Paleoceanographic and paleoclimatic changes during the Plio-Pleistocene of the Salaverry Basin, Peru Offshore: Evidences from Benthic Foraminifera, Carbon and Oxygen Stable Isotope Geochemistry and distribution of Gypsum grains

Benthic foraminiferal studies have been used significantly as potential proxy to understand paleoceanographic and paleoclimatic changes over geologic time. Our study was pursued to analyze core sediment samples of ODP Hole 680B, Salaverry Basin, Peru Offshore of intervals covering up to 90.5 mbsf of the Plio-Pleistocene age. Previous studies on micropaleontological analyses were performed only up to 45 mbsf. However present study was performed on Benthic Foraminiferal census count, stable carbon and oxygen isotopes, total organic carbon and Gypsum grains distribution analysis up to depth 90.5 mbsf and the obtained results has been used to understand paleoceanographic and paleoclimatic changes during the Plio-Pleistocene. Proxy data signifies the basin was aerially to sub-aerially exposed during the Pliocene (90.5 to 61.4 mbsf) due to intense compressional tectonic episodes which facilitated upliftment of outer shelf high as well as generation of folded structures parallel to the trench within the Salaverry and Lima Basins. This upliftment restricted incursion of marine water into the basin as evident by higher (>80%) abundances of gypsum grains and devoid of any foraminifera. Presence of foraminifera, gypsum within the sequence from 61.4 to 45 mbsf, signifies that the basin had undergone tectonic subsidence owing to normal faulting which had developed as the basin was under an extensional tectonic setting during the late Pliocene. This subsidence was also evidenced by the presence of mixed type of grains which signifies presence of slump deposits. Whereas sediments of younger sequence (above 45 mbsf) were deposited under the profound influence of climatically induced sea level fluctuations. Benthic foraminiferal species Bolivina seminuda which is a marker of Oxygen Minimum Zone had been flourished during this time. Their depleted oxygen isotopic values records the intervals of sea level rise during the climatic warmth which facilitated strong upwelling events and formation of Oxygen Minimum Zone. Total organic carbon data reflect the accumulation of predominantly marine organic carbon within the sediments.