Coupled delta Ca-44/40

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Wang, Jiuyuan, Jacobson, Andrew D., Zhang, Hua （张华）, Ramezani, Jahandar, Sageman, Bradley B., Hurtgen, Matthew T., Bowring, Samuel A., Shen, Shu-zhong (沈树忠)
• Format: Report
• Language: English
• Published: PERGAMON-ELSEVIER SCIENCE LTD 2019
• Subjects: Calcium isotopes; Radiogenic Sr isotopes; Stable Sr isotopes; end-Permian; Chemical weathering; Diagenesis; CALCIUM ISOTOPE FRACTIONATION; STABLE SR-ISOTOPE; MULTICOMPONENT CARBONATE SYSTEM; EARLY MARINE DIAGENESIS; PHOTIC-ZONE EUXINIA; TRIASSIC BOUNDARY; SOUTH CHINA; OCEAN ACIDIFICATION; NANPANJIANG BASIN; TRACE-ELEMENT; Geochemistry & Geophysics; Ocean acidification
• Online Access: http://ir.nigpas.ac.cn/handle/332004/27957; http://ir.nigpas.ac.cn/handle/332004/27958; https://doi.org/10.1016/j.gca.2019.07.035

We report high-resolution high-precision delta Ca-44/40 delta Sr-88/86 and Sr-87/Sr-86 records spanning the Permian-Triassic boundary (PTB) from the Meishan and Dajiang carbonate successions in south China. The goal of the study was to understand the behavior of Ca and Sr isotopes during a time period in Earth history characterized by severe biological and environmental perturbations including a major mass extinction flood basalt volcanism ocean acidification and sea level fluctuations. Dajiang displays negative delta Ca-44/40 and delta Sr-88/86 excursions and invariant Sr-87/Sr-86 ratios in the <60 kyr timeframe between the main extinction horizon and the PTB. The Meishan delta Ca-44/40 and delta Sr-88/86 records are generally shifted to higher values and display both synchronous and asynchronous trends relative to Dajiang. In addition Sr-87/Sr-86 ratios at Meishan are significantly elevated and do not define a clear secular pattern. We reconcile diverse conceptual models for the dataset with the aid of supporting elemental and isotope measurements (e.g. Sr/Ca delta C-13 and delta O-18) as well as sequential leaching experiments. The combined body of evidence indicates that Dajiang sediments experienced recrystallization and neomorphism under rock-buffered conditions that preserved primary signals. In contrast the Meishan records display influences from both primary and secondary processes including local differences in fractionation fluid-buffered early marine diagenesis and late stage diagenetic overprinting. The three isotopic records for Dajiang and to some extent the delta Ca-44/40 and delta Sr-88/86 records for Meishan preserve information about the geochemistry of end-Permian seawater. We find that enhanced weathering of shelf carbonates during sea level fall provides the best explanation for rapidly decreasing seawater delta Ca-44/40 and delta Sr-88/86 values without affecting Sr-87/Sr-86 ratios. (C) 2019 Elsevier Ltd. All rights reserved.