Joerger, 1967) Bown, 1998
(Pl. I, ig. 8a-8c)
Remarks: Nearly circular plates are closely appressed, with
the distal plate larger than the proximal plate. Periphery serrate,
central area has two small slit like openings which are separated
by raised structures resembling two ‘V’ with the acute angles of
the ‘V’s facing one another. A slit like opening lies in the center
of each ‘V’.
Occurrence in India: Known from Bartonian of Jaisalmer.
Genus Reticulofenestra Hay et al., 1966
Reticulofenestra hillae Bukry and Percival, 1971
Remarks: Originally described from Late Eocene of
Mississippi and commonly found in Early Oligocene of several
areas. Fairly large elliptic placoliths are characterized by wide
central collar and small central opening.
Occurrence in India: Known from Bartonian of Kachchh
and Meghalaya.
Reticulofenestra minuta Roth, 1970
(Pl. II, ig. 9a-9b)
Remarks: This species is fairly resistant to calcite
overgrowth and found even when other common coccoliths are
destroyed. It is common in Eocene of Rajasthan, Kachchh, Surat
and other areas of India.
Occurrence in India: Known from Bartonian of Kachchh
and Meghalaya.
Reticulofenestra pseudoumbilica (Gartner, 1967) Gartner, 1969
(Pl. II, ig. 10a-10c)
Remarks: Elliptical placolith, the elliptical central area is
covered by lacy network of bars which join along a longitudinal
issure at the center of the placolith. A collar is present in the
distal side. It resembles with R. umbilica but the central area is
smaller in R. pseudoumbilica which is formed by broken bars of
central area.
Occurrence in India: Known from Bartonian of Jaisalmer.
Reticulofenestra sp.1
(Pl. II, ig. 11a-11c)
Remarks: Subcircular in outline. Proximal and distal both
shields are birefraingent in cross nicols. There appears scalloped
or cribrated appearance of the central area under crossed nicols.
Occurrence in India: Known from Bartonian of Jaisalmer.
Reticulofenestra sp.2
(Pl. IV, ig. 7)
Remarks: Subcircular in outline. The central sieve appears
broken. Central area is about 1/5 of the total diameter of placolith.
Occurrence in India: Known from Bartonian of Jaisalmer.
Reticulofenestra sp.3
(Pl. IV, ig. 8)
Remarks: Elliptical in outline. Its total diameter about 1µm.
Proximal and distal shield almost of the same size. The outline
of proximal shield is crenulated, may be due to dissolution.
Central area is perforated by bar like projections.
Occurrence in India: Known from Bartonian of Jaisalmer.
Genus Pontosphaera Lohmann, 1902
Pontosphaera pectinata (Bramlette and Sullivan, 1961)
Sherwood, 1974
(Pl. II, ig. 6a-7c; Pl. IV, ig. 4-5)
Remarks: Reported to range from NP-14 to NP-17. The
plate is scalloped towards its outer edge and pierced by two
longitudinal or small holes. The scalloping is deined by narrow
radial ridges and furrows, which run inwards towards the centre.
Occurrence in India: Known from Bartonian of Kachchh
and Jaisalmer.
Pontosphaera vesca Sullivan, 1965
(Pl. II, ig. 8a-8c)
Remarks: Originally described by Sullivan (1965). It has
several small elongated pores on its surface which are arranged
in concentric rows. The rim is thin.
Occurrence in India: Known from Bartonian of Jaisalmer.
Genus Blackites Hay and Tome, 1962
Blackites spinosus (Delandre and Fert, 1954)
Hay and Towe, 1962
(Pl. III, ig. 1)
Remarks: The specimens are visible in lateral view under
LM. The spine is broadest at the base and gradually tapers to
needle like spine. Widely reported from Middle Eocene to Early
Oligocene of several regions and usually associated with closely
related B. tenuis. It is very rare in the present assemblage.
Occurrence in India: Known from Bartonian of Kachchh
and Jaisalmer.
Genus Sphenolithus Delandre in Grassé, 1952
Sphenolithus moriformis (Brönnimann and Stradner, 1960)
Bramlette and Wilcoxon, 1967
(Pl. II, ig. 12a-12c)
Remarks: Originally reported from heavily overgrown
material of Early Eocene of Cuba. Sphenoliths with well deined
proximal ring of elements and apical part making low to high
dome. They are widely reported from Early Eocene to Middle
Miocene. This species is known to have no stratigraphic worth.
Occurrence in India: Known from Bartonian of Kachchh
and Meghalaya.
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Plate II
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JYOTSANA RAI, ABHA SINGH AND DIVYAM GULATI
Sphenolithus predistentus Bramlette and Wilcoxon, 1967
(Pl. II, ig. 13a-13b; Pl. IV, ig. 12)
Remarks: Sphenolith with a large apical spine, lat or slightly
depressed at the base which is attached to a single annular ring
of 10-12 lateral spines. Apical stem tapers strongly for about
half its length and then gradually to a pointed or bifurcating tip.
Between crossed nicols the apical spine appears to be formed of
coalesced calcite units of slightly different optical orientation.
Occurrence in India: Known from Bartonian of Kachchh
and Meghalaya.
Sphenolithus cf. S. predistentus Bramlette and Wilcoxon, 1967
(Pl. IV, ig. 11)
Remarks: It is a sphenolith which is characterized by a
proximal ring of small elements surmounted by a spine. The
spine is broadest at the base and becomes conical at the top.
The delicate bifurcating tip is broken in the present specimen.
Though overgrown, resembles with S. predistentus.
Occurrence in India: Known from Bartonian of Jaisalmer.
Genus Thoracosphaera Kamptner, 1927
Thoracosphaera saxea Stradner, 1961
(Pl. IV, ig. 10)
Remarks: Recorded under SEM. Test though broken appears
spherical to sub-spherical showing a mosaic of polygonal
elements with distinct crystal outline. The crescent –shaped pores
are deep seated and seen from broken part of the test. Operculum
is broken in the present specimen. The pores completely pierce
the test wall. The present specimen shows signs of dissolution
and thus the polygonal outline of the elements are not clearly
seen. It was recorded very rare in the present material
Occurrence in India: Known from Bartonian of Kachchh.
Genus Cyclococcolithus Kamptner, 1954
Cyclococcolithus formosus Kamptner, 1954
(Pl. I, ig. 6a-6c; Pl. III, ig. 6)
Remarks: C. formosus was originally described from
Eocene of Paciic Ocean (Kamptner, 1963). This is readily
recognizable species under LM and EM and has been used as
important stratigraphic marker, appearing in Late Early Eocene
and disappearing in early Oligocene, as indicated by Martini
(1971). It is widely recorded in Bartonian equivalent sediments
of Kachchh and Meghalaya basins.
Occurrence in India: Known from Bartonian of Kachchh
and Meghalaya.
Cyclococcolithus kingii Roth, 1970
(Pl. I, ig. 7a-7c; Pl. III, ig. 7-8)
Remarks: Two different forms as holotype and paratype
have been documented under EM for this species (Roth, 1970).
It is recorded as minor constituent of Eocene nannolora from
Kachchh Basin also.
Occurrence in India: Known from Bartonian of Kachchh
and Meghalaya.
Genus Cyclicargolithus Bukry, 1971
Cyclicargolithus loridanus (Roth and Hay in Hay et al., 1967)
Bukry, 1971
(Pl. I, ig. 5a-5c)
Remarks: Originally described from Oligocene of Blake
Plateau. Small to medium sized palcoliths show birefringence of
the distal shield. C. loridanus seems to appear in the upper part
of NP-16 and becomes extinct in Middle Miocene. In Oligocene
it may be extremely abundant at certain levels.
Occurrence in India: Known from Bartonian of Kachchh
and Meghalaya.
Genus Scapholithus Delandre in Delandre and Fert, 1954
Scapholithus fossilis Delandre, 1954
(Pl. IV, ig. 9)
Remarks: Very small form with rhomboidal outline.
Occurrence in India: Known from Bartonian of Jaisalmer.
PRESERVATION
Nannofossil preservation is highly variable in subsurface
sediments. The principal governing processes of preservation are
dissolution and overgrowth, both of which may occur in varying
degree in single sample. For determining the susceptibility of
nannofossils to preservational changes various methods are
proposed by various authors for different environmental setups
(Wise, 1973; Schlanger and Douglas, 1974; Roth, 1978). The
average state of preservation of the nannofossil assemblage in
each sample is designated as follows:
G = good (little or no evidence of dissolution and/or
overgrowth; primary morphological characteristics only slightly
altered; specimens are identiiable to the species level).
M = moderate (specimens exhibit some etching and/or
overgrowth; primary morphological characteristics sometimes
altered; however, most specimens are identiiable to the species
level).
P = poor (specimens are severely etched or exhibit
overgrowth; primary morphological characteristics largely
destroyed; fragmentation has occurred; specimens cannot be
identiied at the species and/or generic level).
13 subsurface samples out of 22 are found to be good in
preservation throughout the succession. The samples at depth
528m, 561m and 579m also showed good preservation with
minor effect of overgrowth only in some species. Remaining
samples are moderately to poorly preserved.
DIVERSITY
Overall the diversity is good to moderate in Tanot #1.
Samples are highly diversiied, most of the samples contain
more than 20 species average in 100 ield of view. Diversity is
maximum in the sample number 528. It is moderate to poor in
the samples 591 and 594. Species range from 4-5 in 100 ield of
view in these samples.
ABUNDANCE AND PRODUCTIVITY
Productivity depends on the overall nannofossil assemblage
recorded from each sample. Independent state of preservation
of nannofossil assemblage is documented herein. To record the
productivity following method is used:A = abundant (21 to 100/10 ield of view)
C = common (11 to 20/10 ield of view)
F = few (3 to 10/10 ield of view)
R = rare (1 to 5/10 ield of view)
EXPLANATION OF PLATE III
1. Blackites spinosus (Delandre and Fert) Hay and Towe, 1962, 2. Coccolithus eopelagicus Bramlette and Riedel, 1961, 3. Coccolithus eopelagicus
Bramlette & Riedel, 1961, 4. Campylosphaera dela (Bramlette and Sullivan) Hay and Mohler, 1967, 5. Coccolithus eopelagicus Bramlette and Riedel, 1961,
6. Cyclococcolithus formosus Kamptner, 1963, 7. Cyclococcolithus kingii Roth, 1970, 8. Cyclococcolithus kingii Roth, 1970, 9. Discoaster barbadiensis
Tan Sin Hok, 1927, 10. Discoaster barbadiensis Tan Sin Hok, 1927, 11. Discoaster barbadiensis Tan Sin Hok, 1927, 12. Discoaster saipanensis Bramlette
and Riedel, 1954.
Journal of the Palaeontological
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Plate III
RAI, SINGH AND GULATI
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JYOTSANA RAI, ABHA SINGH AND DIVYAM GULATI
In general the productivity of Tanot #1 samples ranges
between very abundant to rare (Fig.3). In the whole succession
no sample is found to be barren. Sample numbers 528 and
615 are the most productive hence used for SEM studies.
Productivity is high in the samples ranging 528m to 615m depth.
There is gradual decrease of productivity in the sample at 591m
and 594m, after that it slowly increases from the depth of 600m
to 627m.
LOW PRODUCTIVITY ZONES IN ASSEMBLAGES
Nannofossil assemblage in the whole succession is
luctuating. One low productivity zone has been recorded
throughout the succession alternating with high productivity
zones. This zone is recorded in Middle Bartonian at depth ranging
between 591m to 594m. The succession above and below of this
zone are highly productive. The low productivity zone contains
occurrence of only few sturdy (mostly reticulofenestrid)
forms viz. Cribrocentrum reticulatum, Reticulofenestra sp.,
Reticulofenestra minuta and Sphenolithus predistentus.
EOCENE NANNOFOSSIL BIOSTRATIGRAPHY
Comprehensive zonal schemes employing a variety of
planktonic fossil groups including calcareous nannoplankton are
available. For Cenozoic the calcareous nannoplankton zonation
scheme of Martini (1971) with zonal code NP for Paleogene is
based on hemipelagic/epicontinental sequences of Europe and
tropical regions. A few zonal markers had restricted nearshore,
deep sea or high or low latitude distribution or displayed
extended vertical ranges in different latitudes. Therefore, the
modiied version of zonal scheme based on those provided by
Martini (1971) are currently used with well chosen cosmopolitan
marker species, which is being further reined with progress in
research (Okada and Bukry, 1980).
In the present study of Tanot #1, investigations are based
on well-cutting samples only. In general, nannofossils are well
preserved which do not hinder the identiication of important
markers. The nannofossil assemblages are exceptionally
well preserved and highly diverse at some levels and low to
moderately diverse at some levels in the Tanot #1, is noted with
rare to abundant occurrences of selected number of species.
In the Middle Eocene, Bartonian contains upper part of
NP16 and NP17. Thus the original deinition of zone NP17 is
important for zonal assignment of nannoplankton assemblage
recovered from Khuiala-Bandah formations. Presence of C.
reticulatum and D. saipanensis in sample numbers 615 (oldest
occurrence) and 528 (youngest occurrence) suggests the
assemblage belonging to NP 17 Zone. However presence of C.
dela in oldest 627 number sample extends the NP 17 Zone upto
this level belonging to Bartonian age. The emended deinition of
NP 17 Zone is as follows.
NP 17 DISCOASTER SAIPANENSIS ZONE EMEND
RAI 1988
Deinition - FAD of D. saipanensis to FAD of Ch.
oamaruensis
Author - Martini, 1970a; emended Rai, 1988. The emended
deinition of NP 17 would include upper part of NP 16 and NP
17 in the zonation scheme of Martini (1971). This deinition
has been adopted (Fig.2) throughout. The emended deinition
of NP 17 would correspond to Bartonian as suggested by Aubry
(1985a) and would encompass both P13 O. beckmanni and P14
T. rohri planktonic foraminiferal Zones. Emended deinition of
NP 17 would partly correspond to CP 14 R. umbilica Zone of
Okada and Bukry (1980). Frequent occurrence of Cribrocentrum
reticulatum (= Reticulofenestra reticulata) in Harudi Formation
suggests that it cannot be older than Bartonian or upper NP 16
(Aubry, op. cit.).
ZONAL ASSIGNMENT
ASSEMBLAGE
OF
THE
PRESENT
NP-17 Discoaster saipanensis zone
Deinition: Interval from the last occurrence of
Chiasmolithus solitus (Bramlette and Sullivan, 1961) to the irst
occurrence of Chiasmolithus oamaruensis (Hay et al., 1966).
Author: Martini, 1970
Martini (1970) suggested last occurrence of Sphenolithus
furcatolithoides Locker (1967) and irst occurrence of
Helicosphaera compacta (Bramlette and Wilcoxon, 1967) in the
lower part of NP17.
Discoaster saipanensis is well developed and common
species in Indian Eocene and in view of the absence of traditional
Chiasmolith markers has been used to emend the deinition of
Discoaster saipanensis zone of Martini (1970), so that it can be
used for dating other shallow marine low latitude assemblages
lacking marker Chiasmoliths. The emended deinition of NP17
would correspond to Bartonian as suggested by Aubry (1985).
Frequent occurrences of Cribrocentrum reticulatum in Bandah
formation suggest that it cannot be older than Bartonian (Fig.4).
PALAEOCEANOGRAPHIC REMARKS
In response to activation of basinal faults probably coinciding
with the collision of Indian-Asiatic landmasses around 40my,
grossly arresting the spreading rate during Bartonian, a shallow
epeiric sea invaded the margin of the Jaisalmer Basin and laid
down the Bandah Formation. The eustatic global rise showed its
imprints of inundating both eastern and western part of Indian
craton. Nannofossil assemblage of Discoaster saipanensis
NP17 Zone emended Rai (1988) has been recognized earlier
both in the Kachchh Basin, western India (Rai, 1997, 2007)
and in the Dilni River section of Meghalaya in eastern India
(Rai and Garg, 2009). Though, the entire Bartonian spans (41.337my) ca. four million years, there appears that the nannofossil
assemblage pertains to only 1.5my time slice (39.5-38.0 my) of
eustatic rise (Fig.4). Late Eocene (Priabonian) is a hiatus both
in the Kachchh and Jaisalmer basins, whereas the sea remained
on the craton in Mehgalaya and encroached the Cambay Basin
during the Priabonian.
EXPLANATION OF PLATE IV
1. Discoaster saipanensis Bramlette and Riedel, 1954, 2. Pemma basquensis (Martini) Baldi-Beke, 1971, 3. Pemma basquensis (Martini) Baldi-Beke,
1971, 4. Pontosphaera pectinata (Bramlette and Sullivan) Sherwood, 1974, 5. Pontosphaera pectinata (Bramlette and Sullivan) Sherwood, 1974,
6. Cribrocentrum reticulaum (Gartner and Smith) Perch-Nielsen, 1971, 7. Reticulofenestra sp. 2, 8. Reticulfenestra sp.3, 9. Scapholithus fossilis Delandre,
1954, 10. Thoracosphaera saxea Stradner, 1961, 11. Sphenolithus cf. S. predistentus Bramlette and Wilcoxon, 1967, 12. Sphenolithus predistentus
Bramlette and Wilcoxon, 1967.
Journal of the Palaeontological
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Plate IV
RAI, SINGH AND GULATI
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JYOTSANA RAI, ABHA SINGH AND DIVYAM GULATI
CONCLUSIONS
1.
2.
3.
4.
5.
6.
7.
8.
The nannofossil assemblage recorded from Tanot #1 is
moderately diversiied and well preserved.
In all 38 species belonging to 18 genera are recorded.
The assemblage belongs to the late Middle Eocene or
precisely dated as Bartonian (partim).
The Scanning electron microscopy suggests overgrown
nature of most of the forms.
Presence of Cribrocentrum reticulatum, Dicoaster
saipanensis suggests NP 17 Discoater saipanensis Zone
(Martini, 1971 emend. Rai, 1988). This is correlatable
with parts of both P13 Orbulinoides beckmanni and P14
Truncorotaloides rohri planktonic foraminiferal Zones
(Blow, 1969) and a part of D11 dinolagellate Zone (Costa
and Manum, 1988) of Bartonian age.
Record of B. bigelowii and other pentaliths, L. minutus
(holococcolith) suggests nearness to the shore.
Coeval nannofossil record, though more diversiied in the
adjacent Kachchh Basin in western India and less diverse
assemblage from Dilni River Section, Meghalaya, eastern
India suggests imprints of eustatic global sea level rise
(Haq et al., 1987) affecting and inundating cratons of the
both extremities of India.
The nannofossil diversity, richness in organic material
maturity from samples representing Bandah Formation
suggests possibility of petroleum source material. Record
of adequate structural traps will help in inding hydrocarbon
rich horizons in Jaisalmer Basin.
ACKNOWLEDGEMENTS
The authors (J. R. and A. S.) are thankful to Prof. Sunil
Bajpai, Director Birbal Sahni Institute of Palaeobotany,
Lucknow for encourgement. D. G. expresses gratitude to the
Director, BSIP for allowing to carry out this work as sixth
semester petroleum engineering project work assigned at the
University of Petroleum and Energy Studies, Dehradun. Dr.
Rahul Garg, BSIP and Dr. R. Saxena, KDMIPE, Dehradun are
duly thanked for the critical review of the manuscript. Oil India
Limited is thanked for supply of samples under study.
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Manuscript Accepted February 2014
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JYOTSANA RAI, ABHA SINGH AND DIVYAM GULATI
Abha Singh