The Lower Cretaceous (Barremian) Kuhnpasset sedimentary sequence of northeast Greenland contains many carbonate deposits in different stratigraphic positions in the area of Wollaston Forland, several of which have previously been identified as having a hydrocarbon seep origin based on their macrofossil content and morphology. Most of the seep carbonates contain complex internal microfabrics, including abundant yellow calcite and banded and botryoidal cement with δ13C values as low as −54 ‰. These δ13C values are characteristic of carbonate microfabrics with biogenic methane as the major carbon source and carbonate authigenesis caused by sulfate-driven anaerobic oxidation of methane (SD-AOM). Such 13C-depletion confirms a methane seep origin of most of the Kuhnpasset carbonate deposits. Molecular fossils from the seep carbonates prove methanotrophic archaea were involved in the SD-AOM consortia, based on 13C-depleted 2,6,10,15,19-pentamethylicosane (PMI; δ13C: −122 to −113 ‰) and the co-eluting crocetane and phytane (−124 to −105 ‰). The carbon source for the Kuhnpasset seeps was biogenic methane with a δ13C value of approximately −70 ‰, as calculated from compound-specific δ13C values of archaeal lipid biomarkers. The δ13C values of the biomarkers of sulfate-reducing bacteria, the synthrophic partners of archaea in SD-AOM, including iso- and anteiso-C15/17 fatty acids are less 13C-depleted (−107 to −87 ‰) than the archaeal biomarkers – a pattern known from modern seep environments. Preservation of bacterial fatty acids is rare for Mesozoic seep deposits, revealing excellent biomarker preservation and low thermal maturity of the Kuhnpasset seep deposits. The common isoprenoid hydrocarbon biomarkers of SD-AOM in the Kuhnpasset seep carbonates are accompanied by 13C-depleted isoprenoic acids (phytanoic acid: −112 to −101 ‰); these compounds are attributed to the early degradation of glycerol diether membrane lipids such as archaeol or sn2-hydroxyarchaeol, which are not preserved in the samples. Similarly, regular PMI-acid (−120 to −107 ‰) probably represents a derivative of extended archaeol or extended hydroxyarchaeol. The molecular fossil inventories in the Kuhnpasset seep carbonates and the predominance of early diagenetic banded and botryoidal cement are characteristic of the dominance of ANME-2 consortia adapted to high methane flux with the sulfate-methane transition zone (SMTZ) positioned at shallow sediment depth. Abundant wood fragments and well-preserved leafy conifer shoots enclosed in the Kuhnpasset seep deposits indicate a shallow marine paleoenvironment of deposition close to the former shoreline.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)