SAKAI, TETSUYA, The University of Tsukuba, Ibaraki, Japan; and FUJIO MASUDA, Osaka University, Osaka, Japan

ABSTRACT: Parasequence Sets in the Plio-Pleistocene Kakegawa Group, Shizuoka, Japan

The Plio-Pleistocene Kakegawa Group crops out in the western Shizuoka Prefecture, central Honshu, Japan. The Kakegawa Group consists of successive deposits from alluvial fan to continental slope and submarine fan environments. Chronological studies based on biostratigraphy, magnetostratigraphy and fission-track dating, show this group ranges from 3 to 1 Ma in age. This group corresponds to a third order depositional sequence and the thickness is 150 to 300 m. Stratigraphic analysis of volcanic ash layers verify onlap-downlap relation, and lowstand, transgressive and highstand systems tracts are recognized.

The transgressive and highstand systems tracts are characterized by coasening and shallowing upward cycles, that is parasequence sets. Gravel or sandy lag deposits are on the parasequence boundaries at shoreface to shelf environments. Condensed zones are recognized at outer shelf to slope environments, directly on or slightly above the parasequence boundaries. Gravelly channel-fill and longshore bar deposits are well developed in the parasequence sets of the transgressive systems tract, but are not found in the highstand one.

According to the fission track-dating, a transgressive-regressive cycle of the Kakegawa Group can be correlated to global eustatic sea-level curve represented by oxygen isotope ratio of foraminifera tests. This indicates that the depositional sequence is controlled mainly by global eustatic sea-level change. Particularly, the number of parasequences between 1.9 and 1.6 Ma roughly corresponds with the number of several tens of (Ky) cycles of global eustatic sea-level curve. Lithological interfingering is well explained by the development of the parasequence sets.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.