石油探鉱における石灰質ナンノ化石の役割

その生層序学, シーケンス層序学および古海洋学的有効性

抄録

Calcareous nannofossil as a powerful tool for petroleum exploration was discussed from the aspects of biostratigraphy, sequence stratigraphy and paleoceanography.
This minute fossil is a biostratigraphically useful indicator, especially for the Plio-Pleistocene and the lower to middle Miocene marine sediments distributed along the coast of the Sea of Japan in the northeast of Japan. It is utilized for the recognition and distinction of the three foraminiferal markers, Globorotalia inflata beds, otherwise frequently confused each other.
Calcareous nannofossil is used for sequence stratigraphic analysis as well, in petroleum exploration. The peaks of calcareous nannofossil abundance are assigned to the condensed sections in the Gulf of Mexico. They are widely traceable in the region, and they are also useful for the identification of sequences and systems tracts. The change of calcareous nannofossil assemblages caused by sea level changes was apparently recognized in the Quaternary section of boreholes drilled on the edge of the shelf.
Finally, calcareous nannofossil is applied to the reconstruction of paleoceanographic changes in the pelagic environment. The T_N value based on the composition of the Recent calcareous nannoplankton shows a good correspondence with the δ¹⁸O curve in three cores collected from the Tasman Sea. The T_N curves are obviously related to glacial/interglacial cycles. Therefore, it indicates that the change of sea surface temperature was recorded as the change of nannofloral assemblage.