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Stratigraphy, sedimentary structures, and textures of the late Neoproterozoic Doushantuo cap carbonate in south China

Ganqing Jiang, Martin J. Kennedy, Nicholas Christie-Blick, Wu Huaichun and Zhang Shihong
Stratigraphy, sedimentary structures, and textures of the late Neoproterozoic Doushantuo cap carbonate in south China
Journal of Sedimentary Research (July 2006) 76 (7-8): 978-995


The 3- to 5-m-thick Doushantuo cap carbonate in south China overlies the glaciogenic Nantuo Formation (ca. 635 Ma) and consists of laterally persistent, thinly laminated and normally graded dolomite and limestone indicative of relatively deep-water deposition, most likely below storm wave base. The basal portion of this carbonate contains a distinctive suite of closely associated tepee-like structures, stromatactis-like cavities, layer-parallel sheet cracks, and cemented breccias. The cores of tepees are composed of stacked cavities lined by cements and brecciated host dolomicrite. Onlap by laminated sediment indicates synsedimentary disruption of bedding that resulted in a positive seafloor expression. Cavities and sheet cracks contain internal sediments, and they are lined by originally aragonitic isopachous botryoidal cements with acicular radiating needles, now replaced by dolomite and silica. Pyrite and barite are common, and calcite is locally retained as a primary mineral. These features share morphological and petrographic attributes with modern and ancient methane seeps in which methane gas and fluids provide both a force for physical disruption from buoyancy and a source of alkalinity for significant cementation. The presence of delta (super 13) C values as low as -41 per mil in well preserved limestone crusts and cements within and immediately above the tepee-like structures provides unequivocal evidence for methane influence, and the widespread distribution of identical sedimentary structures and paragenetic cement sequences across the entire basin at the same basal cap carbonate level is consistent with gas hydrate destabilization and the development of methane seeps as a result of postglacial warming of the ocean. Considering the broad distribution of similar features at the same stratigraphic level in other cap carbonates globally, we suggest that the late Neoproterozoic postglacial methane release may have influenced the oceanic oxygen level as well as contributed to postglacial warming via the greenhouse effects of methane.

ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 76
Serial Issue: 7-8
Title: Stratigraphy, sedimentary structures, and textures of the late Neoproterozoic Doushantuo cap carbonate in south China
Affiliation: University of Nevada-Las Vegas, Department of Geoscience, Las Vegas, NV, United States
Pages: 978-995
Published: 200607
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 120
Accession Number: 2006-088305
Categories: Sedimentary petrologyStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., geol. sketch map
Secondary Affiliation: University of California at Riverside, USA, United StatesLamont-Doherty Earth Observatory, USA, United StatesChina University of Geosciences, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 200649
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