Abstract The 130-year history of study of the Cenomanian–Turonian Eagle Ford and Woodbine Groups ... more Abstract The 130-year history of study of the Cenomanian–Turonian Eagle Ford and Woodbine Groups of Texas has created a complicated and often confusing nomenclature system. Deciphering these nomenclatures has frequently been hindered by outdated biostratigraphic studies with inaccurate age interpretations. To resolve these issues, a comprehensive compilation and vetting of available biostratigraphic, geochemical, and lithologic data from Eagle Ford and Woodbine outcrops and subsurface penetrations was undertaken, which was then tied to a large network of wells in both south and east Texas. Composite sections were built for four outcrop areas of central and north Texas (Dallas, Red River, Waco, Austin), five outcrop areas from west Texas (Langtry, Del Rio, Big Bend, Chispa Summit, Quitman Mountains), four subsurface areas from south Texas (Webb County, Atascosa County, Karnes County, DeWitt/Gonzales Counties), and two cross sections from the east Texas subsurface (basin center and eastern margin). The resulting datasets were utilized to construct age models and characterize depositional environments, including paleoceanography. In agreement with previous studies, the total organic carbon (TOC)-rich Lower Eagle Ford was interpreted to have been deposited under anoxic to euxinic conditions and the Upper Eagle Ford under dysoxic to anoxic conditions. The Oceanic Anoxic Event 2 (OAE2) interval is missing at all locations north of Atascosa County; when present it is characterized as having been deposited under oxic to suboxic conditions. High abundances of radiolaria and calcispheres identified within recrystallized medial to distal limestones of the Lower Eagle Ford indicated limestone formation during periods of enhanced water-column mixing and increased primary productivity, in contrast to proximal limestones composed of planktonic foraminifera and inoceramid prisms concentrated by bottom currents. Standardized nomenclature systems and age models are proposed for each of the outcrop and subsurface areas. Proposed changes to existing nomenclatures include reassignment of the Tarrant Formation of the Eagle Ford to the Lewisville Formation of the Woodbine in the Dallas area and the Templeton Member of the Lewisville Formation to the Britton Formation of the Eagle Ford in the Red River area. The proposed term “Waller Member” of Fairbanks (2012) for the former Cloice Member of the Lake Waco Formation in the Austin area is recognized with a new stratotype proposed and described, although the Waller Member is transferred to the Pepper Shale Formation of the Woodbine. The Terrell Member is proposed for the carbonate-rich section at the base of the Boquillas Formation in the Langtry and Del Rio areas, restricting the Lozier Canyon Member to the organic-rich rocks underlying the Antonio Creek Member. The south Texas subsurface is divided into the Upper Eagle Ford and Lower Eagle Ford Formations, with the clay-rich Maness Shale Member at the base of the Lower Eagle Ford and the foraminifera grainstone dominated Langtry Member at the top of the Upper Eagle Ford. Use of the term “middle Eagle Ford” for the clay-rich facies south of the San Marcos arch is not recommended.
Image analysis techniques were used to characterize the composition of waste-entrained concrete, ... more Image analysis techniques were used to characterize the composition of waste-entrained concrete, and to provide quantitative data on the size, shape and location of each component in the samples. Multiple samples were analyzed to determine the degree of heterogeneity in the sample. Homogeneous samples were characterized by soils that occur in numerous, small isolated islands within the large, convoluted cement objects. Compressive strength is high because of the presence of hardened concrete framework. Porosity is restricted to nonsoil zones, lowering the probability of leaching by percolating fluids. The heterogeneous samples contain numerous cement islands within a soil matrix. Compressive strength is low because the load must be supported by the soil rather than the cement. Long fluid pathways, often in contact with the soil characterize these samples.
Abstract The 130-year history of study of the Cenomanian–Turonian Eagle Ford and Woodbine Groups ... more Abstract The 130-year history of study of the Cenomanian–Turonian Eagle Ford and Woodbine Groups of Texas has created a complicated and often confusing nomenclature system. Deciphering these nomenclatures has frequently been hindered by outdated biostratigraphic studies with inaccurate age interpretations. To resolve these issues, a comprehensive compilation and vetting of available biostratigraphic, geochemical, and lithologic data from Eagle Ford and Woodbine outcrops and subsurface penetrations was undertaken, which was then tied to a large network of wells in both south and east Texas. Composite sections were built for four outcrop areas of central and north Texas (Dallas, Red River, Waco, Austin), five outcrop areas from west Texas (Langtry, Del Rio, Big Bend, Chispa Summit, Quitman Mountains), four subsurface areas from south Texas (Webb County, Atascosa County, Karnes County, DeWitt/Gonzales Counties), and two cross sections from the east Texas subsurface (basin center and eastern margin). The resulting datasets were utilized to construct age models and characterize depositional environments, including paleoceanography. In agreement with previous studies, the total organic carbon (TOC)-rich Lower Eagle Ford was interpreted to have been deposited under anoxic to euxinic conditions and the Upper Eagle Ford under dysoxic to anoxic conditions. The Oceanic Anoxic Event 2 (OAE2) interval is missing at all locations north of Atascosa County; when present it is characterized as having been deposited under oxic to suboxic conditions. High abundances of radiolaria and calcispheres identified within recrystallized medial to distal limestones of the Lower Eagle Ford indicated limestone formation during periods of enhanced water-column mixing and increased primary productivity, in contrast to proximal limestones composed of planktonic foraminifera and inoceramid prisms concentrated by bottom currents. Standardized nomenclature systems and age models are proposed for each of the outcrop and subsurface areas. Proposed changes to existing nomenclatures include reassignment of the Tarrant Formation of the Eagle Ford to the Lewisville Formation of the Woodbine in the Dallas area and the Templeton Member of the Lewisville Formation to the Britton Formation of the Eagle Ford in the Red River area. The proposed term “Waller Member” of Fairbanks (2012) for the former Cloice Member of the Lake Waco Formation in the Austin area is recognized with a new stratotype proposed and described, although the Waller Member is transferred to the Pepper Shale Formation of the Woodbine. The Terrell Member is proposed for the carbonate-rich section at the base of the Boquillas Formation in the Langtry and Del Rio areas, restricting the Lozier Canyon Member to the organic-rich rocks underlying the Antonio Creek Member. The south Texas subsurface is divided into the Upper Eagle Ford and Lower Eagle Ford Formations, with the clay-rich Maness Shale Member at the base of the Lower Eagle Ford and the foraminifera grainstone dominated Langtry Member at the top of the Upper Eagle Ford. Use of the term “middle Eagle Ford” for the clay-rich facies south of the San Marcos arch is not recommended.
The hydrocarbon-rich, Artesa Mundo-Nuevo Carbonate Platform, located in the northwestern portion ... more The hydrocarbon-rich, Artesa Mundo-Nuevo Carbonate Platform, located in the northwestern portion of the Sierra de Chiapas fold and thrust belt in southeastern Mexico, is structurally complex; consequently, the geometry of the platform and its margins cannot be discerned based solely on seismic data. Cretaceous geologic models were derived from environmentally significant lithofacies contained in 173 cores from 37 wells. Potential reservoirs in these intervals were also evaluated. The lack of a documented platform edge to the north and the similarity of facies in the Reforma-Jalpa area, located immediately to the north of the study area, suggest a connection between these areas/platforms throughout most of the Cretaceous. The southern boundary of the Artesa Mundo-Nuevo Platform is indicated by a lateral change to deep water lithofacies. The eastern margin was seen in cores (occurrence of deep water lithofacies) until the Late Cretaceous. The western boundary was not discerned from co...
Radiolaria have been collected and identified from the water column and from Holocene sediments o... more Radiolaria have been collected and identified from the water column and from Holocene sediments of the Gulf of Mexico and adjacent waters using Nansen closing nets, DUCA high speed nets, gravity cores and box cores. Radiolarians in the water column and the sediments can be used as indicators of horizontal and vertical water movements, degrees of eutrophism and oceanographic seasonality. Most radiolarian species appear to be indicative of one or more water masses that enter the Gulf of Mexico through the Yucatan Passage; none of the identified species are endemic to the Gulf of Mexico. Living radiolarian diversities and densities are now in the waters over the Texas continental shelf and in the oligotrophic open Gulf of Mexico in comparison to the oligotrophic open ocean Sargasso Sea and the boundary currents off Florida and southern California. The nature of the empty radiolarian test assemblage in the water column suggests that radiolarians in Recent sediments settle to the sea flo...
The presence of living specimens of Spongaster pentas and related spongodiscid forms, Buccinospha... more The presence of living specimens of Spongaster pentas and related spongodiscid forms, Buccinosphaera invaginata, Collosphaera tuberosa and others in plankton and Quaternary sediment samples from the Gulf of Mexico is evidence of a unique radiolarian population that is composed in part of relict and expatriated radiolarian forms. These relict and expatriated populations may have survived in the Gulf because: 1) the closure of the Tethys Seaway by the uplift of the Panamanian Block isolated the equatorial and temperate Atlantic waters and blocked radiolarian faunas from entering the Pacific and Indian Oceans; 2) temperate and perhaps equatorial radiolarian faunas of the Pacific and Indian Oceans have contributed to the temperate and equatorial Atlantic radiolarian faunas since the closure of Panama; 3) the ability of relict and related forms to carry on symbiotic relationships with algal associates may have enabled these forms to adapt and survive. This information adds insight into o...
The Eagle Ford play in south Texas extends along strike from the San Marcos arch in the northeast... more The Eagle Ford play in south Texas extends along strike from the San Marcos arch in the northeast into the Maverick Basin along the international border with Mexico. The highest initial oil production is in a strike-parallel belt between the Karnes trough and the Cretaceous shelf margin. Three lithologies comprise the bulk of the Eagle Ford Shale in this area: argillaceous mudrock (shale), calcareous mudrock (marl), and limestone. The marls consist mainly of coccoliths and contain more total organic carbon (TOC) and have higher porosities than the other lithologies. The sand- and silt-sized grains in the marls and limestones consist predominantly of planktonic foraminifera, radiolarians, and calcispheres, with lesser amounts of inoceramid fragments and other carbonate grains. The limestones may be partly to entirely recrystallized. The strength and rigidity of the rocks increase with calcite content—the limestones are stronger and more rigid than the marls. Argillaceous mudrock (sha...
Living radiolarians, planktonic foraminiferans and pteropods have been collected from the waters ... more Living radiolarians, planktonic foraminiferans and pteropods have been collected from the waters of the Gulf of Mexico and adjacent seas using Nansen closing nets, DUCA high speed plankton nets, and water bottles. These samples included other shelled microplankton (diatoms, dinoflagellates, silicoflagellates, etc.), non-shelled microplankton (bluegreen algae, dinoflagellates, etc.) and larger plankton (e.g. copepods, chaetognaths). Radiolarian, planktonic foraminiferan and peteropod species compositions, diversities and densities were compared with those of other plankton, and were related to physical and chemical oceanographic parameters. Our studies suggest that certain radiolarian, planktonic foraminiferan and pteropod species may be nannoherbivores, bacterivores, detritivores, and/or associated with symbiotic algae and may be characteristic of eutrophic, mesotrophic or oligotrophic conditions. This information can be applied to studies of the fossil record for finer resolution o...
Abstract Oligocene and Miocene-age carbonates were studied in outcrop and from the subsurface alo... more Abstract Oligocene and Miocene-age carbonates were studied in outcrop and from the subsurface along the southern margin of the hydrocarbon-rich Macuspana Basin and Chiapas fold belt. A multi-disciplinary approach integrating biostratigraphy, sedimentology, 3D seismic data, and sequence stratigraphic concepts allowed establishment of a regional geologic model for use in hydrocarbon exploration. During the Oligocene lowstand, a deep-water ramp was deposited towards the basin center in the east. Drowning of this ramp in the basal Miocene resulted in a westward shift in deposition up the paleoslope. The Miocene-age Macuspana Limestone Formation (100 to 400 meters thick) consists of three, 3rd -order sequences (Caliza-I – Caliza-III). Cycle-base marine shales contain distinctive planktonic foraminifer assemblages, which allow age determination of these maximum flooding surfaces. Five biofacies based on foraminifer distributions, and twelve environmentally significant lithofacies are recognized. Carbonate deposition changed from the initial steepening of the gentle ramp (Caliza-I) into a rimmed shelf with a lagoon (Caliza-III). Basinward progradation was, in part, a response to forced regression. Deeper water, basin and outer ramp facies show no evidence of debris flows or turbidites. Barrier reefs were not observed; instead, mud-rich, biostromal patch reefs are present on the inner ramp that developed during ramp highstand systems tract. Syn-sedimentary tectonism related to shale movement affected the internal architecture of the ramp. Positive areas were sites of reef development and high-energy grainstone deposition. Three potential reservoirs are identified with fracture and matrix porosity: 1) Upper Oligocene ramp; 2) Caliza-I; and, 3) Caliza-III. Caliza-II appears to lack reservoir potential.
Abstract Detailed petrologic study of the Cotton Valley Limestone and application of Upper Jurass... more Abstract Detailed petrologic study of the Cotton Valley Limestone and application of Upper Jurassic reef analogues from Europe and North Africa has resulted in the development of an integrated exploration model specific to the East Texas Basin. A variety of reef types exhibiting multiple stages of reef growth occur along the Cotton Valley Reef trend. Cotton Valley reefs grew along the shelf margin from the Late Kimmeridgian to the Kimmeridgian - Tithonian boundary. The reefs are composed of corals, calcareous algae, calcareous and siliceous sponges, and microbolites that formed a progression from shallow to deeper water. The reefs were composed of stacked biostromes or low-relief bioherms. Their pinnacle character or prominent elevation above the sea floor was manifested because reef growth occurred at a time of strongly starved sedimentation within the basin that was associated with arid or semi-arid climatic conditions. Multi-stage diagenesis has affected porosity, and structural variability along the trend further complicates the geology. Coral-rich reef facies that originally had greater amounts of metastable aragonitic skeletal material were deposited in shallower water depths. These skeletons were more susceptible to leaching and the creation of secondary biomoldic pores. These reefs also had greater potential for subaerial exposure and freshwater diagenesis that resulted in the partial leaching and the creation of matrix microporosity. Those reefs that were located in structurally favorable positions for more frequent or prolonged periods of exposure appear to have thicker and more numerous porous zones. Substantial macroporosity was occluded by late burial cementation; however, early hydrocarbon migration helped to preserve porosity.
Bed-parallel disc fractures started at bit level, within the core, at bedding irregularities. Hac... more Bed-parallel disc fractures started at bit level, within the core, at bedding irregularities. Hackle plumes indicate that spreading velocity of disc fractures was greatest toward core centers and decreased toward core margins in response to changes in tensile stress intensity.
Abstract The 130-year history of study of the Cenomanian–Turonian Eagle Ford and Woodbine Groups ... more Abstract The 130-year history of study of the Cenomanian–Turonian Eagle Ford and Woodbine Groups of Texas has created a complicated and often confusing nomenclature system. Deciphering these nomenclatures has frequently been hindered by outdated biostratigraphic studies with inaccurate age interpretations. To resolve these issues, a comprehensive compilation and vetting of available biostratigraphic, geochemical, and lithologic data from Eagle Ford and Woodbine outcrops and subsurface penetrations was undertaken, which was then tied to a large network of wells in both south and east Texas. Composite sections were built for four outcrop areas of central and north Texas (Dallas, Red River, Waco, Austin), five outcrop areas from west Texas (Langtry, Del Rio, Big Bend, Chispa Summit, Quitman Mountains), four subsurface areas from south Texas (Webb County, Atascosa County, Karnes County, DeWitt/Gonzales Counties), and two cross sections from the east Texas subsurface (basin center and eastern margin). The resulting datasets were utilized to construct age models and characterize depositional environments, including paleoceanography. In agreement with previous studies, the total organic carbon (TOC)-rich Lower Eagle Ford was interpreted to have been deposited under anoxic to euxinic conditions and the Upper Eagle Ford under dysoxic to anoxic conditions. The Oceanic Anoxic Event 2 (OAE2) interval is missing at all locations north of Atascosa County; when present it is characterized as having been deposited under oxic to suboxic conditions. High abundances of radiolaria and calcispheres identified within recrystallized medial to distal limestones of the Lower Eagle Ford indicated limestone formation during periods of enhanced water-column mixing and increased primary productivity, in contrast to proximal limestones composed of planktonic foraminifera and inoceramid prisms concentrated by bottom currents. Standardized nomenclature systems and age models are proposed for each of the outcrop and subsurface areas. Proposed changes to existing nomenclatures include reassignment of the Tarrant Formation of the Eagle Ford to the Lewisville Formation of the Woodbine in the Dallas area and the Templeton Member of the Lewisville Formation to the Britton Formation of the Eagle Ford in the Red River area. The proposed term “Waller Member” of Fairbanks (2012) for the former Cloice Member of the Lake Waco Formation in the Austin area is recognized with a new stratotype proposed and described, although the Waller Member is transferred to the Pepper Shale Formation of the Woodbine. The Terrell Member is proposed for the carbonate-rich section at the base of the Boquillas Formation in the Langtry and Del Rio areas, restricting the Lozier Canyon Member to the organic-rich rocks underlying the Antonio Creek Member. The south Texas subsurface is divided into the Upper Eagle Ford and Lower Eagle Ford Formations, with the clay-rich Maness Shale Member at the base of the Lower Eagle Ford and the foraminifera grainstone dominated Langtry Member at the top of the Upper Eagle Ford. Use of the term “middle Eagle Ford” for the clay-rich facies south of the San Marcos arch is not recommended.
Image analysis techniques were used to characterize the composition of waste-entrained concrete, ... more Image analysis techniques were used to characterize the composition of waste-entrained concrete, and to provide quantitative data on the size, shape and location of each component in the samples. Multiple samples were analyzed to determine the degree of heterogeneity in the sample. Homogeneous samples were characterized by soils that occur in numerous, small isolated islands within the large, convoluted cement objects. Compressive strength is high because of the presence of hardened concrete framework. Porosity is restricted to nonsoil zones, lowering the probability of leaching by percolating fluids. The heterogeneous samples contain numerous cement islands within a soil matrix. Compressive strength is low because the load must be supported by the soil rather than the cement. Long fluid pathways, often in contact with the soil characterize these samples.
Abstract The 130-year history of study of the Cenomanian–Turonian Eagle Ford and Woodbine Groups ... more Abstract The 130-year history of study of the Cenomanian–Turonian Eagle Ford and Woodbine Groups of Texas has created a complicated and often confusing nomenclature system. Deciphering these nomenclatures has frequently been hindered by outdated biostratigraphic studies with inaccurate age interpretations. To resolve these issues, a comprehensive compilation and vetting of available biostratigraphic, geochemical, and lithologic data from Eagle Ford and Woodbine outcrops and subsurface penetrations was undertaken, which was then tied to a large network of wells in both south and east Texas. Composite sections were built for four outcrop areas of central and north Texas (Dallas, Red River, Waco, Austin), five outcrop areas from west Texas (Langtry, Del Rio, Big Bend, Chispa Summit, Quitman Mountains), four subsurface areas from south Texas (Webb County, Atascosa County, Karnes County, DeWitt/Gonzales Counties), and two cross sections from the east Texas subsurface (basin center and eastern margin). The resulting datasets were utilized to construct age models and characterize depositional environments, including paleoceanography. In agreement with previous studies, the total organic carbon (TOC)-rich Lower Eagle Ford was interpreted to have been deposited under anoxic to euxinic conditions and the Upper Eagle Ford under dysoxic to anoxic conditions. The Oceanic Anoxic Event 2 (OAE2) interval is missing at all locations north of Atascosa County; when present it is characterized as having been deposited under oxic to suboxic conditions. High abundances of radiolaria and calcispheres identified within recrystallized medial to distal limestones of the Lower Eagle Ford indicated limestone formation during periods of enhanced water-column mixing and increased primary productivity, in contrast to proximal limestones composed of planktonic foraminifera and inoceramid prisms concentrated by bottom currents. Standardized nomenclature systems and age models are proposed for each of the outcrop and subsurface areas. Proposed changes to existing nomenclatures include reassignment of the Tarrant Formation of the Eagle Ford to the Lewisville Formation of the Woodbine in the Dallas area and the Templeton Member of the Lewisville Formation to the Britton Formation of the Eagle Ford in the Red River area. The proposed term “Waller Member” of Fairbanks (2012) for the former Cloice Member of the Lake Waco Formation in the Austin area is recognized with a new stratotype proposed and described, although the Waller Member is transferred to the Pepper Shale Formation of the Woodbine. The Terrell Member is proposed for the carbonate-rich section at the base of the Boquillas Formation in the Langtry and Del Rio areas, restricting the Lozier Canyon Member to the organic-rich rocks underlying the Antonio Creek Member. The south Texas subsurface is divided into the Upper Eagle Ford and Lower Eagle Ford Formations, with the clay-rich Maness Shale Member at the base of the Lower Eagle Ford and the foraminifera grainstone dominated Langtry Member at the top of the Upper Eagle Ford. Use of the term “middle Eagle Ford” for the clay-rich facies south of the San Marcos arch is not recommended.
The hydrocarbon-rich, Artesa Mundo-Nuevo Carbonate Platform, located in the northwestern portion ... more The hydrocarbon-rich, Artesa Mundo-Nuevo Carbonate Platform, located in the northwestern portion of the Sierra de Chiapas fold and thrust belt in southeastern Mexico, is structurally complex; consequently, the geometry of the platform and its margins cannot be discerned based solely on seismic data. Cretaceous geologic models were derived from environmentally significant lithofacies contained in 173 cores from 37 wells. Potential reservoirs in these intervals were also evaluated. The lack of a documented platform edge to the north and the similarity of facies in the Reforma-Jalpa area, located immediately to the north of the study area, suggest a connection between these areas/platforms throughout most of the Cretaceous. The southern boundary of the Artesa Mundo-Nuevo Platform is indicated by a lateral change to deep water lithofacies. The eastern margin was seen in cores (occurrence of deep water lithofacies) until the Late Cretaceous. The western boundary was not discerned from co...
Radiolaria have been collected and identified from the water column and from Holocene sediments o... more Radiolaria have been collected and identified from the water column and from Holocene sediments of the Gulf of Mexico and adjacent waters using Nansen closing nets, DUCA high speed nets, gravity cores and box cores. Radiolarians in the water column and the sediments can be used as indicators of horizontal and vertical water movements, degrees of eutrophism and oceanographic seasonality. Most radiolarian species appear to be indicative of one or more water masses that enter the Gulf of Mexico through the Yucatan Passage; none of the identified species are endemic to the Gulf of Mexico. Living radiolarian diversities and densities are now in the waters over the Texas continental shelf and in the oligotrophic open Gulf of Mexico in comparison to the oligotrophic open ocean Sargasso Sea and the boundary currents off Florida and southern California. The nature of the empty radiolarian test assemblage in the water column suggests that radiolarians in Recent sediments settle to the sea flo...
The presence of living specimens of Spongaster pentas and related spongodiscid forms, Buccinospha... more The presence of living specimens of Spongaster pentas and related spongodiscid forms, Buccinosphaera invaginata, Collosphaera tuberosa and others in plankton and Quaternary sediment samples from the Gulf of Mexico is evidence of a unique radiolarian population that is composed in part of relict and expatriated radiolarian forms. These relict and expatriated populations may have survived in the Gulf because: 1) the closure of the Tethys Seaway by the uplift of the Panamanian Block isolated the equatorial and temperate Atlantic waters and blocked radiolarian faunas from entering the Pacific and Indian Oceans; 2) temperate and perhaps equatorial radiolarian faunas of the Pacific and Indian Oceans have contributed to the temperate and equatorial Atlantic radiolarian faunas since the closure of Panama; 3) the ability of relict and related forms to carry on symbiotic relationships with algal associates may have enabled these forms to adapt and survive. This information adds insight into o...
The Eagle Ford play in south Texas extends along strike from the San Marcos arch in the northeast... more The Eagle Ford play in south Texas extends along strike from the San Marcos arch in the northeast into the Maverick Basin along the international border with Mexico. The highest initial oil production is in a strike-parallel belt between the Karnes trough and the Cretaceous shelf margin. Three lithologies comprise the bulk of the Eagle Ford Shale in this area: argillaceous mudrock (shale), calcareous mudrock (marl), and limestone. The marls consist mainly of coccoliths and contain more total organic carbon (TOC) and have higher porosities than the other lithologies. The sand- and silt-sized grains in the marls and limestones consist predominantly of planktonic foraminifera, radiolarians, and calcispheres, with lesser amounts of inoceramid fragments and other carbonate grains. The limestones may be partly to entirely recrystallized. The strength and rigidity of the rocks increase with calcite content—the limestones are stronger and more rigid than the marls. Argillaceous mudrock (sha...
Living radiolarians, planktonic foraminiferans and pteropods have been collected from the waters ... more Living radiolarians, planktonic foraminiferans and pteropods have been collected from the waters of the Gulf of Mexico and adjacent seas using Nansen closing nets, DUCA high speed plankton nets, and water bottles. These samples included other shelled microplankton (diatoms, dinoflagellates, silicoflagellates, etc.), non-shelled microplankton (bluegreen algae, dinoflagellates, etc.) and larger plankton (e.g. copepods, chaetognaths). Radiolarian, planktonic foraminiferan and peteropod species compositions, diversities and densities were compared with those of other plankton, and were related to physical and chemical oceanographic parameters. Our studies suggest that certain radiolarian, planktonic foraminiferan and pteropod species may be nannoherbivores, bacterivores, detritivores, and/or associated with symbiotic algae and may be characteristic of eutrophic, mesotrophic or oligotrophic conditions. This information can be applied to studies of the fossil record for finer resolution o...
Abstract Oligocene and Miocene-age carbonates were studied in outcrop and from the subsurface alo... more Abstract Oligocene and Miocene-age carbonates were studied in outcrop and from the subsurface along the southern margin of the hydrocarbon-rich Macuspana Basin and Chiapas fold belt. A multi-disciplinary approach integrating biostratigraphy, sedimentology, 3D seismic data, and sequence stratigraphic concepts allowed establishment of a regional geologic model for use in hydrocarbon exploration. During the Oligocene lowstand, a deep-water ramp was deposited towards the basin center in the east. Drowning of this ramp in the basal Miocene resulted in a westward shift in deposition up the paleoslope. The Miocene-age Macuspana Limestone Formation (100 to 400 meters thick) consists of three, 3rd -order sequences (Caliza-I – Caliza-III). Cycle-base marine shales contain distinctive planktonic foraminifer assemblages, which allow age determination of these maximum flooding surfaces. Five biofacies based on foraminifer distributions, and twelve environmentally significant lithofacies are recognized. Carbonate deposition changed from the initial steepening of the gentle ramp (Caliza-I) into a rimmed shelf with a lagoon (Caliza-III). Basinward progradation was, in part, a response to forced regression. Deeper water, basin and outer ramp facies show no evidence of debris flows or turbidites. Barrier reefs were not observed; instead, mud-rich, biostromal patch reefs are present on the inner ramp that developed during ramp highstand systems tract. Syn-sedimentary tectonism related to shale movement affected the internal architecture of the ramp. Positive areas were sites of reef development and high-energy grainstone deposition. Three potential reservoirs are identified with fracture and matrix porosity: 1) Upper Oligocene ramp; 2) Caliza-I; and, 3) Caliza-III. Caliza-II appears to lack reservoir potential.
Abstract Detailed petrologic study of the Cotton Valley Limestone and application of Upper Jurass... more Abstract Detailed petrologic study of the Cotton Valley Limestone and application of Upper Jurassic reef analogues from Europe and North Africa has resulted in the development of an integrated exploration model specific to the East Texas Basin. A variety of reef types exhibiting multiple stages of reef growth occur along the Cotton Valley Reef trend. Cotton Valley reefs grew along the shelf margin from the Late Kimmeridgian to the Kimmeridgian - Tithonian boundary. The reefs are composed of corals, calcareous algae, calcareous and siliceous sponges, and microbolites that formed a progression from shallow to deeper water. The reefs were composed of stacked biostromes or low-relief bioherms. Their pinnacle character or prominent elevation above the sea floor was manifested because reef growth occurred at a time of strongly starved sedimentation within the basin that was associated with arid or semi-arid climatic conditions. Multi-stage diagenesis has affected porosity, and structural variability along the trend further complicates the geology. Coral-rich reef facies that originally had greater amounts of metastable aragonitic skeletal material were deposited in shallower water depths. These skeletons were more susceptible to leaching and the creation of secondary biomoldic pores. These reefs also had greater potential for subaerial exposure and freshwater diagenesis that resulted in the partial leaching and the creation of matrix microporosity. Those reefs that were located in structurally favorable positions for more frequent or prolonged periods of exposure appear to have thicker and more numerous porous zones. Substantial macroporosity was occluded by late burial cementation; however, early hydrocarbon migration helped to preserve porosity.
Bed-parallel disc fractures started at bit level, within the core, at bedding irregularities. Hac... more Bed-parallel disc fractures started at bit level, within the core, at bedding irregularities. Hackle plumes indicate that spreading velocity of disc fractures was greatest toward core centers and decreased toward core margins in response to changes in tensile stress intensity.
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Papers by Joan M Spaw