Geochemistry of Ediacaran cap dolostones across the Yangtze Platform, South China: implications for diagenetic modification and seawater chemistry in the aftermath of the Marinoan glaciation
Posted on 2017-05-04 - 11:46
Cap dolostones of the Ediacaran Doushantuo Formation (Yangtze Platform, South China) from various palaeowater depths were studied to evaluate the extent of their diagenetic alteration and to assess temporal and spatial variations of seawater chemistry in the aftermath of the Marinoan glaciation. Diagenetic fluid overprint is common in cap dolostone lithologies. However, the mobilization of trace elements and the modification of Sr and O isotopic compositions are variable and were controlled by multiple stages of fluid overprint. The highest 87Sr/86Sr ratios (up to 0.7246) occur in cap dolostones from the palaeo-slope environment at the Huanglianba section, whereas cap dolostones deposited in platform settings and in one of the distal basinal settings reveal 87Sr/86Sr ratios close to the proposed late Neoproterozoic seawater composition (0.7077). Shale-normalized REE + Y patterns of carbonate leachates display enrichments of heavy over light REE and superchondritic Y/Ho ratios, typical of seawater. However, Y/Ho ratios in the cap dolostones are always lower than modern seawater values, which is interpreted to reflect dilution of the seawater signal by continent-derived meltwater influx during deglaciation. Negative Ce anomalies in carbonate leachates from platform and slope sections suggest that oxidized conditions existed in shallow marine environments shortly after the Marinoan glaciation, whereas positive or no resolvable Ce anomalies in basin settings indicate that the latter remained anoxic. Redox stratification of the Yangtze margin at the beginning of the Ediacaran is further supported by the relative enrichment of redox-sensitive trace metals in basinal sections. These data may indicate moderately anoxic (less than 10µM dissolved O2) and presumably manganous conditions during the deposition of cap dolostones in the deeper realms of the Yangtze basin.
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Hohl, Simon V.; Becker, Harry; Jiang, Shao-Yong; Ling, Hong-Fei; Guo, Qingjun; Struck, Ulrich (2017). Geochemistry of Ediacaran cap dolostones across the Yangtze Platform, South China: implications for diagenetic modification and seawater chemistry in the aftermath of the Marinoan glaciation. Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.3770957.v1
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AUTHORS (6)
SH
Simon V. Hohl
HB
Harry Becker
SJ
Shao-Yong Jiang
HL
Hong-Fei Ling
QG
Qingjun Guo
US
Ulrich Struck
CATEGORIES
KEYWORDS
ratioEdiacaran Doushantuo Formationsectionresolvable Ce anomaliesSouth Chinaredox-sensitive trace metalsDiagenetic fluid overprintREEYangtze Platformcontinent-derived meltwater influxSrcap dolostone lithologiesMarinoan glaciation Cap dolostonescap dolostonesNegative Ce anomaliesseawater chemistrysettingEdiacaran cap dolostonesMarinoan glaciationcarbonate leachates display enrichmentsGeology