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At least 163 records · Page 9Linked to original sources
USGS1991

Sedimentation and tectonics of the Sylhet trough, Bangladesh

The Sylhet trough, a sub-basin of the Bengal Basin in northeastern Bangladesh, contains a thick fill (12 to 16 km) of late Mesozoic and Cenozoic strata that record its tectonic evolution. Stratigraphic, sedimentologic, and petrographic data collected from outcrops, cores, well logs, and seismic lines are here used to reconstruct the history of this trough. The Sylhet trough occupied a slope/basinal setting on a passive continental margin from late Mesozoic through Eocene time. Subsidence may have increased slightly in Oligocene time when the trough was located in the distal part of a foreland basin paired to the Indo-Burman ranges. Oligocene fluvial-deltaic strata (Barail Formation) were derived from incipient uplifts in the eastern Himalayas. Subsidence increased markedly in the Miocene epoch in response to western encroachment of the Indo-Burman ranges. Miocene to earliest Pliocene sediments of the Surma Group were deposited in a large, mud-rich delta system that may have drained a significant proportion of the eastern Himalayas. Subsidence rates in the Sylhet trough increased dramatically (3-8 times) from Miocene to Pliocene-Pleistocene time when the fluvial Tipam Sandstone and Dupi Tila Formation were deposited. This dramatic subsidence change is attributed to south-directed overthrusting of the Shillong Plateau on the Dauki fault for the following reasons. (1) Pliocene and Pleistocene strata thin markedly away from the Shillong Plateau, consistent with a crustal load emplaced on the northern basin margin. (2) The Shillong Plateau is draped by Mesozoic to Miocene rocks, but Pliocene and younger strata are not represented, suggesting that the massif was an uplifted block at this time. (3) South-directed overthrusting of the Shillong Plateau is consistent with gravity data and with recent seismotectonic observations. Sandstone in the Tioam has a marked increase in sedimentary lithic fragments compared to older rocks, reflecting uplift and erosion of the sedimentary cover of the Shillong Plateau. If the Dauki fault has a dip similar to that of other Himalayan overthrusts, then a few tens of kilometers of horizontal tectonic transport would be required to carry the Shillong Plateau to its present elevation. Uplift of the Shillong Plateau probably generated a major (∼300 km) westward shift in the course of the Brahmaputra River.

Geological Society of America Bulletin↗
USGS1969

A geophysical study of North Park and the surrounding ranges, Colorado

A geophysical study in the North Park basin and surrounding mountains, Colorado illustrates the structural relationship of various sedimentary, metamorphic, and igneous rock units. Bouguer anomalies from 1330 gravity stations range from −210 mgal over Precambrian metamorphic rocks in the mountains to −260 mgal in the Walden syncline and —280 mgal in the North Park syncline. Steep gradients delineate a fault which strikes west-northwest along the north flank of the North Park syncline. Two models fitted to the gravity data show 1 to 2 km relief on this steeply dipping fault. Density contrasts between Precambrian metamorphic and igneous rocks produce anomalies of as much as 25-mgal amplitudes in the Park and Medicine Bow Ranges. A 30-km-long seismic refraction profile, parallel to the most negative Bouguer anomaly values in the North Park basin, shows velocities increasing from 2.5 to 3.4 km/sec within Tertiary rocks at depths ranging from 1.2 to 2.0 km. Mesozoic sedimentary rocks have a velocity of 4.0 to 4.5 km/sec, a very high velocity in view of the predominance of Upper Cretaceous rocks. Precambrian basement with a velocity of 6.25 km/sec underlies the profile at depths ranging from 3.5 to 4.5 km. Strong second arrivals across the profile, observed at distances of more than 14 km from the shotpoints and interpreted as SP reflections, verified the refraction model. An aeromagnetic survey shows numerous anomalies ranging from 100 to 200γ in the Park and Rabbit Ears Ranges and in the Never Summer Mountains, to 400γ in the Front Range, and to 1200γ over the Medicine Bow Range. Positive anomalies in the Park, Medicine Bow, and Front ranges overlie metamorphic rocks. Magnetic and gravity data suggest that the Never Summer Mountains are separated from the Front Range by a north-trending, steeply east-dipping reverse fault, extending beneath the Front Range along the Colorado River valley. The magnetic data indicate that this fault may connect with a possible fault that is parallel to the Laramie River valley. In the Rabbit Ears Range, a series of magnetic anomalies show that igneous rocks are present in the eastern part of the range. A northeast-trending positive magnetic anomaly, which is parallel to foliation trends reported in Precambrian rocks, extends from the Park Range across the North Park basin to the Medicine Bow Range. On the basis of this anomaly, the high seismic velocity of the Precambrian basement, and computed profiles fitted to the gravity and magnetic data, we infer that much of the basin is underlain by high-density metamorphic rock. As shown by gravity data, the deepest part of the basin is 2.7 km below sea level, resulting in a maximum relief of 6.7 km on the basement, relative to the Medicine Bow Range. A 25-mgal negative gravity anomaly and a zone of negative magnetic anomalies outline a large granitic intrusion in the Park Range, which probably extends northeast beneath the North Park basin and connects with granitic rocks in the Medicine Bow Range.

Colorado↗
USGS1985

Quaternary tectonic setting of the 1983 Borah Peak earthquake, central Idaho

The 1983 Borah Peak earthquake was accompanied by extensive surface faulting along a part of the Lost River fault that has abundant evidence of latest Quaternary (last 15,000 yr) offset. This fault and two similar range-front normal faults along the Lemhi Range and Beaverhead Mountains lie in an area of basin-and-range structure in central Idaho that is part of a roughly V-shaped belt of latest Quaternary surface faulting that extends from the Wasatch fault, through the Yellowstone area, to the Lost River fault. The position of this belt may be related to the outward migration of a thermal front associated with the northeastward progression of late Cenozoic silicic volcanism along the Yellowstone-Snake River Plain axis. The central segments of the Lost River, Lemhi, and Beaverhead faults have been active more recently, and probably more active throughout Quaternary time, than the southern and northern segments. The main 1983 surface faulting occurred in an area of high structural relief along a central segment of the Lost River fault that has ruptured in latest Quaternary time, which suggests that comparable areas along other range fronts in the area should be regarded as likely sites of future surface faulting. Other perspective of fault behavior suggest additional possible sites, and all segments of the range-front faults are regarded as capable of surface faulting.

Idaho↗
USGS1980

Tremors from earthquakes and blasting in the Powder River basin of Wyoming and Montana

Coal in the Powder River Basin of Wyoming and Montana (fig. 1) is greatly in demand. It can be economically mined from the surface, and the land is much easier to reclaim than land above underground mines that has been damaged by subsidence or by underground fires. Exploitation of the vast coals resources in the basin has caused a rapid influx of population into the area and an associated increase in building construction. The activity has also generated concern about possible regulation of development. With these facts in mind, the U.S Geological Survey has been investigating the geologic implications of development in the Powder River Basin. One area of study has been the effect of earth tremors caused by blasting in the large coal surface mines or by naturally occurring earthquakes. The basin proper was classified by Algermissen and Perkins (1976) as belonging to a region of low seismic risk. Naturally occurring earthquakes are, therefore, mainly of scientific interest, unless of course there was an isolated event that occurred near a populated area or a surface mine. We are not aware of any damage to people or to property caused by blasting in the coal surface mines even though thousands of tons of explosives are detonated each year in the basin. The maximum weight of an individual explosive charge and the time interval between blasts are regulated so that any nearby structures will not be damaged or the residents disturbed. Blasting, nevertheless, does produce seismic tremors that can be recorded over 200 kilometers away. In addition, at one mine, some very low order aftershocks were recorded relatively close to the source within 2 hours after blasting.

Montana; Wyoming↗
USGS1990

Hydrothermally derived petroleum: examples from Guaymas Basin, Gulf of California, and Escanaba Trough, northeast Pacific Ocean

In the Guaymas Basin, a spreading axis in the Gulf of California, petroleum having a wide range of compositions forms by hydrothermal alteration of organic matter in Quaternary sediment composed mainly of marine diatomaceous ooze and muddy turbidites. In Escanaba Trough, at the southern end of the Gorda Ridge spreading axis offshore northern California, petroleum is formed by hydrothermal processes acting on mainly terrigenous organic material in Quaternary turbiditic river-derived sediment. Comparisons of the distributions of hydrocarbons - n-alkanes, isoprenoids, terpanes, steranes, and aromatics - show that chemical differences among four petroleum samples are such that two samples from Guaymas Basin can be distinguished from two samples from Escanaba Trough. Distinguishing characteristics resulting from differences in sources include n-alkane distributions and certain sterane ratios; distinguishing characteristics resulting from differences in thermal histories of the organic matter include hopane and sterane epimer ratios and various distributions of polycyclic aromatic hydrocarbons. These oils differ from conventionally derived petroleum in that they are admixtures of products generated over a wide range of thermal regimes, and their generation, expulsion, and migration occurred simultaneously over an instantaneous geological time period. The potential economic significance of hydrothermal derived petroleum is uncertain, but the fact that petroleum can form at active oceanic spreading axes adds a new facet to understanding the processes of petroleum generation, expulsion, and migration.

Escanaba Trough and Guaymas Basin in the system of↗
USGS2000

High-resolution seismic reflection surveys and modeling across an area of high damage from the 1994 Northridge earthquake, Sherman Oaks, California

Approximately 3.6 km of P-wave seismic-reflection data were acquired along two orthogonal profiles in Sherman Oaks, California to determine whether shallow (less than 1-km depth) geologic structures contributed to the dramatic localized damage resulting from the 1994 Northridge earthquake. Both lines, one along Matilija Avenue and one along Milbank Street, crossed areas of both high and low damage. We believe these data reveal a geologic structure in the upper 600 m that contributed to the increased earthquake ground shaking in the high-damage areas south of and along the Los Angeles River. Of interest in these data is a reflection interpreted to be from bedrock that can be traced to the north along the Matilija Avenue profile. This reflecting interface, dipping northward at 15°–22°, may be an important impedance boundary because it is the lower boundary of a wedge of overlying low-velocity sediments. The wedge thins and terminates in the area where we interpret down-warped reflections as evidence of a shallow subbasin. The low-velocity subbasin sediments (V s of 200 m/sec V p of 500 m/sec) may be up to 150 m thick beneath the channelized Los Angeles River. The area across the subbasin experienced greater earthquake damage from possible geometric focusing effects. Three-dimensional basin effects may be responsible for the variable damage pattern, but from these seismic profiles it is not possible to determine the regional structural trends. Two-dimensional elastic and SH-mode finite-difference modeling of the imaged structural geometry along Matilija Avenue suggests that a peak horizontal-velocity amplification factor of two-and-over can be explained in the high-damage area above the shallow subbasin and sediment wedge. Amplification factors up to 5 were previously observed in aftershock data, at frequencies of 2 to 6 Hz. Amplification in the elastic simulation at the Santa Monica Mountains range-front on the southern end of the Matilija profile, with the geologic layering and geometry interpreted from the seismic data, is also consistent with aftershock observations.

Bulletin of the Seismological Society of America↗
USGS2002

Unconventional shallow biogenic gas systems

Unconventional shallow biogenic gas falls into two distinct systems that have different attributes. Early-generation systems have blanketlike geometries, and gas generation begins soon after deposition of reservoir and source rocks. Late-generation systems have ringlike geometries, and long time intervals separate deposition of reservoir and source rocks from gas generation. For both types of systems, the gas is dominantly methane and is associated with source rocks that are not thermally mature. Early-generation biogenic gas systems are typified by production from low-permeability Cretaceous rocks in the northern Great Plains of Alberta, Saskatchewan, and Montana. The main area of production is on the southeastern margin of the Alberta basin and the northwestern margin of the Williston basin. The huge volume of Cretaceous rocks has a generalized regional pattern of thick, non-marine, coarse clastics to the west and thinner, finer grained marine lithologies to the east. Reservoir rocks in the lower part tend to be finer grained and have lower porosity and permeability than those in the upper part. Similarly, source beds in the units have higher values of total organic carbon. Patterns of erosion, deposition, deformation, and production in both the upper and lower units are related to the geometry of lineament-bounded basement blocks. Geochemical studies show that gas and coproduced water are in equilibrium and that the fluids are relatively old, namely, as much as 66 Ma. Other examples of early-generation systems include Cretaceous clastic reservoirs on the southwestern margin of Williston basin and chalks on the eastern margin of the Denver basin. Late-generation biogenic gas systems have as an archetype the Devonian Antrim Shale on the northern margin of the Michigan basin. Reservoir rocks are fractured, organic-rich black shales that also serve as source rocks. Although fractures are important for production, the relationships to specific geologic structures are not clear. Large quantities of water are coproduced with the gas, and geochemical data indicate that the water is fairly fresh and relatively young. Current thinking holds that biogenic gas was generated, and perhaps continues to be, when glacial meltwater descended into the plumbing system provided by fractures. Other examples of late-generation systems include the Devonian New Albany Shale on the eastern margin of the Illinois basin and the Tertiary coalbed methane production on the northwestern margin of the Powder River basin. Both types of biogenic gas systems have a similar resource development history. Initially, little technology is used, and gas is consumed locally; eventually, sweet spots are exploited, widespread unconventional reservoirs are developed, and transport of gas is interstate or international. However, drilling and completion techniques are very different between the two types of systems. Early-generation systems have water-sensitive reservoir rocks, and consequently water is avoided or minimized in drilling and completion. In contrast, water is an important constituent of late-generation systems; gas production is closely tied to dewatering the system during production. Existing production and resource estimates generally range from 10 to 100 tcf for both types of biogenic gas systems. Although both system types are examples of relatively continuous accumulations, the geologic frameworks constrain most-economic production to large geologic structures on the margins of basins. Shallow biogenic gas systems hold important resources to meet the increased domestic and international demands for natural gas.

American Association of Petroleum Geologists Bulle↗
USGS1974

Buried Triassic basin in the central Savannah River area, South Carolina and Georgia

A basin filled with Triassic red beds, located on the South Carolina–Georgia line ∼32 km southeast of Augusta, Georgia, is buried beneath ∼350 m of Coastal Plain sediments. An extensive aeromagnetic survey, seismic refraction and reflection surveys, and geophysical logs and samples from three wells define the extent and character of the basin. This basin, herein named the Dunbarton Triassic basin, is ∼50 km long, 10 km wide, and trends northeast. The northwest margin of the basin is well defined by the aeromagnetic survey, a seismic reflection traverse, and a well that passed through 485 m of Triassic fanglomerate before entering the crystalline metamorphic rocks below. Near the center of the Triassic basin, a well passed through 902 m of maroon Triassic mudstone and sandstone of fluvial origin without penetrating the bottom of the basin. The permeability of the Triassic rock is extremely low, and water-transmitting fractures were not penetrated. Even slight water-level disturbances in the Triassic wells require many years to recover. Total dissolved solids of the water from the Triassic basin are about twice that in the crystalline metamorphic rocks that surround it. The inferred geologic history of this basin is similar to the history of Triassic basins that crop out in North Carolina.

Georgia, South Carolilna↗
USGS2011

Controls on large landslide distribution and implications for the geomorphic evolution of the southern interior Columbia River basin

Large landslides (>0.1 km 2 ) are important agents of geomorphic change. While most common in rugged mountain ranges, large landslides can also be widespread in relatively low-relief (several 100 m) terrain, where their distribution has been relatively little studied. A fuller understanding of the role of large landslides in landscape evolution requires addressing this gap, since the distribution of large landslides may affect broad regions through interactions with channel processes, and since the dominant controls on landslide distribution might be expected to vary with tectonic setting. We documented >400 landslides between 0.1 and ∼40 km 2 across ∼140,000 km 2 of eastern Oregon, in the semiarid, southern interior Columbia River basin. The mapped landslides cluster in a NW-SE–trending band that is 50–100 km wide. Landslides predominantly occur where even modest local relief (∼100 m) exists near key contacts between weak sedimentary or volcaniclastic rock and coherent cap rock. Fault density exerts no control on landslide distribution, while ∼10% of mapped landslides cluster within 3–10 km of mapped fold axes. Landslide occurrence is curtailed to the NE by thick packages of coherent basalt and to the SW by limited local relief. Our results suggest that future mass movements will localize in areas stratigraphically preconditioned for landsliding by a geologic history of fluviolacustrine and volcaniclastic sedimentation and episodic capping by coherent lava flows. In such areas, episodic landsliding may persist for hundreds of thousands of years or more, producing valley wall slopes of ∼7°–13° and impacting local channels with an evolving array of mass movement styles.

Idaho, Oregon, Washington↗
USGS2007

Geology and Mineral Resources of the East Mojave National Scenic Area, San Bernardino County, California

The rocks of the East Mojave National Scenic Area (EMNSA) record a history of dynamic geologic events that span more than 1,800 million years (m.y.). These geologic events contributed significantly to development of the spectacular vistas and panoramas present in the area today. The oldest rocks underlie much of the northern part of the EMNSA. These rocks were subjected to extreme pressures and temperatures deep in the Earth's crust about 1,700 million years ago (Ma). They were subsequently intruded by granitic magmas from about 1,695 to 1,650 Ma, by additional granitic magmas at about 1,400 Ma and, later, at about 1,100 Ma, by iron-rich magmas that crystallized to form dark igneous rocks termed diabase. Unusual potassium- and magnesium-rich rocks, emplaced at about 1,400 Ma, crop out in a few places within and near the EMNSA. Their distinctive composition results from very small degrees of partial melting of mantle peridotite that was highly enriched in incompatible trace elements. At Mountain Pass, just outside the northeast boundary of the EMNSA, the potassium- and magnesium-rich rocks are accompanied by a rare type of carbonatite, an igneous rock composed of carbonate minerals, that contains high-grade rare earth element mineralization. Subsequent to these igneous-dominated events, sedimentary strata began to be deposited at about 1,000 Ma; mostly sandstone and shale were deposited initially in marine and, less commonly, in continental environments along the west edge of the core of the North American continent. Sedimentation eventually culminated in the widespread deposition of thick marine limestones from about 400 to about 245 Ma. These limestones represent a continental-shelf environment where shallow-water limestone formed to the east and deeper water limestone formed to the west. The end of the formation of these sedimentary deposits probably was caused by uplift of the shelf, which marked the beginning of a long period of tectonic upheaval. At about 170 Ma, widespread emplacement of coarse-grained granitic magmas began again in the region; some of these magmas also erupted as volcanic rocks. Additional episodes of magmatism took place at about 100 Ma and at 75 Ma. Most of the metallic-mineral occurrences in the EMNSA are associated with the igneous rocks that range in age from 170 to 75 Ma. During each of these magmatic events, the previously deposited sedimentary strata were buckled and broken as the entire region, part of a continental-scale fold and thrust belt, underwent crustal shortening and compression. A period of tectonic quiescence characterized the region from about 65 Ma to about 20 Ma. The quiet period ended abruptly with widespread volcanism along the southern and eastern parts of the EMNSA. The major gold deposits in the Castle Mountains are associated with this episode of volcanism. During this volcanic outburst, the crust extended laterally in several areas that border the EMNSA: along the lower Colorado River 65 km to the east, in the Kingston Range 20 km to the north, and in the central Mojave Desert 75 km to the southwest. This extensional deformation is characterized by the superposition of upper-crustal rocks over midcrustal rocks along large flat-lying faults, several of which project beneath rocks now exposed at the surface in the EMNSA. The near-surface rocks of the EMNSA, however, apparently escaped much of this intense extensional deformation. High-angle faults, which cut several of the mountain ranges, possibly have undergone several periods of movement, which date back to approximately 70 to 100 Ma. Some faults are of local importance to the physiographic development of the mountain ranges and intervening basins, and, in places, the faults seem to have localized various kinds of ore bodies and mineral occurrences. Volcanism and extensional deformation waned from 14 to 11 Ma. By approximately 10 Ma, widespread erosion had produced broad erosional dome-shaped mountains in the n

Bulletin↗
USGS2021

New insights into organic matter accumulation from high-resolution geochemical analysis of a black shale: Middle and Upper Devonian Horn River Group, Canada

Organic matter (OM) accumulation in organic matter-rich mudstones, or black shales, is generally recognized to be controlled by combinations of bioproductivity, preservation, and dilution. However, specific triggers of OM deposition in these formations are commonly difficult to identify with geochemical proxies, in part because of feedbacks that cause geochemical proxies for these controls to vary synchronously. This apparent synchronicity is partly a function of sample spacing, commonly at decimeter to meter intervals, which may represent longer periods of time than is required for the development of feedbacks. Higher resolution data sets may be required to fully interpret OM accumulation. This study applies a novel combination of technologies to develop a high-resolution geochemical data set, integrating energy-dispersive X-ray fluorescence (EDXRF) and infrared imagery analyses, to record proxies for redox conditions, bioproductivity, and clastic and carbonate dilution in millimeter-resolution profiles of 133 core slabs from the Middle and Upper Devonian Horn River shale in the Western Canada Sedimentary Basin, which provides decadal-scale temporal resolution. A comparison to a more coarsely sampled data set from the same core results in substantially different interpretations of variations in bioproductivity, redox, and dilution proxies. Stratigraphic distributions of organic matter accumulation patterns (bioproductivity-control, siliciclastic/carbonate-dilution, and redox conditions-control) show that organic enrichment events were highly varied during deposition of the shale and were closely related to second- and third-order sea-level changes. High-resolution profiles indicate that bioproductivity was the predominant trigger for organic matter accumulation in a second-order highstand, particularly during deposition of third-order transgressive systems tracts. Organic matter accumulation was largely controlled by dilution from either carbonate or clastic sediments in a second-order lowstand. Bioproductivity-redox feedbacks developed on timescales of decades to centuries.

British Columbia, Northwest Territories↗
USGS1995

Tectonic setting of the Portland-Vancouver area, Oregon and Washington: Constraints from low-altitude aeromagnetic data

Seismic activity in the Portland-Vancouver metropolitan area may be associated with various mapped faults that locally offset volcanic basement of Eocene age and younger. This volcanic basement is concealed in most places by young deposits, vegetation, and urban development. The U.S. Geological Survey conducted an aeromagnetic survey in September 1992 to investigate the extent of these mapped faults and possibly to help identify other seismic and volcanic hazards in the area. The survey was flown approximately 240 m above terrain, along flight lines spaced 460 m apart, and over an area about 50 × 50 km. These magnetic data indicate a pronounced northwest-striking magnetic lineation east of the Willamette River in downtown Portland associated with a fault concealed beneath Quaternary sedimentary deposits and previously inferred from shallow well data. The magnetic lineation confirms the existence of the fault and suggests that it has had a prolonged history: (1) Although well data indicate <200 m of vertical offset of underlying volcanic basement, models based on the aeromagnetic data from downtown Portland suggest reverse faulting with up to 1 km of offset deeper in the section. (2) The magnetic lineation associated with this fault extends southeast to the Clackamas River drainage, a distance of 50 km and considerably beyond the mapped extent of the fault. A northwest-striking magnetic anomaly located southwest of the Tualatin Mountains corresponds closely with another mapped fault and with mixed reverse and strike-slip faulting during a seismic swarm (M ≤ 3) in 1991. We believe these and other anomalies in the aeromagnetic data reflect the Portland Hills fault zone, believed to be the southwestern boundary of a structural basin now occupied by Portland and Vancouver. The postulated northeastern boundary of the basin, the Frontal fault zone, is also evident, although less well represented in the aeromagnetic data. Aeromagnetic anomalies, geologic mapping, and earthquake focal-plane solutions demonstrate a complex deformational history in the Portland-Vancouver area since middle Miocene time that includes elements of compression, extension, and dextral slip. These complexities reflect Portland-Vancouver's unique position within a north-south transition in tectonic styles along the Cascadia margin, from compressional in the north to extensional in the south.

Oregon, Washington↗
USGS2005

Neotectonics of the offshore Oak Ridge fault near Ventura, southern California

The Oak Ridge fault is a large-offset, south-dipping reverse fault that forms the south boundary of the Ventura Basin in southern California. Previous research indicates that the Oak Ridge fault south of the town of Ventura has been inactive since 200-400 ka ago and that the fault tip is buried by ??? 1 km of Quaternary sediment. However, very high-resolution and medium-resolution seismic reflection data presented here show a south-dipping fault, on strike with the Oak Ridge fault, that is truncated at 80 m depth by an unconformity that is probably at the base of late Pleistocene and Holocene sediment. Furthermore, if vertically aligned features in seismic reflection data are eroded remnants of fault scarps, then a subsidiary fault within the Oak Ridge system deforms the shallowest imaged sediment layers. We propose that this subsidiary fault has mainly left-slip offset. These observations of Holocene slip on the Oak Ridge fault system suggest that revision of the earthquake hazard for the densely populated Santa Clara River valley and the Oxnard coastal plain may be needed.

Bulletin of the Seismological Society of America↗
USGS1959

History of Imuruk Lake, Seward Peninsula, Alaska

A study of Imuruk Lake, a large, shallow lake in north-central Seward Peninsula, Alaska, illuminates the climatic history of northwestern Alaska and the tectonic history of central Seward Peninsula during Pleistocene and Recent time. Special interest attaches to the older lake sediments, because they contain evidence concerning the climate, fauna, and flora that existed in the vicinity of Bering Strait at a time when the Bering land bridge was open and when animal and plant populations were being exchanged between the eastern and western hemispheres. The lake is 8 miles long and less than 10 feet deep; bottom sediments consisting of reworked wind-blown silt bury a rolling bedrock topography of much greater relief. Analysis of the hydrologic regime indicates that much of the water draining into the lake is lost by evaporation; smaller quantities are lost by discharge through the outlet, the Kugruk River, and by leakage into the lava flows along the lake shore. Changes in the duration and temperature of the summer ice-free season would result in changes in the amount of water lost by evaporation and thus in appreciable changes in lake level. Imuruk Lake occupies an initial low area on basaltic lava flows of Quaternary age, but the initial low area has been modified by faulting and now lies in a poorly defined graben. Topographic evidence confirmed by study of lacustrine terraces indicates that until recently Imuruk Lake drained westward into the Noxapaga River instead of eastward into the Kugruk River. A history of repeated warping of the lake basin, on which is superimposed a history of oscillating lake level which is due to changes in climate, is recorded by three systems of abandoned shore-line features found along the shores: a warped shore cliff of probable Illinoian age, a double set of warped terraces of probable Wisconsin age, and a low, horizontal terrace of Recent age. Bones of bison, horse, and mammoth were found in peaty sediments containing many twigs but no large wood; their presence indicates that these mammals, at least, were capable of surviving in a tundra environment during cold stages of the Pleistocene epoch and at a time when the Bering land bridge was in existence nearby. The sediments filling the deeper parts of the bedrock basin of Imuruk Lake probably contain an uninterrupted pollen record that reflects vegetation changes in central Seward Peninsula beginning in middle Illinoian time and terminating a few thousand years ago. Core drilling and pollen analysis of these sediments would greatly amplify our understanding of late Pleistocene events in the vicinity of the Bering land bridge.

Alaska↗
USGS1982

Hydrology of the surficial aquifer in the Floyd River Basin, Iowa

The Floyd River basin was studied to provide water-resources Information for a typical surficial aquifer in northwest Iowa. Data collection included test drilling, water-level measurements, and chemical analyses of surface and ground water. The Floyd River basin drains 961 square miles of highly dissected to gently rolling topography. Major streams generally are flanked by flood plains underlain by uncemented sand and-gravel deposits. Most of the basin is directly underlain by glacial drift of Pleistocene age which is In turn underlain by rocks of Cretaceous age. Sand-and-gravel deposits underlying the major flood plains and in buried bedrock channels within the drift comprise the surficial aquifer. The surficial aquifer ranges from 10 to 40 feet In thickness and averages about 20 feet thick. Both unconfined and confined conditions occur in the aquifer and water levels range from 2 to 55 feet below land surface. An aquifer test conducted in the surficial aquifer where it is about 25 feet thick and is confined by an overlying low permeability bed Indicated an average hydraulic conductivity of 383 feet per day and a storage coefficient of 0.0001. The well was pumped at 650 gallons per minute for 43 hours. An observation well about 70 feet from the pumping well had a maximum drawdown of about 10 feet.

Iowa↗
USGS2010

Assessment of undiscovered conventional oil and gas resources, onshore Claiborne Group, United Statespart of the northern Gulf of Mexico Basin

The middle Eocene Claiborne Group was assessed for undiscovered conventional hydrocarbon resources using established U.S. Geological Survey assessment methodology. This work was conducted as part of a 2007 assessment of Paleogene-Neogene strata of the northern Gulf of Mexico Basin, including the United States onshore and state waters (Dubiel et al., 2007). The assessed area is within the Upper Jurassic-CretaceousTertiary composite total petroleum system, which was defined for the assessment. Source rocks for Claiborne oil accumulations are interpreted to be organic-rich, downdip, shaley facies of the Wilcox Group and the Sparta Sand of the Claiborne Group; gas accumulations may have originated from multiple sources, including the Jurassic Smackover Formation and the Haynesville and Bossier shales, the Cretaceous Eagle Ford and Pearsall (?) formations, and the Paleogene Wilcox Group and Sparta Sand. Hydrocarbon generation in the basin started prior to deposition of Claiborne sediments and is currently ongoing. Primary reservoir sandstones in the Claiborne Group include, from oldest to youngest, the Queen City Sand, Cook Mountain Formation, Sparta Sand, Yegua Formation, and the laterally equivalent Cockfield Formation. A geologic model, supported by spatial analysis of petroleum geology data, including discovered reservoir depths, thicknesses, temperatures, porosities, permeabilities, and pressures, was used to divide the Claiborne Group into seven assessment units (AUs) with three distinctive structural and depositional settings. The three structural and depositional settings are (1) stable shelf, (2) expanded fault zone, and (3) slope and basin floor; the seven AUs are (1) lower Claiborne stable-shelf gas and oil, (2) lower Claiborne expanded fault-zone gas, (3) lower Claiborne slope and basin-floor gas, (4) lower Claiborne Cane River, (5) upper Claiborne stable-shelf gas and oil, (6) upper Claiborne expanded fault-zone gas, and (7) upper Claiborne slope and basin-floor gas. Based on Monte Carlo simulation of justified input parameters, the total estimated mean undiscovered conventional hydrocarbon resources in the seven AUs combined are 52 million bbl of oil, 19.145 tcf of natural gas, and 1.205 billion bbl of natural gas liquids. This article describes the conceptual geologic model used to define the seven Claiborne AUs, the characteristics of each AU, and the justification behind the input parameters used to estimate undiscovered resources for each AU. The great bulk of undiscovered hydrocarbon resources are predicted to be nonassociated gas and natural gas liquids contained in deep (mostiy >12,000-ft [3658 m], present-day drilling depths), overpressured, structurally complex outer shelf or slope and basin-floor Claiborne reservoirs. The continuing development of these downdip objectives is expected to be the primary focus of exploration activity for the onshore middle Eocene Gulf Coast in the coming decades. ?? 2010 U.S. Geological Survey. All rights reserved.

American Association of Petroleum Geologists Bulle↗
USGS1985

Depositional Relations of Umpqua and Tyee Formations (Eocene), Southwestern Oregon

Studies of the depositional relations of the Umpqua and Tyee Formations (Eocene) in southwestern Oregon indicate a need for reassessing the correlations and currently used terminology. The Umpqua Formation (as herein restricted) consists of as much as 10,000 ft (3,000 m) of mudstone, sandstone, and conglomerate of nonmarine to deep marine origin. A basaltic basement that underlies the sedimentary rocks in most of the area and was formerly included in the Umpqua is herein considered a separate unit and assigned to the Siletz River Volcanics. A proposal to subdivide the Umpqua into three unconformity-bounded formations (in ascending order: Roseburg, Lookingglass, and Flournoy Formations) in the area west of Roseburg, Oregon, is not recognized in this report because of quest onable correlations and limited extent of some units. Foremost of these questionable correlations is that of the Flournoy Formation with rocks formerly assigned to the Tyee Formation in areas as far north as the latitude of Salem, Oregon. My investigations of depositional facies and lithologic criteria do not substantiate this correlation. The Tyee Formation, which conformably overlies the Umpqua, is a predominantly sandstone unit about 6,000 ft (1,800 m) thick, deposited in environments ranging from shallow marine and nonmarine deltaic on the south, to slope and deep marine basinal to the north. Deposition across the Umpqua-Tyee boundary contact represents a change in tectonic setting from active plate margin of the Umpqua to more stable marginal basin deposition of the Tyee. This change is also reflected in a change in provenance as indicated by the characteristic arkosic and micaceous aspects of Tyee sandstones.

Oregon↗
USGS1952

Glaciation and drainage changes in the fish Lake Plateau, Utah

The Fish Lake Plateau , nearly centrally located among the High Plateaus of Utah , exhibits glacial and other geomorphic features of regional significance. The plateau is divided into two areas by Fish Lake and the wide valley of Sevenmile Creek. The Fish Lake trough is a structural basin; Sevenmile Valley may be largely erosional. Volcanic rocks of Tertiary age underlie most of the plateau ; early Tertiary sedimentary rocks are also present. Glaciated canyons with well-developed cirques are especially prominent along the east-facing sides of the Fish Lake trough and Sevenmile Valley. Ice-eroded features occur over much of the plateau top. Near the mouths of several of the glaciated canyons are two conspicuous sets of moraines. The older set is more extensive and less rugged than the younger and occurs at somewhat lower elevations. Two substages of glaciation thus recognized are correlated with Wisconsin I and II of Ray; probable correlatives of Wisconsin III, IV, and V are represented by moraines which are younger than these two sets. Fish Lake drains north into Fremont River, a tributary of the Colorado River. An abandoned southern outlet and waterfall, the latter at a higher elevation than the present elevation of the original northern bedrock divide, indicate drainage reversal. Evidence is presented which suggests that this reversal was pre-glacial and probably the result of fault-block tilting.

Utah↗