Abstract
This paper attempts to construct the sequence stratigraphic framework for the lower to middle portion of thick turbiditic basin-filling successions of the Niigata-Shin'etsu basin, Northern Fossa Magna, central Japan, located in a tectonically active arc-arc junction zone between the NE and SW Japan arcs. Analyses of outcrop sections, well logs and 2D seismic sections in the Nishikubiki-Takada Plain area reveal that the targeted stratigraphic interval, including the upper Neogene Nambayama, Nodani, Kawazume and Nadachi Formations, can be divided into nine third-order depositional sequences: Sequence Nkb-W, -V, -U, -T, -S, -Q, -P, -K and -KZ in a stratigraphic ascending order. In accordance with previously proposed turbidite sequence models, each depositional sequence shows characteristic stacking patterns of turbidite facies successions, which can be used for dividing the sequences into systems tracts. The lower to middle part of the sequence, consisting of relatively sandy turbidites with stacks of upward-fining and overlying upward-coarsening successions, may correspond to FSST (falling-stage systems tract) and LST (lowstand systems tract). The overlying upward-fining part corresponds to TST (transgressive systems tract), and the obscure upward-coarsening part at the top of the sequence, corresponds to HST (highstand systems tract). The TST to HST intervals of some sequences contain characteristic foraminiferal assemblage zones; e.g., Globorotalia rikuchuensis zone, Blue zone, and No. 3 Globorotalia inflata bed, all of which indicate the inflow of an open-sea ocean current into the Sea of Japan during a relative sea-level rise and highstand. This characteristic pattern of turbidite sequence succession seems to vary in response to the submarine-fan type; e.g., sandy radial fan and channel levee system. The present results represent fundamental information for basin-wide correlations and the reconstruction of tectono-sedimentary processes of the Fossa Magna region.
