Spatiotemporal evolution of late Neoproterozoic marine environments on the Yangtze Platform (South China)

Linking continental weathering and marine C-P cycles

authored by: Simon V. Hohl, Shao Yong Jiang, Harry Becker, Hai Zhen Wei, Guang Yi Wei, Juan Xu, Qingjun Guo, Sebastian Viehmann, David van Acken
Abstract: 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 REY_SN systematics 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 Ce_SN anomalies and ambient seawater shifts to more radiogenic initial ⁸⁷Sr/⁸⁶Sr and ¹⁸⁷Os/¹⁸⁸Os, but unradiogenic ¹⁴³Nd/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.
External Organisation(s): Nanjing University
Freie Universität Berlin (FU Berlin)
China University of Geosciences
Institute of Geographical Sciences and Natural Resources Research Chinese Academy of Sciences
University of Vienna
University College Dublin
State Key Laboratory of Marine Geology
Type: Article
Journal: Global and planetary change
Volume: 216
ISSN: 0921-8181
Publication date: 09.2022
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Oceanography, Global and Planetary Change
Sustainable Development Goals: SDG 14 - Life Below Water
Electronic version(s): https://doi.org/10.1016/j.gloplacha.2022.103927 (Access: Closed)