Methane‐flux‐dependent lateral faunal changes in a Late Cretaceous chemosymbiotic assemblage from the Nakagawa area of Hokkaido, Japan

Abstract

A Late Cretaceous carbonate body (2 m in maximum diameter) surrounded by clastic rocks, recently discovered in the Nakagawa area (Hokkaido, Japan), is interpreted as a methane‐seep deposit, on the basis of negative carbon isotopic composition (as low as −43.5‰), variable sulphide sulphur isotopic composition, high carbonate content, and in situ fractures. It most likely formed owing to methane‐bearing pore‐water diffusion. We estimate that the concentration of methane decreased toward the margin of the carbonate body, and that only small carbonate concretions were precipitated at a certain distance from the methane‐seep centre. These spatial characteristics coincide well with the observed pattern of faunal distribution. The gastropod‐dominated association (indeterminate abyssochrysids and ataphrids and the acmaeid limpet Serradonta sp. are most common) co‐occurs with lucinid and thyasirid bivalves (Thyasira sp., Myrtea sp., and Miltha sp.), and was found within and just above the methane‐derived carbonate body. Acharax and Nucinella (solemyoid bivalves) are more typical of the peripheral part of the methane‐influenced sediments. We suggest that this pattern of faunal distribution reflects the decreasing concentration of methane and apparently also hydrogen sulphide when moving from the centre of discharge toward the periphery of the methane seep.

First discovery and characterizations of late Cretaceous seep carbonates from Xigaze in Tibet, China

“…Since the "seep-search strategy" was proposed by Campbell and Bottjer [22], more and more ancient seep deposits were discovered and studied. Today, ancient hydrocarbon seeps have already been recognized from Devonian to Quaternary strata in almost all continents based on occurrences of seep carbonates and/or fossil chemosynthetic assemblages [10,13,14,[16][17][18][19][20][23][24][25][26][27][28]. However, seep carbonates are rarely found from ancient strata in the mainland China.…”

Carbonate Sediments Microbially Induced by Anaerobic Oxidation of Methane in Hydrocarbon-Seeps

“…−40‰, whereas the later precipitated minerals have almost 0‰ (vs. PDB; Jenkins et al, 2007b;Fig. 5).…”

“…Two are well investigated, i.e., Yasukawa and Omagari seeps ( Fig. 2; Hikida et al, 2003;Jenkins et al, 2007b). The Yasukawa and Omagari seep deposits are exposed along the Abeshinai River.…”

“…80 million years ago). The Omagari Formation, which is composed of alternating greenish sandstone and sandy siltstone with some intercalations of gravel beds, was deposited on the continental-shelf margin to the continental slope (Jenkins et al, 2007b;Takahashi et al, 2007).…”

“…The body, together with its lateral flank, is representative of the Yasukawa seep as a whole. Using lithological and geochemical signatures as our criteria, we can say that the carbonates were formed under the influence of AOM in a hydrocarbon seep environment (Jenkins et al, 2007b.…”