Organic Limestone Research Articles

Calcareous nannofossils biostratigraphy and Paleoclimatology of the Bekhme Formation, Bekhere anticline, Dhouk area, Kurdistan region, Northern Iraq

A Detailed Calcareous nannofossil study conducted on the Bekhme Formation that is cropped out at the Southern limb of the Bekhere anticline, eastern ward of the Dohuk city near Bajlur village, northern Iraq. The Bekhme Formation is composed of marly limestone, Organic limestone and fossiliferous limestone. The nannopaleontological classification of these calcareous nannofossils led us to determine thirty-four genus/species belonging to nine families. The nannobiostratigraphic analysis suggested three calcareous nannofossils biozones from oldest to youngest are: (1) Quadrum sissinghii Interval Zone; (2) Quadrum trifidum Interval Zone; (3) Tranolithus phacelosus Interval Zone. These biozones suggest that the studied section from the Bekhme Formation is the Middle to Late Campanian, and it refers to temperature fluctuations which considered as possible warm time period at subtropical areas.

A Study on Geotechnical Properties of Weak Rocks in Sudan

Weak rocks are available in different areas in Sudan. These include sandstone, mudstone, siltstone usually referred to as Nubian Formations (N.F.). Clastic limestones are present in other areas of Sudan. Organic limestones in the form of coralline deposits are present in eastern Sudan, mainly on the Red Sea coast. Weak rocks constitute an important geological feature on which the foundations of most of the important structures are resting. The sandstone is also used as a primary buildingmaterial or as a facing stone over other construction. The geotechnical properties of these formations were investigated bydifferent insitu and laboratory testing methods. This paper summarizes the origin, distribution of Nubian formation and limestone. The paper also presents most of available data on the geotechnical properties of these formations. It is concluded that the Nubian formation and limestone coral deposit are weak rocks with poor quality of core samples; hence feld testingmay give better geocharacterization result for such deposit.

Pervious low-calcium fly ash geopolymer concrete using gap-graded limestone coarse aggregates in ambient curing

This paper describes the research of pervious geopolymer concrete using limestone from Timor Island in Indonesia as coarse aggregate. No sand was used to make this pervious geopolymer concrete. Two types of crushed limestone aggregates used were coral limestone (organic limestone) and limestone (calcilutite). Abrasion losses of the aggregates using Los Angeles Machine test were 18.9% for limestone (calcilutite) and 34.98% for coral limestone. Those aggregates had many characteristics such as 10-20 mm of diameter length, angular shapes and apparent specific density 2.74-2.75. The mass ratios of aggregate to geopolymer paste were varied from 2.86 to 6.91. To make the geopolymer paste, it was used Class F or Low-Calcium Fly Ash from Bolok-Kupang Coal Fired Power Plant as a rich silica-alumina of precursor material. Meanwhile, the mass ratio of natrium silicate solution to natrium hydroxide solution 10 M was 1.0 and the mass ratio of fly ash to alkaline solution was 2.0. Ambient curing was applied to all specimens. Mechanical characteristics obtained at the age of 28 days of hardened pervious geopolymer concrete were: (1) compression strength, (2) splitting tensile strength, and (3) abrasion losses using Los Angeles Machine Test. Besides, density of hardened specimens were also obtained. In addition, the comparisons of mechanical properties of pervious geopolymer concretes using coral limestone and limestone (calcilutite) as coarse aggregate were also conducted. According to the results of this research, it is feasible to make pervious geopolymer concrete using Timor limestone as coarse aggregate due to its mechanical characteristics.

Early Neolithic pottery of Ifri n'Etsedda, NE-Morocco – Raw materials and fabrication techniques

Ifri n'Etsedda is a rock shelter in northeastern Morocco, at the southern flank of the Kebdana Mountains. The site was discovered in 2008 and excavated during three field campaigns between 2012 and 2014 and provides Epipalaeolithic and Neolithic deposits. From the Neolithic deposits we analyzed 30 pottery sherds by macroscopic determination, Infrared (IR) Spectroscopy, polarizing microscope and thermodilatometric analysis (TDA) in order to determine information about the clay and natural inclusions in the clay and temper materials used as well as the manufacturing process. In addition, we identified and sampled 12 potential raw materials sources during one survey campaign in 2015, which were analyzed by IR spectroscopy as well. We identified 8 groups by means of inclusions in the clay: extrusive igneous rocks (EIR), EIR with amphiboles, EIR with fragments of micro quartz, granite, dolerite or gabbro with fibrous quartz and unidentified spherulites, schist, organic limestone and grog. Trends in the succession of clay traditions could be identified. Most of the pottery was fired in an oxidizing atmosphere and were placed upside down in a pit. Burning temperatures range between 800 and 1000 °C. No local clay source seems to have been used for the pottery production at Ifri n'Etsedda. With regard to the small artifact samples size as well as the incomplete raw material survey, further studies are needed to shed more light on Ifri n'Etsedda pottery.

Anatomically preserved cardiocarpalean ovules in the late Palaeozoic Angara floral province of Russia

A new species of Cardiocarpus from the Sim River Basin in the southern Urals of Russia is the first anatomically preserved cardiocarpalean ovule from the Permian of the Angara floral province. Specimens are preserved in a soft organic limestone with large numbers of juvenile bactritoid protoconchs. Ovules are roughly ellipsoidal in the major plane, up to 6.0–7.5 mm in length and 5.3 mm in width, with a diminutive wing and a rounded chalaza. The outer surface of the ovules is smooth. In longitudinal sections, two vascular tissue channels traverse the sclerotesta at the chalaza, and appear to extend to near the apex within each wing. There is a simple, dome-shaped pollen chamber at the apex, which lies below a narrow micropyle. The sclerotesta consists of one or two layers of longitudinally orientated cells at the interior, and sclereids that are radially elongated towards the periphery. The sarcotesta is incompletely preserved, but displays an outer layer of cells that are somewhat elongated towards the long axis of the ovule. Numerical cladistic analysis reveals little correlation between the structure of cardiocarpalean morphotaxa and the phylogenetic relationships of the plants that produced them, where affinities are known. Cardiocarpus angarensis sp. nov. enriches our understanding of Permian spermatophytes in temperate climates of the Northern Hemisphere, and reveals that ovules similar to those of Euramerican and Cathaysian provinces characterized an Angaran spermatophyte. Journal compilation © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155, 297–305. No claim to original US government works.

The main lithoid material origin of the Temple of Hercules in San Marco d'Alunzio (Sicily, Italy)

This study compares four samples of travertine collected in the lithoid material of the Temple of Hercules (III-IV century B.C.) in San Marco d’Alunzio (Messina) and other four samples of the same lithotype collected in an outcrop found in the surroundings of Alcara Li Fusi (Messina). Analyses on sedimentary petrology, paleontology, XRay diffraction and infrared spectroscopy have been carried out on both series of samples. Chemical analyses, for the determination of the major and trace elements, were carried out too. Sedimentary petrology and paleontological studies have indicated that all samples consist of Quaternary soft and porous organic limestones with plant remains, formed in wet and warm zones. X-ray diffraction analyses have shown that studied travertines are prevalently made up of calcite. Infrared spectroscopy studies also showed small quantities of kaolinite and dolomite. Chemical analyses have confirmed the compositional homogeneity among the different samples. Data, as a whole, allow us to hypothesize that the travertines used to build the Temple of Hercules were extracted in the surroundings areas of Alcara Li Fusi, in ancient open quarries set up in Quaternary travertines.

FACIES CONTROL ON THE COMPOSITION OF SERPUKHOVIAN AND EARLY BASHKIRIAN FORAMINIFERAL ASSEMBLAGES IN THE MIDDLETIEN-SHAN MOUNTAINS, CENTRAL ASIA

Serpukhovian-lower Bashkirian deposits are widely developed in the Middle Tien-Shan Mountains of Uzbekistan and adjacent countries of Central Asia. These deposits formed in a sedimentary basin exhibiting four distinctive facies that differ in foraminiferal diversity and population density. The facies types, named for mountain ranges containing representative sections, are called 1) Talassic, for inner shelf, shallow- water marine carbonates; 2) Ugamic, for carbonaceous deposits accumulating on an open, shallow-water, outer carbonate shelf platform; 3) Karzhantauic, for interbedded volcaniclastics and shallow-water marine carbonates deposited on a eroded surface; and 4) Paltauic, for basinal beds containing thin-bedded, graded and laminated organic limestones and interbedded turbidites. A statistical program (Sorenson's Coefficients of Species Similarity) was used to compare assemblages in eight foraminiferal zones from coeval fades across the basin. Highest similarity coefficients occur in the early Serpukhovian and are probably related to a marine transgression that flooded the basin. Regression and volcaniclastic sedimentation account for lower coefficients in the remainder of the Serpukhovian. Increased foraminiferal diversity and abundance in the earliest Bashkirian were probably caused by the opening of new connections to adjacent Paleotethyan basins only to be followed by more restricted environmental conditions and lower similarity coefficients later in the early Bashkirian.

THE VENEZUELAN HYDROCARBON HABITAT, PART 1: TECTONICS, STRUCTURE, PALAEOGEOGRAPHY AND SOURCE ROCKS

Venezuela forms part of an important hydrocarbon province, defined by the presence of prolific Cretaceous source rocks, which extends across northern South America. By early 1997, the country had produced 53 billion barrels of oil. Reserves are estimated to total 73 billion barrels of oil and 146 TCF of gas with 250 billion barrels recoverable in the Heavy Oil Belt. Most reserves are located within the intermontane Maracaibo and foreland Barinas‐Apure and Eastern Venezuela Basinx They correspond to more than 1.5 trillion BOE originally in place.The province's hydrocarbon history began with a broad passive margin over which the sea transgressed throughout much of the Cretaceous. Limestones and shales followed basal sands and included rich source rocks. Convergence between the distal part of the area and the Caribbean Plate created an active margin that migrated southwards, so that flysch and wildflysch followed the transgressive facies. The process culminated in Lute Cretaceous to Middle Eocene orogeny with the emplacement of southward‐vergent nappes and the development of northward‐deepening foredeeps. Flysch and wildflysch formed in the north while important deltaic—paralic reservoir sands accumulated in the south. Major phases of hydrocarbon generation from Jurassic‐Cretaceous source rocks occurred across the entire margin of northern South America during the orogeny. They are recorded by Jurassic ‐ Middle Cretaceous graphitic marbles, schists and quartzites (metamorphosed, organic limestones and shales and oil‐bearing sandstones) in the Coastal and Northern Ranges of Venezuela and Trinidad. They probably charged giant fault and stratigraphic traps analogous to today's Oficina‐Temblador and Heavy Oil Belt accumulations.From Late Eocene to Recent times, transpressive interaction between northern South America and neighbouring parts of the Caribbean and the Pacific inverted Mesozoic extensional systems below the remaining passive margin. The area became subdivided into a series of intermontane, foreland and pull‐apart basins bounded by transpressional uplifts, the latter sufering considerable shortening and strike‐slip displacement. Sedimentation progressed from deep marine to deltaic and molassic facies, providing reservoir sands and local source rocks.Inverted faults and foreland flexuring and interplay between structuration and sedimentation produced abundant structural and stratigraphic traps. Hydrocarbons from earlier accumulations suffered further maturation in place, remigrated to younger traps or escaped to the surface. Further hydrocarbon generation, involving Upper Cretaceous source rocks, occurred in local foredeep kitchens. Minor contributions also came from Tertiary source rocks.

Peculiarities of Petroleum Formation in Highly Bituminous, Siliceous, Shaly, Carbonaceous Facies, Timan-Pechora Basin, USSR: ABSTRACT

Over 50 oil and gas fields with total reserves of about 6 × 109 BOE have been discovered in the Timan-Pechora basin, one of the most important Russian frontiers. Almost all the sequence is productive, although major reserves are confined to two stratigraphic intervals beneath regional seals. Principal source rocks are the so-called Domanik facies, 25 to 150 m (82 to 492 ft) thick, represented by rapidly alternating black shales, chert, marls, and siliceous and organic limestones. Exclusively sapropelic organic matter averages 5 to 7% and reaches 20% or more. Soluble bitumen is very abundant (1 to 2 wt. %) and contains all the components characteristic of crudes: from light oils to heavy tars and typical high-molecular asphaltenes. These characteristics exi t even on the basin's periphery where Domanik facies are only marginally mature. In other areas, Domanik facies are mature; they are probably overmature in the deepest troughs. Outside the area covered by Domanik facies, pools and even significant shows are absent. Deposition of this prominent facies began during the end of early Frasnian time in a wide stagnant sea that covered the eastern edge of the Russian platform. Beginning in the late Frasnian, shallow-water carbonate sedimentation resumed along the basin's edges and on uplifted blocks. Condensed Domanik deposits continued to form in the gradually deepening sea on the east side of the basin. Barrier reefs and clastic terraces that prograded basinward formed along the northern and western boundaries. The deep-water trough was finally filled by thick clastics at the end of early Tournaisian time. The unusual composition of Domanik facies and their exceptional enrichment by sapropelic organic matter result in their peculiarities as petroleum source rocks. Lithology of the rocks, particularly the abundance of huge carbonate concretions fully or partly replaced by silica, suggests a long delay in lithification and the relative importance of the late diagenetic stage of oil generation. This explains the presence of immature oils in underlying Devonian clastics and their absence elsewhere in the sequence. On the other hand, Domanik facies, owing to significant silicification that trapped giant amounts of bitumen in the rocks, became a natural repository of oil during geologic history. This oil migrated because of fracturing, especially during stages of tectonic activity. Spatial istribution of oil types and deposits of solid bitumen in traps having different ages of formation, clearly shows predominance of pulse-like vertical migration. Migration of oil from the Domanik continued during late stages of geologic history along with block uplifting, cooling of the sedimentary cover, and absence of sedimentation. Thus, methods of applied geochemistry that invoke models of heating should not be applied to Domanik-type rocks and more geologic data are required to assess their role as oil sources. End_of_Article - Last_Page 561------------

Organic remains and traces from the Dalradian of Benderloch, Argyll

Synopsis Organic remains from Dalradian slumped deposits, identified as oncolites, catagraphs and possible Bryozoa, are described. Correlation with organic forms from U.S.S.R. is noted. Borings into organic limestone clasts are mentioned and regarded as being due to parasitic algae.

Case History of the University Block 9 (Wolfcamp) FieldA Gas-Water Injection Secondary Recovery Project

On the whole, the Wolfcamp has responded well to this system of alternating gas injection and water injection - better than it would have responded to natural depletion or waterflooding. Operations are expected to improve substantially with injection rates scheduled on the basis of simulated reservoir material balancing rather than stock-tank material balancing. Introduction The University Block 9 (Wolfcamp) reservoir, located 8 miles south of Andrews, Tex., was discovered in 1953. The limestone, domal feature at a depth of 8,400 to 8,500 ft was discovered as a result of seismic work in the area. A pressure-maintenance, miscible-displacement, peripherally patterned project was begun shortly after unitization in 1960, and the alternate gas-water injection phase of operations has been continued to the present time. Thus far, the project has yielded more than 2 1/4 times the estimated primary reserves and has been a very successful and profitable operation. The results of the field performance should be beneficial to others considering similar secondary recovery projects. Geological and Reservoir Descriptions The Wolfcamp reservoir of the University Block 9 field (Fig. 1) was discovered by the Atlantic Refining Co.'s No. 1-A University "9AGH". Located on the eastern edge of the Central Basin Platform, the domal, limestone feature (Fig. 2) appears to have been deposited as a combination of draping and carbonate buildup over the underlying Pennsylvanian shelf carbonates. Of the three Wolfcamp zones, the lowest zone is the most productive. It consists of 4 to 45 ft of organic limestone with intercrystalline-to-vugular porosity and has an oil-water contact at approximately 5,370 ft subsea. The nonproductive middle zone is composed of 10 to 40 ft of shaly limestone with irregularly deposited shale stringers. The productive upper zone consists of approximately 10 ft of limestone with intercrystalline porosity. In 1957–58 an engineering committee made a study of the reservoir for secondary recovery purposes. They made material balance and volumetric calculations to determine the original reserves of oil and volume of the reservoir. Statistical analyses of cores, capillary pressure data, reservoir fluid, and well logs were used pressure data, reservoir fluid, and well logs were used to determine the basic reservoir data applied in the material balance and volumetric calculations. Respective material balance and volumetric calculations were 90.32 million and 90.70 million reservoir bbl for reservoir volume, and 50.8 million and 51.0 million STB for original oil in place. Primary Performance Primary Performance The reservoir performance from the initial pressure of 3,500 psig to the saturation pressure of 1,775 psig indicated a performance typical of fluid-expansion drive. Below the bubble-point pressure the reservoir performed by solution-gas drive with no evidence of performed by solution-gas drive with no evidence of water encroachment. The reservoir performance with respect to water production, GOR, bottom-hole pressure, and oil production is shown in Figs. 3 and 4. pressure, and oil production is shown in Figs. 3 and 4. JPT P. 1485

Upper Devonian Stratigraphy and Structure, Western Canadian Arctic Islands: ABSTRACT

Upper Devonian strata (Melville Island Group) in the western Arctic Islands are part of a clastic wedge at least 10,000 ft thick. The strata represent the uppermost part of the Lower to Middle Paleozoic sequence of the Franklinian miogeosyncline. Three major depositional facies are recognized. (1) Marine shelf facies--interbedded green, very fine-grained, argillaceous quartz sandstone, siltstone, and shale with a few marine fossils. Organic limestones are rare. (2) High energy shoreline facies--white, fine to coarse-grained, well-sorted quartz sandstone with plant and fish remains. (3) Low energy shoreline facies--interbedded, very fine-grained, argillaceous quartz sandstone, siltstone, shale, and coal. On Bathurst and Melville Islands, the Group is divided into the Hecla Bay Formation (early to middle Frasnian) consisting mainly of high-energy shoreline facies, and the overlying Griper Bay Formation consisting of 2 informal members. The lower member (mid to late Frasnian) consists of marine shelf facies, and the upper member (early to middle Famennian) consists of high- and low-energy shoreline facies. On Prince Patrick and Banks Islands only the Griper Bay Formation is developed. Two informal members are recognized, the lower comprising the entire Frasnian stage, and the upper a part of the Famennian. The source area for the sediments is interpreted to have been a tectonic highland situated along the present western continental margin. Mississippian (Ellesmerian) deformation resulted in the development of open anticline-syncline couples and normal faults. On Bathurst and Melville Islands these structures trend east-west. In contrast, the structures trend north-south on Banks Island. This sharp bend in the Ellesmerian fold belt may be interpreted to be an orocline superimposed on the Franklinian geosyncline during the Ellesmerian orogeny. Restoration of the orocline clarifies otherwise irreconcilable facies relations in the Upper Devonian strata of the Western Arctic Islands. End_of_Article - Last_Page 2491------------

Characteristics of Permian and Triassic carbonate sediments in eastern Szechwan and western Hupeh; their classification as reservoir rocks

In eastern Szechwan and western Hupeh there are widely developed various types of carbonate rocks in the Permian and Triassic. The carbonate rocks form a complete cycle, beginning with the deposition of normal marine organic limestone and ending with the deposition of anhydrite and rock salt, either saline or lagoonal. The order of deposition was as follows: 1) normal marine biogenic and biogenic-clastic limestones, 2) dolomitized limestones, 3) oolitic and clastic limestones, 4)primary dolomites, 5) anhydrite, and 6) rock salt. These carbonate rocks were then affected by various secondary alterations, mainly dolomitization, calcitization and recrystallization, as a result of which coarse-grained dolomites, nodular dolomites and carbonate breccias were formed. However, most of the carbonate breccias in this region are connected with the hydration and solution of anhydrites. The significance of different types of carbonate rock, in their bearing on the accumulation of oil and gas, varies. Carbonate reservo...

Performance of a Miscible Flood with Alternate Gas-Water Displacement

Abstract A miscible displacement project was begun in 1960 in the Midland Farms (Wolfcamp) field. Initially, enriched gas was injected which was equivalent to 2 per cent of the project-area hydrocarbon pore volume. This solvent volume, which is small compared to volumes proposed in some of the literature, was followed by a residue gas buffer and is being displaced by alternate gas and water slugs. Favorable response, such as increased reservoir pressure, increased producing capacity and apparent miscible-bank movement indicates predicted recoveries may be achieved. Additional performance may prove many field applications now considered impractical can be economically justified. Introduction A full-scale miscible-drive project has been in operation in the Midland Farms (Wolfcamp) field since May, 1960. The project utilized a propane volume equivalent to 1 per cent of the hydrocarbon pore volume in the project area. It began with the injection of 13.9 million gal of residue gas which, with the propane, formed the enriched gas phase of about 2 per cent hydrocarbon pore volume. The enriched gas was followed with a dry-gas buffer, and now alternate slugs of water and residue gas are being utilized as the displacing media. Geological and Reservoir Data The Midland Farms (Wolfcamp) field, one the many fields in the huge Midland Farms complex, is located approximately 14 miles southeast of Andrews, Tex. The location of the field with relation to other major fields in the general area is shown in Fig. 1. The field lies on the western edge of the Midland basin in a transition zone between the Central Basin Platform and the Midland basin. Fig. 2 illustrates the Wolfcamp structure contoured on the top of the limestone section which is considered the top of the reef build-up in the area. The pay section, ranging in depth from 8,350 ft to 8,500 ft, is composed of fine- to medium-crystalline organic limestone. Some oolitic deposits are present which are associated with the better-quality pay. In some wells, Wolfcamp reefing is absent. The degree of reef build-up at the various wells determines the structure. Fig. 3 is an illustration of the typical pay characteristics of the field. Table 1 lists the reservoir rock and fluid properties. Primary Performance and Secondary Recovery Planning Until secondary recovery was started, the reservoir had operated since discovery in 1953 under a solution gas- drive mechanism. Through May, 1960, the cumulative production for the field amounted to 1.97 million STB. During the primary production phase the average reservoir pressure had declined to approximately 1,600 psi. As a result, the producing wells in many cases had also reached a stage requiring artificial lift equipment. Fig. 4 graphically illustrates the field performance since discovery. The field was unitized for the purpose of conducting secondary recovery operations. Although initial plans were to water flood the reservoir, laboratory experiments were conducted which indicated that a miscible drive could be established with moderate propane requirements. Subsequently, the enriched gas-drive project was selected, based on favorable incremental economics over conventional water flooding. JPT P. 372^

A propos de depots du Pliocene superieur et du Quaternaire sur la cote nord de l'ile de Minorque (Baleares)

Abstract Remnants of upper Pliocene and early Quaternary formations have recently been discovered at the summit of the Atalaya promontory, the easternmost and highest of three promontories on the northern coast of the island of Minorca (Spain). Study of the beds indicates that the underlying Jurassic-Cretaceous formations were abraded and then subjected to karst erosion. The basal bed of the Pliocene-Quaternary sequence is a decalcification clay, the product of the karst phenomena. Overlying the clay is an organic limestone with abundant foraminifera and Microcodium indicative of littoral conditions produced by partial submergence of the northern coast. Two microbreccias, the upper more compact than the lower, overlie the organic limestone and also contain abundant foraminifera. The microbreccias are clearly marine littoral, evenly bedded below, crossbedded above, and the result of submarine currents. A lighter colored limestone petrographically identical to the lower organic bed overlies the microbreccias. Final uplift (probably Recent) produced the existing cliffs and exposed the Pliocene-Quaternary formations. The age of the sequence is tentatively assigned on the basis of the presence of Microcodium.

Geology of Devonian Beaverhill Lake Formation, Swan Hills Area, Alberta, Canada

Throughout most of west-central Alberta, the Beaverhill Lake formation consists of interbedded dense limestones and shales, but in the Swan Hills area a productive unit of porous clastic and organic limestones, the Swan Hills member, is present near the base of the formation. This member contains an early Waterways fauna and represents early Beaverhill Lake reefing. At the western border of the type area, the Swan Hills member occupies the entire Beaverhill Lake interval and interfingers with dolomite beds underlying reefs of post-Beaverhill Lake Woodbend age. To date, all known hydrocarbons in the Beaverhill Lake formation are trapped in localized reef build-ups of the Swan Hills member, but the regional pinch-out edge of this member is only in the early stages of being xplored for stratigraphic traps.

Geology of Devonian Beaverhill Lake Formation, Swan Hills Area, Alberta: ABSTRACT

Throughout most of west-central Alberta, the Beaverhill Lake formation consists of interbedded dense limestones and shales, but in the Swan Hills area a productive unit of porous clastic and organic limestones, the Swan Hills member, is present near the base of the formation. This member contains an early Waterways fauna and represents early Beaverhill Lake reefing. At the western border of the type area, the Swan Hills member occupies the entire Beaverhill Lake interval and interfingers with dolomite beds underlying reefs of post-Beaverhill Lake Woodbend age. To date, all known hydrocarbons in the Beaverhill Lake formation are trapped in localized reef build-ups of the Swan Hills member, but the regional pinch-out edge of this member is only in the early stages of being xplored for stratigraphic traps.

Le volcan sous-marin d'age acadien de Sidi-Said-Maachou (Maroc occidental)

Abstract At three localities in the Sidi-Saied-Maachou area, a complex of volcanic rocks has been identified in the thick, otherwise uniform series of Acadian (Cambrian) green schists of the plateau region of Morocco, which is considered to represent a submarine volcano. Purplish schists, layers of organic limestone, and pyroclastic material, laid down in deep water, are cut by vertical dikes which fed sills and submarine flows of basic lava. The eruption was calm, resembling, on a much smaller scale, the emplacement of greenstones in geosynclines.

The Habitat of oil in the Eastern Gulf Coast

The eastern Gulf Coast, comprising the states of Mississippi and Florida and those portions of A labama and Georgia not included in the Appalachin Mountains and the Piedmont Plateau, covers about 166,000 square miles. About 95 ,000 cubic miles of Paleozoic sediments are included in this area, occupying two widely separated basins. The better known of these is the Black Warr ior of northeastern Mississippi and northwestern A labama, in which the f irst hydrocarbon production of both of these states was found. The other, herein named the Suwannee River Basin, lies in southern Georgia, northern Florida, and southeastern Alabama. It is nonproductive. The most important basin wi th in the eastern Gulf Coast f rom the standpoint of oil production is the Mississippi Salt which is continuous wi th a similar basin in Louisiana on the west, and extends into Alabama on the east. Minor production has been obtained from four of the 49 shallow salt domes proven by dr i l l ing in this basin. The major production from Mesozoic reservoirs in the province is derived from salt upl i f ted structures which f lank the salt basin on the north and south. Important Tert iary (Eocene Wilcox) production is largs'y confined to four counties in southwestern Mississippi. I t is obtained principal ly f rom structural ly modif ied stratigraphic traps. Southern Florida, since early Cretaceous t ime at least, has been a shallow plat form area characterized by carbonate and evaporite deposition wi th no important non carbonate elastics. Two fields have been discovered to date, producing from a highly organic limestone of Lower Cretaceous, Glen Rose age. The present northeastern boundary of rich Miocene production in South Louisiana and the Louisiana tidelands is approximately coincident wi th the 10,000 foot isopach of Miocene sediments. Present informat ion, which indicates rapid thinning of the M\iocene and its graduat ion to a carbonate facies east and northeast of this l ine, suggests objectives for exploration in the Mississippi A labama Florida coastal and offshore areas wi l l be in sediments other than Miocene, on structures other than salt domes.

Petrography and Petrology of Scurry Reef, Scurry County, Texas

The Scurry reef of Scurry County, Texas, is a subsurface feature 23 miles long and 4-8 miles wide that is of Permian and Carboniferous age. The reef is a low mound composed chiefly of clastic organic limestone with minor amounts of black bituminous claystone. The reef limestone consists of three main textural types: calcilutite, calcarenite, and calcirudite. The calcilutite is composed mainly of particles too fine to be resolved under the petrographic microscope. Part of this fine material appears to be comminuted organic debris; the remainder may be chemically precipitated ooze. The calcarenite forms a gradational series between sorted, rounded debris in clear crystalline calcite cement and unsorted, angular debris in a matrix of lithified lime mud. The calcirudite is composed of angular, granule- to boulder-sized fragments in a matrix of lithified lime mud or lime sand. The fragments consist of organic debris and pre-existing reef limestone and claystone. The limestone contains minor amounts of secondary calcite, dolomite, and chert. Characteristic structures in the limestone are stylolites, joints, irregular fractures, and slump structures. The vast bulk of observable porosity was formed by leaching solutions. This condition may have been accomplished principally by the enlargement of primary openings through the removal of the least stable constituents. The Scurry reef was formed from the hard parts of organisms that lived, died, and were buried in essentially one locality. The two major faunal elements that could be identified in the reef are the Crinoidea and the Foraminifera, principally Fusulinidae. Corals constitute a minor element and are not numerous enough to be important here as reef-forming organisms. It is suggested that the welding of lime mud and the constant precipitation of calcite cement rigidified the accumulating material and thus acted as a substitute for the rigid organic framework that characterizes many reefs.