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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.

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: Wood-fall associations from Late Cretaceous deep-water sediments of Hokkaido, Japan. Lethaia , Vol. 42, Sunken wood (wood-fall) in the deep sea today is colonized and consumed by diverse invertebrate communities that show phylogenetic relationships to the chemotrophic fauna on whale carcasses, hydrothermal vents and hydrocarbon seeps. Here we document Late Cretaceous examples of wood-fall communities from deep-water sediments of the Yezo Group on Hokkaido, Japan, consisting of provannid, skeneiform, and patelliform gastropods, and thyasirid and nuculanid bivalves. These species are similar or identical to those found on plesiosaur bones and at hydrocarbon seeps in the same sediments, showing that many members of the modern chemotrophic deep-sea fauna colonized this range of habitats at least since Late Cretaceous time. We also document for the first time faecal chimneys in boreholes in these wood fragments, which were presumably built by xylophagain bivalves. ᮀ Chemosynthetic communities , deep sea ,

Sixteen gastropod species from two Campanian (Upper Cretaceous) PAN, ul. Twarda 51/55, Poland; HADEEP, Ocean Research Institute, University of Tokyo, Japan; Yoshinori Hikida [nmhikida@coral.ocn.ne.jp

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