This paper describes briefly the geology of the Oashizawa, the Ohmata-Shiratama and the Oguni routes in the Shinjo Oil field, northeastern Japan, which areas were selected to meet the requirement for co-works on the diagenesis of sedimentary rocks supervised by K. TAGUCHI to provide the geological meanings regarding the samples collected for study. For further details, the reader should refer to the cited literatures.

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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.

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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.

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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.

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24 mudstone samples from Shinjo Oil Field and Nishiyama Oil Field (Neogene Tertiary, Japan) were examined by gas chromatography-mass spectrometry to investigate the extent of configurational isomerization (epimerization) of the so-called biological marker compounds (steranes and triterpanes).
The increases of the ratios of 20S/20R-24-ethyl-5α(H), 14α(H), 17α(H)-cholestane and of 22S/22R-17α(H), 21β(H)-bishomohopane (C₃₂) with maturation were recognized clearly. However, it was also recognized that the rate of epimerization of sterane was relatively higher than of triterpane in two sedimentary Basin in Japan in comparison with Paris Basin (France), Uinta Basin (U. S. A.) and Bohai Bay Basin (China). It was considered that the effect of the difference of heating rate among the sedimentary Basins appeared. That is, higher rates of epimerization of sterane than of triterpane in Japanese two Basins are possiblly due to relatively higher heating rates which are attributable to high geothermal gradients and high rates of burial.
In addition, the evaluation of the level of maturation by the equivalent reaction temperature and equivalent reaction time, which would be determined by the two kinetic parameters such as the extent of epimerization of sterane and triterpane, was proposed based on the kinetic considerations in this paper.

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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.

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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.

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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.

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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.

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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.

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Main constituent clay minerals in the Oashizawa specimens are smectite, mica/smectite mineral and chlorite/smectite mineral. The former two minerals occur with small amounts of mica, kaolinite and chlorite. It is clear from the mineralogical properties that the mica/smectite mineral was formed from smectite by adding alkaline cation and increasing temperature. This transformation starts by increasing the alkaline cation content and smectite changes to mica/smectite mineral with g=0 in the early stage. The mineral formed transforms to mica/smectite mineral with g=1 by encreasing temperature and pressure. The minerals with g=1 occur mainly in relatively lower parts of the Kusanagi Formation. Chlorite/smectite mineral can be formed from montmorillonite by adding Mg and Fe cations, but the genesis is not certain for the mineral found in the lowest part of the Kusanagi Formation.

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The plant derived solid organic matter in sediments bears the two geological evidences of sedimentary conditions and diagenetical to metamorphic grade of the host sedimentary rock if it is analyzed or measured properly. The object to study precise grade of organic metamorphism has to be restricted to a certain maceral in order to avoid variation of the values caused by the diversity of the matter. The most applicable effective method at present after identifying or separating the macerals is the coal microscopic measurements of vitrinite reflectance and sporinite fluorescence spectra under incident light. The two methods are applicable not only for dealing with coal seam but also with phytoclasts or kerogen, and the latter is the more effective for analyzing the lowest stage of the organic metamorphism including diagenesis and the former is for the diagenetical to the more higher stages where the fluorescent substance vanished. X-ray diffraction method for analyzing the degree of graphite crystalization is effective for grading the highest stage of organic metamorphism, but the contamination and dilution by other macerals than vitrinite affect the diffraction pattern in the lower stages, consequently the additional maceral analysis or concentration of vitrinite in the object matter is required for the more minute and exact analysis by this method.
It is suggested that present geological subject by applying the methods of analyzing the organic metamorphism to the Japanese Islands as a part of neotectonic island arc system is a precise analysis of stratigraphic and regional variation of the pattern in the Cenozoic group in connection with the present geophysical data around the islands. Practical application of the methods has been executed by the author to reveal a pair of organic metamorphism (AIHARA, 1980) between the forearc and backarc Paleogene coal-bearing groups in the island arcs reflecting a good coincidence with the Cenozioc terrestrial heat flow condition. Standing on a view point that the lower stage of organic metamorphism including diagenetical alteration implicates the succeeding more higher grade of metamorphism, the latter of the older ages will be analyzed and deduced analogically by this geological reasoning.

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In this paper the present anthor's opinions concerning the carbonaceous matter in sedimentary rocks and their graphitization processes are briefly reviewed.
Carbonaceous matter contained in sediments and sedimentary rocks as a chief constituent of coal and coaly shale, and as dispersed fine-grained particles in non-coaly rocks show progressive change of crystallinity. Their crystallographic transformation from amorphous to graphite structure corresponds well to the transition of authigenic and metamorphic minerals under diagenetic and metamorphic conditions.
Consequently carbonaceous matter is available to estimate the diagenetic and/or metamorphic degree of host rocks in which the matter is contained.

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High concentration (0.0182-0.0721μmole/g) of d-alloisoleucine has been found in a 1064cm blue mud sediment core taken from the abyssal plain of the northern part of Shikoku Basin (actual location: 31° 13.05′N, 134° 49.07′E, water depth: 4313m).
The amount of isoleucine racemization increases linearly with increasing depth below the sediment-seawater interface.
An age of 88.4×10³ years for the deepest portion (sample number 52, burial depth 1020-1028cm) in this core was calculated using a value of first-order rate constant at 2°C of 15.77-5939/T for isoleucine.
Calculated average sedimentation rate of the Quaternary deep-sea sediments in this area is about 12cm/1000yr.

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Porosity-depth relationships in the Neogene argillaceous and arenaceous sediments at the deeply-drilled representative wells of Japan were studied. The relationships both in the Neogene argillaceous sediments of Hokkaido and Niigata areas are closely resembled. In average argillaceous sediments of Japan, about 1200m in burial depth corresponds to 50 per cent in absolute porosity; 1600m to 40 per cent, 2100m to 30 per cent, 2700m to 20 per cent, and 3700m to 10 per cent. On the contrary, porosity-depth relationships in the Neogene arenaceous sediments in both areas are considerably differed. Porosities in arenaceous sediments of Niigata are always higher than those recognized at the same burial depth of Hokkaido. ‘Porosity Window’, which was newly termed in the paper, in the Neogene sediments of Niigata is much bigger than those of Hokkaido. 10 per cent porosity in argillaceous sediments and 20 per cent porosity in arenaceous sediments are very important to define the process of diagenesis in both sediments. Argillaceous rock type based on porosity range and mineral facies in the rock indicate the paleo-temperature and burial depth and can utilize to petroleum exploration.

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Opal-A in sediments is transformed to quartz through opal-CT. In this process, opal-CT changes in its internal structure: the d (101) spacing of opal-CT decreases progressively with the passage of time. The decreasing rate is strongly dependent on the reaction temperature.
In this paper, summarizing previous experimental works, some kinetic relations between the d (101) spacing and the thermal history are discussed and several problems to estimate the thermal history of sediments by using the kinetic relations are stated.

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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).

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To investigate phase relations in the analcime solid solution-alkaline solution system, amorphous materials of composition NaAlSi₂O₆, NaAlSi_2.5O₇ and NaAlSi₃O₈ were treated in the temperature range 120-450°C at 1, 000 bar P_fluid with pure water, Na₂CO₃ solutions (1/8M, 1/4M and 1M) and NaOH solutions (0.1N and 1N). The run durations varied from 1 to 90 days but were usually shorter than 50 days.
Phase assemblages synthesized are single phillipsite, phillipsite+analcime, single analcime, analcime+albite (+quartz), and albite (+quartz). The single phillipsite assemblage were obtained only at the lowest temperature region of the NaAlSi₂O₆-H₂O system, and quartz appeared occasionally in the higher temperature region of the NaAlSi₃O₈-1N NaOH system. Si/Al ratio of the synthetic analcime (solid solution) decreases with increase in Na⁺ concentration or alkalinity in the same alkaline solution system.
Syntheses in alkaline solution system result in lower temperature limits for the fields of the phase assemblages compared with those in pure water system. But, the relationship that the boundary temperature falls with increase in the Na⁺ concentration or the alkalinity is found only in the same alkaline solution system. Temperature range of the single analcime field expands generally by treating with alkaline solution in the NaAlSi₂O₆-solution system. In the NaAlSi₃O₈-solution system, which is considered to be important in study on diagenesis, temperature range of the single analcime field expands easily by treating with Na₂CO₃ solution, but the field does not expand and becomes rather unstable by treating with NaOH solution because of the high pH value.
Linear relationship is found between log of the reaction time and reciprocal of the absolute temperature for the phase reactions in the system investigated as shown in Fig. 7. Slope of the lines for the phillipsite-analcime reactions is more gentle than that for the analcime-albite reactions.

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Authigenic zeolites of vitric tuffs interbedded with the Neogene strata in the Noshiro oil field of Akita prefecture are mainly formed by the increase of geothermal temperature during burial diagenesis of marine sediments. The variations in the zeolite zones in this field, such as the upheaval type and the depression type zeolite zones, are closely related to the differences of the structural movements in the Noshiro sedimentary basin.
The upheaval type zeolite zone distributed in the Hiyama-Tomine area corresponds to the Ohgata-Natsui upheaval belt where is thin depositional area since the Onnagawa stage in the Middle Late Miocene. On the other hand, the depression type zeolite zone distributed in the Noshiro plain corresponds to the continueous sinking area in this basin. The difference of sedimentation in this basin began in the later Onnagawa stage and violently increased during the Tentokuji stage in the Pliocene.
The classified types of zeolite zones have been caused by the areal variation in paleo-temperature during burial diagenesis.

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Trioctahedral clay minerals such as saponite, chlorite-saponite mixed layer and chlorite are widely found in the Green-tuff formation composed mainly of Miocene pyroclastic rocks. Two modes of occurrence in saponite are recognized, namely cavity fillings precipitated from solution and glass replacements. The former is rich in Fe but poor in Al, while the later is rich in Al and Fe.
Al-Fe saponite seems to be transformed to chlorite through interstratification of chlorite and saponite by absorption of Mg(OH)₂ and release of SiO₂. Trioctahedral clay minerals in the Green-tuff formation is rich in Al than that in deep sea basalt. Tetrahedral Al is likely to be controlled by formation temperature.
Refractive indices of trioctahedral clay minerals are shown in Fig. 4. Birefrengence is the most diagnostic feature in the distinction between them under microscope.

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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.

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