Variations in Sr-87/Sr-86 ratios of calcites in Chinese loess: a proxy for chemical weathering associated with the East Asian summer monsoon

• Published in: Palaeogeography, Palaeoclimatology, Palaeoecology
• Main Authors: Yang, JD, Chen, J, An, ZS, Shields, G, Tao, XC, Zhu, HB, Ji, JF, Chen, Y
• Format: Article in Journal/Newspaper
• Language: English
• Published: ELSEVIER SCIENCE BV 2000
• Subjects: chemical weathering; east Asian monsoon; loess and paleosols; soil carbonates; Sr isotope; Physical Geography; Geology; Paleontology; MAGNETIC-SUSCEPTIBILITY; NORTH-ATLANTIC; CLIMATE; DEPOSITS; OSCILLATIONS; LUOCHUAN; RECORD; EVENTS; Geography; Physical; Geosciences; Multidisciplinary; Four Peaks; North Atlantic
• Online Access: http://ir.ieecas.cn/handle/361006/11916; https://doi.org/10.1016/S0031-0182(99)00159-5

Sr-87/Sr-86 ratios of loess-paleosol calcites of Luochuan in China over the past 130 ka display a regular change with increasing trend of Sr-87/Sr-86 ratios in the following order: loess calcite-->weakly pedogenetic, paleosol calcite-->paleosol calcite-->pure secondary calcite. The observed variations in the Sr-87/Sr-86 record of loess-paleosol calcites correlate closely with the records of the magnetic susceptibility, coarse-grain fraction content in the same profile [An et al., Chin. Sci, Bull. 39 (1994) 182-184] and the SPECMAP stacked delta(18)O record of global ice volume [Imbrie et al,, in Berger et al, (Eds.), Milankovitch and Climate, Part I, Reidel, Boston, 1984, pp. 269-305]. Strata from the last glacial consist mostly of loesses and weakly developed paleosols and have lower Sr-87/Sr-86 ratios, averaging 0.71079. Paleosols which developed during the last interglacial have higher Sr-87/Sr-86 ratios, averaging 0.71131. The four periods (ca. 125-110, 98-90, 80-75 and 9-5 ka B.P.) of increased summer monsoonal rainfall coincide with the four peaks in Sr-87/Sr-86 values. A series of 87Sr/86Sr high frequency, high amplitude fluctuations is superimposed on the last glacial-interglacial cycle over the past 130 ka, occurring on millennium timescales with an average time span of about 3 ka during the last glacial. The fluctuations of the Sr-87/Sr-86 ratios of the Luochuan loess-paleosol calcites lie in the range 0.71036-0.71176 for the past 130 ka, The study shows that the Sr isotopic system in loess-paleosol calcites may therefore be an excellent proxy of chemical weathering on continents associated with the East Asian summer monsoon. (C) 2000 Elsevier Science B.V. All rights reserved.