Clay mineralogy of the Late Cretaceous and early Tertiary successions of the Cauvery Basin (southeastern India): implications for sediment source and palaeoclimates at the K/T boundary

Clay mineral analyses were carried out on late Maastrichtian–early Palaeocene (Cretaceous–Tertiary) sedimentary rocks in the Ariyalur area of the Cauvery Basin (southeastern India). These investigations were aimed at determining the sedimentary provenance and palaeoclimate of the area in the latest Cretaceous and earliest Tertiary. The late Cretaceous deposits show significant palaeogeographic variation in clay mineral contents across the study area. Mixed-layer illite-smectites dominate the clay mineral content of the uppermost Maastrichtian of all areas, with elevated smectite, illite, palygorskite, sepiolite, kaolinite and chlorite occurring at intervals through the succession. This combination and widespread variation in the clay mineral suite suggests a lithologically highly variable source terrain and lack of sediment mixing during transport. Mixed-layer clays occur with both kaolinite and palygorskite, interpreted in terms of a seasonal (warm and wet, warm and dry) source area. The uppermost Maastrichtian of the Niniyur section displays an upward increase in illite content, suggesting that the adjacent continental area became strongly influenced by physical weathering just prior to the K/T boundary. The return of mixed-layer clays, smectite, illite and kaolinite during the early Tertiary suggests that chemical weathering in a seasonal climate once again controlled the formation of clay minerals. These results imply that the volcanism associated with the Deccan Traps had no sudden effect on the Cretaceous or Tertiary sedimentation and clay mineralogy of this area.