Untitled research work

The development of petroleum deposits in a basin may generally be controlled by the shape of the basin and by the sedimentary environments. It is very important to clarify the evolutionary changes of the paleoenvironment and paleogeography of the basin for the elucidation of the process of the oil accumulation. Studies on the paleoenvironment and paleogeography of the Niigata Neogene sedimentary basin by the combinations of the isopach, lithofacies and biofacies maps are undertaken parallel with paleoecological analysis of the foraminifera by using computer based on massive recent ecological data. The ecological analysis of foraminifera of more than 200 wells in the Niigata sedimentary basin makes it possible to construct a series of paleoenvironmental maps showing the basin evolution from the Teradomari to the Haizume stages. The biofacies changes and their relationship with thickness of the respective stratigraphic units by the isopach map are analyzed. Consequently, the paleobathymetrical conditions, the bottom confiiguration of sedimentary basin and changes in the structure of the Niigata sedimentary basin can be worked out. The general features of the sedimentary basin during the time of the respective stages which yielded foraminifers as related with development and migration are revealed as shown in the Figs. (1-24). The quantity-distribution (foraminiferal number, arenaceous and shallow foraminifera contents, planktonic/benthonic foraminifera ratios) of foraminifets not only served to indicate the paleogeographical features above mentioned but also are good guides in paleoenvironmental analysis of the respective stages of the Niigata basin. The foraminiferal number in sediments is useful in inferring total organic contents and in determining the organic type, both of which reflect the productivity of marine organism_??_.