A comprehensive approach to the study of methane‐seep deposits from the Lincoln Creek Formation, western Washington State, USA

Abstract

A comprehensive approach using palaeontology, petrography, stable isotope geochemistry and biomarker analyses was applied to the study of seven small methane-seep carbonate deposits. These deposits are in the Oligocene part of the Lincoln Creek Formation, exposed along the Canyon and Satsop Rivers in western Washington. Each deposit preserves invertebrate fossils, many representing typical seep biota. Authigenic carbonates with d 13 C values as low as )51& PDB reveal that the carbon is predominately methane derived. Carbonates contain the irregular isoprenoid hydrocarbons 2,6,11,15tetramethylhexadecane (crocetane) and 2,6,10,15,19-pentamethylicosane (PMI), lipid biomarkers diagnostic for archaea. These lipids are strongly depleted in 13 C (d 13 C values as low as )120& PDB), indicating that archaea were involved in the anaerobic oxidation of methane. Small filaments preserved in the carbonate may represent methanotrophic archaea. Archaeal methanogenesis induced the formation of a late diagenetic phase, brownish calcite, consisting of dumbbell-shaped crystal aggregates that exhibit d 13 C values as high as +7& PDB. Clotted microfabrics of primary origin point to microbial mediation of carbonate precipitation. Downward-directed carbonate aggregation in the seeps produced inverted stromatactoid cavities. Large filaments, interpreted as green algae based on their size, shape, arrangement and biomarkers, imply that deposition occurred, in places, in water no deeper than 210 m.

Changing redox conditions at cold seeps as revealed by authigenic carbonates from Alaminos Canyon, northern Gulf of Mexico

“…To date, only two locations in the GoM are known, namely Bush Hill (Feng et al, 2009a) and Chapopote (Naehr et al, 2009), that have seep carbonates dominated by aragonite. The carbonate microfabrics found in AC 645 samples are similar to those of other seep deposits (Roberts and Aharon, 1994;Naehr et al, 2000Naehr et al, , 2009Peckmann et al, 2002;Feng et al, 2009a;Feng and Roberts, 2010;Roberts et al, 2010a). Botryoidal aragonite has been interpreted as microbially induced carbonate phase (Roberts et al, 1993).…”

Carbonate-hosted methanotrophy represents an unrecognized methane sink in the deep sea

“…13 C-depleted lipids such as crocetane and archaeol at Aleutian margin seeps 27 , lipids and ANME 16S rRNA genes at Gulf of Cadiz structures 28 , and an ANME-2-derived extended sn-2-hydroxyarchaeol found in multiple seep carbonate mounds 29 are all suggestive of methanotrophic archaeal involvement, but offer limited insight on contemporary metabolic activity. The presence of biomarkers within mounds is often used forensically in an effort to reconstruct antecedent microbial communities and past conditions of carbonate precipitation 30 ; such studies have offered evidence of AOM and methanogenesis in association with authigenic carbonates during and potentially after their formation 31 . The suggestion of microbial involvement with carbonate crust formation 20 , predicated on the detection of low-abundance ANME 16S rRNA gene sequences and 13 C-depleted archaeal lipids, challenged the interpretation of carbonate precipitation products as exclusively fossil deposits.…”

Paleocene methane seep and wood-fall marine environments from Spitsbergen, Svalbard

“…Beauchamp and Savard, 1992;Peckmann et al, 2002;Hammer et al, 2011). It might be formed due to the recrystallization of the yellow aragonite precursor, precipitated in the immediate vicinity of the methanotrophic consortia participating in AOM (Hagemann et al, 2012).…”

“…Those comprise mostly fossil forearc (e.g. Peckmann et al, 2002;Kuechler et al, 2012), rift (e.g. Gaillard et al, 1992;Kaim et al, 2013), and backarc basins (e.g.…”