Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Journal of Geology”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37Linked to original sources
USGS1974

Unique cartographic characteristics of ERTS

The ERTS television sensing system has unique cartographic advantages over aircraft and satellite film systems. These are longer life combined with greater coverage, transmission of data in near real time, orthogonality, excellent geometric precision for planimetric mapping, suitability for automation (because of the basically continuous image on a mathematically definable map projection), radiometric fidelity, and the extension of sensing capability to near-infrared wavelengths.

Journal of Research of the U.S. Geological Survey↗
USGS1975

The distribution of seepage within lakebeds

The mutual exchange of water between lakes and contiguous permeable ground-water bodies, which are thin relative to the diameter of the lakes, was modeled digitally. A significant rate of seepage was found to extend only a relatively short distance from shore, thus forming a narrow band around the lake's perimeter. This near-shore concentration of seepage is an effect only of the geometry of the ground-water flow system, which is governed by the geometry of the body of permeable material, the spatial distribution of permeability within it, and the form of the water table. Near-shore seepage occurs independently of the presence of fine-grained, lowpermeability sedimentary bottom materials in the central part of the lake. Digital modeling indicates that the velocity of seepage generally decreases at an exponential rate as a function of distance from shore. Field measurements of seepage rates through the bottom of Lake Sallie, west-central Minnesota, confirm the model results by demonstrating that both the near-shore seepage band and the exponential decrease in seepage velocity actually exist.

Minnesota, Wisconsin↗
USGS1975

Evaluation of stochastic models describing movement of sediment particles on riverbeds

Various stochastic models have been proposed to describe the movement of sediment particles on the riverbed. Here it is attempted to summarize in an integrated form and to generalize the most important theoretical results in this field. The approach adopted in this paper is based on the fact that most of the stochastic models are only special cases of a particular kind of random walk on the straight line.

Journal of Research of the U.S. Geological Survey↗
USGS1975

Lower Keweenawan volcanic rocks of Michigan and Wisconsin

Unconformable sequences of Keweenawan volcanic rocks occur in Michigan and adjacent Wisconsin. The sequences differ in types of rocks, magnetic properties, metamorphic grade, and pattern of structural deformation; they had different vent areas and were deposited in basins that were only partly overlapping. The older sequence includes the Bessemer Quartzite and two newly named formations that are here assigned to the lower Keweenawan. The younger sequence includes the well-known Portage Lake Volcanics and a younger unnamed formation, both of middle Keweenawan age. Formerly the older rocks were interpreted as a fault-repeated part of the Portage Lake Volcanics, but new evidence indicates that these older rocks had been metamorphosed and tilted and were being eroded in middle Keeweenawan time.

Michigan, Wisconsin↗
USGS1975

A typical cross section based on magnetic data of lower and middle Keweenawan volcanic rocks, Ironwood area, Michigan

A north-trending aeromagnetic profile of a sequence of east-striking Keweenawan volcanic rocks near Ironwood, Mich., can be matched to a calculated profile over a model consisting of a series of dipping layers. (The dips were those measured by H. A. Hubbard along the north-trending valley of the Black River.) Remanent and induced magnetizations of 39 oriented cores from the Black River valley were determined by K. G. Books; felsite from Chippewa Hill and basalt from Algonquin Falls of middle Keweenawan age have normal Keweenawan magnetization and lower Keweenawan Powder Mill rocks have reverse magnetization. In the model these magetizations were assigned to 26 layers which alternated with very weakly magnetized layers. The best match of the calculated composite anomalies of remanent and induced magnetization and the aeromagnetic profile occurs if a deeper block of steeply dipping Powder Mill rocks is assumed to underlie the middle Keweenawan flows.

Michigan↗
USGS1975

Replacement barite deposit, southern Independence Mountains, Nevada

Allochthonous Devonian chert, metaquartzite, and greenstone in the Blue Basin quadrangle,, southern Independence Mountains, Nevada, are mineralized with barite forming a deposit of possible commercial grade and size. Textural evidence indicates that the barite was deposited in the host rocks principally by replacement, to a lesser extent by a process involving displacement and expansion of the host-rock material, and to a very minor extent by fracture filling.

Nevada↗
USGS1975

Diagenesis of Miocene siliceous shales, Temblor Range, California

Siliceous Monterey Shale and related shales of the Temblor Range, Calif., are subdivided into three depth-controlled zones characterized by different forms of silica. These are, in descending stratigraphic order: (1) Biogenic opal zone, with remains of diatoms and other siliceous organisms, (2) diagenetic cristobalite zone, and (3) diagenetic quartz zone. Using the top of the youngest marine unit, the overlying Etchegoin Formation, as datum, the transition from biogenic opal to disordered cristobalite occurs within the Monterey Shale of Chico Martinez Creek at -730 m, and the ordered cristobalite-to-microquartz transition at about -2,030 m. Temperatures that prevailed at these transition depths while the sedimentary pile lay at the bottom of the sea are estimated at about 50° and 110°C, respectively. Diagenetic cristobalite manifests, downward through a 1,300-m interval of section, a progressive decrease in its d (101) spacing because of a gradual ordering of its internal structure through adjustments in the solid state. Diagenetic microquartz forms only from well-ordered cristobalite that provides the most appropriate concentration of dissolved silica for precipitation of microquartz. Scanning electron micrographs of the silica mineral in pores of rocks made up of disordered cristobalite show aggregates of well-formed bladed crystals, like those described from deep-sea cherts. The pore silica minerals in rocks made up of ordered cristobalite occur as dendritic growths of poorly formed stubby crystals, and the change in crystal habit could be an external expression of the internal ordering process.

California↗
USGS1975

Tectonic setting of the Tertiary volcanic rocks of the Olympic Peninsula, Washington

Lower and middle Eocene abyssal and Hawaiian type tholeiitic basalts form two accumulations that apparently were once far out on the east flank of the Juan de Fuca Ridge, within the Juan de Fuca plate. One of these (more than 15 km thick) is near the eastern and southeastern periphery of the Olympic Peninsula, and the other (about 5 km thick) is on the north. The tholeiites stratigraphically overlie and interfinger with Paleocene(?) and lower and middle Eocene marine turbidites and shales; one flow includes boulders that, like clasts in the sediments, were derived from the North American continental plate immediately to the east. The basalts are overlain stratigraphically by middle Eocene to middle Miocene clastic marine sedimentary rocks, which are in turn overlapped unconformably on the south and west by upper Miocene (?) and Pliocene, chiefly shallow-marine clastic rocks. These various peripheral rocks flank a middle or late Miocene structurally complex dome, or orocline convex to the east, in which originally east dipping and low angle late Eocene to late Miocene underthrusts are flexed. The outermost underthrust of the complex separates the chiefly volcanic peripheral rocks to the north, east, and south from stratigraphically correlative and comparable, though predominantly sedimentary, core rocks arranged in northwest trending arcuate belts or packets bounded by fault zones. Before underthrusting, and perhaps oroclinal folding connected with doming, the pre-middle Miocene section was possibly 150 to 200 km wide compared with the present Olympic Peninsula which is 120 km wide. The section accumulated on the ocean floor near the western margin of the continent, before and during subduction of the oceanic crust.

Washington↗
USGS1975

Tectonics of the western Valley and Ridge foldbelt, Pendleton County, West Virginia - a summary report

A belt of high anticlines, the Nittany anticlinorium, occupies the western Valley and Ridge foldbelt in the central Appalachians. It extends southwestward from the Nittany arch of central Pennsylvania into the Virginias. An investigation of the tectonics of this anticlinorium in Pendleton County, W. Va., rules out active basement involvement in the deformation of the area. Cross-sectional models consistent with the accumulated data show that Middle Cambrian through Middle Ordovician carbonate rocks are technically stacked, shingle-fashion, from southeast to northwest below predominantly folded younger strata that have undergone less lateral shortening. Differential shortening in this area is of the proper order to balance cover deformation in the Allegheny synclinorium to the west. Field relations suggest a long period of abnormally high fluid pressures in Lower Devonian and older strata during deformation. At this time, the area was under sufficient northwest, near-horizontal compressive stress for abundant quartz deformation lamellae to form. Gravity sliding is ruled out as the deforming mechanism for this part of the Appalachian foldbelt. No significant tectonism appears to have occurred prior to Pennsylvanian time in this area.

West Virginia↗
USGS1975

Quaternary faults at San Diego Bay, California

Acoustic-reflection profiles of subbottom strata reveal numerous faults that cut Quaternary deposits within and directly outside of San Diego Bay. These faults, together with previously mapped onshore faults, constitute the Rose Canyon fault zone that forms the local west boundary of the Santa Ana tectonic block, which is bounded on the east by the Elsinore fault zone. The minor earthquakes that have been felt in San Diego during historic time and accurately recorded during the past 41 yr are too infrequent to explain the observed rate of slip. The principal faulting is inferred to take place during moderate earthquakes similar to previous ones recorded along the west side of the Santa Ana block in 1933 at Long Beach, Calif., and in 1956 at San Miguel, Baja California. The known magnitudes of these previous events suggest that earthquakes in San Diego could attain a magnitude of approximately 6.5. An offset of the coast at Point La Jolla, when divided by the offset associated with previously studied earthquakes of magnitude 6.5, suggests that such events occur there at an average of approximately once every 600 yr.

California↗
USGS1975

Age of volcanism, intrusion, and mineralization in the Thomas Range, Keg Mountain, and Desert Mountain, western Utah

Twenty-six new age determinations by the fission-track method establish a chronology for volcanism, intrusion, and mineralization in the Thomas Range, Keg Mountain, and Desert Mountain, in western Utah. The fission-track ages confirm D. R. Shawe's three-fold classification of igneous rocks. The oldest group of rocks consists of flows, agglomerates, and some ash-flow tuffs that were deposited 38-39 m.y. ago. The middle group contains widespread rhyolitic ash-flow tuffs that originated from local volcanic centers 30-32 m.y. ago. A dike emplaced along the probable ring-fracture zone of the Keg caldera about 31 m.y. ago indicates that caldera collapse occurred soon after eruption of ash-flow tuffs. Rocks believed to belong-to the middle group also were intruded by the quartz monzonite of Desert Mountain 27-30 m.y. ago. Little or no igneous activity took place within the next 20 m.y., during which time the region was strongly broken by Basin-and-Range faulting. Rhyolites of the youngest group were extruded 8-10 m.y. ago in the Keg Mountain area and 6-7 m.y. ago in the Thomas Range. The beryllium-fluorite mineralization at Spor Mountain occurred after the rhyolitic volcanism in the Thomas Range.

Utah↗
USGS1975

The Oligocene volcanic center at Eureka, Nevada

A volcanic center covering an area of about 80 km 2 near Eureka, Nev., and active in the early Oligocene, is characterized by rhyolitic, rhyodacitic. and andesitic pyroclastic rocks, lava flows, and shallow intrusive bodies. These rocks were emplaced as intertonguing and interpenetrative units during a 5-m.y. interval; most of the volcanism was in the last 3 million years of this period (36 to 33 m.y. ago).

Nevada↗
USGS1975

Geomorphic evidence for late Holocene tilting in southern San Mateo County, California

Relations between the stream channels and the alluvial deposits along Bradley Creek and the lower part of Butano Creek suggest that the area has been tilted very recently, and localized swampy conditions supply additional supporting evidence. Radiocarbon dates show that some of the valley alluvium along Butano Creek was deposited no more than 750-800 yr ago, and tilting must have Occurred since that time.

California↗
USGS1975

Fossil fishes from the Pliocene or Pleistocene Cache Formation, Lake County, California

The remains of fossil fishes comprising three species were found in the Cache Formation in Lake County, Calif. The rocks containing the fossils are considered to be late Pliocene or early Pleistocene. The species are all freshwater and primarily quiet-water types that now live in Clear Lake and the waters of the surrounding area, suggesting continuity between the present lake and a lake represented by the rocks of the Cache Formation.

California↗
USGS1975

Spectrochemical determination of trace elements in galena

A semiquantitative spectrochemical method is described by means of which 10-mg samples of galena can be analyzed for their trace element content. Results on 40 elements are reported as six logarithmically spaced intervals per order of magnitude and obtained by visual comparison with standards prepared in spectrographically pure lead sulfide. Detection limits are generally between 1 and 20 ppm (except for Ce, Na, Sr, Ta, and Zn, which are 50 to 100 ppm). Replicate analyses of galena samples indicate a precision comparable to other semiquantitative spectrochemical methods used for the analysis of geochemical samples. Results obtained from the analysis of 129 galena samples are summarized.

Journal of Research of the U.S. Geological Survey↗
USGS1976

Fracturing and subsidence of the land surface caused by the withdrawal of ground water in the Milford area, Utah

Fracturing and subsidence of the land surface in the Milford area of Utah have resulted from the decline of water levels due to pumping in unconsolidated deposits of Quaternary age. To the writers' knowledge, these are the first such effects of ground-water withdrawal reported in Utah. The fracturing is in an area about 1 mile (1.6 km) wide and 11 miles (18 km) long near Milford, in an unsaturated clay-silt zone (locally peaty at top) in the upper part of the principal ground-water reservoir. The fractures range in length from several feet to more than 100 feet (30 m), and their maximum measured depth in 1972 was 4 feet (1.2 m). Land subsidence in the Milford area is demonstrated by three lines of evidence: (1) collapse structures, (2) well casings that protrude higher above the land surface than when first placed in the borehole, and (3) lower elevations at National Ocean Survey (formerly U.S. Coast and Geodetic Survey) bench marks in 1970 than in 1908. This evidence shows that land subsidence in the Milford area is of two types, each having a different origin. One type has a near-surface origin in the clay-silt zone in the upper part of the principal groundwater reservoir, and the other is in the lower artesian aquifers of the principal ground-water reservoir. The amount of observed subsidence ranges from 0.05 foot (0.015 m) at the bench mark at Read to about 6 feet (1.8 m) at collapse structures in the Hay Springs area.

Utah↗