Carbon isotope evidence for widespread methane seeps in the ca. 635 Ma Doushantuo cap carbonate in south China
Abstract
Distinctive sedimentary structures, textures, and extremelynegative <IMG SRC="/math/delta.gif" ALT="{delta}" BORDER="0">13Ccarb values from the Ediacaran Doushantuo cap carbonate(ca. 635 Ma) in south China were taken as evidence for a methanehydrate destabilization event, but existing data for a methane-derived<IMG SRC="/math/delta.gif" ALT="{delta}" BORDER="0">13Ccarb signature were reported from a single locality in theYangtze Gorges area. Here we report negative <IMG SRC="/math/delta.gif" ALT="{delta}" BORDER="0">13Ccarb valuesas low as -48<IMG SRC="/math/permil.gif" ALT="{per thousand}" BORDER="0"> (Vienna Peedee belemnite) from two additionalsections 6 km and 55 km from the original locality. These negative<IMG SRC="/math/delta.gif" ALT="{delta}" BORDER="0">13Ccarb values were obtained from isopachous cements that fillstromatactis-like cavities, sheet cracks, and fractures, andfrom partially recrystallized carbonate crusts, consistent withcarbonate precipitation at cold methane seeps. The new datasupport a widespread methane release event following the Nantuoglaciation in south China (ca. 635 Ma), which may have contributedto the origin of unusual sedimentary and isotope features ofcap carbonates.
- Publication:
-
Geology
- Pub Date:
- May 2008
- DOI:
- 10.1130/G24513A.1
- Bibcode:
- 2008Geo....36..347W