Oligo-Miocene marine bivalves from the Kutch Basin (western India) and their biogeographic implications in the context of Tethyan closure

Abstract

The Oligo-Miocene marine deposits of the Kutch Basin in western India display a diverse faunal assemblage during and after the separation of the Tethyan seaway. We documented 22 genera and 35 species of bivalves from this basin, collected from 11 time-constrained shell beds of three formations – Maniyara Fort (Chattian), Khari Nadi (Aquitanian), and Chhasra (Burdigalian–Langhian) representing a period of ~9 My (24.4–15 Ma). Three new species, Anomia vakram, Callista ramparensis, and Tucetona bharati, were described. Oligo-Miocene bivalves of the Kutch Basin, representing the Western Indian Province (WIP), demonstrate a complex pattern of changing affinity to coeval fauna of the Mediterranean-Iranian Province (MIP) and the Eastern African-Arabian Province (EAAP) and Eastern Indian Province (EIP). The Kutch Basin witnessed a rise in genus affinity with all provinces during the Early Miocene, driven by the development of shallow water habitats due to seaway constriction. However, the rise in species similarity among WIP, EAAP, and EIP suggests a strengthening provincialism around the Indian Ocean following the seaway closure. Overall, the Oligo-Miocene bivalves of the WIP remain underexplored, highlighting the need for more fossil molluscan data outside the MIP for comprehensive biogeographic analysis.