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| Titel |
Comprehensive geobiological characterization of a bituminous carbonate facies with Ediacara-type fossils (Shibantan Member, South China) |
| VerfasserIn |
Jan-Peter Duda, Martin Blumenberg, Volker Thiel, Klaus Simon, Maoyan Zhu, Joachim Reitner  |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106068
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| Publikation (Nr.) |
 EGU/EGU2015-5721.pdf |
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| Zusammenfassung |
| The Shibantan Member (Dengying Formation, Ediacaran Period) is one of only few
carbonate settings with Ediacara-type fossils worldwide (e.g. Ding & Chen, 1981; Sun, 1986;
Xiao et al., 2005; Shen et al., 2009; Chen et al., 2014). However, only little is known about
the sedimentology and biogeochemistry of the environments in which these organisms throve.
Here we provide a comprehensive geobiological characterization of the Shibantan
Member, addressing the interplay between sedimentary and (bio-) geochemical
processes.
Sedimentary analysis revealed that black laminated limestones of the lower
Shibantan Member were deposited after a sudden local deepening in a subtidal lower-
to middle ramp environment close to the storm wave base, while the dark wavy
dolomites of the upper Shibantan Member were deposited in a subtidal middle ramp
environment between storm- and fair weather wave base. Sedimentation in the
Shibantan basin was generally highly dynamic as evidenced by a distinct slumping
horizon and mass-flow deposits that were possibly due to synsedimentary tectonic
processes.
The microbial-mat associated biota including Ediacara-type fossils is restricted to the
lower Shibantan Member. Sedimentary analysis of this part reveals a close relationship
between autochthonous mat growth and allochthonous and/or para-autochthonous event
deposition. During deposition of the lower Shibantan Member the water column was
probably temporarily stratified, with a sub- to anoxic water layer (evidenced by Ni/Co-,
V/(V+Ni) and V/Sc ratios) overlain by a oxygenated upper layer (evidenced by negative Ce
anomalies and low V/Cr ratios). However, such stratification was not permanent, as mixing
by storm events is evidenced by hummocky cross stratification structures. 13C-enrichments in
carbonates of the Lower Shibantan Member (δ13C = +3.3 to +4.0o VPDB) together with
13C-depletions of syngenetic n-alkanes cleaved from the respective extraction residue
using catalytic hydropyrolysis (HyPy; δ13C = -31.7 to -36.3o VPDB) indicate a
significant withdrawal of 12C by primary producers that thrived within the microbial
mats. At the same time, sulphurised biomarkers in the bitumen and HyPy-treated
extraction residue hint at organic matter decomposition and concomitant sulphide
production by sulphate-reducing bacteria. Given the sedimentological evidence for
periodical ventilation of the water column by storms, sulphide oxidising bacteria
were possibly favoured whenever oxygen became available at the sediment-water
interface.
Taken together, the environments in which the microbial-mat-associated biota including
Ediacara-type fossils throve were highly dynamic due to a complex interplay of geological
and biological processes.
References
Chen Z., Zhou C., Xiao S., Wang W., Guan C., Hua H., Yuan X., 2014. New Ediacara
fossils preserved in marine limestone and their ecological implications. Scientific Reports,
4
Ding Q. and Chen Y., 1981. Discovery of soft metazoan from the Sinian System
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53-57.
Shen, B., Xiao S., Zhou C., Yuan X., 2009. Yangtziramulus zhangi New Genus and
Species, a Carbonate-Hosted Macrofossil from the Ediacaran Dengying Formation in the
Yangtze Gorges Area, South China. Journal of Paleontology, 83(4): 575-587.
Sun W., 1986. Late precambrian pennatulids (sea pens) from the eastern Yangtze Gorge,
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Xiao S., Shen B., Zhou C., Xie G., Yuan X., 2005. A uniquely preserved Ediacaran fossil
with direct evidence for a quilted bodyplan. Proceedings of the National Academy of
Sciences of the United States of America, 102(29), 10227-10232. |
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