Abstract
The types of organic matter in 296 Neogene Tertiary rocks from 11 wells of the Niigata Plain were determined by the visual kerogen method, and the stratigraphical and areal distributions of kerogen types were studied in relation to the paleoenvironment reported in Part 1 by Maiya et al. (1980).
The sapropelic (amorphous) kerogen and arenaceous foraminifera contents have similar stratigraphic trend pattern. The type of organic matter reflects the precursor of kerogen and its depositional environment, and the arenaceous foraminifera contents represent the paleodepth in this area according to Maiya et al. (1980) These suggest that the type of organic matter closely relates to the paleoenvironment.
The relationship between the paleogeography and the kerogen type revealed that the Niigata Plain at the Teradomari to the middle Nishiyama stage has the general tendency such as the deep sea is abundant in the sapropelic kerogen and as the shallow sea is rich in the woody, coaly, and herbaceous kerogen. However, the case that the sapropelic kerogen was not necessarily related to the paleodepth was partialy occurred. This may be considered that amounts of the sapropelic kerogen decreased as following results. (1) the autochthonous sapropelic kerogen was diluted by the allochthonous woody, coaly, and herbaceous kerogen; and (2) the sapropelic kerogen was oxidized easilier than the others, in the case of the input of the sea water by the turbidity current and mass sliding in the deeper depth.
