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At least 253 records · Page 14Linked to original sources

Contrasting perspectives on the Lava Creek Tuff eruption, Yellowstone, from new U–Pb and 40Ar/39Ar age determinations

The youngest major caldera-forming event at Yellowstone was the ~ 630-ka eruption of the Lava Creek Tuff. The tuff as mapped consists of two major ignimbrite packages (members A and B), linked to widespread coeval fall deposits and formation of the Yellowstone Caldera. Subsequent activity included emplacement of numerous rhyolite flows and domes, and development of two structurally resurgent domes (Mallard Lake and Sour Creek) that accommodate strain due to continual uplift/subsidence cycles. Uplifted lithologies previously mapped on and adjacent to Sour Creek dome were thought to include the ~ 2.08-Ma Huckleberry Ridge Tuff, cropping out beneath Lava Creek Tuff members A and B. Mapped outcrops of this Huckleberry Ridge Tuff material were sampled as welded ignimbrite (sample YR345) on Sour Creek dome, and at nearby Bog Creek as welded ignimbrite (YR311) underlain by an indurated lithic lag breccia containing blocks of another welded ignimbrite (YR324). Zircon near-rim U–Pb analyses from these samples yield weighted mean ages of 661 ± 13 ka (YR345: 95% confidence), 655 ± 11 ka (YR311), and 664 ± 15 ka (YR324) (combined weighted mean of 658.8 ± 6.6 ka). We also studied two samples of ignimbrite previously mapped as Huckleberry Ridge Tuff on the northeastern perimeter of the Yellowstone Caldera, ~ 12 km ENE of Sour Creek dome. Sanidines from these samples yield 40 Ar/ 39 Ar age estimates of 634.5 ± 6.8 ka (8YC-358) and 630.9 ± 4.1 ka (8YC-359). These age data show that all these units represent previously unrecognized parts of the Lava Creek Tuff and do not have any relationship to the Huckleberry Ridge Tuff. Our observations and data imply that the Lava Creek eruption was more complex than is currently assumed, incorporating two tuff units additional to those currently mapped, and which themselves are separated by a time break sufficient for cooling and some reworking. The presence of a lag breccia suggests that a source vent lay nearby (< ~ 3 km) for some of the tuffs and that the Yellowstone Caldera boundary in this area could be reconsidered.

Wyoming

New insight into the origin of manganese oxide ore deposits in the Appalachian Valley and Ridge of northeastern Tennessee and northern Virginia, USA

Manganese oxide deposits have long been observed in association with carbonates within the Appalachian Mountains, but their origin has remained enigmatic for well over a century. Ore deposits of Mn oxides from several productive sites located in eastern Tennessee and northern Virginia display morphologies that include botryoidal and branching forms, massive nodules, breccia matrix cements, and fracture fills. The primary ore minerals include hollandite, cryptomelane, and romanèchite. Samples of Mn oxides from multiple localities in these regions were analyzed using electron microscopy, X-ray analysis, Fourier transform infrared spectroscopy, and trace and rare earth element (REE) geochemistry. The samples from eastern Tennessee have biological morphologies, contain residual biopolymers, and exhibit REE signatures that suggest the ore formation was due to supergene enrichment (likely coupled with microbial activity). In contrast, several northern Virginia ores hosted within quartz-sandstone breccias exhibit petrographic relations, mineral morphologies, and REE signatures indicating inorganic precipitation, and a likely hydrothermal origin with supergene overprinting. Nodular accumulations of Mn oxides within weathered alluvial deposits that occur close to breccia-hosted Mn deposits in Virginia show geochemical signatures that are distinct from the breccia matrices and appear to reflect remobilization of earlier-emplaced Mn and concentration within supergene traps. Based on the proximity of all of the productive ore deposits to mapped faults or other zones of deformation, we suggest that the primary source of all of the Mn may have been deep seated, and that Mn oxides with supergene and/or biological characteristics resulted from the local remobilization and concentration of this primary Mn.

Tennessee, Virginia

Detection and characterization of pulses in broadband seismometers

Pulsing - caused either by mechanical or electrical glitches, or by microtilt local to a seismometer - can significantly compromise the long‐period noise performance of broadband seismometers. High‐fidelity long‐period recordings are needed for accurate calculation of quantities such as moment tensors, fault‐slip models, and normal‐mode measurements. Such pulses have long been recognized in accelerometers, and methods have been developed to correct these acceleration steps, but considerable work remains to be done in order to detect and correct similar pulses in broadband seismic data. We present a method for detecting and characterizing the pulses using data from a range of broadband sensor types installed in the Global Seismographic Network. The technique relies on accurate instrument response removal and employs a moving‐window approach looking for acceleration baseline shifts. We find that pulses are present at varying levels in all sensor types studied. Pulse‐detection results compared with average daily station noise values are consistent with predicted noise levels of acceleration steps. This indicates that we can calculate maximum pulse amplitude allowed per time window that would be acceptable without compromising long‐period data analysis.

Bulletin of the Seismological Society of America

Geologic framework of the Alaska Peninsula, southwest Alaska, and the Alaska Peninsula terrane

The Alaska Peninsula is composed of the late Paleozoic to Quaternary sedimentary, igneous, and minor metamorphic rocks that record the history of a number of magmatic arcs. These magmatic arcs include an unnamed Late Triassic(?) and Early Jurassic island arc, the early Cenozoic Meshik arc, and the late Cenozoic Aleutian arc. Also found on the Alaska Peninsula is one of the most complete nonmetamorphosed, fossiliferous, marine Jurassic sedimentary sections known. As much as 8,500 m of section of Mesozoic sedimentary rocks record the growth and erosion of the Early Jurassic island arc. A thinner, but still thick (as much as 5,400 m), sequence of Tertiary sedimentary rocks that are predominantly continental overlies the Mesozoic section. A brief regression in early Tertiary time on the Alaska Peninsula and granodiorite plutonism in the Shumagin, Semidi, and Sanak Islands was followed by deposition of fluvial and minor marine clastic strata. This was followed by deposition of transgressive marine clastic strata and initiation of the Meshik arc, shown by an areally extensive outpouring of volcanic and volcaniclastic rocks and debris between late Eocene and earliest Miocene time. Late Miocene time was marked by another brief transgression and northwest- to southeast-directed compression, followed by renewed volcanism and plutonism which initiated the modern Aleutian magmatic arc. Extensive glacial and glaciomarine deposits of late Pleistocene age create an extensive lowland physiographic province on the northwest side of the Alaska Peninsula and join isolated mountain masses to the Alaska Peninsula on the southwest. Multiple active volcanoes and volcanic peaks dominate the skyline of the Alaska Peninsula and represent the continuation of magmatic activity that has formed the Aleutian arc since late Miocene time. The Alaska Peninsula has had a long and involved history since Paleozoic time. We propose that the Paleozoic and Mesozoic rocks that constitute much of the Alaska Peninsula be called the Alaska Peninsula terrane. Using the concept of subterranes, we divide the terrane into two distinct but tectonically related subterranes: the Chignik and Iliamna subterranes, which share a limited common geologic history. The Iliamna subterrane has served at most times as a source area for the Chignik subterrane; however, some rock units are in common across the subterranes. The Iliamna and Chignik subterranes are in part separated by the Bruin Bay fault system. The Iliamna subterrane is composed of moderately deformed early Mesozoic marine sedimentary and volcanic rocks and schist, gneiss, and marble of Paleozoic(?) and Mesozoic age, and plutonic rocks of the Alaska-Aleutian Range batholith. Characteristic of the Chignik subterrane are little-deformed, shallow-marine to continental clastic sedimentary rocks ranging in age from Permian to latest Cretaceous. However, deep-marine, volcaniclastic, and calcareous rocks form important components of the older rocks in the subterrane. The two subterranes of the Alaska Peninsula terrane are characterized by radically different structural and metamorphic styles. The nonplutonic rocks of the Iliamna subterrane are characterized by metamorphism up to amphibolite-facies grade and intense folding. In the Chignik subterrane, the structural style is dominated by large, open, en echelon anticlinal structures, normal faulting, and thrust and high-angle reverse faults that have minor displacement in a northwest to southeast direction. In the Outer Shumagin and Sanak Islands, rocks assigned to the Chugach terrane are characterized structurally by tight, generally northeast-trending folds. Dips in these rocks tend to be steep, rarely less than 35&deg;, and overturned beds are locally common. The boundaries separating the Alaska Peninsula terrane from other terranes are commonly indistinct or poorly defined. A few boundaries have been defined at major faults, although the extensions of these faults are speculative through some areas. The west side of the Alaska Peninsula terrane is overlapped by Tertiary sedimentary and volcanic rocks and Quaternary deposits.

Alaska

Potential for deep basin-centered gas accumulation in Hanna Basin, Wyoming

The potential for a continuous-type basin-centered gas accumulation in the Hanna Basin in Carbon County, Wyoming, is evaluated using geologic and production data including mud-weight, hydrocarbon-show, formation-test, bottom-hole-temperature, and vitrinite reflectance data from 29 exploratory wells. This limited data set supports the presence of a hypothetical basin-centered gas play in the Hanna Basin. Two generalized structural cross sections illustrate our interpretations of possible abnormally pressured compartments. Data indicate that a gas-charged, overpressured interval may occur within the Cretaceous Mowry, Frontier, and Niobrara Formations at depths below 10,000 ft along the southern and western margins of the basin. Overpressuring may also occur near the basin center within the Steele Shale and lower Mesaverde Group section at depths below 18,000 to 20,000 ft. However, the deepest wells drilled to date (12,000 to 15,300 ft) have not encountered over-pressure in the basin center. This overpressured zone is likely to be relatively small (probably 20 to 25 miles in diameter) and is probably depleted of gas near major basement reverse faults and outcrops where gas may have escaped. Water may have invaded reservoirs through outcrops and fracture zones along the basin margins, creating an extensive normally pressured zone. A zone of subnormal pressure also may exist below the water-saturated, normal-pressure zone and above the central zone of overpressure. Subnormal pressures have been interpreted in the center of the Hanna Basin at depths ranging from 10,000 to 25,000 ft based on indirect evidence including lost-circulation zones. Three wells on the south side of the basin, where the top of the subnormally pressured zone is interpreted to cut across stratigraphic boundaries, tested the Niobrara Formation and recovered gas and oil shows with very low shut-in pressures.

Bulletin

Effects of thermal variability on broadband seismometers: Controlled experiments, observations, and implications

Isolating seismic instruments from temperature fluctuations is routine practice within the seismological community. However, the necessary degree of thermal stability required in broadband installations to avoid generating noise or compromising the fidelity in the seismic records is largely unknown and likely application dependent. To quantify the temperature sensitivity of seismometers over a broad range of frequencies, we artificially induced local temperature changes on three different models of seismometers to measure the effect of thermal variations on seismometer output. We found that diurnal temperature changes above 0.002°C root mean square (rms) showed significant changes in velocity and acceleration output in comparison to thermally stable reference measurements. We also found that sensor incoherent self‐noise increased with temperature variation; these increases in noise can be modeled as 1 / f "> 1 / f noise (pink noise), and are unlikely to be easily corrected for. These experimental results are compared with the data from Incorporated Research Institutions for Seismology (IRIS) U.S. Geological Survey (USGS) Global Seismographic Network (GSN) station TUC (Tucson, Arizona). This station is well instrumented with temperature sensors and has three different broadband seismometers, each of which uses a different method of thermal isolation. We show that the water bricks and borehole installations give ample temperature attenuation to thermally isolate seismometers from diurnal thermal variability that would compromise seismic data. We find that seismometer installations that provide thermal stability below 0.002°C rms could help to improve long‐period vertical seismic data across the GSN by decreasing temperature‐driven 1 / f "> 1 / f noise.

Bulletin of the Seismological Society of America

Optimizing surveys of fall-staging geese using aerial imagery and automated counting

Ocular aerial surveys allow efficient coverage of large areas and can be used to monitor abundance and distribution of wild populations. However, uncertainty around resulting population estimates can be large due to difficulty in visually identifying and counting animals from aircraft, as well as logistical challenges in estimating detection probabilities. Photographic aerial surveys can mitigate these challenges and can allow flight at higher altitudes to minimize disturbance of birds and improve safety for surveyors. We evaluated a photographic aerial survey that incorporated a systematic sampling design with automated photo capture and processing for fall-staging geese at Izembek Lagoon, Alaska, in 2017–2019. Ocular aerial surveys have been completed at Izembek Lagoon for >40 years. For the new photo survey, we used a commercial system to automatically trigger cameras at preset points. We then applied a machine-learning algorithm trained to automatically identify and count geese in our photos, manually corrected those counts, and quantified the algorithm's accuracy. We translated corrected counts into density and extrapolated mean density across the entire lagoon to estimate total population size for Pacific brant ( Branta bernicla ) and cackling geese ( B. hutchinsii ). The automated algorithm undercounted geese, but successfully identified the small subset of photos containing geese. Manual correction was therefore needed only for photos automatically identified as containing geese, allowing substantial reduction of workload. Manually-corrected, photo-based estimates of Pacific brant and cackling goose population sizes were larger and more precise than ocular estimates in all 3 years. To reduce costs with little penalty for variance around population estimates, the photographic survey design could be optimized by reducing the number of transects to ~67% of the current number while still manually correcting all photos in which the automated algorithm detected geese. Further years of both ocular and photo surveys would be needed to calibrate the photo estimates against the >40-year timeseries of the ocular survey, after which the photo series could successfully guide management of Pacific brant. As technologies continue to advance, we expect photographic surveys with automated counting to be easily implemented and advantageous to many monitoring programs.

Alaska

Avian response to conservation buffers in agricultural landscapes during winter

Native herbaceous vegetation cover along row‐crop field edges (i.e., field buffers) increases breeding densities of many bird species. However, the effect of field buffers on bird species during the non‐breeding season is less understood. We compared density, avian richness, and avian conservation value on row‐crop fields containing buffers strategically designed for wildlife versus fields without buffers in 3 southeastern U.S. states during winter 2007 and 2008. Fields with buffers were enrolled in U.S. Department of Agriculture, Conservation Reserve Program practice Habitat Buffers for Upland Birds (CP33), which targets restoration of northern bobwhite ( Colinus virginianus ) and other upland bird species. Overall species richness did not differ on fields with buffers versus fields without buffers in 2007, but was 29% greater on fields with buffers in 2008. Swamp sparrows ( Melospiza georgiana ), song sparrows ( M. melodia ), field sparrows ( Spizella pusilla ), and red‐bellied woodpeckers ( Melanerpes carolinus ) had greater densities on fields with buffers compared with fields without buffers. Increasing field‐buffer width did not result in greater bird densities. Our results suggest a small change in primary land use (≈7%) produced a disproportionate population response by some grassland‐dependent and woodland bird species during winter. Because field buffers provide a direct source of winter food and cover resources, they may be a pragmatic means to provide critical non‐breeding habitat with little alteration of existing agricultural systems.

Arkansas, Kentucky, Mississippi

Water resources inventory of Connecticut Part 5: lower Housatonic River basin

The 557 square miles of the lower Housatonic River basin in western Connecticut include the basins of two major tributaries, the Pomperaug and Naugatuck Rivers. Nearly all water is derived from precipitation, which averaged 47 inches per year during 1931-60, In this period an additional 570 billion gallons of water per year entered the basin in the main stem of the Housatonic River at Lake Lillinonah, and some water was imported by water-supply systems from outside the basin. Almost half the precipitation--21.6 inches--was lost from the basin by evapotranspiration. Except for small amounts exported, the remainder discharged as runoff and underflow into Long Island Sound. Variations in streamflow at 6 long-term continuous-record gaging stations are summarized in standardized graphs and tables that can be used to estimate streamflow characteristics at other sites. For example, mean flow and two low-flow characteristics, the 7-day annual minimum flow for 2-year and 10-year recurrence intervals, have been determined for many partial-record stations throughout the basin. Of the 37 principal lakes, ponds, and reservoirs in the basin, 6 have usable storage of more than 1 billion gallons. The “maximum safe draft rate” (described in: “Storage of Water in Lakes and Reservoirs”) of the largest of these, Thomaston Reservoir near Thomaston, is 75.6 million gallons per day for the 10-year and 20-year recurrence intervals of annual lowest mean flow. Floods have occurred during every month, at one time or another. The two greatest floods on the Naugatuck River in historical time occurred 2 months apart in 1955. The larger, in August, had a peak of 106,000 cfs (cubic feet per second) at Beacon Falls. Since then, the likelihood of major floods has been considerably reduced by a program of flood control in the basin. Water can be obtained from three aquifers under-lying the basin-stratified drift, till, and bedrock. Stratified drift covers about 16 percent of the basin, mostly in valleys and lowlands, and its saturated part generally ranges in thickness from 10 feet in small valleys to 200 feet in the Housatonic River valley. Its transmissivity ranges from 0 to 47,000 ft 2 /day (feet shared per day). Till, deposited directly by glacial ice, forms a widespread but discontinuous mantle over bedrock in most upland areas and extends beneath stratified drift in lowlands; it ranges in thickness from 0 to 200 feet. The median value of 31 published determinations of hydraulic conductivity of till in southern New England is 0.67 ft/day and ranges from 0.013 to 29 ft/day. Crystalline bedrock underlies most of the basin and is composed principally of granite, gneiss, and schist. Sedimentary volcanic bedrock underlies only the Pomperaug River basin. Regardless of rock type, water is obtained mostly from fractures. Streambed deposits are significant features of the hydrogeologic system because they affect the amount of water from streams and lakes that can be induced to infiltrate aquifers. Based on field tests, characteristic values of vertical hydraulic conductivity of streambed deposits are 0.40 ft/day for fine-grained deposits and 14 ft/day for gravelly deposits. Ground-water supplies generally range in yield from several millions of gallons per day from large well fields to 1 gpm (gallons per minute) from single wells. Large supplies, with yields of 100 gpm or more from individual wells, are most commonly obtained from stratified drift. Yields to be expected from screened wells tapping this aquifer can be calculated by use of a series of graphs in conjunction with estimates of transmissivity and aquifer thickness. The yields of 14 principal ground-water reservoirs are estimated from aquifer characteristics and also from the amount of water that can be obtained from aquifer storage, from interception or runoff, and from infiltration of streamflow at low-flow conditions, using a hypothetical well-field arrangement for each reservoir. It is assumed that induced infiltration is restricted to an amount equal to the 7-day annual minimum stream-flow for a 2-year recurrence interval. Yields range from 1.4 to 15 mgd (million gallons per day) during periods of no recharge, and from 2.0 to 17 mgd during recharge periods. Small to moderate water supplies can be obtained from any of the aquifers under suitable conditions. For example, data from 294 wells in the basin indicate that yields of a few gallons per minute can be obtained from bedrock at most sites. The likelihood of obtaining an adequate domestic supply is slightly greater in granite than in schist and also is greater where the overburden is stratified drift rather than till. Chemical analyses of precipitation samples collected monthly from five stations in the basin during a 9-month period in 1966 show that rainfall is acidic and that sulfate is the dominant anion, probably because of industrial fumes and smoke within and near the basin. Where unaffected by man’s activities, water in the basin is generally low in dissolved-solids concentration, is of the calcium magnesium bicarbonate type, and is soft to moderately hard. In general, streamflow is less mineralized than ground water, particularly when it consists largely of direct runoff. However, streamflow becomes more highly mineralized during low-flow conditions, when most of it consists of more highly mineralized water discharged from aquifers. The median value of dissolved-solids concentration of water at 22 stream sites was 51 mg/1 (milligrams per liter) during high flow, and 68 mg/1 during low flow within the study period. Iron and manganese occur naturally in objectionable concentrations in parts of the basin, particularly in streams draining swamps and in water from bedrock containing iron and manganese-bearing minerals. Man’s activities have degraded the quality of water in streams in much of the basin, except in the Pomperaug subbasin. In the Naugatuck River basin, the degradation in quality is shown by wide and erratic changes in dissolved-solids concentration, excessive amounts of certain trace elements, a low dissolved oxygen content, and abnormally high temperatures. Ground water is degraded principally by induced infiltration of stream water containing chemical wastes, by wastes stored on the ground and by effluents from septic tanks. Below its confluence with the Naugatuck River, much of the Housatonic River and adjoining marshes, wetlands, and aquifers contain salt water. Measurements of specific conductance during low-flow conditions in 1969 indicate that the dissolved-solids concentration of water in the estuary ranged from 210 mg/1 near Twomile Island to 20,000 mg/1 near Long Island Sound. The quantity and quality of water in the basin are satisfactory for a wide variety of uses, and, with suitable treatment, the water may be used for most purposes. In 1967, the total amount of water used in the basin was about 194 billion gallons. About 90 percent of this was used for industrial purposes, and 95 percent of the industrial water was obtained from surface-water sources. In the same year, 17 municipal and private water-supply systems supplied water of satisfactory quality to about three-fourths of the population.

Connecticut

Pop-up archival transmitting (PAT) tags: A method to investigate the migration and behavior of Pacific halibut ( Hippoglossus stenolepis ) in the Gulf of Alaska

Pop-up archival transmitting (PAT) tags provide a fisheries-independent method of collecting environmental preference data (depth and ambient water temperature) and migration distance. In this study, we evaluate the use of pop-up archival transmitting tags as a method to investigate demersal fish. We report the results from eight pop-up archival transmitting tagged Pacific halibut Hippoglossus stenolepis (from 107 to 165 cm FL) that were released in and around Resurrection Bay, Alaska. Commercial fishermen recovered three tags, while five tags transmitted data to Argos satellites. Horizontal migration was not consistent among fish as four Pacific halibut remained in the vicinity of release while the other four traveled up to 358 km from the release site. Vertical movement was not consistent among fish or over time; however, they spent most of their time at depths of 150 to 350 m. The minimum and maximum depths reached by any of the Pacific halibut were 2 m and 502 m, respectively. The fish preferred water temperatures of approximately 6°C, but experienced temperatures between 4.3 and 12.2°C. Light attenuation with depth prevented geolocation software and light sensing hardware from accurately estimating geoposition for the majority of days. The methods, adapted from investigations on large pelagic fish, proved to be effective for studying Pacific halibut in the northern Gulf of Alaska. PAT tags allowed us to obtain high accuracy locations of the fish at the end of the tag deployments as well as preliminary data to identify approximate seasonal locations and to characterize their depth and temperature characteristics. By using PAT tags, we will be able to ensure tag returns during the winter season (which is closed to fishing) and gain valuable biological information even if fish migrate large distances or to unexpected locations.

Alaska Fishery Research Bulletin