(1) By extensive chemical analysis of works from oil producing Neogene Tertiary in Japan the extractive organic matter contents increase toward the geologically lower horizons and show two prominant peaks, one in lower Miocene so-called hard shale beds and the other in dark mudstone of uppermost Miocene-lowest Pliocene age.
(2) Present distribution of Pre-Miocene complex and Post-Miocene sediments leads the idea that existed Paleogene uplifted zone are replaced by geosyncline while the basins on both flanks uplified into ranges such as Hida in central Honshu and Ilidaka in Hokkaido. As soon as new central uplift built a remarkable developement, older uplift striking sunk on the contrary. It is the zone that Neogene geosyncline occured. In this process, it is limited only to the begginning stage of the sinking that the submarine environment in the sunlight permiting the organic to live and the sedimentary environment beyond the action of the wave making possible the organic matter to preserve are satisfied at the same time.
(3) The migration of oil taking place generally from high pressure area are laid clown toward low pressure area and naturally in a basin from thick sediment zone toward thinner zone. This movement finished during early depositional period, because mainly the oil fields have been exploratecl rather on the sedimentary high of a formation containing the reservoirs than on the elevation between the structures.
The anticlinal structure in the oil producing area has certain two tendencies. One is the thrusting anticline over the pre-existense anticlinal structure so-called under block and another a symmetrical large anticline near the central part in the basin.
But, it is rather reasonable that the main oil productive reservoir have been discovered in the former and in the horizon containing aboundant organic matter.
(4) Therefore, we can be applied a probability of oil fields in the non explorated area from such relation of geosyncline and oil fields.

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The author has been studying on clay minerals in the oil-hearing Neogene Tertiary sedimentary rocks of Northwest Honshû, Japan. In this paper he describes his provisional criteria for analysis of clay minerals in sedimentary rocks, with his basic considerations and laboratory experiments, which he conducted. He adds supplementary notes on the qualitative analysis to his preceding paper²⁰⁾. He also summarizes some noteworthy sedimentological relations, which have been considered by him to exist in sedimentary sequences of many geological basins.
Contents of this paper are as follows:
1) Progress of basic experiments for the establishment of the criteria and some result of qualitative analysis are described.
a) X-ray diffraction analysis applied to centrifugal fractions of mudstones due to random powder method.
b) X-ray diffraction analysis combined with various reagent-treatments and heat-treatment, applied to centrifugal fractions of mudstones due to powder orientation method.
2) He determined clay mineral suit of montmorillonite-illite-chlorite (± minor amount of montmorillonite-illite mixed layer), for the oil-bearing Neogene Tertiary sedimentary rocks in Northwest Honshû, Japan.
3) He proposed a classification of mudstones due to relative amount of clay minerals and quartz.
4) He found the striking negative correlation between the montmorillonite log (or clay mineral log) and the log of “Cl'-concentration of interstitial water” in mudstones, prepared for the exploration well Mitsuke SK. 1 (or Tamugiyama SK. 1). Based on consideration of it, he interpreted that a part of the so-called interstitial water, is composed of that delivered from interlayer water of montmorillonite crystals, through the pretreatment or heating up to 110°C of core samples. This interpretation is supported by the result of another experiment of his own, in which the oscillation method of X-ray diffraction analysis during heating up to 900°C, is applied to a centrifugal fraction of a mudstone cored from the depth of 1098m of the well Tamugiyama SK. 1.
5) The author determined clay-mineralogical divisions on the montmorillonite log, and he found that these divisions coincide with fossil foraminiferal subzonules.
6) On the Q-M (quartz-montmorillonite) diagrams characteristic distribution curve can be drawn for each fossil foraminiferal biotope unit in the Mitsuke and Tamugiyama sections. Existence of a kind of sedimentological relation is suggested by the comparison of relative positions of these characteristic distribution curves on Q-M diagrams with their corresponding foraminiferal faunal assemblages.
7) The author describes the possibility to determine characteristic distribution curves on the M-I-Chl (montmorillonite-illite-chlorite) triangular diagrams for geological formations or members.
8) The criteria for analysis of clay minerals in sedimentary rocks, which he proposed, are described.
9) In conclusion, present status and future problems of the sedimentary clay mineralogy, especially that concerning petroleum exploration and exploitation, are summarized.

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Investigating the organic constituents of mudstone over 700 samples, the writer ascertained that the characteristics in the organic matter of rock is closely related to the oil producing capacity of formations.
To determine the characters of mudstone in organic matter, the measurements used in this study are follows: Amount of extracts obtained by thermal extraction; hydrocarbon and non-hydrocarbon contents of extracts are determined by chromatography; calculated hydrocarbon contents of rocks (HyR) and ratio of carbon in hydrocarbons to total organic carbon (Ch/Co). Since the latter two coefficients, HyR and Ch/Co, are suitable to represent the characteristics of organic matter in rock, the writer tentatively adopted them as the indices of the oil generation capacity of rocks.
The values of HyR and Ch/Co of mudstone samples from the productive formations (Niigati) are 15 ppm and 0.0015 in the minimum, 1, 500 ppm and 0.20 in the maximum, averaging 208 ppm and 0.0208. In the productive formations, the mudstones occuring adjacent, both stratigraphically and horizontally, to oil reservoirs, show higher values of HyR and Ch/Co than those of the corresponding horizons apart from reservoirs. The mean values in non-productive (Kanto and Miyazaki) formations measure 36 and 30 ppm in HyR, 0.0041 and 0.0043 in Ch/Co. Thus in productive formations, these values are strikingly higher than in non-productive formations. This relation may have been resulted from the difference in depositional environments of the formations. The mudstones of non-productive 'formations were deposited in the sea where the bottom current was prominent and the oxidation was active due to the condition open to the ocean, whereas those of productive formations were deposited under the reductive environments without prominent bottom current and flanked by emerging zones.

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The purpose of this paper is to discuss the oil possibilities of Cretaceous system along the central parts of Hokkaido, chiefly concerned v, ith detailed discussion and consideration related to the following points of view. First, as the direct evidect of potential Cretaceous system, the occurrences of oil and or gas showings primary in situ or originated from the Cretaceous system were investigated and then their crude oil and gas in character were examined, hereby from the viewpoint of geochemical evolution of the crude the comparison of crude bearing in the Cretaceous system to the one produced from Neogene in Northeast Honshu or Paleogene were taken place. From this results, it became clear that the characters of the crude bearing in the Cretaceous system were light to medium, and extraordinaly abundant in gasoline and kerosene fraction as compared with the crudes belong to the tertiary system. By gas chromatic analysis, they are abnormal type in crude oil which are rich in cyclohexane and cyclomethylhexane, naphthenic compounds, poor in below n-hexane and rich in n-octane, this indicates that they belong to older type of oil and it is as well believed that they have been subjected to the distillation by migration or thermal distillation action for a long time. Furthermore, it is interesting that the crude oil contained in the Poronai formation, Paleogene are similar in character with those belong to the Cretaceous system. Showings are most predominant over the Hakobuchi group and the middle Yesso group are next to them. The sandstones as the valuable reservoir rocks have good developed in the Hakobuchi group qualitatively and qualitatively as well. To the contrary, the sandstones belong to the middle Yesso group have their predominace with a view of their wide distributional area and continuity. The mudstones supposed to he the mother rocks of oil are almost classified to “Q-type mother rock” (correspond to upper Teradomari and Funagawa formations), and it seems to indicate that either the migration of petroleum were relatively fast through them or the petroleum were squeezed out at the early stage from them. As a whole, as to the organic contents extracted from the mudstones of the Cretaceous system, they are inferior to the one found in oil fields of Northeast Honshu but concerning the total amounts of mudstones, those are superior to these, and the total original reserves estimated by Emery's method amount to 731, 000, 000 tons, and it supposed that they show about 5, 4 folds as much as the sum total reserves in Niigata and Akita prefectures. Several uplift areas are infered by means of the preparation of the isopach maps and hereby the distribution of oil and or gas showings are concentricaly abundant along the marginal parts of the sedimentary basins situated around these uplift areas or west of them. Their distributions are independent of the structures or are apart from the anticlinal axis found on surface today. These differ from the occurrences of showings originated from Tertiary system and so it is suggested that the petroleum migration may have taken place prior to or earlier stage of the deformation formed by Cretaceous system today. Moreover the possibilities of cretaceous oil seem largely promising for accumulation by migation beneath the present Tertiary system, along the marginal parts of the sedimentary basins located west of uplift areas or around them.

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In Tenpoku district, petroleum exploration has been continued from 1914, but only 6 oil and 1 gas pools have been discovered, and their main producing horizon is neogene Mapsuporo formation.
Considering the variation of lithofacies and thickness of neogene tertiary formation of this district, it can be distinguished that the geological condition during the deposition of these formations undergo considerble transformation and fluctuation. The writer can explain these phenomena more clearly for Masuporo and Wakkanai formations, because at those stages more geological data are available.
At Masuporo stage, it is recognized that there were several uplift parts such as Masuporo, Matsuozawa, Kiyokawa and Chikubetsu, and depression areas such as Magaribuchi, Utakoshibetsu and Sarakitomanai.
The nature of these uplift and depression areas are different in their genesis and development. From the earlier stage of Magaribuchi, Soya, and Onishibetsu, some parts of these differences had been succeeded.
But later Wakkanai stage, the configuration of the sedimentary basin is widely changed and simplified.
The center of sinking is clearly distinguished along Wakkanai-Sarakitomanai trend, and the west and east margins of the basin are graduary made clear of their presence.
The writer presents a hyposesis to explain the mode of occurence of petroleum in Tenpoku district.

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The Ishikari oil and gas producing depression of the surrounding region covers an area lying between 42°36' and 43°50' N. lat., and 141°30' and 142°15' E. long., which occupies the western part of central Hokkaido.
In the rolling hills of this region, 4 oil fields have only been developed and produced about 300, 000 kl in cumulative crude, up to 1955. After 1956, however, 2 oil and 3 gas new fields have been discovered by the result of the recent exploration on this depression, and stratigraphically most of the producing horizons are restricted to the marine Fureoi and Morai groups of middle to upper Miocene in age.
This report is showing 90 anticlines, 59 synclines, 6 tectonic zones and 8 uplifts on this area. From the isopath maps on the depression, the writer explains the subsurface structure at each formations of Miocene to Pliocene and so-called Paleozoic in age.
The structural development history are summarized as follows:
I. All the new found oil and gas-bearing structures were generated at later Atsuta stage, these were widespread generally during pre-Morai-post-Atsuta in time and developed to one of the peak at Morai stage, accompanied several flucturation such as clear differentiation of the sedimentary basin and remakable westwards transformation of the sinking belt. And on some parts of the dipression, the folding have been succeeded at Takikawa stage, and is completed at the Quternary age.
II. Some groups of the folding, it is distinguished there were the relation with several uplift zone at Takinoue-Fureoi stages after post-later Oligocene Poronai-pre-early Miocene Momijiyama in age. Few of these uplifts have been reflected the relief of the paleostructures in pre-Tertiary age, such as well-known Shintotsugawa and Umaoi anticlines. In the depositional position of the sedimentary basins, the former belongs on the shelf of post-so-called Paleozoic and the latter on the hinge line of Cretaceous to Paleogene Tertiary deposits. There are not a few unknown part on this area, but judging from the oil geologic condition as to deposition of sediments and the geohistorical factors of the established facts, the writer thinks that it should be more concentrated future prospecting and exploration for petroleum and natural gas at the folding zone of eastern part of this area.

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In the Tokachi region, situated in eastern part of Hokkaido, some oil seeps are found from early days. However, the oil exploration surveys started in 1956, and the well drilling are not carried out up to 1961.
In this paper, the compiling studies of the results of surface geological surveys, seismic surveys, and gravitational surveys are described, and the possibility of oil production at the south-eastern part of Tokachi region is considered.
Results of the studies are as follows;
(a) The standard stratigaphic order of oil-bearing Neogene system in the Tokachi region is amost established, and the correlation to the Tertiary Formations of oil producing area in central Hokkaido is become clear.
(b) The shape and property of the sedimentary basin are nearly cleared up.
(c) The main source rock of petroleum may be the Taiki and equivalent Toberi, Kawakami Group, and their wide development is expected in this region. The reservoir rocks are contained in these groups, and at the lowest course-grained parts of the overlied Tokachi Group.
(d) The author presumes that the oil accumlations at the Sarubetsu anticline and some anticlinal structures of its western side are the most hopeful zone.

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Tsugaru district in Aomori Prefecture is kown as one of the district of rich oil seepages, but not yet discovered oil field. Through the writer's geological survey for several years, and the synthetic considerations with the results of geophisical survey and explorating wells, became clear the geological sequences and correlations in each area of Tsugaru district. According to the relations between stratigraphy, structures of basement and Tertiary rocks, and changing of lithological and biological facies, the outline of orogenic evolution of oil-bearing Tertiary in Tsugaru district was able to elucidate.

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Oil occurence in basins may generally be related to the relief of basins bottom and to the sedimentary environments.
To clarify the process of the oil accumulation, the study of paleography is a important method and a basic information for the oil exploration.
The writer studied on the stratigraphy of the Neogene strata developed in the surrounding area of the Dewa hilly lands, which include the southern part of the Akita and Yamagata, the eastern part of Miyagi prefectures, and introduced several time-stratigraphic units and its formations. The strgtigraphical relationships of each province are discussed, and inter-provincial correlation are shown in Table 1.
On the study of the isopach map, down ward sinking and upward movement area of the sedimentary basin are clarified. But isopach map alone will not give a trusty aspect of a depositional basin. The lithofacies and the biofacies are equally important method for the restoration of basin depth and sediment-tary environments. Combinations of the lithofacies, biofacies and isopach, make the aspect of a depositional basin clear. Accordingly, on the basis of the ecological study of the fossil foraminifera, the six biofacies are recognized, namely (1) littoral zone biofacies, (2) inner neritic zone biofacies, (3) outer neritic zone biofacies, (4) bathyal zone biofacies, (5) deep stagnant zone biofacies, (5) deep stagnant zone biofacies, (6) shallow stagnant zone biofacies.
The writer prepared the paleogeographical maps of the Nishikurosawa stage, Onnagawa stage, Funakawa stage, Kitaura stage and Wakimoto stage, making account of the lithofacies, biofacies and isopach, those are shown in Fig. 18-22.
As the result of the study, the Dewa Hilly lands was situated on the subsiding zone during the Onnagawa stage, but in the late Funakawa stage, was slowly uplifted from south to north.
Oil occurence is closely related to the paleogeographical aspects. Submarine ridges in the deeper stagnant sea are one of the most favorable places for the oil accumuration. The Amarume and Fukura oil fields may be an example of this relationship.
The Innai-Katsurazaka and Horiuchi oil fields are situated in the hinge belt, where the sand-shale ratio is bitween 1/8 to 1.

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Studies on the biofacies of the sediments distributed in the Shonai-, Shinjo-, Nikabo-, and Yajima areas in the northwestern part of Yamagata Prefecture were undertaken parallel with stratigraphical, paleontological and structural analyses. This project was planned to understand the differences in both lateral and vertical distributions of the different lithofacies according to horizon and stratigraphical unit because of the intimate relationship with oil-producing and carrier beds.
For the purpose of the study the Funakawa and Kitaura formations of upper Miocene age and of extensive distribution in the oil-fields of northwestern Japan and important as oil carriers were selected. The Funakawa which is subjacent with conformity to the Kitaura in all of the areas is studied in this work.
Lithofacies change in the middle and lower parts of the Kitaura and Funakawa stages is particularly noteworthy in the Funakawa south of the line combining Shinjo and Kuraoka where sand intercalations abruptly increase and the facies becomes tuffaceous, whereas in the Kitaura which is dominantly of sandy siltstone but in the Nikabo and Shinjo areas tuffaceous sandstone intercalations increase and in the latter mentioned area an alternation is developed and lignite becomes intercalated. By the increase in sandstone there is developed in the south of Shinjo a peninsular deposit.
Details of lithofacies changes were recorded over the whole areas studied and their relationship with thickness of the respective stratigraphic units, faunal yield and their contents were analysed, by which the paleobathymetrical conditions, paleosedimentary basin bottom configuration and changes in the structure of the basin could be worked out.
Of the Foraminifera washed out from numerous samples taken both vertically and laterally within the Funakawa and Kitaura formations, studies were progressed as to their quantity-analyses with regard to lithofacies and horizon as well as position. From the characteristic features of the different Foraminifera distinguished and the assemblages recognized there could be discriminated arenaceous and calcareous assemblages of the neritic zone and calcareous assemblages of deeper water zones. The relationship of these two different assemblages to their environments (lithofacies, horizon, stratigraphic position, etc.) was inferred from biofacies construction.
Also interpreted was the relation between arenaceous planktonic Foraminifera and calcareous benthonic ones, which resulted in when the characteristic features of the above-mentioned were incorporated with the various aspects of them already stated, the general features of the sedimentary basin during the time of the respective horizons which yielded the Foraminifera as related with development and migration was clarified as described in detail in the text.
The various assemblages of the Foraminifera not only served to indicate the features above-mentioned but also were good guides in paleobathymetrical analyses of the respective horizons of the Funakawa and Kitaura formations, the results being supported from the bathymetrical ranges of the Foraminifera on the shallow to deep waters offing Yamagata and Akita Prefecturs.

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Recent deep drilling by Teikoku Oil Co. is adding much new subsurface geologic information, making possible an interpretation of the central portion of Shonai Plain. The present study is a report on the subsurface stratigraphy and the structure of that region, related to hydrocarbon deposit. Three matters in particular are reported.
1) There is a newly discovered Jurizuka Uplift which is gently descending to Sakata city and increasing the thickness of the tertiary formation to the north.
2) The gentle anticlinal structure is disclosed near Sagoshi and its core is composed of the pyroclastic sediment of green tuff formation. On the crestal part of this anticrine, a small amount of hydrocarbon is found, but not so productive as the lacking of the potential reservoir.
3) The writer discusses the petroleum accumulation in Narahashi-Ishinazaka oil field, related to the sedimentation and the growth history of each anticline in Shonai Basin.

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In this paper the writer confirms the Araya mudstone facies in the Shiiyan stage from the compiled basis of the recent explorations, and explains the effects of this facies took a principal part in the process of the generation, migration and accumulation of oil and gas in the Niigata basin.

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The writer describes the stratigraphy and the structural development of the Chuetsu District, and discusses the relation between them and petroleum geology. The results are summarized as follows: I. The structural development was analized by the isopach maps and the restored sections, with the lapse of time, from Tsugawan Stage to Recent. The deposition of sediments, which were controled by the relative movement of basement, arose sinking belts and stable areas. Those positions changed their places with age. Structures are classified as follows:
(1) Structures, which are banks or highs throughout Tsugawan Stage to Recent. (Yahiko, Niitsu)
(2) Structures, which were banks in early stages, but submerged under plains now. (Kamo, Mitsuke)
(3) Structures, which generated in the intermediate stage, then developed on perfect structures.
(Teradomari, Amaze, Nishiyama, Kashiwazaki, Chuoyutai)
(4) Structures, which generated in earlier stage, but then submerged, and rejuvenated lastly.
(Sekihara, Katakai, Ojiya, Matto, Iwata, Hachikoku, Torigoe, Higashiyama, Nigoro, Takezawa, Tamugiyama)
II. Many of oil-bearing structures were banks or stable areas, when oil-bearing zones deposited.
III. Oil reservoirs in this district are mainly lenticular in shape macroscopically, so, oils, once traped, cannot migrate thereafter. Accordingly, hydrodynamic theory of oil accumulation cannot be applied to this district.
IV. In oil reservoirs in volcanics and pyroclastics, migration and accumulation of oil are took place mainly along fissures. So, maturation of oils in these types of reservoirs is low degree.
V. Volcanics in this district are of submarine eruptions. Accordingly, volcanic banks are made, which are suitable for genesis of petroleum deposits.
VI. Volcanics, making burried structures, have great possibilities of oil accumulations by differential compaction, being caused by difference of compressibility between volcanics and muds. Such structures act as resistant mass for folding.
VII. To form oil deposits, some degree of thickness of succeeding formations are required. Lack of deposition is unfavorable for oil accumulation. Cap rock is necessory, and Nishiyama Formation is best one.
VIII. Garvity of oils is closely related on nature of oil reservoirs.
IX. According to above mentioned, the writer concludes that insitu origin theory of oil accumulation-theory of early genesis of oil-is suitable. Migration and accumulation of oil in this district are probably accomplished in time unit “epoch” at latest.
Conclusively, each structure has individual development history. So, to estimate the oil possibility of certain horizon of one structure, we must study the structural situation, sedimentary environment, and accumulation area, when that horizon being deposited. Geologic cross section, seen now, cannot tell of these knowledge. Systematic analysis of stratigraphy and tectonic deformation from earlier stage to Recent, is a key to this understanding. Thorough examination of such analysis brings more profits in oil finding. It is a problem, however, how we can find burried structures under vast plains. Of course, we must adopt geophysical methods on the plains at first, but above mentioned analysis is more important. So, we must try pioneer borings to get such data. It is the greatest matter of concern.

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The middle parts in Niigata Prefecture including major oil fields exists as the most remarkable area, and these oil fields mainly belongs to Bodaiji-Kamo Uplift and Kakuda-Yahiko Uplift was grown after Teradomari stage in Neogene Tertiary age.
In this paper are disscussed how have developed historicaly and structurely, and then as the conclusion for migration and accumulation of oil from these area introduced following two important points:
(1) The end of the regional migration of oil accumulated on the paleostructure to Shiiya stage.
(2) The local migration of oil are distinctly after Nishiyama stage and petroleum (or gas) finaly was trapped in the structure according to the structural movement after Uonuma stage.

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Geological Survey of Japan, Japan Petroleum Exploration Company, Teikoku Oil Company and other organs are vigorously carrying out exploration works of petroleum and natural gas through out the Kwanto Plain.
In this paper the writer makes clear the surface shape of the basement of Kwanto Plain through compiling gravimetric, seismic and well data which have been got by the above organs.
The writer shows Miocene paleogeography based on knowledges from overlying Miocene series, and he presents histrical views on the surface shape of the basement and his tectonic views on the structure of the basement.
He distinguished a Cenozoic (especially Tertiary) sinking trough, and concludes that the so-called Kwanto basin forming movement is one type of the sinking of the above mentioned Cenozoic sinking trough in a new phase.

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