Atmospheric methane from organic carbon mobilization in sedimentary basins — The sleeping giant?

Early Eocene climatic optimum: Environmental impact on the North Iberian continental margin

“…The magnitude of the d 13 C decrease is difficult to estimate, as some diagenetic overprint cannot be ruled out for the marlstone record; however, a conservative decrease of 1.5‰ is reliably recorded by limestones. Such a decrease could suggest that 13 C-depleted carbon was extensively released into the ocean-atmosphere system, intensifying the greenhouse effect and contributing to global warming (Kroeger et al, 2011). Such processes are recorded by a 1.19‰ decrease in the Barinatxe-Gorrondatxe d 18 O lime record and eventually caused the abundance and diversity of tropical planktic foraminifera to increase moderately to 69% at 185 m, ~160 k.y.…”

“…Under such circumstances, organic matter decomposition by methanogenic microorganisms enhances pore-water alkalinity and favors authigenic precipitation of carbonate minerals (Huggett et al, 2000;Malone et al, 2002;Hendry et al, 2006). Continental slopes, such as that located at the Eocene North Iberian continental margin, are characterized by high organic matter and sediment supplies, which produce optimal conditions for methanogenesis (D'Hondt et al, 2002;Sivan et al, 2007;Dickens, 2011;Gu et al, 2011;Kroeger et al, 2011).…”

“…The early Eocene climatic optimum has been linked to high atmospheric pCO 2 concentrations and elevated greenhouse gas concentrations (Lowenstein and Demicco, 2006;Zachos et al, 2008;Kroeger et al, 2011). Increased weathering of silicate rocks is the most cited mechanism for the subsequent CO 2 drawdown, which may have been modulated by continental drift across climatic belts (Berner et al, 1983;Smith et al, 2008;Kent and Muttoni, 2013), but changes in the style of subduction have also been suggested (Lee et al, 2013).…”

Thermal evolution of the New Zealand Hikurangi subduction margin: Impact on natural gas generation and methane hydrate formation – A model study

“…Similarly, our modelling results indicate that hydrates containing mainly microbial methane are much more widespread than hydrates containing mainly thermogenic methane, whereas hydrate accumulations formed from thermogenic methane more likely are localized, but with high hydrate saturations. However, methane originating from petroleum source rocks likely has undergone complex fractionation and mixing, and therefore may be difficult to detect (Abrams, 2005;Kroeger et al, 2011;Milkov, 2011).…”

Evidence of a widespread paleo-pockmarked field in the Orange Basin: An indication of an early Eocene massive fluid escape event offshore South Africa

“…The identification of such fossil leakage episodes, both at a local and regional scale, could be part of the evidence for an association between methane release from the geosphere and some of the observed carbon isotopic excursions in the paleoclimatic record, especially for the Paleocene-Eocene Thermal Maximum (e.g. Dickens et al, 1995Dickens et al, , 1997Zachos et al, 2008;Kroeger et al, 2011).…”