南部八代海における底生有孔虫の L/Tl 値から見積もられる相対的堆積速度とタフォノミー

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The ratio of the number of living specimens to the total number of living specimens and empty tests (L/Tl value) of benthic foraminifers in the bottom surface sediments has been used as an index of relative sedimentation rate at each sampling station. In an attempt to clarify whether or not the L/Tl values can be applied to shallow and semi-closed inland seas, where high energy current system persist, we analyzed the benthic foraminiferal assemblages in the topmost sediments of 73 core samples collected from 74 stations in southern Yatsushiro Kai (Sea). The L/Tl values were calculated and compared with the sedimentation rates, which were independently estimated by the vertical changes of mercury contents in the cores. It has been shown that the L/Tl values near the straits influenced by strong bottom currents were higher than the expected sedimentation rates, suggesting that the foraminiferal tests had been transported and/or destructed after death. The L/Tl values were also higher in the area of fine-to very fine-grained sand substrata surrounding the straits, a result which can be explained by the post-mortem destruction of the empty tests especially of the species that have a thin test. Furthermore, the L/Tl values in nearshore areas were lower than expected, probably reflecting the extraordinary rainfalls in the last few years that supplied an unusual amount of sediments through rivers. These results indicate that the L/Tl values need to be used with caution when applying to the sediments of shallow inland seas.
日本古生物学会の論文
1998-12-20

南部八代海における底生有孔虫の L/Tl 値から見積もられる相対的堆積速度とタフォノミー

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