Geochemical characteristics and sedimentary environment of the Salawusu section

Abstract

The chemical compositions of and the contents of CaCC3, free Fe2O3 and REE in the sediments of the Salawusu section have been analyzed to investigate the geochemical features of different sedimentary facies and explore their sedimentary environments during the Late Pleistocene. The contents of CaCO3. free Fe2O3 and ΣREE in lacustrine deposits of the middle part of the section are higher than those in the other parts, except SiO2 which shows an opposite trend. According to the distribution characteristics of the components mentioned above, the section may be divided into four parts which are equivalent to those divided in terms of lithologic characters and sedimentary facies. More remarkable characteristics were observed with respect to the distribution of CaCO3, free Fe2O3, ΣREE and SiC2/ AI2O3 and FeO/ Fe2O3 ratios, which can be adopted as the geochemical indices for paleoclimate division. From the above, four paleoclimate stages have been distinguished for the deposition process. The first stage, dated at 0.20–0.15 Ma, is characterized by a dry and cold climate; the second stage, ranging from 0.15 to 0.07 Ma, by a warm and slightly dry climate; the third stage, about 0.07 — 0.01Ma, by a cold and humid climate; and prevailing in the last ten thousand years is the fourth stage, with the climate changing gradually from warm-humid to warm-dry.