Abstract
Vitrinite reflectance (Re%, mean random reflectance) was measured on the collinite macerals separated from the Neogene clastic sediments distributed in the Nishikubiki area of the northern Fossa Magna region. In this study, samples were collected from two regions, the North (N) and the South (S), along the limbs of the Nambayama anticline in the western part of Joetsu City.
The regression lines between log Re(%) and stratigraphic horizon based on thickness of the sediments in the study area show similar gradients with those of the MITI exploratory test wells around this area. This result suggests that the nearly same maximum paleotemperature gradient prevailed in the Nishikubiki area.
Vitrinite reflectance values between the two regions show that the South region is about 0.6% higher than the North region at the same stratigraphic horizon of the Nambayama Formation, suggesting about 1700m difference in original burial depth.
