Changes in depositional systems and sequences in response to basin evolution in a rifted and inverted basin: an example from the Neogene Niigata-Shin'etsu basin, Northern Fossa Magna, central Japan

Abstract

The Niigata-Shin'etsu basin, which occurs along the eastern margin of the Sea of Japan, was generated in Middle Miocene time as a failed rift basin in relation to the backarc opening of the Japan arc, and was converted to a compressional basin in Late Miocene time. The basin-filling succession can be divided into four tectonostratigraphic units (stages), based on characteristics of depositional systems, depositional sequences, tectonic-subsidence rate, and sediment supply. These units coincide in time with major tectonic events during backarc rifting and subsequent basin inversion. Unit I (16–13.5 Ma) represents a syn-rift stage, characterized by rapid basin subsidence. The rate of accommodation exceeded the rate of accumulation, resulting in a retrogradational stacking pattern of muddy slope to basin floor systems. Unit II (13.5–6.5 Ma) represents a post-rift thermal-subsidence stage. The rate of accommodation nearly equaled the rate of accumulation, resulting in an aggradational stacking pattern of five third-order depositional sequences, mainly comprising submarine-fan turbidite systems affected by supply of coarse clastics. Unit III (6.5–1 Ma) represents the basin-inversion stage, showing no subsidence or uplift. The accumulation rate exceeded the rate of accommodation, resulting in rapid progradation of depositional sequences composed of slope, shelf, shallow-marine, delta, and fluvial systems. Unit IV (1 Ma–present) represents an intense compressional stress field; sedimentation has been restricted to a synclinal area due to syndepositional folding and uplift. Changes in basin subsidence rate and sediment supply, resulting from tectonics and climate change in the basin and the provenance, strongly affected characteristics of the depositional systems and sequences. The change in basin subsidence also created a basinwide depositional cycle, whereas eustasy-affected relative sea-level changes created higher-order depositional sequences during relatively stable phases of tectonics.