Siliceous sponge spicules included in the Neogene mudstones in the vicinity of the Shinjo basin, Yamagata Prefecture, Northeast Japan show a diagenetic alteration from the milky white nature having smooth surfaces into transparent or translucent one having granular structures through a flaky stage from an upper stratigraphic horizon downward. Spicules in a lower horizon have many pits and/or nodes caused by corrosion on their surfaces. So both the diagenetic alteration and the corrosion were concurrent in the strata examined and a disappearance of spicules by corrosion occurred in some lower parts of the strata.

抄録全体を表示

The states of organic nitrogen and ammonium nitrogen in 34 mudstone samples collected from the west and east of the Shinjo Basin have been investigated. The results show that org. C/total N ratios are near 10 in most of the samples from the west of the Shinjo Basin showing that microbial activity was dominant in the sedimentary environment and organic matters supplied were almost decomposed until the ratio reached 10, a characteristic value of decomposed residue of microorganisms. While the ratios are more higher in samples from the east of the Shinjo Basin together with samples from the Okawa Formation (the west of the Shinjo Basin), showing that organic matters in these samples are terrestrial in origin and microbial decomposition of the organic matters which have high C/N ratio did not progress until the ratio reached 10.
Ammonium nitrogen in samples was separated into 3 parts, soluble NH₄-N with H₂O, exchangeable NH₄-N with 1N KCI and fixed NH₄-N, and the percentage of each state of NH₄-N and org. N to total N was calculated. The percentage shows that solv. NH₄-N is negligible in all samples, and exch. NH₄-N is less than 10% except for a few samples which contain much clinoptilolite and mordenite. In most of the samples, nitrogen consists mainly of org. N and/or fixed NH₄-N. From the distributive pattern of fixed NH₄-N/total N ratio in samples, stratigraphic horizons in which fixed NH₄-N/total N ratios are high are recognizable. A discussion has been given about the high ratio of fixed NH₄-N on the basis of an assumption that org. N changed to NH₄-N which was fixed in authigenic minerals during diagenesis.

抄録全体を表示

Amino acids in a concentration of 10^-9M/g were recovered from the Miocene hard shale fragments. In order to examine whether the amino acids are indigenous or not, the adsorption test was conducted. The rock fragments were immersed in a prepared solution of seven kinds of amino acids in a concentration of 10^-7M/ml. Adsorption occurred in the following order of amount; basic amino acid>neutral amino acids>acidic amino acid. Clay minerals played an important role in amino acid adsorption to argillaceous rocks. It is concluded that the amino acids detected from the hard shale fragments are possibly not indigenous but of contaminant.

抄録全体を表示

The degree of organic maturation with burial depth in surface sediments of Middle Miocene age from Oashizawa, Ohmata-Shiratama and Oguni routes in the Shinjo Oil field, northeastern Japan was examined.
Studies for the organic maturation included the analysis of organic carbon, extractable organic matter, hydrocarbons, fatty acids and kerogens, the measurement of the reflectance value of vitrinite in kerogen and the organic analysis by means of ROCK-EVAL (ESPITALIE, et al., 1977).
The results are summarized as follows:
(1) Stratigraphic distribution pattern of total organic carbon content showed similar one as the equivalent sediments of Japan Sea side, but their actual average contents showed relatively lower values than ones from Japan Sea side.
(2) Kerogens from sediments of the Kusanagi Formation and part of the Furukuchi Formation indicated to belong to Type I or II, namely to be excellent ones as petroleum source materials. On the other hand, kerogens from the Okawa Formation sediments also indicated to be likely Type I or II, but the results are uncertain at the present time, owing to insufficient analysed numbers of samples and the probable alteration of the samples by igneous activity.
(3) Various parameters for the organic maturation including hydrocarbon and bitumen ratios, vitrinite reflecance (Ro) CPI_n-p and CPI_FA showed the existence of the threshold of principal zone of oil formation near the upper parts of the Kusanagi Formation. Namely, the result indicates that Dewa Hill areas have uplifted and have been exposed after going through the sinking of burial as deep as to attain the formation of the threshold.
(4) On the other hand, the degree of the organic maturation from the Oguni route which corresponds to the marginal part of the Shinjo Sedimentary basin showed to be distinctly lower than one from the equivalents in Ashizawa route which corresponds to be central part of the basin.
(5) There were found several noticable points on the mutual relationships between the organic maturation and inorganic (mineralogical) diagenetic alteration based on the research by co-workers of a larger study of “Diagenesis of Sedimentary Rocks” supervised by K. TAGKCHI. However, with respect to this, further examinations are needed owing to incomplete discussions among co-workers.

抄録全体を表示

The conditions on treating sedimentary rocks with hydrofluoric acid to determine fixed NH₄-N in sedimentary rocks have been investigated. The results showed that treatment of sedimentary rock samples with HF (1:1) and 1N H₂SO₄ at 80°C for 1hr. effects quantitative release of fixed NH₄-N from the samples and that the treatment does not cause significant decomposition of organic nitrogen in the samples to ammonium.

抄録全体を表示

Stratigraphic examination of ¹H-NMR T₁ on the dioxane-insoluble organic matter of the Miocene argillaceous rocks gives the following conclusions. The rock samples were selected from a pile of rock collection of the Miocene formations around Shinjo Basin, northeastern Japan.
1. T₁ values increase gradually from the upper horizon to the lower in the Miocene sequence developed along Oashizawa, northwest of Shinjo City. The linear relation between log T₁ and stratigraphic horizon indicates that ¹H-NMR T₁ is a possible parameter for organic maturation.
2. The Miocene Ogunigawa Group developed in the east of Shinjo Basin in correlated stratigraphically to the Kusanagi Formation in the west. T₁ values of the former are comparable to those of the Furukuchi Formation which overlies conformably on the Kusanagi Formation. This fact is consistent with the rather shallow burial of the Ogunigawa Group deduced from the geological evidences.

抄録全体を表示

The stable carbon isotope study has been carried out with organic compounds of sediment samples collected along the Oashizawa route in the Shinjo sedimentary basin. These samples are sandy to muddy sediments of Miocene and represent about 1600m thick sediments. Organic carbon and bitumen components become abundant in the lower part (the Kusanagi Formation), indicating the oil generation around this zone.
The δ¹³C of the bitumen and kerogen gradually change from -26 to -22‰ and -25 to -21‰, respectively, from the top to bottom sediments. However, the δ¹³C exhibits a small change towards the positive or negative side from horizon to horizon. This changing trend shows that, as a whole, the sources of organic materials gradually changed with time from marine to terrestrial accompaning with a frequent reversed change in a small degree from horizon to horizon.
The difference of the δ¹³C between the bitumen and kerogen components within a single horizon is about 1‰, This difference is very consistent throughout with every horizon and no detectable change is noted even with the horizons where oil generated. This obsevation suggests that no further chemical reaction with respect to carbon isotopes was involved in the oil-generating zone in comparison to non-oil genarating zone. It also indicates that the oil component migrated horizontally at each horizon without chemically contaminating other horizons.

抄録全体を表示

Hydrocarbons extracted from sedimentary rocks (Shinjo oil field, northeastern Japan, Miocene) were analyzed by using capillary gas chromatography and gas chromatography-mass spectrometry. The following compounds were identified: C₁₃-C₃₈ n-alkanes, C₂₇-C₃₀ steranes with configurations at C-5, C-14, C-17 (α or β) and at C-20 (R or S), C₂₇-C₂₉ diasteranes with configurations at C-13, C-17 (α or β) and at C-20 (R or S), C₂₇-C₂₉ sterenes, mono- and tri-aromatized steranes, hopanes, naphthalene and its alkyl (C₁-C₄) derivatives, phenanthrene and its alkyl (C₁-C₃) derivatives, pyrene, fluoranthene, chrysene, and perylene.
With increasing burial (diagenesis), decrease of CPI of n-alkanes to 1.0, epimerization of 20R steranes to 20S ones, aromatization of steranes, and increase of polynuclear aromatic hydrocarbons were observed.

抄録全体を表示

Mica/smectite interstratified minerals are formed from smectite by adding alkali ions and increasing temperature. This transformation starts by increasing the alkali ion content and smectite changes to mica/smectite interstratified minerals with g=0 in the early stage of the transformation. The minerals formed transform to mica/smectite with g=1 by increasing temperature and pressure. On the other hand, mica changes to mica/smectite interstratified minerals by hydrothermal alteration. The minerals formed from mica usually show the interstratif ications with g=1 and 2. Some mineralogical data of the minerals formed by the two processes are given here and we show the considerations showing the formations of the minerals.

抄録全体を表示

In Japan, a fairly large part of the sediments which had been altered diagenetically was superposed by various kinds of hydrothermal alterations. Practically it is rather difficult to discriminate the hydrothermal alterations of alkaline solutions from the diagenetic ones, because of production of same authigenic minerals. For the purpose of discrimination of both alterations, the writers characterized the mineralogical properties, mineral assemblage, relation to the original rocks, authigenic minerals, series of alteration, and type and morphology of zoning. The last is the most discrimitive and practical.

抄録全体を表示

The On'nagawa Formation in Akita Sedimentary Basin is composed of siliceous mudstone and volcaniclastics. The volocaniclastic facies have been productive reservoirs of oil and gas fields in the Neogene Akita Basin, North Japan. The mudstone facies have been recognized to be potential source rocks for hydrocarbons pools in the reservoirs. After a long period of oil and gas production in the basin, a potential exploration concept of a new play in the siliceous rocks is required to keep the productivity of the basin.
This study reports a basic description of physical properties of the siliceous mudstone facies in order to provide a basis for the idea of shale play in the On'nagawa Formation. Wireline logs (GR, Δt, ρ_b) are basic data for our description of the physical rock properties as well as descriptions of cutting lithology.

抄録全体を表示

Recent radiolarian ooze and upper Jurassic siliceous shale are comparatively examined (Plates I and II). It is disclosed in the siliceous shale that authigenic dolomite and calcite, both rimmed with rhodochrosite (Plate III), and microcrystalline rhodochrosite coexist in a single sample (Figure 1 and Table 1), and that a cryptocrystalline filling of a radiolarian skeleton consists of chlorite, mica clay mineral and quartz (Table 2).
Isotopic age determinations carried out for the Mesozoic siliceous rocks in Central Japan are summarized in Table 3; and duration of chemical diagenesis is discussed based on the results of the geochronological and biostratigraphical studies recently reported by MIZUTANI (1981), MIZUTANI and SHIBATA (1983), and SHIBATA and MIZUTANI (1980, 1982).

抄録全体を表示

¹H spin-lattice relaxation time (T₁) of dispersed insoluble organic matter (kerogen) as measured by NMR gives a regular increase with increasing burial depth. This evidence is indicated by 94 analytical data in the six boreholes: MITI-Hamayuchi, MITI-Wakkanai, MITI-Embetsu, Tsubetsu, Yufutsu-oki B-4 and Nishikatakai SK-1 D and in the two outcrop sections, Umanokamiyama and Oashizawa. The T₁ versus vitrinite reflectance (R₀) suggests a linear relationship between the two variables with a high correlation coefficient. T₁ could be an evaluation parameter effective for organic maturation during burial diagenesis.

抄録全体を表示