All issues
Volume 119, Issue 5
Displaying 1-4 of 4 articles from this issue
- |<
- <
- 1
- >
- >|
Articles
-
Takeshi Makinouchi, Masayoshi Tsukamoto, Tohru Danhara, Tohru Yamashit ...2013 Volume 119 Issue 5 Pages 335-349
Published: May 15, 2013
Released on J-STAGE: September 28, 2013
JOURNAL FREE ACCESSGeological profiling and tephra analysis of muddy sediments has clarified subsurface geology in the eastern part of the Nohbi Plain:
(1) The upper pumiceous sand member of the Late Pleistocene Atsuta Formation (D3U) contains two intercalated muddy horizons, and it is rare to find the pumice in the basal section.
(2) The lower marine clay member of the Atsuta Formation (D3L) contains an intercalated ash fall bed of the Nagashima tephra (B75-2).
(3) The intercalated Nagashima tephra lies at the upper horizon of the D3L member in the study area (eastern Nohbi Plain), whereas this tephra lies at the lower horizon in the western Nohbi Plain. The implications of this difference in the tephra horizon are unclear and needs further investigation.
(4) The D3L member in the eastern Nohbi Plain has a thickness equal to the same member in the western Nohbi Plain.
(5) In the eastern Nohbi Plain, the middle Pleistocene Ama-Yatomi Formation contains an intercalated thick marine clay bed (Dmc-m) in which the Ata-Th tephra (240 ka) lies at the middle section.
(6) The westward-tilting Nohbi Plain appears to have caused smaller amounts of subsidence in the eastern part compared to the western part; however, the marine D3L and Dmc-m members in the east have thicknesses comparable to the same units in the west; it is as yet unclear why this is the case.View full abstractDownload PDF (7007K) -
Susumu Tanabe, Yoshiro Ishihara2013 Volume 119 Issue 5 Pages 350-367
Published: May 15, 2013
Released on J-STAGE: September 28, 2013
JOURNAL FREE ACCESSThe age and depth of the Uppermost Alluvium in the coastal lowlands of Japan indicates that minor sea-level drop, termed the “Yayoi regression”, occurred at 3–2 ka; however, this “Yayoi regression” is not a eustatic phenomenon. Sedimentary facies analysis and radio-carbon dating in the Tokyo and Nakagawa Lowlands indicate that: (1) flood plain sediments of the Uppermost Alluvium are located at depths >1 m below the present sea level, and (2) the morphology of fluvial channel sediments of the Uppermost Alluvium changes from sheet-like (7–3 m below present sea level, deposited at 3–2 ka) to anastomosing (<3 m below present sea level, deposited at 2–0 ka). Sheet-like and anastomosing sand bodies typically form during lowstand and transgressive fluvial systems, respectively. This suggests that relative sea level was lower than the present at 3–2 ka, before rising in the Tokyo and Nakagawa Lowlands to current levels between 2 ka and the present day.View full abstractDownload PDF (18337K) -
Yoshiaki Sugamori2013 Volume 119 Issue 5 Pages 368-374
Published: May 15, 2013
Released on J-STAGE: September 28, 2013
JOURNAL FREE ACCESSPaleozoic strata are known to be present in the Tanto area of Toyooka City, in Hyogo Prefecture, but these sediments are poorly documented. This study indicates that these sediments are dominated by mudstones and felsic tuffs with conglomerates and red cherts that are intercalated with the felsic tuffs. Mudstones in the study area contain a radiolarian fossil assemblage that includes Pseudoalbaillella aff. longicornis Ishiga and Imoto, and this assemblage is indicative of a latest Early Permian to middle Middle Permian age of deposition. These lithological and geochronological features suggest that Paleozoic strata in the study area correlate with the Shimomidani Formation of the Akiyoshi or “Shidaka” terranes, consistent with previous research.View full abstractDownload PDF (2432K) -
Tomonori Naya, Chikara Hiramatsu, Akira Furusawa, Yukio Yanagisawa, Ka ...2013 Volume 119 Issue 5 Pages 375-395
Published: May 15, 2013
Released on J-STAGE: September 28, 2013
JOURNAL FREE ACCESSThe chronostratigraphy of a 1505 m deep hot spring well drilled in Otone town, Saitama Prefecture, in the central Kanto Plain of Japan, was determined by tephrostratigraphy, and calcareous nannofossil and diatom biostratigraphy and is correlated with Neogene and Quaternary sequences that outcrop within the Kanto Plain area. Units A (depth 1434–1505 m), B–E (depth 773–1434 m), and F (depth 0–773 m) correlate with the Middle Miocene Hiki Group of the Hiki Hills, the Middle–Late Miocene Tokigawa Group of the Hiki and Iwadono hills and the Late Pliocene–Pleistocene Kazusa and Shimosa groups of the Boso Peninsula, respectively. The Niwaya unconformity is thought to separate Units A and B, and the Kurotaki unconformity correlates with the base of Unit F. The base of the Kazusa Group has also been identified in the Kazo1–Shobu1 Line seismic section and reaches a maximum depth of ca. 1000 m at Shobu town.View full abstractDownload PDF (7911K)
- |<
- <
- 1
- >
- >|