Geosystems and Geoenvironment (Aug 2022)
K-Pg boundary transition and attendant degeneration of clay lattices in late Maastrichtian-early Danian shelf facies of the Langpar formation, Meghalaya, India
Abstract
Environmental effects of the Deccan volcanism and potential causes for the Cretaceous-Palaeogene (K-Pg) boundary mass extinction have not been resolved completely. Earlier studies on shallow-marine facies of the Um-Sohryngkew River (USR) K-Pg boundary section revealed notable cell parametric variations and changes in the inter-atomic distances in illite and kaolinite lattices associated with the yellowish brown clayey (JP-12) and shaly marlite (JP-14) layers of the CF3 and P0 biozones which correspond to negative Ce anomalies and sudden break in the planktonic foraminifers abundance, respectively. Similar studies are lacking on a contiguous, well-preserved shelf-facies of the Mahadeo-Cherrapunji road (MCR) section. In this contribution we address environmental shift across K-Pg boundary using clay minerals. Obtained results are compared to the clay attributes of the USR succession. X-ray diffraction patterns revealed Illite > Illite/Smectite > kaolinite > Chlorite > Montmorilloite assemblages throughout the MCR succession. This in combination and widespread variation in the clay mineral assemblages suggest highly variable source terrains and lack of sediment mixing during transport. Illite/Smectite mixed-layer clays occur with both kaolinite and chlorite, reveal a seasonal weather (warm-wet, warm-dry) variation in the source area. A major deviation in the cell parameters, and inter-atomic distances, and distortion in the physil lattices associated with the gray calcareous shale layer that lie between biozones CF1-P0 of both the USR and MCR sections is attributed to K-Pg boundary transition events including frequent local sea-level changes, Abor volcanic extrusions, Indian and Eurasian plates collision, and green-house effects of the Deccan volcanism.
