Geochemical insights from the Middle-Paleocene to Early Eocene Offshore sedimentary strata of the Mannar Basin, Sri Lanka: deciphering paleo-oceanic dynamics

Abstract

The Mannar Basin, located offshore of Sri Lanka, contains a sedimentary record spanning from the Cretaceous to the present, with a well-preserved sequence from the Middle Paleocene to Early Eocene. This study focuses on the Middle Paleocene to Early Eocene sedimentary section, using comprehensive whole rock major and trace element geochemical analyses to investigate paleo-oceanic conditions in the Northern Indian Ocean during this critical interval. Examination of redox-sensitive trace elements revealed temporal shifts in paleoclimatic conditions, indicative of warmer climates during the mid-late Paleogene period. Variations in elemental ratios, such as Rb/Sr and Sr/Cu, reflect changes in weathering intensity and terrestrial input, mirroring shifts in precipitation and climatic regimes. Insights from Zr/Rb ratios highlight past hydrodynamic conditions, suggesting deeper water and lower hydro energy environments. Fluctuations in Zr/Rb values, notably in the P/E samples, suggest relatively heightened wave energy during warmer climatic conditions in the tropical northern Indian Ocean. Diverse Paleogene depositional geomorphologies and seismic data point to increased total rare earth element (ΣREE) concentrations at the P/E boundary, attributed to amplified terrestrial input. Shale-normalized REE patterns and positive interelemental relationships further underscore the influence of terrigenous sources on sedimentary REE distributions. Negative Ce anomalies within studied sections suggest oxygenated environments during deposition, with minimal fluctuations in the bottom water oxygen content. Positive correlations between Ce/Ce* ratios and terrigenous materials emphasize the impact of detrital siliciclastic materials on sedimentary redox conditions. Overall, these geochemical findings provide critical evidence for significant shifts in paleoceanic conditions during the Paleocene–Eocene transition. The integration of multiple geochemical proxies elucidates the interplay between climatic fluctuations, hydrodynamic regimes, and terrestrial input, underscoring the Mannar Basin’s role as a valuable archive of past environmental change.