Methane‐flux‐dependent lateral faunal changes in a Late Cretaceous chemosymbiotic assemblage from the Nakagawa area of Hokkaido, Japan
Methane‐flux‐dependent lateral faunal changes in a Late Cretaceous chemosymbiotic assemblage from the Nakagawa area of Hokkaido, Japan
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DOI：
10.1111/j.1472-4669.2007.00106.x
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发表时间：
2007-06
期刊：
影响因子：
3.7
通讯作者：
R. Jenkins;A. Kaim;Y. Hikida;K. Tanabe
中科院分区：
文献类型：
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作者：
R. Jenkins;A. Kaim;Y. Hikida;K. Tanabe
最近在日本北海道中川地区发现了一个被碎屑岩包围的晚白垩世碳酸盐岩体（最大直径2 m），根据其负碳同位素组成（低至- 43.5‰）、多变的硫化物硫同位素组成、高碳酸盐含量和原位裂缝的特征，被解释为甲烷渗漏矿床。它很可能是由于含甲烷的孔隙水扩散而形成的。我们估计，甲烷的浓度向碳酸盐岩边缘下降，在离甲烷渗漏中心一定距离处，只有少量的碳酸盐岩凝结物沉淀。这些空间特征与观测到的动物分布格局吻合良好。腹足类为主的关联（不确定的深渊纲和无足纲，以及最常见的深渊纲帽贝Serradonta sp.）与lucinid和thyasiid双壳类（Thyasira sp., Myrtea sp.和Miltha sp.）共同发生，并在甲烷衍生的碳酸盐体内部和上方发现。在甲烷影响的沉积物的外围部分，较典型的是粗晶石类（Acharax）和双壳类（Nucinella）。我们认为，这种动物分布模式反映了甲烷和硫化氢浓度从甲烷排放中心向甲烷渗漏外围移动时的下降趋势。
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.