Geochemical characteristics of sediments from East Dongting Lake and their implications for provenance and weathering

Dongting Lake is the second-largest freshwater lake in China. To better understand the geochemical characteristics of the sediment in different seasons and identify the possible provenance, 44 sediment samples collected from East Dongting Lake (ED Lake) in summer (ED-S) and winter (ED-W) were used for elemental geochemical analysis. Geochemically, the sediment samples are classified as shale, and the chondrite normalized rare earth element (REE) patterns of the ED-S and ED-W have light REE (LREE) enriched, flat heavy REE (HREE) patterns with a negative Eu anomaly. In the present study, the correlations between certain elements show that the variations in ΣREE contents in sediments may be due to the concentrations of heavy minerals like monazite, whereas grain size is not responsible for that variations. Chemical index of alteration (CIA), plagioclase index of alteration (PIA) values, A-CN-K diagram, and Th/U ratios of the ED-S and ED-W sediment indicate a moderate to high intensity of chemical weathering in the source area. The Al 2 O 3 /TiO 2 ratio, discriminant function diagram, REE patterns, and elemental ratios indicate the contribution of sediments from felsic and intermediate source rocks. The provenance index (PI) based on REEs geochemical parameters suggest that elemental compositions of sediment in East Dongting Lake approach the Upper Yangtze River.