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At least 37 records · Page 2Linked to original sources
USGS2022

U.S. Geological Survey Core Research Center: A gateway to subsurface discovery for geoscience research

The U.S. Geological Survey (USGS) operates the Core Research Center (CRC) in Denver, Colorado, USA, a public access repository of rock cores from over 9800 wells and drill cuttings from over 53 000 wells, primarily from states in or adjacent to the Rocky Mountain Region. Annually, approximately 1400 visitors use the collection for traditional and innovative research. The CRC has an online, searchable database which includes downloadable core photos, analytical data, and thin-section images. When visitors sample for analyses, the results must be returned to the CRC for public dissemination providing immediate, free access to users while sparing the finite, irreplaceable collection from redundant testing. A representative quantity of every core depth is preserved in perpetuity. Studies on CRC materials, paired with new extraction methods, have unlocked new productive deposits. Materials drilled and curated decades ago remain in high demand while materials receiving little attention today may be crucial for future research. The collection provides immediate, inexpensive access to subsurface materials at a fraction of the cost of new drilling, sparing money, time and environmental impacts.

Geological Society, London, Special Publications↗
USGS2000

Environmental Contaminants and Terrestrial Vertebrates: Effects on Populations, Communities, and Ecosystems

The desire of resource managers, risk assessors, and the general public to better understand the consequences of environmental contamination has produced a strong and growing need for information on the effects of contaminants on populations and groups of species, and over moderate to large areas of land or water. However, the problems associated with research involving populations and groups of species or large and complex geographic areas, especially in terrestrial environments, are well known within the scientific community. With the previous thoughts in mind, an interactive symposium was held at the University of Maryland in October 1998. The purpose of the symposium was to review and critically evaluate our understanding of the effects of contaminants on terrestrial vertebrates at levels of organization above that of the individual. Invited background and technical presentations provided a common baseline of information for symposium participants. Discussion groups were then asked to critically evaluate the topics of two technical sessions. Several presentations of recent or ongoing research provided participants with examples of current approaches to assessments of the effects of contaminants on terrestrial vertebrates at the population or higher level of organization. The book consists of 10 chapters written by presenters at the symposium and three chapters conveying the reports of discussion group.

SETAC Special Publications Series.↗
USGS2009

Relationship of fluviodeltaic facies to coal deposition in the lower Fort Union formation (Palaeocene), south-western North Dakota

Facies analysis of the Ludlow and Tongue River Members of the Palaeocene Fort Union Formation provides an understanding of the relationship between fluviodeltaic environments and associated coal deposition in the south-western Williston Basin. The Ludlow Member consists of high-constructive delta facies that interfinger with brackish-water tongues of the Cannonball Member of the Fort Union Formation. The lower part of the Ludlow Member was deposited on a lower delta plain that consisted of interdistributary crevasse and subdelta lobes. The upper part of the Ludlow Member was deposited in meander belts of the upper delta plain. The delta plain facies of the Ludlow Member is overlain by alluvial plain facies consisting of swamp, crevasse-lobe, lacustrine, and trunk meander belt deposits of the Tongue River Member. The Ludlow delta is believed to have been fed by fluvial systems that probably flowed from the Powder River Basin to the Williston Basin undeterred by the Cedar Creek Anticline. However, the evidence indicates that the Cedar Creek Anticline was prominent enough, during early Tongue River Member deposition, to cause the obstruction of the regional fluvial system flowing from the SW, and the formation of local drainage. The Ludlow Member contains 18 coal beds in the area studied, of which the T-Cross and Yule coals are as thick as 4 m (12 ft). Abandoned delta lobes served as platforms where coals formed, which in turn, were drowned by mainly fresh water and subordinate brackish water. Repetition of deltaic sedimentation, abandonment, and occupation by swamp led to preservation of the T-Cross and Oyster coals in areas as extensive as 260 km 2 (< 100 miles 2 ).

North Dakota↗
USGS2004

Geochemistry of coastal tarballs in southern California—A tribute to I. R. Kaplan

In the southern offshore California borderland, natural oil seeps occur mainly in the Santa Barbara Channel and Santa Monica Bay. Coastal tar residues (tarballs) from beaches bordering these water bodies were analyzed for six geochemical parameters: stable carbon isotopic compositions (δ 13 C) and four biomarker ratios (C 28 IC 29 hopane, sterane/hopane, refractory index, bisnorhopane index), and the presence or absence of trisnorhopane. The objectives of this study were to group these residues and infer possible sources and transport directions. Three major groups were established. Two groups are likely from natural seeps near the Channel Islands, whereas the third group probably comes from seeps within Santa Monica Bay. Residues from all groups occur on the Channel Islands and on mainland beaches from as far south as San Diego to Point Reyes north of San Francisco.

California↗
USGS1987

Unconformity between Coast Range ophiolite and part of the lower Great Valley sequence, South Fork of Elder Creek, Tehama County, California

The South Fork of Elder Creek is located on private property about 6 mi (10 km) northwest of Paskenta, Calif. (Fig. 1). To visit this locality it is necessary to call Mr. Les Sutfin (916-824-4628) and arrange to pick up the key to the gate at his home in Corning. From the Paskenta Store, drive 3.3 mi (5.3 km) north on the Toomes Camp road to the locked gate on the north side of the road. From here, take the Pellows Road (four-wheel drive vehicle recommended) 3.6 mi (5 km) north to the end of the road, then walk west along the trail parallel to the South Fork of Elder Creek for approximately 0.5 mi (0.8 km) to the unconformity(Fig. 2).

DNAG Special Publication↗
USGS1991

Faulting and seismic activity

This chapter traces some of the ideas and concepts leading to the current understanding of the process of faulting and earthquake generation, gives examples of engineering geology investigations contributing to that understanding, describes some engineering projects that have been strongly influenced by the process, and suggests needed research. Each of these topics is discussed in sequence. The understanding of faulting and earthquakes and of the significance of these to engineering has developed over several centuries. John Michell in 1761 was probably the first to publish a cross section of a clearly recognizable fault (Adams, 1938, Fig. 66). Michell did not attribute earthquakes to faulting, but proposed the important idea that seismic vibrations were the result of the propagation of elastic waves in the earth (Adams, 1938). Charles Lyell (1830) emphasized the uplift and depression of land that accompanies earthquakes. He did not attribute earthquakes to faulting, but a contemporary of his evidently did, for the following statement appeared in a review of Lyell’s book (Scrap, 1830, p. 463): The sudden fracture of solid strata by any disruptive force must necessarily produce a violent vibratory jar to a considerable distance along the continuation of these strata. Such vibrations would be propagated in undulations, which may be expected, when influencing a mass of rocks several thousand feet at least in thickness, to produce on the surface exactly the wave-like motion, the opening and shutting of crevices, the tumbling down of cliffs and walls, and other characteristic phenomena of earthquakes. This idea was apparently disregarded, and coseismic faulting, some of which reached the ground surface, was generally considered to be the result rather than the cause of earthquakes until the time of G. K. Gilbert.

DNAG Special Publication↗
USGS1982

Atlantic continental margin of the United States

The objective of this Decade of North American Geology (D-NAG) volume will be to focus on the Mesozoic and Cenozoic evolution of the U.S. Atlantic continental margin, including the onshore coastal plain, related onshore Triassic-Jurassic rift grabens, and the offshore basins and platforms. Following multiple compressional tectonic episodes between Africa and North America during the Paleozoic Era that formed the Appalachian Mountains, the Mesozoic and Cenozoic Eras were dominated by tensional tectonic processes that separated Africa and North America. Extensional rifting during Triassic and Early Jurassic times resulted in numerous tensional grabens both onshore and offshore, which filled with nonmarine continental red beds, lacustrine deposits, and volcanic flows and debris. The final stage of this breakup between Africa and North America occurred beneath the present outer continental shelf and continental slope during Early or Middle Jurassic time when sea-floor spreading began to form new oceanic crust and lithosophere between the two continents as they drifted apart. Postrift subsidence of the marginal basins continued in response to cooling of the lithosphere and sedimentary loading. Geophysical surveys and oil-exploration drilling along the U.S. Atlantic continental margin during the past 5 years are beginning to answer many questions concerning its deep structure and stratigraphy and how it evolved during the rifting and early sea-floor-spreading stages of the separation of this region from Africa. Earlier geophysical studies of the U.S. continental margin used marine refraction and submarine gravity measurements. Single-channel seismic-reflection, marine magnetic, aeromagnetic, and continuous gravity measurements became available during the 1960s.

DNAG Special Publication↗
USGS1982

Ancient plate boundaries in the Bering Sea region

Plate tectonic models of the Bering Sea suggest that the abyssal Bering Sea Basin is underlain by oceanic crust, a supposition supported by refraction and magnetic data. The oceanic crust is thought to be a remnant of the Kula(?) plate that was isolated within what is now the Bering Sea when the proto-Aleutian arc began to form between the Alaska Peninsula and Kamchatka in late Mesozoic or earliest Tertiary times. Prior to the formation of the Aleutian arc, the Kula(?) plate moved NW, directly underthrusting eastern Siberia; the plate’s eastern edge either obliquely underthrust or slid past the Bering Sea margin along a transform boundary. The Koryak Range in eastern Siberia is composed in part of mélange units that include Palaeozoic and Mesozoic allochthonous blocks juxtaposed within a matrix of Cretaceous sedimentary rocks. Structural trends suggest that these blocks were accreted into the Koryak area from the south along an ancient subduction zone formed by underthrusting of the Kula(?) plate. The base of the Bering Sea continental margin that extends from eastern Siberia to the Alaska Peninsula—the so-called Beringian margin—is underlain by a thick (7–10 km) sedimentary section along the base of the slope. Rocks dredged from the basement exposed farther up the slope (1500–2000 m deep) include shallow-water Upper Jurassic sandstone that is unconformably overlain by shallow-water Eocene to Miocene diatomaceous mudstone. Fauna in the dredge samples indicate that the shelf edge has subsided several kilometres since late Palaeogene time, perhaps in response to the cessation of motion relative to the adjacent oceanic plate and subsequent sediment loading of the oceanic plate. Uplift of the former plate boundary exposed in the Koryak Range occurred principally in late Cenozoic time, and collapse of the adjacent plate boundary, the Beringian margin, began in earliest Tertiary time and has continued to the present. Both tectonic events occurred after the site of active plate collision shifted south to near the present Aleutian Trench. We are uncertain as to why these two ancient, yet adjacent former plate boundaries should behave so differently, i.e. why one area was folded and uplifted while the other was extensionally deformed and subsided, both apparently in response to the cessation of convergent or strike-slip plate motion.

Geological Society, London, Special Publications↗
USGS1984

Models for the deposition of Mesozoic-Cenozoic fine-grained organic-carbon-rich sediment in the deep sea

The widespread occurrence of organic-carbon-rich strata (‘black shales’) in certain portions of Jurassic, Cretaceous and Cenozoic sequences has been well-documented from Deep Sea Drilling Project sites in the Atlantic and Pacific Oceans and from sequences, now exposed on land, originally deposited in the Tethyan ocean. These ancient black shales usually have been explained by analogy with examples of modern deep-sea sediments in which organic matter locally is preserved by (1) increasing the supply of organic matter, (2) increasing the rate of sedimentation, and/or (3) decreasing the oxygen content of the bottom water. However, detailed examination of many black shales reveals characteristics that cannot be explained by simple local models, including: their approximate coincidence in time globally; their occurrence in a variety of different environments, including open oxygenated oceans, restricted basins, deep and shallow water; their interbedding with organic-carbonpoor strata which often dominate a so-called black shale sequence; their deposition by pelagic, hemipelagic, turbiditic and other processes; and the variations in type and amount of organic matter that occur even within the same sequence. A more complex model for the origin of black shales therefore appears most appropriate, in which the cyclic preservation of organic matter depends on the interplay of the three main variables, namely supply of organic matter, sedimentation rate, and deep-water oxygenation, each of which varies independently to some extent. The variation and relative importance of these parameters in individual basins and widespread black shale deposition in general are linked globally and temporally by changes in global sea-level, climate and related changes in oceanic circulation. An important and often overlooked factor for the supply of organic matter to deep-basin sediments is the frequency and magnitude of redepositional processes. The interplay of these variables is discussed in relation to the middle Cretaceous and Cenozoic organic-carbon-rich strata, in particular, which show marked differences in the relative importance of the different variables.

Geological Society of London Special Publications↗
USGS1987

Crustal extension along a rooted system of imbricate low-angle faults: Colorado River extensional corridor, California and Arizona

The upper 10 to 15 km of crystalline crust in the 100-km-wide Colorado River extensional corridor of mid-Tertiary age underwent extension along an imbricate system of gently dipping normal faults. Detachment faults cut gently down-section eastward in the direction of tectonic transport from a headwall breakaway, best expressed in the Old Woman Mountains, California. Successively higher and more distal allochthons are displaced farther from the headwall, some as much as tens of kilometres. The basal fault(s) cut initially to depths of 10 to 15 km, the palaeothickness of a tilted allochthonous slab of basement rocks above the Chemehuevi-Whipple Mountains detachment fault(s). Hanging wall blocks tilt consistently toward the headwall as shown by dips of capping Tertiary strata and of originally horizontal Proterozoic diabase dykes. Block tilts and the degree of extension increase northeastward across much of the corridor. The faults are interpreted as rooting under the unbroken Hualapai Mountains and Colorado Plateau on the down-dip side of the corridor in Arizona. Slip on faults at all exposed levels of the crust was unidirectional, and totals an estimated 50 km. These data and inferences support the concept that the crust in California moved out from under Arizona along a rooted, normal-slip shear system. Brittle thinning above the sole faults affected the entire upper crust, and in places wholly removed it along the central part of the corridor. Upwarp exposed metamorphic core complexes in footwall domes.

Geological Society Special Publication↗
USGS1989

Evolution of the western part of the Coast plutonic–metamorphic complex, South-Eastern Alaska, USA: A summary

The western Cordillera of North America extends for over 6000 km from the tip of Baja California to the Alaska Range. It includes a wide variety of metamorphic and plutonic terrains, but none is more spectacular scenically or geologically than the Coast plutonic-metamorphic complex (Brew & Ford 1984) of western Canada and south-eastern Alaska. This report briefly describes the evolution of the western part of the complex, integrating information from the deformational, plutonic and metamorphic events. Most of the original studies are reported by the authors in U.S. Geological Survey Circular numbers 733, 751, 823-B, 868, 939, 945, 967 and 978, and are not cited specifically here. This summary does not contain either a comprehensive bibliography or a comparison of the metamorphic histories of south-eastern Alaska with the adjacent parts of British Columbia. The Coast plutonic-metamorphic complex is here divided into three major elements: the western metamorphic, the central granitic and the eastern metamorphic zones (Fig. 1). The western metamorphic belt is extremely long (900 km), and narrow (7–25 km). It consists of regional dynamothermally and regional thermally metamorphosed rocks with mineral assemblages ranging from prehnite-pumpellyite to upper amphibolite facies, scattered mesozonal to epizonal granitic bodies, and a few concentrically zoned mafic-ultramafic masses. The metamorphic grade and the amount of deformation increase from south-west to north-east, culminating at, or slightly to the north-east of, the ‘great tonalite sill’: a remarkable 700-km-long, 3- to 25-km-wide vertical to northeast-dipping belt of mostly syntectonic plutons of approximately the same age, composition and structural

Alaska↗
USGS1996

Deep-sea ostracode shell chemistry (Mg:Ca ratios) and late Quaternary Arctic Ocean history

The magnesium:calcium (Mg:Ca) and strontium:calcium (Sr:Ca) ratios were investigated in shells of the benthic ostracode genus Krithe obtained from 64 core-tops from water depths of 73 to 4411 m in the Arctic Ocean and Nordic seas to determine the potential of ostracode shell chemistry for palaeoceanographic study. Shells from the Polar Surface Water (−1 to −1.5°C) had Mg:Ca molar ratios of about 0.006–0.008; shells from Arctic Intermediate Water (+0.3 to +2.0°C) ranged from 0.09 to 0.013. Shells from the abyssal plain and ridges of the Nansen, Amundsen and Makarov basins and the Norwegian and Greenland seas had a wide scatter of Mg:Ca ratios ranging from 0.007 to 0.012 that may signify post-mortem chemical alteration of the shells from Arctic deep-sea environments below about 1000 m water depth. There is a positive correlation ( r 2 = 0.59) between Mg:Ca ratios and bottom-water temperature in Krithe shells from Arctic and Nordic seas from water depths <900 m. Late Quaternary Krithe Mg:Ca ratios were analysed downcore using material from the Gakkel Ridge (water depths 3047 and 3899 m), the Lomonosov Ridge (water depth 1051 m) and the Amundsen Basin (water depth 4226 m) to test the core-top Mg:Ca temperature calibration. Cores from the Gakkel and Lomonosov ridges display a decrease in Mg:Ca ratios during the interval spanning the last glacial/deglacial transition and the Holocene, perhaps related to a decrease in bottom water temperatures or other changes in benthic environments.

Geological Society Special Publication↗
USGS1996

Late Quaternary transgressive large dunes on the sediment-starved Adriatic shelf

The Adriatic epicontinental basin is a low-gradient shelf where the late-Quaternary transgressive systems tract (TST) is composed of thin parasequences of backbarrier, shoreface and offshore deposits. The facies and internal architecture of the late-Quaternary TST in the Adriatic epicontinental basin changed consistently from early transgression to late transgression reflecting: (1) fluctuations in the balance between sediment supply and accommodation increase, and (2) a progressive intensification of the oceanographic regime, driven by the transgressive widening of the basin to as much as seven times its lowstand extent. One of the consequences of this trend is that high-energy marine bedforms such as sand ridges and sand waves characterize only areas that were flooded close to the end of the late-Quaternary sea-level rise, when the wind fetch was maximum and bigger waves and stronger storm currents could form. We studied the morphology, sediment composition and sequence-stratigraphical setting of a field of asymmetric bedforms (typically 3 m high and 600 m in wavelength) in 20-24 m water depth offshore the Venice Lagoon in the sediment-starved North Adriatic shelf. The sand that forms these large dunes derived from a drowned transgressive coastal deposit reworked by marine processes. Early cementation took place over most of the dune crests limiting their activity and preventing their destruction. Both the formation and deactivation of this field of sand dunes occurred over a short time interval close to the turn-around point that separates the late-Quaternary sea-level rise and the following highstand and reflect rapid changes in the oceanographic regime of the basin.

Geological Society Special Publication↗
USGS1996

Iron and manganese oxide mineralization in the Pacific

Iron, manganese, and iron-manganese deposits occur in nearly all geomorphologic and tectonic environments in the ocean basins and form by one or more of four processes: (1) hydrogenetic precipitation from cold ambient seawater, (2) precipitation from hydrothermal fluids, (3) precipitation from sediment pore waters that have been modified from bottom water compositions by diagenetic reactions in the sediment column and (4) replacement of rocks and sediment. Iron and manganese deposits occur in five forms: nodules, crusts, cements, mounds and sediment-hosted stratabound layers. Seafloor oxides show a wide range of compositions from nearly pure iron to nearly pure manganese end members. Fe/Mn ratios vary from about 24 000 (up to 58% elemental Fe) for hydrothermal seamount ironstones to about 0.001 (up to 52% Mn) for hydrothermal stratabound manganese oxides from active volcanic arcs. Hydrogenetic Fe-Mn crusts that occur on most seamounts in the ocean basins have a mean Fe/Mn ratio of 0.7 for open-ocean seamount crusts and 1.2 for continental margin seamount crusts. Fe-Mn nodules of potential economic interest from the Clarion-Clipperton Zone have a mean Fe/Mn ratio of 0.3, whereas the mean ratio for nodules from elsewhere in the Pacific is about 0.7. Crusts are enriched in Co, Ni and Pt and nodules in Cu and Ni, and both have significant concentrations of Pb, Zn, Ba, Mo, V and other elements. In contrast, hydrothermal deposits commonly contain only minor trace metal contents, although there are many exceptions, for example, with Ni contents up to 0.66%, Cr to 1.2%, and Zn to 1.4%. Chondrite-normalized REE patterns generally show a positive Ce anomaly and abundant ΣREEs for hydrogenetic and mixed hydrogenetic-diagenetic deposits, whereas the Ce anomaly is negative for hydrothermal deposits and ΣREE contents are low. However, the Ce anomaly in crusts may vary from strongly positive in East Pacific crusts to slightly negative in West Pacific crusts, which may reflect the redox conditions of seawater. The concentration of elements in hydrogenetic Fe-Mn crusts depends on a wide variety of water column and crust surface characteristics, whereas concentration of elements in hydrothermal oxide deposits depends of the intensity of leaching, rock types leached, and precipitation of sulphides at depth in the hydrothermal system.

Geological Society Special Publication↗
USGS1998

Sediment delivery to the Gulf of Alaska: Source mechanisms along a glaciated transform margin

Sediment delivery to the Gulf of Alaska occurs via four areally extensive deepwater fans, sourced from grounded tidewater glaciers. During periods of climatic cooling, glaciers cross a narrow shelf and discharge sediment down the continental slope. Because the coastal terrain is dominated by fjords and a narrow, high-relief Pacific watershed, deposition is dominated by channellized point-source fan accumulations, the volumes of which are primarily a function of climate. The sediment distribution is modified by a long-term tectonic translation of the Pacific plate to the north along the transform margin. As a result, the deep-water fans are gradually moved away from the climatically controlled point sources. Sets of abandoned channels record the effect of translation during the Plio-Pleistocene.

Geological Society Special Publication↗
USGS1998

Ordovician K-bentonites in the Argentine Precordillera: Relations to Gondwana margin evolution

Ordovician K-bentonites have now been recorded from >20 localities in the vicinity of the Argentine Precordillera. Most occur in the eastern thrust belts, in the San Juan Limestone and the overlying the Gualcamayo Formation, but a few ash beds are known also from the central thrust belts. The oldest occur in the middle Arenig I. victoriae lunatus graptolite ( Oe. evae conodont) Zone, and the youngest in the middle Llanvirn P. elegans ( P. suecicus ) Zone. Mineralogical characteristics, typical of other Ordovician K-bentonites, include a matrix of illite/smectite mixed-layer clay and a typical felsic volcanic phenocryst assemblage: biotite, beta-form quartz, alkali and plagioclase feldspar, apatite, and zircon, with lesser amounts of hornblende, clinopyroxene, titanite and Fe-Ti oxides. The proportions of the mineral phases and variations in their crystal chemistry are commonly unique to individual (or small groups of) K-bentonite beds. Glass melt inclusions preserved in quartz are rhyolitic in composition. The sequence is unique in its abundance of K-bentonite beds, but a close association between the Precordillera and other Ordovician sedimentary basins cannot be established. The ash distribution is most consistent with palaeogeographical reconstructions in which early Ordovician drifting of the Precordillera occurred in proximity to one or more volcanic arcs, and with eventual collision along the Andean margin of Gondwana during the mid-Ordovician Ocloyic event of the Famatinian orogeny. The Puna-Famatina terrane northeast of the Precordillera might have served as the source of the K-bentonite ashes, possibly in concert with active arc magmatism on the Gondwana plate itself.

Geological Society Special Publication↗