ODP Site797から見い出された燐酸塩岩層の有機地球化学的特徴

概要

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Phosphatic mudstone layers have been found from the depth 465-485mbsf, ODP Site 797, Japan Sea. The only phosphatic mineral detected by XRD was apatite. Total organic carbon (TOC), total sulfur and lipids were determined for 17 siliceous mudstone and 9 phosphatic mudstone samples. Phosphatic mudstone are characterized by (1) higher TOC content relative to that of the siliceous mudstone; (2) the C/S ratio was observed to exhibit a significant increase at the phosphatic mudstone layer, defining the lower siliceous with a low value from the upper siliceous zone with a high value; (3) n-alkane distribution consisting of a mixture of high molecular weight components with odd predominance (land plant origin) and low molecular weight homologs without odd predominance (bacteria origin); (4) pristane/phytane ratios in the range 1.14-2.30 with an average of 1.67; (5) high C_<27>/C_<29> and C_<27>/C_<28> sterane ratios showing relatively large input of diatoms; (6) abundant of neohop-13(18)-ene and hop-17(21)-ene originated from bacteria. CPI (Carbon Preference Index) and hopanoid based ββC_<31>/(ββ+βα+αβ)C_<31> ratio do not change at the zone boundary of diagenetic silica minerals. The maturation of organic matter has not been affected by diagenetic silica mineral zoning, and quartz does not act as a catalyst.
日本有機地球化学会の論文
1998-12-25