Stratigraphy, sedimentary structures, and textures of the late neoproterozoic doushantuo cap carbonate in south China

Publication Type  Journal Article
Year of Publication  2006
Authors  Jiang, G. Q.; Kennedy, M. J.; Christie-Blick, N.; Wu, H. C.; Zhang, S. H.
Journal Title  Journal of Sedimentary Research
Volume  76
Issue  7-8
Pages  978-995
Journal Date  Jul-Aug
ISBN Number  1527-1404
Accession Number  ISI:000240959700002
Key Words  gas hydrate destabilization; oceanic methane hydrate; gulf-of-mexico; u-pb ages; snowball earth; ice ages; authigenic carbonates; massive dissociation; mackenzie mountains; northwestern canada
Abstract  

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 C-13 Values as low as -41 parts per thousand 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.

Notes  

090ODTimes Cited:9Cited References Count:119

URL  <Go to ISI>://000240959700002
DOI  Doi 10.2110/Jsr.2006.086