Stable isotopic evidence for methane seeps in Neoproterozoic postglacial cap carbonates

LDEO Publication: 
Publication Type  Journal Article
Year of Publication  2003
Authors  Jiang, G. Q.; Kennedy, M. J.; Christie-Blick, N.
Journal Title  Nature
Volume  426
Issue  6968
Pages  822-826
Journal Date  12/2003
ISBN Number  0028-0836
Accession Number  ISI:000187342000053
LDEO Publication Number  6549
Key Words  earths coldest intervals; snowball earth; gas hydrate; precipitation; excursions; deposits; dissociation; paleocene; record; USA

The Earth's most severe glaciations are thought to have occurred about 600 million years ago, in the late Neoproterozoic era(1,2). A puzzling feature of glacial deposits from this interval is that they are overlain by 1-5-m-thick 'cap carbonates' (particulate deepwater marine carbonate rocks) associated with a prominent negative carbon isotope excursion(3-8). Cap carbonates have been controversially ascribed to the aftermath of almost complete shutdown of the ocean ecosystems for millions of years during such ice ages - the 'snowball Earth' hypothesis(4,5). Conversely, it has also been suggested that these carbonate rocks were the result of destabilization of methane hydrates during deglaciation and concomitant flooding of continental shelves and interior basins(3). The most compelling criticism of the latter 'methane hydrate' hypothesis has been the apparent lack of extreme isotopic variation in cap carbonates inferred locally to be associated with methane seeps. Here we report carbon isotopic and petrographic data from a Neoproterozoic postglacial cap carbonate in south China that provide direct evidence for methane-influenced processes during deglaciation. This evidence lends strong support to the hypothesis that methane hydrate destabilization contributed to the enigmatic cap carbonate deposition and strongly negative carbon isotopic anomalies following Neoproterozoic ice ages. This explanation requires less extreme environmental disturbance than that implied by the snowball Earth hypothesis(4,5).


754QMTimes Cited:61Cited References Count:26

URL  <Go to ISI>://000187342000053
DOI  Doi 10.1038/Nature02201