MIDDLE JURASSIC (BATHONIAN) MARINE GASTROPODS FROM THE JAISALMER, WESTERN INDIA

1. MIDDLE JURASSIC (BATHONIAN) MARINE
GASTROPODS FROM THE JAISALMER
BASIN, WESTERN INDIA
S. Saha1, *, S.S. Das1, S. Mondal2, and D. Mukherjee3
1Geological Studies Unit, Indian Statistical Institute, 203, B. T. Road, Kolkata 700108, India
2Department of Earth Sciences, Indian Institute of Science Education and Research (IISER)
Kolkata, Mohanpur, West Bengal 741246, India
3Geological Survey of India, Palaeontology Division I, 15, Kyd Street, Kolkata, India

2. INTRODUCTION
 The Jaisalmer Basin, is a pericratonic basin, situated on western margin of the Indian plate, is significant for its
fossiliferous Jurassic sedimentary rocks.
 Jaisalmer Basin hosts Mesozoic sediments deposited at the time of repeated marine transgression-regression
cycles, during the Early Jurassic (Pliensbachian) (Rai and Jain 2013). Mesozoic sediments range from the Triassic
to the Early Cretaceous (Krishna 1987), representing coastal, estuarine, as well as shallow to mid-shelf
environments (Fürsich et al. 1992) .
 We mainly focus on the Jurassic sediments of Jaisalmer Basin, ranging from the Early (older than Bajocian) to
Late (latest Tithonian) Jurassic (Saha et al., 2021). The Bathonian sediments here are mainly shallow-marine
mixed siliciclastics-carbonates (Pandey et al. 2009).
 The basin is well-known as a storehouse of diverse Jurassic ammonite fauna. However, although gastropods
are also present in the same sediments, this fossil group receives less attention than ammonites. Our recent studies
have reported the biostratigraphic distribution of gastropods from the Lower to Upper Jurassic sediments of the
Jaisalmer Basin. In the present study, we provide for the first time a detailed description of some of the marine
gastropod faunas.

3. LOCATION
 Present study area belongs to Jaisalmer, which is one of the major cities in the state of Rajasthan in western
India.
(1) An outline map of India showing Jaisalmer
Basin; (2) Simplified map of the Jaisalmer Basin
showing Jurassic exposures; (3) Locality map of
Jaisalmer. Asterisk (★) showing the present
Bathonian outcrops from where the studied
specimen has been collected
The fossiliferous locality from where the
studied specimens were collected is situated 1
km north of the Jaisalmer city (26°55'10.9'' N,
70°53'19.9'' E)

4. STRATIGRAPHY OF THE AREA
Formation Member Age
Bhadasar Kolar Donger Tithonian
Baisakhi
Lanela
Late
Kimmeridgian
Ludharwa
Middle
Kimmeridgian
Rupsi
Early
Kimmeridgian
Late Oxfordian
Basal
Early to Middle
Oxfordian
Jaisalmer
Jajiya
Kuldhar
Late Callovian
Middle
Callovian
Early Callovian
Bada Bag Late Bathonian
Middle
Bathonian
Fort
Early Bathonian
Joyan
Bajocian
Hamira
Lathi
Thaiat
Odania
Figure : Generalized
statigraphic succession of
the Bathonian outcrop of
Jaisalmer Basin (Figure
not to scale)

5. MATERIALS AND METHODS
 Molluscan specimens were collected from the Fort Member of the Jaisalmer Formation, which is situated 1 km
north of the Jaisalmer city.
 The samples were collected following random surface sampling protocols and put in plastic bags. 32cm. X
23cm. in size.
 In the laboratory, Smaller specimens were separated from larger ones by using sieves.
 Among invertebrates the fossil assemblages include mainly molluscan taxa (bivalves, and gastropods).
 We have recorded 45 gastropod specimens from Fort Member belonging to five species of four genera (four
families).
Palaeobiogeographic study

6. AMPULLINA SP. 1
Figure. (1-8) Ampullina sp. 1 (1-4)
Apertural, abapertural, apical, basal
views (ISI/g/Jur/Jal/AMP 1); (5-8)
Apertural, abapertural, apical, basal
views (ISI/g/Jur/Jal/AMP 2). Scale
bars = 1 cm.
 Ampullina Bowdich ,1822 is an extinct genus in the clade Caenogastropoda ranging from the Middle Triassic to
the Lower Pliocene age.
 Ampullina sp. 1 is characterised by
small to medium-sized; spire moderately
high; whorls convex with a prominent
ramp; shell surface smooth; moderately
open umbilicus; aperture oval in shape.

7. AMPULLINA SP. 2
Figure. (1-7) Ampullina sp. 1 (1-3) Apertural, abapertural, apical
views (ISI/g/Jur/Jal/AMP 7); (4-7) Apertural, abapertural, apical,
basal views (ISI/g/Jur/Jal/AMP 8). Scale bars = 1 cm.
 Ampullina sp. 2 has small-sized shell; spire high; whorls convex
with inclined ramp; smooth whorl surface; umbilicus open and
narrow; aperture ear-shaped, axially elongated.
 Ampullina sp. 1 from the same horizons of Jaisalmer is larger,
high spire, less number of whorls and having more obtuse apical
angle than the Ampullina sp. 2. These two species are also differ
in apertural shape: A. sp. 1 has oval shaped aperture, but ear-
shaped, axially elongated aperture present in A.sp. 2.

8. PIETTEIA SP.
Figure. (1-4) Pietteia sp. (1, 3) Apertural and abapertural views
(ISI/g/Jur/Jal/PIE 1); (2, 4) Apertural and abapertural views (ISI/g/Jur/Jal/PIE
2). Scale bars = 1 cm.
 Pietteia sp. is characterised by Shell small to medium-sized; spire
moderately high; whorls convex with slightly opisthocline axial ribs; axial
ribs interrupted by spiral threads forming small nodes at crossing points;
strong and sharp carina on the body whorl; Aperture oval with siphonal
canal.

9. TALANTODISCUS SP.
 Talantodiscus is a depressed and nodose genus of the Mesozoic
Era, belonging to the family Pleurotomariidae.
 Talantodiscus sp. is characterized by its highly depressed form with
the diameter always exceeding the height of shell, nodose
ornamentation, base ornamented by sinuous spiral threads, and a broad
selenizone situated at upper third of the outer face of whorl.
Figure. (1-6) Talantodiscus sp. (1-3, 5) Apical, basal, Apertural,
abapertural views (ISI/g/Jur/Jal/TAL 1); (4, 6) Sketches of figure 3
and figure 5 respectively. Scale bars = 1 cm.

10. PTYGMATIS SP.
Figure. (1-4) Ptygmatis sp. (1-2) Abapertural and apertural views
(ISI/g/Jur/Jal/PTY 1); (3-4) Abapertural and apertural views
(ISI/g/Jur/Jal/PTY 2). Scale bars = 1 cm.
 Ptygmatis sp. is characterized by its highly turreted form with the
impressed suture, high spire, flat surface with six whorls, concave
whorls.

11. GASTROPOD INDET
Figure. (1-2) Unidentified gastropod 1: Apertural and
Abapertural views (ISI/g/Jur/Jal/GAS 1); (3-4) Unidentified
gastropod 2: Apertural and Abapertural views
(ISI/g/Jur/Jal/GAS 2). Scale bars = 1 cm.

12. PALAEOBIOGEOGRAPHIC STUDY
TALANTODISCUS
Map showing the palaeogeographic distribution of Ampullina (1), Pietteia (2), Talantodiscus (3), and Ptygmatis
(4) and the possible seaways for biotic exchange.

13. MAJOR REFERENCES
1. Krishna J (1987) An overview of the Mesozoic stratigraphy of Kachchh and Jaisalmer basins. J Palaeontol Soc
India 32: 136-149
2. Krishna J (2017) The Indian Mesozoic chronicle. Springer, Singapore, pp. 1-694.
3. Pandey DK, Choudhary S (2007) Sequence stratigraphic framework of Lower to lower Middle Jurassic sediments
of the Jaisalmer Basin, India. Beringeria 37: 121–131.
4. Pandey DK, Choudhary S, Bahadur T, Swami N, Sha J (2012) A review of the Lower – lowermost Upper Jurassic
lithostratigraphy of the Jaisalmer Basin, western Rajasthan, India-an implication on biostratigraphy. Vol Jur 10:
61–82.
5. Pandey DK, Fürsich FT, Alberti M (2014) Stratigraphy and Palaeoenvironments of the Jurassic Rocks of the
Jaisalmer Basin: Field Guide. Beringeria, Spec Iss 9: 1–111.
6. Saha, S., Das, S. S., & Mondal, S., 2021. Gastropod biozonation for the Jurassic sediments of Kutch and Jaisalmer
Basins and its application in interbasinal correlation. Mesozoic Stratigraphy of India, Society of Earth
Scientists Series, Springer, p. 333-372.

14. ACKNOWLEDGMENTS
• DST-INSPIRE.
• Geological Studies Unit, Indian Statistical Institute.
• Department of Geology, University of Calcutta.
• I express my profound gratitude to Professor Subhendu Bardhan of Jadavpur University
whose constant support constantly inspired me in this study.
• Faculty Members and Research Scholars of Geological Studies Unit, Indian Statistical
Institute.

15. THANK YOU