Compressional and transverse wave velocity, porosity and air permeability for eleven samples collected from surface localities in Boso peninsula are measured. The all of samples facies, are mudstone ranging Pleistocene and Miocene in geological age. Main results obtained are as follows. 1) The density of mudstone samples between Kasamori and Kokumoto, Ohara and Kiyosumi Formation, increase with geological age, 2) The porosity-geological age relation of mudstone samples show almost similar density-geological age relation. 3) The above information indicates that the process of sedimentation is continuous and smoothly in the above Formation comparatively. 4) The compressional wave velosities of mudstone samples increase with geological age between Kasamori and Otadai Formation, these before Kiwada Formation not increase with geological age. 5) The air permeabilities of mudstone samples between Kasamori and Otadai Formation show high anomalies, these before Kiwada Formation show normal values.
The Daijima Formation, originally described as non-marine (HUZIOKA, 1959), is uncon- formably overlain at the type locality on the Oga peninsula by the marine Nishikurosawa Formation. However, recent discoveries of marine fossils (OKAMOTO, 1980 MS etc.) indicate that there is a possibility that the Daijima Formation could be marine, at least in the northern half of the area that has been desc- ribed as the Daijima Formation. Both the Daijima and the Nishikurosawa Formations were influenced by a warm current environment. The former is characterized by the Daijima flora (HUZIOKA. UMEMURA, 1979); the latter by warm planktonic foraminifera (IKEBE, 1962).
The carbonate rocks are abundantly distributed in the Miocene Nadakayama (Onnagawa) Formation of the southeastern part of the Yashima district, Northeast Japan. In order to obtain some informations on the sedimentary geochemistry of the Neogene carbonate rocks, 15 carbonate rocks collected from 23 carbonate horizons found in an outcrop of the Onnagawa siliceous mudstone sequence of 45m in thickness were examined through the microscopic observation, X-ray diffractometry and chemical analysis of organic matter. Also, 12 siliceous mudstone sampled in stratigraphic sequence of the same outcrop were examined for comparison with the data of the carbonate rocks. The carbonate rocks are generally dolomitic and occur as bed or large lense, or nodule in siliceous mudstone. Sometimes, micronodules are found in bedded carbonates. Sedimentary structures such as graded bedding and laminations, and tracefossils are occasionally observed in those carbonate rocks and also in siliceous mudstone. The results of X-ray diffractometry and chemical analysis of organic matter are summarized as follows. The carbonate rocks are composed of dolomite, quartz, feldspar, montmorillonite, illite, chlorite and concomitant glauconite and pyrite. The relative abundance of clay minerals in clay fraction under 2am and of pigments in carbonate rocks resemble those in siliceous mudstone. Quartz and total organic carbon are more abundantly and dolomite are less contained in bedded carbonate rocks than in nodular carbonate rocks. Quartz and total organic carbon are contained in siliceous mustone three times as much as in carbonate rocks. The stratigraphic variation of the amount of quartz and of total organic carbon in carbonate rocks, however, resemble those in siliceous mudstone, and the stratigraphic variation of the amount of dolomite in carbonate rocks seems to be in inverse relation to the one of the amount of quartz in siliceous mudstone. On the basis of those results and other informations, some considerations on the depositional environment and the formation process of these rocks were also made.
Water saturation-porosity product, which is a measure of volume of water saturaing a given volume of a reservoir, can be estimated directly from conductivity or resistivity log responses. This simple method can apply for only a relatively well consolidated reservoir, where the factors a, m, and n in Archie's (1942) porosity and water saturation equations are 1, 2, and 2, respectively. Volume of oil or gas in a given reservoir volume is given by the difference detween the volume of water if the reservoir were fully saturated with water and the actual volume of water in the reservoir. Knowing the thickness of the reservoir and the area of oil or gas accumulation, the total volume of the accumulated oil or gas can be calculated quickly by going through the charts included in this paper. Although the method described in this paper requires a certain reservoir condition expressed by the a, m, and n values, it has a practical application in the area where only resistivity logs are available.