Bioerosion, encrustation, and taphonomic pathways of <i>Nummulites</i> tests and the palaeoenvironmental implications: Oligocene interval of the Kutch Basin, India

Investigating carbonate substrate communities within a palaeoenvironmental and taphonomic framework allows for tracking the pre-burial conditions and history of the substrate and its inhabitation. In this investigation, we integrate a comprehensive examination of bioerosion, encrustation, predation, ethology, and their implications for palaeoenvironments. This study aims to highlight the taphonomic pathways of Larger Benthic Foraminifera (LBF). As an analog, the Nummulites accumulations from the Basal Member of the Oligocene (Chattian) Maniyara Fort Formation in the Kutch Basin of Gujarat have been presented. Among the bioerosion traces identified are Entobia megastoma, Curvichnus isp., Maeandropolydora sulcans, Radulichnus isp., Linichnus bromleyi, and algal microborings, along with corrasion pits and fractures. Among the encrustations, bivalves (Ostreidae), polychaete annelids (serpulids), rotaliid foraminifera (megalospheric Nummulites), and bryozoans (Cheilostomatida) have been recognized. Microborings created by sponges and polychaete worms are primarily attributed to the domichnia, whereas exploratory bite marks by elasmobranchs and grazing traces by gastropods are attributed respectively to the predation and grazing ethological categories. An autochthonous to para-autochthonous nature of Nummulites accumulation is suggested by the presence of non-bioeroded and bioeroded/encrusted tests, thick-bedded nummulitic packstone and grainstone, abundant larger and flat Nummulites spp., and non-preferred imbrications. The inferred depositional setting is shallow-marine, potentially between the middle and the inner carbonate ramp as indicated by a novel approach to analyse the bioerosional-encrustational taphonomic pathways for LBF accumulations. In general, this study is focused on the various carbonate-platform environments and their correlations with the palaeomarine ecosystems vis-à-vis the taphonomic pathways that have influenced the fossil record.