Interaction between depositional environment and associated taphonomic conservation of the Upper Jurassic bivalves of Kutch, Gujarat, India

Kutch, a pericratonic basin at the western margin of India, provides a unique opportunity for paleontologists to study the interaction between depositional environments and taphonomic preservation of the bivalve shells, which prevail an enigmatic story in the true sense. Kutch holds thick marine sediments of approximately 3000 meters ranging from the Middle Jurassic to the Early Cretaceous period. However, this study represents a case study showing the relationship between the change in depositional environment and taphonomic preservation at the temporal scale from spatially distant two areas of Kutch, Wagad Uplift, and Lakhapar. Bharodiya and Kakarva, two localities of eastern Wagad Uplift and Lakhapar of the Kutch Mainland, preserve two differentially preserved bivalve shells regarding the depositional environment and associated energy conditions at different temporal intervals. The Kimmeridgian rocks from the Wagad Uplift show a convex upward-oriented shell, high degree of fragmentation and disarticulation, and size sorting, and suggest a transgressive lag deposit that has been reworked and deposited in a high energy condition. The taphonomic features of the Lakhapar area display a high diversity of bivalve fauna, a low degree of disarticulation and fragmentation, and a lack of any preferred orientation, indicating a maximum flooding zone sequence with low energy sediment starved offshore depositional environment. These two changes in deposition environment from the Kimmeridgian to the Tithonian period resulted in an inverse relationship between species richness and energy condition. The high-energy environment preferred to preserve large thick shelled bivalves and the low-energy condition preserved the small-sized taxa with more diverse compositions. Hence, the paleontological signals can be disentangled with the help of the preservation potential and taphonomic signatures.