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At least 901 records · Page 50Linked to original sources
USGS2011

A national plan for assisting states, federal agencies, and tribes in managing white-nose syndrome in bats

White-nose syndrome (WNS) is a disease responsible for unprecedented mortality in hibernating bats in the northeastern U.S. This previously unrecognized disease has spread very rapidly since its discovery in January 2007, and poses a considerable threat to hibernating bats throughout North America. As WNS spreads, the challenges for understanding and managing the disease continue to increase. Given the escalating complexity of these challenges, a highly coordinated effort is required for State, Federal, and Tribal wildlife agencies, and private partners to respond effectively to WNS and conserve species of bats. The plan proposed herein details the elements that are critical to the investigation and management of WNS, identifies key action items to address stated goals, and outlines the role(s) of agencies and entities involved in this continental effort.

Report↗
USGS2014

Technical review of managed underground storage of water study of the upper Catherine Creek watershed, Union County, northeastern Oregon

Because of water diversions during summer, flow in Catherine Creek, a tributary to the Grande Ronde River in northeastern Oregon, is insufficient to sustain several aquatic species for which the stream is listed as critical habitat. A feasibility study for managed underground storage (MUS) in the upper Catherine Creek watershed in Union County, Oregon, was undertaken by Anderson Perry and Associates, Inc., to address the issue of low flows in summer. The results of the study were released as a report titled “Upper Catherine Creek Storage Feasibility Study for Grande Ronde Model Watershed,” which evaluated the possibility of diverting Catherine Creek streamflow during winter (when stream discharge is high), storing the water by infiltration or injection into an aquifer adjacent to the stream, and discharging the water back to the stream in summer to augment low flows. The method of MUS would be accomplished using either (1) aquifer storage and recovery (ASR) that allows for the injection of water that meets drinking-water-quality standards into an aquifer for later recovery and use, or (2) artificial recharge (AR) that involves the intentional addition of water diverted from another source to a groundwater reservoir. Concerns by resource managers that the actions taken to improve water availability for upper Catherine Creek be effective, cost-efficient, long-term, and based on sound analysis led the National Fish and Wildlife Foundation to request that the U.S. Geological Survey conduct an independent review and evaluation of the feasibility study. This report contains the results of that review. The primary objectives of the Anderson Perry and Associates study reviewed here included (1) identifying potentially fatal flaws with the concept of using AR and (or) ASR to augment the streamflow of Catherine Creek, (2) identifying potentially favorable locations for augmenting streamflow, (3) developing and evaluating alternatives for implementing AR and (or) ASR, and (4) identifying next steps and estimated costs for implementation. The Anderson Perry study was not intended as a comprehensive evaluation of feasibility, but, rather, an effort to develop a concept and preliminary evaluation of feasibility. Additionally, the feasibility study was limited to using existing data from which additional data needs were to be identified. The feasibility study mostly accomplished the goals of identifying potential fatal flaws and developing a project implementation plan. However, a more practical discussion of conclusions regarding the feasibility, likelihood for success, achievement of goals, and overall project costs could have received greater emphasis and would be of value to decision makers. With regard to objective (2), the subject report analyzed information from several possible sites examined for an MUS system. Sufficient cause is provided in the subject report to identify the basalt aquifer in the Milk Creek sub-area as having the greatest potential for MUS. Therefore, this review is primarily focused on the Milk Creek sub-area and the basalt aquifer.

Oregon↗
USGS1975

Comparison of fission-track, K-Ar, and Rb-Sr radiometric age determinations from some granite plutons in Maine

Fission-track ages have been determined on eight apatite and four sphene concentrates separated from plutonic rocks in Maine. K-Ar and Rb-Sr ages for some of these rocks were previously published. In northeastern Maine the whole-rock Rb-Sr, biotite K-Ar, and apatite fission-track ages are concordant at 400-420 million years, whereas in south-central Maine the apatite fission-track age is 150 m.y. and the biotite K-Ar age is about 250 m.y. At intermediate positions along the traverse the whole-rock Rb-Sr, biotite K-Ar, and sphene fission-track ages agree fairly well in the range 390-325 m.y., but the apatite fission-track ages are all about 100 m.y. younger. This pattern is consistent with the hypothesis of burial metamorphism and uplift as proposed in 1970 by Zartman, Hurley, Krueger, and Giletti to explain the abundance of Permian K-Ar ages in central New England.

Maine↗
USGS2007

Regional analysis of ground-water recharge

A modeling analysis of runoff and ground-water recharge for the arid and semiarid southwestern United States was performed to investigate the interactions of climate and other controlling factors and to place the eight study-site investigations into a regional context. A distributed-parameter water-balance model (the Basin Characterization Model, or BCM) was used in the analysis. Data requirements of the BCM included digital representations of topography, soils, geology, and vegetation, together with monthly time-series of precipitation and air-temperature data. Time-series of potential evapotranspiration were generated by using a submodel for solar radiation, taking into account topographic shading, cloudiness, and vegetation density. Snowpack accumulation and melting were modeled using precipitation and air-temperature data. Amounts of water available for runoff and ground-water recharge were calculated on the basis of water-budget considerations by using measured- and generated-meteorologic time series together with estimates of soil-water storage and saturated hydraulic conductivity of subsoil geologic units. Calculations were made on a computational grid with a horizontal resolution of about 270 meters for the entire 1,033,840 square-kilometer study area. The modeling analysis was composed of 194 basins, including the eight basins containing ground-water recharge-site investigations. For each grid cell, the BCM computed monthly values of potential evapotranspiration, soil-water storage, in-place ground-water recharge, and runoff (potential stream flow). A fixed percentage of runoff was assumed to become recharge beneath channels operating at a finer resolution than the computational grid of the BCM. Monthly precipitation and temperature data from 1941 to 2004 were used to explore climatic variability in runoff and ground-water recharge. The selected approach provided a framework for classifying study-site basins with respect to climate and dominant recharge processes. The average climate for all 194 basins ranged from hyperarid to humid, with arid and semiarid basins predominating (fig. 6, chapter A, this volume). Four of the 194 basins had an aridity index of dry subhumid; two of the basins were humid. Of the eight recharge-study sites, six were in semiarid basins, and two were in arid basins. Average-annual potential evapotranspiration showed a regional gradient from less than 1 m/yr in the northeastern part of the study area to more than 2 m/yr in the southwestern part of the study area. Average-annual precipitation was lowest in the two arid-site basins and highest in the two study-site basins in southern Arizona. The relative amount of runoff to in-place recharge varied throughout the study area, reflecting differences primarily in soil water-holding capacity, saturated hydraulic conductivity of subsoil materials, and snowpack dynamics. Climatic forcing expressed in El Niño and Pacific Decadal Oscillation indices strongly influenced the generation of precipitation throughout the study area. Positive values of both indices correlated with the highest amounts of runoff and ground-water recharge.

Professional Paper↗
USGS1982

Geology of the Jabal Riah area, Kingdom of Saudi Arabia

The Jabal Riah area is in the southern part of the Jibal al Hamdah quadrangle (lat 19?00'00'' to 19?07'S0'' N., long 45?37'30'' to 43?45'00' E.) in the southeastern Precambrian Shield, Asir Province, Kingdom of Saudi Arabia. The Jabal Mahanid group of ancient gold mines, which is part of the Jabal Ishmas-Wadi Tathlith gold belt, is in the west-central part of the area. Rocks in the Jabal Riah area consist of Precambrian layered metasedimentary and metavolcanic rocks intruded by Precambrian igneous rocks. The metamorphic rocks are, from oldest to youngest, interlayered hornblende and biotite schist, quartz-biotite schist, hornblende schist, serpentinite, and chlorite schist. The igneous rocks are, from oldest to youngest, diorite-gabbro including dikes, granodiorite, monzogranite-granodiorite, leucocratic quartz porphyry, rhyolite, and aplite and pegmatite dikes. A large area of jasper replaces serpentinite. On the valley floors, recent alluvium and pediment deposits overlie the bedrock. The structure of the area is dominated by a dome centered over the eastern border of the area; leucocratic quartz porphyry forms the core of the dome. Minor folds and faults are present. The Jabal Mahanid group of ancient gold mines is on a northwest-trending vein system, and major ancient mine areas are found where the system splits or changes direction. The veins consist of zones of brecciated and crushed rock, which are generally less than 0.5 m wide but may be as wide as 1 m. These zones contain quartz and calcite stringers and commonly are along hornblende schist-serpentinite contacts; however, they also cut both units. Most aplite, pegmatite, and quartz dikes in the area are thin and discontinuous and are intruded along the vein trend. Similar veins, at the same stratigraphic interval, have been found beyond the northeastern part of the map area. The veins contain detectable gold and silver (median gold, approximately 0.14 ppm; median silver, approximately 1 ppm). Gold and silver are most abundant in calcium-rich rocks and veins; silver was not detected in igneous rocks. Altered wall-rock zones are mineralized as much as 10 m away from the veins. Away from the Jabal Mahanid vein-system, silver was detected in the jasper. Gold and silver were detected in minor brecciated and sheared structures and in metasedimentary rocks. Gold was detected in sericitized margins of the leucocratic quartz porphyry, in unaltered rhyolite, and in aplite dikes. The presence of unusual amounts of gold and silver over a wide area is indicated by the ancient gold mines along veins at or near the hornblende schist-serpentinite contact in the map area and to the south in the Hajrah-Hamdah area and by the widespread evidence of precious metals in igneous rocks and other vein structures. A domed-shaped area, approximately 30 km in diameter, is outlined by the hornblende schist-serpentinite contact and has leucocratic quartz prophyry in the middle. Additional study of this area might reveal economic concentrations of gold and silver.

Open-File Report↗
USGS2015

The 2008 phreatomagmatic eruption of Okmok volcano, Aleutian Islands, Alaska: Chronology, deposits, and landform changes

Okmok volcano, Aleutian Islands, Alaska, explosively erupted over a five-week period between July 12 and August 23, 2008. The eruption was predominantly phreatomagmatic, producing fine-grained tephra that covered most of northeastern Umnak Island. The eruption had a maximum Volcanic Explosivity Index (VEI) of 4, with eruption column heights up to 16 km during the opening phase. Several craters and a master tuff cone formed in the caldera as a result of phreatomagmatic explosions and accumulated tephra-fall and surge deposits. Ascending magma continuously interacted with an extensive shallow groundwater table in the caldera, resulting in the phreatomagmatic character of the eruption. Syneruptive explosion and collapse processes enlarged a pre-existing lake, created a second, entirely new lake, and formed new, deep craters. A field of ephemeral collapse pits and collapse escarpments formed where rapid groundwater withdrawal removed material from beneath capping lava flows. This was the first significant phreatomagmatic event in the U.S. since the Ukinrek Maars eruption in 1977.

Alaska↗
USGS1990

Geological interpretation of combined Seabeam, Gloria and seismic data from Anegada Passage (Virgin Islands, north Caribbean)

The Anegada Passage (sensu lato) includes several basins and ridges from Southeast of Puerto Rico to the corner of the Virgin Islands Platform. Seabeam (Seacarib I) and Gloria long-range sidescan sonar surveys were carried out in this area. These new data allow us to propose an interpretation of the Anegada Passage. Most of the features described are related to wrench faulting: (a) St Croix and Virgin Islands Basins are pull-apart basins created in a right-lateral strike-slip environment based on their rhomboidal shape and seismic data (e.g. the flower structure). These two pull-aparts are divided into two sub-basins by a curvilinear normal fault in the Virgin Islands Basin and a right-lateral strike-slip fault in the St Croix Basin. (b) Tortola Ridge and a 'dog's leg' shaped structure are inferred to be restraining bends between two right-lateral strike-slip faults. (c) We identified two ENE-WSW volcanic lineaments in the eastern area and one volcano lying between Virgin Islands and St Croix Basins. (d) As shown by the seismic activity main wrench motion occurs along the north slope of Virgin Islands Basin and through Anegada Passage. A branching of this main fault transmits the transtensional motion to St Croix Basin. A two-stage story is proposed for the creation of the basins. A first extensional event during Eocene(?)-Oligocene-lower Miocene time created Virgin Islands, St Croix Basins and the tilted blocks of St Croix Ridge. A second transtensional event from Pliocene to Recent gave the present day pattern to this area. However, the displacement along the strike-slip faults is no more than 15 km long. The proposed geodynamic model is based on the separation of the northeastern Caribbean boundary into two blocks. In the West, the indenter of Beata Ridge gives a northeastern motion to Hispaniola Block. In the East, as a result of Hispaniola Block's motion, the Puerto Rico-Virgin Islands Block could escape in an east-northeast direction.

Anegada Passage↗
USGS2023

Characterization of a complex sand-rich gas hydrate reservoir system in the Indian marine continental margin with downhole log and seismic data

Logging-while-drilling (LWD) and coring data were acquired in Areas A, B, C and E during the National Gas Hydrate Program Expedition 02 (NGHP-02). At Sites NGHP-02-16, −17, −20, −23 and −24 of Area B in the Indian Krishna-Godavari Basin, the gas hydrate-bearing sand-rich reservoirs directly in contact with an underlying water-saturated sediment were revealed near the seismic-inferred bottom simulating reflector (BSR) along a large anticlinal structure. Lithofacies analysis of cores show that the lower gas hydrate-bearing reservoir section at these sites is an interbedded unit with thin fine-sand layers alternating with clay-rich layers. We reanalyzed the LWD data including resistivity, compressional-wave and shear-wave acoustic velocities to assess and compare the spatial variation of sand-hosted gas hydrate and possible related free-gas accumulations. The presence of free gas-bearing sediments in direct contact with gas hydrate-bearing sediments was confirmed at Sites NGHP-02-20 and −24 along the northeastern flank of the anticline. The sand-rich reservoirs associated with the Area B anticlinal feature reveal different pore-filling constituents and variable boundary conditions, including gas hydrate/water contacts and gas hydrate/free gas contacts. We infer that the sedimentary depositional history at Sites NGHP-02-20 and −24, may have resulted in an upward shift of the base of gas hydrate stability zone, that could have led to in situ gas hydrate dissociation and the accumulation of free gas and coexistence interval below the log-inferred gas hydrate-bearing reservoir sections. This study demonstrates that reservoir heterogeneity and fluid migration were major factors affecting the distribution of gas hydrate and free gas in the identified sand-rich reservoirs.

Journal of Marine and Petroleum Geology↗
USGS1981

Dating of Archean basement in northeastern Wyoming and southern Montana.

Rb-Sr whole-rock and U-Pb zircon ages of granite and gneiss cores from three deep drill holes extend known occurrences of Archean rocks in the subsurface of NE Wyoming and S Montanta. Rb-Sr and K- Ar mineral ages are discordant and reflect early or middle Proterozoic disturbance. Highly altered rocks occur in a thin zone immediately below the sub-Cambrian unconformity. Samples from a few metres deeper in the basement are much fresher but show the effects of this alteration in filled fractures and thin adjacent alteration haloes. Whole-rock Rb-Sr systems have retaioned a fair degree of integrity in spite of increased susceptibility to modification because of the disturbed mineral systems. Interaction of the rocks with water a few metres below the sub-Cambrian unconformity probably occurred for only a relatively short time. Fractures filled rapidly with secondary minerals such as chlorite, anhydrite, and carbonate to maintain a relatively impermeable crystalline basement in which the silicates and their contained isotopic systems were preserved.- Author

Geological Society of America Bulletin↗
USGS1974

Phosphatic zone in the lower part of the Maquoketa Shale in northeastern Iowa

The basal beds of the Maquoketa Shale in northeastern Iowa include a basal silty phosphorite layer that is thickest near Dubuque. In Clayton County, Iowa, the bed averages about 1 foot thick (30 centimeters) and contains 22.5 percent P 2 0 5 . Phosphatic dolomite that is 8 10 feet (2.4 3 meters) thick and occurs higher in the Maquoketa was observed only in Dubuque County. The thickest and most phosphatic rock in the Maquoketa appears to be coextensive with dark-brown shale, which also occurs mainly in Dubuque County. Rare-earth content of the phosphatic rock decreases southeastward across the area, ranging from 2,000 to about 120 parts per million. The thin low-grade phosphorite is typical of the platform-type phosphorite facies and may be' genetically related to the emergence of the Ozark uplift as an island late in the Ordovician period.

Iowa↗
USGS1975

Ordovician and middle Silurian rocks of the Wildhorse window, northeastern Pioneer Mountains, central Idaho

Along Wildhorse Creek in the northeastern Pioneer Mountains, autochthonous Ordovician and Silurian rocks of an eastern carbonate assemblage are exposed in a structural window through allochthonous flysch deposits of the Mississippian Copper Basin Group. Graptolite-bearing Middle and Upper Ordovician dolomite and cherty dolomite 210 ft (64 m) thick are lithologically and faunally similar to the Hanson Creek Formation of central Nevada and the Saturday Mountain Formation of central Idaho. Monograptus -bearing Middle Silurian platy limestone at least 130 ft (40 m) thick resembles the Roberts Mountains Formation of central Nevada and rocks improperly designated Trail Creek Formation in the Bayhorse region of central Idaho. Allochthonous age-equivalent units of a more western transitional assemblage (the type Phi Kappa and Trail Creek Formations) occur 5 mi (8 km) west of the Wildhorse window, along the crest of the Pioneer Mountains.

Idaho↗
USGS1979

Spatial variation in total element concentration in soil within the Northern Great Plains coal region and Regional soil chemistry in Bighorn and Wind River basins, Wyoming and Montana

PART A: To objectively determine the changes in chemical character of an area subjected to mining and reclamation, prior information is needed. This study represents a broadscale inventory of total chemical composition of the surficial materials of the Northern Great Plains coal region (western North and South Dakota, eastern Montana, and northeastern Wyoming); data are given for 41 elements in A and C soil horizons. An unbalanced, nested, analysis-of-variance design was used to quantify variation in total content of elements between glaciated and unglaciated terrains, for four increasingly smaller geographic scales, and to quantify variation due to sample preparation and analysis. From this statistical study, reliable maps on a regional basis (>100 km) were prepared for C, K, and Rb in A and C soil horizons; for N a, Si, Th, D, and Zn in A-horizon soil; and for As, Ca, Ge, and Mg in C-horizon soil. The distribution of variance components for the remaining 29 elements did not permit the construction of reliable maps. Therefore, a baseline value for each of these elements is given as a measure of the total element concentration in the soils of the Northern Great Plains coal region. The baseline is expressed as the 95-percent range in concentration to be expected in samples of natural soils. PART B: A reconnaissance study of total concentrations of 38 elements in samples of soils (0-40 cm deep, composite) from the Bighorn and Wind River Basins of Montana and Wyoming indicates that the geographic variation for most elements occurs locally (5 km or less). However, in the Bighorn Basin, Zn exhibits significant regional variation (between geologic units); and in the Wind River Basin, AI, Cr, K, Mn, Mo, Ni, U, and V exhibit similar variation. For the remaining elements, the lack of regional variation suggests that a single summary statistic can be used to estimate a baseline value that reflects the range in concentration to be expected in samples of soils in each basin. The concentrations of most of these elements in both basins are not much different from those measured independently in the Powder River Basin of Wyoming or in the Western United States. In addition, data from an analysis of variance provide an estimate of the number of random samples within an area of specified size (10 km square, approximately a township) that are needed to prepare a reliable map of total element concentration in soils for each of the elements in each of the basins.

Montana, North Dakota, Saskatchewan, South Dakota,↗
USGS1996

Use of dye tracing in water-resources investigations in Wyoming, 1967-94

During 1967-94, the U.S. Geological Survey made numerous applications of dye tracing for water-resources investigations in Wyoming. Many of the dye tests were done in cooperation with other agencies. Results of all applications, including some previously unpublished, are described. A chronology of past applications in Wyoming and a discussion of potential future applications are included. Time-of-travel and dispersion measurements were made in a 113-mile reach of the Wind/Bighorn River below Boysen Dam; a 117-mile reach of the Green River upstream from Fontenelle Reservoir and a 70-mile reach downstream; parts of four tributaries to the Green (East Fork River, 39 miles; Big Sandy River, 112 miles; Horse Creek, 14 miles; and Blacks Fork, 14 miles); a 75-mile reach of the Little Snake River along the Wyoming-Colorado State line; and a 95-mile reach of the North Platte River downstream from Casper. Reaeration measurements were made during one of the time-of-travel measurements in the North Platte River. Sixty-eight dye-dilution measurements of stream discharge were made at 22 different sites. These included 17 measurements for verifying the stage-discharge relations for streamflow-gaging stations on North and South Brush Creeks near Saratoga, and total of 29 discharge measurements at 12 new stations at remote sites on steep, rough mountain streams crossing limestone outcrops in northeastern Wyoming. The largest discharge measured by dye tracing was 2,300 cubic feet per second. In karst terrane, four losing streams-North Fork Powder River, North Fork Crazy Woman Creek, Little Tongue River, and Smith Creek-were dye-tested. In the Middle Popo Agie River, a sinking stream in Sinks Canyon State Park, a dye test verified the connection of the sink (Sinks of Lander Cave) to the rise, where flow in the stream resumes.

Water-Resources Investigations Report↗
USGS1974

Tectonic significance of the Kodiak-Bowie seamount chain, northeastern Pacific

The hypothesis of a fixed melting spot reference frame (M) for relative plate motion is tested in the northeastern Pacific Ocean, where the Kodiak-Bowie seamount chain intersects the northern triple junction between the Pacific, American, and Juan de Fuca plates. Available age determinations on Kodiak and Giacomini Seamounts provide an estimated average rate of volcanic propagation along the chain of 6.5 cm per yr and allow estimates of plate movements relative to the melting spot. The inferred motion of the American plate relative to M is close to that observed along the Yellowstone-Snake River Plain volcanic trend and broadly supports the concept of a fixed melting spot reference frame. However, the convex northward curvature of the Kodiak-Bowie chain and of several chains to the south does not support the hypothesis. The lack of parallelism between these seamounts and the Hawaiian chain suggests slow relative movement between the Kodiak-Bowie and Hawaiian melting spots.

Geology↗
USGS2018

Quaternary sediment thickness and bedrock topography of the glaciated United States east of the Rocky Mountains

Beginning roughly 2.6 million years ago, global climate entered a cooling phase known as the Pleistocene Epoch. As snow in northern latitudes compacted into ice several kilometers thick, it flowed as glaciers southward across the North American continent. These glaciers extended across the northern United States, dramatically altering the landscape they covered. East of the Rocky Mountains, the ice coalesced into continental glaciers (called the Laurentide Ice Sheet) that at times blanketed much of the north-central and northeastern United States. To the west of the Laurentide Ice Sheet, glaciers formed in the mountains of western Canada and the United States and coalesced into the Cordilleran ice sheet; this relatively smaller ice mass extended into the conterminous United States in the northernmost areas of western Montana, Idaho, and Washington. Throughout the Pleistocene, landscape alteration occurred by (1) glacial erosion of the rocks and sediments; (2) redeposition of the eroded earth materials in a form substantially different from their source rocks, in terms of texture and overall character; and (3) disruption of preexisting drainage patterns by the newly deposited sediments. In many cases, pre-glacial drainage systems (including, for example, the Mississippi River) were rerouted because their older drainage courses became blocked with glacial sediment. The continental glaciers advanced and retreated many times across those areas. During each ice advance, or glaciation, erosion and deposition occurred, and the landscape was again altered. Through successive glaciations, the landscape and the bedrock surface gradually came to resemble their present configurations. As continental ice sheets receded and the Pleistocene ended, erosion and deposition of sediment (for example in stream valleys) continued to shape the landscape up to the present day (albeit to a lesser extent than during glaciation). The interval of time since the last recession of the glaciers is called the Holocene and, together with the Pleistocene, constitutes the Quaternary Period of geologic time; this publication characterizes the three-dimensional geometry of the Quaternary sediments and the bedrock surface that lies beneath. The pre-glacial landscape was underlain mostly by weathered bedrock generally similar in nature to that found in many areas of the non-glaciated United States. Glacial erosion and redeposition of earth materials produced a young, mineral-rich soil that formed the basis for the highly productive agricultural economy in the U.S. midcontinent. Extensive buried sands and gravels within the glacial deposits also provided a stimulus to other economic sectors by serving as high-quality aquifers supplying groundwater to the region’s industry and cities. An understanding of the three-dimensional distribution of these glacial sediments has direct utility for addressing various societal issues including groundwater quality and supply, and landscape and soil response to earthquake-induced shaking. The Quaternary sediment thickness map and bedrock topographic map shown here provide a regional overview and are intended to supplement the more detailed work on which they are based. Detailed mapping is particularly useful in populated areas for site-specific planning. In contrast, regional maps such as these serve to place local, detailed mapping in context; to permit the extrapolation of data into unmapped areas; and to depict large-scale regional geologic features and patterns that are beyond the scope of local, detailed mapping. They also can enhance the reader’s general understanding of the region’s landscape and geologic history and provide a source of information for regional decision making that could benefit by improved predictability of bedrock depth beneath the unconsolidated Quaternary sediments. To enable these maps to be analyzed in conjunction with other types of information, this publication also includes the map data in GIS compatible format.

Scientific Investigations Map↗
USGS1972

Reconnaissance geology of the Precambrian rocks in the Bi'r Ghamrah quadrangle, Kingdom of Saudi Arabia

Three sequences of volcanic and sedimentary rocks are identified in the Precambrian rocks of the Bi'r Ghamrah quadrangle at the eastern edge of the Precambrian Shield in central Saudi Arabia. The oldest sequence is called the Bi'r Khountina Group. It consists of conglomerate marble, andesite, and graywacke. Unconformably overlying this group is a sequence of graywacke with minor lava called the Murdama Group. In a small area in the southern part of the quadrangle, these rocks are unconformably overlain by rhyolitic tuff and rhyolite tentatively correlated with the Shammar Rhyolite. The older of these sedimentary and volcanic rocks were intruded by diorite and gabbro and by a large pluton of alkalic granite. A contact metamorphic aureole was formed in the Bi'r Khountina and Murdama Groups adjacent to the granite, and feeder dikes of the Sbmmmar Rhyolite(?) intrude the granite. The Bi'r Khountina Group is folded into a south-plunging asymmetrical anticlinorium, the west limb of which is repeated across northwest-trending faults. The Murdama Group appears to have been folded along the same axes, but the contact aureole against the alkalic granite and the imprint of the west-northwest striking Najd fault zone cause the rocks of the Murdama Group to appear to trend westward. Results of spectrographic and chemical analyses of wadi sand, heavy-mineral concentrates, and detrital magnetite show small anomalies. The ultramafic rocks intruded prior to the deposition of the Murdama Group are the source of anomalous chromium and lanthanum and of threshold nickel, scandium, and vanadium. The intrusive rocks younger than the Murdama Group are sources for anomalous lead and threshold silver, boron, barium, beryllium, zirconium, lanthanum, and tin. One small ancient working, probably opened for gold, is present, and at least four places in the Precambrian part of the quadrangle ere potentially favorable for gold, silver, and lead. Chromite is a potential resource in the northeastern part of the quadrangle.

Open-File Report↗
USGS1973

Interpretation of a high-grade Precambrian terrane in northern Idaho

A terrane of high-grade metamorphic rocks in northern Idaho and northeastern Washington is almost completely surrounded by low-grade rocks of the Precambrian Belt Supergroup. The high-grade terrane includes both Belt and pre-Belt rocks. Four events of folding and metamorphism occurred in the high-grade terrane. The first three events may have been associated with the Late Cretaceous emplacement of quartz monzonite of the Kaniksu batholith; the fourth may have been associated with a slightly later emplacement of granodiorite or with a Tertiary plutonic and volcanic episode. A much older event of plutonism in the high-grade terrane is recorded by zircon, which was dated by the Pb-U method at 1,500 m.y. from pre-Belt meta-igneous augen gneiss. Evidence of regional events intermediate in age between 1,500 and 100 m.y. has been found in the surrounding low-grade rocks but not in the high-grade terrane.

Idaho↗
USGS2005

Catastrophic meltwater discharge down the Hudson Valley: A potential trigger for the Intra-Allerød cold period

Glacial freshwater discharge to the Atlantic Ocean during deglaciation may have inhibited oceanic thermohaline circulation, and is often postulated to have driven climatic fluctuations. Yet attributing meltwater-discharge events to particular climate oscillations is problematic, because the location, timing, and amount of meltwater discharge are often poorly constrained. We present evidence from the Hudson Valley and the northeastern U.S. continental margin that establishes the timing of the catastrophic draining of Glacial Lake Iroquois, which breached the moraine dam at the Narrows in New York City, eroded glacial lake sediments in the Hudson Valley, and deposited large sediment lobes on the New York and New Jersey continental shelf ca. 13,350 yr B.P. Excess 14 C in Cariaco Basin sediments indicates a slowing in thermohaline circulation and heat transport to the North Atlantic at that time, and both marine and terrestrial paleoclimate proxy records around the North Atlantic show a short-lived (<400 yr) cold event (Intra-Allerød cold period) that began ca. 13,350 yr B.P. The meltwater discharge out the Hudson Valley may have played an important role in triggering the Intra-Allerød cold period by diminishing thermohaline circulation.

Geology↗