Implications for catchment weathering, provenance, and climatic records from a late Pleistocene to present sedimentary sequence in Gujarat, India

Kumar, Kamlesh , Sharma, Anupam , Srivastava, Pradeep , Thakur, Biswajeet

2023-01-01 QUATERNARY RESEARCH 2023   111(卷), null(期), (148-165页)

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To ascertain weathering, provenance, and paleoclimate of the last ca. 29 ka in mainland Gujarat, western India, a sedimentary profile of similar to 7.5 m was measured, described, and sampled at Pratappura and a multiproxy analysis was conducted. To determine weathering, silty-sand and sandy-silt facies were analyzed, and log Na2O/K2O versus log SiO2/Al2O3 was plotted, which shows clustering in the quartz arenite and sub-litharenite categories, indicating low to moderate weathering. The chemical index of alteration (CIA) is 55-74, and was plotted versus the index of chemical variability (ICV) of 1.50, with samples clustered mainly between subalkali basalt and picrite, indicating the dominance of a mafic component. While depleted chondrite normalized light rare earth element (REE) (La/Yb <1) levels suggest the prevalence of a mafic source in the catchment, identical chondrite normalized REE patterns indicate that sediments were well homogenized. Using multiple proxies, the measured profile was subdivided into five paleoclimatic zones. Zone-I (29-18 ka) exhibits decreasing moisture, C-org, chi(lf), Al2O3, TiO2, and Fe2O3 trends, while higher values of CO3-2 and delta C-13 indicate a change from a warm-humid to semiarid climate. Zone-II (18-11 ka) shows signs of the beginning of aridity ca. 18 ka during the Last Glacial Maximum (LGM). Several proxies in zone-III show wetter climatic conditions from the early Holocene (ca. 11-4 ka) due to the onset of the SW monsoon, with the trend continuing in zone-IV (4-2 ka). In zone-V, the climate appears to have been similar to the modern conditions in the area from 2 ka-present.