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At least 1,225 records · Page 68Linked to original sources
USGS2002

Habitat and environment of islands: primary and supplemental island sets

The original intent of the study was to develop a first-order synopsis of island hydrology with an integrated geologic basis on a global scale. As the study progressed, the aim was broadened to provide a framework for subsequent assessments on large regional or global scales of island resources and impacts on those resources that are derived from global changes. Fundamental to the study was the development of a comprehensive framework—a wide range of parameters that describe a set of "saltwater" islands sufficiently large to Characterize the spatial distribution of the world’s islands; Account for all major archipelagos; Account for almost all oceanically isolated islands, and Account collectively for a very large proportion of the total area of the world’s islands whereby additional islands would only marginally contribute to the representativeness and accountability of the island set. The comprehensive framework, which is referred to as the “Primary Island Set,” is built on 122 parameters that describe 1,000 islands. To complement the investigations based on the Primary Island Set, two supplemental island sets, Set A—Other Islands (not in the Primary Island Set) and Set B—Lagoonal Atolls, are included in the study. The Primary Island Set, together with the Supplemental Island Sets A and B, provides a framework that can be used in various scientific disciplines for their island-based studies on broad regional or global scales. The study uses an informal, coherent, geophysical organization of the islands that belong to the three island sets. The organization is in the form of a global island chain, which is a particular sequential ordering of the islands referred to as the "Alisida." The Alisida was developed through a trial-and-error procedure by seeking to strike a balance between "minimizing the length of the global chain" and "maximizing the chain’s geophysical coherence." The fact that an objective function cannot be minimized and maximized simultaneously indicates that the Alisida is not unique. Global island chains other than the Alisida may better serve disciplines other than those of hydrology and geology.

Professional Paper↗
USGS1999

Lava Falls Rapid in Grand Canyon: Effects of Late Holocene debris flows on the Colorado River

Lava Falls Rapid is the most formidable reach of whitewater on the Colorado River in Grand Canyon and is one of the most famous rapids in the world. Debris flows in 1939, 1954, 1955, 1966, and 1995, as well as prehistoric events, completely changed flow through the rapid. Floods cleared out much of the increased constrictions, but releases from Glen Canyon Dam, including the 1996 controlled flood, are now required to remove the boulders deposited by the debris flows.

Arizona↗
USGS1998

The nature and timing of tectonism in the western facies terrane of Nevada and California; an outline of evidence and interpretations derived from geologic maps of key areas

Along the outer miogeocline of Nevada and Southern California, lower Paleozoic siliceous sediments and basalt flows, the western facies terrane emerged in Late Devonian time and were deeply eroded; but structural evidence that this event, the Antler Orogeny, involved intense folding and thrust faulting is notably scarce. Almost all the intense folding and thrust faulting of Proterozoic to Permian strata dates from the Jurassic to Eocene interval. If this tectonic history is valid, then the genesis of the Antler Orogeny is reduced to a question of vertical tectonics. Pre-Jurassic contraction involving subduction and collision with island arcs is not indicated or required, but the ultimate origin of Paleozoic tectonism remains unclear.

Professional Paper↗
USGS1998

An outline of tectonic, igneous, and metamorphic events in the Goshute-Toano Range between Silver Zone Pass and White Horse Pass, Elko County, Nevada; a history of superposed contractional and extensional deformation

Seven kinds of fault-bounded tracts are described. One of the tracts provides a good example of Mesozoic contractional folding and faulting; six exemplify various aspects of Miocene extensional faulting. Massive landslide deposits resulting from Tertiary faulting are described. Mesozoic intrusive rocks and extensive exposures of Miocene volcanic rocks are described and dated. The age ranges of stratigraphic units were based on numerous conodont collections, and ages of igneous rocks were determined by argon/argon and fission-track methods. The geologic complexity of the Goshute-Toano Range provides opportunities for many additional productive structural studies.

Professional Paper↗
USGS1998

Aquatic habitats in relation to river flow in the Apalachicola River floodplain, Florida

This study is part of a larger effort to identify fresh water needs throughout the region and develop a mechanism for basinwide water management. Quantitative estimates of the amount of aquatic habitat in the floodplain in relation to river flow are presented. Plates show streams, lakes, and floodplain forests connected to the main river channel at selected flows; an analysis of long-term flow record in the Apalachicola River; and a review of the literature regarding fishes in floodplains of the Apalachicola River and other rivers of the Eastern United States. Examples show how this report can be used to assess impacts of flow alterations on aquatic habitats and fishes.

Florida↗
USGS1998

Geochemical studies of rare earth elements in the Portuguese pyrite belt, and geologic and geochemical controls on gold distribution

This report describes geochemical and geological studies which were conducted by the U.S. Geological Survey (USGS) and the Servicos Geologicos de Portugal (SPG) in the Portuguese pyrite belt (PPB) in southern Portugal. The studies included rare earth element (REE) distributions and geological and geochemical controls on the distribution of gold. Rare earth element distributions were determined in representative samples of the volcanic rocks from five west-trending sub-belts of the PPB in order to test the usefulness of REE as a tool for the correlation of volcanic events, and to determine their mobility and application as hydrothermal tracers. REE distributions in felsic volcanic rocks show increases in the relative abundances of heavy REE and a decrease in La/Yb ratios from north to south in the Portuguese pyrite belt. Anomalous amounts of gold are distributed in and near massive and disseminated sulfide deposits in the PPB. Gold is closely associated with copper in the middle and lower parts of the deposits. Weakly anomalous concentrations of gold were noted in exhalative sedimentary rocks that are stratigraphically above massive sulfide deposits in a distal manganiferous facies, whereas anomalously low concentrations were detected in the barite-rich, proximal-facies exhalites. Altered and pyritic felsic volcanic rocks locally contain highly anomalous concentrations of gold, suggesting that disseminated sulfide deposits and the non-ore parts of massive sulfide deposits should be evaluated for their gold potential.

Professional Paper↗
USGS1998

Reservoir quality and diagenetic evolution of Upper Mississippian rocks in the Illinois Basin; influence of a regional hydrothermal fluid-flow event during late diagenesis

Conventional reservoir quality data for more than 300 wells provided by the Illinois and Indiana State Geological Surveys were analyzed to determine the factors governing porosity and permeability in the Upper Mississippian Bethel Sandstone and Cypress Sandstone, two of the principal producing units in the Illinois Basin. In addition, approximately 150 samples of the Bethel Sandstone-Cypress Sandstone interval from about 80 wells in the Illinois Basin were collected for mineralogical and geochemical analysis to reconstruct the burial and diagenetic history and to establish the timing of diagenesis relative to the entrapment of hydrocarbons. One aspect of the study involved linking inorganic and organic diagenesis to late Paleozoic tectonism and hydrothermal fluid-flow events in the region.

Professional Paper↗
USGS1999

Desert winds: Monitoring wind-related surface processes in Arizona, New Mexico, and California

The 18-year Desert Winds Project established instrumented field sites in the five major regions of the North American Desert to obtain meteorological, geological, and vegetation data for natural desert sites affected by wind erosion. The eight chapters in this volume describe the settings and operation of the stations and summarize eolian-related research to date around the stations. The report includes studies of the sand-moving effectiveness of storm winds, wind-erosion susceptibility of different ground-surface types, relations of dust storms to meteorological conditions, mediation of wind erosion by vegetation, remote sensing to detect vegetation changes related to climate change, and comparison of regional dust deposition to that near Owens (dry) Lake.

Arizona, California, New Mexico↗
USGS1999

Lithofacies, depositional environments, and regional stratigraphy of the lower Eocene Ghazij Formation, Balochistan, Pakistan

The coal-bearing, lower Eocene Ghazij Formation is exposed intermittently over a distance of 750 kilometers along the western margin of the Axial Belt in north-central Pakistan. Underlying the formation are Jurassic to Paleocene carbonates that were deposited on a marine shelf along the pre- and post-rift northern margin of the Indian subcontinent. Overlying the formation are middle Eocene to Miocene marine and nonmarine deposits capped by Pliocene to Pleistocene collision molasse. The lower part of the Ghazij comprises mostly dark gray calcareous mudrock containing foraminifers and rare tabular to lenticular bodies of very fine grained to finegrained calcareous sandstone. We interpret the lower portion of this part of the Ghazij as outer-shelf deposits, and the upper portion as prodelta deposits. The middle part of the formation conformably overlies the lower part. It comprises medium-gray calcareous mudrock containing nonmarine bivalves, fine- to medium-grained calcareous sandstone, and rare intervals of carbonaceous shale and coal. Sandstone bodies in the middle part, in ascending stratigraphic order, are classified as Type I (coarsening-upward grain size, contain the trace fossil Ophiomorpha, and are commonly overlain by carbonaceous shale or coal), Type II (mixed grain size, display wedge-planar cross stratification, and contain fossil oyster shells and Ophiomorpha), and Type III (finingupward grain size, lenticular shape, erosional bases, and display trough cross stratification). These three types of bodies represent shoreface deposits, tidal channels, and fluvial channels, respectively. Mudrock intervals in the lower portion of this part of the formation contain fossil plant debris and represent estuarine deposits, and mudrock intervals in the upper portion contain fossil root traces and represent overbank deposits. We interpret the middle part of the Ghazij as a lower delta plain sequence. Overlying the middle part of the Ghazij, possibly unconformably, is the upper part of the formation, which comprises calcareous, nonfossiliferous, light-gray, brown, and red-banded mudrock, and rare Type III sandstone bodies. Much of the mudrock in this part of the formation represents multiple paleosol horizons. Locally, a limestone-pebble conglomerate is present in the upper part of the formation, either at the base or occupying most of the sequence. We interpret all but the uppermost portion of the upper part of the Ghazij as an upper delta plain deposit. Thin sections of Ghazij sandstones show mostly fragments of limestone, and heavy-liquid separations reveal the presence of chromite. Paleocurrent data and other evidence indicate a northwestern source area. During earliest Eocene time, the outer edge of the marine shelf off the Indian subcontinent collided with a terrestrial fragment positioned adjacent to, but detached from, the Asian mainland. This collision caused distal carbonateplatform deposits to be uplifted, and an intervening intracratonic sea, the Indus Foreland Basin, was created. Thus for the first time, the depositional slope switched from northwest facing to southeast facing, and a northwestern source for detritus was provided. We conclude that the Ghazij was deposited as a prograding clastic wedge along the northwestern shore of this sea, and that the formation contains sedimentologic evidence of a collisional event that predates the main impact between India and Asia.

Balochistan↗
USGS1903

The Carboniferous formations and faunas of Colorado

In the following pages the geology and paleontology of the Carboniferous rocks of Colorado are discussed from the viewpoint of the stratigraphic paleontologist. This viewpoint is also that of one not personally acquainted with the field in question, except in very small measure. I made or assisted in making a few collections of fossils, and enjoyed the privilege of being connected for a month with a field party under the charge of Mr. Whitman Cross during the season of 1900. Most of the extensive collections which I have studied are the work of others, and the strata, in their characters and mutual attitudes, have been viewed only through the pages of geologic reports. The tendencies of my work are almost exclusively toward the historical geology, for from the nature of the case, even had I wished, it would have been difficult to dear with the structural or economic phases of the subject.

Colorado↗
USGS1930

Geologic history of the Yosemite Valley

The problem of the origin of the Yosemite Valley inherently demands a solution in quantitative terms. Its essence is, To what extent is the valley a product of glacial action, to what extent a product of stream erosion? The principal result of the investigations upon which this report is based is the determination within narrow limits of the preglacial depth of the Yosemite Valley and of other facts concerning its preglacial development which permit fairly definite estimates of the proportionate shares of work performed by stream and by glacier. The investigations comprise a detailed survey of the glacial and geomorphologic features of the Yosemite region and an equally intensive study of its rock formations, supplemented by reconnaissance work of both kinds in adjoining parts of the Sierra Nevada. The petrologic studies were made by Frank C. Calkins; the glacial and geomorphologic survey by Francois E. Matthes. Detailed mapping of the morainal system of the ancient Yosemite Glacier has served not only to determine the farthest limits reached by that glacier but to throw new light on the significance of the hanging valleys of the Yosemite region. It is reasonably certain that the glacier never extended more than about a mile beyond the site of El Portal. The hanging side valleys of the Merced Canyon below El Portal, therefore, hang not because of any glacial deepening suffered by that canyon. The explanation is offered that they hang because their streamlets have been unable to trench as rapidly as the Merced River since the rejuvenation of the Merced by the last uptilting of the Sierra Nevada. The streamlets were handicapped not only by their comparatively small volume but also by the fact that their courses trend northwestward and southeastward, substantially at right angles to the direction of the tilting, and therefore have remained essentially unsteepened, whereas the Merced's course trends southwestward, directly down the slope of the Sierra block, and therefore has been appreciably steepened. Projection of the longitudinal profiles of these hanging valleys forward to the axis of the Merced Canyon shows that they are closely accordant in height. Their profiles indicate a series of points on a former profile of the Merced with respect to which the side streams had graded their courses prior to the last uplift. This old profile can be extended upward into the glaciated part of the Merced Canyon above El Portal and even into the profoundly glaciated Yosemite Valley, accordant points being furnished by a number of hanging side valleys (due allowance being made for glacial erosion suffered by those valleys). However, not all the hanging valleys of the Yosemite region are accordant with this set. Several of them, including the upland valley of Yosemite Creek, constitute a separate set indicating another old profile of the Merced at a level 600 to 1,000 feet higher than the first. Others, including the hanging gulch of lower Bridalveil Creek, point to an old profile of the Merced about 1,200 feet lower than the first. There are thus three distinct sets of hanging valleys produced in three cycles of stream erosion. The valleys of the upper set, like those of the middle set, were left hanging as a result of rapid trenching by the Merced induced by an uplift of the range, there having been two such uplifts. Only the valleys of the lower set hang because of glacial deepening and widening of the Yosemite Valley, the cycle in which they were cut having been interrupted by the advent of the Pleistocene glaciers. They consequently indicate the preglacial depth of the Yosemite Valley. That depth, measured from the brow of El Capitan, was about 2,400 feet; measured from the rim at Glacier Point it was about 2,000 feet.

California↗