Petrography and Depositional Environment of Bathonian Callovian Sediments Exposed along Kuldhar River Section, Jaisalmer Basin, Western India

Abstract

This study investigates the petrography and depositional environment of the Bathonian Callovian sediments exposed along the Kuldhar River section represents the Bada Bag and Kuldhar members of the Jaisalmer Formation in the Jaisalmer basin. An integrated analysis of outcrop, microfacies and petrographic features were undertaken to interpret the depositional environment. Twenty one thin sections were prepared from carbonate beds for detailed petrographic study. The results indicate that the packstone beds are predominantly composed of ooids and bioclasts, with micrite forming the principal cementing material. The combined petrographic evidence and fossil assemblages suggest that these sediments deposited in a shallow-marine environment.

Introduction

The Jaisalmer Basin, a pericratonic shelf basin in western India, is renowned for its well-exposed and fossil-rich Mesozoic sedimentary successions, particularly the Jurassic strata. Its importance stems from the abundance of marine fossils, well-preserved sedimentary structures, diverse depositional environments, and dinosaur footprints, making it an important area for palaeontological, sedimentological, and stratigraphic research.

The Mesozoic succession of the basin rests on Precambrian basement rocks and records a progressive change in depositional environments. Sedimentation began with non-marine fluvial, deltaic, and lacustrine deposits, followed by marginal-marine conditions and eventually alternating terrestrial, marginal-marine, and fully marine environments. The Jurassic succession is divided lithostratigraphically into four formations: Lathi, Jaisalmer, Baisakhi, and Bhadasar.

The Jaisalmer Formation is a predominantly calcareous and highly fossiliferous unit ranging from the Bajocian to Oxfordian. It contains a diverse assemblage of ammonites, brachiopods, bivalves, gastropods, echinoids, crinoids, bryozoans, and corals. The formation is important for reconstructing depositional history, faunal succession, marine transgression, and regional correlation, particularly with the Kachchh Basin.

The Bathonian–Callovian interval of the Jaisalmer Formation comprises the Fort, Bada Bag, and Kuldhar members. The present study focuses on the carbonate succession of the Bada Bag and Kuldhar members, exposed along the Kuldhar River section in the western Jaisalmer Basin.

Materials and Methods

For the study, 21 rock samples were collected from two locations along the Kuldhar River section. The succession was measured bed-by-bed at centimetre scale, and thin sections were prepared from well-cemented carbonate rocks for petrographic analysis. Carbonate rocks were classified using established schemes of Folk (1959, 1962), Dunham (1962), Embry and Klovan (1971), and James (1984). The Folk (1962) classification was primarily adopted because it is based on the relative proportions of allochems. Petrographic observations were carried out using Nikon Eclipse E200 and Nikon E8400 petrological microscopes.

Conclusion

Sediments have abundant fossils record and composed of various skeletal grains such as echinoderms, brachiopods, crinoids, bivalves, gastropods, corals, foraminifera, and bryozoans. Ooids and peloids are main inorganic substances which is poorly to well sorted. Based on field observations, fossils assemblage and petrography, it has been inferred that Bathonian Callovian sediments of Kuldhar River section were deposited in open marine environments during fluctuating sea level in high energy shallow depth to deep marine environment.

References

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Copyright © 2026 Ashish Jinjwadiya, Kailash Choudhary, Jitendra Kumar Sharma. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.