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At least 55 records · Page 3Linked to original sources
USGS2020

Classification of oil spill by thicknesses using multiple remote sensors

Satellite Synthetic Aperture Radar (SAR) is an operational tool for monitoring and assessment of oil spills. Satellite SAR has primarily been used to detect the presence/absence of oil, yet its ability to discriminate oil emulsions within a detected oil slick has not been fully exploited. Additionally, one of the challenges in the past has been the ability to deliver strategic information derived from satellite remote sensing in a timely fashion to responders in the field. This study presents methods for the rapid classification of oil types and estimated thicknesses, from which information about thick oil and oil emulsions (i.e., “actionable” oil) can be delivered in an operational timeframe to responders in the field. Experiments carried out at the OHMSETT test facility in New Jersey demonstrate that under specific viewing conditions, a single polarization satellite SAR image can record a signal variance between thick stable emulsions and non-emulsified oil. During a series of field campaigns in the Gulf of Mexico with in situ measurements of oil thickness, multiple satellite data were obtained including fully polarimetric C-band SAR imagery from RADARSAT-2 and multispectral imagery from ASTER and WorldView-2. One campaign included the airborne polarimetric UAVSAR L-band sensor. An oil/emulsion thickness classification product was generated based on RADARSAT-2 polarimetric imagery using entropy and the damping ratio derivations. Herein, we present the classification methods to generate oil thickness products from SAR, validated by sea-truth observations, the multispectral imagery, and the UAVSAR data. We tested the ability to deliver these products with minimum latency to responding vessels via NOAA. During field operations in the Gulf of Mexico, a satellite SAR-based product of oil delineation by relative thickness was delivered to a responding vessel 42 min after the RADARSAT-2 data acquisition. This proof-of-concept test using satellite SAR and multispectral imagery to detect emulsions and deliver a derived information product to a vessel in near-real-time points directly to methods for satellite-based assets to be used in the near future for oil spill tactical response operations.

Louisiana↗
USGS1998

Geologic map of the MTM -85280 quadrangle, Planum Australe region of Mars

The polar deposits on Mars are of great interest because they probably record martian climate variations (Thomas and others, 1992). The area shown on this map includes polar layered deposits with distinct low-albedo features and a sharp boundary between the layered deposits and the moderately cratered unit that forms the floor of Chasma Australe. Detailed mapping of this quadrangle was undertaken to further investigate the geologic relations between the albedo features and the layered deposits and to better constrain the recent geologic history of the south polar region. Dark dunes in the north polar region appear to be derived from erosion of the layered deposits, but the source of dark material in the south polar region is less clear (Thomas and Weitz, 1989). The presence of dark material in the brighter, redder layered deposits is paradoxical (Herkenhoff and Murray, 1990a); resolving this paradox is likely to result in a better understanding of the origin and evolution of the layered deposits and, therefore, the mechanisms by which global climate variations are recorded. Published geologic maps of the south polar region of Mars have been based on images acquired by either Mariner 9 (Condit and Soderblom, 1978; Scott and Carr, 1978) or the Viking Orbiters (Tanaka and Scott, 1987). The extent of the layered deposits mapped previously from Mariner 9 data is different from that mapped using Viking Orbiter images, and the present map agrees with the map by Tanaka and Scott (1987): the floor of Chasma Australe is not mapped as layered deposits. The residual polar ice cap, areas of partial frost cover, the layered deposits, and two nonvolatile surface units - the dust mantle and the dark material - were mapped by Herkenhoff and Murray (1990a) at 1:2,000,000 scale using a color mosaic of Viking Orbiter images. This mosaic and an additional Viking color mosaic were used to confirm the identification of the nonvolatile Amazonian units for this map and to test hypotheses for their origin and evolution. The colors and albedos of these units, as measured in places outside this map area, are presented in table 1 and figure 1. Accurately measuring the color and albedo of the units in this map area was not possible due to low signal/noise in the part of the red/violet mosaic (corrected for atmospheric scattering) that includes this area (Herkenhoff and Murray, 1990a). However, color/albedo unit boundaries in this area are visible in color mosaics that have not been corrected for atmospheric scattering effects. Therefore, while the color and albedo of various units on this map cannot be precisely quantified and compared with the values in table 1 and figure 1, color/albedo units can still be recognized. Because the resolution of the color mosaics is not sufficient to map these units in detail at 1:500,000 scale, contacts between them were recognized and mapped using higher resolution black-and-white Viking and Mariner 9 images. Only two possible impact craters in the layered deposits have been found in the area mapped; both are slightly elongate rather than circular. One, 1.6 km in diameter at lat 86.6° S., long 268°, was recognized by Plaut and others (1988); the other, about 3 km in diameter, is at lat 82.8° S., long 277°. Although the crater statistics are poor (only 16 likely impact craters found in the entire south polar layered deposits), these observations generally support the conclusions that the south polar layered deposits are Late Amazonian in age and that some areas have been exposed for at least 120 million years (Plaut and others, 1988; Herkenhoff and Murray, 1992, 1994). However, the recent cratering flux on Mars is poorly constrained, so inferred ages of surface units are uncertain. The Viking Orbiter 2 images used to construct the base were taken during the southern summer of 1977, with resolutions no better than 180 m/pixel. (The "less than 100 m per picture element" in Notes on Base of the controlled photomosaic base [U.S. Geological Survey, 1986] is incorrect.) A digital mosaic of Mariner 9 images was also constructed to aid in mapping. The Mariner 9 images were taken during the southern summer of 1971-72 and have resolutions as high as 90 m/pixel. However, usefulness of the Mariner 9 mosaic is limited by incomplete coverage and atmospheric dust opacity.

IMAP↗
USGS2007

Two middle Pleistocene glacial-interglacial cycles from the Valle Grande, Jemez Mountains, northern New Mexico

A long-lived middle Pleistocene lake formed in the Valle Grande, a large moat valley of the Valles caldera in northern New Mexico, when a post-caldera eruption (South Mountain rhyolite) dammed the drainage out of the caldera. The deposits of this lake were cored in May 2004 (GLAD5 project, hole VC-3) and 81 m of mostly lacustrine silty mud were recovered. A tentative chronology has been established for VC-3 with a basal tephra Ar-Ar date of 552 +/- 3 ka, a correlation of major climatic changes in the core with other long Pleistocene records (deep sea oxygen isotope records and long Antarctic ice core records), and the recognition of two geomagnetic field polarity events in the core which can be correlated with globally recognized events. This record spans a critical interval of the middle Pleistocene from MIS 14 (552 ka) to MIS 10 (~360 ka), at which time the lacustrine sediments filled the available accommodation space in the caldera moat. Multiple analyses, including core sedimentology and stratigraphy, sediment density and rock magnetic properties, organic carbon content and carbon isotope ratios, C/N ratios, and pollen content reveal two glacial/interglacial cycles in the core (MIS 14 to MIS 10). This record includes glacial terminations V and VI and complete sections spanning interglacials MIS 13 and MIS 11. In the VC-3 record, both of these interglacials are relatively long compared with the intervening glacials (MIS 14 and MIS 12), and interglacial MIS 13 is significantly muted in amplitude compared with MIS 11. These features are similar to several other mid-Pleistocene records. The glacial terminations are quite abrupt in this record with notable changes in sedimentation, organic carbon content, C/N ratios and watershed vegetation type. Termination V is the largest climate change evident in this part of the middle Pleistocene. The glacial inceptions tend to be more gradual, on the order of a few thousand years.

New Mexico↗
USGS1977

Paleomagnetic poles and polarity zonation from Cambrian and Devonian strata of Arizona

Basal Paleozoic Tapeats Sandstone (Early and Middle Cambrian) in northern and central Arizona exhibits mixed polarity and a low-latitude paleomagnetic pole. Carbonates of Middle and early Late Cambrian age, and directly superposed carbonate and carbonate-cemented strata of latest Middle(?) and early Late Devonian age, are characterized by reversed polarity and high-latitude poles. The high-latitude Middle Cambrian pole, which appears to record a large but brief excursion of the polar wandering path, is considered provisional pending additional work. The Devonian data from Arizona indicate that a shift of the pole to a “late Paleozoic” position had occurred by Middle Devonian time.

Arizona↗
USGS2012

The Steens Mountain (Oregon) geomagnetic polarity transition: 3. Its regional significance

Study of the variations of direction and intensity of the geomagnetic field as recorded by the Miocene lava flows on Steens Mountain, southeastern Oregon, has resulted in a detailed description of total field behavior during a reversal in polarity. In addition to information about the polarity reversal itself, the detailed paleomagnetic record includes several thousand years of geomagnetic history preceding and following the polarity transition at 15.5 Ma. In order to test the feasibility of using this record as a means of correlation in this part of the western United States, comparisons are made of reconnaissance and previously published paleomagnetic records obtained from what has been thought to be the Steens Basalt or rocks of equivalent age. Despite the fact that many of these earlier studies were not done in detail and were not intended for correlation purposes, convincing similarities among some of the records are evident. The Steens Basalt paleomagnetic record does, indeed, have potential as a correlation tool during this time of widespread basaltic volcanism. Additionally, paleomagnetic data from flows that were sampled in detail yield a middle Miocene paleomagnetic pole at 88.3°N, 209.0° (α 95 = 6.3°) for the High Lava Plains of Oregon. This pole position is statistically indistinguishable from the earth's rotational axis and implies that no tectonic rotation of this region has occurred since these lava flows were erupted. Data from selected sites within the coeval part of the Columbia River Basalt Group yield a paleomagnetic pole at 88.7°N, 171.6°E (α 95 = 4.0°). The Columbia River Basalt Group pole is statistically indistinguishable from either the rotational axis or from the High Lava Plains pole. These findings indicate no post‐20 Ma differential rotation between south‐eastern Washington and south‐central Oregon, in contrast to previous interpretations.

Journal of Geophysical Research B: Solid Earth↗
USGS2024

A seismic nodal deployment to understand magmatic structure in the vicinity of the Pahala earthquake swarm

In summer-fall 2022, 80 three-component SmartSolo IGU-BD3C-5 nodal seismometers were deployed surrounding the Pāhala seismic swarm on the Island of Hawaiʻi, with the goal of improving seismicity catalogs, and seismic velocity images of the crust and upper mantle in this region. The Pāhala swarm, located south of Mauna Loa and Kīlauea, has been the site of a multiyear sustained swarm of seismicity at depths of ~ 25 – 40 km, with order of magnitude increases in rate in 2015, and then again in 2019. This seismicity is possibly related to the input of magma from the mantle plume below, which may then be subsequently transported to volcanic edifices. However, these processes remain enigmatic, in part due to a lack of precise earthquake locations and seismic velocity models in this region. Here we provide an overview of the deployment, an assessment of the quality of the collected data, and discuss the viability of the dataset for local earthquake relocation, tomography, and teleseismic receiver functions. Through comparisons with proximal permanent broadband and short period instruments, we find that the nodes produce high quality data, particularly at periods shorter than 5 s, although we find, document, and correct discrepancies with the gain and polarities of the instruments. We successfully record signals from teleseismic earthquakes, even at periods longer than 5 s (the corner of the flat response of the nodes). We also record local earthquakes, including details related to source characteristics. This indicates that the data is likely to prove useful for investigations using both local and teleseismic earthquake signals to better understand the connections between the deep and shallow magmatic systems of Hawaiʻi. While this deployment provides a snapshot in time, its success may provide a useful benchmark for future studies as the volcanic systems of Hawaiʻi continue to evolve in the future.

Hawaii↗
USGS1978

Geologic map of the Mare Australe area of Mars

The south polar region of Mars is among the most geologically diverse on the planet. The areas is within the heavily cratered hemisphere of Mars bu t is distinguished by a variety of younger, regionally extensive deposits and a n a ssemblage of unique erosional forms. The spectrum of units varies from the oldest to the youngest on the planet. The oldest unit, typif ying t h e cratered hemisphere, is the material of ancient large craters, most of which have undergone advanced degradation. These ancient crater materials are overlain by a variety of regional deposits, including extensive intercrater debris blankets, r i dged volcanic flows, and massive eolian deposits that eroded to form complex cliff-rimmed pits. In the central zone of the polar region, south of roughly 75 ˚ S., these depositional units are, in turn, unconformably overlain by a t remendous sedimentary complex 1,500-2,000 km in diameter, consisting of 40 or more regularly spaced horizontal starta . Each stratum retains apparently uniform thickness (several tons of meters) over hundreds of kilometers; erosional unconformities between starta have not as yet been identified. Resting on the uppermost surface of this layered terrain is the perm anent residual polar ice cap. This complex stratigraphic record may ultimately hold the keys t o the initial atmospheric evolution, climatological fluctuations, and the history, budget, and mobility of wate r on the planet.

IMAP↗
USGS2015

A global satellite assisted precipitation climatology

Accurate representations of mean climate conditions, especially in areas of complex terrain, are an important part of environmental monitoring systems. As high-resolution satellite monitoring information accumulates with the passage of time, it can be increasingly useful in efforts to better characterize the earth's mean climatology. Current state-of-the-science products rely on complex and sometimes unreliable relationships between elevation and station-based precipitation records, which can result in poor performance in food and water insecure regions with sparse observation networks. These vulnerable areas (like Ethiopia, Afghanistan, or Haiti) are often the critical regions for humanitarian drought monitoring. Here, we show that long period of record geo-synchronous and polar-orbiting satellite observations provide a unique new resource for producing high resolution (0.05°) global precipitation climatologies that perform reasonably well in data sparse regions. Traditionally, global climatologies have been produced by combining station observations and physiographic predictors like latitude, longitude, elevation, and slope. While such approaches can work well, especially in areas with reasonably dense observation networks, the fundamental relationship between physiographic variables and the target climate variables can often be indirect and spatially complex. Infrared and microwave satellite observations, on the other hand, directly monitor the earth's energy emissions. These emissions often correspond physically with the location and intensity of precipitation. We show that these relationships provide a good basis for building global climatologies. We also introduce a new geospatial modeling approach based on moving window regressions and inverse distance weighting interpolation. This approach combines satellite fields, gridded physiographic indicators, and in situ climate normals. The resulting global 0.05° monthly precipitation climatology, the Climate Hazards Group's Precipitation Climatology version 1 (CHPclim v.1.0, http://dx.doi.org/10.15780/G2159X ), is shown to compare favorably with similar global climatology products, especially in areas with complex terrain and low station densities.

Earth System Science Data↗
USGS1990

Seasonal movements of adult female polar bears in the Bering and Chukchi seas

Ten adult female polar bears ( Ursus maritimus ) were fitted with satellite telemetry collars during March 1986 in the Kotzebue Sound area of the Chukchi Sea. During March-April 1987, 2 of these bears were refitted with satellite telemetry collars and an additional 10 adult females were collared in the northern Bering and eastern Chukchi seas. Data for 1,560 point locations recorded through May 1988 indicated that female polar bears in the Bering and Chukchi seas were resident in western Alaskan waters from November through March, then moved northward with the receding pack ice during April and May. They remained in the northern and northwestern Chukchi Sea during June through September, often adjacent to the Soviet coastline. Satellite telemetry data indicated that 4 females marked in Alaskan waters of the Chukchi Sea apparently denned in the vicinity of Wrangel Island during winter 1987/1988. Denning in American territory of bears marked in the Chukchi and Bering seas has not been documented using satellite telemetry data. Some polar bears moved from the Chukchi Sea into the western Beaufort Sea during summer and fall, then returned to the Chukchi and Bering seas the following winter. Movements of bears from the Chukchi Sea into the central or eastern Beaufort Sea were not documented through spring 1988. These data document that polar bears occuring in the Bering and Chukchi seas are shared internationally between the United States and the Soviet Union.

Alaska↗
USGS2017

Geochronology and paleoenvironment of pluvial Harper Lake, Mojave Desert, California, USA

Accurate reconstruction of the paleo-Mojave River and pluvial lake (Harper, Manix, Cronese, and Mojave) system of southern California is critical to understanding paleoclimate and the North American polar jet stream position over the last 500 ka. Previous studies inferred a polar jet stream south of 35°N at 18 ka and at ~ 40°N at 17–14 ka. Highstand sediments of Harper Lake, the upstream-most pluvial lake along the Mojave River, have yielded uncalibrated radiocarbon ages ranging from 24,000 to > 30,000 14 C yr BP. Based on geologic mapping, radiocarbon and optically stimulated luminescence dating, we infer a ~ 45–40 ka age for the Harper Lake highstand sediments. Combining the Harper Lake highstand with other Great Basin pluvial lake/spring and marine climate records, we infer that the North American polar jet stream was south of 35°N about 45–40 ka, but shifted to 40°N by ~ 35 ka. Ostracodes ( Limnocythere ceriotuberosa ) from Harper Lake highstand sediments are consistent with an alkaline lake environment that received seasonal inflow from the Mojave River, thus confirming the lake was fed by the Mojave River. The ~ 45–40 ka highstand at Harper Lake coincides with a shallowing interval at downstream Lake Manix.

California↗
USGS2005

A 40,000-year woodrat-midden record of vegetational and biogeographical dynamics in north-eastern Utah

Aim A conspicuous climatic and biogeographical transition occurs at 40-45° N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time-scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat ( Neotoma ) middens to the south]. To overcome these limitations, we are extending the woodrat-midden record northward into the lowlands of the central Rocky Mountains. Location Woodrat middens were collected from crevices and rock shelters on south-facing slopes of Dutch John Mountain (2000-2200 m, 40°57′ N, 109°25′ W), situated on the eastern flanks of the Uinta Mountains in north-eastern Utah. The site is near the regional limits for Pinus ponderosa, P. edulis, P. contorta, Cercocarpus ledifolius var. intricatus, Abies concolor, Ephedra viridis and other important western species. Methods We analysed pollen and plant macrofossils from the 40,000-year midden sequence. The middens represent brief, depositional episodes (mostly years to decades). Four middens represent the early to full-glacial period (40,000–18,000 cal-yr bp), eight middens are from the late-glacial/early Holocene transition (13,500–9000 cal yr bp), and 33 middens span the mid-to-late Holocene (last 7500 years). Temporal density of our Holocene middens (one every c. 210 years) is comparable with typical Holocene pollen sequences from lake sediments. Results Early to full-glacial assemblages are characterized by low diversity and occurrence of montane conifers ( Picea pungens, Pseudotsuga menziesii, P. flexilis, Juniperus communis ) absent from the site today. Diversity increases in the late-glacial samples with the addition of J. scopulorum, J. horizontalis, C. montanus, C. ledifolius var. intricatus and mesic understory species. The coniferous trees and J. communis declined and J. osteosperma appeared during the late-glacial/Holocene transition. Juniperus osteosperma populations have occupied the site throughout the Holocene. Pinus ponderosa was established by 7500 cal-yr bp, and has occurred at least locally ever since. Montane conifers and J. horizontalis persisted until c. 5500 cal-yr bp. The signature events of the late Holocene were the invasions of P. edulis and Ephedra viridis and establishment of pinyon–juniper woodland in the last 800 years. Main conclusions The Dutch John Mountain midden record adds to an emerging picture in which mid-elevation conifers ( P. flexilis, Pseudotsuga menziesii, Picea pungens, J. scopulorum, J. communis ) dominated vegetation over a wide area of the Colorado Plateau and adjacent Rocky Mountains. Rather than being fragmented, as often assumed in phylogeographical studies, these species had broader and more-connected distributions than they do in the region today. Paradoxically, subalpine conifers ( Picea engelmannii, A. lasiocarpa ) occurred at higher elevations to the south, possibly representing declining precipitation from south to north owing to southward displacement of the polar jet stream. The Dutch John Mountain record displays a series of extinction and invasion events. Most of the extinctions were local in scale; nearly all constituents of fossil midden assemblages occur within a few kilometres of Dutch John Mountain, and some occur at least locally on its slopes. The sole exception is J. horizontalis , which is regionally extinct. In contrast to extinctions, Holocene invasions were regional in scale; J. osteosperma, P. ponderosa, P. edulis and Ephedra viridis immigrated from glacial-age source populations far to the south.

Utah↗
USGS2021

Seal body condition and atmospheric circulation patterns influence polar bear body condition, recruitment, and feeding ecology in the Chukchi Sea

Polar bears ( Ursus maritimus ) are experiencing loss of sea ice habitats used to access their marine mammal prey. Simultaneously, ocean warming is changing ecosystems that support marine mammal populations. The interactive effects of sea ice and prey are not well understood yet may explain spatial‐temporal variation in the response of polar bears to sea ice loss. Here, we examined the potential combined effects of sea ice, seal body condition and atmospheric circulation patterns on the body condition, recruitment, diet, and feeding probability of 469 polar bears captured in the Chukchi Sea, 2008‐2017. The body condition of ringed seals ( Pusa hispida ), the primary prey of females and subadults, was related to dietary proportions of ringed seal, feeding probability, and the body condition of females and cubs. In contrast, adult males consumed more bearded seals ( Erignathus barbatus ) and exhibited better condition when bearded seal body condition was higher. The litter size, number of yearlings per adult female, and the condition of dependent young were higher following winters characterized by low Arctic Oscillation (AO) conditions, consistent with a growing number of studies. Body condition, recruitment, and feeding probability were either not associated or negatively associated with sea ice conditions, suggesting that, unlike some subpopulations, Chukchi Sea bears are not currently limited by sea ice availability. However, spring sea ice cover declined 2% per year during our study reaching levels not previously observed in the satellite record and resulting in the loss of polar bear hunting and seal pupping habitat. Our study suggests that the status of ice seal populations is likely an important factor that can either compound or mitigate the response of polar bears to sea ice loss over the short‐term. In the long‐term, neither polar bears nor their prey are likely robust to limitless loss of their sea ice habitat.

Alaska↗
USGS2012

Paleomagnetic evidence for the timing of collapse and resurgence of the Lake City Caldera, San Juan Mountains, Colorado

Rocks of the 23.1‐m.y.‐old Lake City caldera consist of the compositionally zoned Sunshine Peak Tuff, postcollapse intracaldera lava flows, and resurgent quartz syenite intrusions. Declinations of reversely magnetized ( I = −45° to −75°) Sunshine Peak Tuff change from easterly ( D = 93°–130°) throughout most of the tuff to southerly ( D = 195°–207°) within the late eruptive phases. The postcollapse lava flows are also reversely magnetized, and their emplacement appears to have spanned resurgence of the caldera. In contrast, the uppermost levels of the resurgent intrusion record two distinct components of magnetization: a reversed component isolated by thermal demagnetization typically at temperatures greater than 400°C and a normal component defined by thermal demagnetization at lower temperatures. A baked‐contact test implies that emplacement and initial cooling of the intrusion occurred during a time of reversed polarity and that continued cooling at lower blocking temperatures took place during normal polarity. Assuming that the reversed directions of the extrusive and intrusive rocks record a single period of reversed polarity as suggested by the paleomagnetic and radiometric age data, the time for caldera development (from eruption of the ash flow tuffs to emplacement of the resurgent intrusion) was less than about 300,000 years on the basis of best estimates of durations of reversed polarities in the early Miocene. The estimated 300,000‐year time span for the development of the Lake City caldera is very close in duration to the radiometrically determined time spans of much younger (Pleistocene) calderas having similar dimensions and similar volumes of erupted material.

Colorado↗
USGS1992

Imaging of Venus from Galileo: Early results and camera performance

Three images of Venus have been returned so far by the Galileo spacecraft following an encounter with the planet on UT February 10, 1990. The images, taken at effective wavelengths of 4200 and 9900 A??, characterize the global motions and distribution of haze near the Venus cloud tops and, at the latter wavelength, deep within the main cloud. Previously undetected markings are clearly seen in the near-infrared image. The global distribution of these features, which have maximum contrasts of 3%, is different from that recorded at short wavelengths. In particular, the "polar collar," which is omnipresent in short wavelength images, is absent at 9900 A??. The maximum contrast in the features at 4200 A?? is about 20%. The optical performance of the camera is described and is judged to be nominal. ?? 1992.

Advances in Space Research↗
USGS1996

Expanded record of Quaternary oceanographic change: Amerasian Arctic Ocean

Four sediment cores collected from the Northwind and Mendeleyev ridges, Arctic Ocean, from 1089 m to 1909 m water depth, provide an oceanographic record extending back into the Matuyama reversed polarity chron. Benthic foraminiferal analyses show four prominent assemblage zones: Bolivina arctica , Cassidulina teretis , Bulimina aculeata , and Oridorsalis tener from the upper Matuyama reversed polarity chronozone through the Brunhes normal polarity chronozone. These assemblage zones represent depth-dependent benthic foraminiferal biofacies changes associated with oceanographic events that occurred in the Amerasian basin at ∼780 and 300 ka, and indicate oceanographic influence from the North Atlantic. Recognition of these benthic assemblage zones in Arctic cores from the Alpha Ridge indicates that the benthic foraminiferal zonations in intermediate to deep water (>1000 m) Arctic cores may be more useful than preexisting lithostratigraphic zonations and should provide important information pertaining to the Quaternary paleoceanographic evolution of the Arctic Ocean.

Geology↗
USGS2005

Geology and insolation-driven climatic history of Amazonian north polar materials on Mars

Mariner 9 and Viking spacecraft images revealed that the polar regions of Mars, like those of Earth, record the planet's climate history. However, fundamental uncertainties regarding the materials, features, ages and processes constituting the geologic record remained. Recently acquired Mars Orbiter Laser Altimeter data and Mars Orbiter Camera high-resolution images from the Mars Global Surveyor spacecraft and moderately high-resolution Thermal Emission Imaging System visible images from the Mars Odyssey spacecraft permit more comprehensive geologic and climatic analyses. Here I map and show the history of geologic materials and features in the north polar region that span the Amazonian period (???3.0 Gyr ago to present). Erosion and redeposition of putative circumpolar mud volcano deposits (formed by eruption of liquefied, fine-grained material) led to the formation of an Early Amazonian polar plateau consisting of dark layered materials. Crater ejecta superposed on pedestals indicate that a thin mantle was present during most of the Amazonian, suggesting generally higher obliquity and insolation conditions at the poles than at present. Brighter polar layered deposits rest unconformably on the dark layers and formed mainly during lower obliquity over the past 4-5 Myr (ref. 20). Finally, the uppermost layers post-date the latest downtrend in obliquity <20,000 years ago. ?? 2005 Nature Publishing Group.

Nature↗
USGS1997

Geochronologic and paleomagnetic evidence defining the relationship between the Miocene Hiko and Racer Canyon tuffs, eccentric outflow lobes from the Caliente caldera complex, southeastern Great Basin, USA

Outflow sheets of the Hiko tuff and the Racer Canyon tuff, which together extend over approximately 16 000 km 2 around the Caliente caldera complex in southeastern Nevada, have long been considered to be products of simultaneous or near-simultaneous eruptions from inset calderas in the west and east ends, respectively, of the caldera complex. New high-precision 40 Ar/ 39 Ar geochronology and paleomagnetic data demonstrate that emplacement of the uppermost part of the Racer Canyon tuff at 18.33±0.03 Ma was nearly synchronous with emplacement of the single outflow cooling unit of the much larger overlying Hiko tuff at 18.32±0.04 Ma. Based on comparison with the geomagnetic polarity time scale derived from the sea-floor spreading record, we conclude that emplacement of the first of several outflow cooling units of the Racer Canyon tuff commenced approximately 0.5 m.y. earlier. Only one paleomagnetic polarity is found in the Hiko tuff, but at least two paleomagnetic reversals have been found in the Racer Canyon tuff. The two formations overlap in only one place, at and near Panaca Summit northeast of the center of the Caliente caldera complex; here the Hiko tuff is stratigraphically above the Racer Canyon tuff. This study demonstrates the power of combining 40 Ar/ 39 Ar and paleomagnetic data in conjunction with phenocryst compositional modes to resolve problematic stratigraphic correlations in complex ash-flow sequences where use of one method alone might not eliminate ambiguities.

Bulletin of Volcanology↗
USGS1977

1976 preliminary handbook for U.S.G.S. Central California microearthquake network

This Handbook is a preliminary version of the 1976 addition to the Handbook for U.S.G.S. Central California Microearthquake Network, 1969 to 1975 (Houck and others, 1976). This report is similar in form and content to that report, except that tables on active stations, polarity source events, and saved tapes have not been included. It is anticipated that these tables and others will be included in an overall compilation of data on the Central California Microearthquake Network which will be published in late 1977. This report should provide adequate 1976 information for most Handbook users in the interim. The data in this report should be considered preliminary. They have not been proofread and verified to the degree which would be proper for a final report. The tape configuration and station finder data are probably quite reliable, and the film configuration data are probably almost as good. Film polarity data are sparse for some time periods and questionable readings have not yet been rechecked. A major realignment of stations on film was made from 9 - 12 September. Station finder records for this period assume that the station trace position changed at the time of its appearance in the new position. Actually, some stations may have been recorded in two positions or not at all during part of the realignment period. Use station finder records for this period with caution. On 30 January the polarities of ANV, BKO, ELG, LTW, LWR, MIX, PNM and PNP were changed at the Develocorder.

Open-File Report↗