Late Paleocene to Late Eocene Calcareous Nannofossils in the Mannar Basin, Sri Lanka; Implications for Paleoeutrophication Conditions

With a few paleoclimatic assessments in Sri Lanka using calcareous nannofossils as paleoclimatic proxies, the current study focuses on reconstructing the temporal evolution of sea surface paleoclimatic conditions (thermocline and nutricline levels) by studying samples from Dorado-North hydrocarbon exploration well, Mannar Basin. The recovery of well-preserved calcareous nannofossils from Late Paleocene to Late Eocene sediment samples was made possible using the standard smear slide preparation method. Semiquantitative analysis was conducted examining the relative abundance of Discoaster, coccolith size distribution and stratigraphic distribution of Reticulofenestra and Coccolithus under the polarizing light and scanning electron microscopes. Observing two different co-occurrences of the above-mentioned parameters indicates growing eutrophic conditions from the Late Paleocene to the Late Eocene which were identified from the selected sediment sequence from the Mannar Basin. The sudden influx of terrigenous sediments and the intensified greenhouse climate that occurred during the Late Eocene could be considered for the observed rapid expansion of eutrophication conditions around 55 Ma.