No abstract

No abstract

A fauna of provannid and provannid‐like shells is described from Upper Cretaceous seep carbonates in Hokkaido, Japan. We describe two new provannid species, Provanna tappuensis sp. nov. and Desbruyeresia kanajirisawensis sp. nov., with preserved protoconchs of unquestionable provannid type with decollate apex. This material confirms the occurrence of Provannidae as early as the Middle Cenomanian. We also describe Hokkaidoconcha gen. nov. and a new family Hokkaidoconchidae fam. nov., with two named species, H. hikidai sp. nov. and H. tanabei sp. nov. Hokkaidoconchidae are possibly related to the Provannidae, judging from a similar, but not decollate larval shell, although the juvenile teleoconch whorls differ in being of a general cerithimorph appearance and the details of the aperture are unknown. Furthermore, we review the published fossil record of Provannidae and Abyssochrysidae, and we consider that in those older than the Eocene, there is no evidence preserved that unequivocally supports a position there. The Jurassic Acanthostrophia acanthica from Italy seems to be the oldest known record of Abyssochrysidae, and the most reliable occurrence of the family, older than from the Miocene. Other fossil, pre‐Miocene species that have been classified in the Abyssochryssidae are provisionally referred to Hokkaidoconchidae. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154, 421–436.

No 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.

The objective of this report is to document first Mesozoic occurrences of chemosynthesis-based Tokyo, Tokyo, Japan; Yoshitsugu Kobayashi ykobayashi@museum.hokudai.ac.jp and Hiroki Echizenya etizen@museum.hokudai.ac.jp, Hokkaido University Museum, Kita 10, Nishi 8, Sapporo, Hokkaido, Japan; Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see creativecommons.org), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

No abstract

No abstract