Three Dimensional Analysis of a Large Sandy-flysch Body, Mio-Pliocene Kiyosumi Formation, Boso Peninsula, Japan

Three dimensional analysis of flysch sequence is very important as it makes substantially possible to compare the depositional process of it with that of the current submarine fan model and to clarify the phased development of submarine fan sedimentation. Such study has been almost lacking until now. The Kiyosumi Formation is composed of a large lenticular sandy-flysch body, measuring 850 m in maximum thickness and more than 20 km in E-W direction along the folding axis and more than 6 km in N-S direction. The Kiyosumi Formation is divided into five units by means of six main tuff marker-beds. Each unit is composed mainly of both channel deposits and depositional tongue. Channel deposits are characterized by an upward thinning cycle beginning with thick pebbly sandstones and ending with thin siltstone-dominated alternations and by accompanying a large trough-like erosive morphology at the base attaining up to some 50 m in maximum depth and more than 5 km in maximum width. The depositional tongue is characterized by extensive and thick sandstone-dominated alternations downcurrent of the channel deposits and shows negligible basal erosion. Further downcurrent, the depositional tongues are replaced by siltstone-dominated alternations or massive siltstones. The Kiyosumi Formation has been deposited by the lateral supply from north into the E-W trending restricted slope basin by the same process as that of the recent submarine fans. Channel deposits in each unit seem to have been deposited on the upper-fan segment. Depositional tongue in each unit must have formed a suprafan (NORMARK, 1970) on the middle fan segment. Siltstone-dominated alternations or massive siltstones must have been deposited on the lower-fan segment or basin floor. However each depositional tongue in the Kiyosumi Formation, covering a wide area more than 20 km, occupys a much more extensive segment on a fan than suprafans on recent submarine fans. Individual thick sandstone beds also continue persistently as wide as the tongue. The channel deposits and the depositional tongue in the lowermost unit show a peculiar distribution as fan sedimentation. They seem to be the deposits at "a preparatory stage" of fan sedimentation or at "a pre-fan-sedimentation stage" during which preexisting reliefs on the basin floor are smoothed and an equilibrium profile of the slope-fan-basin is attained. The phased retreat of the terminus of channel deposits from the lowermost unit to the uppermost unit caused the first order upward thinning cycle detected throughout the Kiyosumi Formation. Shift of the channel to the different site was caused by beginning of each second order upward thinning cycle commonly observed in the channel deposits or by the rejuvenation of turbidity currents. The causes of these multiple upward thinning cycles, characterizing the vertical variation of the flysch sequence in the Kiyosumi Formation, are also discussed

ボウソウハントウニオイテキョダイナサシツフリッシュセキセイタイオナスチュウシン - センシントウキヨスミソウノサンジゲンカイセキ

京都大学0048新制・課程博士理学博士甲第2118号理博第544号新制||理||291(附属図書館)5977UT51-53-M98京都大学大学院理学研究科地質学鉱物学専攻(主査)教授 中沢 圭二, 教授 笹嶋 貞雄, 教授 亀井 節夫学位規則第5条第1項該当Kyoto UniversityDA

Marine sediment cores from the continental shelf around Anvers Island, Antarctic Peninsula region

Sediment core samples are described from the area adjacent to Anvers Island north of the Antarctic Peninsula. The sequence is divided into three lithologic units, siliceous mud, alternation sandy silt and siliceous mud, and sandy silt with gravel, in descending order. These units suggest sedimentary environmental changes from under the ice sheet, to marine with highly influenced by fluctuation of the ice sheet, and finally to open marine. These major environmental changes are dated to ca. 16 ka BP and ca. 11.5 ka BP, respectively, based on uncorrected radiocarbon ages of organic carbon

AREAL AND VERTICAL VARIATION OF HEAVY MINERAL COMPOSITION OF THE SURFACE SEDIMENTS, ROSS SEA, ANTARCTICA

In this paper are shown the results of heavy mineral analysis of ice-rafted sand fractions of muddy sediments from several gravity cores around the Ross Sea collected during the TH91 and TH92 Antarctic research cruises by the Technology Research Center, Japan National Oil Corporation, using the R/V HAKUREI-MARU. Samples for the analysis were collected from two levels of the cores, i.e. late Holocene S-group samples in the upper part and last glacial to early Holocene D-group samples in the lower part of the cores. Both the S-group and D-group samples are comprised of the same kinds of heavy minerals and show the nearly completely same distribution patterns of the frequency of those minerals. These patterns suggest the existence of at least two petrographic provinces, i.e. western and central-eastern areas, which must reflect the difference of the provenances of East Antarctica and West Antarctica. Especially, olivine and clinopyroxene with titanaugite, dominantly distributed in the western area, were probably supplied from the late Quaternary McMurdo alkaline basaltic volcanics fringing the eastern margin of the Victoria Land. The strong similarity of the distribution pattern of heavy mineral composition between the S-group and D-group samples suggests the long-term stability of flow patterns of icebergs in the Ross Sea. Such stability must be controlled by the submarine topography in the Ross Sea, which plays the most important role in the Ross Sea, controlling not only the types of sediments, but also the flow patterns of icebergs

Preliminaly report of the TH96 geological and geophysical survey results in Bransfield Strait and its vicinity

Geophysical and geological surveys of the JNOC TH96 cruise on the R/V HAKUREI-MARU, in the Pacific margin of the northern Antarctic Peninsula, were carried out in the 1996-97 austral summer season. The early and later halves of the cruise were devoted to a continental margin survey of the western and northern margins of the northern Antarctic Peninsula, respectively. The seismic data are interpreted together with the data which were aquired in this area during JNOC TH80, 88 and PetroBras and British Antarctic Survey cruises. The geophysical data in the southwestern margin show typical passive continental margin character with abyssal plain-continental slope-continental shelf from sea to land. The thickness of the sedimentary sequence in the abyssal plain is about 3 s (twt). The development of the continental rise between abyssal plain and continental slope is very poor, compared with more mature passive continental margins. The area north of the Antarctic Peninsula is interpreted as the triple junction area among the Antarctic-Scotia-(former) Phoenix plates. The seismic data in the area show distributed highly deformed sedimentary basins and volcanic features. The deformation trend is interpreted to be controlled by the regional trend of simstral trans-tensional movement between the Antarctic and Scotia plates