Trasport process affecting marine environmental change is commonly unsteady. Role of the various unsteady transportation mechanisms is elucidated only by repeated observation at fixed stations and systematic analytical study of the cored sediments. Procedure of the study of the core should be 1) check of sedimentary structure, 2) pickup of sample materials from the each structural divisions, 3) high resolusion age determination, 3') fractionation based on particle sizes by means of sieving and decantation, 4) chemical analysis of the each fractionated materials.

抄録全体を表示

Rhythmical patterns in stratigraphy are potential sources of information about past Earth history. A number of studies have been performed to elucidate past climate change, dynamical state of Earth-Moon system, occurrence of recursive earthquakes, and periodic meteoroid impacts on Earth. In these studies, coincidence of observed periodicity and some postulated periods of forcing is used to identify their origins. However, fractuations of the Earth environments are produced by very complicated interaction between many internal elements induced by external causes with different periodicities. It is not always possible to elucidate causes of rhythmical patterns uniquely. We point out that such observed fractuations show statistical properties related to self similarity or fractal. Fractal rescaled range (R/S) analysis is applied to Holocene lacustrine sediments in Jigokudani Valley, Tateyama Volcano, Central Japan. The rhythmical sediments are characterized by a scaling parameter of H=0.6-0.7. Some important aspects of rhythmical sediments analysis are discussed.

抄録全体を表示

The Cenomanian-Turonian Mikasa Formation of the Yezo Supergroup distributed in western-central Hokkaido, represents sandy shallow shelf to coastal sediments along the western margin of the Late Cretaceous Yezo Basin. It constitutes two or three coarsening-upward sequences, each of which is bounded by the upper surface of a transgressive lag composed of coarse-grained sandstone to conglomerate just above a sharp-based ravinement surface. The relation between observed ravinement surfaces and inferred sequence-bounding unconformities is briefly discussed from the viewpoit of sequence stratigraphy. Local and relative sea-level changes during Cenomanian to late Turonian are preliminarily inferred from the sedimentary facies distribution of the Mikasa Formation.

抄録全体を表示

Development of sedimentary basin fills in the Japanese convergent margin during the Mesozoic through Cenozoic generally corresponds to changing periods of oceanic plate motion. Modes of transgression-regression cycles in the sedimentary basin fills are represented by several major types: rapid transgression followed by slow regression is typical in the Mio-Pleistocene successions; slow transgression and rapid regression are in the Paleogene-Cretaceous successions, rapid transgression and regression interrupted by longer stillstand are in the Jurassic-Triassic successions. The different modes of transgression-regression cycles can be a result of interacting two major variables of the relative rate of accommodation space development and sediment influx. Variation of the two important variables can best be interpreted in terms of tectonic movement in the Japanese convergent margin and eustatic sea-level changes during the Mesozoic through Genozoic.

抄録全体を表示

Recent sedimentologic and geologic studies have revealed that coastal alluvial-fan sedimentation is sensitively influenced by sea-level changes. A brief introduction to recent understanding of the sea-level control is made in this paper from geomorphologic point of view. The framework presented elsewhere by the author gives a synthetical explanation of morphologic evolution and depositional processes of coastal alluvial-fans controlled by relative sea-level changes and resulting stratigraphic sequences. This framework should be further examined through field observations and thereby will be improved.

抄録全体を表示

Fluctuations of carbonate compensation depth (CCD) were observed through the fluctuation of carbonate contents in the bottom surface sediment located just above the CCD and the micritic limestone-nodular cherts sequences of the Jurassic age in the western Pacific. Fluctuations are caused by changes in oceanographic conditions due through climatic fluctuation histories including the glacial-interglacial histories, and influence on the absorption capacity of CO₂ to the ocean from the atmosphere.

抄録全体を表示

Pelagic sediments in the north and south central Pacific were analysed for Mn, Fe, Co, Ni, Cu, Zn and Pb. The relation between contents of these metal elements and sedimentary facies, and controlling factors of the regional variation of them were discussed. Sediment samples used in this study were collected along two c. a. 4500km-long transects which runs from the east of the Wake Ialand down to the west of Tahiti. The number of the samples were 115, consisting of 21 bottom-surface samples and 91 segments of several sediment cores.
Vertical distribution pattern of the elements are classified into three types; 1) gradual decreasing of the contents as the depth in the core increases, 2) irregular changing with plural maximums of the contents, and 3) gradual increasing of the contens as the depth in the core increases. The pattern is, however, not necessarily common to all the elements even in a same core. Contents of the elements become lower as the sediment sample contrains much siliceous organic remains. The elements, except Fe and Cu, are more abundant in the zeolitic sediments than in the pelagic clay.
Horizontal distribution of the elements in the bottom surface sediments indicates that all the elements other than Cu attain their maximum contents in the southernmost part of the study area, i. e. the Penrhyn Basin, and that Cu content attains its maximum in the northern part of the Central Pacific Basin. It is no exaggeration to say that the Penrhyn Basin sediments are residual matters of oceanic basalt, as far as available Al/Ti ratio suggests. Relatively low Fe/Mn ratio in the Penrhyn Basin sediments can be explained, in accordance with the Al/Ti ratio, by expectable Fe depletion during zeolite formation from the basalt. Origin and behavior of Ti in the sediments should, however, be studied, as it is possible that mobile Ti having other origin than the basalt is rich in the sediments. On the other hand the highest Cu content mentioned above, higher than 400ppm, should simply be caused by higher biogenic productivity, especially of radiolarians. Extremely high Cu/Ni rations, higher than 2.5, in the same area support this view.

抄録全体を表示

The strong ocean current, Kuroshio prevailing along the Pacific coast of Southwest Japan is an important factor for modern sedimentary processes in the shelf to basin area. Both of surficial sediment and bedform distribution reflect the bottom flows related to the Kuroshio. These effects are commonly observed along offshore of Southwest Japan.

抄録全体を表示

Many nallow sedimentary basins of early Cretaceous age are developed along the major tectonic zones of the Kurosegawa belt and the Usuki-Yatsushiro Tectonic Line, the axial zone of Kyushu. These Cretaceous formations show a wide variety of sedimentary facies, paleocurrent patterns, sedimentary cycles. Two types of stratigraphic sequence can be distinguished among the Cretaceous formations, differing in sedimentary processes and environments from with each other. One is a shallow-marine sequence (The Kawaguchi, Kesado-Yatsushiro, and Sakamoto Formations), indicating fluvio-deltaic systems, and the other is a turbidite sequence (the Uminoura, Hachiryuzan, Hinagu, and Tomochi Fromations), suggesting more deeper marine, elongate turbidite fan systems. They occur repeatedly and are associated with unconformities, commonly. These abrupt changes of sedimentary facies and environments suggest the rapid subsidence and rise of sedimentary basins, that might be controlled by vertical movement of strike-slip motion along major tectonic zones.

抄録全体を表示

The Honjyo and Nango Olistoliths in the Nichinan Group, ranging from late Oligocene to earlist Miocene times, are interpreted as representative bodies of the deep-sea fan deposits accumulated at a transformed forearc margin. In spite of their different depositional sites, they represent similar sedimentation patterns and processes, suggesting a mud-rich and elongated fan system. The extrabasinal controls on the strike-slip tectonics and the sea-level change at latest Oligocene are discussed.

抄録全体を表示

茨城県南部の上部更新統は古東京湾の堆積物である. これには, 低角くさび状斜交層理や平行葉理をもった分級のよい細粒砂からなる沿岸砂州堆積物が発達する. 沿岸砂州堆積物の堆積構造から砂州の比高を求め, 堆積場の古水深を推定する方法 (増田・岡崎, 1985) を紹介し, 加えて, その沿岸砂州堆積物と当時の海岸との距離 (離岸距離) を推定する新しい方法を提唱する.

抄録全体を表示