No abstract

No abstract

No abstract

A controversial stratigraphic section, the Taneichi Formation, is exposed along the Pacific Coast of northeastern Honshu, the main island of the Japanese Archipelago. Although most sediments of the formation have long been dated as late Cretaceous, the northern section of it has been assigned to (i) the Upper Cretaceous; (ii) the Paleogene; or (iii) the Neogene. In the present report, we present the data of palynological and sedimentological studies, showing that the northern section should be assigned to the Neogene. A more important point in the present study is that we invoke some basic principles of fluvial sedimentology to resolve this stratigraphic subject. The lignite layers full of Paleogene–Miocene dinoflagellate cysts and pollen assemblages drape over the boulder‐sized (>40 cm in diameter) clasts in the northern section. However, the layers totally consist of aggregates of small lignite chips, indicating that the lignites are allochthonous materials. The mega‐clasts with derived microfossils in the lignites are thought to have been deposited as Neogene fluvial (flood) sediments in the newly formed Japanese Archipelago. Prior to the Miocene, the northern Honshu was part of the Eurasian Plate, thus the boulder‐sized clasts cannot be envisaged as long river flood deposits along the continental Paleogene Pacific Coast. Instead, the mega‐clasts with the draping lignites were probably derived from nearby Miocene highlands in the newly born island arc.

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.