Extensive Early Cretaceous (Albian) methane seepage on Ellef Ringnes Island, Canadian High Arctic

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 delta (super 13) C = -47 ppm to -35 ppm and delta (super 18) O = -4.0 ppm to +0.7 ppm. Isoprenoids in organics from one of the seeps are significantly depleted in (super 13) C, with the most negative delta (super 13) C value of -118 ppm and -113 ppm 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 (super 13) C values (-92 ppm) 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 approximately 10,000 km (super 2) , 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.