Vitrinite reflectivity and authigenic minerals in the Neogene sediments of the Green Tuff region, Japan.

Abstract

The Neogene strata of the Green Tuff region have a thickness of several thousand meters, of which pyroclastic sediments constitute the dominant part. Authigenic mineral zones in the Neogene strata are arranged in descending order: fresh glass zone, clinoptilolite-mordenite zone, analcime zone, and albite zone.
Coals and finely dispersed coaly particles in the sediments were used for measuring the vitrinite reflectivity. The reflectivity measurements at the boundary between fresh glass and clinoptilolite-mordenite zones are about 0.3%. Present data are insufficient to determine vitrinite reflectivity at the top of analcime and albite zones. Past temperature estimated from the vitrinite reflectivity measurements in each zone is within the limits of the temperature stability of the diagnostic minerals in each zone. In general, the vitrinite reflectivity in the Miocene sediments of the Green Tuff region is higher than that of coals in the Paleogene coalfields which are of commercial importance in Japan. The higher reflectivity of the Green Tuff region is due to the volcanic activities in the Neogene time.