The geology of Sri Lanka captures one of the longest and most complete records of Jurassic to Miocene tectonic evolutions from the mid-latitudes of the southern hemisphere to the equatorial northern hemisphere. Sedimentary basins in Sri Lanka provide a natural laboratory with which to reconstruct paleoclimate during the island's northward voyage from Gondwana to Asia. Here, drill core cuttings were obtained from the Barracuda hydrocarbon exploration well in the offshore Mannar Basin, Sri Lanka. CHNS elemental analysis, gas chromatography-mass spectrometry, and stable C and N isotopic analyses were performed. The results suggest the deposition of organic carbon depleted (average total organic carbon (TOC) = 0.97) sediments under the arid climate of the Early Campanian. Separation of the Laxmi Ridge-Seychelles and Seychelles from the Indian plate and sea-level regression may have enhanced the deposition of organic carbon-rich (average TOC = 1.34) and terrestrial organic matter (OM)-rich (average C/N ratio = 20.36) sediments during the Late Campanian to Late Maastrichtian. CaCO3-rich (average = 32.5) Upper Cretaceous sediments then show a period of high productivity under a warm climate. The Deccan-Reunion basalt likely acted as a major contributor to the mass extinction of coccolithophores/foraminifera at the Late Maastrichtian followed by a reduction of CaCO3 and organic carbon content. The Early-Late Paleocene was characterized by the deposition of algal-derived OM with a terrestrial contribution (average C/N ratio = 15.75) under oxic depositional conditions (average C/S ratio = 16.21). However, the depositional environment changed drastically to one of oxygen-poor marine conditions (average C/S ratio = 6.83) during the Late Paleocene to the Early Oligocene due to weak oceanic circulation under a greenhouse climate. In contrast, the deposition of CaCO3-rich sediments since the Late Paleocene (average = 40.2) is linked to the movement of the Indian plate into nor
展开▼
