Petroleum Source Beds Research Articles

Hydrocarbon Prospects of Bering Sea Shelf South of St. Lawrence Island, Alaska: ABSTRACT

Hydrocarbon prospects of the Bering Sea shelf are encouraging because of the presence of numerous, large sediment-filled basins, a variety of structural and stratigraphic traps, and potential reservoir beds. The large shelf area south of St. Lawrence Island is underlain by at least 13 sediment-filled basins. One of these basins, Bristol Bay basin, extends offshore from the Alaska Peninsula and contains more than 3 km of section. Nearby on the northwest is St. George basin, a graben approximately 300 km long and 50 km wide that includes a section about 10 km thick. The northwestern region of the shelf near Siberia is underlain by the large Navarin basin province (40,000 sq km), which comprises three subshelf basins that contain sections as much as 15 km thick. Structural traps for hydrocarbons occur as folds associated with growth faults flanking the basins, strata draped over basement blocks, regional dip divergence in the upper sedimentary basin sequence, and thinning of beds against the basement flanks of the basins. Diapirlike folds as well as large anticlinal structures occur in the Navarin basin province. Rocks dredged from the Beringian continental slope include volcanic sandstone of Late Jurassic age, mudstone of Late Cretaceous age, and less consolidated deposits of early Tertiary age. Pyrolytic analyses of these rocks indicate that none are good source beds for petroleum; however, the samples are generally sandy units that may not be representative of finer grained possible source beds that may be present along the margin or within the subshelf basins. Tertiary samples are generally porous--probably because of abundant diatom frustules. The permeability of these rocks is variable. Tertiary outcrops can be traced as seismic reflectors to the subshelf basins, where, if the beds remain diatomaceous, potential reservoir beds may be present. Table End_of_Article - Last_Page 745------------

Effect of Oil and Bitumen Saturation on Source-Rock Pyrolysis: GEOLOGIC NOTES

Mass production of pyrolysis instrumentation such as the Rock-Eval has led to general application of whole-rock pyrolysis as a means of identifying and characterizing petroleum source beds. One of the problems inherent in the whole-rock technique is the effect of petroleum or bitumen on the measured amount of thermally extracted hydrocarbons from the kerogen. Under pyrolysis, migrated oil or bitumen in the rock gives a major response near 250 to 350°C on the program (S1). However, solid bitumen and the heavy-end fraction of petroleum produce a measurable response (S2) in the 350 to 450°C range as well as in the same region where kerogen conversion to hydrocarbons occurs. Thus, large quantities of bitumen or migrated petroleum in rocks can affect the size and the maximum temperature of the S2 peak and can cause nonsource rocks to be misidentified as source rocks. These problems can be overcome by rinsing the sample in a chlorinated hydrocarbon solvent prior to analysis.

Atmospheric Circulation and Upwelling in Paleozoic, with Reference to Petroleum Source Beds: ABSTRACT

Liquid hydrocarbons are formed from phytoplankton deposited in marine sediments. Phytoplankton are not distributed uniformly throughout the ocean surface waters. They are sparse over most of the area of the ocean, but are abundant in zones of upwelling where water rich in nutrients is brought to the lighted surface waters. Locations of these organically productive upwelling zones in the past can be predicted using a combination of paleogeographic and paleo-oceanographic modeling. This provides valuable information on likely times and geographic areas in which oil source beds were deposited. Upwelling is caused by steady, prevailing winds resulting in divergence of currents or the movement of currents away from landmasses. These winds are parts of major atmospheric circulation systems. Their characteristics depend on latitude, season, and the sizes and positions of oceans and continents, but have a physical basis. They can, therefore, be modeled for past continental configurations, and it follows that upwelling can also be predicted. Atmospheric circulation and upwelling maps for seven stages in the Paleozoic, using new paleogeographic reconstructions, show that upwelling zones of each stage are related to regions with source beds of that age. Although upwelling does not automatically result in source beds and all source beds do not occur in ancient End_Page 507------------------------------ upwelling zones, knowing the past areas of upwelling and abundant phytoplankton productivity is vital for assessing the potential richness and extent of possible oil source beds. End_of_Article - Last_Page 508------------

Petroleum Source Beds on Continental Slopes and Rises

Continental slopes commonly are sites of high marine organic productivity and frequently contain reducing bottom conditions, quiet water, and intermediate sedimentation rates, all of which favor deposition of organic-rich sediments. These deposits typically have high percentages of aquatic organic matter with high petroleum yields as contrasted to relatively organic-lean shelf deposits which contain primarily low-yield terrestrial organic matter. Conversion of organic matter in potential source beds to oil and gas requires a combination of temperature and time. These variables are controlled primarily by the geothermal gradient, the rate of burial, and the age of the source interval. Most divergent margins need between 2 and 4 km of overburden for oil generation and from 3 to 7 km for gas generation. Typically cooler and younger convergent margins and deltaic margins must have even greater burial depth to achieve the same results. Continental margins, including present slopes and rises, can contain oil and gas source beds when minimum requirements of organic content, kerogen type, and thermal maturity are met. Migration and accumulation are most efficient, however, where reservoir sequences prograde over source beds in areas of structural complexity. Preservation of trapped petroleum requires effective seals and minimal structural readjustment after accumulation. All these conditions can be found on present slopes and rises, although they are not common, and must be considered as part of any economic evaluation of these largely untested deep-water realms.

Petroleum Source Beds on Continental Slopes and Rises: ABSTRACT

Petroleum Source Beds on Continental Slopes and Rises: ABSTRACT

Source Beds of Petroleum in Denver Basin: ABSTRACT

Source Beds of Petroleum in Denver Basin: ABSTRACT

Petroleum Source Beds in Mississippian Flysch, Eastern Great Basin and Western Rocky Mountains: ABSTRACT

Petroleum Source Beds in Mississippian Flysch, Eastern Great Basin and Western Rocky Mountains: ABSTRACT

Petroleum Source Beds in Pilot Shale of Eastern Great Basin: ABSTRACT

Petroleum Source Beds in Pilot Shale of Eastern Great Basin: ABSTRACT

Structural History and Oil Potential of Offshore Area from Cape Hatteras to Bahamas

The present Atlantic Coastal Plain and continental shelf were parts of the crystalline Appalachians in late Paleozoic time when North America was joined to the African continent, according to current interpretation of plate tectonics. In Early Triassic time this province was uplifted by subcrustal intrusion of hot mantle material which caused a series of rift valleys to develop with trends roughly parallel with the present continental rise. This was the site of a major rift system and the convection cell which later formed the Mid-Atlantic Ridge. This rift system connected the Mediterranean Sea with the newly opened Gulf of Mexico; these were areas of extensive evaporite deposition in Late Triassic and Early Jurassic times. Normal sea water entering during Smackover (Late Jurassic) deposition permitted the growth of great carbonate banks and reefs from the Cape Hatteras area southward to the Bahamas. Active separation of Africa and North America also moved the upwelling lavas of the Mid-Atlantic Ridge away from the coastlines. Cooling of the hot mantle material under the continental margin caused downward flexing of the crust toward the ocean to form a new miogeosyncline. There the deposition of sediments probably kept pace with the crustal downwarp. The subject area is between the Bahama carbonate platform and a mainly siliciclastic depositional province indicated north of Cape Hatteras. The strata are presumed to be transitional in environment of deposition. The shallow-water carbonates are likely to include many rocks with excellent reservoir properties. Source beds for petroleum, as well as shales and fine-grained carbonates and possibly evaporites, which could serve as cap rocks, should be abundant. Although compressive folding seems to be absent as a mechanism for structural growth, block faulting in the basement will serve the same purpose. High basement blocks are favorable sites for bank and reef development and commonly produce structural uplift by renewed movement. Conditions expected here present a challenge for imaginative thinking by geologists. The many similarities to such areas of prolific oil production as the Tampico-Tuxpan embayment and the Jurassic producing province in Saudi Arabia give cause for an optimistic view that giant oil accumulations may be present. Water depths over the Blake Plateau present another type of challenge to operators. The mechanical difficulties should not be insurmountable if industry has sufficient economic incentives to justify the effort. The reasonable expectation of finding oil in sufficiently large accumulations is the most basin of such incentives.

Petroleum Potential on Continental Rise Off Central California: ABSTRACT

The JOIDES program has demonstrated the technical feasibility of drilling in the deep ocean. However, except for petroleum shows in the Sigsbee Knolls in the Gulf of Mexico, there is no firm evidence of petroleum reservoirs in the deep ocean beyond the limits of the continental slope to require economic use of such technology. Emery suggested the possibility of vast petroleum resources in deep water adjacent to the continents in the areas of hemipelagic sedimentation. One such area adjacent to the United States is the continental rise off California between Point Conception and Cape Mendocino, which covers 200,000 sq km and consists of three major submarine fans, the Arguello, Monterey, and Delgada, at depths of about 3,000 m to 4,500 m. The fans are composed of continental debris carried down submarine canyons and deposited on the fan through a system of branching and meandering submarine End_Page 1461------------------------------ channels. During the depositional growth of the fan, the active channelway shifted periodically, producing abandoned channels. The coarser sediment naturally confined to the channel became covered, after abandonment, by finer grained material. The interchannel deposits, composed chiefly of green hemipelagic muds, are potential petroleum source beds because of their significant carbon content. Thus abandoned channels after sufficient burial and invasion from source beds make excellent stratigraphic traps, especially near the mouth of tributary submarine canyons where the grain size would be larger and the channel width and depth greater. Off central California, potential stratigraphic traps would be seaward of the mouths of the Arguello, Sur-Partington-Lucia, Monterey-Carmel, Ascension, Pioneer, Farallon, Bodega, and Delgada canyons as shown by subbottom profiling. The proximity of such potential reserves to the United States makes buried channels on large-scale deep-sea fans particularly attractive prospects similar to prospects in turbidite basins of the California borderland. End_of_Article - Last_Page 1462------------

Structural History and Oil Potential of Offshore Area from Cape Hatteras to Bahamas: ABSTRACT

The present Atlantic Coastal Plain and continental shelf were parts of the crystalline Appalachians in late Paleozoic time when North America was joined to the African continent, according to current interpretation of plate tectonics. In Early Triassic time this province was uplifted by subcrustal intrusion of hot mantle material which caused a series of rift valleys to develop with trends roughly parallel with the present continental rise. This was the site of a major rift system and the convection cell which later formed the Mid-Atlantic Ridge. This rift system connected the Mediterranean Sea with the newly opened Gulf of Mexico; these were areas of extensive evaporite deposition in Late Triassic and Early Jurassic times. Normal sea water entering during Smackover (Late Jurassic) deposition permitted the growth of great carbonate banks and reefs from the Cape Hatteras area southward to the Bahamas. Active separation of Africa and North America also moved the upwelling lavas of the Mid-Atlantic Ridge away from the coastlines. Cooling of the hot mantle material under the continental margin caused downward flexing of the crust toward the ocean to form a new miogeosyncline. There the deposition of sediments probably kept pace with the crustal downwarp. The subject area is between the Bahama carbonate platform and a mainly siliciclastic depositional province indicated north of Cape Hatteras. The strata are presumed to be transitional in environment of deposition. The shallow-water carbonates are likely to include many rocks with excellent reservoir properties. Source beds for petroleum, as well as shales and fine-grained carbonates and possibly evaporites, which could serve as cap rocks, should be abundant. Although compressive folding seems to be absent as a mechanism for structural growth, block faulting in the basement will serve the same purpose. High basement blocks are favorable sites for bank and reef development and commonly produce structural uplift by renewed movement. Conditions expected here present a challenge for imaginative thinking by geologists. The many similarities to such areas of prolific oil production as the Tampico-Tuxpan embayment and the Jurassic producing province in Saudi Arabia give cause for an optimistic view that giant oil accumulations may be present. Water depths over the Blake Plateau present another type of challenge to operators. The mechanical difficulties should not be insurmountable if industry has sufficient economic incentives to justify the effort. The reasonable expectation of finding oil in sufficiently large accumulations is the most basin of such incentives.

Fibrous Calcite, a Middle Devonian Geologic Marker, with Stratigraphic Significance, District of Mackenzie, Northwest Territories

Fibrous calcite beds containing cone-in-cone structures occur in outcrops and in core and cuttings from the subsurface, at a constant stratigraphic position near the base of the Hare Indian Formation, throughout parts of Anderson, Peel, Mackenzie, and Great Bear Plains in the District of Mackenzie. These remarkably persistent beds have a maximum thickness of 2.75 in. (7 cm) and occur throughout an area of about 15 000 mi2 (24 000 km2). Their most northerly observed exposure is near the junction of Anderson and Wolverine Rivers, and the most southerly is at Powell Creek about 220 mi (354 km) away. The fibrous calcite marker beds are rock stratigraphie units that probably developed in partly consolidated muds close below the water/sediment interface in response to undetermined changes in the physicochemical environment. Organic material and plant remains in the surrounding sediments probably acted as catalysts to initiate nucleation and growth of the calcite fibers. The zone of fibrous calcite occurs within and delineates the approximate areal distribution of a sequence of sediments rich in organic remains, sediments favorable to the formation of petroleum source beds. Closely associated strata are likely to be of interest to industry.

Evaluating Source Beds for Petroleum: ABSTRACT

Geochemists have made considerable progress in recent years in evaluating source beds for crude oil and natural gas. Petroleum is generated from disseminated sedimentary organic matter by thermochemical processes. A certain amount of time and temperature (thermal energy) is essential to produce the thermal cracking reactions causing the generation of petroleum. As the temperature is raised, the time for the reactions to occur is decreased. The same thermochemical processes that result in the generation of oil and hydrocarbon gases also contribute to the maturation and the ultimate destruction of oil and natural gas. Methane and graphite are the stable end products of these reactions. The exposure time-temperature relations necessary for the generation of petroleum and its expulsion from the source bed have been determined with sufficient accuracy from geochemical data to permit predictions of the approximate stage of generation or diagenesis in advance of sample analysis. Also, the conditions under which oil and condensate are thermally destroyed have been reasonably well established from empirical data. Geochemists are gradually improving their understanding of the factors that control source-bed performance. Factors such as the minimum amount and quality of organic matter necessary for effective oil source beds have been quantified rather accurately. A balanced program includes evaluation of both the extractable organic matter and the residual organic matter in a source bed. The evaluation of extractable organic matter includes conventional analyses of organic carbon, total extractable organic matter, and extractable hydrocarbons. Evaluation of the extractable organic matter and extractable hydrocarbons include the study of heavy (C15-C30) hydrocarbon distributions and infrared spectra. Elemental analysis of carbon, hydrogen, nitrogen, and oxygen is a method used to investigate the diagenetic (carbonization) stage of residual organic matter. Pyrolysis techniques have been developed to investigate organic matter from the standpoint of its remaining generating capability. Examples from the literature confirm that, in general, young source beds must be exposed to sustained higher temperatures than old source beds to attain peak generation. If 2 source beds of the same age and with identical burial histories were subjected to significantly and uniformly different temperatures, the hotter would be in a more advanced stage of organic matter diagenesis. End_of_Article - Last_Page 640------------

Diagenesis of Gulf Coast Clayey Sediments and Its Possible Relation to Petroleum Migration

The writer has established reference intervals in the subsurface on the basis of apparent systematic interlayer water loss of swelling clay minerals. The intervals are used in much the same manner as the familiar indicators for metamorphism, but are present at sufficiently shallow depths to be evident within oil-bearing strata of the Gulf Coast. The resulting conclusion is that clay-mineral diagenesis indicators may prove to be important petroleum-evaluation markers as well as fundamental properties of sedimentary basins. Sedimentary basins are viewed as combinations of gases, liquids, and semisolids distributed through a solid matrix. During geologic development the interstitial components segregate by migration and produce various commercially exploitable concentrations. Water, the principal fluid component of the sedimentary section, is thought to migrate in three separate stages. Initially, pore water and excessive (more than two) clay-water interlayers are removed by the action of overburden pressure. This initial water flow (which is essentially completed after the first few thousand feet of burial) reduces the water content of the sediment to about 30 percent, most of which is in the semi-solid interlayer form. A second stage of dehydration is thought to occur when the heat absorbed by the burie sediment becomes sufficiently great to mobilize the next-to-last water interlayer in an M(H2O)x + ^DgrHr = 1 + XH2O fashion. The final stage of sediment dehydration which extracts the last remaining water monolayer from clay lattices is apparently very slow, even by geologic standards, requiring tens or possibly hundreds of millions of years depending upon the geothermal and burial history of the sediment. Petroleum hydrocarbons which are distributed throughout the matrices of potential source beds in normal frequencies of 300-3,000 ppm are thought to be too sparse to initiate continuous fluid flow. In normal marine sediments, however, the water associated with clay minerals is present to a considerable depth in the order of 200,000 ppm, and therefore it is reasoned that this phase forms the connection between petroleum source and reservoir beds. The first and last dehydration stages are probably unimportant in Gulf Coast oil migration, inasmuch as they occur, respectively, at levels too shallow and too deep to intersect the interval of maximum liquid petroleum availability. The amount of water in movement during the second stage, at a level which does intersect this interval, is 10-15 percent of the compacted bulk volume and represents a significant fluid displacement capable of redistributing any mobile subsurface component. A measure of the degree to which the second-stage interlayer water has been discharged into the system can be noted on X-ray diffractograms. The movement appears to occur in a relatively restricted, depth-dependent temperature zone in which the average dehydration temperature of the points measured is 22 °F. With the use of an empirically derived P/T curve and a geothermal-gradient map, a set of regional subsurface dehydration contours can be constructed. A plot of 5,368 liquid petroleum production depths referenced to this dehydration surface shows an almost perfect Gaussian distribution. It seems significant that, although the dehydration depths range from 4,000 to 16,000 ft, hydrocarbon production depths are distributed in a statistically consistent relation to the calculated clay-dehydration contour surface.

Pennsylvanian Evaporite Cycles And Petroleum Production, Southern Rocky Mountains: ABSTRACT

Cyclic evaporite deposits of Desmoinesian Pennsylvanian age are associated with carbonate-mound petroleum reservoirs in the Paradox and Eagle basins of southeastern Utah and western Colorado. In both basins there are basin-type evaporites associated with starved-basin trough sediments that cover a complete range of evaporitic deposits including hypersaline potash beds, halite, anhydrite, very fine-grained dolomite, and black sapropelic muds. A broad facies belt of petroleum-bearing biogenic carbonates and fine clastics occurs in cyclic association on the mildly tectonic basin shelves. Coarse arkosic facies and narrow belts of biogenic carbonates occupy the tectonically active basin edges adjacent to the Uncompahgre and Front Range highlands of the Ancestral Rockies. Fiv major juxtaposed evaporite-carbonate mound cycles are mappable in the Paradox basin. Each major cycle contains several subcycles showing different degrees of completeness; individual salt, anhydrite, and black shale beds demonstrate a well-defined microcyclic sedimentation pattern, perhaps related to annual or seasonal climatic changes. The major cycles and most subcycles can be correlated throughout the basin by use of mechanical logs. Microstratigraphic studies of evaporite cores indicate that individual microcycles can be traced for relatively large distances where sufficient cores are available. The evaporite environment is believed to be directly responsible for the presence of petroleum deposits in the Paradox basin because of its role in the genesis of organic-rich basinwide potential petroleum source beds, improvement of reservoir quality by dolomitization in some places, and the indirect influence of the sapropelic shale-bed geometry in determining size and positioning of carbonate-mound reservoir belts. Conversely, some detrimental effect of the evaporite phase is found in the sealing of some original porosity by later anhydrite infilling. Most of the petroleum deposits occur in shelf carbonate reservoirs along the southwest flank of the basin. However, probably even greater potential reserves are locked in sapropelic fractured shale beds in the central basin salt anticline area, not now recoverable under the limitations of present exploitation technology. Evaporite deposits equivalent in age to those of the Paradox basin are present in the Eagle basin of northwestern Colorado. Although thinner than the Paradox evaporites, and more closely interrelated with clastic sediments, these beds occur also in a well-developed cyclic evaporite-black shale depositional sequence. Significant petroleum deposits in facies association with the evaporite section have not yet been found in the Eagle basin, although in most of the basin area drilling density is sparse. End_of_Article - Last_Page 544------------

PALAEOGEOGRAPHY OF THE AUSTRALIAN PERMIAN IN RELATION TO OIL SEARCH

Aspects of Permian glaciomarine sedimentation in Australia in relation to petroleum generation are treated in the light of the "Gondwana-land" hypothesis and recent studies in palaeolatitudinal distribution of Tertiary oilfields. The Permian segment of the Gondwana (U. Dev. to Trias.) succession is characterised by Glossopteris-Gangamopteris flora, glacial. glaciomarine and glaciofluvial sediments, coal measures and cyclothems.Evolution of the Hunter-Bowen Geosyncline of eastern Australia was accompanied by major volcanic activity along an arc-like archipelago. Sedimentation in this longitudinal ortho-geosynclinal belt linked acrosn the continent via shallow infra-basins and intra-cratonic basins to a series of graben-troughs (Perth, Carnarvon, Fitzroy and Bonaparte) developing about the western margin of Neo-Australia. These latter elongate and generally extremely deep "basins" were early manifestations of, and incipient riftings related to, the embryonic Indian Ocean.The Permian (south) palaeomagnetic pole was located approximately 30 degrees of are west of south from Melbourne, placing Australia in relatively high southern latitudes. Middle to Upper Tertiary oilfields of the Northern Hemisphere on the other hand have been indicated elsewhere to be products of tropical palaeolatitudes from which it has been implied that warm temperatures may be critical in oil formation.Recent investigations indicate that, acre for acre, Antarctic waters are potentially richer in organic life than any other. This is related primarily to abundance of nitrates and phosphates brought into sunlit (20 or more hours per day in summer) waters by upwelling currents. In consequence a high nutrient status of marine waters may be more important than palaeolatitudes in facilitating organic build-up in accumulating sediments. More research into contemporaneous sedimentation in relation to "Antarctic Convergence" in continental shelf settings is undoubtedly desirable.The great variety of Australian palaeo-environments of Permian age includes those of the open sea, continental shelf, hinge-line, barred embayment and alternating marine to fresh water basin. These offer a range of settings favourable to the entombment of organic matter under a variety of conditions presumed favourable to the formation of petroleum source-beds. Encouraging discoveries at Yardarino (W.A.), Gidgealpa (S.A.) and Cabawin (Qld.) justify accelerated exploration for commercial petroleum in the Australian Permian.

Petroleum Evolution: Progress and Problems: ABSTRACT

The three-fold concept of the origin of hydrocarbons from organic materials in a source bed, their primary migration from the source rock during compaction, and their accumulation in traps, has been a part of geological philosophy since the early days of petroleum exploration. But except for adding some substantiating geologic evidence, it was not until the talents of chemists, biologists, and physicists were directed at these problems that new information with profound implications to concepts of petroleum evolution was obtained. For example, studies of carbon isotopes in sediments and crude oils suggest that terrestrial plants, instead of marine plants and animals, may be the principal primary substance from which petroleum is derived. Further, the discovery of hydrocarbons in Recent sediments demonstrated the early formation and availability of petroliferous materials in depositional basins. However, characterization has revealed differences in the nature and abundance of hydrocarbons in Recent sediments compared with crudes and ancient rocks, indicating that modification and formation of hydrocarbons during diagenesis may be essential for the development of a source rock. Further, the distribution and character of hydrocarbons in ancient sediments indicate that some environments lead to the generation of mo e hydrocarbons than others, confirming the geologic opinion that there is a considerable range of variation in the nature of petroleum source beds. However, the recognition and evaluation of source rocks on the basis of absolute hydrocarbon content may be an oversimplification in that the hydrocarbons may not be indigenous, or may have formed subsequent to primary migration, or that some rocks may have yielded only a small part of their indigenous hydrocarbons. Finally, comparison of crude oil-source rock pairs indicates that the development of geochemical correlation techniques will be difficult and complicated by the likelihood that primary migration is inefficient, selective, and probably causes considerable modification of hydrocarbons en route. Although contributions of non-geologists are essential, laboratory results will probably remain obscure unless interpreted in the light of a thorough knowledge of geological factors. The problem of petroleum evolution seems ripe for an integrated attack by geologists supported by physicists, chemists, biologists, and geochemists. The belief that an ultimate comprehension of petroleum evolution can only be developed by the interpretation of experimental and analytical data on a sound geological basis should be the underlying philosophy of future research on petroleum evolution. End_of_Article - Last_Page 114------------

Geologic Aspects of Origin of Petroleum

Geologic Aspects of Origin of Petroleum

Fossiliferous Paleozoic Localities in Merida Andes, Venezuela

Despite both the paucity of information relative to Paleozoic sedimentation and the lack of systematic publication of data by various workers, the deposition of marine fossiliferous strata during this Era was widespread in western Venezuela. This current study of the fossiliferous Paleozoic sedimentary strata of the Merida Andes of western Venezuela and the availability of supporting data from Colombia and Ecuador attest the extensive deposition of marine fossiliferous rocks during the Cambrian, Ordovician, Devonian, Pennsylvanian, and Permian periods. In Venezuela the extent of Paleozoic sediments into areas which have not been subjected to subsequent metamorphism is no doubt much greater than heretofore supposed. The probabilities of thin to thick remnants of Paleozoic ediments capping the Guayana shield extending beneath the Ilanos of western Venezuela and the possibilities within these remnants for source and (or) reservoir beds of petroleum are not beyond conjecture. Thirteen marine fossiliferous Paleozoic localities from the Merida Andes of western Venezuela are described in detail. In addition to the systematic presentation of stratigraphic data for each area, the illustrations include location maps giving distribution of the Paleozoic strata and their accessibility. Marine deposition was widespread in western Venezuela during the Paleozoic Era. The most extensive marine record is that of the Late Paleozoic subera, the Mucuchachi group of the Devonian period. Silurian marine sediments are not known in Venezuela. Marine sediments of Pennsylvanian and Permian age are also widespread. All marine fossiliferous Paleozoic strata are in the southeastern sector of the Merida Andes.

The Introduction to the Geochemical Researches of the Onnagawa and the Funakawa Petroliferous Formations

The environments of sedimentation and their relations to the geochemical studies, of the Onnagawa and the Funakawa formations (Tertiary age) which are major petroleum source beds in Japan are discussed and the auther's opnion that the Onnagawa formation consists of the characteristic sediments of the “flysch” type is presented in this paper.