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Salt water intrusion in the Mekong River, Vietnam, was studied using a towing type echo-sounder (Model SC-3) and water quality meter (TPM CLOROTEC) observation instruments during spring tide of the low flow season in May, 2005. Observations were taken at two stations located at points 26 and 8km from the river mouth. Measurements were taken at hourly intervals for 24 hours during one week, using several instruments set on the river bottom. A joint towing observation system using echo-sounder and water quality meters has been proved its usefulness for analyzing the time-space behavior of salt intrusion in the Mekong River. Precise measurements of tide-related phenomena including water level, bottom currents and water quality (temperature, salinity, turbidity and chlorophyll-a) at two stations revealed detailed movements of the saline water-mass.

Salt water intrusion in the Mekong River has been studied using a newly-developed acoustic reflection profiling system (Model SC-3). This system determines the spatial distribution of the halocline by measurements of water quality, especially of salinity. This system was made by improvement of a 200kHz precision echo sounder. In the intermediate flow seasons of Dec., 2000 and Jan., 2002, salt water was present only downstream of the mound at 8km in ebb tide, but progressed upstream beyond the mound at 14km toward flood tide. A typical wedge-like profile was obtained at the observation toward flood tide on 28 Dec., 2000. Time series echo-sounding profiles obtained from ebb tide toward rising tide on 2 and 4 Jan., 2002 at the river mouth station is in accordance with each salinity profile. In the low flow season of May 2001, salt water reached as far upstream as the mound at 28km near flood tide, and possibly entered the pool at 33km. The echo-sounding salinity profiles and the surface salinity data reveal the presence of strongly vertically-mixed water in the entire area invaded by salt water, although partly stratified structures may be formed during slack tide. The present echo-sounding system has proven to be very effective in unraveling the time-space behavior of salt water intrusion in the Mekong River.

This article reports field observation of Paleogene clastic successions in two areas in north-western Kyushu and provides a preliminary interpretation of their sedimentary environments on the basis of lithological facies. In the sections from Sakito-Oshima Island, the Ichigoshima, Sakito, Maze and Tokuman Formations were logged. They are, except their basal part, interpreted to represent an overall transgression from fluvial, estuarine, shelf, and then to deep marine environments during the latest Eocene to Early Oligocene. A sedimentary cycle of a Middle Eocene age from nonmarine, to deep marine, and then to shallow marine environments was able to be reconstructed from the observation in the sections from the Amakusa-Shimoshima area, where the Fukuregi, Shikiyama and Toishi Formations were examined. These evidence will be adapted in the interpretation of fossil dinoflagellate cysts and molluscs which is the principal intent of the present project.

Bottom sediments and invertebrate benthic faunas were recovered by dredge sampling at four stations off the Tassha coast of Sado Island in the Japan Sea. Nineteen crustacean and 144 molluscan species were found in the bottom sediments. Among the decapod crustaceans, Australeremus triserratus (Ortmann) was identified for the first time in the Japan Sea. The following nine molluscan species were newly found around Sado Island: Emarginula fragilis Yokoyama, Nodiscala matajiroi Kuroda, Pyreneola semipicta (Sowerby III), Dimiya filipina Bartsch, Spondylus barbatus Reeve, Agatha lepidula Habe, Cycladicama semiasperoides (Nomura), Abrina lunella (Gould) and Pitar japonicum Kuroda and Kawamoto. The grain size analysis revealed that the bottom sediments were classified into two groups: coarse-grained sand at shallower nearshore sites and fine-grained sand at a deeper offshore site. The cluster analysis for the molluscan faunas was concordant to the grain size classification of the sediments.

The Oligocene to lower Miocene Muro group in the Kii Peninsula represents the later stage of the Shimanto geosyncline which was widely extended along the Pacific coast of Southwest Japan from late Jurassic to earliest Miocene time. The Muro group is composed mainly of flysch-type alternations of sandstone and mudstone, intercalating conglomerates, thick-bedded sandstones and conglomeratic mudstones. These sequences are well exposed in the southern coast area in the peninsula. Based on the analyses of the sedimentary features such as grading, stratification and clast fabric, and field occurrence as well, the conglomerates are referred to have been transported and deposited by grain flow and turbidity current combined. Thick-bedded sandstones are considered to have been transported and deposited by turbidity current. It is safely concluded that conglomeratic mudstones such as pebbly mudstone and angular fragment-bearing mudstone were transported and deposited by debris flow. All of these coarse sediments were deposited in proximal suit of deposition. There are observed several channel-scours and -fills in the upper formation of the Muro group, which indicate the submarine fan deposition of the formation. Paleocurrent analysis based on sole marks and clast fabrics shows that the provenances existed not only to the north, but also to the south of the basin. General trends of the channels and paleocurrents in channel fillings indicate the distributary channel system developed on the submarine fan in the southern side of the basin. The existence of the Kuroshio Paleoland estimated to the south of the Shimanto terrain by the Kishu Shimanto Research Group is strongly supported by the present study.

The Neogene System in and around the Samburu Hills, northern Kenya, is divided into seven main formations on the basis of stratigraphy and geochronology, which in ascending order are the Nachola, Aka Aiteputh, Namurugungule, Nanyangaten, Kongia, Nagubarat and Tirr Tirr Formations. The Nachola and Aka Aiteputh Formations of Makinouchi et al. (1984) have been redefined. The Nachola Formation, which is widely distributed along the Baragoi River, is the lowest part of the Neogene System and either unconformably overlies the Precambrian Basement Complex or is in fault contact with it. It consists mainly of basalts, phonolitic trachytes and their pyroclastics, and sediments. The Aka Aiteputh Formation conformably overlies the Nachola Formation and occurs in the Nachola area and the Samburu Hills. It is mainly composed of basalts intercalated with trachytes, trachytic pyroclastics and sediments. The Namurungule Formation consists chiefly of clastic sediments with intercalations of mud flow deposits and tuffs, and covers the Aka Aiteputh Formation. No structural gap between the Aka Aiteputh and Namurungule Formations is recognizable. The Nanyangaten Formation, consisting of basalt lavas, which is one of the "undifferentiated basalts" of Mainouchi et al. (1984), unconformably overlies the Nachola and Aka Aiteluth Formations. Kenyapithecus occurs in the Aka Aiteputh Formation at Site BG-X of the Nachola area (Ishida et al., 1984). The bed containing Kenyapithecus accumulated between 15.4 Ma and 12.8 Ma according to K-Ar dating of volcanic rocks (Itaya & Sawada, 1987). On the other hand, the Samburu hominoid fossil occurs in the Namurungule Formation (Makinouchi et al., 1984; Ishida et al., 1984) whose K-Ar age is between 10.8 Ma and 7.3 Ma (Itaya & Sawada, 1987). A major structural gap is recognized between the Namurungule and Nanyangaten Formations indicating that a significant tectonic disturbance in the (northern Kenya Rift) took place between about 10 Ma and 7 Ma based on geological data obtained by this work and Makinouchi et al. (1984), and geochronological data of Itaya & Sawada (1987).