SEARCH · Geology Reports

Results for “Rock Products”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources

USGS1994

Lead isotope compositions as guides to early gold mineralization: The North Amethyst vein system, Creede district, Colorado

The North Amethyst vein system, which is hosted by approximately 27 Ma Carpenter Ridge Tuff and approximately 26 Ma Nelson Mountain Tuff, has two mineral associations separated by brecciation and sedimentation in the veins. The early association consists of quartz, rhodonite, hematite, magnetite, electrum (Au (sub 0.3-0.5) Ag (sub 0.7-0.5)) , and Mn carbonate, Au-Ag sulfide, Ag sulfosalt, and base metal sulfide minerals. The later mineral association cuts the Mn- and Au-bearing assemblages and consists of quartz, calcite, sericite, chlorite, hematite, adularia, fluorite, base metal sulfides, and Ag-bearing tetrahedrite.Our detailed studies show that the Pb isotope compositions of paragenetically early galenas associated with Au-rich mineralization in the North Amethyst vein system are relatively unradiogenic ( 206 Pb/ 204 Pb: 18.826-18.881, 207 Pb/ 204 Pb: 15.588-15.602, and 208 Pb/ 204 Pb: 37.790-37.926) compared to Pb isotope compositions of galenas formed later at about 25 Ma during Ag and base metal mineralization ( 206 Pb/ 204 Pb: 19.041-19.115, 207 Pb/ 204 Pb: 15.627- 15.672, and 208 Pb/ 204 Pb: 37.829-38.057). New Pb isotope data for the central and southern parts of the Creede district, which are located 5 to 7 km south of the North Amethyst area, agree with the results of a regional study by Doe et al. (1979) that included five samples from the main part of the Creede district. Galenas and adularia from the central and southern Creede district and galenas from the Bondholder district, 7 km north of the North Amethyst area, are similar to the Pb isotope compositions of galenas formed later in the North Amethyst area during Ag and base metal mineralization. Galenas from the Alpha-Corsair vein, which was mined for Ag prior to 1910, are isotopically similar to galenas associated with North Amethyst Au-stage mineralization. This isotopic similarity suggests that unexplored segments of the Alpha-Corsair structure may have the same mineralogy as the North Amethyst Au stage; thus, the Alpha-Corsair structure has the potential for high gold contents.Pb isotope compositions from the late stage of the North Amethyst vein system and from the Bondholder and central and southern Creede mining districts are more radiogenic than the host volcanic rocks of the central cluster of the San Juan volcanic field. Our Pb isotope results indicate that early Au mineralization of the North Amethyst area may represent the product of an older and relatively local hydrothermal system distinct from that of the younger base metal and Ag mineralization found throughout the region. Fluids that deposited Au minerals may have derived their Pb isotope composition by a greater degree of interaction with shallow, relatively less radiogenic volcanic wall rocks. The younger, base metal and Ag-rich mineralization that overprints the Au mineralization in the North Amethyst area clearly has a more radiogenic isotopic signature, which implies that the later mineralization derived a greater component of its Pb from Proterozoic source rocks, or sediments derived from them.Paragenetically early sulfide-rich vein assemblages have the least radiogenic galenas and generally also have the highest Au contents. Thus, identification of paragenetically early vein assemblages with relatively unradiogenic Pb isotope compositions similar to those of the North Amethyst area provides an additional exploration tool for Au in the central San Juan Mountains area.

Colorado↗

USGS2008

Compilation of Stratigraphic Thicknesses for Caldera-Related Tertiary Volcanic Rocks, East-Central Nevada and West-Central Utah

The U.S. Geological Survey (USGS), the Desert Research Institute (DRI), and a designee from the State of Utah are currently conducting a water-resources study of aquifers in White Pine County, Nevada, and adjacent areas in Nevada and Utah, in response to concerns about water availability and limited geohydrologic information relevant to ground-water flow in the region. Production of ground water in this region could impact water accumulations in three general types of aquifer materials: consolidated Paleozoic carbonate bedrock, and basin-filling Cenozoic volcanic rocks and unconsolidated Quaternary sediments. At present, the full impact of extracting ground water from any or all of these potential valley-graben reservoirs is not fully understood. A thorough understanding of intermontane basin stratigraphy, mostly concealed by the youngest unconsolidated deposits that blanket the surface in these valleys, is critical to an understanding of the regional hydrology in this area. This report presents a literature-based compilation of geologic data, especially thicknesses and lithologic characteristics, for Tertiary volcanic rocks that are presumably present in the subsurface of the intermontane valleys, which are prominent features of this area. Two methods are used to estimate volcanic-rock thickness beneath valleys: (1) published geologic maps and accompanying descriptions of map units were used to compile the aggregate thicknesses of Tertiary stratigraphic units present in each mountain range within the study areas, and then interpolated to infer volcanic-rock thickness in the intervening valley, and (2) published isopach maps for individual out-flow ash-flow tuff were converted to digital spatial data and thickness was added together to produce a regional thickness map that aggregates thickness of the individual units. The two methods yield generally similar results and are similar to volcanic-rock thickness observed in a limited number of oil and gas exploration drill holes in the region, although local geologic complexity and the inherent assumptions in both methods allow only general comparison. These methods serve the needs of regional ground-water studies that require a three-dimensional depiction of the extent and thickness of subsurface geologic units. The compilation of geologic data from published maps and reports provides a general understanding of the distribution and thickness of tuffs that are presumably present in the subsurface of the intermontane valleys and are critical to understanding the ground-water hydrology of this area.

Data Series↗

USGS2017

Real-time specific surface area measurements via laser-induced breakdown spectroscopy

From healthcare to cosmetics to environmental science, the specific surface area (SSA) of micro- and mesoporous materials or products can greatly affect their chemical and physical properties. SSA results are also widely used to examine source rocks in conventional and unconventional petroleum resource plays. Despite its importance, current methods to measure SSA are often cumbersome, time-consuming, or require cryogenic consumables (e.g., liquid nitrogen). These methods are not amenable to high-throughput environments, have stringent sample preparation requirements, and are not practical for use in the field. We present a new application of laser-induced breakdown spectroscopy for rapid measurement of SSA. This study evaluates geological samples, specifically organic-rich oil shales, but the approach is expected to be applicable to many other types of materials. The method uses optical emission spectroscopy to examine laser-generated plasma and quantify the amount of argon adsorbed to a sample during an inert gas purge. The technique can accommodate a wide range of sample sizes and geometries and has the potential for field use. These advantages for SSA measurement combined with the simultaneous acquisition of composition information make this a promising new approach for characterizing geologic samples and other materials.

Energy and Fuels↗

USGS2022

Reserve growth in oil fields of the North Sea

The assessment of petroleum resources of the North Sea, as well as other areas of the world, requires a viable means to forecast the amount of growth of reserve estimates (reserve growth) for discovered fields and to predict the potential fully developed sizes of undiscovered fields. This study investigates the utility of North Sea oil field data to construct reserve-growth models. Oil fields of the North Sea provide an excellent dataset in which to examine the mechanisms, characteristics, rates and quantities of reserve growth because of the high level of capital investments, implementation of sophisticated technologies and careful data collection. Additionally, these field data are well reported and available publicly. Increases in successive annual estimat es of recoverable crude oil volumes indicate that oil fields in the North Sea, collectively and in each country, experience reserve growth. Specific patterns of reserve growth are observed among countries and primary producing reservoir-rock types. Since 1985, Norwegian oil fields had the greatest volume increase; Danish oil fields increased by the greatest percentage relative to 1985 estimates; and British oil fields experienced an increase in recoverable oil estimates for the first ten years since 1985, followed by a slight reduction. Fields producing primarily from clastic reservoirs account for the majority of the estimated recoverable oil and, therefore, these fields had the largest volumetric increase. Fields producing primarily from chalk (limestone) reservoirs increased by a greater percentage relative to 1985 estimates than did fields producing primarily from clastic reservoirs. Additionally, the largest oil fields had the greatest volumetric increases. Although different reserve-growth patterns are observed among oil fields located in different countries, the small number of fields in Denmark precludes construction of reserve-growth models for that country. However, differences in reserve-growth patterns among oil fields that produce from primarily clastic and primarily chalk reservoirs, in addition to a greater number of fields in each of the two categories, allow separate reserve-growth models to be constructed based on reservoir-rock type. Reserve-growth models referenced to the date of discovery and to the date of first production may be constructed from North Sea field data. Years since discovery or years since first production are used as surrogates for, or measures of, field-development effort that is applied to promote reserve growth. Better estimates of recoverable oil are made as fields are developed. Because much of the field development occurs some time later than the field discovery date, reserve-growth models referenced to the date of first production may provide a more appropriate measure of development than does date of discovery. ?? 2005 EAGE/Geological Society of London.

Petroleum Geoscience↗

USGS2006

North Slope, Alaska: Source rock distribution, richness, thermal maturity, and petroleum charge

Four key marine petroleum source rock units were identified, characterized, and mapped in the subsurface to better understand the origin and distribution of petroleum on the North Slope of Alaska. These marine source rocks, from oldest to youngest, include four intervals: (1) Middle-Upper Triassic Shublik Formation, (2) basal condensed section in the Jurassic-Lower Cretaceous Kingak Shale, (3) Cretaceous pebble shale unit, and (4) Cretaceous Hue Shale. Well logs for more than 60 wells and total organic carbon (TOC) and Rock-Eval pyrolysis analyses for 1183 samples in 125 well penetrations of the source rocks were used to map the present-day thickness of each source rock and the quantity (TOC), quality (hydrogen index), and thermal maturity (Tmax) of the organic matter. Based on assumptions related to carbon mass balance and regional distributions of TOC, the present-day source rock quantity and quality maps were used to determine the extent of fractional conversion of the kerogen to petroleum and to map the original TOC (TOCo) and the original hydrogen index (HIo) prior to thermal maturation. The quantity and quality of oil-prone organic matter in Shublik Formation source rock generally exceeded that of the other units prior to thermal maturation (commonly TOCo > 4 wt.% and HIo > 600 mg hydrocarbon/g TOC), although all are likely sources for at least some petroleum on the North Slope. We used Rock-Eval and hydrous pyrolysis methods to calculate expulsion factors and petroleum charge for each of the four source rocks in the study area. Without attempting to identify the correct methods, we conclude that calculations based on Rock-Eval pyrolysis overestimate expulsion factors and petroleum charge because low pressure and rapid removal of thermally cracked products by the carrier gas retards cross-linking and pyrobitumen formation that is otherwise favored by natural burial maturation. Expulsion factors and petroleum charge based on hydrous pyrolysis may also be high compared to nature for a similar reason. Copyright ?? 2006. The American Association of Petroleum Geologists. All rights reserved.

American Association of Petroleum Geologists Bulle↗

USGS1969

Interstitial water studies on small core samples, Deep Sea Drilling Project, Leg 1

The most dramatic variations in pore water composition occurred in Holes 2 and 3 in the Gulf of Mexico. Both holes showed a strong increase in salinity with depth, evidently owing to diffusion from underlying salt bodies. However, on Challenger Knoll (Hole 2) a sharp drop in salinity was observed in the cap rock of the salt dome in which chloride fell to only 4.8 percent. The drop is attributed to production of fresh water during the formation of native sulfur. Outside of the Gulf of Mexico, changes in total salinity with depth did not exceed a few percent, but differences in diagenetic modification of the ionic ratios of sea water were pronounced. In nondiapiric strata in the Gulf of Mexico (Hole 1) both magnesium and potassium were depleted in the pore waters, whereas in the open ocean holes (4, 5, 6, and 7), potassium appeared in excess. Water content (porosity) of the cores was irregular.

Initial reports of the Deep Sea Drilling Project↗

USGS2001

Lahar-hazard zonation for San Miguel volcano, El Salvador

San Miguel volcano, also known as Chaparrastique, is one of many volcanoes along the volcanic arc in El Salvador. The volcano, located in the eastern part of the country, rises to an altitude of about 2130 meters and towers above the communities of San Miguel, El Transito, San Rafael Oriente, and San Jorge. In addition to the larger communities that surround the volcano, several smaller communities and coffee plantations are located on or around the flanks of the volcano, and the PanAmerican and coastal highways cross the lowermost northern and southern flanks of the volcano. The population density around San Miguel volcano coupled with the proximity of major transportation routes increases the risk that even small volcano-related events, like landslides or eruptions, may have significant impact on people and infrastructure. San Miguel volcano is one of the most active volcanoes in El Salvador; it has erupted at least 29 times since 1699. Historical eruptions of the volcano consisted mainly of relatively quiescent emplacement of lava flows or minor explosions that generated modest tephra falls (erupted fragments of microscopic ash to meter sized blocks that are dispersed into the atmosphere and fall to the ground). Little is known, however, about prehistoric eruptions of the volcano. Chemical analyses of prehistoric lava flows and thin tephra falls from San Miguel volcano indicate that the volcano is composed dominantly of basalt (rock having silica content <53%), similar to the lava erupted by Hawaiian volcanoes. The chemical composition of eruptive products and the lack of evidence of large cataclysmic eruptions suggests that prehistoric eruptions probably were similar in nature to the historical eruptions. Unlike San Salvador and San Vicente volcanoes, San Miguel volcano does not appear to have had a history of violent explosive eruptions.

El Transito;San Jorge;San Miguel;San Rafael Orient↗

USGS2012

Water quality and mass transport in four watersheds in eastern Puerto Rico: Chapter E in Water quality and landscape processes of four watersheds in eastern Puerto Rico

Water quality of four small watersheds in eastern Puerto Rico has been monitored since 1991 as part of the U.S. Geological Survey's Water, Energy, and Biogeochemical Budgets program. These watersheds represent a montane, humid-tropical environment and differ in geology and land cover. Two watersheds are located on granitic rocks, and two are located on volcaniclastic rock. For each bedrock type, one watershed is covered with mature rainforest in the Luquillo Mountains, and the other watershed is undergoing reforestation after being affected by agricultural practices typical of eastern Puerto Rico. A subwatershed of the Icacos watershed, the Guabá, was also monitored to examine scaling effects. The water quality of the rivers draining forest, in the Icacos and Guabá (granitic watersheds) and Mameyes (a volcaniclastic watershed), show little contamination by human activities. The water is well oxygenated and has a nearly neutral pH, and nutrient concentrations are low. Concentrations of nutrients in the disturbed watersheds, the Cayaguás (granitic rock) and Canóvanas (volcaniclastic rock), are greater than in the forested watersheds, indicating some inputs from human activities. High in-stream productivity in the Canóvanas watershed leads to occasional oxygen and calcite supersaturation and carbon dioxide undersaturation. Suspended sediment concentrations in all watersheds are low, except during major storms. Most dissolved constituents derived from bedrock weathering or atmospheric deposition (including sodium, magnesium, calcium, silica, alkalinity, and chloride) decrease in concentration with increasing runoff, reflecting dilution from increased proportions of overland or near-surface flow. Strongly bioactive constituents (dissolved organic carbon, potassium, nitrate, ammonium ion, and phosphate) commonly display increasing concentration with increasing runoff, regardless of their ultimate origin (bedrock or atmosphere). The concentrations of many of the bioactive constituents eventually decrease at runoff rates greater than 3 to 10 millimeters per hour, presumably reflecting an increased relative contribution from overland flow. Sulfate behaves like the nonbioactive constituents in the Canóvanas, Cayaguás, and Mameyes watersheds but like a bioactive constituent in the Icacos and Guabá watersheds. Storms resulted in several anomalous sample compositions. Runoff waters from a number of storms - mostly hurricanes, but also other storms - have exceptionally high chloride concentrations, presumably resulting from windborne seasalt from the ocean, and low nitrate concentrations, reflecting a dominance of maritime air masses contributing moisture to the storms. High-potassium samples, without high chloride, are also associated with some smaller storms that followed Hurricane Georges in 1998; they are likely related to the breakdown of fallen vegetation. Finally, occasional low-silica events are observed in the Icacos and Guabá watersheds in the years prior to Hurricane Georges, but not after; this difference may be related to a change in hydrologic flow paths.

Professional Paper↗

USGS2001

Microbial lime-mud production and its relation to climate change

Microbial calcification has been identified as a significant source of carbonate sediment production in modern marine and lacustrine environments around the globe. This process has been linked to the production of modern whitings and large, micritic carbonate deposits throughout the geologic record. Furthermore, carbonate deposits believed to be the result of cyanobacterial and microalgal calcification suggest that the potential exists for long-term preservation of microbial precipitates and storage of carbon dioxide (CO 2 ). Recent research has advanced our understanding of the microbial-calcification mechanism as a photosynthetically driven process. However, little is known of the effects of this process on inorganic carbon cycling or of the effects of changing climate on microbial-calcification mechanisms. Laboratory experiments on microbial cellular physiology demonstrate that cyanobacteria and green algae can utilize different carbon species for metabolism and calcification. Cyanobacterial calcification relies on bicarbonate (HCO 3 – )utilization while green algae use primarily CO 2 . Therefore, depending on which carbonate species (HCO 3 – or CO 2 ) dominates in the ocean or lacustrine environments (a condition ultimately linked to atmospheric partial pressure PCO 2 ), the origin of lime-mud production by cyanobacteria and/or algae may fluctuate through geologic time. Trends of cyanobacteria versus algal dominance in the rock record corroborate this conclusion. These results suggest that relative species abundances of calcareous cyanobacteria and algae in the Phanerozoic may serve as potential proxies for assessing paleoclimatic conditions, including fluctuations in atmospheric PCO 2 .

AAPG Studies in Geology↗

USGS1986

Geology of the Harrisonburg and Bridgewater quadrangles, Virginia

The Harrisonburg and Bridgewater quadrangles comprise an area of approximately 117 square miles in Rockingham County in northwestern Virginia.This area is in the western part of the Shenandoah Valley, a portion of the Valley and Ridge physiographic province, and contains parts of three major geologic structures-the Staunton and North Mountain thrust faults and the Massanutten synclinorium.The roeks within the two quadrangles are folded and faulted limestones, dolomites, shales, and sandstones of Paleozoic age. These rocks have been divided into groups, formations, and members that include the Elbrook and Conococheague formations (Cambrian), the Stonehenge Formation, the Beekmantown Group, the New Market Limestone, and the Lineolnshire, Edinburg, and Martinsburg formations (Ordovieian), the Massanutten Sandstone and the Bloomsburg Formation (Silurian), and probably Upper Silurian and Iower and Middle Devonian limestones and shales that are not exposed but are judged to be on Massanutten Mountain. Triassic diabase dikes and Eocene volcanic pipes intrude the Paleozoic sequence locally. Much of the sequenee is eovered by alluvium or talus of Quaternary age. Selected strata of the Cambrian and Ordovician carbonate roek sequence are sources for road aggregate, agricultural lime, concrete aggregate, dimension stone, tettazzo, portland cement, flux stone, and pellet lime. Some of the carbonate rocks may be potential sources of lead and zinc minerals. Ordovician shale formations have potential for structural clay products.

Virginia↗

USGS2014

A deposit model for carbonatite and peralkaline intrusion-related rare earth element deposits

Carbonatite and alkaline intrusive complexes, as well as their weathering products, are the primary sources of rare earth elements. A wide variety of other commodities have been exploited from carbonatites and alkaline igneous rocks including niobium, phosphate, titanium, vermiculite, barite, fluorite, copper, calcite, and zirconium. Other elements enriched in these deposits include manganese, strontium, tantalum, thorium, vanadium, and uranium. Carbonatite and peralkaline intrusion-related rare earth element deposits are presented together in this report because of the spatial, and potentially genetic, association between carbonatite and alkaline rocks. Although these rock types occur together at many locations, carbonatite and peralkaline intrusion-related rare earth element deposits are not generally found together. Carbonatite hosted rare earth element deposits are found throughout the world, but currently only five are being mined for rare earth elements: Bayan Obo, Daluxiang, Maoniuping, and Weishan deposits in China and the Mountain Pass deposit in California, United States. These deposits are enriched in light rare earth elements, including lanthanum, cerium, praseodynium, and neodynium. The principal rare earth element-minerals associated with carbonatites are fluocarbonates (bastnäsite, parisite, and synchysite), hydrated carbonates (ancylite), and phosphates (monazite) with bastnäsite being the primary ore mineral. Calcite and dolomite are the primary gangue minerals. At present, the only rare earth element production from a peralkaline intrusion-related deposit is as a byproduct commodity at the Lovozero deposit in Russia. Important rare earth element minerals found in various deposits include apatite, eudialyte, loparite, gittinsite, xenotime, gadolinite, monazite, bastnäsite, kainosite, mosandrite, britholite, allanite, fergusonite, and zircon, and these minerals tend to be enriched in heavy rare earth elements. Carbonatite and alkaline intrusive complexes are derived from partial melts of mantle material, and neodymium isotopic data are consistent with the rare earth elements being derived from the parental magma. Deposits and these associated rock types tend to occur within stable continental tectonic units, in areas defined as shields, cratons, and crystalline blocks; they are generally associated with intracontinental rift and fault systems. Protracted fractional crystallization of the magma leads to enrichment in rare earth elements and other incompatible elements. Rare earth element mineralization associated with carbonatites can occur as either primary mineral phases or as mineralization associated with late stage orthomagmatic fluids. Rare earth element mineralization associated with alkaline intrusive complexes may occur as primary phases in magmatic layered complexes or as late-stage dikes and veins. The greatest environmental challenges associated with carbonatite and peralkaline intrusion-related rare earth element deposits center on the associated uranium and thorium. Considerable uncertainty exists around the toxicity of rare earth elements and warrants further investigation. The acid-generating potential of carbonatites and peralkaline intrusion-related deposits is low due to the dominance of carbonate minerals in carbonatite deposits, the presence of feldspars and minor calcite within the alkaline intrusion deposits, and only minor quantities of potentially acid-generating sulfides. Therefore, acid-drainage issues are not likely to be a major concern associated with these deposits. Uranium has the potential to be recovered as a byproduct, which would mitigate some of its environmental effects. However, thorium will likely remain a waste-stream product that will require management since progress is not being made towards the development of thorium-based nuclear reactors in the United States or other large scale commercial uses. Because some deposits are rich in fluorine and beryllium, these elements may be of environmental concern in certain locations.

Scientific Investigations Report↗

USGS1958

The solusphere - its inferences and study

Water is a fundamental geologic agent active in rock decomposition, erosion, and synthesis. Solutes in water are of particular interest to geochemists as sources of raw material for synthesis or as products of decomposition. When geochemical studies move from the laboratory into natural environment many variables relating to solute hydrology must be considered. As a focal point there has been designed a graphical representation of solute hydrology, the solusphere, which embodies the concepts of land-water occurrence and movement on which are superimposed geologic, biologic, physical, chemical, and cultural processes affecting solutes. The solusphere is demonstrated by passing an imaginary plane through the centre of the earth. This plane intercepts concentric zones designated as rock flowage, saturation, aeration, surface activity, and atmosphere. Transport processes carry solutes within and between zones without alteration or conversion. However, whether stationary or in motion, the water's solute character is constantly subject to (1) alteration processes that change concentration by addition or subtraction of solutes or solvent without loss of solute identities, and (2) conversion processes that change the chemical state and form of solutes. The geochemist is concerned with specific conversion processes, but he also must consider transport, alteration, and other conversion processes that are continually modifying the materials with which he is dealing in nature. The solusphere is an attempt to organize processes affecting the chemical quality of land waters into a unified field of science much like the field of marine chemistry.

Geochimica et Cosmochimica Acta↗

USGS1984

Production induced boiling and cold water entry in the Cerro Prieto geothermal reservoir indicated by chemical and physical measurements

Chemical and physical data suggest that the relatively shallow, western part of the Cerro Prieto reservoir is bounded below by low permeability rocks, and above and at the sides by an interface with cooler water. There is no continuous permeability barrier around or immediately above the reservoir. Permeability within the reservoir is dominantly intergranular. Mixture with cooler water rather than boiling is the dominant cooling process in the natural state, and production causes displacement of hot water by cooler water, not by vapour. Local boiling occurs near most wells in response to pressure decreases, but no general vapour zone has formed. ?? 1984.

Geothermics↗

USGS2012

Determining the source and genetic fingerprint of natural gases using noble gas geochemistry: a northern Appalachian Basin case study

Silurian and Devonian natural gas reservoirs present within New York state represent an example of unconventional gas accumulations within the northern Appalachian Basin. These unconventional energy resources, previously thought to be noneconomically viable, have come into play following advances in drilling (i.e., horizontal drilling) and extraction (i.e., hydraulic fracturing) capabilities. Therefore, efforts to understand these and other domestic and global natural gas reserves have recently increased. The suspicion of fugitive mass migration issues within current Appalachian production fields has catalyzed the need to develop a greater understanding of the genetic grouping (source) and migrational history of natural gases in this area. We introduce new noble gas data in the context of published hydrocarbon carbon (C 1 ,C 2+ ) ( 13 C) data to explore the genesis of thermogenic gases in the Appalachian Basin. This study includes natural gases from two distinct genetic groups: group 1, Upper Devonian (Marcellus shale and Canadaway Group) gases generated in situ, characterized by early mature ( 13 C[ C1 C2 ][ 13 C 1 13 C 2 ]: –9 ), isotopically light methane, with low ( 4 He) (average, 1 10 3 cc/cc) elevated 4 He/ 40 Ar and 21 Ne / 40 Ar (where the asterisk denotes excess radiogenic or nucleogenic production beyond the atmospheric ratio), and a variable, atmospherically (air-saturated–water) derived noble gas component; and group 2, a migratory natural gas that emanated from Lower Ordovician source rocks (i.e., most likely, Middle Ordovician Trenton or Black River group) that is currently hosted primarily in Lower Silurian sands (i.e., Medina or Clinton group) characterized by isotopically heavy, mature methane ( 13 C [C1 – C2] [ 13 C 1 13 C 2 ]: 3 ), with high ( 4 He) (average, 1.85 10 3 cc/cc) 4 He/ 40 Ar and 21 Ne / 40 Ar near crustal production levels and elevated crustal noble gas content (enriched 4 He, 21 Ne , 40 Ar ). Because the release of each crustal noble gas (i.e., He, Ne, Ar) from mineral grains in the shale matrix is regulated by temperature, natural gases obtain and retain a record of the thermal conditions of the source rock. Therefore, noble gases constitute a valuable technique for distinguishing the genetic source and post-genetic processes of natural gases.

New York↗

USGS1997

Selection of the Mars Pathfinder landing site

The Mars Pathfinder spacecraft will land on a depositional fan near the mouth of the catastrophic outflow channel, Ares Vallis (19.5°N, 32.8°W). This site offers the prospect of analyzing a variety of rock types from the ancient cratered highlands, intermediate-age ridged plains, and reworked channel deposits. Analyses of these rocks by Pathfinder instruments will enable first-order scientific questions to be addressed, such as differentiation of the crust, the development of weathering products, and the nature of the early environment, as well as their subsequent evolution on Mars. Constraints imposed by (1) spacecraft and rover designs (which are robust), (2) entry, descent, and landing, (3) scientific potential at various sites, and (4) safety were important considerations in site selection. Engineering constraints require a 70 km by 200 km smooth, flat (low slopes) area located between 10° and 20°N that is below 0 km elevation, with average radar reflectivity, little dust, and moderate rock abundance. Three regions on Mars are between 10° and 20°N and below 0 km elevation: Chryse, Amazonis, and Isidis-Elysium. Science considerations favor sites at the mouths of outflow channels (grab bag sites offer an assay of rock types on Mars), highland sites (early crustal differentiation and climate), and sites covered with dark (unoxidized) material. Sites are considered safe if they are clearly below 0 km elevation, appear acceptably free of hazards in high-resolution (<50 m/pixel) Viking orbiter images and have acceptable reflectivity and roughness at radar wavelengths, thermal inertia, rock abundance, red to violet ratio, and albedo. Recent 3.5-cm wavelength radar observations were used to verify elevation, reflectivity, and roughness within the landing ellipses. Three sites meet all of these criteria: Ares Vallis, Tritonis Lacus, and Isidis. Although Isidis appears to be safer than Tritonis and Ares, the greater scientific potential at Ares Vallis resulted in its selection. Comparisons of the Grand Coulee (channel) and the depositional Ephrata Fan of the Channeled Scabland in eastern Washington, with Ares Vallis and its depositional fan also suggest the Ares Vallis landing site is safe and scientifically interesting.

Journal of Geophysical Research Planets↗

USGS1950

Ground-water problems in the Philadelphia area [Pennsylvania]

Large quantities of ground water are used by the Philadelphia Naval Base and many industries in south Philadelphia, as well as by municipalities near Philadelphia in both Pennsylvania and New Jersey. The areal contact between unconsolidated sand, gravel, and clay strata of the Atlantic Coastal Plain and consolidated rocks of the Piedmont province extends in a northeast-southwest line through central Philadelphia. This line of contact, the so-called Fall Line, sharply separates the area of highly productive sand and gravel aquifers of the Coastal Plain from the less productive bedrock aquifers of the Piedmont Plateau. The daily withdrawal of ground water from sand and gravel in the Philadelphia area, including Bristol, Pa., and Trenton, N. J., is approximately 110 million gallons. Wells around Philadelphia yield an additional 13 million gallons a day from consolidated rocks of the Piedmont province. The Raritan formation of Cretaceous age is the principal aquifer for wells in south Philadelphia and the adjacent Camden area. The large quantity of water pumped and the limited extent of this aquifer in the area provide a potentially serious interstate water problem. Ground-water levels in the strategically important Naval Base area have not declined seriously as yet, but increasing withdrawal planned in adjacent New Jersey is expected to lower water levels in south Philadelphia The Delaware and Schuylkill Rivers are believed to be the chief sources of recharge to the Raritan formation, even though heavy pumping on either side of the Delaware River may be expected to affect water levels on the other side. Recharge appears to be adequate generally for present rates of withdrawal, but further studies are needed for an evaluation of the safe maximum yield of the area. The chemical quality of ground water pumped from the Raritan formation is satisfactory for most purposes, but periodic analyses indicate that the concentration of dissolved solids is increasing. This deterioration of the chemical quality probably is due to the character of the water and bottom sediments of the Delaware and Schuylkill Rivers. Shallow aquifers in south Philadelphia contain large amounts of gases generated by the decay of river silts and city refuse occupying low areas. The States of Pennsylvania and New Jersey, together with the municipalities concerned, are coordinating their efforts for a practical solution to the ground-water problems of the Philadelphia area.

Pennsylvania↗

USGS1976

Amino acids and gases in some springs and an oil field in California

Samples of water and gas were collected from six springs and two wells in the Upper Cretaceous Great Valley sequence and Franciscan Formation underlying the Coast Range of northern California and from four oil wells penetrating Tertiary sedimentary rocks in the Kettleman North Dome oil field. Comparison of the dissolved free amino acid compositions of the waters from the two locations show overlapping ranges with many more similarities than differences. The detection of nonprotein amino acids (sarcosine, β -amino n -butyric acid, and others) indicates the protein degradation is partly chemical rather than strictly biological. Other low molecular weight degradation products (methane, ethane, nonvolatile organic acids, and other organic chelating agents) were found. This may be one mechanism for the transportation of organic matter from the source rocks to the reservoir rocks of an oil deposit.

California↗

USGS1989

Development of the Wink Sink in west Texas, U.S.A., due to salt dissolution and collapse

The Wink Sink, in Winkler County, Texas, is a collapse feature that formed in June 1980 when an underground dissolution cavity migrated upward by successive roof failures until it breached the land surface. The original cavity developed in the Permian Salado Formation salt beds more than 400 m (1,300 ft) below ground level. Natural dissolution of salt occurred in the vicinity of the Wink Sink in several episodes that began as early as Salado time and recurred in later Permian, Triassic, and Cenozoic times. Although natural dissolution occurred in the past below the Wink Sink, it appears likely that the dissolution cavity and resultant collapse described in this report were influenced by petroleum-production activity in the immediate area. Drilling, completion, and plugging procedures used on an abandoned oil well at the site of the sink appear to have created a conduit that enabled water to circulate down the borehole and dissolve the salt. When the dissolution cavity became large enough, the roof failed and the overlying rocks collapsed into the cavity. Similar collapse features exist where underground salt beds have been intentionally dissolved during solution mining or accidentally dissolved as a result of petroleum-production activity. ?? 1989 Springer-Verlag New York Inc.

Environmental Geology and Water Sciences↗