SEARCH · Geology Reports

Results for “Sedimentary Geology”

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 865 records · Page 48Linked to original sources

USGS1965

Geology and ground water in the central part of Apache County, Arizona

The central part of Apache County, Ariz., includes an area of about 3,300 square miles between the Navajo Indian Reservation to the north and U.S. Highway 60 to the south. Sedimentary rocks in the area range from Pennsylvanian to Quaternary in age and from 2,000 to more than 6,000 feet in thickness. The strata were tilted to the northeast, and part of the Upper Triassic and all the Jurassic and Lower Cretaceous rocks were eroded away before strata of Late Cretaceous age were deposited. Basaltic lava flows and cinder cones, representing four general periods of eruption in late Miocene to Quaternary time, are widespread in the southern part of the area. Pennsylvanian and Permian rocks overlie basement rocks of granite and diorite and include the Supai Formation, the Coconino Sandstone, and the Kaibab Limestone. The Supai Formation is 1,000 to 2,000 feet thick and consists of interbedded red and brown mudstone, siltstone, sandstone, limestone, and evaporites. It contains water of very poor quality outside Apache County. The Coconino Sandstone is 200 to 250 feet thick and consists of light-gray fine- to medium-grained sandstone. It contains water suitable for domestic use in the south and water unsuitable for most purposes in the north. The Coconino Sandstone underlies all Central Apache County in the subsurface. The yellowish-gray to dark-gray Kaibab Limestone is present in the southern two-thirds of the area and is 0 to 350 feet thick. It contains water where it is fractured and combines with the Coconino Sandstone to form a single hydrologic unit that yields from 6 to 74 gpm (gallons per minute) of water per foot of drawdown. An unconformity Heparates the Permian rocks from the overlying Triassic rocks, which comprise the Moenkopi and Chinle Formations and the Wingate Sandstone. The Moenkopi Formation is 35 to 250 feet thick and consists of intercalated brownish-red siltstone, sandstone, and conglomerate. It contains salty water in some areas but is dry in most. The Chinle Formation is 0 to 1,550 feet thick and unconformably overlies the Moenkopi. The Chiule consists of multicolored claystone, mudstone, siltstone, sandstone, and conglomerate. Some of the sandstone units yield small amounts of water, usually of a quality unsuitable for domestic use. The Wingate Sandstone is about 250 feet thick and is present only in the extreme northeastern corner of the area. It consists of intercalated, reddish-brown sandstone and siltstone and does not contain water. The Upper Cretaceous rocks comprise the Dakota Sandstone, from 50 to 115 feet thick; the Mancos Shale, about 150 feet thick; and the Mesaverde Group, as much as 200 feet thick. These rocks consist of yellowish-gray, light-green, and reddish-brown sandstone and carbonaceous siltstone. Some of the sandstone units contain water of suitable quality for domestic use, and wells in these units yield from 10 to 1,000 gpm. Sedimentary rocks of Eocene(?) age are about 800 feet thick and unconformably overlie Cretaceous rocks. They consist of light-brown and medium-red conglomerate, sandstone, and siltstone. These sedimentary rocks contain small amounts of water suitable for domestic use and yield from 10 to 25 gpm in the Springerville area. The Datil Formation of Miocene(?) Tertiary age consists of more than 800 feet of sedimentary rocks, which are composed largely of volcanic fragments. The Datil Formation does not contain water in the one small area where it crops out. The Bidahochi Formation of Pliocene age consists of 0 to 800 feet of white, green, and brown claystone, mudstone, and sandstone. Locally it yields from 10 to 50 gpm of water suitable for domestic use. Quaternary rocks consist of as much as 500 feet of alluvium, sand, gravel, travertine, cinders, and lava. The alluvium along the large drainages contains water that differs in quality from place to place. In most areas where it occurs, the lava

Water Supply Paper↗

USGS1983

Geologic and geophysical investigations of Climax Stock intrusive, Nevada

The Climax stock is a composite granitic intrusive of Cretaceous age, composed of quartz monzonite and granodiorite, which intrudes rocks of Paleozoic and Precambrian age. Tertiary volcanic rocks, consisting of ashflow and ash-fall tuffs, and tuffaceous sedimentary rocks overlie the sedimentary rocks and the stock. Erosion has removed much of the Tertiary volcanic rocks. Hydrothermal alteration of quartz monzonite and granodiorite is found mainly along joints and faults and varies from location to location. The Paleozoic carbonate rocks have been thermally and metasomatically altered to marble and tactite as much as 457 m (1,500 ft) from the contact with the stock, although minor discontinuous metasomatic effects are noted in all rocks out to 914 m (3,000 ft). Three major faults which define the Climax area structurally are the Tippinip, Boundary and Yucca faults. North of the junction of the Boundary and Yucca faults, the faults are collectively referred to as the Butte fault. The dominant joint sets and their average attitudes are N. 32? W., 22? NE; N. 60? W., vertical and N. 35? E., vertical. Joints in outcrop are weathered and generally open, but in subsurface, the joints are commonly filled and healed with secondary mineral s. The location of the water table and the degree of saturation of the granitic rocks are presently unknown. Measurement from drill holes indicated that depth to perched water levels ranges from 30 to 244 m (100-800 ft). Recent field investigations have shown the contact between the Pogonip marble and the granodiorite is a contact rather than a fault as previously mapped. The thickness of the weathered granodiorite is estimated to be 8 to 46 m (25 to 150 ft).

Open-File Report↗

USGS2018

A multidisciplinary-based conceptual model of a fractured sedimentary bedrock aquitard: improved prediction of aquitard integrity

A hydrogeologic conceptual model that improves understanding of variability in aquitard integrity is presented for a fractured sedimentary bedrock unit in the Cambrian-Ordovician aquifer system of midcontinent North America. The model is derived from multiple studies on the siliciclastic St. Lawrence Formation and adjacent strata across a range of scales and geologic conditions. These studies employed multidisciplinary techniques including borehole flowmeter logging, high-resolution depth-discrete multilevel well monitoring, fracture stratigraphy, fluorescent dye tracing, and three-dimensional (3D) distribution of anthropogenic tracers regionally. The paper documents a bulk aquitard that is highly anisotropic because of poor connectivity of vertical fractures across matrix with low permeability, but with ubiquitous bed parallel partings. The partings provide high bulk horizontal hydraulic conductivity, analogous to aquifers in the system, while multiple preferential termination horizons of vertical fractures serve as discrete low vertical hydraulic conductivity intervals inhibiting vertical flow. The aquitard has substantial variability in its ability to protect underlying groundwater from contamination. Across widespread areas where the aquitard is deeply buried by younger bedrock, preferential termination horizons provide for high aquitard integrity (i.e. protection). Protection is diminished close to incised valleys where stress release and weathering has enhanced secondary pore development, including better connection of fractures across these horizons. These conditions, along with higher hydraulic head gradients in the same areas and more complex 3D flow where the aquitard is variably incised, allow for more substantial transport to deeper aquifers. The conceptual model likely applies to other fractured sedimentary bedrock aquitards within and outside of this region.

Minnesota↗

USGS1975

Geology of Porcupine Mountains in Carp River and White Pine Quadrangles, Michigan

The Porcupine Mountains are the eroded remnants of the upper limb of an anticline that is faulted along most of its southern, overturned, limb. The exposed rocks include about 5,000 ft (1,525 m) of middle Keweenawan intermediate to mafic lava flows interbedded with subordinate lithic sedimentary rocks and also include about 3,000 ft (915 m) of overlying middle and upper Keweenawan sedimentary rocks. The sediments are derived from lower Keweenawan and older rocks. The structural relief is at least 8,000 ft (2,440 m) between the crest of the Porcupine Mountains anticline and the trough of the Iron River syncline about 5 mi (8 km) to the south. The reverse fault along the southern, overturned, limb of the anticline has a displacement of about 5,000 ft (1,525 m).

Michigan↗

USGS1989

Preliminary geologic map of the Al Jawf Quadrangle, sheet 29D, Kingdom of Saudi Arabia

The Al Jawf quadrangle (Sheet 29 D) lies in the northwestern part of the Kingdom of Saudi Arabia about 900 km north of Jeddah. The quadrangle is located between lat 29°00'-30°00' N. and long 39°00'-40°30' E. It includes the southeastern rim of the Sirhan-Turayf basin, and is underlain by sedimentary rocks of Paleozoic to Cenozoic age. More than half of the quadrangle is covered by surficial deposits. The Phanerozoic sedimentary rocks of the map area were deposited under both marine and continental conditions. Marine deposits, produced by transgressions and regressions of the sea, are of outershelf to near-shore and coastal-lagoon origin, and the continental deposits are largely of fluvial and deltaic origin. Part of the Miocene-Pliocene rocks are believed to have been deposited in a lacustrine environment. Tensional structures, such as linear macro joints, grabens, block-faulting, and some folding are characteristic of the geology of the map area, and reflect a combination of Red Sea rifting and movement of the Hail Arch. This report introduces a new structural concept that extends the Wadi as Sirhan graben complex southeastward in the Al Jawf quadrangle into the An Nafud (Great Desert). This concept greatly increases the area of interest in the potentially oil-and-gas-bearing rocks of the Wadi as Sirhan region to include those of the An Nafud basin. Discovery of the largest specimen of Prototaxites sp. in the world, in the Al Jubah area of the northeastern part of the quadrangle, has helped solve a long-standing stratigraphic problem involving Devonian and Cretaceous rocks of the southeastern part of the Sirhan-Turayf basin. Phosphorite, a commodity of major economic interest in the Sirhan-Turayf basin, is exposed in the map area along escarpments that form the southeastern rim of the basin. The grade of the phosphorite is as much as 21 percent P 2 O 5 , but the beds are thin and lenticular.

Open-File Report↗

USGS1982

The Giles County, Virginia, seismogenic zone-- Seismological results and geological interpretations

This paper describes and interprets a newly-recognized 40-km-long seismogenic zone, which is inferred to have been the locus of a damaging earthquake in 1897. That shock was the second largest known to have occurred in the southeastern United States (MMI VIII, m b estimated at 5.8, felt over 725,000 km 2 ). It struck Giles County in southwestern Virginia, and a recurrence would affect populous regions on and near the central Atlantic seaboard. This paper attempts to aid in evaluating that hazard by presenting and synthesizing new seismological data with geological inferences and deductions. A five-station, 60-km aperture seismic network has been in operation in the Giles County locale since early 1978. For the subsequent 3-year monitoring period, 10 microearthquakes (M < 2) have been detected. Eight of those 10 events, plus an additional 4 relocated felt earthquakes (3.2 < M < 4.1; 1959-1976) have a tabular distribution centered at Pearisburg, Virginia. That distribution is about 40 km long, 10 km wide, strikes N. 43° E., and has a nearly vertical extent of from 5 km to 25 km in depth. Thus, a Giles County seismogenic zone is defined presently by 12 earthquakes that span 4 orders of magnitude (0 < M < 4) and 2 decades of time (1959-1980). We conclude that the 1897 earthquake occurred on that seismogenic zone. From the orientation of the tabular zone, from evidence that greatest horizontal compressive stress trends east-northeasterly at seismogenic depths in and near Giles County and from sparse P-wave first-motion data, we infer that the monitored microseismicity probably occurs by right-reverse motion on the seismogenic zone, with the southeast side dropping down with respect to the northwest side. In the Giles County locale, the upper 3-6 km of the crust are Paleozoic sedimentary rocks that have moved some tens of kilometers northwest on nearly horizontal detachment faults. The above-mentioned reliable hypocenters for the region lie below the deepest likely detachment, indicating that Giles County seismicity probably has no simple relationship to surface geology. Since Precambrian time, three deformational episodes could have formed steep faults under today's surface structures, at the observed hypocentral depths. These episodes were as follows: (1) As the Iapetus Ocean (Atlantic's predecessor) opened in late Precambrian or early Paleozoic time, northeast-striking normal faults formed, probably at the inferred Iapetan continental edge in central Virginia and at least as far northwest of that locus as Giles County. (2) In late Paleozoic time, detachment faults loaded the crust with several kilometers of overthrust sedimentary rocks, perhaps forming northeast-striking thrust-load faults in a brittle analogue of isostatic depression caused by thrust masses and much lighter continental glaciers. (3) As the Atlantic Ocean opened in Mesozoic time, other northeast-striking normal faults formed on the present continental margin and inland of it. The N. 43° E.-striking seismogenic zone seems most likely to have resulted from compressional reactivation of an Iapetan normal fault, which also may have been reactivated by late Paleozoic compression and Mesozoic extension. First, the seismogenic zone probably does not occur on a thrust-load fault. The zone underlies detached structures of southern Appalachian orientations (east-northeast), but those structures are not known to be displaced where they cross the zone. Thus, if the zone occurs on a thrust-load fault, the fault and its coeval causative central Appalachian detachments would pre-date the southern Appalachian structures. That deduction contradicts stratigraphic and structural estimates of relative ages of southern and central Appalachian detachments. Second, the zone probably does not result from a Mesozoic normal fault, because known locations of Mesozoic normal faults and grabens are well to the southeast of Giles County. Not yet known is where else in the East reactivated Iapetan normal faults might generate shocks similar to that of 1897. However, our analysis enables us to suggest specific geological and geophysical investigations that may produce results useful in answering that question. Such investigations can concentrate on defining the area of probable occurrence of other Iapetan normal faults, and on determining whether the one inferred to underlie Giles County is uniquely active or is typical of others that might exist elsewhere.

Virginia↗

USGS1995

Geologic, geochemical, and isotopic studies of a carbonate- and siliciclastic-hosted Pb-Zn deposit at Lion Hill, Vermont

Zn-, Pb-, Cu-, and Fe-bearing rocks of the Lion Hill area in western Vermont formed during the Early Cambrian by syngenetic sedimentary-exhalative and diagenetic replacement processes. Sphalerite, galena, chalcopyrite, pyrite, and, locally, magnetite form stratabound and broadly stratiform lenticular zones, -300 meters long and 25-50 meters thick, which are uneconomic at the present time. The lenses are structurally disrupted and metamorphosed to greenschist facies, probably due to the Taconic orogeny. Textural evidence suggests that mineralizing fluids permeated the sediments prior to lithification and that a dilatant fracture zone, possibly a feeder zone, contains some of the discordant veins at Lion Hill. The veins may have formed when the sediments were in a plastic, semiconsolidated state. The association of layered iron formation containing base-metal sulfide minerals provides possible lithologic evidence for syngenetic mineralization by submarine exhalative activity. Sand bars and tidal channels present in the sedimentary section could have acted as permeable pathways for movement of mineralizing fluids. The complex interlayering in the sedimentary sequence of carbonate and siliciclastic rock types having widely varying permeabilities created numerous fluid traps. Homogenization temperatures of primary and secondary inclusions in vein sphalerite range from 152°C to 196°C; salinities range from 11.5 to 14.0 equivalent weight percent NaCl. δ 34 S values of sulfides from Lion Hill vary from -25.9 to +10.0 per mil, and fall within the expected range for sulfide produced from bacteriogenic reduction of sulfate with δ 34 S values of 25 to 30 per mil. In addition, some pyrite probably formed from sulfate in trapped pore fluid that resulted in heavier isotopic values characteristic of more closed-system behavior. Three sphalerite samples that have heavier sulfur isotopic values may reflect a change in the source of sulfur during a later episode of mineralization, perhaps a change to a deep-seated source. Lead isotopic compositions of galenas from mineralized zones at Lion Hill range from 18.351 to 18.632 for 206 Pb/ 204 Pb, from 15.546 to 15.618 for 207 Pb/ 204 Pb, and from 38.126 to 38.496 for 208 Pb/ 204 Pb. The lead isotopic compositions of galena from Lion Hill and fluid inclusion and sulfur isotopic values for the Lion Hill sulfides are more like those of Pb-Zn-Ag deposits of Ireland than those of MVT or Appalachian-type Zn deposits. The prospect of an Irish-type sedimentary-exhalative origin for stratabound Pb-Zn deposits of the Paleozoic shelf of North America is of considerable importance to understanding the timing of mineralization relative to platform evolution and for evaluating the mineral resource potential of the region. Our study of the Lion Hill deposit indicates a potential for Irish-type Pb-Zn deposits in platform rocks of western Vermont; however, at Lion Hill they contain enrichments of Pb, Zn, and Cu rather than a Pb, Zn, and Ag association.

Vermont↗

USGS2002

Geologic map of the Bernalillo NW quadrangle, Sandoval County, New Mexico

The Bernalillo NW quadrangle is located in the northern part of the Albuquerque basin, which is the largest basin or graben within the Rio Grande rift. The quadrangle is underlain by poorly consolidated sedimentary rocks of the Santa Fe Group. These rocks are best exposed in the southwestern part of the quadrangle in the Rincones de Zia, a badland topography cut by northward-flowing tributary arroyos of the Jemez River. The Jemez River flows through the northern half of the quadrangle; extensive fluvial and eolian deposits cover bedrock units along the river. The structural fabric of the quadrangle is dominated by dozens of generally north striking, east and west-dipping normal faults and minor folds associated with the Neogene Rio Grande rift.

Miscellaneous Field Studies Map↗

USGS2002

Surficial geology along the Spokane River, Washington and its relationship to the metal content of sediments (Idaho-Washington stateline to Latah Creek confluence)

The purpose of this study is 1. to document the geographic distribution of Holocene (deposited in the last 11,000 years) sedimentary lithologies in and along the Spokane River, 2. to document the downstream variation of metal contents (especially lead [Pb] and zinc [Zn] ) by sedimentary lithology, and 3. to compare the metal contents of different sedimentary lithologies. This data is used to gain some understanding of the physical and chemical processes that control those metal contents. It is hoped this study can be used to guide potential future remedial actions aimed at reducing the biologic impact of metal-enriched sediments in this area. This work was undertaken in cooperation with the Washington Department of Ecology and the Environmental Protection Agency.

Idaho, Washington↗

USGS2002

Geologic framework of the regional ground-water flow system in the Upper Deschutes Basin, Oregon

Ground water is increasingly relied upon to satisfy the needs of a growing population in the upper Deschutes Basin, Oregon. Hydrogeologic studies are being undertaken to aid in management of the ground-water resource. An understanding of the geologic factors influencing ground-water flow is basic to those investigations. The geology of the area has a direct effect on the occurrence and movement of ground water. The permeability and storage properties of rock material are influenced by the proportion, size, and degree of interconnection of open spaces the rocks contain. These properties are the result of primary geologic processes such as volcanism and sedimentation, as well as subsequent processes such as faulting, weathering, or hydrothermal alteration. The geologic landscape in the study area evolved during about 30 million years of volcanic activity related to a north-south trending volcanic arc, the current manifestation of which are today’s Cascade Range volcanoes. The oldest rock unit in the upper Deschutes Basin study area, the John Day Formation, is a sequence of upper Eocene to lower Miocene volcanic and sedimentary rocks. Weathering and alteration of the rocks has resulted in very low permeability; consequently, the unit forms the hydrologic basement for the regional ground- water flow system throughout much of the area. The Deschutes Formation and age-equivalent deposits that overlie the John Day Formation, in contrast, are highly permeable and are the most widely used ground-water-bearing units in the study area. The Deschutes Formation consists of a variety of volcanic and sedimentary deposits ranging in age from late Miocene to Pliocene (approximately 7.5 to 4.0 million years). Three distinct depositional environments previously described for the formation provide useful hydrogeologic subdivisions. The ancestral Deschutes River deposits and some units within the arc- adjacent alluvial-plain region are among the highest yielding units within the Deschutes Formation, with some wells producing up to a few thousand gallons per minute. Opal Springs basalt, Pelton basalt, and the rhyodacite dome complex near Steelhead Falls are particularly productive subunits within the Deschutes Formation and provide tens to hundreds of cubic feet per second of ground-water discharge to the Deschutes and Crooked Rivers, upstream of Round Butte Dam. Most ground-water recharge in the upper Deschutes Basin occurs in Quaternary deposits of the Cascade Range and Newberry Volcano. These deposits are highly permeable, and the fractured character of the lava flows facilitates rapid infiltration of precipitation and snowmelt, as well as movement of ground water to lower elevations. Additional recharge from canal leakage occurs along sections of unlined canals near Bend, constructed on lava flows from Newberry Volcano. Hydrothermal alteration and secondary mineralization at depth beneath the Cascade Range and Newberry Volcano has drastically reduced the permeability of the material in those regions, effectively restricting most ground water to the strata above the altered rocks. The top of the hydrothermally altered region is considered the base of the regional ground-water system beneath the Cascade Range and Newberry Volcano. Structural features influence ground-water flow within the upper Deschutes Basin mainly by juxtaposing materials with contrasting permeability. This juxtaposition can be caused by fault movement or by the influence of a fault on subsequent deposition. Several depositional centers have formed along the base of fault-line scarps or in grabens within the study area, and the infilling sedimentary deposits have permeability that differs from the surrounding rocks. The effects of faults on ground-water flow may be masked in some areas. For example, the water-table gradient changes slope in the vicinity of the Sisters fault zone, but the slope change also corresponds with a major precipitation gradient change; therefore, any influence of the fault zone is unclear. Geologic units in the Deschutes Basin were divided into several distinct hydrogeologic units. In some instances the units correspond to existing stratigraphic divisions. In other instances, hydrogeologic units correspond to different facies within a single stratigraphic unit or formation. The hydrogeologic units include Quaternary sediment, deposits of the Cascade Range and Newberry Volcano, four zones within the Deschutes Formation and age-equivalent rocks that roughly correspond with depositional environments, and pre-Deschutes-age strata.

Water-Resources Investigations Report↗

USGS1982

Uraniferous opal, Virgin Valley, Nevada: Conditions of formation and implications for uranium exploration

Uraniferous, fluorescent opal, which occurs in tuffaceous sedimentary rocks at Virgin Valley, Nevada, records the temperature and composition of uranium-rich solutions as well as the time of uranium-silica coprecipitation. Results are integrated with previous geologic and geochronologic data for the area to produce a model for uranium mobility that may be used to explore for uranium deposits in similar geologic settings. Uraniferous opal occurs as replacements of diatomite, or silicic air-fall ash layers in tuffaceous lakebeds of the Virgin Valley Formation (Miocene) of Merriam (1907). Fission-track radiography shows uranium to be homogeneously dispersed throughout the opal structure, suggesting coprecipitation of dissolved uranium and silica gel. Fluid inclusions preserved within opal replacements of diatomite have homogenization temperatures in the epithermal range and are of low salinity. Four samples of opal from one locality all have U-Pb apparent ages which suggest uraniferous opal precipitation in late Pliocene time. These ages correspond to a period of local, normal faulting, and highangle faults may have served as vertical conduits for transport of deep, thermalized ground water to shallower levels. Lateral migration of rising solutions occurred at intersections of faults with permeable strata. Silica and some uranium were dissolved from silica-rich host strata of 5–20 ppm original uranium content and reprecipitated as the solutions cooled. The model predicts that in similar geologic settings, ore-grade concentrations of uranium will occur in permeable strata that intersect high-angle faults and that contain uranium source rocks as well as efficient reductant traps for uranium. In the absence of sufficient quantities of reductant materials, uranium will be flushed from the system or will accumulate in low-grade disseminated hosts such as uraniferous opal.

Nevada↗

USGS2015

Curiosity’s robotic arm-mounted Mars Hand Lens Imager (MAHLI): Characterization and calibration status

MAHLI (Mars Hand Lens Imager) is a 2-megapixel, Bayer pattern color CCD camera with a macro lens mounted on a rotatable turret at the end of the 2-meters-long robotic arm aboard the Mars Science Laboratory rover, Curiosity. The camera includes white and longwave ultraviolet LEDs to illuminate targets at night. Onboard data processing services include focus stack merging and data compression. Here we report on the results and status of MAHLI characterization and calibration, covering the pre-launch period from August 2008 through the early months of the extended surface mission through February 2015. Since landing in Gale crater in August 2012, MAHLI has been used for a wide range of science and engineering applications, including distinction among a variety of mafic, siliciclastic sedimentary rocks; investigation of grain-scale rock, regolith, and eolian sediment textures and structures; imaging of the landscape; inspection and monitoring of rover and science instrument hardware concerns; and supporting geologic sample selection, extraction, analysis, delivery, and documentation. The camera has a dust cover and focus mechanism actuated by a single stepper motor. The transparent cover was coated with a thin film of dust during landing, thus MAHLI is usually operated with the cover open. The camera focuses over a range from a working distance of 2.04 cm to infinity; the highest resolution images are at 13.9 µm per pixel; images acquired from 6.9 cm show features at the same scale as the Mars Exploration Rover Microscopic Imagers at 31 µm/pixel; and 100 µm/pixel is achieved at a working distance of ~26.5 cm. The very highest resolution images returned from Mars permit distinction of high contrast silt grains in the 30–40 µm size range. MAHLI has performed well; the images need no calibration in order to achieve most of the investigation’s science and engineering goals. The positioning and repeatability of robotic arm placement of the MAHLI camera head have been excellent on Mars, often with the hardware arriving within millimeters of expectation. Stability while imaging is usually such that the images are sharply focused; some exceptions—thought to result from motion induced by wind—have occurred during longer exposure LED-illuminated night imaging. Image calibration includes relative radiometric correction by removal of dark current and application of a flat field. Dark current is negligible to minor for typical daytime exposure durations and temperatures at the Gale field site. A pre-launch flat field product is usually applied to the data but new products created from images acquired by MAHLI of the Martian sky are superior and can provide a relative radiometric accuracy of ~6%. The camera lens imparts negligible distortion to its images; camera models derived from pre-launch data, with CAHV and CAHVOR parameters captured in their archived labels, can be applied to the images for analysis. MAHLI data and derived products, including pre-launch images, are archived with the NASA Planetary Data System (PDS). This report includes supplementary calibration and characterization data that are not available in the PDS archive (see supplement file MAHLITechRept0001_Supplement.zip).

MSL MAHLI Technical Report↗

USGS2012

Status of groundwater quality in the San Fernando--San Gabriel study unit, 2005--California GAMA Priority Basin Project

Groundwater quality in the approximately 460-square-mile San Fernando--San Gabriel (FG) study unit was investigated as part of the Priority Basin Project of the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The study area is in Los Angeles County and includes Tertiary-Quaternary sedimentary basins situated within the Transverse Ranges of southern California. The GAMA Priority Basin Project is being conducted by the California State Water Resources Control Board in collaboration with the U.S. Geological Survey (USGS) and the Lawrence Livermore National Laboratory. The GAMA FG study was designed to provide a spatially unbiased assessment of the quality of untreated (raw) groundwater in the primary aquifer systems (hereinafter referred to as primary aquifers) throughout California. The assessment is based on water-quality and ancillary data collected in 2005 by the USGS from 35 wells and on water-quality data from the California Department of Public Health (CDPH) database. The primary aquifers were defined by the depth interval of the wells listed in the CDPH database for the FG study unit. The quality of groundwater in primary aquifers may be different from that in the shallower or deeper water-bearing zones; shallow groundwater may be more vulnerable to surficial contamination. This study assesses the status of the current quality of the groundwater resource by using data from samples analyzed for volatile organic compounds (VOCs), pesticides, and naturally occurring inorganic constituents, such as major ions and trace elements. This status assessment is intended to characterize the quality of groundwater resources in the primary aquifers of the FG study unit, not the treated drinking water delivered to consumers by water purveyors.

California↗

USGS1950

Tin, copper, and uranium at Majuba Hill, Nevada

Uranium minerals occur with ores of copper, tin, and silver at Majuba Hill, Nevada. During World War I, the Majuba Hill mine produced about 4,000 tons of 12 percent copper ore, and during World War II about 23,000 tons of ore containing 2 to 4 percent copper and enough tin ore to furnish from 10 to 15 tons of metallic tin. No uranium has been produced. The bedrock geology of Majuba Hill consists of a complex; volcanic neck or plug composed of rhyolite porphyry, porphyritic rhyolite, quartz feldspar porphyry, breccia dikes, and irregular breccia masses. This plug intruded Triassic (?) sedimentary rocks, chiefly shale. The principal loci of ore deposition were (l) parts of the breccia bodies, particularly where they were porous and where they were silicified and tourmalinized, and (2) a few small pre-mineral fractures adjacent to the breccia masses, Intense hydrothermal alteration resulted in the formation of sericite, quartz, and tourmaline in the wall rocks. This was accompanied or followed by deposition of arsenopyrite, pyrite, cassiterite, fluorite, and several primary sulfide minerals of copper. All of the ore bodies exposed in the mine are highly oxidized, and a profusion of secondary minerals of copper and iron have been found. The only uranium minerals detected are the phosphates torbernite and matatorbernite and the arsenate zeunerite. These are widely disseminated throughout the mine in small amounts associated with the secondary minerals of copper and iron along minor fault surfaces, bedding planes in the shale, and in porous parts of the breccia. A primary uranium mineral has not been found. The secondary uranium minerals appear to be most abundant where copper ore is highest grade. Although unoxidized uranium ore has not been found, it is inferred from this relation that the deposition of the original uranium minerals favored those areas where primary copper mineralization was most intense. There may have been an intimate association of uranium with silver in the ore, but this has not been established. The U 3 O 8 content of samples of copper ore ranges from .0.002 to 0.30 percent. Because the bottom of the oxidized ore has not been reached in mining or exploration, the downward extensions of the known ore bodies of secondary minerals would appear to be worthy of investigation to determine the grade and extent of the primary ore.

Nevada↗

USGS2022

Perspectives on premetamorphic stratabound tourmalinites

Stratabound tourmalinites are metallogenically important rocks that locally show a close spatial association with diverse types of mineralization, especially volcanogenic massive sulfides (VMS) and clastic-dominated (CD) Zn-Pb deposits. These tourmalinite occurrences pan the geologic record from Eoarchean to Jurassic. Host lithologies are dominated by clastic metasedimentary rocks but in some areas include metavolcanic rocks, marble, or metaevaporites. Stratabound and stratiform (conformable) tourmalinites commonly display sedimentary structures such as graded beds, cross-beds, and rip-up clasts. In most cases, field and microtextural relationships are consistent with a synsedimentary to the early diagenetic introduction of boron as a precursor to tourmaline formation. Whole-rock geochemical data for major, trace, and rare earth elements (REE) provide valuable insights into tourmalinite origins. Al-normalized values relative to those for least-altered host metasedimentary rocks suggest that tourmalinites in proximal settings at or near hydrothermal vent sites characterized by high fluid/rock regimes (e.g., Sullivan Pb-Zn-Ag deposit, Canada) have very different signatures than those in low fluid/rock, distal settings (e.g., Broken Hill Pb-Zn-Ag deposit, Australia). The high fluid/rock regimes at Sullivan show large mass changes of +60 % for Mg and +180 % for Mn, as well as large variations in abundances of light and middle REE. In contrast, tourmalinite formation in low fluid/rock regimes yields minimal Al-normalized changes in major elements, trace elements, and REE. Boron isotope values of tourmalinite-hosted tourmaline vary widely from -26.1 to +27.5 ‰, and are attributed mainly to boron sources (e.g., sediments, evaporites) with generally minor influence from processes such as formational temperature, fluid/rock ratio, and secular variation in seawater δ 11 B values. Laterally extensive stratiform tourmalinites formed mainly by syngenetic or early diagenetic processes on or beneath the seafloor. The syngenetic process is attributed to the interaction of vented B-rich brines with aluminous minerals in sediments, whereas the diagenetic process involves the selective replacement of aluminous sediments by B-rich fluids. Modern examples of tourmalinites, as yet undiscovered, may exist in metalliferous sediments of the Red Sea and the eastern Pacific Ocean, in altered volcaniclastic sediments within active seafloor-hydrothermal systems of the South Pacific, and in hydrothermal mounds and vents associated with mafic sill complexes in extensional basins as in the North Sea and South China Sea. Stratabound tourmalinites that contain base-metal sulfides, high Mn concentrations (>1 wt. % MnO), or positive Eu anomalies can be valuable exploration guides for base-metal sulfide deposits in sedimentary and volcanic terranes.

Journal of Geosciences↗

USGS1990

Preliminary geologic map of the Wadi As Sirhan Quadrangle, sheet 30C, Kingdom of Saudi Arabia

The Wadi as Sirhan quadrangle lies in the northwestern pan of Saudi Arabia on the border with Jordan. It is located in the west-central part of the Sirhan-Turayf basin and is underlain by Silurian to Miocene-Pliocene sedimentary rocks that are partly covered by volcanic flows. The map area also contains large areas of surficial sand and gravel. The study area is mainly a structural depression formed by the Wadi as Sirhan graben complex, and it is flanked by highlands of moderate altitude. The Wadi as Sirhan graben is believed to have been formed by tensional forces associated with rifting in the Red Sea. The map area contains the Thaniyat, Ghinah, and Arqah phosphorite members, and the phosphate-bearing Sib member. Hypothetical estimates of mineral resource potential of the phosphate rock in the quadrangle are high, but most prospects are either covered with too much overburden or are too thin and of too low a grade to be considered for economic exploitation at this time. Several deep drill holes in the Wadi as Sirhan depression have penetrated thick sequences of marine rocks that are potential sources of oil and gas. Geological and geophysical conditions are favorable for the accumulation of hydrocarbons, and additional exploration is recommended.

Open-File Report↗

USGS1968

Resurgent cauldrons

Resurgent cauldrons are defined as cauldrons (calderas) in which the cauldron block, following subsidence, has been uplifted, usually in the form of a structural dome. Seven of the best known resurgent cauldrons are: Valles, Toba, Creede, San Juan, Silverton, Lake City, and Timber Mountain. Geologic summaries of these and Long Valley, California, a probable resurgent caldera, are presented. Using the Valles caldera as a model, but augmented by information from other cauldrons, seven stages of volcanic, structural, sedimentary, and plutonic events are recognized in the development of resurgent cauldrons. They are: (I) Regional tumescence and generation of ring fractures; (II) Calderaforming eruptions; (III) Caldera collapse; (IV) Preresurgence volcanism and sedimentation; (V) Resurgent doming; (VI) Major ring-fracture volcanism; (VII) Terminal solfatara and hot-spring activity. These stages define the terminal cycle of resurgent cauldrons, which in the Valles caldera spanned more than 1 million years. The known and inferred occurrence of the seven stages in the eight cauldrons discussed, together with some time control in four cauldrons, indicates that resurgent doming is early in the postcollapse history; hence, it seems part of a pattern and not fortuitous. Doming of the cauldron block by magma pressure is preferred to doming by stock or laccolithic intrusion, although these processes may be subsidiary. Magma rise that produces doming may be explained in several ways, but the principal cause is not known. Nor is it known why some otherwise similar calderas do not have resurgent domes, although size and thickness of the cauldron block and the degree to which it was deformed during caldera collapse may be factors. All known resurgent structures are larger than 8 miles in diameter and are associated with silicic and, presumably, high-viscosity magmas. Genetically, resurgent cauldrons belong to a cauldron group in which subsidence of a central mass takes place along ring fractures and is related to eruption of voluminous ash flows, thereby differing from Kilauean-type calderas. It is proposed that typical Krakatoan-type calderas differ in that collapse is chaotic and ring fractures are not essential to their formation. Krakatoan calderas typically occur in the andesitic volcanoes of island arcs or the eugeosynclinal environment, and their sub-volcanic analogues are not known, whereas resurgent and related Glen Coe-type cauldrons are more common in cratonic or post-orogenic environments as are their sub-volcanic analogues - granitic ring complexes. Granitic ring complexes, such as Lirue, Sande, Ossipee, and Alnsj0, are probably the closest sub-volcanic analogues of resurgent calderas. The source areas of most of the ash-flow sheets of western United States and Mexico are yet to be found. It is suggested that many of them will prove to be resurgent structures. Present evidence suggests that ore deposits are more commonly associated with resurgent cauldrons than with other cauldron types.

Memoir of the Geological Society of America↗

USGS2014

Geologic map of the west-central Buffalo National River region, northern Arkansas

This map summarizes the geology of the west-central Buffalo National River region in the Ozark Plateaus region of northern Arkansas. Geologically, the region lies on the southern flank of the Ozark dome, an uplift that exposes oldest rocks at its center in Missouri. Physiographically, the map area spans the Springfield Plateau, a topographic surface generally held up by Mississippian cherty limestone and the higher Boston Mountains to the south, held up by Pennsylvanian rocks. The Buffalo River flows eastward through the map area, enhancing bedrock erosion of an approximately 1,600-ft- (490-m-) thick sequence of Ordovician, Mississippian, and Pennsylvanian carbonate and clastic sedimentary rocks that have been mildly deformed by a series of faults and folds. Quaternary surficial units are present as alluvial deposits along major streams, including a series of terrace deposits from the Buffalo River, as well as colluvium and landslide deposits mantling bedrock on hillslopes. This report provides a geologic map database of the map area that improves understanding of the regional geologic framework and its influence on the regional groundwater flow system. Furthermore, additional edits were made to the Ponca and Jasper quadrangles in the following ways: new control points on important contacts were obtained using modern GPS; recent higher resolution elevation data allowed further control on placement of contacts; some new contacts were added, in particular the contact separating the upper and lower Everton Formation.

Arkansas↗