Implications of a geochemical approach to reconstruct the Maastrichtian–Danian seaways of central India: The planktic foraminifera-bearing Jhilmili intertrappean revisited

Abstract

Maastrichtian–Danian sedimentary sequences associated with Deccan volcanism are commonly interpreted to be deposited in fluviatile-lacustrine environments, except for the nearshore marine outcrops in Razol province (Rajahmundry). Discovery of Danian zone-P1a planktic-foraminifera, from a thin-horizon of an otherwise entirely lacustrine-palustrine Jhilmili intertrappean section in central India, makes this section unique, with reliable age-constraints. The presence of this foraminifera-bearing unit was used to postulate the existence of an ∼800 km marine-seaway from the west up to central India. Occurrences of non-marine biota in the foraminifera-bearing horizon and the absence of associated lithotopes and biotopes characteristic of marine transgressive events in this section is noteworthy. This study focuses on trace-element geochemistry and clay-mineralogy of the Jhilmili section to explore changes in depositional conditions along this section and obtain insights on the ambient waters from which Unit 3 was deposited. High-resolution sampling has been conducted and geochemical proxies such as Sr/Ba, Y/Ho (whole-rock, clay-fractions) and REE+Y (carbonates) have been utilized. Geochemical parameters suggest a non-marine environment for the entire section except the middle-unit showing brackish conditions because of storm/tsunami induced seawater mixing into freshwater depositional settings. Lithofacies, fossil-assemblage and variations in geochemical ratios indicate short-term episodic mixing of marine elements, possibly through storm/tsunami related activity in the lacustrine-palustrine freshwater ecosystem. Previous palaeobiological records from outcrops in the Godavari Rift indicate that seawater possibly entered through the Godavari rift. This study provides additional insights for the Maastrichtian–Danian paleogeography of central India.