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At least 55 records · Page 3Linked to original sources
USGS1956

Carbonatites: A review

The carbonatites are essentially carbonate-silicate rock with a great variety of other minerals. In this review the writer stresses the field and geochemical relationships of the carbonatites and alkalic igneous rocks and concludes that carbonatites were deposited by carbonatic solutions having a wide range of temperature, pressure, and concentration and derived from alkalic magmas during the process of silicate crystallization. Brogger's concept of carbonate magma is evaluated in the light of more recent field and laboratory investigations, and the conclusion is reached that a carbonate magma in the normal sense is less likely to exist than carbonate-rich solutions which at elevated temperature and pressure can have a higher concentration of dissolved ingredients than normally believed for hydrothermal solutions. At many localities the carbonatites occur as veinlike or dikelike bodies or as cores in volcanic plugs of alkalic rocks. Recent investigations indicate that the carbonatites and related alkalic rocks represent a relatively unevaluated category of ore deposits that contain an impressive reserve of such rare commodities as niobium (columbium), titanium, zirconium, rare earths, barium, strontium, uranium, magnetite, phosphate, vermiculite, and agricultural lime.

GSA Bulletin↗
USGS1956

Direct radiometric measurement by gamma-ray scintillation spectrometer: Part I: Uranium And Thorium Series In Equilibrium

Where uranium and thorium are in secular equilibrium with their decay products, these elements may be determined by this direct radiometric method if the materials show more than 0.01 per cent equivalent uranium. This method is based on the measurement in a scintillation spectrometer of the relative amplitude of the response from the 238 kev gamma ray from Pb 212 . Tests on known samples containing different relative proportions of uranium and thorium have verified the predicted precision of better than 4 per cent standard deviation per single comparison with a standard when the element measured is a major contributor to the activity.

GSA Bulletin↗
USGS1956

Direct radiometric measurement by gamma-ray scintillation Spectrometer: Part II: Uranium, Thorium, and Potassium in Common Rocks

The method described in Part I of this report has been extended to the measurement of the uranium and thorium series and potassium in common rocks, or materials of comparable activity, in which the series are in secular equilibrium. The counting rate in an additional band centered on the photopeak from the 1.46 Mev gamma ray of K 40 permits the measurement of potassium and the removal of the counts due to the potassium in the other channels.

GSA Bulletin↗
USGS1957

Notes on the structural geology of Puerto Rico

Two major structural and stratigraphic rock units occur in Puerto Rico: the older complex, ranging in known age from Late Cretaceous to late Paleocene or early Eocene and the middle Tertiary sequence, ranging from late Oligocene possibly to late Miocene. The former rocks are eugeosynclinal in character and are very badly faulted but for the most part apparently only moderately folded. With the exception of a large, partly low-angle thrust, the writer has not recognized evidence of strong tangential stresses. Intra-formational folding in the older complex is interpreted as caused by submarine sliding (slump structure). Except in the vicinity of the larger plutonic intrusions and in the northeastern and southwestern corners of the island, the main strike alignment of the older complex is northwestward. The plutons are roughtly concordant with the structure of the country rock and show varying degrees of differentiation. Their average composition seems to be more acidic than that of the volcanic and volcanogenetic rocks into which they are intruded. The middle Tertiary sequence is nonvolcanic, made up dominantly of calcareous marine sediments. It crops out on the north and south sides of the island and in structural troughs on the west coast. On the north coast the beds dip gently to the north, and, except for slight terracings and a flexure at the northwestern corner of the island, are not folded. The middle Tertiary sequence on the south side of the island is somewhat folded. Seismic-reflection studies of the north coast indicate, however, a pronounced northward thickening, possibly some folding, and unconformities at depth. Unconformities which may be local have also been noted at several places on the surface. Several large faults in the middle Tertiary sequence have been recognized in both the north- and south-coast belts. The pattern of master joints that is inferred in the north-coast middle Tertiary belt from topographic alignments seems to indicate (1) control by fades contacts, (2) possible downwarping associated with the sinking of an arm of the Puerto Rican Trench, and (3) tension during upwarping along the island axis. The dates of the major diastrophic events that are decipherable from the Puerto Rican data are: (1) early Tertiary (possibly late Paleocene, but more probably Eocene), when the older complex was deformed; (2) Miocene, when the middle Tertiary sequence was deformed; (3) late Pliocene and possibly early Pleistocene, when block faulting on a large scale produced the present topographic relief. Remnants of the fault scarps resulting from the latter deformation occur widely. Quaternary marine deposits and marine terraces suggest that Puerto Rico has been relatively unaffected by crustal movement at least since the late Pleistocene.

Puerto Rico↗
USGS1957

Thermal effects of the ocean on permafrost

In high latitudes the large difference between the mean annual temperature at the ground surface and in the unfrozen sediments beneath bodies of water can affect ground temperatures to depths of several hundred feet. The effect is of particular interest near the edge of the ocean where it depends upon the magnitude of the temperature difference between the land surface and ocean bottom, the thermal properties of the ground materials, and past changes in climate and/or shore-line configuration. Theoretical considerations suggest that, except where there are transgressing shore lines, permafrost to depths greater than about 100 feet beneath the ocean bottom is not to be expected at points farther than a few thousand feet offshore. Similar considerations indicate that geothermal installations along the Arctic coast can give information regarding post-Pleistocene shore-line changes. The geothermal effects of bodies of water offer an explanation for the anomalously large outward earth-heat flow recently reported by A. D. Misener for Resolute Bay, Cornwallis Island, N. W. T., Canada.

GSA Bulletin↗
USGS1957

Thermal waters of volcanic origin

Waters of widely differing chemical compositions have been considered at least in part volcanic in origin, and are commonly associated with each other in the same area. Do any or all of these types contain volcanic components, and if so, how are the different types derived? To determine the probable characteristics of volcanic waters, the writer has selected hot-spring groups that are particularly high in temperature and associated heat flow, are associated with late Tertiary or Quaternary volcanism, and are therefore most likely to contain some water and chemical components of direct volcanic origin. Of the different types of water that occur in these groups, one of the most common is characterized chemically by a dominance of sodium chloride. Isotopic evidence indicates that the contribution of water of direct volcanic origin is not large and is probably no more than 5 per cent in typical sodium-chloride springs. The compositions of volcanic waters are believed to be determined by: [1] type of magma and stage of crystallization; [2] temperature and pressure of the emanation at different stages during and after departure from the magma; [3] chemical composition, relative quantity, and depth of penetration of mixing meteoric water and water of other origin; and [4] reactions with wall rocks. Although the type of magma and its stage of crystallization are of major interest and have been emphasized in the past, the outstanding characteristics of volcanic emanations at and near the surface of the earth seem to be controlled for the most part by the other factors. Nonvolatile compounds are slightly to highly soluble in steam at high pressure, and high-density steam has solvent properties similar to those of liquid water. In the volcanic sodium-chloride waters, the high ratio of lithium to sodium and potassium is shown to indicate that alkalies were transported as alkali halides dissolved in a dense vapor. This in turn demands a deep circulation of meteoric water for steam to condense at high pressure and for the halides to remain in solution. The depth of circulation of meteoric water in the sodium-chloride spring systems is believed to be in the order of 2 miles. Where circulation of meteoric water is shallow, the vapors rise and expand at low pressure, which does not permit transport of substances of low volatility; some type of water other than the sodium-chloride type is formed. The common volcanic sodium-chloride waters are therefore concluded to be the diluted product of high-density emanations, modified by reactions with wall rocks and by precipitation of the less soluble components. Emanations at high temperature and relatively low pressure consist almost entirely of steam and volatile components. Their compositions are therefore relatively simple, and their ability to transport matter of low volatility is very limited. The sodium-chloride type is probably gradational into acid-sulfate-chloride waters. There is some evidence that, under conditions not well understood, sulfur may be emitted as SO 2 , SO 3 , or other sulfur species of intermediate valence, rather than as H 2 S or S. Other major types of volcanic waters are called sodium bicarbonate, acid sulfate, and calcium bicarbonate; the first two tend to be distinct, but the calcium-bicarbonate type clearly grades into the sodium-chloride type. The writer concludes that, in general, all these are derived from the sodium-chloride waters as a result of physical environment or of reactions with wall rocks.

GSA Bulletin↗
USGS1957

Magmatic, connate, and metamorphic waters

Some major types of water of “deep” origin are believed to be recognizable from their chemical and isotopic compositions. Oil-field brines dominated by sodium and calcium chlorides differ markedly from average ocean water. In general, the brines are believed to be connate in origin (“fossil” sea water) with a negligible to high proportion of meteoric water. Many brines, particularly in pre-Tertiary rocks, are much higher in salinity than sea water and are greatly enriched in calcium as well as sodium chloride. Brines near the salinity of sea water are generally higher, relative to sea water, in bicarbonate, iodine, boron, lithium, silica, ammonium, and water-soluble organic compounds, and lower in sulfate, potassium, and magnesium. Many changes take place after sea water is entrapped in newly deposited marine sediments: (1) Iodine, silicon, boron, nitrogen, and other elements have been selectively concentrated in organisms that decompose during and after burial in sediments. Many of the elements may redissolve in the interstitial water. (2) Bacteria are active in the sediments and reduce sulfate to sulfide and produce methane, ammonia, carbon dioxide, and other products. (3) Some elements have been selectively removed from sea water by inorganic processes, such as adsorption on clays and colloidal matter. When this matter is reconstituted by diagenetic and other changes, some components are redissolved. The abundance of lithium and possibly boron and other elements may be controlled to a considerable extent by these inorganic processes. (4) The interstitial water may react chemically with enclosing sediments and produce dolomite, reconstituted clays, and other minerals. The high loss of magnesium relative to calcium in most connate waters is probably caused by such reactions. Volcanic hot-spring waters of different compositions have been discussed in an accompanying paper (White, 1957). The most significant type is believed to be dominated by sodium chloride, and is best explained as originating from dense gases driven at high temperature and pressure from magma and containing much matter of low volatility that is in solution because of the solvent properties of high-density steam. This dense vapor is condensed in and greatly diluted by deeply circulating meteoric water. Most other types of volcanic water are believed to be derived from the sodium-chloride type. Volcanic sodium-chloride waters are similar in many respects to connate waters but are believed to be distinguishable by relatively high lithium, fluorine, silica, boron, sulfur, CO 2 , arsenic, and antimony; by relatively low calcium and magnesium; and by lack of hydrocarbons, water-soluble organic compounds, and perhaps ammonia and nitrate. Relatively high boron and combined CO 2 are alone not reliable indicators of a volcanic origin. During compaction, rocks lose most of their interstitial high-chloride water; much additional water may then be lost during progressive metamorphism, and the content changes from about 5 per cent in shale to perhaps 1 per cent in gneiss. This expelled water is here called metamorphic. Because of pressure and permeability gradients, it must normally escape upward and mix with connate and meteoric water. Even though large quantities must exist, no example of metamorphic water has been positively identified. Some thermal springs in California are high in salinity and relatively low in temperature and apparent associated heat flow. Some are clearly connate in origin. Other springs are characterized by very high combined carbon dioxide and boron, relative to chloride. Their compositions are considerably different from known connate and volcanic waters and are believed to be best explained by a metamorphic origin. Although some major types of deep water seem to be recognizable, there is much danger of oversimplifying the problems. Many waters are no doubt mixtures of different types, and some of high salinity result from dissolution of salts by meteoric water.

GSA Bulletin↗
USGS1958

Geology of the north half of the Mt. Abbot quadrangle, Sierra Nevada, California

The north half of the 15-minute Mt. Abbot quadrangle lies across the crest of the Sierra Nevada. The Cretaceous granitic rocks that underlie most of the area form eight large discordant plutons that range from quartz diorite to alaskite; the largest pluton is coarse prophyritic quartz monzonite. Pre-batholithic metasedimentary and metavolcanic rocks and metagabbro and metadiorite are minor. The porphyritic quartz monzonite sent gently dipping dikes as much as 200 feet thick into its walls. These dikes in places make up more than half the height of exposed contact zones. A broad border zone of protoclastic flaser gneiss was formed in part of the pluton and in the adjacent wall rocks and dikes. A contact between granodiorite and calcareous metasedimentary rocks swarms with dark inclusions. Their origin, puzzling in most places, is here clearly due to progressive hybridization of calc-silicate xenoliths; the changes take place within a few tens of yards of the contact. The xenoliths were amphibolitized concentrically and reconstituted to typical dark-inclusion texture and mineralogy and were drawn out from blocky xenoliths into spindle shapes. Elsewhere, large irregular xenoliths of metadiorite were assimilated by alaskite. Within the resulting complex is a thick series of alaskite flow layers crowded with xenocrysts showing graded “bedding”. All the granitic plutons were intrusive; assimilation of mafic wall rocks by felsic magmas may have caused much of the diversity.

California↗
USGS1958

Geology of Kapingamarangi Atoll, Caroline Islands

Kapingamarangi Atoll of the Caroline Islands consists of a peripheral reef, 1000-4000 feet across, surrounding a nearly circular lagoon which is 5 by 6 nautical miles in area and about 240 feet at maximum depth. Thirty-three islands, most of which are less than half a mile in length, are scattered along the eastern half of the peripheral reef. At least 75 patch reefs, most of which are small, nearly symmetrical mounds, rise to the surface of the lagoon. The peripheral reef and the patch reefs, composed largely of the stony structures of corals and coralline algae, have flat upper surfaces, apparently the result of bevelling by waves during a recent lowering of sea level. The islands on the peripheral reef are formed of partially consolidated stratified sediments composed of clastic limestone particles and the shells of marine animals. These islands are migrating lagoonward across the reef flat because of erosion on the seaward sides and the growth of beaches and bars on the opposite sides. Soils on the islands are poorly developed and retain much of the texture, structure, and composition of the parent rock or sediment. They consist chiefly of mechanical mixtures of carbonaceous material and lime gravel, lime sand, or lime mud. Phosphorite is present on some islands and is still forming locally where apatite derived from bird guano is reacting with limestones. The tidal fluctuation of ground-water lenses, determined on islands of several sizes, ranges from about 4 to 18 inches. In one very small island where the water is brackish, the rise is much greater. The time lag between tidal movements and the rise and fall of fresh water in the islands ranges from a few minutes on very small islands up to 5 hours on some large ones. This time lag is controlled by the permeability of rocks composing an island and varies from one area to another according to the distribution of rock types. The lagoon contains six concentric belts of bottom sediment; in each, the composition and texture depend on the depth of water in which it occurs. Lime sand and lime gravel derived for the most part from the shells of animals form most of the sediment, but a lime mud covers the bottom of the deepest parts of the lagoon. Waves and currents cause gradation between types of sediment to a depth of about 30 feet, but little mixing was detected at greater depths.

Kapingamarangi Atoll, Caroline Islands↗
USGS1958

Uranium deposits under conglomeratic sandstone of the Morrison Formation, Colorado and Utah

In southwestern Colorado and southeastern Utah, strata of conglomeratic sandstone are localized at the base of the Brushy Basin Member of the Morrison Formation of Jurassic age. These discrete lithologic units contain sedimentary structures oriented in a prevailing easterly direction. They are believed to cover about one-third of the underlying Salt Wash Member in southwestern Colorado and southeastern Utah, and they locally rest on ore-bearing sandstone in the Salt Wash Member. Eastward-trending planar cross-stratification and trough cross-stratification and a general westward coarsening of sediments in the conglomeratic sandstone strata suggest that they are the products of stream aggradation from westerly source areas. Uranium-vanadium deposits in the uppermost, almost continuous, layer of sandstone of the Salt Wash Member are classified according to their association with the conglomerate strata. Of the 363 deposits studied in the uppermost sandstone layer of the Salt Wash Member, 101 are known to be directly beneath conglomeratic sandstone strata, 211 are below the projected extension of conglomeratic sandstone strata, 33 are beyond the safe limits of such projection, and 18 are lateral to the margins of conglomeratic sandstone strata. At places, near clusters of deposits in the uppermost sandstone of the underlying Salt Wash Member, conglomeratic sandstone strata of the Brushy Basin Member are also mineralized. It is postulated that ground-water movement during deposition of the Morrison Formation in Late Jurassic time localized the uranium and vanadium. The direction of this ground-water movement is believed to have been related to streams that deposited the conglomeratic strata, so that in the ore-bearing sandstone metal ions contained in the ground water were localized in places of high transmissibility and in the vicinity of decaying organic debris. According to the age of the ores, precipitation of the metals was much later than their localization, probably during Late Cretaceous or early Tertiary time.

Colorado, Utah↗
USGS1958

Stratigraphy of Upper Pennsylvanian and lower Permian rocks in the Sand Canyon area, Otero County, New Mexico

The Magdalena Group of Pennsylvanian age and, in ascending order, the lower tongue of the Abo Sandstone (herein named the Danley Ranch Tongue), the Hueco Limestone, the upper tongue of the Abo Sandstone (herein named the Lee Ranch Tongue), and the Yeso Formation of Permian age are well displayed in the southern part of the Sacramento Mountains. The contact of the Pennsylvanian rocks with the overlying Permian rocks is unconformable throughout the area. Locally the relief before deposition of the Abo was so great that in places the Danley Ranch Tongue of the Abo is absent because of nondeposition. At these places there is prominent angular discordance between the Pennsylvanian and Permian rocks. The red beds of the Danley Ranch Tongue interfinger with and grade southward into the overlying Hueco Limestone. Red beds of the Lee Ranch Tongue of the Abo Sandstone also grade southward into the Hueco and cannot be traced south of the southern part of the Sacramento Mountains. The Lee Ranch Tongue is believed to be stratigraphically lower than the Deer Mountain Red Shale Member of the type Hueco Limestone. The herein named Otero Mesa Member of the Yeso Formation is believed to occupy an intermediate stratigraphic position between the Lee Ranch Tongue and the Deer Mountain Red Shale.

New Mexico↗
USGS1958

Recent underwater surveys using low-frequency sound to locate shallow bedrock

Underwater investigations at Lake Mead, Chicago, Passamaquoddy Bay, and on Long Island established the characteristics of sound waves that can be used in shallow geophysical exploration by the sonar method. At Lake Mead the sediments were for the most part clay of high water content which was easily penetrated by low-power sound at a frequency of 14.2 kilocycles. The greatest depth of penetration was 140 feet. Sound having frequencies of 50 and 80 kilocycles did not penetrate. At Chicago, sound at a frequecy of 11 kilocycles and an output power of 800 watts gave a satisfactory delineation of bedrock beneath Lake Michigan. The maximum distance to bedrock was about 135 feet. At Passamaquoddy Bay a sound frequency of 6 kilocycles and about 700 watts of output power gave much better delineation of bedrock. A frequency of 6 kilocycles at the lower output power was much better than 11 kilocycles at higher power. About 250 feet of penetration was attained. Pulsed power was used in each of these investigations. The pulse lengths were long—about 14–25 milliseconds. Bedrock was mapped at Lake Mead, Chicago, and Passamaquoddy Bay. The methods of ordinary hydrographic surveying were used for horizontal and vertical positioning. For horizontal positions the ordinary three-point sextant-fix method was used. For vertical positioning, recording gages suitably placed and supplemented by staff gages were used. All data were tied into the third-order control net of the U. S. Coast and Geodetic Survey. In connection with a study for a proposed Midwestern waterway, the technical problem was reviewed and the techniques considerably improved. New equipment was built and evaluated on Long Island Sound. It operated with pulsed power at a frequency of 6 kilocycles, and pulse length was controlled and variable from 1 to 9 milliseconds. Output acoustic power was about 2500 watts. With the transducer in ordinary operating positions as much as 400 feet of sediment was penetrated. With the transducer placed directly on the bottom of the water in Huntington Bay about 750 feet of penetration was attained. Several innovations in sonar techniques, which are desirable for sediment exploration, and which give much more detailed information than the earlier equipment are described. The techniques required for stratigraphic interpretation of the sound records are described briefly. A method for the determination of sound velocities is discussed. Multiple echoes and other effects complicate the interpretation of records and are explained. The problems of geological control encountered also are mentioned.

Illinois, Maine, Nevada, New Brunswick, New York↗
USGS1958

Lower ordovician section near Chambersburg, Pennsylvania

The Lower Ordovician series (Beekmantown group) is at least 3500 feet thick near Chambersburg, Pennsylvania, approximately 1200 feet thicker than was earlier estimated. Reverse faulting in the upper part of the section may have obscured the youngest Early Ordovician and oldest Middle Ordovician beds in the area, so that the total thickness of the Lower Ordovician series may be comparable to the thickness measured in Maryland. The Beekmantown group is represented by the Stonehenge limestone and the Rockdale Run formation. Moving the base of the Stonehenge downward to include about 200 feet of strata previously referred to the underlying Conococheague formation facilitates regional correlation without impairing mappability. Newly discovered fossils from the Rockdale Run formation add notably to the faunas of the upper part of that formation. Comparison of a trilobite-brachiopod faunule near the top of the Diparelasma zone (Cotter-Powell equivalent) with similar fossils in Zone J of the Utah-Nevada sequence suggests that Zone J may be no younger than the Powell dolomite of the Ozark region. Difficulty in recognizing correlatives of the Smithville and Black Rock formations suggests the need for restudy of these units in the Ozark region. Evidence from the Chambersburg section neither proves nor contradicts the hypothesis of continuous deposition from Early Ordovician to Middle Ordovician time in the central Appalachian area.

Pennsylvania↗
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↗