Miura Peninsula Research Articles

Anin situVesicomyid-dominated Cold-seep Assemblage from the Lowermost Pleistocene Urago Formation, Kazusa Group, Forearc Basin Fill on the Northern Miura Peninsula, Pacific Side of Central Japan

Abstract. We describe the modes of occurrence of a vesicomyid-dominated fossil assemblage in the lowermost Pleistocene Urago Formation, a forearc basin fill on the Miura Peninsula, Pacific side of central Japan. The assemblage consists mostly of Calyptogena (Archivesica) kawamurai (Kuroda) with a minor amount of Conchocele bisecta (Conrad). The shells occur in cross-bedded and massive sandstones of an outcrop that is approximately 25 m wide and 10 m high. The sandstones are interpreted to have been formed by migration of dunes under northward- to eastward-directed bottom currents, judging from the dips of their foreset laminae. Many of the shells are disarticulated and show evidence of reworking by bottom currents, as indicated by their convex-up positions with their commissure planes dipping southwestward (up-current direction) or concordant with the cross laminae. In the massive sandstones, some articulated vesicomyids are preserved in their life position, that is, perpendicular to the bedding plane wit...

Geology and age model of the Lower Pleistocene Nojima, Ofuna, and Koshiba Formations of the middle Kazusa Group, a forearc basin‐fill sequence on the Miura Peninsula, the Pacific side of central Japan

AbstractWe present field and core observations, nannofossil biostratigraphy, and stable oxygen isotope fluctuations in foraminiferal tests to describe the geology and to construct an age model of the Lower Pleistocene Nojima, Ofuna, and Koshiba Formations (in ascending order) of the middle Kazusa Group, a forearc basin‐fill succession, exposed on the northern Miura Peninsula on the Pacific side of central Japan. In the study area, the Nojima Formation is composed of sandy mudstone and alternating sandy mudstone and mudstone, the Ofuna Formation of massive mudstone, and the Koshiba Formation of sandy mudstone, muddy sandstone, and sandstone. The Kazusa Group contains many tuff beds that are characteristic of forearc deposits. Thirty‐six of those tuff beds have characteristic lithologies and stratigraphic positions that allow them to be traced over considerable distances. Examination of calcareous nannofossils revealed three nannofossil datum planes in the sequences: datum 10 (first appearance of large Gephyrocapsa), datum 11 (first appearance of Gephyrocapsa oceanica), and datum 12 (first appearance of Gephyrocapsa caribbeanica). Stable oxygen isotope data from the tests of the planktonic foraminifer Globorotalia inflata extracted from cores were measured to identify the stratigraphic fluctuations of oxygen isotope ratios that are controlled by glacial–interglacial cycles. The observed fluctuations were assigned to marine isotope stages (MISs) 49–61 on the basis of correlations of the fluctuations with nannofossil datum planes. Using the age model obtained, we estimated the ages of 24 tuff beds. Among these, the SKT‐11 and SKT‐12 tuff beds have been correlated with the Kd25 and Kd24 tuff beds, respectively, of the Kiwada Formation on the Boso Peninsula. The Kd25 and Kd24 tuff beds are widely recognized in Pleistocene strata in Japan. We used our age model to date SKT‐11 at 1573 ka and SKT‐12 at 1543 ka.

Promotion of education for disaster mitigation connecting administration and local residents -Challenge of the Research Group for Active Faults in the Miura Peninsula-

Promotion of education for disaster mitigation connecting administration and local residents -Challenge of the Research Group for Active Faults in the Miura Peninsula-

Radiolarian biostratigraphy of the Zushi Formation in the northern part of the Miura Peninsula, central Japan, and a proposal defining the RN9 subzone

Radiolarian biostratigraphy of the Zushi Formation in the northern part of the Miura Peninsula, central Japan, and a proposal defining the RN9 subzone

Lithology and upper boundary of the Olduvai Subchronozone in a core recovered from the middle Kazusa Group (Lower Pleistocene) on the Miura Peninsula, Pacific side of central Japan

Lithology and upper boundary of the Olduvai Subchronozone in a core recovered from the middle Kazusa Group (Lower Pleistocene) on the Miura Peninsula, Pacific side of central Japan

Neogene-Quaternary boundary of the Miura-Kazusa Groups in Miura peninsula

Neogene-Quaternary boundary of the Miura-Kazusa Groups in Miura peninsula

Submarine landslide structure in the lower Pleistocene slope deposits, exposed at the Miura Peninsula, central Japan.

Submarine landslide structure in the lower Pleistocene slope deposits, exposed at the Miura Peninsula, central Japan.

Tidal rhythmites in a deep sea environment: An example from Mio-Pliocene Misaki Formation, Miura Peninsula, Japan

The Mio-Pliocene Misaki Formation, Miura Peninsula, Japan is characterized by alternation of mafic scoriaceous pebbly sandstone, pumiceous sandstone and siltstone, and mudstone formed in a fore-arc basin in an arc–arc collisional zone. The qualitative as well as quantitative evidences of tide during the Misaki sedimentation in the Jogashima area, Miura Peninsula are presented here. The lunar synodic period of ∼28 days/lunar month extracted from the Misaki tidal rhythmite agrees well with the published Miocene tidal rhythmite data. The couplet series of the Misaki tidal rhythmite, however, is often interrupted by downslope resedimentation via turbidity currents, intense penecontemporaneous deformation and bioturbation. Association of deep sea turbidites, mass flow deposits and tidal rhythmite suggest Misaki sedimentation in the Miura Peninsula took place in a submarine canyon setting.

三浦半島断層群周辺の地下水のラドン222濃度の特徴

三浦半島断層群周辺の地下水のラドン222濃度の特徴

New marine diatoms from the Miocene Abuzurii Formation, the Miura Peninsula, central Japan

New marine diatoms from the Miocene Abuzurii Formation, the Miura Peninsula, central Japan

三浦半島南東部沖金田湾における海底活断層の発見(新称:金田湾断層)

三浦半島南東部沖金田湾における海底活断層の発見(新称:金田湾断層)

The First Record and Larval Development of Melanochlamys sp. (Mollusca; Gastropoda; Cephalaspidea) from Sagami Bay, Miura Peninsula, central Japan

The First Record and Larval Development of <i>Melanochlamys</i> sp. (Mollusca; Gastropoda; Cephalaspidea) from Sagami Bay, Miura Peninsula, central Japan

11. 三浦半島沿岸における暖流系アワビ類の混獲率と再生産

11. 三浦半島沿岸における暖流系アワビ類の混獲率と再生産

Records of Insects Found on the Coast ofthe Miura Peninsula, Kanagawa Prefecture, 1st Report

Records of Insects Found on the Coast ofthe Miura Peninsula, Kanagawa Prefecture, 1st Report

Geological evidence of recurrent great Kanto earthquakes at the Miura Peninsula, Japan

[1] The Tokyo metropolitan area's well-documented earthquake history is dominated by the 1703 and 1923 great Kanto earthquakes produced by slip on the boundary between the subducting Philippine Sea plate and the overlying plate. Both earthquakes caused ∼1.5 m of uplift at the Miura Peninsula directly above the inferred fault rupture, and both were followed by tsunamis with heights of ∼5 m. We examined cores ∼2 m long from 8 tidal flat sites at the head of a small bay on the peninsula. The cores penetrated two to four layers of shelly gravel, as much as 0.5 m thick, with abundant shell fragments and mud clasts. The presence of gravel indicates strong tractive currents. Muddy bay deposits that bound the gravel layers show vertical changes in grain size and diatom assemblages consistent with abrupt shoaling at the times of the currents. The changes may further suggest gradual deepening of the bay during the intervals between the strong currents. We infer, based on 137Cs, 14C, and 210Pb dating, that the top two shelly gravel layers represent tsunamis associated with the 1703 and 1923 great Kanto earthquakes, and that the third layer was deposited by a tsunami during an earlier earthquake. The age range of this layer, AD 1060–1400, includes the time of an earthquake that occurred in 1293 according to a historical document. If so, the recurrence interval before the 1703 earthquake was almost twice as long as the interval between the 1703 and 1923 earthquakes.

Attempt to restore coastline in southern part of Miura Peninsula before 1923 Kanto Earthquake using old edition topographic map

Attempt to restore coastline in southern part of Miura Peninsula before 1923 Kanto Earthquake using old edition topographic map

流水域におけるトウキョウサンショウウオの卵嚢分布状況およびその流失割合

The Tokyo salamander (Hynobius tokyoensis) indigenous in the Miura peninsula, is threatened with extirpation due to habitat loss from development. Artificial breeding sites in running water were introduced; however, many of the sites are not considered to be high quality breeding habitat. This species normally deposits its egg-sacs in still water, attached to a suitable twig, leaf or grass stem. We studied the retention of egg-sacs at two different types of running water sites. Our study showed that 48.7% of egg-sacs were washed away at natural stream sites, and 76.8% of egg-sacs were washed away by small streams created by erosion at abandoned rice paddy sites. We created still water sites in the abandoned rice paddies, and the results showed that only 5.3% of the egg-sacs were washed away. For conservation of this species, it may be necessary to protect a wide variety of riparian zones, groundwater systems, and forested areas.

Fish Fauna in the Southwestern Coast of Miura Peninsula - VII

Fish Fauna in the Southwestern Coast of Miura Peninsula - VII

三浦半島南部，小網代湾の津波堆積物調査から推定された過去三回の関東地震:--1703年元禄関東地震の一つ前の関東地震について--

三浦半島南部，小網代湾の津波堆積物調査から推定された過去三回の関東地震:--1703年元禄関東地震の一つ前の関東地震について--

Growth and Maturation of Sargassum ringgoldianum in Odawa Bay, Miura Peninsula, Kanagawa Prefecture

Growth and Maturation of Sargassum ringgoldianum in Odawa Bay, Miura Peninsula, Kanagawa Prefecture