Glaucony in a core from upper continental slope off Madras, Bay of Bengal

Abstract

A 1.32 m long gravity core collected from the upper continental slope off Madras at 495 m water depth shows two distinct lithe units-a lower (94-132 cm) greenish clayey sand unit with glaucony ranging from 60-90% and an upper (0-94 cm) greenish grey sandy clay unit with glaucony ranging from 1-20%. Glauconitised grains consist of dark green and deeply cracked ellipsoidal faecal pellets and foraminiferal casts. The XRD peaks of the glauconitised grains are subdued with broad base and assymmetric sides reflecting the disordered crystallographic structure. The K2O content (5.16%) of the grains points to less evolved stage. SEM studies reveal the presence of irregular blades of clay mineral particles in the rim and unidentifiable mineral laths in the core portions of the grains. The formation of glaucony facies probably took place during late Pleistocene lowered sea level. The study suggests that the glaucony is buried during subsequent-Holocene transgression. Based on the morphology and K2O content, the age of the glaucony is inferred to be around 20000 y B.P., corresponding to the last glacial maximum (LGM).