Abstract
We carried out sequence stratigraphic analyses for the Neogene Shiiya and Nishiyama Formations in the Kitakambara Area of the Niigata Sedimentary Basin in the northern part of Niigata Prefecuture, central Japan. The objective was to clarify the characteristics of depositional sequences in a tectonically active area. Fourteen 4th order depositional sequences (S1∼S5, N1∼N9) and two 3rd order depositional sequences are recognized in the strata by integrating data from surface geology, well log patterns, seismic sections and microfossils. Characteristic relationships between the depositional sequences and fossil foraminifers are recognized as follows ; No. 2 and No. 3 Globorotaria inflata beds correspond to HST (highstand systems tract) of the 3rd order sequences, and dextral-coiling Neogloboquadrina pachyderma dominant zones (SD-1 and SD-3 Zone of Moriya, 1995) correspond to HST and TST (transgressive systems tract). Spatial distribution maps of depositional systems of each 4th order depositional sequence indicate that there were several sediment supply systems, forming submarine fan systems in the basin. Along with these sediment supply systems, coarse clastics were deposited, whereas slope to basin floor mud facies tend to be developed between these supply systems.Compared to the sequence stratigraphic model in a passive margin, the following unique sedimentation is pointed out in the Neogene strata in the Kitakambara Area ; a) As sediment supply frequently varied and shelf territory was narrow, submarine fan systems were prominently developed even in HST of the 3rd order sequences at the basin center. b) Local uplift and fault zones in the basin such as Niitsu Hills, were active during deposition, and then caused areal tectonic onlap surface, submarine hiastus, erosional surface and chaotic sedimentation.Consequently, it is suggested that tectono-stratigraphic analyses should be carried out simultaneously with conventional sequence stratigraphic analysis when analyzing tectonically active basins.
