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

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At least 757 records · Page 42Linked to original sources
USGS1973

Lower Jurassic ammonite from the south-central Sierra Nevada, California

A Lower Jurassic ammonite has been found in metasiltstone of the Boyden Cave roof pendant, south-central Sierra Nevada, Calif. Although too poorly preserved to permit positive generic and specific identification, its general shape, coiling, and ornamentation are characteristic of Early Jurassic forms. Strata associated with the fossiliferous rocks in the pendant include quartzite, andalusite hornfels, and marble. This assemblage differs strikingly from nearby volcanic rocks to the east, some of which in the Ritter Range pendant also contain Lower Jurassic fossils. The presence of nonvolcanic Lower Jurassic rocks of the Boyden Cave pendant lying west of coeval volcanic rocks of the Ritter Range pendant is anomalous and may be the result of large-scale tectonic dislocations.

California↗
USGS1973

Deep-sea fan paleocurrent patterns of the Eocene Butano Sandstone, Santa Cruz Mountains, California

The Butano Sandstone is an Eocene continental borderland deep-sea fan deposit located in the Santa Cruz Mountains, Calif. Paleoslope measurements from contorted strata within it yield a regional northward paleoslope for the fan. Detailed paleocurrent measurements from conglomerate clast orientations, flute casts, groove casts, current-ripple markings, small-scale cross-strata, convolute laminations, and flame structures yield a sediment-dispersal pattern characterized by northward transport of coarser grained sediments downfan along major channels and transport of finer grained sediments outward and away from channels by overspilling. The overall paleocurrent pattern is oriented radially outward from the fan apex and indicates that the growth, development, and dispersal of sediments on this ancient deep-sea fan resembled that on modern deep-sea fans.

California↗
USGS1973

Current slope-stability studies in the San Francisco Bay region

An extensive program of slope-stability studies is presently underway in the San Francisco Bay region, California. Work to date has resulted in the publication of estimates of landslide damage, an estimated-landslide-abundance map of the region, new slope maps prepared by photomechanical processes, photointerpretive maps of landslide, colluvial, and other surficial deposits, and maps of relative slope stability. These studies indicate that landsliding is a major slope-erosion process in the region, that the damage resulting from landsliding is very great, and that additional development in the upland parts of the region should not be undertaken without careful evaluation of slope stability.

California↗
USGS1973

Stream-profile analysis and stream-gradient index

The generally regular three-dimensional geometry of drainage networks is the basis for a simple method of terrain analysis providing clues to bedrock conditions and other factors that determine topographic forms. On a reach of any stream, a gradient-index value can be obtained which allows meaningful comparisons of channel slope on streams of different sizes. The index is believed to reflect stream power or competence and is simply the product of the channel slope at a point and channel length measured along the longest stream above the point where the calculation is made. In an adjusted topography, changes in gradient-index values along a stream generally correspond to differences in bedrock or introduced load. In any landscape the gradient index of a stream is related to total relief and stream regimen. Thus, climate, tectonic events, and geomorphic history must be considered in using the gradient index. Gradient-index values can be obtained quickly by simple measurements on topographic maps, or they can be obtained by more sophisticated photogrammetric measurements that involve simple computer calculations from x, y, z coordinates.

Journal of Research of the U.S. Geological Survey↗
USGS1973

Identification of a lithium-bearing smectite from Spor Mountain, Utah

Chemical analyses, X-ray diffraction data, and cation exchange determinations are given for a lithium-bearing smectite. The X-ray data and Greene-Kelly's lithium test indicate the presence of both dioctahedral and trioctahedral phases. The exchange determinations indicate that the lithium is in the structure of the clay, and the chemical data are intermediate between those for hectorite and montmorillonite. All data indicate that the clay is a mixture of hectorite and montmorillonite.

Utah↗
USGS1973

A Precambrian diamictite below the base of the Stillwater Complex, southwestern Montana

The metasedimentary rocks of Precambrian age below the base of the Stillwater Complex, southwestern Montana, contain a metamorphosed diamictite similar to diamictite in strata of late Precambrian and Early Cambrian age in Canada and the Western United States. The diamictite consists of a quartz-cordierite matrix containing an average 10-15 percent of rock fragments diverse in shape, size, angularity, lithologic types, and textures. The diamictite unit is poorly sorted, crops out discontinuously for 14 miles, and locally has a crude layering containing dropstones. Its origin is debatable, but the rock is suggestive of glacial marine deposition. The minimum age of the diamictite of the complex is 2,750 m.y. from U-Pb determination on zircon of intrusive quartz monzonite, the maximum 3,140 m.y. as determined on zircon from metasedimentary rocks interbedded with the diamictite.

Montana↗
USGS1973

Metamorphic facies indicated by vein minerals in basal beds of the Great Valley sequence, northern California

A reexamination of reported blueschist mineral localities in the basal strata of the Great Valley sequence revealed only prehnite-pumpellyite facies minerals. Franciscan graywacke thrust below the Great Valley rocks contains lawsonite-quartz blueschist assemblages. At a common pressure of about 4 kb, the Franciscan blueschists formed at lower temperatures than the overlying Great Valley prehnite-bearing rocks, lending support to tectonic models that involve rapid subduction of the Franciscan rocks.

California↗
USGS1973

Boron-bearing potassium feldspar of authigenic origin in closed-basin deposits

Silicic vitric tuffs in saline, alkaline lacustrine deposits are commonly altered to a variety of zeolites and potassium feldspar. The tuffs generally show a lateral gradation, in a basinward direction, of fresh glass to zeolites and then to potassium feldspar. Zeolites were formed early in diagenesis by reaction of the glass with the interstitial water. The feldspar, however, was formed later by reaction of the zeolites with interstitial water, and its formation can be correlated with water of relatively high salinity and alkalinity. Semiquantitative spectrographic analyses for boron in the zeolites and potassium feldspar show that most of the boron resides in the relatively late feldspar. The boron content of the zeolites is commonly less than 100 ppm, whereas the boron content of the potassium feldspar is commonly greater than 1,000 ppm. Boron apparently substitutes for aluminum in the feldspar structure and causes distortion of the monoclinic unit cell such that the b and c dimensions are shortened. These boron-bearing potassium feldspars having anomalous cell parameters seem unique to saline, alkaline lacustrine deposits and could serve as a prospecting aid for locating buried saline minerals.

Journal of Research of the U.S. Geological Survey↗
USGS1973

Permian paleogeography of the Arctic

Three large land areas were dominant in the Arctic during the Permian: Fennoscandia, central and southern Siberia (Angara), and Canada. Smaller landmasses were in China, the Seward-Chukotskiy region, northern and eastern Siberia, and near Alaska. Coal deposits and strata bearing land plants covered a large area in central Siberia; saline basins containing red beds formed in the Zechstein, Perm, and West Texas basins as the seas withdrew, generally in the later Permian. Eugeosynclinal troughs, apparently limited to the Pacific border regions, were marked by volcanism and deposition of predominantly clastic sediments in many areas. Platform and miogeosynclinal deposits, dominated by carbonate rocks, preceded saline deposition in the basins and persisted on shallow shelves adjacent to the geosynclines. The Arctic Permian marine fauna evolved in middle Permian time because of partial isolation of the Arctic areas from the southern ocean. Endemism, latitudinal temperature controls, and the effect of ocean currents explain in large part the faunal patterns in Permian seas. Post-Permian tectonic movements account for anomalies in the present positions of some rock sequences and fossils. Northeasterly drift and counterclockwise rotation of the northern landmasses are suggested. Right-lateral shear along the southern edge of Asia is supported, followed by northward movement of peninsular India.

Journal of Research of the U.S. Geological Survey↗
USGS1973

Pliocene marine fossils in the Paso Robles Formation, California

Marine invertebrates from the Paso Robles Formation recently discovered near Atascadero, Calif., indicate that the basal part of this chiefly nonmarine deposit is of provincial early Pliocene age. Heretofore the lack of direct fossil or radiometric evidence of the age of the Paso Robles has made it a difficult unit to place in the late Cenozoic history of the Coast Ranges. The assemblage is dominated by Ostrea vespertina and by Nettastomella rostrata , a rock-boring bivalve; its mode of preservation indicates that the fossils are in place and have not been recycled from older marine formations. This occurrence suggests that during the early Pliocene a seaway connected the present southern Salinas Valley area with the northern part of the Santa Maria basin; the fossils occur about halfway between the southernmost exposures of the Pancho Rico Formation near San Miguel and fossiliferous strata east of Pismo Beach, both marine units of early Pliocene age.

California↗
USGS1973

Galkhaite, (Hg,Cu,Tl,Zn) (As,Sb)S2, from the Getchell mine, Humboldt County, Nevada

The first reported occurrence in the United States of galkhaite (Hg,Cu,Tl,Zn)(As,Sb)S 2 is at the Getchell mine, Humboldt County, Nev. The mineral occurs as brownish-black cubes associated with graphite, pyrite, and realgar. In polished section galkhaite is grayish white and isotropic with a deep-red internal reflection; reflectivity at 590 nm is 21.6 percent. Spectrographic analysis gave Hg 42 percent, Cu 5 percent, Zn 1.5 percent, Fe 0.7 percent, Tl 5 percent, As 24 percent, Sb 0.3 percent, and S (by difference) 21.3 percent. The mineral is cubic, a=10.36, and the strong lines of the X-ray powder pattern are 2.99 (100), 4.21 (90), 2.76 (80), 1.831 (70), 7.25 (60), 2.58 (40), 1.561 (40). The pattern is very similar to that of tetrahedrite except for the strong lines at 7.25, 4.21, and 2.76.

Nevada↗
USGS1973

Disseminated pyrite in a latite porphyry at Texan Mountain, Hudspeth County, Texas

A pyrite-bearing latite porphyry that contains fragments of syenite and a quartz porphyry intruded into the Cretaceous Cox Sandstone are well exposed in a roadcut at Texan Mountain, Hudspeth County, Tex. The pyrite, which occurs along tiny fractures as well as disseminated, and the multiple episodes of intrusion, coupled with copper minerals in veins in the overlying Cox Sandstone, indicate a slight potential for porphyry-type copper or molybdenum deposits at depth.

Texas↗
USGS1973

Soda Creek springs - metamorphic waters in the eastern Alaska Range

The Soda Creek springs are a group of small, cold mineral springs on the southern flank of the eastern Alaska Range. The spring waters contain anomalous concentrations of carbon dioxide, sodium, chlorine, sulfate, boron, and ammonia and are actively precipitating deposits of calcite and aragonite. Sparingly present in these deposits are mixed-layer illite-montmorillonite clays and zeolite minerals. Low-temperature metamorphic reactions in subjacent marine sedimentary rocks of Jurassic and Cretaceous age may have produced the fluids and silicate minerals. With only a few exceptions, cool bicarbonate-rich springs in Alaska are concentrated south of the Denali fault system in south-central Alaska, southeastern Alaska, and along the Kaltag-Tintina fault system. These areas are characterized by active or recently active tectonism, major faults and folds, and an abundance of marine sedimentary rocks.

Alaska↗
USGS1973

A calorimetric determination of the standard enthalpies of formation of huntite, CaMg3 (CO3)4 , and artinite, Mg2(OH)2 CO3 * 3H2O, and their standard Gibbs free energies of formation

The enthalpies of formation, ΔH° f, of huntite, CaMg 3 (CO 3 ) 4 , and artinite, Mg 2 (OH) 2 CO 3 * 3H 2 O, have been determined by HCl solution calorimetry using a constant-volume isoperibol reaction calorimeter. For the reaction CaO(c) + 3MgO(c) + 4CO 2 (g) = CaMg 3 (CO 3 ) 4 (c), the enthalpy change at 298.15 K, ΔH° 298 , is -123,203±145 cal mol -1 . For the reaction 2MgO(c) + 4H 2 O(l) + CO 2 (g)=Mg 2 (OH) 2 CO 3 * 3H 2 O(c), we obtained -45,132±100 cal mol -1 . These results combined with the standard enthalpies of formation of CaO, MgO, H 2 O, and CO 2 lead to ΔH° 298 (huntite) = -1,082,600±375 cal mol -1 and ΔH° 298 (artinite) = -698,043±170 cal mol -1 . Using recently determined values for the standard entropies of huntite, CaMg 3 (CO 3 ) 4 , and artinite, Mg 2 (OH) 2 CO 3 * 3H 2 O, and of Mg, Ca, C, O 2 , and H 2 , we calculate ΔG° f,298 (huntite) = -1,004,707±390 cal mol -1 and ΔG° f,298 (artinite) = -613,924±180 cal mol -1 .

Journal of Research of the U.S. Geological Survey↗
USGS1973

The enthalpies of formation of nesquehonite, MgCO3 * 3H2O, and hydromagnesite, 5MgO * 4CO2 * 5H2O

The enthalpies of formation, ΔH° f , of nesquehonite, MgCO 3 * 3H 2 O, and hydromagnesite, 5MgO * 4CO 2 * 5H 2 O, have been determined by HCl solution calorimetry. For the reaction MgO(c) + CO 2 (g) + 3H 2 O(l) = MgCO 2 * 3H 2 O(c), the enthalpy change at 298.15 K is -29,781*40 cal mor' . For the reaction 5MgO(c) + 4CO 2 + 5H 2 O = 5MgO * 4CO 2 * 5H 2 O, the enthalpy change at 298.15 K is -120,310±120 cal. For MgCO 3 * 3H 2 O the standard molar enthalpy and standard Gibbs free energy of formation, ΔH° f,298 and ΔG° f,298 are -472,576+110 and 412,040±120 cal. ΔH° f,298 and ΔG° f,298 for 5MgO * 4CO 2 * 5H 2 O are -1,557,090±250 and -1,401,71 0±250 cal.

Journal of Research of the U.S. Geological Survey↗
USGS1973

Chemical analysis of rutile - a pyrocatechol violet spectrophotometric procedure for the direct microdetermination of zirconium

The ZrO 2 content of rutile is determined spectrophotometrically by a direct pyrocatechol violet procedure. The sample is decomposed by potassium pyrosulfate fusion in a transparent quartz crucible, and a sulfuric acid solution of the melt is used for the determination at a pH of 5.1. Of the elements commonly present in rutile, only titanium and niobium occur in concentrations large enough to interfere. Titanium and niobium interference is overcome by adding the titanium and niobium contents of the sample to the standard zirconium solutions used for the standard zirconium curve. The absorbance is measured at 570 nm. Beer's law is obeyed within the range of 0.05-1.50 ppm ZrO 2 . In the presence of 50 ppm TiO 2 , the range is 0.15-1.50 ppm ZrO 2 . The tolerances of 47 elements were determined. The sensitivity is 0.0058 ug Zr/cm 2 . The variables in the method were studied, and typical results are given for commercial rutile concentrates.

Journal of Research of the U.S. Geological Survey↗
USGS1973

Spectrophotometric determination of tungsten in rocks by an isotope dilution procedure

Samples are decomposed with hydrofluoric acid and perchloric acid in the presence of W 181 tracer. Molybdenum is extracted from a hydrochloric acid solution with tributyl phosphate. Tungsten is separated from most other elements by extraction of the a-benzoinoximate into chloroform. Stannous chloride in concentrated hydrochloric acid is used to strip tungsten and reduce it to W +5 . The amount of tungsten is determined spectrophotometrically after extraction as the thiocyanate complex into amyl alcohol. The correction for chemical losses is determined by counting W 181 .

Journal of Research of the U.S. Geological Survey↗
USGS1973

Spectrochemical computer analysis - argon-oxygen d-c arc method for silicate rocks

Use of an argon-oxygen atmosphere eliminates the interference of cyanogen bands with many sensitive analytical lines. The jet-controlled atmosphere also improves the stability of the arc. These procedural changes, coupled with computerized analysis of the spectra, result in increased detectability, precision, and speed as compared to the former visual semiquantitative technique.

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