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The Inner New York Bight, at the head of the Hudson shelf channel, has been the site for ocean disposal of various waste products since at least 1888. Natural channel-like bathymetry expressed in 1845 is today a series of hills rising to within 12 m (40 ft.) of the water surface superimposed upon a broad lobate mound. This topographic inversion created over the past nine decades is attributable to disposal of materials (soil, sand, and stone) of varying composition generated during construction in the New York metropolitan area. Data indicate approximately 765 · 10 6 m 3 (1 · 10 9 yd 3 ) of waste has been dumped in that region from 1888 to 1934. Isopach maps, sea-floor profiles, seismic records, and vibratory cores show much of the fill has remained in place in spite of bottom currents of approximately 25 cm/sec (0.5 knot) and a wave climate of H s = 0.76 m (2.5 ft.); T = 5−15 sec. Man-made islands proposed for the inner continental shelf for siting power, port, or recreational facilities will use large volumes of stable material for core fill, which could be waste materials such as those described. Effective regional coastal-zone planning should recognize uses for past and future waste material as such practices would conserve sand and gravel resources for other high-volume needs (shoreline nourishment and protection and construction aggregate) and alleviate some of the site-selection problems in land disposal of waste.

To make efficient use of isopach maps and lithofacies maps that are indispensable in oil exploration, it is required that such maps were prepared on the basis of stratigraphic units distinguished by significant time plane.The Cretaceous sediments which are widely distributed in the axial zone of Hokkaido are divided, in descending order, into the Hakobuchi group, the Upper Yezo group, the Middle Yezo group, the Middle Yezo group, the Lower Yezo group, and the Sorachi group. However, since this stratigraphic division is based largely on lithology, the boundaries of the respective groups may sometimes intersect the time plane obliquely. If such is the case, then the maps that were prepared from the stratigrephic division would be meaningless.Therefore, the present writer examined the propriety of the past methods of defining the base of the Middle Yezo group. His aim was to discern the base of the Middle Yezo group as a time plane and clarify the scope and significance of the Intra-Yezo disturbance.The writer has reached the following conclusion : The Intrayezo disturbance took place in a limited period of time during late Albian. It formed the uplifted zone that stretches north-south centering on the Ashibetsu mountains, and also upraised the west marginal area of the Hidaka mountains. This disturbance probably represents a crustal movement in the middle period of the history of development of a sedimentary basin.

Fossa Magna is a remarkable tectonic zone which divides the Japanese main island (Honshu) into two parts, those are northeastern Japan and southwestern Japan. This tectonic zone runs from Niigata Prefecture through Nagano Pref. to Shizuoka Pref. and was introduced by E. Naumann in 1885.In the northern part of the Fossa Magna, the Niigata Tertiary sedimantary basin is in contact with the Nagano basin. Strong tectonic movement and Quaternary volcanoes make it very difficult to directly combine these two basins.The writers tried to compile these basins from the view point of petroleum geology and to give some considerations about the possibility of petroleum in the Nagano district.At first, they made a stratigraphic correlation of the Nagano and the Nishikubiki (southwestern margin of the Niigata basin) districts. Afterward, they considered sedimentary conditions and sedimentary enviroments using foraminiferal data and isopach maps, then estimated the existence of "Nishikubiki up-lift" (provisional name) to the northwest of this area. They supposed that this uplift stands opposite the "Nagano Central up-lift" which is located along the southeast of this area. With the progress of intermittent rising of these up-lifts during the Neogene age, the sedimentary basin between the Nishikubiki and Nagano Central up-lifts became deeper and narrower. A vast amount of sand and mud deposited in the basin. Some of these sediments show flysh facies.The writers considered, as well, about the occurrence of many oil-gas showings and oil-gas fields of the Nagano district in connection with the geologic development of this area. It is important, above all, that the Aoki and the Bessho formations (lower-middle Miocene) are valuable as the source rook and that some oil showings were found in the "Green Tuff" (lower miocene pyroclastic rocks).

The main features of the Waulsortian (Upper Tournaisian and Lower Vise'an) carbonate mudbank complex of Eire are described and the paleogeography outlined. The distribution and lithological characters of the Waulsortian limestones and associated sediments are briefly described. The Waulsortian rocks comprise a large mudbank complex, together with numerous discontinuous banks which formed in the lagoon on the landward side of the complex. The complex originally extended over an area of about 7,000 square miles in Eire. Thickness variations are shown on an isopach map. The development of the complex was controlled by two (or more) stable structural blocks on the Variscan foreland. These allowed the accumulation of a great thickness of Waulsortian limestone in the Shannon (NW. Co. Limerick and S. Co. Clare) and Cork areas before lateral spreading began. Bank growth took two main forms. These, the knoll and sheet forms, are briefly described and illustrated. The mechanism of growth is less certain. It is sugg...

Various geophysical methods are discussed in relation to their possible value in locating limestone reefs, with special emphasis on the gravity meter and seismograph. The effects of possible velocity variations through reefs on reflections from below a reef body are examined. Relationships between the shallow and deep horizons indicate that time isopach maps of such seismic data extremely valuable. A suggested exploration procedure describes several detailing methods, and emphasizes the important role of the interpreter in solving the problems associated with exploration for limestone reefs.

This preliminary report--part of a detailed hydrologic study--based on isopach contours plotted from nearly 900 cores gives an outline of the subsurface Tertiary stratigraphy and structures of Beauce (France). The isopachs make it possible to recognize the limits of the Burdigalian, upper Aquitanian limestones, the lower Aquitanian molasse, the lower Stampian Fontainebleau sands, the upper Stampian limestones, and the Sannoisian and Eocene lower lacustrine limestones. Structural features deduced show a great variation in the thickness of the lacustrine series.

“Obanazawa pumice bed” is extensively distributed in Obanazawa basin and its vicinity along the middle-stream of the Mogami river. This deposit was first described by Prof. Y. Tomita as the deposit under the fluvial agency of the Niu river at the time of the explosion of Funagata volcano (in Ou mountains), at the source of this river.The writers exmained about 160 exposures and made the isopach map of the deposit. From this map, the volume of Obanazawa pumice was roughly estimated 0.19km. The deposit attains a maximum exposed thickness in the western border of its distribution area, namely in the vicinity of Hijiori spa. Further, Obanazawa pumcie bed is found on the surfaces of hill-land and higher-middle terraces (Sabane-Obanazawa surfaces).These observations about the distribution of Obanazawa pumcie and some other evidences indicate that Obanazawa pumcie was deposited as a fallen tephra originated from Hijiori cladera (Dewa range). In the writers' opinion taking the result of pollen analyses and archeological sruvey into consideration, Obanazawa pumice bed belongs to the upper Pleistocene or lowest Holocene age.

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.

General stratigraphy and palaeontology on the Niigata Oilfield region are described and discussed on the compiled basis of the recent geological and geophysical survey with the application of the knowledge of oceanography, palaeoecology and sedimentlogy.The writer proposes the new stage scheme for this region, they are, from lower to upper, the Tsukawan, the Teradomarian, the Shiiyan, the Nishiyaman, the Haizumean, the Yamayan, the Ogunian and Oyaman. Fig. 1. shows the columuar section of the Tsukawan. Fig. 2. is the isopach map of the shiiya formation. Here, the writer gives a new idea on the developmet of the geologic structure of this region. That is, although there are some differences in degree on scale, on age and in place, the deposition, local denudation, folding and faultng are carried on continuouously and progressively, accompanied with the upheaval and subsidence of the basement bl_??_ck and igneons action. Also at present, it is carrying on. This idea is shown diagramatically in Fig. 3, in which direction of arrow shows one component of the four-dimensioned vector including time factor. This phenomenon, the word of "evolutional cnange" being proposed for it, is believed to be the true attitude of the earth's crust.

The principal biofacies--continental, brackish, littoral, epineritic, infraneritic,and benthonic--are reviewed and applied to the formations of the late Tertiary basin in the lower Cheliff river region, western Algeria. Comparisons are made with Lowman's reference profile in the Gulf of Mexico. It is concluded that the isopach map reflects faithfully, although not necessarily quantitatively, the deformations which affected the bottom of the depositional basin.

Trend surface analysis is a procedure for separating the relatively large-scale systematic changes in mapped data from essentially non-systematic small-scale variations due to local effects. The method can be applied to any contour-type map, and has been used for analysis of gravity maps, isopach maps, facies maps, and maps of igneous and sedimentary rock attributes. When observations can be collected on a rectangular grid, orthogonal polynomial analysis permits convenient separation of the trend from the residuals. When observations are limited in number or are irregularly distributed over the map, non-orthogonal polynomial analysis can be used to determine at least the linear and quadratic components of the trend. These surfaces and deviations from them have value in geological interpretation, and they suggest that even when the complete trend is known, maps of selected trend components may be useful for examining special problems. Polynomial analysis of maps is facilitated by use of high speed computers. Organization of an IBM 650 program is outlined in this paper.

Seismic profiler data from about 200,000 km of traverse in the South Pacific are used to develop a sediment isopach map of the area. They reveal in some detail the marginal trench sediments and the sediments of the equatorial and subantarctic zones. Recent sea-floor spreading is indicated by an abrupt thinning of sediments near the crest of the Pacific-Antarctic ridge. This recent cycle of spreading appears to be related to possible large-scale vertical movements in Melanesia. Recent sea-floor spreading explains some aspects of sediment distribution and tectonic activity but is not clearly applicable to the distribution of older sediments in the South Pacific. The sediment distribution (except near the mid-ocean ridge) in subantarctic waters seems to depend primarily on the effects of a former more northerly location of the polar front and on modern bottom currents. Active trenches occasionally reveal trench sediments that appear to be folded near the continental slopes in profiler records when crossings are made at acute angles to the fold axes. The velocity structure of equatorial sediments is derived from sonobuoy data, and the areal extent of the Cretaceous (‘opaque layer’) reflector is increased.

The Nagaoka Plain is located in the central part of Niigata Prefecture, Japan. It is gently folded area and is bounded by intensely folded hilly areas. Many oil and gas fields have been discovered and developed in these areas. Some of them are characterized by the abundance of pyroclastic reservoir rocks.The writer studied geological development of these areas using some restored stratigraphic sections and isopach maps, and he obtained the following conclusions. (1) Gently folded anticlines in the eastern half of the plain area may have been originated from the synsedimentary upheavals (synchronous highs) which consisted of basement complex and "Green Tuff" (pyroclastic rocks of early Miocene). (2) Foldings of surrounding hilly areas may have been farmed since Nishiyama age early Pliocene). This tectonic movement was possibly caused by block movement of the basement. Thrust faults have extended along the boundary between the folding area and the gently folded area with down thrown anticlines under them. Down thrown anticlines have pyroclastic rocks in their cores and some gas reservoirs have been found in them. (3) There are two types of petroleum deposits of Green Tuff. In the first case, oil and gas migrated at the early stage into the Green Tuff which was making synchronous high by itself (Mitsuke Oil Field type). On the other hand, in the case of Yoshii Gas Field, gas migrated into the Green Tuff at the Teradomari or Shiiya age (late Miocene) when the Green Tuff got to reveal itself as the structural high (Yoshii Gas Field type).

The Bowen Basin is a structurally complex area occupied by a thick sequence of Permian‐Triassic volcanics and sediments whose depositional history is also complex and in many places has controlled the subsequent structural development. The depositional evolution is portrayed by isopach maps of eight regional rock units recognised in the Bowen Basin sequence. This sequence was deposited in a series of downwarps and on adjacent, less rapidly subsiding shelf areas. This paper discusses the shape, distribution, and persistence in time of the downwarps and shelf areas and indicates the relationship between them and the present structural elements of the Bowen Basin. The relationship of the depositional history of the Bowen Basin to the problems of exploration for oil and gas in the Basin is also discussed.

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.

SUMMARY A clastic deposit is represented by several diagrams. C-M diagrams in which C is the one-percentile, M the median of the grain-size distribution, characterize the coarsest fractions of the samples. F-M, L-M and A-M diagrams in which F, L and A, respectively, are the percentages by weight in the samples of grains finer than 125, 31 and 4 μ characterize the finest fractions. As a group, these diagrams form the “grain-size image” of a deposit. The above parameters were selected because they are closely related to transport and deposition mechanisms. As a consequence, the grain-size image gives fairly precise information on hydraulic conditions under which a deposit is formed. A large number of deposits were compared by means of their grain-size images. This comparison shows that some texture characteristics are related to the environment of deposition while others are controlled by basin mobility. Mobility should, therefore, be considered when comparing sediments of different basins and particularly recent and ancient sediments. Relationships which exist between certain sizes of clastic grains and the most probable deposition mechanism are used to classify clastic sediments by subdividing them into types indicative of their genesis. Grain-size types can be represented on maps and cross-sections. Grain-size facies maps of ancient formations represent lateral variations of texture and of hydraulic conditions across all basin environments and do not necessitate a reconstruction of these environments, which, often, is questionable. These maps, sell suited to show and project sedimentary trends, complete conventional isopach and sand/shale ratio maps. Integrated with ecological determinations and sedimentary structure descriptions, grain-size facies maps are a means of environment analysis.

The time‐depth curves to the main mapping horizons “C” and “P” in the Cooper basin of Australia are expressed as two distinctly different functions of the form [Formula: see text]. The velocity variations throughout the basin are depicted by a contoured interpretation of the deviations (Delta Z’s of well values from average formula values. The Delta Z interpretations are largely independent of local structure. Consistent isopach and structural maps, computed and contoured by machine using data from the Delta Z (velocity) interpretations and seismic times from 11,450 shotpoints, fit the well information but could not practicably be kept up to date with new velocity and seismic control because of computer program limitations. The work involved in manually updating the velocity adjusted maps in subsequent years was reduced by the tabulated data lists made by the computer. The computer method for reviewing the interpretations was revived in 1970 when exploration activity mushroomed and improved contouring programs became available in Australia.

The results of a gravity and magnetic survey of the Uinta Mountains and surrounding area are presented and discussed. A relatively high Bouguer anomaly over the core of the range and low anomalies over the flanking basins are caused by low-density sedimentary rock in the basins. A density map and an isopach map of a ‘Tertiary’ section have been constructed from the gravity data, which are in general agreement with known geology. The mean free-air anomaly of +8 mgal shows that the area, including the basins, is in approximate iso-static equilibrium. The mean Bouguer anomaly of −225 mgal corresponds to a mantle depth of 50 km. A large negative magnetic anomaly is associated with the main structure of the range and has been interpreted as having been caused by a batholithic intrusion of low-susceptibility rock, by upwarping of the Curie isotherm requiring a minimum thermal gradient of 27°C km−1, or by a susceptibility decrease caused by tectonic stresses. A positive magnetic anomaly is associated with a fault zone at the east end of the range; it corresponds to high-density rock that is shown by gravity data.

A treatment of the Upper Devonian commercial gypsum deposits of the Moscow Basin. An isopach map, cross-section, and a correlation are included to illustrate facies changes within the evaporitic section. The primary origin of these deposits is emphasized and supported by carefully controlled stratigraphic data. --L. M. LeRoy.

Potential studies in the accumulation of coal-bearing strata as being important in further understanding the natural history of coal are discussed. These lines of approach include regional isopach studies of the stratigraphic unit containing coals, and the individual coal beds; bulk petrographic and lithofacies studies of the non-coal strata; biofacies and ecologic studies; and, tectonism during the deposition of the sedimentary units concerned.

Summary Stratigraphic mapping methods were developed largely for sub-surface studies, but the same techniques can be used with surface data where sections of the stratigraphic unit are available over an area instead of along a relatively narrow strip. The basic maps include a structure contour map and an isopach map to show the geometry of the stratigraphic unit, and one or more contour-type facies maps that show variations in rock composition. Interpretation of the maps is commonly aided by trend surface analysis that removes local fluctuations from the data and permits clearer examinations of the broad patterns of areal variation.

Seismic data in the Indian Ocean are used to construct an isopach map of unconsolidated sediments. The major thickness of sediments is found in the following places: (a) the Indus and Ganges cones, which comprise about 40% of the sediment of the Indian Ocean; (b) basins adjacent to the continents on the east and west containing largely terrigenous sediments; (c) a zone south of the Polar Front, which is high in biologic productivity and where extensive non-stratified accumulations of sediment occur. Sediment cores indicate that the sediments in this last category are largely siliceous oozes. The crestal area of the mid-oceanic ridge is consistently bare of sediment to a distance of at least 100 km from the axis, except on the southwestern branch where thick sediment pockets have been found within 100 km of the crest. This relative abundance of sediment close to the ridge axis in places on the southestern branch may be related to a much slower spreading rate here than elsewhere, or to the complications introduced by the numerous fracture zones offsetting the ridge crest.

Correlations between 159 cores from the Southern Ocean has been established using paleomagnetic polarity changes. Isopach charts of the sediments using the Brunhes/Matuyama boundary (0·7 million years) and the Matuyama/Gauss boundary (2·35 million years) reveal regional changes in sedimentation rates that can be related to changes in Antarctic glaciation. This influenced paleocurrent structure and sedimentary conditions. Brunhes age sediments range from 0 to more than 16 meters in thickness, and reveal scour zones or areas of low deposition beneath the circumpolar current and where currents flow along the bottom from the Wedeell and Ross seas. Matuyama sediments are generally thinner and do not show the effects of the circumpolar current in the area of investigation. The position of the belt of siliceous oozes and probably the 0°C surface-water isotherm has migrated sporadically south more than 5° of latitude from Gauss to Brunhes time in response to waning glaciation. Antarctic glaciation was initiated more than 5·0 million years ago, but insufficient data are presently available to delineate earlier history.

The Cretaceous sequence in Hokkaido might be classified two major groups by the orogenic cycles. The agency of the first orogenic cycle origenated in Okhotsk Sea and shift the basin in the direction of south-west. It is in the cycle that the Lower Cretaceous (Neocomian-Cenomanian) formations were deposited. The second that was caused by the elevation of the Honshil arc moved the basin in the direction of east, from the western Honshu are to the eastern Pacific Ocean. In this cycle, the Upper Cretaceous (Turonian-Maestrichtian) formation were deposited. Each of the major cycles has two minor cycles. The former break of them is between the Neocomian and Aptian, and latter between the Campanian and Maestrichtian. Corresponding with them, each several breaks of fauna could be recognized. Particularly, the faunal break between the Cenomanian and Turonian is most dominant. The isopach maps of each formation are shown, Figs. 1-4. The depositional cross section from east to west is shown, Fig. 5.

A classification scheme is proposed based on measurements made on the resulting pyroclastic fall deposits, the significant parameters being the area of dispersal and degree of fragmentation of the material. An empirical measure of the first is the area enclosed by the 0.01 Tmax isopach (where Tmax is the maximum thickness of the deposit), called D, which ranges from less than 10 km2 for deposits of strongly cone-building type to more than 1000 km2 for deposits of strongly sheet-forming type. An empirical measure of the second is the percentage of material finer than 1 mm in the deposit, or more simply at the point where the 0.1 Tmax isopach crosses the dispersal axis. The latter value, called F, varies from less than 20 for deposits in which fragmentation was mainly achieved by the tearing apart of magma, to more than 80 where it was largely due to thermal shock resulting from the quenching of lava by water.

The areas around Tokyo Bay offer the standard stratigraphic column of the Quaternary system in Japan. The writers have investigated the geomorphology and surface geology of the latest Quaternary in these areas. The results are summarized as follows:1) The latest Quaternary marine and fluvial deposits (theso-called Alluvial deposits) in and around Tokyo Bay were accumulated during the regression and transgression that had occurred since the beginning of the Late Wisconsin (or WurmIII) glacial age or about 35, 000 B. P..2) Subsurface data from boring cores in the coastal areas is now sufficient for presenting the distribution of the depths of the base of the latest Quaternary deposits (fig. 2) and for presenting the section of sedimentary facies of the latest Quaternary deposits around Tokyo Bay from Hommoku Cape to Futtsu Cape (fig. 3). The deposits can be divided into two members, the Upper and the Lower, based on the cycle of sedimentation.3) According to the mineral composition of the volcanic ash beds covering the terrace surfaces, the ashes on Aoyagi terrace (fig, 4, right) is correlated to the upper part of ones on Tachikawa terrace (fig4, left).4) Fig. 5 shows the detailed isopach map (numericals in meters) of the latest Quaternary deposits along the lower part of the Tama River.5) The longitudinal profiles of the terraces, the buried terraces and recent water course of the Tama River are projected in fig. 6. From the figs. 5 and 6, the gravel bed forming Haijima terrace can be correlated to the buried gravel bed of 60m below sea level at the mouth of the Tama, and the gravel bed forming Tachikawa terrace to the buried gravel bed of 20-40m below sea level. These two terraces have a steep gradient caused by the lowering of the sea level during the Late Wisconsin glacial age.6) In conclusion, the writers have established the landform evolution of the areas during the latest Quaternary epoch. The sequence of the features is as follows:1. Deposition of the gravel bed forming Tachikawa terrace and the buried gravel bed of 20-40m below sea level at the mouth of the Tama.2. Deposition of the gravel bed forming Aoyagi terrace and Egota (or Ekoda) Conifer bed.3. Deposition of Tachikawa volcanic ash beds during 1 and 2.4. Deep entrenchment of rivers……deposition of the gravel bed forming Haijima terrace……forming of submarine terrace of 100m below sea level.5. Rapid transgression……deposition of the Lower member of the latest Quaternary formation.6. Retarded transgression (Allerod)……forming of terrace now buried 20-30m in depth.7. Re-transgression……deposition of the Upper member of the latest Quaternary formation.8. Building of wave-cut terrace now buried less than 10m in depth and terrace of less than 4m in depth……forming of alluvial plain of Shitamachi.7) The above evolution reflects world-wide events. The correlation between the development of landforms of Tokyo Bay and the eustatic changes of sea level is estimated as shown in fig. 7.

The Burrell Lapilli was erupted in 1655 A.D. over the ESE sector of Mount Egmont. Contour maps of Mo values, and the percentages of lapilli grade sizes > 16 mm and 16–8 mm, show lobes to the NE, SE, and ESE. The SE and ESE lobes coincide with lapilli positions on the isopach map but the NE lobe is not reflected in the thickness contours. The lower part of the lapilli deposit was distributed by winds blowing SE, the middle part by stronger winds blowing ESE, and the upper part by winds blowing NE. With increasing distance elongation axes of lobes for the isornedian and isopach maps rotate northwards indicating that during the main phases of eruption low level winds were WNW, while higher level winds were S or SW.

The Silurian System of the Great Basin comprises at least three major facies: (1) a dolomite fades, developed in Utah and in eastern and central Nevada (Laketown dolomite and Lone Mountain dolomite), (2) a limestone facies, locally dolomitized, exposed in central Nevada (Roberts Mountains formation), and (3) a chert-shale facies, probably deposited originally in central and western Nevada, but since carried eastward into central Nevada by large-scale thrust faulting. Mapping in the Roberts Mountains region in central Nevada shows that the Lone Mountain dolomite and the Roberts Mountains formation are largely, and perhaps wholly, lateral equivalents. Evidence from textures, structures, and fossils indicates that the Lone Mountain dolomite represents a reef complex, most of whose original features are obliterated by dolomitization, and that the Roberts Mountains formation comprises deeper-water reef-flank, off-reef, and basin deposits. A regional isopach map shows a generally north-trending band through the...

Main oil reservoirs of the Sarukawa field are of the lower Tentokuji formation. In this paper, the writer discusses the time of their formation, considering (a) porosity of mudstones calculated from sonic logging data, (b) isopach and depositional conditions, and (c) nature of crude oil. The writer concludes that oil migration had been initiated before the end of the early Tentokuji age, that the formation of oil pools had finished before the late Tentokuji age, and that part of oil remigrated after the Shibikawa orogenesis.

The welded acid tuffs that are a minor constituent of the volcanic pile are hard felsitic rocks, usually highly vesicular, with a basal glassy layer. They usually have the characteristic microtexture of welded tuffs, but field criteria are more reliable in distinguishing them from lavas and non-welded tuffs. An isopach map is given of the Skessa tuff, which is the product of a single subaerial eruption. The original extent of the welded parts of this tuff is estimated to have been 100 square miles, and its average thickness 25 to 30 feet ; peripheral outcrops are not welded, and cover an additional 70 square miles. In the welded parts the tuff particles were deformed, roughly aligned, and welded together under their own weight and momentum and the accumulated tuff remained plastic long enough for vesicles to form. A classification of tuff deposits into five grades is proposed which is based on the plasticity and temperature of the tuff particles. The Skessa tuff is a representative of the rather rare grade in which the particles had the highest plasticity and, presumably, temperature. Bubbles of basaltic glass that occur in the tuff appear to indicate simultaneous eruption of acid and basic magma.

North American stratigraphic principles as developed by geologists mapping on continents can be applied to deep-sea sediments. The ability of the Deep Sea Drilling Project to obtain long cored intervals at many ocean basin sites can provide sufficient data for the definition and recognition of rock-stratigraphic units (e.g., formations). Deep-sea sediments should be divided and reported in terms of distinctive lithologic units, which may be assigned rock-stratigraphic names if there is reasonably good evidence of their continuity. This practice is preferable to current stratigraphic practices in oceanography of designating sediments in chronostratigraphic terms. The generally accepted North American usage of formation as a mappable lithologic unit devoid of any time connotation is recommended over the European usage of formation which commonly is actually a chronostratigraphic unit correlated across major facies changes. Legs 8 and 9 of the Deep Sea Drilling Project recovered 3,000 m of core in 15 sites (Sites 69-84), spread over a distance of 7,500 km along the equatorial Pacific. Two leg 8 sites (74, 75) and all Leg 9 sites (77-84) were cored to basalts. Sites 70 and 77 were divided into several lithologic units that served as a standard of reference for Legs 8 and 9 sites respectively. The consistent stratigraphic sequence (homotaxial) and areal distribution of these lithologic units led participants on Legs 8 and 9 jointly to adopt four oceanic formation names: the Line Islands Oceanic Formation, Marquesas Oceanic Formation, Clipperton Oceanic Formation, and San Blas Oceanic Formation. These formations are lithologically distinct, Tertiary, diachronous units that can be traced at least 4,500 km. T e most useful and objective criteria to define these formations are color differences, which are accompanied by mineralogic, textural, and biotic changes. To a lesser degree bedding features further aid in the characterization of these formations. The same stratigraphic principles used on land can be applied to oceanic sediments. New stratigraphic principles are not recommended. Stratigraphic cross sections and paleogeographic facies maps show that the Tertiary depositional history of the central and eastern equatorial Pacific was complex. Two broad sedimentation regimes prevailed; an easterly volcanogenic one and a westerly pelagic one. The upward stratigraphic progression from the highly calcareous Marquesas Oceanic Formation to the more siliceous Clipperton Oceanic Formation supports a general model of sedimentation in which deposition took place in progressively deeper water as sea-floor spreading moved the sites westward. Alternatively, similar lithologic patterns could be achieved by simple sea-floor subsidence in a regionally progressive manner, oceanic currents and upwelling changing position with time, etc. In detail, however, the lithologic patterns are not adequately resolved by such simple models, and other as yet poorly understood factors probably are operative. Paleoequator reconstructions based on isopach and depositional axis isopach maps of chronostratigraphic units support the earlier hypothesis of Morgan, that in the middle Tertiary the north-northwestward migration of the Pacific plate took a more west-northwestward trend. The spatial and temporal distributions of these isopachs with a north-northwestward trend during the early Tertiary and a west-northwestward trend during the late Tertiary suggest that this change took place sometime in the early to middle Miocene (15-25 m.y. ago). Description of deep-sea sediments in terms of lithologic units and the establishing, tracing, and dating of oceanic formations can help provide a stratigraphic framework within which our interpretations must lie. This can result in an improved basis for understanding the interrelations between rock-stratigraphic and chronostratigraphic units; lithologic and biologic sedimentation changes through time and space; sea-floor spreading and its effect on sedimentation patterns; depositional processes; subaerial dispersal patterns; and in better communication between oceanographers and continental stratigraphers.

A high-resolution seismic survey of the Rukwa Rift has imaged the upper 300 m of the Pliocene–Holocene section. The sediments are characterized by aggradational deposition in shallow lacustrine conditions that episodically dried out. Overall the reflection package expands northeastwards towards the Lupa Fault (half-graben bounding fault). Isopach maps for nine intervals (6 m to 65 m thick) show four periods of marked expansion of the section towards the Lupa Fault, interpreted to represent times of fault activity or infilling of fault-created topography during the early stage of fault quiescence. There are three periods of little or much reduced expansion interpreted to represent infilling of the accommodation space between the lake floor and the lake surface during periods of fault inactivity. Cyclicity of such high frequency has not been widely reported for faults which penetrate the crust. The periods of activity show remarkably similar displacement patterns with no lateral migration of the main depocentre, implying that seismic and aseismic slip has persistently clustered in the same parts of the fault. Identification of high-frequency fault cyclicity has implications for sequence stratigraphy in tectonically active areas, since there is a tendency to assume faults do not have cyclic effects on the scale of tens of thousands of years.

Field and laboratory experiments show that color alteration in conodonts is directly related to the depth and duration of burial and the geothermal gradient and correlates with fixed carbon, vitrinite reflectance, palynomorph translucency, and isopach data. Five progressive and irreversible color changes ranging from pale yellow to black are discriminated. Compilation of color alteration index (CAI) maps for limestones of several ages in the Appalachian basin show: (1) a general systematic change from pale yellow (CAI = 1) to black (CAI = 5) from west to east; (2) within a structural belt, older conodonts are darkest; (3) fixed carbon values determined from coals cannot be directly applied to carbonate rocks; (4) several areas of anomalously low CAI values in windows exposing Ordovician rocks within the Blue Ridge-Piedmont terrane. Data show: (1) color alteration of conodonts is time and temperature dependent; (2) the sequence of color change from pale yellow to black found in field collections is the same as that produced by heating alone; (3) upper and lower geologic temperature limits for each CAI determined from a log time versus reciprocal of absolute temperature plot. Water in combination with confined pressure retards color alteration. The color alteration of conodonts ismore » a valuable tool for assessing organic metamorphism because it is a rapid and inexpensive method requiring only standard laboratory techniques and a binocular microscope. The technique provides thermal cutoffs for oil, condensate, and dry gas generation. Conodont color alteration begins near the upper thermal limit for the preservation of many palynomorphs.« less

A hindsight analysis of the Tatum basin in southeastern New Mexico by the statistical technique of multiple discriminant-function analysis, coupled with computerized contouring, was used to "predict" statistically the location of oil fields relatively early in the exploration history of the basin. Using only well data available at the end of 1951, predictions were made for a series of geographic cells, each 1 mi by 1 mi (1.6 by 1.6 km) square, so that the entire area of study, 37 by 41 mi (59 by 66 km) was covered. The predictions were based on analysis of isopach and structure-contour maps. The computer was programmed to identify and measure structural anomalies such as areas in which structural closure was interpreted by machine contouring. The quantified geologic facto s derived from the original data then were ranked by a discriminant-function technique, so as to be placed in order of their contribution in predicting statistically the location of oil pools. The vertical closure of structural anomalies is the best predictor of reserves; the second is the subsea depth of the Silurian-Devonian top. The four best geologic variables give results practically equivalent to those obtained with all the variables together. The predictive model successfully located 8 of the 10 new economic fields in the study area; these fields represent at least 40 million bbl of oil. This quantitative method of regional geologic analysis should be widely applicable to exploration problems in many different structural and environmental settings.

Certain paleoarches, described in geologic literature solely on the basis of thinning or absence of strata, are myths not confirmed by structural evidence. The interval and datum selected for isopach representation are critical and of utmost importance in stratigraphic and structural interpretation. Sub-Trenton isopach maps for Ohio accompany a structure map and stratigraphic section. Postulation of a "Waverly arch" is not justified. The concept of a "Sangamon arch" in Illinois is discussed and rejected. It is suggested that the "Adirondack arch" in New York, Pennsylvania, and West Virginia is not a structural entity, nor is the "Mid-Michigan" ridge.

The Foster sand represents local stream channels that cut into Morrowan strata while draining southeastward in the McAlester basin, Oklahoma. Four channel systems, ranging from 1 to 6 mi wide and up to 20 mi long, have been mapped. During the hiatus these streams brought detritus to the southern part of the basin where marine sedimentation was continuous and the Spiro sand was forming in a shore zone environmental complex that probably included beaches, bars, tidal flats, tidal channels, and lagoons. During a northward transgression the Spiro sand was deposited across the basin and locally overlies the Foster sand. The Foster sand is a fine-grained quartz sandstone with well-rounded, moderately sorted grains. The Spiro sand is most commonly supermature, but is submature or mature locally. This sandstone has subangular to well-rounded, poorly to very well-sorted (1.05 to 0.31 phi), very fine to medium grains (0.11 to 0.30 mm). Intergranular pore space in the Foster and Spiro sands has been reduced by pressure solution and formation of quartz overgrowths, carbonate cement, and chlorite cement. Chlorite is authigenic and apparently of two different ages. The chlorite coats the surface of detrital quartz and preserves intergranular porosity by retarding pressure solution and formation of overgrowths. The Spiro sand has been subdivided into eight facies with limestone, shale, and quartz sandstone end members. Analysis of these facies, primarily by isopach maps and grain size, indicates that dry gas production limits have been established, with the possible exception of reservoirs south of the Choctaw fault in the structurally complex frontal zone of the Ouachita Mountains. The Foster sand is a good dry gas reservoir, but has limited distribution.

A petrographic examination was made of approximately 450 thin sections prepared from the Spraberry formation of the Midland basin, West Texas, and, from the examination, a genetic sequence has been developed. This sequence is divided into two major stages and several substages. Later processes, occurring during the epigenetic stage, were the most important in the development of the section into an economic reservoir. The Spraberry formation is traced throughout the Midland basin and divided into two units, the upper and lower. Isopach, clastic ratio, sand-isopach, and texture maps have been constructed to show the changes of the sedimentary attributes throughout the Midland basin and interpret the depositional history of the rocks. The Midland basin was a restricted intracratonic basin during Spraberry time. All the data indicate a source of sediments on the north or northwest. South of the major area of production the sand and silt were too poorly developed to form favorable reservoirs. On the north, not enough favorable shale was deposited for the formation of large volumes of petroleum.

Many stratigraphic traps are related directly to their respective environments of deposition. An understanding of the depositional environment is essential to successful prospecting for oil or gas in this type of reservoir. Isopach studies of shale sequences directly above, or both above and below, a lenticular reservoir sandstone are of considerable value in reconstructing depositional environments. Variations in thickness of such shale intervals, either directly above a reservoir sandstone, or embracing it, are completely independent of present-day structural configuration. Isopach maps of such genetic sequences serve as realistic indicators for locating certain lenticular sands. Depositional trends of beach sands, strike valley sands, and offshore bars are determined r adily from such studies. Structure maps, constructed on a reliable time marker within the arbitrarily selected genetic interval, serve as a means of locating oil or gas accumulation within any of these reservoir types. In all such studies electrical log data are essential since such genetic sequences seldom are named formational units. The thinner the genetic sequence the greater the necessity for accurate selection of correlation points on electric logs. Deltaic reservoirs are poorly understood and only rarely recognized by the geologist. This type of reservoir is, nevertheless, abundantly preserved in the sedimentary section. Regional isopach studies of depositional environment are a prerequisite for the construction of meaningful exploration maps of this type of reservoir. An understanding of the trends of distributary fingers and of the influence of differential compaction in producing drape structures, likewise, is essential.

The Davis sand lens of the Hardin field is in the Eponides yeguaensis zone of the Yegua (upper Eocene) formation. The sand was first recognized as a separate sand in the Woodley Petroleum Company's Emma Davis well No. 1 where it was encountered from 7,511 to 7,525 feet below the surface. Two gas and distillate wells and one oil well are now producing from the sand. The bar is a separate and sealed reservoir. An isopach map of the interval containing the Davis lens shows a marked thickening within the area where the best development of the Davis sand is found. It discloses that the bar has a long axis of approximately 11,000 feet, an average width of approximately 1,250 feet and a total area of practically 320 acres. The contours of the isopach map are lines of sedimentation from which the section to be penetrated may be postulated in advance of the drill. The Davis "zone," wherein the lens is found, is composed of alternating sand, sandy shale, and shale and is arenaceous in character, indicating lagoonal or tidal-flat deposition. The Davis sand is composed of 98 per cent quartz; it is medium-grained in texture, whereas the typical Yegua sands are fine-grained. The Davis lens was laid down as a barrier beach or off-shore bar by a retreating Yegua sea.

The hydrocarbon distribution in the N sand reservoir in Main Pass Block 35 field is anomalous. In the eastern part of the reservoir, the N sand accumulation contains a gas cap about 120 ft structurally lower than the oil in producing wells in the western part of the reservoir. Geologic and pressure data indicate a common reservoir. A review of the paleostructural history indicates that after 1,000 ft of burial, the relict N sand structural high was in the eastern part of the field near the area of the present-day gas cap. Isopach maps of younger intervals show that the structural high shifted westward. The presence of an N sand gas cap in the time-persistent, but now low, eastern culmination and the absence of a gas cap at the present apex of the reservoir suggest early migration and accumulation of the gas and perhaps of the oil in the eastern area. Later structural tilting would have resulted in adjustment and remigration of the N sand oil column into the developing western apex. Tilting was not sufficient for remigration of the gas column, and thus the gas remained trapped at the present lower site of the eas ern structural high.

The presence of a considerable variation in the thickness of the interval from the base of the Eagle sandstone of Montana time to the top of the Kootenai or Cloverly of Lower Cretaceous age has long been recognized over east-central Montana. As far as is known, however, no systematic study has been published showing the regional variation in thickness or the possible causes of such a phenomenon. This article is therefore an attempt to show by discussion and graphical representation the regional variation of the interval previously described, an interval formerly supposed to include only the Colorado formation of Upper Cretaceous age, but now known to embrace, over the southern part of the state at least, sediments of Montana time. There is also shown overloading of sedime ts over certain parts of the area and the resultant effects on diastrophism and sedimentation, from which additional light is shed on the problem of correlation of the sediments grading from Colorado to Montana time. In order to show some effects of the difference in sedimentation, it has been thought advisable to outline roughly the probable conditions immediately prior to Dakota time, as well as the continued deposition into Montana time, as criteria upon which to draw generalized conclusions. It is suggested that more detailed study of isopach lines may throw more light on proper subsurface mapping, especially of relatively large areas, as well as being an aid in the study of the deposition of sediments.

During the past 10 years many surface and subsurface elevations have been accumulated from several key horizons within that part of Tennessee between Cumberland Plateau on the east and the western valley of Tennessee River on the west. From these data structural contour maps have been compiled on the top of the Chattanooga shale (Kinderhook group of the Mississippian system), on the Pencil Cave horizon (metabentonite bed near the top of the Black River group of the Ordovician system), and on the top of the Knox dolomite group (Cambro-Ordovician system). These maps show the structural configuration of these horizons and permit a study of comparative structure. This comparative study is supplemented by an isopach map of central Tennessee, showing the variations in thickness of the interval between the Chattanooga shale and the Pencil Cave. From these maps many critical facts may be inferred regarding the structural history of the Nashville dome.

Devonian strata are traced throughout the Northern Rocky Mountain and Great Plains areas which include Wyoming, Idaho, Montana, southern Saskatchewan, and Alberta. The diverse Devonian nomenclatures between states and provinces are unified, and the areal limits of applicability of established formational names as cartographic units are demonstrated. Isopach and lithofacies studies are employed as a basis for interpreting the sedimentation processes and patterns responsible for the Devonian rocks now observed. In order to work out the dynamic picture of Devonian sedimentation, it is necessary to subdivide the total section into four operational rock units which are recognizable throughout the area on the basis of suitable lithologic criteria; the individual isopach and lithofacies maps of these units are interpreted in terms of the tectonic and environmental conditions responsible for the patterns exhibited. Finally, an integration of these four arbitrary stages of Devonian sedimentation presents the regional Devonian geologic history. The rock units include a basal Devonian unit, a lower limestone unit, a dolomite-evaporite unit, and a post-evaporite unit. Clastics (shale and sand), carbonates (limestone and dolomite), and evaporites (anhydrite and halite) constitute the three significant petrographic end members used in the statistical lithologic triangle. The two indices defining the lithologic variations are the clastic ratio and evaporite ratio. The important tectonic elements which were active during Devonian sedimentation include: Elk Point basin (Middle Devonian age) extending from east-central Alberta into southern Saskatchewan; Central Alberta basin; Southern Alberta arch; Central Montana positive axis; Southern Montana trough; Wyoming shelf; and Cambridge arch of Eardley in southeastern Montana and Wyoming (northwestern extension of Siouxia landmass). Evaporitic sediments are prominently developed in the basal and dolomite-evaporite units; and normal marine deposits, including reef-carbonates, are characteristic of the lower limestone unit.

The Salt Lake pool is in southeastern New Mexico, approximately midway between Carlsbad and Hobbs. The discovery well was completed in June, 1941, at a total depth of 3,103 feet. As of February 1, 1942, the field contained six wells, producing oil that ranges in gravity from 26 to 30 degrees. Microscopic study of the pay section reveals that much of the oil has accumulated in solution cavities within the dolomitic limestone and that the dolomitic limestone itself is not saturated. Two distinct "pays" are separated by approximately 75 feet of limestone yielding only minor showings of oil. The early appearance of water suggests that the solution cavities contain appreciable amounts of water as well as oil. Free gas is practically lacking and the oil is produced by pumping. The Cowden anhydrite member in the lower part of the Salado salt is believed to be the youngest reliable structural marker. It is believed that much of the structural adjustment that produced closure in the Salt Lake pool occurred during middle Salado time. Therefore, in searching for new pools within this area, the thickening and thinning of the Salado should be carefully studied. Isopach maps of the interval from the top of the Rustler anhydrite to the top of the Cowden anhydrite are very helpful in localizing structure. Isopach maps in the interval from the top of the Cowden to the top of the pay may be very useful in predicting pay characteristics. The methods which were checked one against the other in locating the Salt Lake pool are given herewith in the order used. 1. Regional contouring on a bed below the base of the salt. 2. Preparation of isopach maps on the salt section. 3. Survey of local area by torsion balance. 4. Survey of local area by soil analysis. End_of_Article - Last_Page 908

Lower Cretaceous stratigraphy of the Rocky Mountain region is complicated by problems of nomenclature, lateral extent, correlation, and age variation of the Dakota group. Lower members of the Dakota group have three different relationships to the underlying Morrison formation: (1) in some areas the basal units were deposited in channels and are unconformable on the Morrison; (2) in many areas the basal units have an intertonguing facies relationship with the upper Morrison, and, (3) a regional unconformity at the base of the Dakota group is developed only in the Great Plains region. Regional time lines are necessary for an understanding of facies relations. Marine Jurassic formations define an approximate time line at the base of the Morrison in the northern part of the Rocky Mountain region. The Todilto limestone forms an approximate time line in the San Juan basin, but it can not be related precisely to the marine formations farther north. In the northern part of the region the boundary between the Upper Cretaceous and the Lower Cretaceous is placed at the top of the Mowry shale which is marked by the Clay Spur bentonite bed, an excellent time horizon. The marker bentonite of the Denver basin ("X" bentonite), 100-300 feet above the Mowry shale, can be traced throughout the Powder River basin of Wyoming where it marks the base of the Greenhorn faunal zone (Upper Cretaceous). The "X" bentonite bed, and in its absence, the base of the Greenhorn limestone form an excellent time line. Sediments of the Dakota group were deposited in a sea that advanced from the north and thus these basal sediments become younger in easterly, southerly, and westerly directions. Marine shales of the Thermopolis and overlying Mowry and Graneros formations of Wyoming and Montana were deposited contemporaneously with sandstones of the Dakota group farther south. The lower part of the Dakota group of Wyoming and Montana was deposited contemporaneously with upper Morrison sediments on the south. Over most of the Rocky Mountain region the Dakota group is Lower Cretaceous, but in deposits just south of the San Juan basin the upper part is as young as the Greenhorn limestone, a relation similar to that found in eastern Nebraska, at the type locality, where the Dakota sandstone is largely, if ot entirely, Upper Cretaceous. In Wyoming and Montana, sandstones of the lower Dakota group (Lakota, Fall River, Dakota, Cloverly, Cat Creek, and upper Morrison) produce oil in areas where distinctive, linear, thick sandstones are developed and are notably unproductive in areas of patchy, heterogeneous sand development. In eastern Colorado, the lower part of the Dakota group (Dakota, Lytle, "M", "O", "R", and "T" sandstones) is essentially non-productive. Significant oil production in the Dakota sandstone of western Colorado and the San Juan basin is found in areas characterized by linear sandstone development. "D" and "J" sandstones of the Denver basin produce petroleum from stratigraphic traps and the southeast limit of significant production coincides with the zero isopach of the Mowry shale. Oil production in the Muddy and Newcastle sandstones of Wyoming (equivalents of lower "J") is stratigraphically trapped in or near linear sandstone trends. Structural entrapments are present where linear trends cross structural highs. End_of_Article - Last_Page 1098

The Carboniferous rocks of northern Egypt are mainly in the subsurface; surface exposures are very limited. From the data available, six stratigraphic maps were constructed to show the thickness variations, facies changes, and paleogeology. Thickness maxima are in two main trends: (1) a narrow, linear, NW-SE basin coinciding with the Gulf of Suez and (2) a broad, NE-SW basin (with a thinner section) in the Western Desert. The basins are separated by a northward-extending "basement complex" mass on which no Carboniferous sedimentary rocks are present. Both basins seem to open toward the mouth of the Nile delta and the western part of Sinai. Lithologically, the Carboniferous consists mainly of sandstone with minor limestone-shale intercalations. The shale and carbonate generally increase in amount northward. Northern Sinai has a more carbonate-rich facies than does the northern part of the Western Desert. Though the limestones are marine, the sandstones were deposited in environments ranging from marine to continental. The lithologic characteristics and the thickness of the Carboniferous System were affected both by the tectonic framework of sedimentation and by subsequent geologic events. A large "basement complex" mass separated the eastern tectonically active embayment along the Gulf of Suez from the tectonically more stable Western Desert. The northern shelf region, which generally subsided during Carboniferous sedimentation, constituted the northernmost part of Egypt. The Gulf of Suez embayment therefore is inferred to have formed as early as the Carboniferous. Later structural evolution and denudation in places reduced the thickness of the Carboniferous section. Petroleum is found in the Carboniferous strata of some fields in the Gulf of Suez province. Source rocks probably are not present in the Carboniferous. Therefore, the petroleum probably migrated from younger strata, most likely of Miocene age.

The Hitchcock field in Galveston County, Texas, is an example of the commercial accumulation of oil through combined structural and stratigraphic closure. The producing sand is middle Miocene in age, presumably equivalent to the true Oakville farther updip. The structure of the field is that of a broad, flat dome dipping gently away on three sides while on the fourth side, the east, the trap for oil accumulation is insured by complete lensing-out of the producing sand. The gas cap is very small and several of the highest wells in the field have a high gas-oil ratio. The water level in the field has been ascertained by electrical log and by core examinations. This water level is at 5,158 feet. The field is further complicated by a graben area in the north between two fault of small throws which lower the sand in the graben below the water level and thus serve as a northern boundary to production. A comparison of the structural and isopach maps presented herewith shows the interesting coincidence of the highest part of the gentle dome with the region of equal thickness of the sand. This may serve as an indication of the presence of the structure during deposition. The Miocene beds above the producing sand have been erratically deposited and stratigraphic fluctuation is very prominent between each well. The presence of apparent faults is conceived in the primary study of the electrical logs; however, these faults are created merely by the erratic deposition of sediments. The only true faults in the field are the two north of the producing area and which are shown on the accompanying contour maps and cross sections.