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At least 235 records · Page 13Linked to original sources

USGS1989

Geology of the Arabian Peninsula; shield area of western Saudi Arabia

Western Arabia lies within the low-latitude desert of north Africa and the Middle East, the core being the Arabian segment of the African Shield. The core of complex basement rocks accounts for about 670,000 km 2 , or one-third of the Arabian Peninsula. Reconnaissance mapping of these crystalline rocks, together with bordering sedimentary rocks and volcanic flows, begun in 1950, resulted during the next 13 years in a series of geologic and geographic maps without extensive texts. The maps served as general guides for development of natural resources, including water supplies, ore deposits, and building materials. An intensive exploration program that began in 1963 and involved numerous geologists has vastly increased geologic information. Rainfall in Arabia is meager and episodic, and vegetation is sparse except in isolated copses on the crest of the Hejaz Range. Comparison of flora with similar species in the Sudan, where records of rainfall have long been kept, allows evaluation of mean annual precipitation. Wandering bedouin following fodder created a delicate balance between population and water supply-now disturbed by wells drilled in alluvium and lava fields. A trapezoidal region of Precambrian crystalline rocks lies along the northeast flank of the Red Sea, with two long prongs extending northwest and southeast for a total of 1,800 km. These basement rocks of the Arabian Shield are well exposed on the uplands, scarp mountains, and coastal pediments where the Phanerozoic cover rocks have been stripped as a result of Paleozoic epeirogeny and Tertiary ramping. The shield outcrops are divided into three tectonic provinces by N. 45°W.- trending shear zones of the Najd fault system of latest Proterozoic and possibly earliest Paleozoic time. The southwestern province, the 'Asir1 upland, was sharply uplifted and tilted to the northeast during the Neogene. The northwestern province, consisting of the Ash Shifa'- Hisma upland as well as Jabal Shammar farther east, similarly was uplifted and tilted. These two provinces are separated by the flat-lying median N ajd province, which is chiefly bounded by the principal Najd faults. The outcrops of the shield rocks are of the Late Proterozoic Eonupper Riphean to Vendian or Infracambrian epochs, including the Ediacarian System. The most reliable isotopic ages range from about 900 to 560 m.y., but some Middle Proterozoic rocks may be present in the easternmost shield. The rocks are divided into six lithostratigraphic sequences, two plutonic suites, and an ophiolitic suite. The mafic and ultramafic volcanic and plutonic rocks of the ophiolitic suite everywhere were emplaced tectonically and are probably of different ages in different places. Some ophiolite occurs as obducted blocks, but most is highly deformed and altered to serpentinite in fault zones that mostly define sutures between different tectonic blocks or terranes within the shield. Three of the lithostratigraphic sequences consist of mafic to silicic volcanic rocks and volcanic-derived clastic rocks which, with their subvolcanic plutonic rocks of a dioritic suite, probably formed in oceanic island arcs during convergent plate tectonism. These rocks make up the primary, or first-formed, crust of the shield. Chemical analyses show that the primary shield rocks, regardless of age, are principally calc-alkalic with some associated tholeiitic varieties. Most of the layered rocks are andesitic, but they range from basalt to dacite and in places contain intercalated pillow basalt, marble, chert, and carbonaceous or graphitic schist. Most of the plutonic rocks of the dioritic suite are dioritic, but they range from gabbro to trondhjemite and rarely contain potassium feldspar. The sequences and an associated dioritic suite become younger toward the eastern shield, that is, the primary crust of the shield youngs toward the east. Two western sequences consist of the Jiddah (Samran) and BaishBahah Groups and range in radiometric age from about 900 to 800 m.y.; the eastern sequence consists of the Halaban (Hulayfah) Group and ranges from 800 to about 700 m.y. During subsequent orogeny, most of the rocks were intensely deformed and mostly metamorphosed to upper greenschist facies, but rising in places to the almandine-amphibolite facies. Two other lithostratigraphic sequences with an associated plutonic granitic suite are the products of two mountain-building episodes during which the primary crust was greatly thickened and converted into craton. The two sequences, including largely the Ablah (Al Ays) and Murdama (Shammar) Groups, consist of abundant sedimentary rocks, commonly arkosic, that are the erosional products of the orogenic mountains. They are several thousand meters thick. Less abundant calc-alkalic to alkalic volcanic rocks, commonly dacitic and rhyolitic, are intercalated with the sedimentary rocks. The plutonic rocks of the granitic suite in association with both sequences have syntectonic and posttectonic phases, are products of the orogenies, and are the principal new ingredients making up the craton. Gneiss domes were a significant part of these cratonization orogenies. In association with orogenic crustal heating, some of the low-density, more silicic tonalitic and trondhjemitic rocks of the primary crust rose as gneiss domes. Partial melting in the middle or lower crust below the gneiss domes produced large volumes of granitic magma that intruded the gneiss domes as granodioritic batholiths. The Ablah Group and the older part of the granitic suite are about 775 to 740 Ma old and are associated with the Ablah orogeny and early cratonization in the western and earlier formed half of the shield. The Murdama (Shammar) Group and the younger part of the granitic suite are about 660 to 580 Ma old and are associated with the culminant orogeny and late cratonization that was shieldwide. The granitic suite during both orogenies consists of early, syntectonic granodiorite batholiths associated with the gneiss domes and late, posttectonic monzogranite plutons. Only during the culminant orogeny, late magmatic evolution produced syenogranite and alkali-feldspar granite commonly in circular and ring-structured plutons and with associated explosive volcanic deposits (Shammar Group); final products, some of which have economic potential, were peralkalic and peraluminous. The late plutonism of the culminant orogeny was distinctly bimodal in that subordinate gabbroic rocks are associated with the granites. Various building blocks or terranes of the andesitic and dioritic primary crust were collisionally agglomerated during the Ablah orogeny, early cratonization, whereas the entire shield as currently exposed was further collisionally accreted and compressionally consolidated during the culminant orogeny, final cratonization. Thousands of kilometers of oceanic crust had to be subducted in about 300 m.y. to form the large primary crust of the Arabian Shield. The inevitable collisional events during consumption of such a large volume of oceanic crust invariably led to numerous collisional orogenies that collectively encompass the widely known Pan African tectonic episode. The youngest lithostratigraphic sequence, the Jubaylah Group, is essentially postcratonic, although it is the end product of the collisional culminant orogeny. Final east-west compression of the entire shield from about 580 to 560 m.y. caused the craton to fracture along the large northwest-trending, left-lateral faults and elsewhere along lesser, northeast-trending, right-lateral, conjugate faults of the N ajd fault system. Erosional products of this more localized deformation were the sedimentary rocks of the Jubaylah Group, which also includes intercalated andesitic to basaltic volcanic rocks of a mafic alkalic compositional trend. The collisional edge of an old continental plate (or tectonic fragments thereof), suspected on the eastern edge of the Arabian Shield, has not been shown with certainty to be exposed. Presumably, widespread contamination from such an old continental crust affects U/Pb, Sm/Nd, Rb/Sr, and common lead ratios in the young plutonic rocks of the easternmost shield. One mass of anorthosite near Jabal Khida' on the central eastern edge of the shield may be a fragment of this old continental plate in that associated granodiorite may be as old as 1,600 to 1,800 Ma. Epeirogenic uplift, erosion, and cooling of the uppermost shield during Early and Middle Cambrian time is indicated by an average fission track age of 510±52 m.y., on sphene from diorite (hornblende K-Ar age of 615±12 m.y.) in the southwestern part of the shield. The hiatus was followed by extensive deposition of the Cambro-Ordovician Saq Sandstone in the north and northeast and the Wajid Sandstone in the southeast and south of the shield. The Cambrian Siq Sandstone had already been deposited in the northern part. During the middle and late Paleozoic, broad epeirogeny caused further erosion of the shield until marine transgression deposited the Upper Permian Khuff Formation at least in the eastern part of the shield. In the southwestern shield, the nonmarine Upper Triassic Khums Sandstone was deposited variably on Wajid or Precambrian rocks and is overlain by limestone of the middle Upper Jurassic Amran Formation. Except for shallow marine sandstone of problematic Cretaceous age deposited on the Amran Formation in the south.western shield and on Precambrian rocks in the northwestern shield, the younger beds on the shield are Paleocene and younger, with the possibility that the lowermost are upper Maestrichtian. The early Tertiary beds contain vertebrate fossils of coastal marine or estuarine environment 250 km east of the Red Sea in the central shield. Marginal marine sediments were deposited in a western tongue of the latest Tethys Sea as late as Eocene on the western shield and at least as far south as Jiddah. The great harrats of flood basalt erupted on th~ western shield during late Oligocene and early Miocene at the same time a 2,000-kmlong continental rift valley developed along the future Red Sea axis. Within this rift valley, Baid freshwater tuffaceous lakebeds were deposited between mafic and silicic volcanoes. During late early Miocene time, the Red Sea opened at a rate of 4.4 cm/yr in a firststage movement while continental dikes and swarms of oceanic tholeiitic dikes, gabbro, and granophyre plutonic rocks were intruded into the rift sedimentary and volcanic rocks at the newly formed continental margin. The continental margin was deformed and greatly extended at this time. About 14 or 15 m.y., as the first-stage spreading stopped, the Red Sea Escarpment rose; its erosion caused deposition of coarse conglomerate of the Bathan Formation. About 3,000 m of evaporite was deposited on the young Red Sea oceanic crust during the late Miocene desiccation crisis. A second stage of sea-floor spreading about 4-5 m.y. produced the Red Sea axial trough, consisting of oceanic crust, as well as renewed uplift and tilting of the three tectonic provinces in response to compression from counterclockwise rotation against the Dead Sea Rift. This late movement caused widespread major stream capture, especially along the wadis that formerly drained southwesterly or northwesterly, the channels turning westward through narrow gorges to the coastal plain and the Red Sea.

Professional Paper↗

USGS2024

Site response in the Walnut Creek–Concord region of the San Francisco Bay, California: Ground motion amplification in a fault-bounded basin

Thirty‐seven portable accelerometers were deployed in the eastern San Francisco Bay communities of Walnut Creek and Concord to study site response in a fault‐bounded, urban, sedimentary basin. Local earthquakes were recorded for a period of two years from 2017 to 2019 resulting in 101 well‐recorded events. Site response is estimated by two methods: the reference site spectral ratio method and a source‐site spectral inversion method. The reference site spectral ratio method allows investigation of the variability of site amplification with source azimuth and frequency. The source‐site spectral inversion method yields the best least‐squares fit to site response for a database of ground‐motion records. Both methods show substantial amplification in the Walnut Creek–Concord basin below 2 Hz indicating strong surface‐wave development. Greater amplification is seen for sources aligned along the long axis of the basin. Inversion using close‐in sources at short distances yields lower amplification at longer periods than the entire data set due to reduced surface‐wave generation for steeper angles of incidence. Inversion of site response spectra for shallow shear‐wave velocity using a global search algorithm yields V S30 values consistent with generalized mapping results based on geology and topography but with greater variability due to local site variations. 3D finite‐element modeling shows greater amplification in the Walnut Creek–Concord basin with a basin‐edge effect likely contributing to higher ground motions. Topography is also seen to lead to increased scattering and shadowing effects.

California↗

USGS2011

Characterization of winter foraging locations of Adélie penguins along the Western Antarctic Peninsula, 2001–2002

In accord with the hypotheses driving the Southern Ocean Global Ocean Ecosystems Dynamics (SO GLOBEC) program, we tested the hypothesis that the winter foraging ecology of a major top predator in waters off the Western Antarctic Peninsula (WAP), the Adélie penguin ( Pygoscelis adeliae ), is constrained by oceanographic features related to the physiography of the region. This hypothesis grew from the supposition that breeding colonies in the WAP during summer are located adjacent to areas of complex bathymetry where circulation and upwelling processes appear to ensure predictable food resources. Therefore, we tested the additional hypothesis that these areas continue to contribute to the foraging strategy of this species throughout the non-breeding winter season. We used satellite telemetry data collected as part of the SO GLOBEC program during the austral winters of 2001 and 2002 to characterize individual penguin foraging locations in relation to bathymetry, sea ice variability within the pack ice, and wind velocity and divergence (as a proxy for potential areas with cracks and leads). We also explored differences between males and females in core foraging area overlap. Ocean depth was the most influential variable in the determination of foraging location, with most birds focusing their effort on shallow (<200 m) waters near land and on mixed-layer (200–500 m) waters near the edge of deep troughs. Within-ice variability and wind (as a proxy for potential areas with cracks and leads) were not found to be influential variables, which is likely because of the low resolution satellite imagery and model outputs that were available. Throughout the study period, all individuals maintained a core foraging area separated from other individuals with very little overlap. However, from a year with light sea ice to one with heavy ice cover (2001–2002), we observed an increase in the overlap of individual female foraging areas with those of other birds, likely due to restricted access to the water column, reduced prey abundance, or higher prey concentration. Male birds maintained separate core foraging areas with the same small amount of overlap, showing no difference in overlap between the years. While complex bathymetry was an important physical variable influencing the Adélie penguin's foraging, the analysis of sea ice data of a higher resolution than was available for this study may help elucidate the role of sea ice in affecting Adélie penguin winter foraging behavior within the pack ice.

Deep-Sea Research Part II: Topical Studies in Ocea↗

USGS2011

Phosphorite-hosted zinc and lead mineralization in the Sekarna deposit (Central Tunisia)

The Sekarna Zn–Pb deposit is located in Central Tunisia at the northeastern edge of the Cenozoic Rohia graben. Mineralization comprises two major ore types: (1) disseminated Zn–Pb sulfides that occur as lenses in sedimentary phosphorite layers and (2) cavity-filling zinc oxides (calamine-type ores) that crosscut Late Cretaceous and Early Eocene limestone. We studied Zn sulfide mineralization in the Saint Pierre ore body, which is hosted in a 5-m-thick sedimentary phosphorite unit of Early Eocene age. The sulfide mineralization occurs as replacements of carbonate cement in phosphorite. The ores comprise stratiform lenses rich in sphalerite with minor galena, Fe sulfides, and earlier diagenetic barite. Laser ablation–inductively coupled plasma mass spectrometry analyses of sphalerite and galena show a wide range of minor element contents with significant enrichment of cadmium in both sphalerite (6,000–20,000 ppm) and galena (12–189 ppm). The minor element enrichments likely reflect the influence of the immediate organic-rich host rocks. Fluid inclusions in sphalerite give homogenization temperatures of 80–130°C. The final ice melting temperatures range from −22°C to −11°C, which correspond to salinities of 15–24 wt.% NaCl eq. and suggest a basinal brine origin for the fluids. Sulfur isotope analyses show uniformly negative values for sphalerite (−11.2‰ to −9.3‰) and galena (−16‰ to −12.3‰). The δ 34 S of barite, which averages 25.1‰, is 4‰ higher than the value for Eocene seawater sulfate. The sulfur isotopic compositions are inferred to reflect sulfur derivation through bacterial reduction of contemporaneous seawater sulfate, possibly in restricted basins where organic matter was abundant. The Pb isotopes suggest an upper crustal lead source.

Mineralium Deposita↗

USGS2023

Survival, cause-specific mortality, and population growth of white-tailed deer in western Virginia

Understanding the role of recruitment in population dynamics of white-tailed deer ( Odocoileus virginianus ) is important for management. In the central Appalachian Mountains, deer are part of a largely forested ecosystem that supports 3 carnivore species thought to be capable of influencing white-tailed deer recruitment: black bears ( Urus americanus ), coyotes ( Canis latrans ), and bobcats ( Lynx rufus ). Yet little is known about predation, how other environmental factors influence recruitment, or the importance of neonate survival to white-tailed deer population performance in the region. Our objectives were to identify causes of mortality for neonates, analyze effects of landscape attributes on survival of neonates, estimate survival rates for neonates and adult female white-tailed deer, and to model population growth trends based on current vital rates and hypothetical harvest and neonate survival scenarios. During 2019–2020, we captured 57 neonate deer in Bath County, Virginia, USA, by monitoring 38 pregnant females equipped with global positioning system collars and vaginal implant transmitters and by conducting transect searches for recently born neonates. We observed 37 neonate mortalities and identified cause of death using field and genetic evidence. Mortalities included 28 predation events and 9 deaths from other causes (e.g., abandonment, malnutrition, disease). Black bears accounted for 48.6% of neonate mortalities, and 64.2% of predation events ( n = 18), followed by bobcats ( n = 5) and coyotes ( n = 3). Annual survival for adult female deer was 0.871 and neonate survival to 12 weeks old was 0.310. Elevation was a significant predictor of neonate survival; mortality risk increased 20% for every 100-m increase in elevation. Models of annual population growth using observed vital rates predicted an increasing population (λ = 1.10). A 10% increase in female harvest would still result in a potential population increase of 2% (λ = 1.02), but a 20% increase in harvest rate would result in a potential 7% decline (λ = 0.93). Neonate survival was higher near fertile valley bottoms and lower along forested ridges characterized by shallow, infertile soils and limited edge or early successional forests. While predation, largely influenced by black bears, was the leading cause of neonate mortality and contributed to low neonate survival, we observed little evidence of population decline, and suggest there is opportunity for a modest increase in harvest of female deer.

Virginia↗

USGS1983

Correlation of metal occurrence and terrane attributes in the northwestern conterminous United States

The regional distribution patterns for 20 critical metals derived by an areal-pattern recognition technique leads me to conclude that metals are regularly distributed preferentially in the accreted and cratonic terranes studied in and surrounding the state of Oregon in the northwestern United States. The distribution patterns along distinctively different zones differ in these contrasting crusts across a concealed boundary that is established by strontium isotope data. Copper and gold appear to be abundant in both terranes; nickel, cobalt, chromium, and the platinum-group metals predominate in accreted terranes; lead, zinc, tin, and tungsten are concentrated locally along the boundary zone along the edge and in the interior of the cratonic terrane. The association of metals with accreted terranes and with restricted areas or lineaments in the craton further supports the metallogenetic hypothesis that metal materials are derived mainly from underlying ensialic and ensimatic crusts, and anticipates the possibility for remobilization of these materials along the same broad linear zones over geologic time.

California, Idaho, Montana, Nevada, Oregon, Utah, ↗

USGS2017

Isotopic data for Late Cretaceous intrusions and associated altered and mineralized rocks in the Big Belt Mountains, Montana

The quartz monzodiorite of Mount Edith and the concentrically zoned intrusive suite of Boulder Baldy constitute the principal Late Cretaceous igneous intrusions hosted by Mesoproterozoic sedimentary rocks of the Newland Formation in the Big Belt Mountains, Montana. These calc-alkaline plutonic masses are manifestations of subduction-related magmatism that prevailed along the western edge of North America during the Cretaceous. Radiogenic isotope data for neodymium, strontium, and lead indicate that the petrogenesis of the associated magmas involved a combination of (1) sources that were compositionally heterogeneous at the scale of the geographically restricted intrusive rocks in the Big Belt Mountains and (2) variable contamination by crustal assimilants also having diverse isotopic compositions. Altered and mineralized rocks temporally, spatially, and genetically related to these intrusions manifest at least two isotopically distinct mineralizing events, both of which involve major inputs from spatially associated Late Cretaceous igneous rocks. Alteration and mineralization of rock associated with the intrusive suite of Boulder Baldy requires a component characterized by significantly more radiogenic strontium than that characteristic of the associated igneous rocks. However, the source of such a component was not identified in the Big Belt Mountains. Similarly, altered and mineralized rocks associated with the quartz monzodiorite of Mount Edith include a component characterized by significantly more radiogenic strontium and lead, particularly as defined by 207 Pb/ 204 Pb values. The source of this component appears to be fluids that equilibrated with proximal Newland Formation rocks. Oxygen isotope data for rocks of the intrusive suite of Boulder Baldy are similar to those of subduction-related magmatism that include mantle-derived components; oxygen isotope data for altered and mineralized equivalents are slightly lighter.

Montana↗

USGS1959

Geology and uranium-vanadium deposits of the slick rock district, San Miguel and Dolores counties, Colorado

Sedimentary rocks known in the Slick Rock district in southwestern Colorado range in age from Devonian (?) to Cretaceous, and aggregate about 13,000 feet in maximum thickness. Important uranium-vanadium production has come from deposits in the Salt Wash member of the Morrison formation of Late Jurassic age. The sedimentary rocks are gently folded in the Dolores and Glade anticlines and the Disappointment syncline, and are cut by the Dolores fault zone in the north part of the district and by the Glade fault zone in the south part of the district . Principal fracture sets are oriented approximately parallel to the major faults. Detrital hematite, magnetite, and ilmenite in rocks of the Morrison formation not affected by epigenetic alteration contain appreciable amounts of several of the elements found in the ore deposits . Epigenetic alteration processes have bleached large volumes of rock and largely destroyed these minerals. Such alteration is spatially associated with the Dolores fault zone. Most of the known ore deposits are in the north part of the Slick Rock district in a belt called the Dolores ore zone. The zone lies along the Dolores fault zone but is wider than the fault zone. All known deposits are associated with abundant carbonaceous plant material. Uranium-vanadium deposits in the district are chiefly tabular to lenticular and are roughly parallel to the sedimentary bedding. Some ore bodies, however, are narrow, elongate, and curve sharply across bedding; these bodies have been called "rolls" by the miners. Mineral zoning is evident in some roll bodies; carbonates, goethite (altered from pyrite), selenides, and sulfides are commonly found in concentric layers at the concave edge of rolls. This zoning, and the relationship of roll ore bodies to sedimentary structures and lithology, suggest that ore was deposited at an interface between two solutions, possibly cool connate water and a warmer ore solution. On a district scale, copper and lead are distinctly most abundant in the ore deposits within and immediately adjacent to the Dolores fault zone, and less abundant in deposits toward the edge of the zone. Uranium-vanadium deposits in the district occur only in sandstone that is considered to be epigenetically altered, and the most extensive epigenetic changes have occurred close to ore bodies. It is concluded that ground water, heated and set into circulation near the end of Cretaceous time by igneous intrusions in the La Sal and other centers on the Colorado Plateau, picked up elements from sedimentary rocks where they had been faulted and fractured, and deposited the elements at solution interfaces where accumulations of carbonaceous material provided favorable chemical conditions for precipitation.

Colorado, Utah↗

USGS2009

Hydrothermal processes above the Yellowstone magma chamber: Large hydrothermal systems and large hydrothermal explosions

Hydrothermal explosions are violent and dramatic events resulting in the rapid ejection of boiling water, steam, mud, and rock fragments from source craters that range from a few meters up to more than 2 km in diameter; associated breccia can be emplaced as much as 3 to 4 km from the largest craters. Hydrothermal explosions occur where shallow interconnected reservoirs of steam- and liquid-saturated fluids with temperatures at or near the boiling curve underlie thermal fields. Sudden reduction in confining pressure causes fluids to flash to steam, resulting in significant expansion, rock fragmentation, and debris ejection. In Yellowstone, hydrothermal explosions are a potentially significant hazard for visitors and facilities and can damage or even destroy thermal features. The breccia deposits and associated craters formed from hydrothermal explosions are mapped as mostly Holocene (the Mary Bay deposit is older) units throughout Yellowstone National Park (YNP) and are spatially related to within the 0.64-Ma Yellowstone caldera and along the active Norris-Mammoth tectonic corridor. In Yellowstone, at least 20 large (>100 m in diameter) hydrothermal explosion craters have been identified; the scale of the individual associated events dwarfs similar features in geothermal areas elsewhere in the world. Large hydrothermal explosions in Yellowstone have occurred over the past 16 ka averaging ~1 every 700 yr; similar events are likely in the future. Our studies of large hydrothermal explosion events indicate: (1) none are directly associated with eruptive volcanic or shallow intrusive events; (2) several historical explosions have been triggered by seismic events; (3) lithic clasts and comingled matrix material that form hydrothermal explosion deposits are extensively altered, indicating that explosions occur in areas subjected to intense hydrothermal processes; (4) many lithic clasts contained in explosion breccia deposits preserve evidence of repeated fracturing and vein-filling; and (5) areal dimensions of many large hydrothermal explosion craters in Yellowstone are similar to those of its active geyser basins and thermal areas. For Yellowstone, our knowledge of hydrothermal craters and ejecta is generally limited to after the Yellowstone Plateau emerged from beneath a late Pleistocene icecap that was roughly a kilometer thick. Large hydrothermal explosions may have occurred earlier as indicated by multiple episodes of cementation and brecciation commonly observed in hydrothermal ejecta clasts. Critical components for large, explosive hydrothermal systems include a water-saturated system at or near boiling temperatures and an interconnected system of well-developed joints and fractures along which hydrothermal fluids flow. Active deformation of the Yellowstone caldera, active faulting and moderate local seismicity, high heat flow, rapid changes in climate, and regional stresses are factors that have strong influences on the type of hydrothermal system developed. Ascending hydrothermal fluids flow along fractures that have developed in response to active caldera deformation and along edges of low-permeability rhyolitic lava flows. Alteration of the area affected, self-sealing leading to development of a caprock for the hydrothermal system, and dissolution of silica-rich rocks are additional factors that may constrain the distribution and development of hydrothermal fields. A partial low-permeability layer that acts as a cap to the hydrothermal system may produce some over-pressurization, thought to be small in most systems. Any abrupt drop in pressure initiates steam flashing and is rapidly transmitted through interconnected fractures that result in a series of multiple large-scale explosions contributing to the excavation of a larger explosion crater. Similarities between the size and dimensions of large hydrothermal explosion craters and thermal fields in Yellowstone may indicate that catastrophic events which result in large hydrothermal explosions are an end phase in geyser basin evolution. The Mary Bay hydrothermal explosion crater complex is the largest such complex in Yellowstone, and possibly in the world, with a diameter of 2.8 km in length and 2.4 km in width. It is nested in Mary Bay in the northern basin of Yellowstone Lake, an area of high heat flow and active deformation within the Yellowstone caldera. A sedimentary sequence exposed in wave-cut cliffs between Storm Point and Mary Bay gives insight into the geologic history of the Mary Bay hydrothermal explosion event. The Mary Bay explosion breccia deposits overlie sand above varved lake sediments and are separated locally into an upper and lower unit. The sand unit contains numerous small normal faults and is coextensive with the Mary Bay breccia in its northern extent. This sand may represent deposits of an earthquake-generated wave. Seismicity associated with the earthquake may have triggered the hydrothermal explosion responsible for development of the Mary Bay crater complex. Large hydrothermal explosions are rare events on a human time scale; however, the potential for additional future events of the sort in Yellowstone National Park is not insignificant. Based on the occurrence of large hydrothermal explosion events over the past 16,000 yr, an explosion large enough to create a 100-m-wide crater might be expected every 200 yr.

Wyoming↗

USGS2013

The role of vermetid gastropods in the development of the Florida Middle Ground, northeast Gulf of Mexico

The Florida Middle Ground is a complex of north to northwest trending ridges that lie approximately 180 km northwest of Tampa Bay, Florida. The irregular ridges appear on the otherwise gently sloping West Florida shelf and exhibit between 10-15 m of relief. Modern studies interpret the ridges as remnants of a Holocene coral-reef buildup that today provide a hard substrate for growth of a variety of benthic organisms including hydrocorals, scleractinians, alcyonarians, and algae. Recent rotary coring reveals that the core of the eastern ridge of the Florida Middle Ground complex consists of unconsolidated marine calcareous muddy sand that is capped by a boundstone composed primarily of the sessile vermetid gastropod Petaloconchus sp., and overlays a weathered, fossiliferous limestone. Accelerator Mass Spectrometry radiocarbon ages (uncalibrated) on the 3.6-m thick vermetid worm rock indicate that it developed during a sea-level stillstand in the early Holocene (8,225 ±30-8,910 ± 25 yr B.P.). Our observations suggest that the Florida Middle Ground is a remnant of a series of shore parallel bars that formed in the early Holocene and were capped by a 3.6-m thick unit of vermetid gastropods. During a rapid sea-level rise that began ~8,000 yr B.P. the vermetids growth ceased and the worm rock preserved the ridges structure. Diver observations document that the edges of the ridges are currently being eroded and undermined by biological activity and current action, leading to calving of large capstone blocks.

Florida↗

USGS2020

Beloniformes: Belonidae (Needlefishes) and Hemiramphidae (Halfbeaks)

The order Beloniformes (or Synentognathi) contains two suborders, six families, 37 genera, and about 235 species of atherinomorph fishes (Rosen & Parenti 1981; Collette et al. 1984; Collette 2004). Features common to these fishes include dorsal and anal fins on the rear half of the body, abdominal pelvic fins with six soft rays, no fin spines, lateral line running along the ventral edge of the body, an open nasal pit, and lower pharyngeal bones fused into a triangular plate (leading to the name Synentognathi). Two families, the Flying fishes (Exocoetidae) and the Sauries (Scomberesocidae) are restricted to marine waters but several genera of Needlefishes (Belonidae) and Halfbeaks (Hemiramphidae and Zenarchopteridae) are restricted to fresh waters and other genera contain estuarine, freshwater, and marine species. The family name Belonidae, based on the type genus Belone, means needle in reference to the unusually long and slender jaws of most Needlefishes. Similarly, the family name Hemiramphidae means half-beak, alluding to the conspicuous presence of a long slender lower jar and a short upper jaw in most species. Two species of Needlefishes (Belonidae, Strongylura) and two species of Halfbeaks (Hemiramphidae, Hyporhamphus) occur in North American fresh waters.

Book chapter↗

USGS1969

Glaciation on the continental margin off New England

The Pleistocene glacial limit in the marine environment off New England can be traced by plotting the seaward limit of abundant sandy gravel and the position of shoals. Maximum limit of the last glaciation was probably along an irregular line extending through Nantucket Shoals, across Great South Channel, northern Georges Bank, and at least to the edge of the Scotian Shelf. If, as we assume, glaciers lowered sea level approximately 130 m, the ice margin was probably a subaerial one on Nantucket Shoals and Georges Bank, and it was bordered by outwash and meltwater channels leading away from the ice front. On the Scotian Shelf, the margin may have bordered directly on the ocean, to judge by the lack of shoals and the widespread dispersion of gravel out to the shelf edge. The glaciofluvial nature of the original deposits and marine reworking during the eustatic rise in sea level have made it difficult to recognize ice-contact deposits near the limit of maximum glacial advance. The gravel on shallow banks and ledges is in a bimodal mixture with sand. Association of coarse gravel and sand suggests postdepositional reworking of till by marine processes and removal of silt and clay. Gravel in the Gulf of Maine is mixed with sand, silt, and clay, a mixture characteristic of till.

Connecticut, Maine, Massachusetts, New Hampshire, ↗

USGS2023

Predicting climate change impacts on poikilotherms using physiologically guided species abundance models

Poikilothermic animals comprise most species on Earth and are especially sensitive to changes in environmental temperatures. Species conservation in a changing climate relies upon predictions of species responses to future conditions, yet predicting species responses to climate change when temperatures exceed the bounds of observed data is fraught with challenges. We present a physiologically guided abundance (PGA) model that combines observations of species abundance and environmental conditions with laboratory-derived data on the physiological response of poikilotherms to temperature to predict species geographical distributions and abundance in response to climate change. The model incorporates uncertainty in laboratory-derived thermal response curves and provides estimates of thermal habitat suitability and extinction probability based on site-specific conditions. We show that temperature-driven changes in distributions, local extinction, and abundance of cold, cool, and warm-adapted species vary substantially when physiological information is incorporated. Notably, cold-adapted species were predicted by the PGA model to be extirpated in 61% of locations that they currently inhabit, while extirpation was never predicted by a correlative niche model. Failure to account for species-specific physiological constraints could lead to unrealistic predictions under a warming climate, including underestimates of local extirpation for cold-adapted species near the edges of their climate niche space and overoptimistic predictions of warm-adapted species.

Minnesota↗

USGS1987

Playa-lake basins on the Southern High Plains of Texas and New Mexico: Part II. A hydrologic model and mass-balance arguments for their development.

Hydrologic, geologic, geomorphic, and mass-balance data suggest that most of the ∼30,000 playa lake basins on the Southern High Plains have developed by a combination of dissolution of caliche and piping of surface material into the unsaturated zone rather than by eolian processes as has generally been stated. A conceptual model suggests that particulate organic material, much of which is sorbed on smectite clays, is carried downward from the surface into the unsaturated zone by recharging water. The organic material is oxidized to CO 2 , which dissolves in the water, forms carbonic acid, and dissolves lithologic carbonates. Because organic material is transported and oxidized deep in the unsaturated zone, CO 2 concentrations are much higher at depth than in the soil zone, and recharging water remains thermodynamically subsaturated with respect to carbonates and thus able to dissolve them throughout the unsaturated zone. Dissolution promotes lithologic instability, leading to piping and eluviation of material within the unsaturated zone. Playa basins expand laterally as recharge is concentrated at the edge of the playa floor because of lowered permeability in the center that results from accumulation of clays and other fine sediment. Mass-balance calculations of gas, liquid, and solid fluxes beneath a playa basin suggest that sufficient mass is transported to account for the volume of the depression. Particulate flux is estimated by relating it to the CO 2 flux out of the unsaturated zone. Solute flux is estimated from the difference between input values from the playa lake water and that observed in ground water. Gas flux is measured directly from gas samples at specific depths below the: surface.

Geological Society of America Bulletin↗

USGS2019

Harmful algal blooms

This postcard provides details about "Cyanobacterial Harmful Algal Blooms and U.S. Geological Survey Science Capabilities, " Open File Report 2016-1174 , where you can find details about how U.S. Geological Survey (USGS) scientists use traditional methods and emerging technologies in collaboration with numerous partners to lead a diverse range of studies addressing harmful algal bloom (HAB) issues in water bodies throughout the United States. Cutting-edge USGS research in HABs has advanced scientific understanding and led to practical applications that help protect ecological and human health.

General Information Product↗

USGS1971

Selected fluvial monazite deposits in the southeastern United States

Farther southwest in Georgia, around Griffin and Zebullon, along streams tributary to the Flint River in the monazite belt the flood plains are generally small and discontinuous, and only about 1 percent of the sediment is gravel. The area between Griffin, Zebullon, and the Flint River is underlain by biotite schist and biotite gneiss into which biotite granite has been intruded. Only along one stream, Flat Creek, which drains monazite-bearing granite near Zetella, Ga., are the tenors in monazite even moderately high, but a combination of thick, clayey overburden and discontinuous flood plains make the stream unsuitable for placer mining. Elsewhere in the Flint River area the heavy-mineral concentrates contain less than 1 percent monazite. The southwesternmost area in which reconnaissance of the monazite belt was conducted includes a groups of southwest-flowing tributaries to the Chattahoochee River north of Pine Mountain and near La Grange, Ga. A combination of three characteristics of the alluvium make the area unfavorable for mining: (1) the upper half of the sedimentary sequence is clay and silt, (2) there is scant gravel, and (3) much of the sand is fine grained. Monazite is associated with the Snelson Granite, schists, and gneisses north of the Towaliga fault, but even in this area the tenor of most riffle sediments is only 0.1 to 0.5 pound of monazite per cubic yard, and the average tenor of the alluvium is about 0.2 pound per cubic Yard. Rocks south of the Towaliga fault contain scant monazite. The monazite-bearing area in the drainage basin of the Chattahoochee River has no monazite placers. Evidence from the areas on the Flint and Chattahoochee Rivers shows that streams in western Georgia are a much poorer source of monazite than streams farther to the northeast in Georgia, South Carolina, and North Carolina. Also, the northeastern part of the belt in the drainage basins of the Yadkin and Dan Rivers is a poorer source for monazite than the area between the Savannah and Catawba Rivers, S.C.-N.C. Monazite-bearing crystalline rocks in the western belt contain about 0.06 pound of monazite per cubic yard. Residual soil derived from the crystalline rocks contains about 0.3 to 0.4 pound of monazite per cubic yard, and colluvial sediments formed by sheet-wash from saprolite, residual soil, and, rarely, old stream deposits, have an average of 3.1 pounds of monazite to the cubic yard. The data on the tenors of residual and colluvial deposits are far less comprehensive than those an the quantity of monazite in the crystalline rocks, but the tenors are probably of the correct order of magnitude. Neither the crystalline rocks nor the residual soils are ores of monazite. Because the colluvial deposits are thin and have patch distribution they could not be mined independently, but some colluvium could be stripped from the adjoining hills in conjunction with the mining of alluvial deposits in the valleys. It is most unlikely that alluvial monazite placers have formed in the trunk streams leading southeastward out of the monazite belt. Churn drilling on the Broad and North Tyger Rivers, South Carolina, at the east edge of the belt has shown that the bulk of the alluvium is fine-grained sediment that contains 0.2 to 0.4 pound of monazite per cubic yard--tenors that represent no considerable enrichment over those in the crystalline rocks and residual soils. The probable persistence of predominantly fine-grained alluvium downstream to the Coastal Plain and the certain dilution of monazite-bearing concentrates by the inflow of monazite-free suites of heavy minerals between the belt and the fall line suggest that the trunk streams east of the belt are the least favorable sources for alluvial monazite in the Piedmont?

Open-File Report↗

USGS2018

Evidence that climate sets the lower elevation range limit in a high‐elevation endemic salamander

A frequent assumption in ecology is that biotic interactions are more important than abiotic factors in determining lower elevational range limits (i.e., the “warm edge” of a species distribution). However, for species with narrow environmental tolerances, theory suggests the presence of a strong environmental gradient can lead to persistence, even in the presence of competition. The relative importance of biotic and abiotic factors is rarely considered together, although understanding when one exerts a dominant influence on controlling range limits may be crucial to predicting extinction risk under future climate conditions. We sampled multiple transects spanning the elevational range limit of Plethodon shenandoah and site and climate covariates were recorded. A two‐species conditional occupancy model, accommodating heterogeneity in detection probability, was used to relate variation in occupancy with environmental and habitat conditions. Regional climate data were combined with datalogger observations to estimate the cloud base heights and to project future climate change impacts on cloud elevations across the survey area. By simultaneously accounting for species’ interactions and habitat variables, we find that elevation, not competition, is strongly correlated with the lower elevation range boundary, which had been presumed to be restricted mainly as a result of competitive interactions with a congener. Because the lower elevational range limit is sensitive to climate variables, projected climate change across its high‐elevation habitats will directly affect the species’ distribution. Testing assumptions of factors that set species range limits should use models which accommodate detection biases.

Virginia↗

USGS2000

January 30, 1997 eruptive event on Kilauea Volcano, Hawaii, as monitored by continuous GPS

A continuous Global Positioning System (GPS) network on Kilauea Volcano captured the most recent fissure eruption in Kilauea's East Rift Zone (ERZ) in unprecedented spatial and temporal detail. The short eruption drained the lava pond at Pu'u O' o, leading to a two month long pause in its on-going eruption. Models of the GPS data indicate that the intrusion's bottom edge extended to only 2.4 km. Continuous GPS data reveal rift opening 8 hours prior to the eruption. Absence of precursory summit inflation rules out magma storage overpressurization as the eruption's cause. We infer that stresses in the shallow rift created by the continued deep rift dilation and slip on the south flank decollement caused the rift intrusion.

Geophysical Research Letters↗