シーケンス層序学 その可能性を求めて 背弧堆積盆地におけるシーケンス解析 新潟県蒲原地域の例

Abstract

Sequence stratigraphy has been rapidly spreading in the world and causes various sort of debates because sequence stratigraphic interpretations related to mechanisms of deposition make possible three-dimensional estimation of facies distribution and worldwide correlation of strata. The “Exxon Model”, as a basin fill model, has been paid much attention because it displays the significance in the basic concept of sequence stratigraphy and possibilities of applications. The “Exxon Model” which has been constructed as a depositional model for passive margin basins represented by gentle subsidence and relatively stable deposition, however, might not always be applicable to some sedimentary basins without careful considerations for their tectonic and depositional settings.In the Niigata sedimentary basin, as a representative back-arc basin located on central Japan, hydrocarbon exploration for several decades has resulted in a large accumulation of subsurface geologic information. Three-dimensional studies for sequence stratigraphic framework within a back-arc tectonic setting, therefore, are available in this basin.As a result of this study, 12 third and fourth order depositional sequences, which are interpreted to have been formed by relative change of sea level, are now recognized. These depositional sequences are superimposed on a part of a second order depositional sequence considered as a tectonically controlled sequence. The features of fifth or sixth order depositional sequences are superimposed locally in the deposits of the Niigata sedimentary basin. The depositional history of the Niigata sedimentary basin can be divided into following 5 stages, based on the disclosed sequence stratigraphic framework of this basin.i) stage of sedimentary basin formationii) stage of turbidite deposition at basin flooriii) stage of slope progradationiv) stage of shelf extensionv) stage of delta progradation