Preliminary Basin Analysis Based on Sedimentary Structures in the Niigata Neogene Basin, Central Japan

Abstract

Sedimentary structure surveys have been conducted in the Niigata basin for the last 5 years as a method of petroleum exploration. Various sedimentary structures in Tertiary formations are observed in this basin. They indicate a significant change of paleocurrent systems between the Hamatsuda and the Nishiyama ages. From the beginning of the Nishiyama (early Pliocene), paleoccurrents began to be controlled by the structural trend which is well defined at present and called the Niigata trend. In other words, folding with the axes of the Niigata trend is considered to grow after the Hamatsuda age (earliest Pliocene).
Looking at simple paleogeographic maps drawn based on paleocurrents, sandstones seem to have been deposited predominantly in the topographic lows in the basin, without any relation to distance from the source of supply. This fact seems to be incompatible with the classic geological theory that the coarser materials are deposited closest to the source of supply. This fact has to be taken into account for petroleum exploration.