During field mapping of Ellef Ringnes Island, Canadian Arctic Archipelago, 139 isolated Early Cretaceous methane seep deposits were found from 75 field sites. Stable isotopes of the carbonates have values of δ13C = −47‰ to −35‰ and δ18O = −4.0‰ to +0.7‰. Isoprenoids in organics from one of the seeps are significantly depleted in 13C, with the most negative δ13C value of −118‰ and −113‰ for 2,6,10,15,19-pentamethylicosane (PMI) and phytane/crocetane, respectively. These values indicate an origin through methane oxidation, consistent with biomarkers that are characteristic for anaerobic methanotrophic archaea within the seep deposits, accompanied by terminally branched fatty acids showing similar 13C values (−92‰) sourced from sulfate-reducing bacteria. The seep deposits contain a moderate-diversity macrofaunal assemblage comprising ammonites, bivalves, gastropods, scaphopods, “vestimentiferan” worm tubes, and brachiopods. The assemblage is dominated numerically by species that probably had chemosymbionts. The seep deposits formed in the subsurface within strong redox zones, in an otherwise normal marine setting, characterized by oxic waters at high paleolatitudes.
While geographically widespread over an area of ∼10,000 km2, seep deposits on Ellef Ringnes Island occur in a narrow stratigraphic horizon, suggesting a large release of biogenic methane occurred over a brief period of time. This gas release was coincident with a transition from a cold to warm climate during the latest early Albian, and we hypothesize that this may have been related to gas hydrate release.
- Received 27 June 2016.
- Revision received 20 December 2016.
- Accepted 21 February 2017.
- © Geological Society of America