Chronostratigraphic correlation of the Shiose-no-misaki Sandstone and Conglomerate, Oga Peninsula, NE Japan

Abstract

The Shiose-no-misaki Sandstone and Conglomerate SSC in the Oga Peninsula is believed to represent SSC in the Oga Peninsula is believed to represent SSC a latest Eocene to early Oligocene marine succession located on the back-arc side of NE Japan. This unit is, however, isolated from adjacent units, and its stratigraphic position has remained in debate. On a sea cliff adjacent to the type locality of the SSC, surface soil and vegetation recently slid down by heavy rain to disclose a succession that contains the SSC, surface soil and vegetation recently slid down by heavy rain to disclose a succession that contains the SSC SSC and the SSC and the SSC overlying early Miocene non-marine unit correlative to the Daijima Formation. The SSC at the new outcrop comprises scoria-SSC at the new outcrop comprises scoria-SSC lapilli tuff and parallel to wavy laminated fi ne sandstone, both of which are intruded in dike by thinly bedded pumicelapilli tuff, pumice-bearing tuff, sandstone and mudstone as observed also in the adjacent SSC. The overlying succession is SSC. The overlying succession is SSC over 20 m thick and dominated by massive very coarse to coarse sandstone with a basal, normally graded cobble to granule conglomerate 1.3 m thick. Pumice lapilli tuff occurs between the conglomerate and the overlying sandstone with a thickness of 30 cm, and tuffaceous mudstone and coaly shale beds 20 to 30 cm thick occur in between the sandstone. The conglomerate and sandstone commonly contains gravels and/or sand grains of dacite welded tuff derived from the adjacent early Miocene Hokakejima Dacite the lowest unit of the Daijima Formation . Pumice lapilli tuff in the upper unit is 20 Ma in FT age, suggesting slightly younger than the FT ages of 22-21 Ma for the Hokakejima Dacite. The pollen assemblage from the SSC likely refl ects a cool temperate climate that might have prevailed in accordance with Oligocene to Early Miocene cooling. We thus suggest the SSC is a part of the late Eocene to early Oligocene Monzen Formation extensively distributed to the west of SSC is a part of the late Eocene to early Oligocene Monzen Formation extensively distributed to the west of SSC Cape Shiose-no-misaki.

High-temperature emplacement and liquefaction of shallow-water caldera-forming eruption products: Early Miocene Tateyamazaki Dacite in the Oga Peninsula, NE Japan

“…Progressive thermal demagnetization was conducted up to a peak temperature of 650°C by heating in air using a non-inductively wound electric furnace at incremental temperatures of 25 to 100°C. The paleomagnetic data obtained for HKJ-01, SSM-01, SSM-06 and TYZ-02 have been already reported in Kano et al (2008) and Sato et al (2009) for their stratigraphic discussion. They are hereafter referred to and discussed together with a set of newly obtained data.…”

“…12), that have a normal polarity, D/I = −53.0°/57.6°(α 95 = 11.6°) (Sato, 2006). Scoria fragments from SSM-02 and other sites of Cape Shiosenomisaki are correlative in age with the Eocene/Oligocene Monzen Formation (Kano et al, 2008), but their tilt-corrected mean TRM vector is also different from that of the Monzen Formation (Tosha and Hamano, 1988). Small blocks of fine tuff and pumice lapilli tuff mutually intermingle to form a large domain at site TYZ-05.…”

“…20 Ma (Yoshida et al, 2004). The pumice lapilli tuff collected from the relatively homogeneous part of the Tateyamazaki Dacite is dated at 21 Ma, and a thin bed of pumice lapilli tuff in the overlying non-marine sediments of the upper Daijima Formation has an age of 20 Ma (Kano et al, 2008), suggesting a relatively short period of repose between the volcanic rocks of the Daijima Formation.…”