Groundwater evolution processes in the sedimentary formation at the Horonobe, northern Hokkaido, Japan

Stable and noble gas isotopic study of thermal and groundwaters in northwestern Hokkaido, Japan and the occurrence of geopressured fluids

“…Water-rock interactions and mixing are considered to be the dominant evolution processes of the groundwater. However, the Na-Cl type waters have unusually high δD values and low Cl concentrations of -20 to -30‰ and 5,000 to 6,000 mg/L, respectively (Ishii et al, 2006), similar to those of sample No. 8 in the present study.…”

“…These results indicate that groundwater with a high proportion of the 3rd component is widely distributed in the deeper part of this area in the Wakkanai Formation. The enrichment factor (∆D) is defined as the difference between δD that a sample would have if it originated by simple dilution of current sea water by local meteoric water (using the Cl content of the sample to estimate the degree of dilution), and the observed δD of the sample (Ishii et al, 2006). The ∆D increases up to 45‰ at depths below -500 m, where opal A changes to opal CT. At this depth, the H 2 O + contents in the rocks decreases by 2 wt% (Ishii et al, 2006).…”

“…Recently, geopressured fluids with unusually high δD (-20‰) and low Cl concentration (ca. 6,000 mg/L) have been observed along faults in several localities in Japan, e.g., Niigata (Oki et al, 1999;Xu et al, 2006), Horonobe (Ishii et al, 2006), Mobara gas field (Maekawa et al, 2006), and Miyazaki (Ohsawa and Ohi, personal comm.). Fluids in mud volcanoes in various part of the world also have such high δD (-20‰) and low Cl concentrations (e.g., Dia et al, 1999).…”

“…Fluids in mud volcanoes in various part of the world also have such high δD (-20‰) and low Cl concentrations (e.g., Dia et al, 1999). Ishii et al (2006) examined the isotopic and chemical compositions of formation waters in the Horonobe area, including sample No. 8 of the present study (Toyotomi Spa.…”

“…Recently, fluids that have oilfield-like characteristic, with unusually high δD (-20‰) and low Cl concentrations (ca. 6,000 mg/L) have been observed along faults in the Horonobe area (Ishii et al, 2006). These fluids might have originated as a mixture between sea water and Stable and noble gas isotopic study of thermal and groundwaters in northwestern Hokkaido, Japan and the occurrence of geopressured fluids (Received July 14, 2009; Accepted June 7, 2010) Thermal and groundwaters are distributed along the west coast and in the inland region of Northwestern Hokkaido, Japan.…”