Late Quaternary environmental and sea level changes from Kolleru Lake, SE India: Inferences from mineral magnetic, geochemical and textural analyses

Abstract

The present study employs mineral magnetic, geochemical, and textural parameters to elucidate the climate and sea level change signatures from Kolleru lake sediments representing the inter-deltaic part of the KrishnaeGodavari sedimentary basin (KG basin). For this purpose, four cores were obtained which included significant peat. The conventional radiocarbon dating suggested that the peat formation took place during 9 kae6 ka with an average sedimentation rate of 0.31 cm/y. Thermomagnetic analysis identifies titanomagnetite, magnetite and hematite as the dominant magnetic mineralogy of the KG basin sediments. The variation in magnetic mineralogy is related to paleoclimatic and paleoenvironmental processes; the transitions between (titano)magnetite and hematite coincide with peat layers of the cores as indicated by SIRM/c (Saturation Isothermal Remanent Magnetization/Magnetic Susceptibility) and S-ratio defined by IRM 0.3T/SIRM values. The various mineral magnetic parameters, c and Sratio along with major elemental concentrations of Ti, Al, Fe and Zr show signatures of an arid event before 10 ka, between 9 kae8 ka periods and during the last 5.5 ka. The overall climate of warm and humid type was inferred from 10 ka to 9 ka, which correlates with Early Holocene Optima and 6 ka to 5.5 ka of Middle Holocene. The presence of evaporite crystals in the lowermost part of the cores corroborated by mineral magnetic and geochemical proxies indicates sub-aerially weathered facies of the arid Late Pleistocene. Similarly, the peat layers rich in mangrove pollen indicate sea level changes between 10 ka and 6 ka. The sub-surface position of the Pleistocene weathered layer and the Holocene peat layer suggests tectonic subsidence of the area, which is situated over the basement graben, known as Gudiwada sub-basin