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At least 379 records · Page 21Linked to original sources
USGS2012

The Steens Mountain (Oregon) geomagnetic polarity transition: 1. Directional history, duration of episodes, and rock magnetism

The thick sequence of Miocene lava flows exposed on Steens Mountain in southeastern Oregon is well known for containing a detailed record of a reversed‐to‐normal geomagnetic polarity transition. Paleomagnetic samples were obtained from the sequence for a combined study of the directional and intensity variations recorded; the paleointensity study is reported in a companion paper. This effort has resulted in the first detailed history of total geomagnetic field behavior during a reversal of polarity. A comparison of the directional variation history of the reversed and normal polarity intervals on either side of the transition with the Holocene record has allowed an estimate of the duration of these periods to be made. These time estimates were then used to calculate accumulation rates for the volcanic sequence and thereby provide a means for estimating time periods within the transition itself. The polarity transition was found to consist of two phases, each with quite different characteristics. At the onset of the first phase, a one‐third decrease in magnetic field intensity may have preceded the first intermediate field directions by about 600 years. Changes in field direction were confined near the local north‐south vertical plane when the actual reversal in direction occurred and normal polarity directions may have been attained within 550±150 years. The end of the first phase of the transition was marked by a brief (possibly 100–300 years) period with normal polarity and a pretransitional intensity which suggests a quasi‐normal dipole field structure existed during this interval. The second phase of the transition was characterized by a return to very low field intensities with the changes in direction describing a long counterclockwise loop in contrast to the earlier narrowly constrained changes. This second phase lasted 2900±300 years, and both normal directions and intensities were recovered at the same time. Both directional and intensity data document very erratic geomagnetic field behavior during the polarity transition. Changes in magnetic field direction were variable and occurred either (1) in a regular, progressive manner, (2) with sudden, extremely rapid angular changes (58°±21°/year), or (3) with little or no movement for periods of the order of 600±200 years. Changes in magnetic intensity occurred in a like manner and were sometimes correlated with changes in direction, but during other periods both directional and intensity changes occurred independently. Directional changes following the polarity transition occurred in a seemingly normal manner, although intensity fluctuations attest to some instability of the newly reestablished dipole.

Journal of Geophysical Research B: Solid Earth↗
USGS1980

Water-resources investigations of the U.S. Geological Survey in Colorado; fiscal year 1980

Water-resources data-collection activities for October 1, 1979, through September 30, 1980, are summarized for Colorado and bordering States. Fifty-four interpretive hydrologic investigations include: 9 statewide investigations, 6 regional investigations, 11 investigations in the Missouri River basin, 7 investigations in the Arkansas River basin, 3 investigations in the Rio Grande basin, 16 investigations in the Colorado River basin, and 2 multistate investigations. The summaries of the investigations consist of a map showing the location of the areas of investigations and a brief description of the investigation's purpose, objective, approach, progress, and plans.

Colorado↗
USGS1995

National Water-Quality Assessment Program— Pesticides in the Trinity River Basin study unit, Texas, 1968-91

The Trinity River Basin National Water Quality Assessment (NAWQA) study-unit staff began assessment activities in 1991, and in 1992, undertook a retrospective review of existing data on pesticides. The main purpose of this review was to aid in the design of a pesticide-sampling network for the study unit. The review consisted of the compilation, screening, and analysis of available pesticide-sample information. In addition, important environmental factors, which influence the occurrence and distribution of pesticides in the study unit, were identified and compiled. A report of this review and analysis will be released in 1995 (Ulery and Brown, in press). This fact sheet provides a brief overview of significant findings.

Texas↗
USGS1938

Floods of Ohio and Mississippi Rivers, January-February 1937, with a section on the Flood deposits of the Ohio River, January-February 1937

In January and February 1937 the Ohio and mid-Mississippi Rivers experienced floods which, over reaches many hundreds of miles in length, exceeded all previously recorded stages. When measured by the loss of life and property, extent of damage, and general disruption of human activities, these floods constituted a major catastrophe. The floods were caused by a succession of heavy rainstorms that began late in December 1936 and continued nearly to the end of the following January. Although the storms covered a considerable part of the lower Mississippi River Basin and almost the entire Ohio River Basin, the center of heaviest precipitation was in the middle and lower portions of the Ohio River Valley. The total storm period can be subdivided into several individual storms, which were more or less clearly demarked by short intervening periods of little or no precipitation. Although the individual storm periods were the same or nearly the same over wide areas, their subdivisions were somewhat different in the most widely separated parts of the affected areas, with intermediate gradations in the intervening areas. The heaviest rainfall--that of January 20 to 25--was centered in the lower Ohio Valley, and, falling as it did upon a region with soil saturated and waterways already running full, it had the effect of producing extreme floods. The small quantity of snow on the ground over the higher eastern parts of the area at the beginning of the storm period disappeared in a short time. Some of the precipitation occurred in the form of snow, but this snow and the associated cold weather were much less significant in their influence on the floods than in the misery and discomfort they caused to ill-sheltered flood refugees and flood-bound people. Sequence and time of the storms were such that in the upper and smaller tributary basins the associated flood rises tended to clear to a notable degree before the-next flood rises came; hence many of these tributaries were at no time in extreme flood. In the lower reaches of the largest tributaries, and especially on the middle and lower reaches of the Ohio River, there were extreme and almost continuously increasing accumulations of run-off, which culminated in the region of Louisville, Ky., in stages 10 or 11 feet higher than any previously known. The precipitation was heaviest in the Ohio River Basin, and the flood in the Mississippi River, like other notable floods of the past, was caused largely by the extraordinary contributions from the Ohio River. The river stages exceeded those previously recorded for the lower 700 miles on the Ohio River and for 250 miles .on the Mississippi River below the Ohio. At Cairo, Ill., at the mouth Of the Ohio River, the river stage was higher for a period of 19 days, from January 24 to February 11, than at any previous time on record. The height above previous flood stages diminished materially as the flood progressed down the Mississippi. The mean precipitation ever the Ohio River Basin during the storm period was. 12.85 inches. The snow on the ground at the beginning of the period is estimated to have been equivalent to a mean depth of 0.10 inch of water over the basin. Out of the total precipitation 8.9 inches appeared as flood flow. On January 26 the computed volume of water in the stream channels of the Ohio River Basin was 56,000,000 acre-feet, equivalent to a depth of 5.1 inches over the drainage basin. The maximum discharge of the Ohio River at its mouth was 1,880,000 second-feet on February 1. On February 2, the day of the crest stage at the mouth of the Ohio, the computed volume of water on the surface channel system was equivalent to a depth of 3.7 inches over the drainage basin, of which 2.4 inches was in the 337-mile reach of the Ohio River between Louisville, Ky., and the mouth. This water-supply paper presents records of stage and discharge for the period including the floods at about 250 measurement stations, records of stage and discharge for the period including the floods at about 250 measurement stations, records of storage in many reservoirs, a summary of peak discharges with comparative data for other floods at about 470 measurement points, and tables showing crest stages along an aggregate length of stream channel for 5,000 miles. The report also includes basic information in regard to the weather associated with the floods, results of detailed studies of the rainfall and run-off, analyses of the volume of flood waters'in the surface channel systems during the progress of the floods, and many other kinds of flood information. Following the main flood report is a brief report entitled "Flood" deposits of the Ohio River, January-February 1937, a study of sedimentation." An abstract of that report is presented on page 693.

Ohio River, Mississippi River↗
USGS2018

Lake sediment fecal and biomass burning biomarkers provide direct evidence for prehistoric human-lit fires in New Zealand

Deforestation associated with the initial settlement of New Zealand is a dramatic example of how humans can alter landscapes through fire. However, evidence linking early human presence and land-cover change is inferential in most continental sites. We employed a multi-proxy approach to reconstruct anthropogenic land use in New Zealand’s South Island over the last millennium using fecal and plant sterols as indicators of human activity and monosaccharide anhydrides, polycyclic aromatic hydrocarbons, charcoal and pollen as tracers of fire and vegetation change in lake-sediment cores. Our data provide a direct record of local human presence in Lake Kirkpatrick and Lake Diamond watersheds at the time of deforestation and a new and stronger case of human agency linked with forest clearance. The first detection of human presence matches charcoal and biomarker evidence for initial burning at c. AD 1350. Sterols decreased shortly after to values suggesting the sporadic presence of people and then rose to unprecedented levels after the European settlement. Our results confirm that initial human arrival in New Zealand was associated with brief and intense burning activities. Testing our approach in a context of well-established fire history provides a new tool for understanding cause-effect relationships in more complex continental reconstructions.

Scientific Reports↗
USGS1979

Chemical analyses of coal and coal-associated rock samples from the Rosebud and McKay coal beds, Tongue River Member of the Fort Union Formation, Colstrip coal deposit, Rosebud County, Montana

As part of a continuing program by the U.S. Geological Survey to collect and chemically analyze representative samples of U.S. coals, 61 coal and coal-associated rock samples were collected from the Rosebud and McKay beds in the Paleocene Tongue River Member of the Fort Union Formation in Rosebud County, Montana. This area is located in the Montana part of the Powder River region, specifically within the Coistrip coal deposit as defined by Matson and Blumer, 1974. Forty of the samples (36 coal and 4 coal-associated rock) are from the Rosebud bed and 21 samples (all coal) are from the McKay bed. The McKay bed is between 5.5 and 18.6 m. below the Rosebud bed. The samples were collected from the Big Sky Mine and from 13 core holes in sec. 1, 2, and 27, T. 1 N., R. 41 E.; sec. 23 and 35, T. 2 N., R. 41 E.; and in sec. 1, 3, 5, 9, 15, and 16, T. 1 N., R. 40 E. The location of the sample collection area is shown in figure 1. Brief descriptions of all 61 samples are listed in table 1 and locations of sampling sites are shown in figure 2. Estimated strippable coal resources for the Rosebud bed in this area exceed 1,305 metric tons (1,439 million short tons) (Matson and Blumer, 1974). There are currently no estimates of coal resources for the McKay bed from this area. Analyses of samples D172034 through D172051 have previously been published in Swanson and others (1976) and are included here in order to provide a more complete data listing. For additional information on sulfur and trace element contents in the Rosebud and McKay coal beds, see Chadwick, Woodriff and others (1975) and Chadwick, Rice and others (1975).

Montana↗
USGS1983

Ground-followup studies of the 1977 airborne electromagnetic survey in the Assifar and Mulhal areas, Wadi Bidah district, Kingdom of Saudi Arabia

Parts of four airborne electromagnetic (AEM) anomalies were selected for study in order to determine the cause of high conductivity of Precambrian rocks underlying extensive areas in the southern Wadi Bidah district, Kingdom of Saudi Arabia. In the Assifar area, which contains an ancient mine or prospect having the same name, geophysical data suggest that a mineralized body may lie beneath and immediately south of the ancient workings. Many other conductive zones detected during the course of the geophysical survey are thought to be related to metavolcanic rocks containing carbonaceous materials. Detailed geologic mapping, and possibly diamond core drilling, will be necessary to fully evaluate the area. In the Mulhal No. 2 area, located about 2 km south of the Mulhal ancient mine, geophysical studies suggest that mineralized rocks extend about 500 m along strike beneath outcrops of gossanous material. A brief review of the AEM ground-followup studies in the Wadi Bidah district suggests that most, if not all, of the AEM conductors are carbonaceous rocks. Secondary causes of conductivity are intense faulting and shearing.

Open-File Report↗
USGS2018

Historical eruptions and hazards at Bogoslof volcano, Alaska

Bogoslof volcano is a submarine volcano in the southern Bering Sea (53.9272°N, 168.0344°W), located 100 kilometers (km) west of Dutch Harbor/Unalaska, and 40 km north of Umnak Island. The volcano has a relatively long history of scientific investigation and several of its historical eruptions have been documented during brief visits to the area since the late 1700s. The purpose of this report is to provide a modern volcanological perspective on past eruptions of Bogoslof and to readdress some of the eruptive phenomena described in historical documents and reports. We also present for the first time a brief analysis of the hazards posed by Bogoslof eruptions. While this report was being prepared, Bogoslof volcano was in an ongoing state of eruptive activity that began in mid-December 2016. Detectable eruptive activity ended in late August 2017 and the volcano has remained quiet since then. Because we have not yet visited Bogoslof Island and have only a few distal tephra samples from two eruptive events, we will not discuss in detail the 2016–17 eruptive sequence, but will provide some information for comparative purposes. When more detailed data has been collected, a more extensive review of the 2016–17 Bogoslof eruption should be the subject of future reports.

Alaska↗
USGS2019

Eruption age and duration of the ~9 km3 Burney Mountain dacite dome complex, northern California

At ~9 km3, the six dacite domes of Burney Mountain (db1–db6) constitute the most voluminous Quaternary dome complex in the Cascades volcanic arc. Whole-rock geochemistry, electron microprobe, and petrographic data indicate that the domes are magmatically related, which, when integrated with geomorphology and stratigraphy, indicate early (db1, db2, db3) and late (db4, db5, db6) erupted groups. We present 40Ar/39Ar ages of 271.9±4.6 ka (db1), 280.8±8.2 and 281.7±6.8 ka (db2), and 290.2±6.0 ka (db3) along with a previous age of 280±12 ka (db1). These ages scatter over 20 kyr, whereas remanent magnetic directions are similar between 53.3–59.0° inclination and 352.7–355.9° declination. The latter dataset indicates that the dacite domes were emplaced over a geologically brief time interval; not thousands of years. Crystal-size distribution patterns of plagioclase were used to calculate residence times, which we use to infer the duration over which the eruptions likely occurred. Three slopes represent three populations of plagioclase crystals (fine-grained groundmass, coarse-grained groundmass, phenocrysts). A commonly used growth rate for plagioclase in dacitic magmas (10-10 mm/s) yields 9–10 years of growth for the coarse-grained groundmass (early erupted domes of db1, db2, db3), whereas plagioclase in the fine-grained groundmass (late erupted domes of db4, db5, db6) grew over 4–5 years. All plagioclase phenocrysts have apparent residence times of 26–36 years; however, they contain high An>70 resorbed cores with sieve textures, which have euhedral, lower An<65 overgrowth rims. Similarities in chemistry between groundmass plagioclase and phenocryst overgrowth rims indicate that they grew concurrently, and we therefore propose that both have similar residence times. Thus, the Burney Mountain dacite dome complex was emplaced during a single eruptive episode over the course of years to decades at 281.1±4.8 ka (weighted mean age).

California↗
USGS2012

National wildlife refuge visitor survey results: 2010/2011

The U.S. Fish and Wildlife Service (Service) collaborated with the U.S. Geological Survey to conduct a national survey of visitors regarding their experiences on national wildlife refuges. The survey was conducted to better understand visitor needs and experiences and to design programs and facilities that respond to those needs. The survey results will inform Service performance planning, budget, and communications goals. Results will also inform Comprehensive Conservation Plan (CCPs), Visitor Services, and Transportation Planning processes. The survey was conducted on 53 refuges across the National Wildlife Refuge System (Refuge System) to better understand visitor needs and experiences and to design programs and facilities that respond to those needs. A total of 14,832 visitors agreed to participate in the survey between July 2010 and November 2011. In all, 10,233 visitors completed the survey for a 71% response rate. This report provides a summary of visitor and trip characteristics; visitor opinions about refuges and their offerings; and visitor opinions about alternative transportation and climate change, two Refuge System topics of interest. The Refuge System, established in 1903 and managed by the Service, is the leading network of protected lands and waters in the world dedicated to the conservation of fish, wildlife and their habitats. There are 556 National Wildlife Refuges and 38 wetland management districts nationwide, encompassing more than 150 million acres. The Refuge System attracts more than 45 million visitors annually, including 25 million people per year to observe and photograph wildlife, over 9 million to hunt and fish, and more than 10 million to participate in educational and interpretation programs. Understanding visitors and characterizing their experiences on national wildlife refuges are critical elements of managing these lands and meeting the goals of the Refuge System. These combined results are based on surveying at 53 participating refuges during 2010/2011 and contain the following information: * Synopsis: Brief summary of the survey results. * Introduction: An overview of the Refuge System and the goals of the national surveying effort. * Methods: The procedures for the national surveying effort, including selecting refuges, developing the survey instrument, contacting visitors, and guidance for interpreting the results. * Survey Results: Key findings from the survey, including: - Visitor and trip characteristics - Visitors opinions about refuges - Visitor opinions about alternative transportation - Visitor opinions about climate change * Conclusion * References Individual results for each of the 53 participating refuges are available at http://pubs.usgs.gov/ds/643/ as part of USGS Data Series 643.

Data Series↗
USGS2009

A method for creating a three dimensional model from published geologic maps and cross sections

This brief report presents a relatively inexpensive and rapid method for creating a 3D model of geology from published quadrangle-scale maps and cross sections using Google Earth and Google SketchUp software. An example from the Green Mountains of Vermont, USA, is used to illustrate the step by step methods used to create such a model. A second example is provided from the Jebel Saghro region of the Anti-Atlas Mountains of Morocco. The report was published to help enhance the public's ability to use and visualize geologic map data.

Vermont↗
USGS2018

Suspended-sediment transport from the Green-Duwamish River to the Lower Duwamish Waterway, Seattle, Washington, 2013–17

The Green-Duwamish River transports watershed-derived sediment to the Lower Duwamish Waterway Superfund site near Seattle, Washington. Understanding the amount of sediment transported by the river is essential to the bed sediment cleanup process. Turbidity, discharge, suspended-sediment concentration (SSC), and particle-size data were collected by the U.S. Geological Survey (USGS) from February 2013 to January 2017 at the Duwamish River, Washington, within the tidal influence at river kilometer 16.7 (USGS streamgage 12113390; Duwamish River at Golf Course at Tukwila, WA). This report quantifies the timing and magnitude of suspended-sediment transported in the Duwamish River. Regression models were developed between SSC and turbidity and SSC and discharge to estimate 15- minute SSC. Suspended-sediment loads were calculated from the computed SSC and time-series discharge data for every 15-minute interval during the study period. The 2014–16 average annual suspended-sediment load computed was 117,246 tons (106,364 metric tons), of which 73.5 percent or (86,191 tons; 78,191 metric tons) was fine particle (less than 0.0625 millimeter in diameter) suspended sediment. The seasonality of this site is apparent when you divide the year into "wet" (October 16– April 15) and "dry" (April 16–October 15) seasons. Most (97 percent) of the annual suspended sediment was transported during the wet season, when brief periods of intense precipitation from storms, large releases from the Howard Hanson Dam, or a combination of both were much more frequent.

Washington↗
USGS1984

Great Salt Lake, and precursors, Utah: The last 30,000 years

Sediment cores up to 6.5 m in length from the South Arm of Great Salt Lake, Utah, have been correlated. Radiocarbon ages and volcanic tephra layers indicate a record of greater than 30,000 years. A variety of approaches have been employed to collect data used in stratigraphic correlation and lake elevation interpretation; these include acoustic stratigraphy, sedimentologic analyses, mineralogy, geochemistry (major element, C, O and S isotopes, and organics), paleontology and pollen. The results indicate that prior to 32,000 year B.P. an ephemeral saline lake-playa system was present in the basin. The perennial lake, which has occupied the basin since this time, rose in a series of three major steps; the freshest water conditions and presumably highest altitude was reached at about 17,000 year B.P. The lake remained fresh for a brief period, followed by a rapid increase in salinity and sharp lowering in elevation to levels below that of the present Great Salt Lake. The lake remained at low elevations, and divided at times into a north and south Basin, until about 8,000 year B.P. Since that time, with the exception of two short rises to about 1290 m, the lake level has remained near the present elevation of 1280 m. ?? 1984 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS2000

Self-ordering and complexity in epizonal mineral deposits

Epizonal base and precious metal deposits makeup a range of familiar deposit styles including porphyry copper-gold, epithermal veins and stockworks, carbonate-replacement deposits, and polymetallic volcanic rock-hosted (VHMS) deposits. They occur along convergent plate margins and are invariably associated directly with active faults and volcanism. They are complex in form, variable in their characteristics at all scales, and highly localized in the earth’s crust. More than a century of detailed research has provided an extensive base of observational data characterizing these deposits, from their regional setting to the fluid and isotope chemistry of mineral deposition. This has led to a broad understanding of the large-scale hydrothermal systems within which they form. Low salinity vapor, released by magma crystallization and dispersed into vigorously convecting groundwater systems, is recognized as a principal source of metals and the gases that control redox conditions within systems. The temperature and pressure of the ambient fluid anywhere within these systems is close to its vapor-liquid phase boundary, and mineral deposition is a consequence of short timescale perturbations generated by localized release of crustal stress. However, a review of occurrence data raises questions about ore formation that are not addressed by traditional genetic models. For example, what are the origins of banding in epithermal veins, and what controls the frequency of oscillatory lamination? What controls where the phenomenon of mineralization occurs, and why are some porphyry deposits, for example, so much larger than others? The distinctive, self-organized characteristics of epizonal deposits are shown to be the result of repetitive coupling of fracture dilation consequent on brittle failure, phase separation (“boiling”), and heat transfer between fluid and host rock. Process coupling substantially increases solute concentrations and triggers fast, far-from-equilibrium depositional processes. Since these coupled processes lead to localized transient changes in fluid characteristics, paragenetic, isotope, and fluid inclusion data relate to conditions at the site of deposition and only indirectly to the characteristics of the larger-scale hydrothermal system and its longer-term behavior. The metal concentrations (i.e. grade) of deposits and their internal variation is directly related to the geometry of the fracture array at the deposit scale, whereas finer-scale oscillatory fabrics in ores may be a result of molecular scale processes. Giant deposits are relatively rare and develop where efficient metal deposition is spatially focused by repetitive brittle failure in active fault arrays. Some brief case histories are provided for epithermal, replacement, and porphyry mineralization. These highlight how rock competency contrasts and feedback between processes, rather than any single component of a hydrothermal system, govern the size of individual deposits. In turn, the recognition of the probabilistic nature of mineralization provides a firmer foundation through which exploration investment and risk management decisions can be made.

Annual Review of Earth and Planetary Sciences↗
USGS2007

Summary of Survival Data from Juvenile Coho Salmon in the Klamath River, Northern California, 2006

Little is known about the survival of ESA-listed juvenile coho salmon during their seaward migration in the lower Klamath River. In 2006, the Bureau of Reclamation funded a study to estimate the survival of radio-tagged juvenile coho salmon in the Klamath River downstream of Iron Gate Dam. A series of models were evaluated to determine if survival varied between hatchery and wild fish and among several river reaches between the dam river kilometer 33, a total distance of 276 kilometers. The results from 2006, the first year of study, indicated little support for differences in survival between hatchery and wild fish and lower survival in the most upstream reach than in those farther downstream. This document is a brief summary of survival results to date.

Open-File Report↗
USGS1986

Vegetation, climatic and floral changes at the Cretaceous-Tertiary boundary

he western interior of North America has the only known non-marine sections that contain the iridium-rich clay interpreted as the Cretaceous-Tertiary (K-T) boundary1-7. Because vegetation and climate can be directly inferred from physiognomy of leaves8-15 and because leaf species typically represent low taxonomic categories, studies of leaf floras in these sections provide data on the effects of a terminal Cretaceous event on the land flora, vegetation and climate. A previous study based on detailed sampling of leaves and their dispersed cuticle16 in the Raton Basin provides a framework for interpretation of other leaf sequences over 20 degrees of latitude. We conclude that at the boundary there were: (1) High levels of extinction in the south and low levels in the north; (2) major ecological disruption followed by long-term vegetational changes that mimicked normal ecological succession; (3) a major increase in precipitation; and (4) a brief, low-temperature excursion, which supports models of an 'impact winter'. ?? 1986 Nature Publishing Group.

Nature↗
USGS2004

Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of polycyclic aromatic hydrocarbon compounds in sediment by gas chromatography/mass spectrometry

A method for the determination of 28 polycyclic aromatic hydrocarbons (PAHs) and 25 alkylated PAH homolog groups in sediment samples is described. The compounds are extracted from sediment by solvent extraction, followed by partial isolation using high-performance gel permeation chromatography. The compounds are identified and uantitated using capillary-column gas chromatography/mass spectrometry. The report presents performance data for full-scan ion monitoring. Method detection limits in laboratory reagent matrix samples range from 1.3 to 5.1 micrograms per kilogram for the 28 PAHs. The 25 groups of alkylated PAHs are homologs of five groups of isomeric parent PAHs. Because of the lack of authentic standards, these homologs are reported semiquantitatively using a response factor from a parent PAH or a specific alkylated PAH. Precision data for the alkylated PAH homologs are presented using two different standard reference manuals produced by the National Institute of Standards and Technology: SRM 1941b and SRM 1944. The percent relative standard deviations for identified alkylated PAH homolog groups ranged from 1.55 to 6.98 for SRM 1941b and from 6.11 to 12.0 for SRM 1944. Homolog group concentrations reported under this method include the concentrations of individually identified compounds that are members of the group. Organochlorine (OC) pesticides--including toxaphene, polychlorinated biphenyls (PCBs), and organophosphate (OP) pesticides--can be isolated simultaneously using this method. In brief, sediment samples are centrifuged to remove excess water and extracted overnight with dichloromethan (95 percent) and methanol (5 percent). The extract is concentrated and then filtered through a 0.2-micrometer polytetrafluoroethylene syringe filter. The PAH fraction is isolated by quantitatively injecting an aliquot of sample onto two polystyrene-divinylbenzene gel-permeation chromatographic columns connected in series. The compounds are eluted with dichloromethane, a PAH fraction is collected, and a portion of the coextracted interferences, including elemental sulfur, is separated and discarded. The extract is solvent exchanged, the volume is reduced, and internal standard is added. Sample analysis is completed using a gas chromatograph/mass spectrometer and full-scan acquisition.

Water-Resources Investigations Report↗
USGS2013

Summary of 2012 reconnaissance field studies related to the petroleum geology of the Nenana Basin, interior Alaska

The Alaska Division of Geological & Geophysical Surveys (DGGS) recently initiated a multi-year review of the hydrocarbon potential of frontier sedimentary basins in Alaska (Swenson and others, 2012). In collaboration with the Alaska Division of Oil & Gas and the U.S. Geological Survey we conducted reconnaissance field studies in two basins with recognized natural gas potential—the Susitna basin and the Nenana basin (LePain and others, 2012). This paper summarizes our initial work on the Nenana basin; a brief summary of our work in the Susitna basin can be found in Gillis and others (in press). During early May 2012, we conducted ten days of helicopter-supported fieldwork and reconnaissance sampling along the northern Alaska Range foothills and Yukon–Tanana upland near Fairbanks (fig. 1). The goal of this work was to improve our understanding of the geologic development of the Nenana basin and to collect a suite of samples to better evaluate hydrocarbon potential. Most laboratory analyses have not yet been completed, so this preliminary report serves as a summary of field data and sets the framework for future, more comprehensive analysis to be presented in later publications.

Alaska↗