Spatiotemporal evolution of late Neoproterozoic marine environments on the Yangtze Platform (South China): Linking continental weathering and marine C-P cycles

• Published in: Global and planetary change 2022-09, Vol.216, Article 103927
• Main Authors: Hohl, Simon V., Jiang, Shao-Yong, Becker, Harry, Wei, Hai-Zhen, Wei, Guang-Yi, Xu, Juan, Guo, Qingjun, Viehmann, Sebastian, van Acken, David
• Format: Article
• Language: English
• Subjects: C and P cycles; Carbonate osmium isotopes; Nutrient cycling; Shuram anomaly; Sr-Nd isotope stratigraphy; Yangtze Platform
• ISSN: 0921-8181; 1872-6364
• DOI: 10.1016/j.gloplacha.2022.103927

The geodynamic reorganization of major cratonic blocks during the assembly of Gondwana in the late Neoproterozoic caused a (bio)geochemical evolution of marine habitats that witnessed fluctuating seawater oxygenation and nutrient fluxes. Previous studies of carbonates deposited on the Yangtze Platform (South China) have shown their use as reliable archives of paleo-redox and bio-productivity changes intrinsically linked to continental weathering fluxes and water mass cycling. Despite its complex submarine morphology, only a few carbonate-bearing sections comprising deeper depositional environments of the Yangtze Platform have been evaluated. Here we report temporal, lateral, and vertical variations of stable C and radiogenic Sr, Nd, and Os isotopic compositions together with trace element and rare earth and yttrium (REY) systematics in carbonates from the Doushantuo Formation representing different paleo-marine environments of the Yangtze Platform, including I) inner shelf, II) restricted intra-shelf basin, III) slope and IV) deep-water basin sections to trace the extent and evolution of paleo water masses. Variations in shale-normalized (subscript SN) Ce anomalies argue for variably oxidizing atmosphere/ocean conditions. The combination of REYSNsystematics with carbonate associated P enrichments defines three distinct local water masses from which the carbonates precipitated: i) fully oxidized shallow-water, ii) nutrient-poor intra-shelf basin waters, and iii) organic carbon-rich slope and deep-waters with temporal evolution to higher dissolved pO2. Negative carbon isotope excursions in the carbonates such as during the putative Shuram equivalent Doushantuo Negative Carbon Excursion (DOUNCE) correlate with less negative CeSNanomalies and ambient seawater shifts to more radiogenic initial87Sr/86Sr and187Os/188Os, but unradiogenic143Nd/144Nd compositions, arguing for coupling of redox and weathering trends. Our comprehensive geochemical study highlights the vertical and temporal variations of physicochemical water mass properties recorded in late Neoproterozoic Yangtze Platform carbonates until the emergence of the first metazoans. •Intensive geochemical study spanning four paleo-depths on the Yangtze Platform•First carbonate Osmium isotopic compositions from the Late Neoproterozoic•Os, Nd and Sr isotope variations in concert with influx of terrigenous solutions towards the end of the Doushantuo Fm•REY systematics and P enrichments reveal significantly diff