@article{oai:soar-ir.repo.nii.ac.jp:00020464, author = {西村, 瑞恵 and 保柳, 康一}, issue = {4}, journal = {地質学雑誌}, month = {Apr}, note = {The Northern Fossa Magna region is situated at the junction of the Northeast and Southwest Honshu arcs. The Middle to Late Miocene Aoki and Ogawa formations occur in the Komiji Syncline area in the southern part of the Northern Fossa Magna region. The Aoki and Ogawa formations in the study area are divided into thirteen sedimentary facies. On the basis of facies analysis, the upper part of the Aoki Formation was deposited at continental slope and outer shelf, while the Ogawa Formation was at inner shelf and various coastal environments. Within these formations there are conglomerate beds deposited on the transgressive surfaces.
The assemblages of sedimentary facies are characterized either by coarsening-upward or fining-upward features. The coarsening-upward facies assemblage resulted from the regression in a coastal environment, whereas the fining-upward facies assemblage from the regression in a barrirer environment. The distribution and stacking pattern of these regressive facies successions reveal a progradational system of coastal and strand-plain environments, followed by an aggradational system of coastal and barrier island environments and then by a repeat of the progradation-aggradation cycle. The progradational system along the coast resulted from a decrease in accommodation, whereas the aggradational system along the coast depended on an increase in accommodation. Changes in accommodation are equivalent to relative sea-level changes. Therefore, the relative sea-level curve can be described from the changes of accommodation.
The relative sea-level of this area changed in response to eustacy, estimated from the Haq curve. Therefore, the framework of sequence stratigraphy may be applicable to this and other basins of this active region. Two sequence boundaries can be identified in the study area. The lower sequence boundary is placed between the Aoki Formation and the Ogawa Formation, and the other can be identified in the middle part of the Ogawa Formation. These correspond to the 10.5Ma and 8.2Ma sequence boundaries of the eustacy curve, respectively.
Accommodation is a function of bouth eustacy and subsidence. The subsidence of the basin can be calculated from the accommodation and eustacy. This basin subsided during deposition of the Ogawa Formation (from 10Ma to 6Ma) at a rate of 60m per 1Ma Uncorrected for compaction., Article, 地質学雑誌.98(4):337-354(1992)}, pages = {337--354}, title = {陸棚斜面-陸棚-沿岸の堆積システムの変遷と相対的海水準変動 : 北部フォッサマグナ地域中新統青木層・小川層のシークェンス層序学}, volume = {98}, year = {1992} }