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At least 37 records · Page 2Linked to original sources
USGS1991

Geohydrology and water quality in northern Portage County, Ohio, in relation to deep-well brine injection

Geohydrology and water quality of the principal freshwater aquifers near oilfield and gasfield brine-injection wells in northern Portage County, Ohio, were evaluated. Since 1975, 13 wells in this part of the Country have been used to dispose of more than 4.5 million barrels of brine by injection into Silurian carbonate and sandstone rocks that generally are greater than 3,500 feet below land surface. More than 3,000 feet of interbedded shales, sandstones, carbonates, and evaporites separate the freshwater aquifers from these brine-injection zones. The shallowest brine-injection zone is greater than 2,200 feet below sea level. Native fluids in the injection zones have dissolved-solids concentrations greater than 125,000 milligrams per liter and are hydraulically isolated from the freshwater aquifers. No known faults or fracture systems are present in northern Portage County, although abandoned oil and gas wells could exist and serve as conduits for migration of injected brine. Pennsylvanian clastic units are freshwater bearing in northern Portage County, and two bedrock aquifers generally are recognized. The shallower bedrock aquifer (Connoquenessing Sandstone Member of the Pottsville Formation) principally consists of sandstone; this aquifer is separated from a deeper sandstone and conglomerate aquifer in the lower part of the Sharon Member (Pottsville Formation) by shale in the upper part of the Sharon Member that acts as a confining unit. The upper sandstone aquifer is the surficial aquifer where overlying glacial deposits are unsaturated in the uplands; glacial deposits comprise the surficial aquifer in buried valleys where the sandstone is absent. These two surficial aquifers are hydraulically connected and act as a single unit. The lower sandstone and conglomerate aquifer is the most areally extensive aquifer within the project area. From November 1987 through August 1988, ground-water levels remained at least 60 feet higher in the upper sandstone aquifer than in the lower sandstone and conglomerate aquifer at a topographically high recharge area. Water levels in the surficial aquifers and the lower sandstone and conglomerate aquifer were nearly the same along the Cuyahoga River. Ground water in the upper sandstone aquifer flows radially from topographically high recharge areas into the glacial deposits in the buried valleys. Much of the ground water in these surficial aquifers discharges into the Cuyahoga River. Most ground water in the lower sandstone and conglomerate aquifer flows toward discharge areas near the Cuyahoga River and Eagle Creek. In June 1988, the Cuyahoga River gained 15.8 cubic feet per second of water from the aquifers between the northern edge of Portage County and State Route 303. Ground water may have discharged into the upstream end of Lake Rockwell but did not discharge into the downstream end of the Lake during most of the period from October 1987 through September 1988. Measurements of the specific conductance of ground water sampled from areas near the 13 brine-injection wells and along the Cuyahoga River indicate no widespread ground-water contamination related to brine injection. Chemical analysis of water from 25 wells indicates that most ground waters are a calcium bicarbonate type. Water analyses show that four wells sampled contain water with chloride concentrations greater than 250 milligrams per liter. Sodium concentrations in water from these four wells ranged from 67 to 190 milligrams per liter. A mixing diagram constructed from bromide and chloride data was used to distinguish between the sources of elevated chloride concentrations in these four wells. Waters from two of the wells have been mixed with oilfield and gasfield brine, and waters from the other two wells have been mixed with a salt-solution brine such as that derived from diluted highway-deicing salts.

Ohio↗
USGS2020

Statewide assessment of karst aquifers in New York with an inventory of closed-depression and focused-recharge features

Karst is a landscape formed from the dissolution of soluble rock or rock containing minerals that are easily dissolved from within the rock. The landscape is characterized by sinkholes, caves, losing streams, springs, and underground drainage systems, which rapidly move water through the karst. The two forms of karst in New York State include carbonate karst, which forms in carbonate rock (limestone, marble, and dolostone), and evaporite karst, which forms in rock that contains the evaporite minerals gypsum and halite. Past and recent studies of karst across the State have shown that areas of focused recharge in karstic carbonate rock allow contaminants to enter aquifer systems with little attenuation. Focused areas of recharge need to be identified to help prevent such contamination from sources on or adjacent to the karst. The New York State Departments of Environmental Conservation and Health are collaborating with the agricultural community to make farmers and farm-planning advisors more aware of karst and how to manage daily farming activities to reduce their impact on surface water and groundwater resources, especially in karst areas. There is also a need to make regulators, planners, and the general public aware of New York’s karst resources and to properly protect and manage these resources to protect the quality of groundwater and surface water that can flow into, through, and from karst bedrock. Using publicly available geospatial data, karst bedrock and closed depressions over or near karst rock were identified across New York. Carbonate, evaporite, and marble geologic units were selected from a statewide 1:250,000-scale bedrock geology dataset. The selected geologic units were intersected with 7.5-minute quadrangle maps to define the study area. The U.S. Geological Survey has compiled an inventory of closed depressions from statewide digital contour data, scanned 7.5-minute topographic maps known as a digital raster graphics, and light detection and ranging (lidar) digital elevation models. Analysis of the data resulted in the identification of 5,023 closed depressions statewide. The inventory was conducted to eliminate duplication of results from analysis of the three data sources. A series of overlay analyses was conducted using the closed depressions and thematic data known to be key factors in determining the probability of a closed depression contributing to focused groundwater recharge; the thematic data include bedrock geology, soil type, soil infiltration rate, and land cover. Though the extent of karst development is important in understanding the interaction between surface water and groundwater in karst terrains, some of the worst cases of groundwater contamination in karst can occur where only minor karst features might be present. The presence of karst—be it a short section of a solutioned fracture or an extensive cave system—requires careful consideration, forward-looking environmental planning, and consistent water-quality protection to preserve New York State’s water resources.

New York↗
USGS2008

The Lower Triassic Sorkh Shale Formation of the Tabas Block, east central Iran: Succesion of a failed-rift basin at the Paleotethys margin

The Lower Triassic Sorkh Shale Formation is a dominantly red colored marginal marine succession deposited in the north-south trending Tabas Basin of east central Iran. It is correlated with the unconformity-bounded lower limestone member of the Elika Formation of the Alborz Mountains of northern Iran. The Sorkh Shale is bounded by the pre-Triassic and post-Lower Triassic interregional unconformities and consists mainly of carbonates, sandstones, and evaporites with shale being a minor constituent. Detailed facies analysis of the Sorkh Shale Formation resulted in recognition of several genetically linked peritidal facies that are grouped into restricted subtidal, carbonate tidal flat, siliciclastic tidal flat, coastal plain and continental evaporite facies associations. These were deposited in a low energy, storm-dominated inner-ramp setting with a very gentle slope that fringed the Tabas Block of east central Iran and passed northward (present-day coordinates) into deeper water facies of the Paleotethys passive margin of northern Cimmerian Continent. Numerous carbonate storm beds containing well-rounded intraclasts, ooids and bioclasts of mixed fauna are present in the Sorkh Shale Formation of the northern Tabas Basin. The constituents of the storm beds are absent in the fair weather peritidal facies of the Sorkh Shale Formation, but are present throughout the lower limestone member of the Elika Formation. The Tabas Block, a part of the Cimmerian continent in east central Iran, is a rift basin that developed during Early Ordovician-Silurian Paleotethys rifting. Facies and sequence stratigraphic analyses of the Sorkh Shale Formation has revealed additional evidence supporting the Tabas Block as a failed rift basin related to the Paleotethys passive margin. Absence of constituents of the storm beds in the fair weather peritidal facies of the Sorkh Shale Formation, presence of the constituents of the storm beds in the fair weather facies of the Elika Formation (the Sorkh Shale equivalent in the Alborz Paleotethys margin) and southward paleocurrent directions of carbonate storm beds suggest that the low topographic gradient of the ramp in the Tabas failed rift basin was facing the Paleotethys Ocean, where the storms were generated. In addition, northward paleocurrent directions of the fair weather facies and northward increase in carbonate content of the Sorkh Shale sequence further indicate that the Tabas Basin was tectonically a part of the Paleotethys passive margin. It is apparent that relative sea level, basin geometry and tectonic movements along the bounding faults played significant roles during deposition of the Sorkh Shale Formation by controlling accommodation space and facies variations along the Tabas failed rift basin.

Carbonates and Evaporites↗
USGS2007

Identification, prediction, and mitigation of sinkhole hazards in evaporite karst areas

Sinkholes usually have a higher probability of occurrence and a greater genetic diversity in evaporite terrains than in carbonate karst areas. This is because evaporites have a higher solubility and, commonly, a lower mechanical strength. Subsidence damage resulting from evaporite dissolution generates substantial losses throughout the world, but the causes are only well understood in a few areas. To deal with these hazards, a phased approach is needed for sinkhole identification, investigation, prediction, and mitigation. Identification techniques include field surveys and geomorphological mapping combined with accounts from local people and historical sources. Detailed sinkhole maps can be constructed from sequential historical maps, recent topographical maps, and digital elevation models (DEMs) complemented with building-damage surveying, remote sensing, and high-resolution geodetic surveys. On a more detailed level, information from exposed paleosubsidence features (paleokarst), speleological explorations, geophysical investigations, trenching, dating techniques, and boreholes may help in investigating dissolution and subsidence features. Information on the hydrogeological pathways including caves, springs, and swallow holes are particularly important especially when corroborated by tracer tests. These diverse data sources make a valuable database-the karst inventory. From this dataset, sinkhole susceptibility zonations (relative probability) may be produced based on the spatial distribution of the features and good knowledge of the local geology. Sinkhole distribution can be investigated by spatial distribution analysis techniques including studies of preferential elongation, alignment, and nearest neighbor analysis. More objective susceptibility models may be obtained by analyzing the statistical relationships between the known sinkholes and the conditioning factors. Chronological information on sinkhole formation is required to estimate the probability of occurrence of sinkholes (number of sinkholes/km2 year). Such spatial and temporal predictions, frequently derived from limited records and based on the assumption that past sinkhole activity may be extrapolated to the future, are non-corroborated hypotheses. Validation methods allow us to assess the predictive capability of the susceptibility maps and to transform them into probability maps. Avoiding the most hazardous areas by preventive planning is the safest strategy for development in sinkhole-prone areas. Corrective measures could be applied to reduce the dissolution activity and subsidence processes. A more practical solution for safe development is to reduce the vulnerability of the structures by using subsidence-proof designs. ?? 2007 Springer-Verlag.

Conference Paper↗
USGS2010

Geology and undiscovered oil and gas resources in the Madison Group, Williston Basin, North Dakota and Montana

Two of the total petroleum systems (TPS) defined as part of the U.S. Geological Survey (USGS) assessment of the Williston Basin contain Mississippian Madison Group strata: 1) the Bakken-Lodgepole TPS, which includes the Lodgepole Formation; and 2) the Madison TPS, which includes the Mission Canyon, Charles, and Spearfish formations. The Bakken-Lodgepole TPS is defined as the area in which oil generated from the upper and lower shales of the Upper Devonian-Lower Mississippian Bakken Formation has accumulated in reservoirs in the Three Forks, Bakken, and Lodgepole formations. Two conventional assessment units (AU) have been identified within the Bakken-Lodgepole TPS, including one in the Bakken Formation and another in the Waulsortian mound reservoirs of the lower Lodgepole Formation. Lodgepole Formation Waulsortian mound oil production has been restricted to a small part of Stark County, North Dakota. Reservoirs are sealed by middle and upper Lodgepole Formation tight argillaceous limestones. Several nonproductive mounds and mound-like structures have also been identified in the Lodgepole Formation. Productivity correlates closely with the oil window of the Bakken Formation shales, and also indicates the likelihood of limited lateral migration of Bakken Formation oil into Lodgepole Formation reservoirs in North Dakota and Montana. Such considerations limit the estimated mean of undiscovered, technically recoverable resources to 8 million barrels of oil (MMBO) for the Lodgepole Formation conventional reservoirs. The Madison TPS is defined as the area where oil generated from Mission Canyon and Charles formation source rocks has accumulated in reservoirs of the Mission Canyon and Charles formations and in reservoirs within the Triassic Spearfish Formation. One continuous reservoir AU, the Mission Canyon-Charles AU, was defined within the Madison TPS; its boundary coincides with the TPS boundary. There is extensive conventional production throughout the AU on major structures and in stratigraphic-structural traps. The largest fields are on the Little Knife, Billings Nose, and Nesson anticlines. Recent studies show that Madison Group oils were generated from organic-rich Mission Canyon Formation and Ratcliffe Interval carbonates adjacent to the reservoirs. Seals were formed by overlying or lateral evaporites or tight carbonates. Based on available geologic and production data, the undiscovered oil resources for conventional reservoirs in the Mission Canyon-Charles AU were estimated to have a mean of 45 MMBO.

Mountain Geologist↗
USGS1976

Progress report on geology of the Edwards aquifer, San Antonio area, Texas, and preliminary interpretation of borehole geophysical and laboratory data on carbonate rocks

This report describes the geology and porosity of the rocks of the Edwards aquifer, with particular attention to the eastern half of the San Antonio area. The data were obtained from geologic and geophysical studies of nine cored test holes, from laboratory analyses of samples of the aquifer materials, and from recent stratigraphic studies by other investigators. The Georgetown Formation and the Edwards Group or their equivalent stratigraphic units are extensively exposed in central Texas and they occur in the subsurface throughout southern Texas. They consist of a complex sequence of carbonate rocks deposited during Early Cretaceous time under different depositional conditions. Within the study area, the thickness of the carbonate rocks ranges from less than 400 feet (122 m) in the eastern part of the area to more than 600 feet (183 m) in the southwestern part. The depositional environments significantly affected the texture and the composition of the sediments. The Maverick Basin in the southwestern part of the study area was a euxinic basin surrounded by a barrier rudistid reef. Fine-grained carbonates and some associated evaporites occur within this basin. The San Marcos Platform in the eastern part of the study area was intermittently submerged by a transgressing continental sea. Much of the sediments are extensively reworked and burrowed by marine organisms. Several thick sequences of dolomites, evaporites, and associated collapsed deposits occur on the San Marcos Platform. The carbonates of the San Marcos Platform are extensively dissolved within the fresh-water zone. Much of the dissolution is selective of beds containing evaporites or porous dolomites. The dominant structural feature of the study area is a broad homocline that extends from nearly flat-lying beds on the Edwards Plateau to steeply dipping beds of the deep subsurface of the Gulf Coastal Plain. The homocline is interrupted by the Balcones Fault Zone, which is a zone of normal faults that extend across the study area. The intensity and complexity of faulting increases eastward as part of a progression from gentle flexures in the southwestern part of the study area to a complex pattern of tilted fault blocks on the San Marcos Platform.

Texas↗
USGS2022

Data-driven prospectivity modelling of sediment-hosted Zn-Pb mineral systems and their critical raw materials

Demand for critical raw materials is expected to accelerate over the next few decades due to continued population growth and the shifting consumption patterns of the global economy. Sedimentary basins are important sources for critical raw materials and new discoveries of sediment–hosted Mississippi Valley–type (MVT) and/or clastic–dominated (CD) Zn–Pb deposits are likely required to mitigate future supply chain disruptions for Zn, Pb, Ag, Cd, Ga, Ge, Sb, and In. Herein we integrate public geoscience datasets using a discrete global grid to system to model the mineral potential for MVT and CD deposits across Canada, the United States of America, and Australia. Statistical analysis of the model results demonstrates that surface–wave tomography and derivative products from satellite gravity datasets can be used to map the most favourable paleo–tectonic settings of MVT and CD deposits inboard of orogenic belts and at the rifted edges of cratonic lithosphere, respectively. Basin development at pre–existing crustal boundaries was likely important for maintaining the low geothermal–gradients that are favourable for metal transport and generating the crustal fluid pathways that were reactivated during ore–formation, as suggested by the statistical association of both sediment–hosted mineral deposit types with the edges of upward–continued gravity and long–wavelength magnetic anomalies. Multivariate statistical analysis demonstrates that the most prospective combination of these geophysical datasets varies for each geological region and deposit type. We further demonstrate that maximum and minimum geological ages, coupled with Phanerozoic paleogeographic reconstructions, represent mappable proxies for the availability of oxidized, brine–generating regions that are the most likely source of ore–forming fluids (e.g., low– to mid–latitude carbonate platforms and evaporites). Ore deposition was likely controlled by interaction between oxidized, low–temperature brines and sulfidic and/or carbonaceous rocks, which, in some cases, can be mapped at the exposed surface or identified using the available rock descriptions. Baseline weights–of–evidence models are based on regional geophysics and are the least impacted by missing surface information but yield relatively poor results, as demonstrated by the low area–under–the–curve (AUC) for the spatially independent test set on the success–rate plot (AUC = 0.787 for MVT and AUC = 0.870 for CD). Model performance can be improved by: (1) using advanced methods that were trained and validated during a series of semi–automated machine learning competitions; and/or (2) incorporating geological and geophysical datasets that are proxies for each component of the mineral system. The best–performing gradient boosting machine models yield higher AUC for the test set (AUC = 0.983 for MVT and AUC = 0.991 for CD) and reduce the search space by >94%. The model results highlight the potential benefits of mapping sediment–hosted mineral systems at continental scale to improve mineral exploration targeting for critical raw materials.

Ore Geology Reviews↗
USGS1968

Application of ultraviolet reflectance and stimulated luminescence to the remote detection of natural materials

Carbonate rocks and evaporite deposits commonly exhibit relatively high reflectance in the ultraviolet (<3600A), and some outcrops of these materials are selectively shown on ultraviolet imagery. Other materials which are commonly strongly imaged on ultraviolet imagery and photography include water, snow, concrete, and metallic objects, particularly aluminum. Outdoor tests of an active ultraviolet imaging system have demonstrated the feasibility of imaging ultraviolet stimulated luminescence of such minerals as talc, dolomite, and deweylite along quarry faces from distances of several hundred feet. The system features a cathode ray tube transmitter, an image dissector receiver, and a video monitor on which the distribution of luminescent material is imaged as the outcrop is scanned. A pulsed ultraviolet laser emitting at 3371A has been used successfully in the laboratory to stimulate phosphorescence of selected rock and mineral specimens and to discriminate between them on the basis of decay time which ranges from less than three to more than 10 microseconds. Initial results suggest that sodic feldspars have longer decay periods than calcic feldspars. Some granites also appear to have decay periods significantly different from other types of granite in the same locality. Outdoor tests with a high-resolution grating spectrometer were successful in detecting luminescent materials by means of the so-called "Fraunhofer line-depth method". This method is advantageous because it uses the sun so an ultraviolet source and therefore ifs independent of low-powered artificial sources such as cathode ray tubes, lasers, and mercury vapor lamps„ A Fraunhofer line- discriminator suitable for aircraft operation has been constructed, and initial on-the- ground tests are being performed on Rhodamine WT, a luminescent dye used by hydrologists and oceanographers in studies of current dynamics in streams and estuaries.

Open-File Report↗
USGS1968

Stratigraphy of Slick Rock district and vicinity, San Miguel and Dolores Counties, Colorado

The Slick Rock district covers about 570 square miles in western San Miguel and Dolores Counties, in southwestern Colorado. It is at the south edge of the salt-anticline region of southwestern Colorado and southeastern Utah and of the Uravan mineral belt. Deposition of Paleozoic sedimentary rocks in the district and vicinity was principally controlled by development of the Paradox Basin, and of Mesozoic rocks by development of a depositional basin farther west. The Paleozoic rocks generally are thickest at the northeast side of the Paradox Basin in a northwest- trending trough which seems to be a wide graben in Precambrian igneous and metamorphic basement rocks; Mesozoic rocks generally thicken westward and southwestward from the district. Sedimentary rocks rest on a Precambrian basement consisting of a variety of rocks, including granite and amphibolite. The surface of the Precambrian rocks is irregular and generally more than 2,000 feet below sea level and 7,000-11,000 feet below the ground surface. In the northern part of the district the Precambrian surface plunges abruptly northeastward into the trough occupying the northeast side of the Paradox Basin, and in the southern part it sags in a narrow northeasterly oriented trough. Deepening of both troughs, or crustal deformation in their vicinity, influenced sedimentation during much of late Paleozoic and Mesozoic time. The maximum total thickness of sedimentary rocks underlying the district is 13,000 feet, and prior to extensive erosion in the late Tertiary and the Quaternary it may have been as much as about 18,000 feet. The lower 5,000 feet or more of the sequence of sedimentary rocks consists of arenaceous strata of early Paleozoic age overlain by dominantly marine carbonate rocks and evaporite beds interbedded with lesser amounts of clastic sediments of late Paleozoic age. Overlying these rocks is about 4,500 feet of terrestrial clastic sediments, dominantly sandstone with lesser amounts of shale, mudstone, siltstone, and conglomerate, of late Paleozoic and Mesozoic age. Above these rocks is as much as 2,300 feet of marine shale of late Mesozoic age. Perhaps about 5,000 feet of clastic sedimentary rocks, dominantly sandstone and in part shale, of late Mesozoic and early Cenozoic age, overlay the older rocks of the district prior to late Cenozoic erosion... Outside the Slick Rock district the Mancos Shale is overlain by dominantly terrestrial sandstone, mudstone, and coaly beds of the Mesaverde Group of Late Cretaceous age, and younger units such as the Wasatch and Green River Formations of Tertiary age, which once may have extended across the district. These units, totaling possibly 5,000 feet in thickness, were removed by erosion following middle Tertiary uplift of the Colorado Plateau. Igneous rocks of Tertiary age crop out in only one small area in the district, but they are intruded extensively in the Mancos Shale east of the district, and, as shown by deep oil test wells, appear to be intruded widely in the Paradox Member of the Hermosa Formation in the southern part of the district and southeast of the district. Andesite porphyry occurs in a dike on Glade Mountain, microgranogabbro and microgranodiorite occur in thin sills east of the district, and rocks of similar composition form thick sills in the subsurface. All are similar chemically to igneous rocks in the San Juan Mountains southeast of the district and probably were the result of a specific igneous episode. They were intruded most likely during the Miocene. Surficial deposits of Quaternary age include glacial till, terrace gravels, alluvial fans, landslide debris, loess, other soil, alluvium, colluvium, and talus. On Glade Mountain, glacial till of probable early Pleistocene age merges westward with terrace gravels that are correlative with terrace gravels which lie on an old weathered surface of Mancos Shale farther west on the rim of the Dolores River Canyon.

Colorado↗
USGS1994

Geologic history and hydrogeologic setting of the Edwards-Trinity aquifer system, west-central Texas

The Edwards-Trinity aquifer system underlies about 42,000 square miles of west-central Texas. Nearly flat-lying, mostly Comanche (Lower Cretaceous) strata of the aquifer system thin northwestward atop massive pre-Cretaceous rocks that are comparatively impermeable and structurally complex. From predominately terrigenous clastic sediments in the east and fluvialdeltaic (terrestrial) deposits in the west, the rocks of early Trinitian age grade upward into supratidal evaporitic and dolomitic strata, intertidal limestone and dolostone, and shallow-marine, openshelf, and reefal strata of late Trinitian, Fredericksburgian, and Washitan age. A thick, downfaulted remnant of mostly open-marine strata of Eaglefordian through Navarroan age composes a small, southeastern part of the aquifer system. The Trinity Group was deposited atop a rolling peneplain of pre-Cretaceous rocks during three predominately transgressive cycles of sedimentation that encroached upon the Llano uplift. The Fredericksburg and Washita Groups were deposited above the Trinity Group mostly in the lee of the Stuart City reef trend, a shelf margin ridge that sheltered depositional environments in the study area. The Washita Group subsequently was covered with thick, mostly fine-grained Gulf strata. During late Oligocene through early Miocene time, large-scale normal faulting formed the Balcones fault zone, where the Cretaceous strata were downfaulted, intensively fractured, and differentially rotated within a series of northeasttrending fault blocks. In addition to fracturing the rocks in the fault zone and extending the depth of freshwater diagenesis, the faulting vertically displaced the terrain, which steepened hydraulic gradients and maintained relatively high flow velocities near the surface. A shallow regime of dynamic ground-water flow evolved that promoted dissolution and enhanced the transmissivity of the Edwards Group in the Balcones fault zone. Cementation, recrystallization, and mineral replacement caused by deeper, comparatively sluggish ground-water circulation combined to diminish the transmissivity of the underlying Trinity Group, as well as most Cretaceous strata in the Hill Country, Edwards-Plateau, and Trans-Pecos. The Trinity, Fredericksburg, and Washita strata compose a regional aquifer system of three aquifers, whose water-transmitting characteristics generally are continuous in the lateral direction, and two hydraulically tight confining units. The aquifers are the Edwards aquifer in the Balcones fault zone, the Trinity aquifer in the Balcones fault zone and Hill Country, and the Edwards-Trinity aquifer in the Edwards Plateau and Trans-Pecos. The Navarro-Del Rio confining unit overlies the subcrop of the Edwards aquifer, and the Hammett confining unit lies within the updip, basal part of the Trinity aquifer and a small southeastern fringe of the Edwards-Trinity aquifer. The confining units are mostly calcareous mudstone, siltstone, and shale of low-energy terrigenous and openshelf marine depositional environments. The aquifers mainly result from fractures, joint cavities, and porosity caused by the dissolution of evaporites and unstable carbonate constituents. Because the diagenetic effects of cementation, recrystallization, and mineral replacement diminish the hydraulic conductivity of most rocks composing the Trinity and Edwards-Trinity aquifers, transmissivity values average less than 10,000 feet squared per day over more than 90 percent of the study area. However, the effects of tectonic fractures and dissolution in the Balcones fault zone cause transmissivity values to average about 750,000 feet squared per day in the Edwards aquifer, which occupies less than 10 percent of the study area.

Texas↗
USGS2006

Afghan resource assessment fed positive outlook for exploration

Crude oil, natural gas and natural gas liquids/condensate resources are important for the redevelopment of Afghanistan's infrastructure. Improved living and economic conditions in Afghanistan require increasing the availability of energy particularly by exploitation of Afghanistan's petroleum resources. The four total petroleum systems are subdivided into units with homogeneous geologic traits and exploration efforts that include sufficiently homogeneous field-size populations for resource assessment. The greatest volume of undiscovered crude oil is estimated to be in the Afghanistan Eastern Suprasalt Thrusts and Folds Assessment Unit. The greatest volume of undiscovered natural gas is estimated to be in the Afghanistan Jurassic Evaporite Basin Subsalt Carbonates Assessment Unit.

Oil & Gas Journal↗
USGS1983

Geology of the Volga-Ural petroleum province and detailed description of the Ramashkino and Arlan oil fields

The Volga-Ural petroleum province is in general coincident with the Volga-Ural regional high, a broad upwarp of the east-central part of the Russian (East European) platform. The central part of the province is occupied by the Tatar arch, which contains the major share of the oil fields of the province. The Perm-Bashkir arch forms the northeastern part of the regional high, and the Zhigulevsko-Orenburg arch makes up the southern part. These arches are separated from one another by elongate downwarps. The platform cover overlies an Archean crystalline basement and consists of seven main sedimentation cycles as follows: 1) Riphean (lower Bavly) continental sandstone, shale, and conglomerate beds from 500 to 5,000 m thick deposited in aulacogens. 2) Vendian (upper Bavly) continental and marine shale and sandstone up to 3,000 m thick. 3) Middle Devonian-Tournaisian transgressive deposits, which are sandstone, siltstone, and shale in the lower part and carbonates with abundant reefs in the upper; thickness is 300-1,000 m. In the upper carbonate part is the Kamsko-Kinel trough system, which consists of narrow interconnected deep-water troughs. 4) The Visean-Namurian-Bashkirian cycle, which began with deposition of Visean clastics that draped over reefs of the previous cycle and filled in an erosional relief that had formed in some places on the sediments of the previous cycle. The Visean clastics are overlain by marine carbonates. Thickness of the cycle is 50-800 m. 5) Early Moscovian-Early Permian terrigenous clastic deposits and marine carbonate beds 1,000-3,000 m thick. 6) The late Early Permian-Late Permian cycle, which reflects maximum growth of the Ural Mountains and associated Ural foredeep. Evaporites were first deposited, then marine limestones and dolomites, which intertongue eastward with clastic sediments from the Ural Mountains. 7) Continental redbeds of Triassic age and mixed continental and marine elastic beds of Jurassic and Cretaceous age, which were deposited on the southern, southwestern, and northern margins of the Russian platform; they are generally absent in the Volga-Ural province, however. The Volga-Ural oil and gas basin is a single artesian system that contains seven aquifers separated by seals. The areas of greatest hydraulic head are in the eastern parts of the basin near areas where the aquifers crop out on the western slopes of the Ural Mountains. The Peri-Caspian basin is the principal drainage area of the artesian system. Approximately 600 oil and gas fields and 2,000 pools have been found in the Volga-Ural province. Nine productive sequences are recognized as follows: 1) Upper Proterozoic (Bavly beds), which are promising but not yet commercial. 2) Clastic Devonian, which contains the major reserves and includes the main pays of the super-giant Romashkino field. 3) Carbonate Upper Devonian and lowermost Carboniferous, which is one of the main reef-bearing intervals. 4) Visean (Lower Carboniferous) elastics, which are the main pays in the super-giant Arian field. 5) Carbonate Lower and Middle Carboniferous. 6) Clastic Middle Carboniferous Moscovian. 7) Carbonate Middle and Upper Carboniferous. 8) Carbonate-evaporite Lower Permian, which contains the major gas reserves and the lower part of the Melekess tar deposits. 9) Clastic-carbonate Upper Permian, which contains the major part of the Melekess tar deposits. The Volga-Ural province is divided into several productive regions on a basis of differences in structure, distribution of reservoir and source-rock facies, and general composition of the petroleum accumulations. These regions are the Tatar arch, Birsk saddle, Upper Kama depression, Perm-Bashkir arch, Ufa-Orenburg monocline, Melekess-Sernovodsko-Abdulino basin, Zhligulevsko-Orenburg arch, Ural foredeep, and north borders of the Peri-Casplan depression. Exploration activity has declined in recent years; however, interest remains high in several parts of the province, particula

Open-File Report↗
USGS2019

The Zn–Pb mineralization of Florida Canyon, an evaporite-related Mississippi Valley-type deposit in Bongará district, northern Peru

The Florida Canyon evaporite-related Zn–Pb sulfide deposit, in northern Peru, is one of the largest Mississippi Valley-type (MVT) deposits in South America. Triassic carbonate and former evaporite-bearing rocks of the Pucará Group host the ore bodies that comprise two different styles: (i) predominantly stratabound ore associated with hydrocarbon-rich porous dolostones and evaporite dissolution breccias; and (ii) high-grade ore associated with evaporite breccias representing diapiric injections along faults. A dome structure that controls the location of the ore deposit was defined by drillhole spatial data; the dome likely resulted from halokinetic processes during Andean deformation. NNE-trending steeply dipping secondary faults linked to major NW structures appear to control the distribution of ore grades in the deposit. Mineralization post-dated hydrocarbon migration and accumulation. Strontium, carbon, and oxygen data isotopic signatures allow distinction between pre-and syn-mineralization carbonate stages. The sulfur isotopic composition of sulfides in the deposit suggests they precipitated as the result of mixing of a metal-rich fluid with resident hydrogen sulfide in the dome. Local thermochemical sulfate reduction (TSR) may have contributed to the reduced sulfur budget during mineralization.

Economic Geology↗
USGS1995

Stratigraphic and palaeoenvironmental summary of the south-east Georgia embayment: a correlation of exploratory wells

A Continental Offshore Stratigraphic Test (COST) well and six exploratory wells have been drilled in the south-east Georgia embayment. The oldest rocks penetrated are weakly metamorphosed Lower Ordovician quartz arenites and Silurian shales and argillites in the Transco 1005-1 well and Upper Devonian argillites in the COST GE-1 well. These marine strata, which are equivalent to the Tippecanoe sequence in Florida, underlie the post-rift unconformity and represent part of a disjunct fragment of Gondwana that was sutured to the North American craton during the late Palaeozoic Alleghanian orogeny. The Palaeozoic strata are unconformably overlain by interbedded non-marine Jurassic (Bajocian and younger) sandstones and shales and marginal marine Lower Cretaceous sandstones, calcareous shales and carbonates, which contain scattered beds of coal and evaporite. Together, these rocks are stratigraphically equivalent to the onshore Fort Pierce and Cotton Valley(?) Formations and rocks of the Lower Cretaceous Comanchean Provincial Series. The abundance of carbonates and evaporites in this interval, which reflects marine influences within the embayment, increases upwards, eastwards and southwards. The Upper Cretaceous part of the section is composed mainly of neritic calcareous shales and shaley limestones stratigraphically equivalent to the primarily marginal marine facies of the onshore Atkinson, Cape Fear and Middendorf Formations and Black Creek Group, and to limestones and shales of the Lawson Limestone and Peedee Formations. Cenozoic strata are primarily semiconsolidated marine carbonates. Palaeocene to middle Eocene strata are commonly cherty; middle Miocene to Pliocene strata are massive and locally phosphatic and glauconitic; Quaternary sediments are dominated by unconsolidated carbonate sands. The effects of eustatic changes and shifts in the palaeocirculation are recorded in the Upper Cretaceous and Tertiary strata.

Georgia↗
USGS2014

Geologic framework for the national assessment of carbon dioxide storage resources: U.S. Gulf Coast

This report presents 27 storage assessment units (SAUs) within the United States (U.S.) Gulf Coast. The U.S. Gulf Coast contains a regionally extensive, thick succession of clastics, carbonates, salts, and other evaporites that were deposited in a highly cyclic depositional environment that was subjected to a fluctuating siliciclastic sediment supply and transgressive and regressive sea levels. At least nine major depositional packages contain porous strata that are potentially suitable for geologic carbon dioxide (CO 2 ) sequestration within the region. For each SAU identified within these packages, the areal distribution of porous rock that is suitable for geologic CO 2 sequestration is discussed, along with a description of the geologic characteristics that influence the potential CO 2 storage volume and reservoir performance. These characteristics include reservoir depth, gross thickness, net-porous thickness, porosity, permeability, and groundwater salinity. Additionally, a characterization of the overlying regional seal for each SAU is presented. On a case-by-case basis, strategies for estimating the pore volume existing within structurally and (or) stratigraphically closed traps are also presented. Geologic information presented in this report has been employed to calculate potential storage capacities for CO 2 sequestration in the SAUs that are assessed herein, although complete assessment results are not contained in this report.

Alabama, Arkansas, Florida, Georgia, Kentucky, Lou↗
USGS1997

Evaporite karst in the United States

Evaporites, including gypsum (or anhydrite) and salt, are the most soluble of common rocks; they are dissolved readily to form caves, sinkholes, disappearing streams, and other karst features that typically are found in limestones and dolomites. The four basic requirements for evaporite karst to develop are: (1) a deposit of gypsum or salt; (2) water, unsaturated with CaSO4 or NaCl; (3) an outlet for escape of dissolving water; and (4) energy to cause water to flow through the system. Evaporites are present in 32 of the 48 contiguous states, and they underlie about 35-40% of the land area; they are reported in rocks of every geologic system from the Precambrian through the Quaternary. Evaporite karst is known at least locally (and sometimes quite extensively) in almost all areas underlain by evaporites. The most widespread and pronounced examples of both gypsum and salt karst are in the Permian basin of the southwestern United States, but many other areas are also significant. Human activities have caused some evaporite-karst development, primarily in salt deposits. Boreholes may enable (either intentionally or inadvertently) unsaturated water to flow through or against salt deposits, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures above the cavity can cause land subsidence or catastrophic collapse.

Carbonates and Evaporites↗
USGS1997

Evaporite karst of northern lower Michigan

Michigan has three main zones of evaporite karst: collapse breccia in Late Silurian deposits of the Mackinac Straits region; breccia, collapse sinks, and mega-block collapse in Middle Devonian deposits of Northern Lower Michigan, which overlaps the preceding area; and areas of soil swallows in sinks of Mississippian deposits between Turner and Alabaster in Arenac and Iosco counties, and near Grand Rapids in Kent County. The author has focused his study on evaporite karst of the Middle Devonian deposits. The Middle Devonian deposits are the Detroit River Group: a series consisting of limestone, dolomite, shale, salt, gypsum, and anhydrite. The group occurs from subcrop, near the surface, to nearly 1400 feet deep from the northern tip of the Southern Peninsula to the south edge of the “solution front.” Glacial drift is from zero to 350 feet thick. Oil and gas exploration has encountered some significant lost-circulation zones throughout the area. Drilling without fluid returns, casing-seal failures, and lost holes are strong risks in some parts of the region. Lost fluid returns near the top of the group in nearby areas indicate some karst development shortly after deposition. Large and irregular lost-circulation zones, linear and patch trends of large sink holes, and 0.25 mile wide blocks of down-dropped land in the northern Lower Peninsula of Michigan were caused by surface-and ground-water movement along faults into the Detroit River Group. Glaciation has removed some evidence of the karst area at the surface. Sinkhole development, collapse valleys, and swallows developed since retreat of the glacier reveal an active solution front in the Detroit River Group.

Michigan↗