The geochemical analyses of the lower Neogene marine argillaceous rocks from central-Northeast Sarawak, Malaysia, gave the following information on their sedimentary environments. They were mostly derived from the granitic provenance without any indication of mafic to ultramafic components. Generally higher horizons are more enriched in exposed weathered materials resulted from the uplift of the hinterland. Concurrently, the source of the detritus shows recycling nature, suggesting the deformation of the forearc basin during the middle Paleogene time. As for their source-rock potential of the hydrocarbon resources, the bottom water conditions during their deposition seem to have kept rather oxygenated, while the frequent anoxizations are also recognized. These sediments seem to have been deposited in a near shore shallow open ocean situation where the terrestrial organic materials were accumulated. Although the source rock potential is poor due to the post-depositional oxidation, some anoxic event may be developed somewhere onshore to form rather good source rock facies.

View full abstract

In this paper are shown the results of the heavy mineral analysis of ice-rafted sand fractions of undisturbed surface sediments collected from several gravity cores in and around the Ross Sea shelf area during the TH91 and TH92 Antarctic research cruises by Technology Research Center, Japan National Oil Corporation, using R/V Hakurei-maru. The areal distribution pattern of the frequency of each heavy mineral suggests the existence of at least two petrographic provinces, i. e. western and central-eastern areas. Especially, olivine and clinopyroxene with titanaugite, which were probably supplied from the late Quaternary McMurdo alkaline basaltic rocks fringing the eastern margin of the Victoria Land, are exclusively or dominantly distributed in the western area of the Ross Sea. This results support the northward movement of icebergs nearly parallel to the east coast of the Victoria Land at least in the western part of the Ross Sea shelf area.

View full abstract

The size of ancient seaway can be estimated from paleo-wave conditions reconstructed from wave ripples and other sedimentary rock records. Possible combinations of wind speed, fetch and length of wave decay are obtained for a given paleo-wave condition by making a reverse use of wave forecasting and swell forecasting methods. This method is unique in that it pays regard to the process of wave decay. The calculated possible fetches fall into a certain range. The maximum value of calculated fetch is that for fully developed waves having no chance to decay. The range of fetches can be reduced using some sedimentological criteria, e. g. storm/fair weather sedimentation. Reference to present-day ocean waves further provides a basis for omitting unrealistic fetch lengths. Estimated fetch and decay lengths place some constraint on the minimum size of the paleo-seaway.

View full abstract

Major and trace element concentrations of 38 shales and sandstones from Northern Shimanto belt in southwestern Shikoku were determined by X-ray fluorescence. SiO₂ contents range in 56-69wt% for shale, and in 67-78 wt% for sandstone. TiO₂, Al₂O₃, Fe₂O₃, MgO, K₂O, and Rb decrease with increasing SiO₂. This chemical trend could be formed by mixing of mafic and clay minerals with quartz. CaO, Na₂O, Sr, and Ba do not show correlation with SiO₂, and scatters of the contents are large. Concentration of these elements may be controlled by mode and composition of feldspars in sedimentary rocks.

View full abstract

Grain-size distributions of the single transport modes, after sand transport downstream from the brink of an experimental microdelta, are neither Gaussian nor log-hyperbolic. Instead, the sands transported by suspension downstream of the microdelta derive many of their grain-size attributes from those of the sand fed into the flume at its upstream end. Relationships between the grain-size distributions of individual transport modes and the texture of the “original sand” are best demonstrated by normalizing data to the grain size of the “original sand”. The experimental data suggest that the suspension process does not prefer a peculiar size among the grains which can be suspended; i. e., grains present in the suspended load are represented in the same proportion as in the “original sand”. This result can be reproduced by Rouse's diffusion model.

View full abstract

The study area is situated on the right side of the middle of Sai-river, the southern part of the Northern Fossa Magna region. There are large cliff exposures which consist of an upper Miocine sedimentary rocks, Aoki Formation. The sedimentary environment of these rocks was fan-delta slope in the progradational stage of fan-delta system. Exposures show discordances which concave upward, and large slump structures being followed for about 100m. Discordances are interpreted as slump scars formed by downslope sliding or slumping of fan-delta slope sediments. The large slump structure resulted from a slumping sidewall of scar into scarsurface. In this case, slumping and sliding occuerred frequently on the fan-delta slope. Then, a lot of clust were released down-slope and formed lobe shaped sediments. This is characteristic of fan-delta slope sedimentation during the progradational stage and may reflect hightstand of the relative sea-level.

View full abstract

The Tsuyazaki coast of North Kyushu, western Japan, shows well-developed gravel beaches at the southern foot of the headland of Tsuyazaki. They consist mainly of basaltic pebbles to boulders, which are sorted horizontally depending on the distance from the source. Behind the gravel mound, there is a pool composed of sand-sized sediments, where gravels of outsize attached by long kelps are scattered. Such gravels are also randomly found on the nearby sand beach. The origin of gravels of outsize is due to the sailing effect of gravels with kelp-streamers under storm-agitated condition mainly during the winter season. Gravels in such an occurrence are called “parachute gravels”. They are important to understand the occurrence of outsized gravels of coastal deposits.

View full abstract

The Upper Cretaceous Mifune Group, which is well exposed in the Axial Zone of Kyushu, is characterized by nonmarine, brackish water and shallow marine deposits. It overlies the Kiyama metamorphic rocks and serpentinite nonconformably at the northern part and unconformably the Upper Permian Mizukoshi Formation and disconformably the Higo metamorphic rocks at the southern part. The Mifune Group is divided into the Basal, Lower and Upper Formations in ascending order. The Basal Formation (20-50m thick) is composed of conglomerates with red-colored matrix. The Lower Formation (250-750m thick) is composed of sandstones and siltstones with plenty of brackish water and marine molluscan fossils. The Upper Formation (more than 1000m thick) is principally composed of red beds with sandstones and acidic tuff beds.
This paper describes sedimentological features of the Mifune Group, especially on the sedimentary facies and paleocurrent patterns. The results of the investigation are summarized as follows:
1. Seventeen distinct sedimentary facies are recognized, which are grouped into eight facies assemblages. The characteristics of these facies assembleges may suggest a variety of sedimentary environments, such as alluvial fan, lacustrine nearshore, lacustrine offshore, estuarine channel, sandy tidal flat, muddy tidal flat, shoreface and offshore.
2. Small-scale sedimentary structures are recognized in terrestrial red and fine-grained beds, such as graded-bedding, cross lamination, ripple mark and rhythmite-like parallel lamination.
3. Sedimentary facies and paleocurrents data suggest that depositional environments in the northern area were changed from alluvial fan through estuarine channnel and muddy tidal flat to lacustrine offshore in ascending, whereas in the southern area from distal alluvial fan through shallow-sea sandy tidal flat, offshore and shoreface to lacustrine nearshore and lacustrine offshore. During the marine depositional phase, the sea opened eastward and bay-like environments were developed on the west side of the basin.

View full abstract