Abstract
Mudstones of the Middle to Upper Miocene Teradomari Formation are considered to be the main petroleum source rocks for the oil fields in Niigata and, at the type locality, are classified as turbidite (Et) and (hemi) pelagic (Ep) mudstones, according to Bouma sequence division.
Hopanes, steranes and other alkanes extracted from the mudstones were analyzed by GC and GC-MS. Oleanane/hopane ratios and sterane composition suggest that Et contains more terrestrial organic matter than Ep. This result is consistent with the maceral composition (Watanabe and Akiyama, 1996).
Pristane/phytane ratios indicate more anoxic depositional environment of Ep than Et in the Upper Teradomari Formation, while there is no difference between Et and Ep in the Lower Teradomari Formation.
Chemical composition of the pyrolysates of kerogens is different between Et and Ep in the Upper Teradomari Formation in n-alkene/n-alkane ratios and relative amounts of trisnorhopene and C17 isoprenoid. These results are also consistent with the maceral composition of the kerogens.
