Showing papers in "AAPG Bulletin in 1971"
TL;DR: In this article, the conditions of formation and evolution of hydrocarbons during burial and related diagenesis of sediments were investigated in Early Toarcian shales (Early Jurassic) in the Paris basin.
Abstract: The purpose of the study was to investigate the conditions of formation and evolution of hydrocarbons during burial and related diagenesis of sediments. Early Toarcian shales (Early Jurassic), in the Paris basin, were selected because all parameters except temperature and pressure (both related to burial of sediments) remain constant--age, nature of fossil organisms and clay minerals, and conditions of deposition (which were fairly homogeneous in the formation across the surveyed area). The amounts of the different organic constituents and some structural properties of the molecules reveal an orderly variation, depending on maximum depth of burial. At the beginning of burial, the transformation ratio of organic matter to hydrocarbons is low and changes little to a depth of 1,500 m, where the ratio increases markedly with increased depth. A detailed study shows that hydrocarbons present at shallow depth are directly inherited from original living matter or result from early transformation in sediment, without changing the general structure of the molecule (like molecules of steroid and triterpenoid types). When burial becomes sufficiently deep, these characteristic structures are diluted among newly formed hydrocarbons generated by thermal degradation of organic matter. Interpretation of the observations leads to the conclusion that burial (i.e., increase of pressure and especially of temperature) constitutes the determining factor in the evolution of organic matter. The temperature rise promotes the formation of petroleum compounds, particularly hydrocarbons, at the expense of kerogen. A general reaction scheme is proposed, based on hypothesis on the structure of kerogen, and on the observed relations of the various organic compounds.
258 citations
TL;DR: In this paper, the authors proposed an alternative to the accepted tectonic explanation of these cycles, which is based on the seaward progradation of the wedge of sediments, which gives a regressive cycle from open marine shelf or platform to supratidal flat.
Abstract: Repeated regressive cycles are characteristic of the Paleozoic shallow-water carbonates of North America; similar cycles are present, although less abundant, in Mesozoic and Cenozoic strata worldwide. Several of these cyclic carbonates contain major hydrocarbon reservoirs: Permian, Central Basin platform; Mississippian, Saskatchewan; Ordovician and Silurian, Montana. Studies of comparable recent deposits in Florida, the Bahamas, and the Persian Gulf suggest an alternative to the accepted tectonic explanation of these cycles. The Florida Bay lagoon and the tidal flats of the Bahamas and Persian Gulf are traps for fine sediment produced on the large adjacent open platforms or shelves. The extensive source areas produce carbonate mud by precipitation and by the disintegration of organic skeletons. The carbonate mud moves shoreward by wind-driven, tidal or estuarinelike circulation, and deposition is accelerated and stabilized by marine plants and animals. Because the open marine source areas are many times larger than the nearshore traps, seaward progradation of the wedge of sediments is inevitable. This seaward progradation gives a regressive cycle from open marine shelf or platform to supratidal flat. As the shoreline progrades seaward the size of the open marine source area decreases; eventually reduced production of mud no longer exceeds slow continuous subsidence and a new transgression begins. When the source area expands so that production again exceeds subsidence a new regressive cycle starts. The seaward progradation suggested by this model should be observable in ancient deposits. End_of_Article - Last_Page 340------------
201 citations
TL;DR: The results of 30 seismic refraction profiles are presented in five seismic sections in the Caribbean Sea as discussed by the authors, and particular attention was given to areas of complex structure such as Tobago Island, Aves Swell, Netherlands West Indies, Los Roques and Bonaire Trenches, Curacao Ridge, Beata Ridge, Nicaragua Rise, and Cayman Trough.
Abstract: The results of 30 seismic refraction profiles are presented in five seismic sections in the Caribbean Sea. Particular attention was given to areas of complex structure such as Tobago Island, Aves Swell, Netherlands West Indies, Los Roques and Bonaire Trenches, Curacao Ridge, Beata Ridge, Nicaragua Rise, and Cayman Trough. Previous surveys have established that the Colombia and Venezuela Basins crustal structures consist of a 6.1 km/sec layer over a 7.2 km/sec layer, which is underlain by a mantle of normal velocity, 8.1 km/sec. This survey demonstrated that the Nicaragua Rise and Beata Ridge have a 5.4 km/sec layer overlying a 6.7 km/sec layer. Only the upper crustal layer was recorded beneath the Aves Swell and it has a velocity of 6.0 km/sec, similar to that of the basi s. The Curacao Ridge overlies a sediment-filled trough that contains up to 14.5 km of low- and high-velocity sediments and rock. The Netherlands West Indies are underlain by material having a velocity of about 5.5 km/sec. Large accumulations of sediments surround the islands. An average nonturbidite basin sedimentary sequence includes velocities of 1.9, 2.7, and 3.9 km/sec. The reflection profiler shows two acoustically transparent beds in the Venezuela and Colombia Basins (1.9 and 2.7 km/sec layers), separated by a strong reflector representing approximately the Mesozoic-Cenozoic boundary. The surface of the layer underlying the transparent beds is a smooth coherent reflector suggestive of a sedimentary horizon. It is postulated that the Caribbean is a relict of Mesozoic Pacific crust that was emplaced between North and South America during separation from Europe and Africa. The interaction of the Caribbean plate with the circum-Caribbean lands resulted in the formation of geosynclines. The Caribbean plate subsequently has decoupled from the parent Pacific spreading system and is protected from being assimilated into the mantle by the presence of crustal sinks on both the east and west margins.
158 citations
TL;DR: The validity of boron as a salinity index has been established by numerous studies over the past 2 decades as discussed by the authors, which can be expressed as a Freundlich adsorption isotherm for seawater systems, as log B = C1 log S + C2, where B = borons uptake (ppm), S = salinity of the water (pmil), and C1, C2 = constants, dependent on the particular clay.
Abstract: The validity of boron as a salinity index has been established by numerous studies over the past 2 decades. It is known that all the major clay minerals may contain boron which can be correlated with paleosalinity. However, under given conditions, illites will contain the most boron and kaolinites the least. Montmorillonites and probably chlorites are intermediate. Published data indicate that a detrital clay will adsorb boron from solution, fix it at the surface, and later incorporate it within the structure. For seawater systems, this boron uptake can be expressed as a Freundlich adsorption isotherm, as log B = C1 log S + C2, where B = boron uptake (ppm), S = salinity of the water (^pmil), and C1, C2 = constants, dependent on the particular clay. Factors other than salinity that affect boron content are inherited boron, clay mineralogy, grain size, and crystallinity of the clay minerals. Sufficient independent data were available to use an adsorption isotherm to calculate paleosalinities for a kaolinitic Tertiary shale in Nigeria. The constants necessary for calibration of the isotherm were evaluated as: Inherited "kaolinite boron," O; "Kaolinite boron" uptake at 1 ^pmil salinity 1.3 ppm (C2 = 0.11); and "Kaolinite boron" uptake at 35 ^pmil salinity 65 ppm (C1 = 1.28). Boron concentrations, related to kaolinite, were converted graphically to paleosalinities from a log-log calibration curve with the use of these values. Paleosalinities determined in this manner are in good agreement with independent faunal interpretations.
125 citations
TL;DR: In this article, it was shown that microporosity occurs in carbonate carbonate rocks that range from friable to well indurated and intercrystalline micropores may be present in micrite and within ooids, pisolites, micrite intraclasts, pellets, and cryptocrystalline grains.
Abstract: Large pores in carbonate rocks hold and transmit fluids, whereas associated micropores may hold irreducible water; i.e., water not available for flow. Analysis of borehole logs of microporous carbonate rocks can result in misleadingly high calculated water saturations and possibly bypassing of a potential oil or gas reservoir. Microporosity occurs in carbonate rocks that range from friable to well indurated. Intercrystalline micropores may be present in micrite and within ooids, pisolites, micrite intraclasts, pellets, and cryptocrystalline grains. Micropores in ancient rocks appear to result from (1) formation of micrite envelopes, (2) void space present after transition of aragonite to calcite, or (3) incipient weathering and dissolution. Aggrading neomorphism of micrite to microspar tends to destroy microporosity.
87 citations
TL;DR: The Hartland Shale and Jetmore Chalk Members of the Greenhorn Limestone contain 16 burrow-mottled, ledge-forming, chalky limestone beds that can be traced across the entire outcrop as discussed by the authors.
Abstract: In central Kansas the Hartland Shale and Jetmore Chalk Members of the Greenhorn Limestone contain 16 burrow-mottled, ledge-forming, chalky limestone beds that can be traced across the entire outcrop. The same beds are recognized in equivalent strata of the Bridge Creek Limestone Member of westernmost Kansas, and all but one or two can be recognized in a Bridge Creek exposure in southwestern Pueblo County, Colorado. For a distance of nearly 450 mi some of these beds lie on, below, or close to equally persistent bentonite seams. The parallelism of bentonite seams and adjacent or nearly adjacent beds of limestone, and the uniform relative spacing of all the limestone beds prove that some of the latter are time parallel and suggest most convincingly that each of these widespr ad beds is time parallel. In contrast to intervening beds of laminated shaly chalk, the limestone beds lack internal stratification because of activity of a highly mobile infauna. The shaly chalk beds contain higher percentages of terrigenous detritus, organic carbon, and pyrite than the limestone beds, and are interpreted as reflecting greater rates of terrigenous detrital influx and an interstitial reducing environment that was inimical to development of a burrowing infauna. Smaller organic carbon and pyrite content of the limestones is believed to reflect a lower clay content of original sediments, and at least a partly oxidizing interstitial environment, as suggested by the high degree of bioturbation. Despite substrate differences, the aqueous environment directly above the sediment-water interface did not change significantly as sediment type alternated from detritus-rich to detritus-poor, because the shelly epifauna is essentially the same in adjacent be s of shaly chalk and chalky limestone. The widespread, apparently time-parallel limestone beds are believed to be the result of regionally manifested changes in volume of terrigenous detrital influx, coming principally from the west, that were superimposed on a more or less continuous accumulation of carbonate sediments. The noncrushed condition of macrofossils and fecal pellets suggests that limestone beds suffered early lithification; this process was probably influenced by initially greater purity of limestone-forming muds, slower sedimentation, and interstitial circulation resulting from bioturbation.
84 citations
TL;DR: The vertical succession of sedimentary structures and textures at Galveston Barrier Island, Texas, is identical with vertical successions in two ancient barrier complexes, one in the Lower Cretaceous of Montana and the other in the lower Jurassic of England as mentioned in this paper.
Abstract: The vertical succession of sedimentary structures and textures at Galveston Barrier Island, Texas, is identical with vertical successions in two ancient barrier complexes, one in the Lower Cretaceous of Montana and the other in the Lower Jurassic of England. Within both Holocene and ancient examples, there is a gradation upward from (1) irregular interlaminations of siltstone and claystone at the base, through (2) burrowed and generally structureless sandstone, to (3) low-angle and microtrough cross-laminated sandstone, terminating in two of the examples in (4) structureless and rooted sandstone. This sequence represents deposition in (1) lower shoreface, (2) middle shoreface, (3) upper shoreface-beach, and (4) eolian environments, respectively. Analyses of quartz size and content of the Holocene and ancient barriers yield textural and compositional parameters that are environmentally sensitive. Plots of these parameters demonstrate that each of the environments may be distinguished on the basis of thin-section analyses. Consequently, full diameter cores, which show sedimentary structures, may not be necessary for precise environmental interpretation in the subsurface. Indeed, thin sections of sidewall cores may yield significant and reliable environmental interpretations in barrier sandstones. Textural and sedimentary structural similarities between Galveston Island and the ancient examples permit a general model of barrier sedimentation to be developed.
78 citations
TL;DR: In this article, the authors show that extensional stress dominates the upper crust over an area 300-400 km wide and that the observed extensional deformation is not necessarily incompatible with the forces and stress conditions as postulated for an active continental margin.
Abstract: Sea-floor spreading and continental drift seem to imply, for the Pacific segment of South America, upthrust of the continent and compression along its margin. Geologic evidence, however, indicates extension in this area since at least the Miocene. Andean folding has migrated east, away from the Pacific and toward the continent, whereas the tectonic development near the continental margin, which is backland of Andean orogeny, is retrograde and has resulted in a breakdown of the crust mainly along old lineations. There extensional stress dominates the upper crust over an area 300-400 km wide. The observed extensional deformation is not necessarily incompatible with the forces and stress conditions as postulated for an active continental margin. Compression farther inland away from this margin, and continentward migration of fold belts appear to be related directly to the destructive processes that occur in the continental border area.
75 citations
TL;DR: The oldest salt basin of southeastern Mexico, the Isthmian salt basin, usually is referred by most authors to the Triassic-Jurassic. However, it is now possible to date it as pre-Kimeridgian and not older than early Oxfordian (Divesian) as discussed by the authors.
Abstract: The oldest salt basin of southeastern Mexico, the Isthmian salt basin, usually is referred by most authors to the Triassic-Jurassic. However, it is now possible to date the oldest salt basin as pre-Kimeridgian and not older than early Oxfordian (Divesian). This conclusion is based on new data from wells and from studies of the Todos Santos Formation, a unit which has been the object of many studies. A second basin, with salt beds between Late Jurassic strata, below, and Early Cretaceous strata, above, was penetrated in the Turipache No. 1 well near Tuxtla Gutierrez, Chiapas. Information from the La Pita No. 1 and Tortugas No. 1 wells in Guatemala indicates that this basin extended through southern and central Guatemala--perhaps into western Belice (British Honduras). The development of two salt basins of different ages--one on the northwest and the other on the southeast--suggests a northwest to southeast marine transgression along an arcuate line of embayments marginal to the Gulf of Mexico. The marginal position of the basins supports the concept that, before Cretaceous time, the Gulf was a land (shield) area and that the salt basins formed before the foundering of the Gulf was completed at the end of the Mesozoic. The tectonic history of the area includes both Mesozoic and Tertiary crustal movements. Transcurrent faults are present south and southwest of the Yucatan platform; tension or gravity faults characterize the Tertiary basins of the Gulf coastal plain and the eastern side of the Yucatan Peninsula. The transcurrent movement phase is a Cretaceous-early Tertiary event; the tension-movement phase is a middle to late Tertiary event.
74 citations
TL;DR: The results of 33 seismic refraction profiles recorded along two lines, one west-east between Punta del Este and the Rio Grande rise and the other southeast-northwest between the Rio de rise and Rio de Janeiro, are presented in two structure sections, with continuous seismic reflection profiles recorded parallel with the refraction lines as discussed by the authors.
Abstract: The results of 33 seismic refraction profiles recorded along two lines, one west-east between Punta del Este and the Rio Grande rise and the other southeast-northwest between the Rio Grande rise and Rio de Janeiro, are presented in two structure sections, with continuous seismic reflection profiles recorded parallel with the refraction lines. Plots of magnetic and gravity data recorded along the reflection lines are shown with the seismic data. These data, supplemented by previously reported measurements on the northern Argentine shelf and in the Argentine basin, are compiled in a generalized structure map. The seismic section across the Uruguayan continental margin is similar to one previously measured eastward of Rio de la Plata. The continental margin south of Rio de Janeiro contains a sediment-filled shelf embayment and a marginal plateau which extends 450 km out to sea. Possible velocity-age correlations are given for the seismic sections.
TL;DR: In this paper, a vertical sequence of strata in which each lithologic component is related genetically to all the others is defined at the top by a timelithologic marker bed (such as a thin limestone or bentonite) and at the base by either a time-lithology marker bed, an unconformity, or a facies change from marine to non-marine beds.
Abstract: Deltas generally are formed at river mouths during stillstands of sea level under conditions of cyclic transgression or regression. Consequently, they are rarely isolated phenomena, but form in multiples in a predictable fashion. Reservoir facies consist of continuous and discontinuous, bifurcating channel sandstones and delta-front sheet sandstones. The channel sandstones generally thicken downward at the expense of the underlying prodelta clays and may replace selected parts of the delta-front sheet sandstones. The lithologic components of a deltaic complex are interrelated and are referred to collectively as one type of Genetic Increment of Strata (GIS). The GIS is a vertical sequence of strata in which each lithologic component is related genetically to all the others. It is defined at the top by a time-lithologic marker bed (such as a thin limestone or bentonite) and at the base by either a time-lithologic marker bed, an unconformity, or a facies change from marine to nonmarine beds. It generally consists of the total of all marginal marine sediments deposited during one stillstand stage of a shoreline, or it may be a wedge of sediments deposited during a series of cyclic subsidences or emergences. An isopach map of a GIS clearly shows the bifurcating trends of the individual distributari s and the shape of the delta, regardless of the variable lithology of the channel fills. A Genetic Sequence of Strata (GSS) consists of two or more contiguous GIS's and, when isopached, clearly defines the shelf, hinge line, and less stable part of a depositional basin. An isopach map of the McAlester Formation of the Arkoma basin is a good example of a GSS. The oil-productive Booch sandstone is a good example of a deltaic complex occurring within a GIS of this GSS. The upper Tonkawa, Endicott, and Red Fork sandstones of the Anadarko basin are identified as deltaic accumulations within different GIS's. A hypothetical model serves as a basis for establishing the criteria for (1) recognizing successive stillstand positions of a shoreline, (2) predicting paleodrainage courses, (3) predicting positions of a series of deltaic reservoirs, (4) locating isolated channel sandstone reservoirs, and (5) tracing related beach sandstone reservoirs.
TL;DR: In this article, the amount of pore-space reduction caused by solution of grains at points of contact and the additional reduction that would result from precipitation of this dissolved material has been investigated.
Abstract: The amount of pore-space reduction caused by solution of grains at points of contact and the additional reduction that would result from precipitation of this dissolved material has been investigated. For single grains and their associated pore space such reduction in porosity has been calculated for spheres and other geometric forms in various packing arrangements. The relative amounts of porosity reduction may vary greatly, depending on grain shape and angularity, packing, direction of pressure, and amount of solution. The maximum porosity loss by cement relative to porosity loss by solution occurred with spheres in orthorhombic packing, rotated 30°. This is believed to be a maximum for any sand and most closely approached by a well-sorted sandstone made up of very well-rounded grains. A maximum cement-to-solution relation is estimated for sandstones of better or poorer sorting or greater grain angularity. The extrapolation from single grains and their associated pores to sandstones is complicated by the possibility of nonuniform solution or cementation.
TL;DR: The Abadeh Formation as discussed by the authors is a continuous marine carbonate sequence (more than 2,650 m or 8,692 ft thick), commencing with the Artinskian transgression and ending with the regression of probably early Middle Triassic age, was discovered by the writer in 1967 in Central Iran near the town of Abadeeh, lat. 30°55^primeN, long. 53°15^primeE.
Abstract: A continuous marine carbonate sequence (more than 2,650 m or 8,692 ft thick), commencing with the Artinskian transgression and ending with the regression of probably early Middle Triassic age, was discovered by the writer in 1967 in Central Iran near the town of Abadeh, lat. 30°55^primeN, long. 53°15^primeE. The contacts between the different units of this sequence (referred to as the Abadeh section) are apparently transitional and continuous. Artinskian and Guadalupian fossils, mostly fusulinids, are present in the lower part of this section. In the middle part, 41.3 m (135.7 ft) of gray and red limestone compares closely with the Dzhulfian and the Permo-Triassic transition beds, including the lowermost part of the Lower Triassic beds in the region of the Dzhulfian stratotype section along the Armenian border. The upper part of the sequence represents the lower Triassic Claraia beds, locally known as "calcaires vermicules facies." The uppermost part of the section consists of 780 m (2,558 ft) of dolomite, tentatively assigned to the Lower to Middle Triassic. For the Upper Permian and Permo-Triassic transition beds of this section, the global subdivision of the uppermost Permian has been used. As the Julfa sections, including the Dzhulfian stratotype section, are the nearest known sections of this age to the Abadeh region, a semi-detailed correlation between the Abadeh section and the Julfa sections has been attempted. This correlation established that the fossil zones in the Julfa region, assigned to the Dzhulfian Permo-Triassic and lowermost Triassic, are also present in the Abadeh section. The main difference is that the Julfa sections contain more shale, whereas the Abadeh section consists of marine limestone; hence the thickness of the Dzhulfian and Permo-Triassic transition beds in the Abadeh region is less than that of the Julfa reg on. An abrupt change of facies occurs at the contact between the Claraia and Paratirolites beds in the Abadeh region. No trace of any detrital material was observed in this contact which would indicate an erosional and sedimentary gap. The situation at the same horizon in the Julfa region is identical. The similarity between the two regions, 1,100 km (683 mi) apart, suggests that the sharp contact and abrupt change of facies is due to a sudden climatic change, rather than to a regression and a sedimentary gap. This climatic change caused deposition of dolomitic formations in Early to Middle Triassic time in Central Iran and could be the main reason for the extinction of the stenohaline faunas and appearance of the new faunas. In their global subdivision of the Upper Permian, Glenister and Furnish considered the contact between the Guadalupian and Dzhulfian Stages transitional. Study of the Abadeh section suggests that there is a gap between these two stages, filled by a series of about 334 m (1,096 ft) of limestone, shale, and marlstone called the Abadeh Formation, which is pre Dzhulfian and post-Guadalupian in age. The writer proposes that this formation be recognized as representing the Abadehian Stage, between the Guadalupian and Dzhulfian Stages. The Abadeh Formation may help in the correlation of the scattered Upper Permian sections throughout the world.
TL;DR: The structural framework of the southeastern Bahamas has been reconstructed from seismic profiler, magnetic, and gravity data as discussed by the authors, and it has been shown that the seafloor of the Bahamas may have been formed by subsidence of a continental crust and carbonate accretion.
Abstract: The structural framework of the southeastern Bahamas has been reconstructed from seismic profiler, magnetic, and gravity data. The Bahama Escarpment that marks the boundary between the southeastern Bahamas and the deep-sea floor may follow an ancient fracture zone. The geophysical data suggest that the crust beneath the southeastern Bahamas has a thickness (20 km) intermediate between those of the crusts of continents and ocean basins, and that this basement is partly volcanic in origin. The Bahamas may have formed by subsidence of a continental crust and carbonate accretion. If the southeastern Bahamas were formed in this manner, the crustal foundation must be very thin because the carbonate apron may be as thick as 10 km. Another explanation is that the Bahamas are unde lain by oceanic crust, in which case the Bahamas could have been formed in two ways. The northwestern Bahamas may be located at the site of a trough formed before or at the time the Atlantic Ocean was open. After this trough was filled nearly to sea level with terrigenous sediment, carbonate deposition was initiated. The southeastern Bahamas, on the other hand, may be located along a fracture zone that was formed during the opening of the Atlantic. The sedimentary section may be entirely carbonate. As the continents separated, the sediment-filled trough and the fracture zone subsided with carbonate accretion keeping pace with subsidence. The interpretation of the southeastern Bahamas being built on oceanic crust eliminates the problem of its overlap onto Africa in continental drift recon tructions.
TL;DR: In this paper, the reduction in pore space and thickness caused by plastic deformation of grains has been calculated for different proportions of ductile and nonductile, uniformly sized spheres in orthorhombic packing and for other shapes of grains.
Abstract: The reduction in pore space and thickness caused by plastic deformation of grains has been calculated for different proportions of ductile and nonductile, uniformly sized spheres in orthorhombic packing and for other shapes of grains. The relation for uniformly sized spheres in orthorhombic packing is believed to be applicable to well-sorted and rounded natural sands in which compaction has been extensive, and to be a maximum for angular sands or for very well-sorted and extremely well-sorted, well-rounded sands. Applicability to less well-sorted sands is less certain. In sands in which such plastic deformation has not been complete, less reduction in pore space or thickness may be expected. These relations may be helpful in separating the effects of plastic deformation of grains from those caused by grain rotation or fracturing, solution from points of grain contact, and cementation. Experimental investigation of the relation of ductile grain content to reduction in pore space or thickness is considered desirable.
TL;DR: In this article, the geology of the lower part of the Saharan Paleozoic was described during an international sedimentologic field trip, organized by the Algerian Petroleum Institute.
Abstract: This paper briefly describes the geology of the lower part of the Saharan Paleozoic, as presented recently during an international sedimentologic field trip, organized by the Algerian Petroleum Institute, in the northeast part of the crystalline Hoggar massif (Algerian Sahara). After defining the lithostratigraphy that extends from the Upper Cambrian(?) to the Lower Devonian, the writers present the following succession of paleogeographic reconstructions: (1) aggradation of fluvial deposits on a pediplain; (2) progressive transition from the continental deposits to a marine environment; (3) epeirogenic movements preceding the onset of a large continental glaciation; (4) glacial and periglacial deposits following the fluctuations of the continental ice; (5) a glacio-eustat c transgression followed by argillaceous sedimentation; and (6) epeirogenic movements that brought back continental conditions. This general interpretation is based on studies extending over the entire Saharan Paleozoic outcrops.
TL;DR: This article defined three Upper Cretaceous formations exposed in and near San Diego, California, which constitute the Rosario Group, redesignated from its former rank as a formation, and eight partly intertonguing Eocene formations also are defined.
Abstract: This paper defines three Upper Cretaceous formations exposed in and near San Diego, California. The lowest, which consists of boulder conglomerate, is the previously named Lusardi Formation; the intermediate, which consists of siltstone and sandstone, is the Point Loma Formation (new name); and the uppermost, which consists of sandstone and conglomerate, is the Cabrillo Formation (new name). Together these constitute the Rosario Group, redesignated from its former rank as a formation. Eight partly intertonguing Eocene formations also are defined. Of these, six have new names and two are former members raised in rank to formational status. The lowest of the Eocene formations is the Mount Soledad Formation (new name), a marine conglomerate and sandstone unit occurring in th western part of the area. Above and northeast of the Mount Soledad Formation are the laterally equivalent Delmar Formation and Torrey Sandstone (both raised here from member to formational rank) and the Ardath Shale (new name). The Delmar Formation is an oyster-bearing sandy claystone, the Torrey Sandstone is a massively crossbedded sandstone, and the Ardath Shale is a fossiliferous silty shale. Overlying and partly intertonguing with these formations is the Scripps Formation (new name), composed of sandstone, siltstone, and conglomerate, and overlying the Scripps is the chiefly nonmarine Friars Formation (new name), which consists of sandstone and sandy claystone. All these Eocene rocks were formerly included in the La Jolla Formation, which is here elevated to group status. The remain ng part of the Eocene section in the San Diego area, above the La Jolla Group, was formerly called the Poway Conglomerate and is here elevated to group status, and two new formations are designated in its lower part. The lower, which consists of cobble conglomerate, is the newly named Stadium Conglomerate; the upper, which consists chiefly of marine sandstone and siltstone, is the newly named Mission Valley Formation.
TL;DR: In this paper, the so-called irreducible saturations of two unconsolidated core samples were reduced by approximately half after the particles of each core had been well mixed to destroy small-scale packing heterogeneities.
Abstract: Packing heterogeneity is defined as local variation in sorting, or more strictly, local variation in pore-size distribution. Small-scale packing heterogeneities essentially determine the amount of liquid which is held as an irreducible wetting phase saturation in a drained porous rock. The so-called irreducible saturations of two unconsolidated core samples were reduced by approximately half after the particles of each core had been well mixed to destroy small-scale packing heterogeneities. Irreducible saturation is proposed as an index of packing heterogeneity, which may reflect depositional environment and post-deposition history.
TL;DR: In this article, the upper part of the lower member of the Winnipegosis ("platform" member) in south-central Saskatchewan has been studied, showing that the carbonate banks may be younger than carbonate laminites, anhydrite, and halite between banks.
Abstract: Algal oncolites, intraformational conglomerates, and dark carbonaceous-argillaceous layers with planktonic or necktonic fossils are interbedded in the upper part of the lower member of the Winnipegosis ("platform" member) in south-central Saskatchewan. Transitions from agitated open-marine waters to quiet restricted conditions apparently occurred abruptly, as did changes from oxidizing to reducing conditions. The algal oncolites and breccias probably accumulated in shallow water, and their extensive areal distribution indicates a sea floor with little relief, a condition which did not prevail during deposition of the overlying upper Winnipegosis carbonates. In the study area, upper Winnipegosis carbonate banks separate a northern basin from a southern basin and influenced deposition of interbank sediments. Between banks, organic-rich carbonate laminites, which display continuity of specific millimeter laminations over a distance of miles, suggest accumulation under very uniform, quiet-water conditions. Associated anhydrite, some of which grew by displacement in buried sediments, was protected locally from compaction by early diagenetic calcitization and dolomitization. Nodular anhydrites, up to 200 ft thick, overlie carbonate laminites and encase carbonate banks, occurring preferentially on the southeast sides of the banks within the area of study. In an offbank direction, halite appears to be a facies equivalent of anhydrite. Apparently, the banks influenced deposition between banks and may have been the cause of local marine restriction and evaporite formation. A distinctive pisolite cap on Winnipegosis banks is interpreted as an inorganically formed vadose pisolite and provides evidence of subaerial exposure at the termination of bank development. An equivalent pisolite unit is present in anhydrite overlying halite in offbank areas, a situation which suggests that the upper part of the carbonate banks may be younger than the carbonate laminites, anhydrite, and halite between banks. Thus, there were two major phases of bank development, one before deposition of interbank anhydrites and halite and one after. Winnipegosis beds are relatively rich in organic matter, but the relatively low degree of maturation or carbonization may be an important factor in explaining the absence of producing reservoirs in this formation.
TL;DR: A Middle or Late Jurassic palynomorph assemblage has been recovered from calcite caprock of Challenger Knoll in the central Gulf of Mexico as mentioned in this paper, which is dominated by species of Exesipollenites, Spheripollenite, and Classopollis, and probably has been derived from underlying salt beds.
Abstract: A Middle or Late Jurassic palynomorph assemblage has been recovered from calcite caprock of Challenger Knoll in the central Gulf of Mexico. The assemblage is dominated by species of Exesipollenites, Spheripollenites, and Classopollis, and probably has been derived from underlying salt beds. Four major circum-Gulf evaporite deposits--the Louann-Werner of the southeastern United States, the Minas Viejas and the Salina of Mexico, and the Punta Alegre of Cuba--are probably about the same age as the inferred Sigsbee salt.
TL;DR: In this article, six shallow salt domes in the Miocene productive belt of coastal Louisiana were studied to attain an understanding of the structural history during the time of deposition of the sediments penetrated by drilling.
Abstract: Six shallow salt domes in the Miocene productive belt of coastal Louisiana were studied to attain an understanding of the structural history during the time of deposition of the sediments penetrated by drilling. The domes were Clovelly, Cote Blanche, Lake Washington, Napoleonville, Weeks Island, and White Castle. Structural growth of the salt domes was contemporaneous with the deposition of sediments. The known stratigraphic section at the domes consists of about 15,000 ft of interbedded sandstone and shale underlain by a predominantly shale section with abnormally high pore pressures. The physical properties and differences in physical properties of the sandstone and shale sequence, predominantly shale section, and salt of these salt dome structures are partly responsible for the geometry of the structures. Structural details and features which were studied in an effort to understand the history of the salt structures were the "sheath" configuration, indications of uplift and differential subsidence, development of rim synclines, and faulting and fault patterns. Most of the flanking sedimentary rocks were either deposited against the core of the structure or "pierced" by the core shortly after deposition. The core of the structures consists of salt or a combination of salt with shale from the high-pore-pressure section underlying the shallower sandstone and shale sequence. The shale of the core moved and was emplaced in its present position as "sheath" by folding or by a combination of folding and faulting. The shape of the core exerted a control on the radius and rate of divergence of sedimentary intervals away from the core. If the side of the core dips at an angle of up to about 60°, the contours on the major faults in the flanking sedimentary rocks curve in tangentially to the core.
TL;DR: In this paper, a small instrument was developed for the rapid non-destructive measurement of air permeability, which can be used on consolidated and unconsolidated material either in situ or in the form of samples.
Abstract: A small instrument has been developed for the rapid nondestructive measurement of air permeability. It can be used on consolidated and unconsolidated material either in situ or in the form of samples. The permeability measured is an average for the 1 cm-diameter circular area surrounding the tip. One measurement usually takes less than a minute.
TL;DR: In this article, structural and lithologic trends in five areas of this arc indicate that the pre-late Paleozoic ancestral orogenic zone has undergone two phases of penetrative deformation.
Abstract: The pre-late Paleozoic basement complex of nuclear Central America is exposed in an arcuate zone that extends from the Caribbean Sea to Chiapas, Mexico. The trend of this arc parallels fold trends in younger sedimentary rocks on both sides of the arc, which has led to the widespread, previously unsubstantiated assumption that structural trends in the ancestral orogenic zone also form an arcuate regional pattern. Analysis of structural and lithologic trends in five areas of this arc indicates that the pre-late Paleozoic ancestral orogenic zone has undergone two phases of penetrative deformation. Folds of the first phase, which was most intense, are oriented parallel with the arc, as suspected, whereas folds of the second phase have north-trending vertical axial planes. The distribution of lithologies in the orogenic zone suggests that the premetamorphic provenance was the widespread Precambrian terrane of southern Mexico. The angular relationship of basement complex structural trends on opposite sides of the Cuilco-Chixoy-Polochic fault zone, which appears to be the most likely boundary between the Americas and Caribbean plates during Cenozoic time, limits left-lateral offset along this zone to less than 150 km.
TL;DR: The sedimentologic characteristics of the Medina Formation (Silurian) were examined in the sections exposed along the Niagara escarpment in Ontario and New York as discussed by the authors, and the vertical and lateral variations of the textures, fabrics, sedimentary structures, and faunal assemblages indicate a mixed environment of deposition best explained by a deltaic-shallow marine model of sedimentation.
Abstract: The sedimentologic characteristics of the Medina Formation (Silurian) were examined in the sections exposed along the Niagara escarpment in Ontario and New York. The vertical and lateral variations of the textures, fabrics, sedimentary structures, and faunal assemblages indicate a mixed environment of deposition best explained by a deltaic-shallow marine model of sedimentation. The growth of the Medina clastic sequence was related to shifting deltas which, locally, reached the area cut by the natural cross section of the Niagara escarpment. The primary constructive phases of these Medina deltas are well developed in the vicinity of Fulton and between Medina City and Rochester, New York. A third area of direct deltaic clastic input in the Medina sea is present in parts of he DeCew and Niagara Gorge sections. In the Niagara-Ontario area, however, the marine forces were competent enough to rework and redistribute most of the delta-born sediments. The combination of a relatively slow rate of clastic input, a shallow Silurian sea, and a very slow subsidence of the depositional basin yielded a complex interfingering of deltaic topset environments and of prodelta and/or interdeltaic environments. The topset to shoreline environments are characterized by channel sedimentation, beaches, tidal flats--as demonstrated by the presence of Lingula shells still in living position--and high tidal flats to floodplain settings where burrowing organisms flourished. The prodelta parts of the deltas, or the more open-marine environments, are represented by the dolomites and t e gray and red shaly and silty sequences with minor carbonates, which compose the Medina sections in the Hamilton area and which thin eastward and pinch out in the vicinity of Medina City, New York. The Medina Formation is gas productive directly south of the outcrop section, and the constructed sedimentation model can be of value to predict the best reservoir trends in the subsurface.
TL;DR: The authors showed that the concentration of some trace elements (total rock Ni, Co, Cr, V, and Ba) is a function of the clay-mineral content of the rocks and not a direct reflection of their facies type.
Abstract: Previous workers proposed various trace elements as geochemical indicators of reef and nonreef carbonates. Analysis of the data of Chester and Billings and Ragland shows that the concentration of some of these elements (total rock Ni, Co, Cr, V, and Ba, and acid-soluble Ni, Co, V, Pb, Ga, Cu, Fe, Mn, Zn, or K) is a function of the clay-mineral content of the rocks. This gives an energy index for the environment of deposition of the rocks and is not a direct reflection of their facies type.
TL;DR: In this article, the Homoceras ammonoid time equivalent is described in the Carboniferous Zone 19, the first time from North America, in the Lost River Range of Idaho.
Abstract: Carboniferous rocks above the Milligen Formation in the central Lost River Range of south-central Idaho range in age from Late Mississippian (middle Meramecian or middle Visean) through Pennsylvanian (Atokan or Westphalian), as determined by small calcareous foraminifers, corals, and brachiopods. The lower part of the post-Milligen sequence, composed largely of limestone, is Mississippian and is divided into four formations first described by Huh in the Lemhi and Lost River Ranges. These rocks are overlain by an unnamed Pennsylvanian sandstone unit which, in turn, is overlain by a thick sequence of unnamed Pennsylvanian limestone. The composite section in the Lost River Range has a minimum exposed thickness of 7,000 ft. Two partial sections in the Hawley Mountains are des gnated reference sections for the four formations of Mississippian age in the Lost River Range--the Middle Canyon Formation at the base, the Scott Peak Formation, the South Creek Formation, and the Surrett Canyon Formation at the top. Foraminiferal Zones 13(?) through 21 are recognized in the Carboniferous rocks. Zone 19, the Homoceras ammonoid time equivalent, is described herein for the first time from North America. Representatives of megafaunal Zones Pre-E through Post-K are also recognized in the Mississippian and the directly overlying rocks of the Carboniferous sequence. Microfaunas and megafaunas indicate that the Meramec-Chester boundary is near the middle of the Scott Peak Formation, that the Visean-Namurian boundary is near the base of the Surrett Canyon Formation, and that the Mississippian-Pennsylvanian boundary is about at the base of the unnamed sandstone unit. Carbonate lithologies and associated faunas and microfaunas indicate deposition in a marine environment in which there was a general change from quiet water having locally restricted circulation during Middle Canyon Formation deposition to turbulent water that was freely circulating during deposition of the upper strata. Sand in the basal Pennsylvanian rocks may indicate a distant orogenic pulse very near the Mississippian-Pennsylvanian time boundary.
TL;DR: In the Terminos Lagoon as discussed by the authors, the average circulation is reflected in distribution patterns of salinity, sediment size distributions, forams, percent of calcium carbonate in the sediments, and water turbidity.
Abstract: There is a net flow of Gulf of Mexico high salinity water into Terminos Lagoon through the eastern inlet, mixing with runoff from three large rivers, and a net flow of low-salinity lagoon water out through the western inlet. The average circulation is reflected in distribution patterns of salinity, sediment size distributions, forams, percent of calcium carbonate in the sediments, and water turbidity. Relatively high organic productivity is indicated by numerous large standing stocks of forams. The lagoon is on the boundary between biogenic carbonate sediments on the east and detrital river-borne sediments on the west. The modern lagoon barrier began during the Holocene on a foundation of calcilutite when sea level was at about -- 10 m. When it reached about its present level the inlets were east of the present ones. Predominant flow of lagoon water out through the western inlet as at present is indicated by river-borne detritus under a surface cap of biogenic carbonate on the western end of the barrier. The seaward side of the barrier is being eroded, except on the western end, where there is deposition. The lagoon is essentially filled with sediment, and most detritus being delivered by rivers is bypassing the lagoon. It is suggested that deposits similar to those in Terminos Lagoon can be identified in ancient sediments.