HR: 0800h
AN: V41B-0598    [Abstracts]
TI: Origin of fluids from oil/gas fields and hot springs in the Green Tuff region of Japan: ¹²⁹I results from halogen-rich fluids in the Akita and Niigata Basins
AU: * Kashiwagi, Y
EM: Kashiwagi@earth.rochester.edu
AF: University of Rochester, 227 Hutchison Hall, Dept. of Earth and Env. Sci., Rochester, NY 14627, United States
AU: * Kashiwagi, Y
EM: Kashiwagi@earth.rochester.edu
AF: Gakushuin University, Department of Chemistry, Tokyo, 171-8588, Japan
AU: Tomaru, H
EM: tomaru@mail.kitami-it.ac.jp
AF: University of Rochester, 227 Hutchison Hall, Dept. of Earth and Env. Sci., Rochester, NY 14627, United States
AU: Tomaru, H
EM: tomaru@mail.kitami-it.ac.jp
AF: National Institute of Advanced Industrial Science and Technology, Institute for Geo- Resources and Environment, Ibaraki, 305-8567, Japan
AU: Lu, Z
EM: luzunli@earth.rochester.edu
AF: University of Rochester, 227 Hutchison Hall, Dept. of Earth and Env. Sci., Rochester, NY 14627, United States
AU: Fehn, U
EM: fehn@earth.rochester.edu
AF: University of Rochester, 227 Hutchison Hall, Dept. of Earth and Env. Sci., Rochester, NY 14627, United States
AU: Muramatsu, Y
EM: yasuyuki.muramatsu@gakushuin.ac.jp
AF: Gakushuin University, Department of Chemistry, Tokyo, 171-8588, Japan
AB: The Green Tuff region in the Akita and Niigata Basins, Japan, hosts major occurrences of oil and gas as well as of mineral deposits. We measured halogen concentrations and ¹²⁹I/I ratios in oil and gas field brines and hot springs in order to determine the origin of iodine and, indirectly, of hydrocarbons in this area and their association with geological processes during the opening of the Japan Sea. Based on the concentration of iodine, the samples fall into three categories: Group A (I >200μM), Group B (200μM>I >100μM), and Group C (I <100μM). Samples in Groups A and B come predominantly from oil/gas fields and have ¹²⁹I/I ratios below 350×10^-15, corresponding to ages essentially in the Eocene period. In contrast, samples in Group C are generally from hot springs and have ¹²⁹I/I ratios mostly above 400×10^-15, corresponding to Miocene ages. These results indicate that source formations for Group C are associated with the active opening of the Japan Sea, but that those for Groups A and B are organic-rich segments of the late Eocene to Oligocene formations or of the older basement rocks accreted before the opening of the Japan Sea. Because the reservoir formations of oil and gas reservoirs are predominantly of Middle to Late Miocene age, mobilization of these brines could have been associated with the tectonic processes during the opening of the Japan Sea which also led to the formation of the hydrothermal sulfide-sulfate Kuroko Deposits in the same area. The hot springs of Group C probably reflect more directly these processes. Because of the close association of iodine with methane and other hydrocarbons, oil and gas in this area probably is derived also from sources of Eocene age, i.e. considerably older than the Green Tuff formations they currently are residing in.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 3001 Back-arc basin processes
DE: 3075 Submarine tectonics and volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting