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At least 271 records · Page 15Linked to original sources
USGS1966

Hydrochemical facies and ground-water flow patterns in northern part of Atlantic Coastal Plain

The part of the Atlantic Coastal Plain that extends from New Jersey through Virginia was selected as a suitable field model in which to study the relationships between geology, hydrology, and chemical character of ground water. The ground-water flow pattern is the principal hydrologic control on the chemical character of the water. Within the Coastal Plain sediments, the proportions of clay, glauconitic sand, and calcareous material are the principal lithologic controls over the chemistry of the water. A subsurface body of salt water extends from southern New Jersey through southern Virginia and occupies the deposits deeper than about 500 feet below land surface in the eastern part of the Coastal Plain. The position of its top is determined by the relative head, which in turn is influenced by topography, drainage density, and the thickness and permeability of the Coastal Plain sediments. Hydrochemical facies is a term used in this paper to denote the diagnostic chemical aspect of ground-water solutions occurring in hydrologic systems. The facies reflect the response of chemical processes operating within the lithologic framework and also the pattern of flow of the water. The distribution of these facies is shown in trilinear diagrams and isometric fence diagrams and on maps showing isopleths of chemical constituents within certain formations. The occurrence of the various facies within one formation or within a group of formations of uniform mineralogy indicates that the ground-water flow through the aquifer system modifies the distribution of the facies. Flow patterns of fresh ground water shown on maps and in cross sections have been deduced from available water-level data. These patterns are controlled by the distribution of the higher landmasses and by the depth to either bedrock or to the salt-water interface. The mapping of hydrochemical facies shows that at shallow depths within the Coastal Plain (less than about 200 ft) the calcium-magnesium cation facies generally predominates. The bicarbonate anion facies occurs within more of the shallow Coastal Plain sediments than does the sulfate or the chloride facies. In deeper formations, the sodium chloride character predominates. The lower dissolved-solids content of the ground water in New Jersey indicates less upward vertical leakage than in Maryland and Virginia, where the shallow formations contain solutions of higher concentration.

Delaware, Maryland, New Jersey, Pennsylvania, Virg↗
USGS1902

The Geology and Petrography of Crater Lake National Park

Twenty years ago Crater Lake was unknown to the general public, but since then a knowledge of its remarkable features has been spread abroad through the press, and Congress recognized its worth as an educational feature and made it a national park by the act approved May 22, 1902. As defined in the bill, the park is 'bounded north by the parallel forty-three degrees four minutes north latitude, south by forty-two degrees forty-eight minutes north latitude, east by the meridian one hundred and twenty-two degrees west longitude, and west by the meridian one hundred and twenty-two degrees sixteen minutes west longitude, having an area of two hundred and forty-nine square miles'. The Ashland sheet of United States Geological Survey, on the scale of 4 miles to 1 inch, includes the area lying between meridians 122 deg and 123 deg and parallels 42 deg and 43 deg. This map includes the region between Ashland and Crater Lake. On account of the great scientific interest of Crater Lake a special map, known as the Crater Lake special sheet, was prepared on the scale of 1 mile to an inch, including the country immediately adjacent to Crater Lake, between meridians 122 deg and 122 deg 15' and parallels 42 deg 50' and 43 deg 4'. From these two maps the accompanying map of the Crater Lake National Park (Pl. 1) has been prepared. The two papers published here refer practically to the whole region included in the National Park. The one, Part I, treats primarily of the geology, the development of the great volcano, Mount Mazama, and its collapse, which gave birth to Crater Lake; the other, Part II, deals with the petrography, and gives a special description of the various rocks occurring in the park. Origin of the name Mount Mazama - A great impetus to the spread of information concerning Crater Lake was given by the Mazamas of Portland, Oreg., who held a meeting at the lake in August, 1896, which attracted many visitors. The principal features in the history of the lake had previously been made out, and the Mazamas, recognizing the fact that the great peak which was nearly destroyed in preparing the pit for the lake had no name, gave it the name of their own society. Upon the rim of the lake are a number of small peaks, each having its own designation. The term Mount Mazama refers to the whole rim encircling the lake. It is but a mere remnant of the once lofty peak, the real Mount Mazama, which rose far into the region of eternal snow. To get a basis for reconstructing the original Mount Mazama it is necessary to study in detail the structure and composition of its foundation, now so attractively displayed in the encircling cliffs of Crater Lake.

Oregon↗
USGS1981

Petrogenetic modeling of a potential uranium source rock, Granite Mountains, Wyoming

Previous studies of the granite of Lankin Dome have led to the conclusion that this granite was a source for the sandstone-type uranium deposits in the basins that surround the Granite Mountains, Wyo. Q-mode factor analysis of 29 samples of this granite shows that five bulk compositions are required to explain the observed variances of 33 constituents in these samples. Models presented in this paper show that the origin of the granite can be accounted for by the mixing of a starting liquid with two ranges of solid compositions such that all five compositions are granitic. There are several features of the granite of Lankin Dome that suggest derivation by partial melting and, because the proposed source region was inhomogeneous, that more than one of the five end members may have been a liquid. Data for the granite are compatible with derivation from rocks similar to those of the metamorphic complex that the granite intrudes. Evidence for crustal derivation by partial melting includes a strongly peraluminous nature, extremely high differentiation indices, high contents of incompatible elements, generally large negative Eu anomalies, and high initial lead and strontium isotopic ratios. If the granite of Lankin Dome originated by partial melting of a heterogeneous metamorphic complex, the initial magma could reasonably have been composed of a range of granitic liquids. Five variables were not well accounted for by a five-end-member model. Water, CO 2 , and U0 2 contents and the oxidation state of iron are all subject to variations caused by near-surface processes. The Q-mode factor analysis suggests that these four variables have a distribution determined by postmagmatic processes. The reason for failure of Cs0 2 to vary systematically with the other 33 variables is not known. Other granites that have lost large amounts of uranium possibly can be identified by Q-mode factor analysis.

Professional Paper↗
USGS1982

Digital classification of Landsat data for vegetation and land-cover mapping in the Blackfoot River watershed, southeastern Idaho

This paper documents the procedures, results, and final products of a digital analysis of Landsat data used to produce a vegetation and landcover map of the Blackfoot River watershed in southeastern Idaho. Resource classes were identified at two levels of detail: generalized Level I classes (for example, forest land and wetland) and detailed Levels II and III classes (for example, conifer forest, aspen, wet meadow, and riparian hardwoods). Training set statistics were derived using a modified clustering approach. Environmental stratification that separated uplands from lowlands improved discrimination between resource classes having similar spectral signatures. Digital classification was performed using a maximum likelihood algorithm. Classification accuracy was determined on a single-pixel basis from a random sample of 25-pixel blocks. These blocks were transferred to small-scale color-infrared aerial photographs, and the image area corresponding to each pixel was interpreted. Classification accuracy, expressed as percent agreement of digital classification and photo-interpretation results, was 83.0:t 2.1 percent (0.95 probability level) for generalized (Level I) classes and 52.2:t 2.8 percent (0.95 probability level) for detailed (Levels II and III) classes. After the classified images were geometrically corrected, two types of maps were produced of Level I and Levels II and III resource classes: color-coded maps at a 1:250,000 scale, and flatbed-plotter overlays at a 1:24,000 scale. The overlays are more useful because of their larger scale, familiar format to users, and compatibility with other types of topographic and thematic maps of the same scale.

Professional Paper↗
USGS1994

The Loma Prieta, California, earthquake of October 17, 1989: Tectonic processes and models

If there is a single theme that unifies the diverse papers in this chapter, it is the attempt to understand the role of the Loma Prieta earthquake in the context of the earthquake 'machine' in northern California: as the latest event in a long history of shocks in the San Francisco Bay region, as an incremental contributor to the regional deformation pattern, and as a possible harbinger of future large earthquakes. One of the surprises generated by the earthquake was the rather large amount of uplift that occurred as a result of the reverse component of slip on the southwest-dipping fault plane. Preearthquake conventional wisdom had been that large earthquakes in the region would probably be caused by horizontal, right-lateral, strike-slip motion on vertical fault planes. In retrospect, the high topography of the Santa Cruz Mountains and the elevated marine terraces along the coast should have provided some clues. With the observed ocean retreat and the obvious uplift of the coast near Santa Cruz that accompanied the earthquake, Mother Nature was finally caught in the act. Several investigators quickly saw the connection between the earthquake uplift and the long-term evolution of the Santa Cruz Mountains and realized that important insights were to be gained by attempting to quantify the process of crustal deformation in terms of Loma Prieta-type increments of northward transport and fault-normal shortening.

California↗
USGS2017

Titanium

Titanium is a mineral commodity that is essential to the smooth functioning of modern industrial economies. Most of the titanium produced is refined into titanium dioxide, which has a high refractive index and is thus able to impart a durable white color to paint, paper, plastic, rubber, and wallboard. Because of their high strength-to-weight ratio and corrosion resistance, titanium metal and titanium metal alloys are used in the aerospace industry as well as for welding rod coatings, biological implants, and consumer goods. Ilmenite and rutile are currently the principal titanium-bearing ore minerals, although other minerals, including anatase, perovskite, and titanomagnetite, could have economic importance in the future. Ilmenite is currently being mined from two large magmatic deposits hosted in rocks of Proterozoic-age anorthosite plutonic suites. Most rutile and nearly one-half of the ilmenite produced are from heavy-mineral alluvial, fluvial, and eolian deposits. Titanium-bearing minerals occur in diverse geologic settings, but many of the known deposits are currently subeconomic for titanium because of complications related to the mineralogy or because of the presence of trace contaminants that can compromise the pigment production process. Global production of titanium minerals is currently dominated by Australia, Canada, Norway, and South Africa; additional amounts are produced in Brazil, India, Madagascar, Mozambique, Sierra Leone, and Sri Lanka. The United States accounts for about 4 percent of the total world production of titanium minerals and is heavily dependent on imports of titanium mineral concentrates to meet its domestic needs. Titanium occurs only in silicate or oxide minerals and never in sulfide minerals. Environmental considerations for titanium mining are related to waste rock disposal and the impact of trace constituents on water quality. Because titanium is generally inert in the environment, human health risks from titanium and titanium mining are minimal; however, the processes required to extract titanium from titanium feedstock can produce industrial waste.

Professional Paper↗
USGS1960

The Foraminiferal Genus Orbitolina in North America

The foraminiferal genus Orbitolina has been useful as an index fossil in the Cretaceous rocks of the circumglobal equatorial belt for nearly a century. In Europe and the Near and Middle East enough work has been done on the species to allow their use for approximate correlations within the Cretaceous sedimentary rocks. The study of American specimens of Orbitolina, had been almost neglected although they were used in a rather cursory fashion for markers of the Lower Cretaceous Trinity strata. Three species had been described and assigned to Orbitolina in the United States, but the validity of each of the species had been questioned. A study of the genus Orbitolina, its type species, its morphology and the stratigraphic and geographic distribution in North America are presented in this report. Stratigraphic sections were measured throughout the area of Lower Cretaceous outcrop in Texas, New Mexico. and Arizona, and samples of Orbitolina were taken from these measured sections. Several thousand thin sections were prepared from which 8 species of Orbitolina, 7 of them new, were recognized. Orbitolina texana (Roemer) was found to be confined to the lower part of the Glen Rose limestone and its equivalents. Orbitolina, minuta n. sp. is essentially confined to the upper part of the Glen Rose limestone and its equivalents. Four of the species are known only from the Arizona and New Mexico region. The species of Orbitolina are useful stratigraphically, but all their characters-internal as well as external-must be considered. The use of thin sections for the study of Orbitolina is essential. One of the first things that had to be determined was the correct concept of the genus Orbitolina. The type species had not been determined by earlier authors, although four species had been suggested at various times. With careful study of the early literature, it became apparent that the type species is Orbitulites lenticulata Lamarck, 1816=Madreporites lenticularis Blumenbach, 1805 by monotypy. The type species had never been studied using modern techniques. This paper presents the first description and illustrations of the type species based on internal as well as external characters. The American forms of Orbitolina had been referred to the species Orbitolina concava (Lamarck) by Silvestri and others. The necessity of understanding O. concava was apparent. Many misconceptions about O. concava had been developed and propagated until the modern concept no longer included the original material on which the svecies was based. Topotype material of Orbulites concava Lamarck, 1816, was restudied. For the first time both the internal and the external characters are described and illustrated. Orbitolina concava (Lamarck) is not conspecific with any of the North American forms. A thorough knowledge of the morphology of Orbitolina is essential to the interpretation of the features as seen in thin section. Carefully oriented sections were prepared and models built up illustrating the morphology. A new technique was adapted for multiple sectioning of specimens of Orbitolina. Using this technique, several oriented sections can be prepared from one specimen, enabling the correlation of features seen in axial, basal, and tangential sections. This technique should prove useful in the study of similar small objects, and therefore is described and illustrated. The early chambers of microspheric and megalospheric specimens were not well known. A technique for their study was developed and is described. The morphology of the early chambers of both generations is described and illustrated. The nature of the nepionic and neanic chambers of the microspheric generation is described and documented for the first time. The previous supposition of an early trochoid spire in microspheric specimens is rejected in favor of a flaring planispiral coil. This discovery must be considered in a study of the phylogeny. Charts are presented showing the strat

Professional Paper↗
USGS1968

Seismic seiches from the March 1964 Alaska earthquake

Seismic seiches caused by the Alaska earthquake of March 27, 1964, were recorded at more than 850 surface-water gaging stations in North America and at 4 in Australia. In the United States, including Alaska and Hawaii, 763 of 6,435 gages registered seiches. Nearly all the seismic seiches were recorded at teleseismic distance. This is the first time such far-distant effects have been reported from surface-water bodies in North America. The densest occurrence of seiches was in States bordering the Gulf of Mexico. The seiches were recorded on bodies of water having a wide range in depth, width, and rate of flow. In a region containing many bodies of water, seiche distribution is more dependent on geologic and seismic factors than on hydro-dynamic ones. The concept that seiches are caused by the horizontal acceleration of water by seismic surface waves has been extended in this paper to show that the distribution of seiches is related to the amplitude distribution of short-period seismic surface waves. These waves have their greatest horizontal acceleration when their periods range from 5 to 15 seconds. Similarly, the water bodies on which seiches were recorded have low-order modes whose periods of oscillation also range from 5 to 15 seconds. Several factors seem to control the distribution of seiches. The most important is variations of thickness of low-rigidity sediments. This factor caused the abundance of seiches in the Gulf Coast area and along the edge of sedimentary overlaps. Major tectonic features such as thrust faults, basins, arches, and domes seem to control seismic waves and thus affect the distribution of seiches. Lateral refraction of seismic surface waves due to variations in local phase-velocity values was responsible for increase in seiche density in certain areas. For example, the Rocky Mountains provided a wave guide along which seiches were more numerous than in areas to either side. In North America, neither direction nor distance from the epicenter had any apparent effect on the distribution of seiches. Where seismic surface waves propagated into an area with thicker sediment, the horizontal acceleration increased about in proportion to the increasing thickness of the sediment. In the Mississippi Embayment however, where the waves emerged from high rigidity crust into the sediment, the horizontal acceleration increased near the edge of the embayment but decreased in the central part and formed a shadow zone. Because both seiches and seismic intensity depend on the horizontal acceleration from surface waves, the distribution of seiches may be used to map the seismic intensity that can be expected from future local earthquakes.

Professional Paper↗
USGS2007

Analysis of improved government geological map information for mineral exploration: Incorporating efficiency, productivity, effectiveness, and risk considerations

This bulletin/professional paper focuses on the value of geoscientific information and knowledge, as provided in published government bedrock geological maps, to the mineral exploration sector. An economic model is developed that uses an attribute- ranking approach to convert geological maps into domains of mineral favourability. Information about known deposits in these (or analogous) favourability domains allow the calculation of exploration search statistics that provide input into measures of exploration efficiency, productivity, effectiveness, risk, and cost stemming from the use of the published geological maps. Two case studies, the Flin Flon Belt (Manitoba and Saskatchewan) and the south Baffin Island area (Nunavut), demonstrate that updated, finer resolution maps can be used to identify more exploration campaign options, and campaigns thats are more efficient, more effective, and less risky than old, coarser resolution maps when used as a guide for mineral exploration. The Flin Flon Belt study illustrates that an updated, coarser resolution bedrock map enables improved mineral exploration efficiency, productivity, and effectiveness by locating 60% more targets and supporting an exploration campaign that is 44% more efficient. Refining the map resolution provides an additional 17% reduction in search effort across all favourable domains and a 55% reduction in search effort in the most favourable domain. The south Baffin Island case study projects a 40% increase in expected targets and a 27% reduction in search effort when the updated, finer resolution map is used in lieu of the old, coarser resolution map. On southern Baffin Island, the economic value of the up dated map ranges from CAN$2.28 million to CAN$15.21 million, which can be compared to the CAN$1.86 million that it cost to produce the map (a multiplier effect of up to eight).

Professional Paper↗
USGS1955

The natural channel of Brandywine Creek, Pennsylvania

This study of the channel of Brandy wine Creek, Pennsylvania, consists of three parts. The first is an analysis of the changes which take place in the width, depth, velocity, slope of the water surface, suspended load, and roughness factor with changing discharge below the bankfull stage at each of several widely separated cross sections of the channel. Expressed as functions of the discharge, it is found that the variables behave systematically. In every section studied, as the discharge increases, the velocity increases to about the 0.6 power, depth to the 0.4, and load to the 2.0 power of the discharge. The roughness decreases to the 0.2 power of the discharge. The relative magnitudes and the direction of these variations are similar to those which have been observed in other rivers in the United States, primarily in the West. Some modifications of the hypotheses applicable to the western rivers are probably required because on Brandywine Creek the difference between the materials on the bed and in the banks is considerably greater than it is on most of the western rivers studied. In the second part of the paper the progressive changes of the same variables in the downstream direction with increasing discharge at a given frequency are described. Despite the disorderly appearance of the stream, it is found that the variables display a progressive, orderly change in the downstream direction when traced from the headwater tributaries through the trunk stream of Brandywine Creek. At a given frequency of flow, width increases with discharge to about the 0.5 power. Depth increases downstream somewhat less rapidly, while the slope and roughness both decrease in the downstream direction. Despite a decrease in the size of the material on the bed, both the mean velocity and the mean bed velocity increase downstream. The rates of change of these variables are in close accord with the changes observed on rivers flowing in alluvium and in stable irrigation canals. These relationships hold for all flows up to the bankfull stage. Analysis of the streamflow records indicates that the annual maximum discharge equals or exceeds the bankfull stage roughly once every 2 years. The regularity in the behavior of the variables with changing discharges both at-a-station and in the downstream direction and the similar rates of change of the variables on Brandywine Creek and in stable irrigation canals suggest the existence of a quasi-equilibrium in the channel of the creek. Part three of this study is concerned with this concept of equilibrium in streams. By analogy with canals and with several rivers in diverse regions of the United States it may be concluded that this quasi-equilibrium is closely related to the discharge, and to the concentration of the suspended load. The shape and longitudinal profile of the channel are determined by these two independent factors which operate within the limits set by the local geology. The latter determines the initial size, shape, and resistance of the material provided to the channel. The existence of a quasi-equilibrium among the variables studied suggests that most reaches on Brandywine Creek are at grade. This is true if the term "grade," when applied to natural rivers, is synonymous with quasi-equilibrium. The adjustability of the variables in the channel rather than the stability of any particular shape or longitudinal profile of the channel is emphasized when t

Pennsylvania↗
USGS2003

The Role of Geoscience Information in Reducing Catastrophic Loss Using a Web-Based Economics Experiment

What role can geoscience information play in the assessment of risk and the value of insurance, especially for natural hazard type risks? In an earlier, related paper Ganderton and others (2000) provided subjects with relatively simple geoscience information concerning natural hazard-type risks. Their research looked at how subjects purchase insurance when faced with relatively low probability but high loss risks of the kind that characterize natural hazards and now, increasingly, manmade disasters. They found evidence to support the expected utility theory (definitions of economics terms can be found in a glossary at the end of report), yet there remained the implication that subjects with excessive aversion to risk were willing to pay considerably more for insurance than the actuarially fair price plus any reasonable risk premium. Here, we report the results of additional experiments that provide further support for the basic postulates of expected utility theory. However, these new experiments add considerably to the decision environment facing subjects by offering an option to purchase geoscientific information that would assist them when calculating expected losses from hazards more accurately. Using an Internet-based mechanism to present information and gather data in an experimental setting, this research provided subjects with considerable textual and graphical information, and time to process it. Over a period of three months, almost 400 subjects participated in on-line experiments that generated approximately 22,000 usable data points for the empirical analysis discussed in this report. In the design of the experiment, we modeled the decisions to purchase (1) a detailed map giving subjects more information regarding the distribution of losses from a hazard and (2) insurance to indemnify them from any losses should they occur. On the basis of this design, we find strong evidence in support of the expected utility theory. Many of the findings reinforce those found in the early, similar study (Ganderton and others, 2000). However, this research also finds interactions between the decision to become better informed and the decision to insure. We chose an empirical framework that allows for both explicit and implicit (unobservable) correlations between the two decisions. The results suggest that at the end of the computer game subjects recognize the benefits of greater geoscience information. They take advantage of it, but are sensitive to its cost. When subjects use the more detailed information, they are more likely to purchase insurance when it offers a net benefit.

Professional Paper↗
USGS1990

Stratigraphy of the Mesaverde Group in the central and eastern greater Green River basin, Wyoming, Colorado, and Utah

This paper establishes a stratigraphic framework for the Mesaverde Group, nearly 5,000 ft thick, in the central and eastern greater Green River basin based on data from measured outcrop sections and drill holes. Stratigraphic correlations are supported by ammonite zonation. No new stratigraphic names are introduced, and no nomenclature problems are discussed. Five long measured sections through the Mesaverde Group are described. The lower part of the Mesaverde Group, comprising the Rock Springs, Blair, Haystack Mountains, Allen Ridge, and Iles Formations, was deposited during a major eastward regression of the interior Cretaceous seaway of North America during the late Santonian and early Campanian. This regression was followed by regional uplift of the central Rocky Mountain area during the middle Campanian. The regional uplift was accompanied by widespread nondeposition and erosion, which, in turn, were followed by deposition of the Ericson and Pine Ridge Sandstones. The upper part of the Mesaverde Group, comprising the Almond and Williams Fork Formations, was deposited during a major westward transgression of the interior seaway in the early Maestrichtian. The major marine transgressions and regressions of the interior seaway were caused by eustatic changes of sea level, whereas intervening periods of nondeposition and erosion resulted from tectonism in the Sevier orogenic belt west of the study area. Formations of the Mesaverde Group are composed of sediments deposited in a landward-seaward progression of alluvial-plain, floodplain, coastal-plain, barrier-plain, tidal-flat, delta-plain, marine-shoreline, and marine-shelf and slope depositional environments. Each of these depositional environments is represented by specific lithofacies, sedimentary structures, and fossils, which are characteristic of depositional settings determined by water salinity, water depth, sedimentary and diagenetic processes, and the nature of sediment source terranes. The Mesaverde Group was deposited mainly along the western margins of the interior Cretaceous seaway as marine shorelines that trended north to northeast across the study area. Arcuate deltas, which formed at the mouths of major rivers along these shorelines, spread eastward onto shallow marine shelves. Embayed shoreline areas between the deltas were the sites of barrier-island and tidal-flat deposition. Alluvial-plain, flood-plain, and coastal-plain environments were present inland. The marine shorelines were tidally influenced and wave dominated, and shoreline deposits were mostly thick, linear sheets of quartzose sandstone. Deposition was largely controlled by the emergence or submergence of shoreline areas. Stillstands occurred close to local transgressions and regressions, depending on rates of sedimentation and subsidence.

Professional Paper↗
USGS1979

Subsurface stratigraphy and geochemistry of late Quaternary evaporites, Searles Lake, California, with a section on radiocarbon ages of stratigraphic units

Searles Lake is a dry salt pan, about 100 km 2 in area, that lies on the floor of Searles Valley, in the desert of southeast California. Several salt bodies of late Quaternary age lie beneath the surface, mostly composed of sodium and potassium carbonate, sulfate, chloride, and borate minerals. Mud layers separate the salt bodies, which contain interstitial brine that is the source of large quantities of industrial chemicals. The value of annual production from the deposit exceeds $30 million; total production to date exceeds $1 billion. The salts and muds were deposited during Pleistocene and Holocene times by a series of large lakes (200 m maximum depth, 1,000 km 2 maximum area) that fluctuated in size in response to climatic change. Salts were deposited during major dry (interpluvial) episodes, muds during wet (pluvial) episodes that correlate with glacial advances in other parts of North America and the world. Data based on cores from the deposit are used in this paper to establish the stratigraphy of the deposit, the chemical and mineral compositions of successive units, and the total quantities of components contained by them. These parameters are then used to determine the geochemical evolution of the sedimentary layers. The results provide a refined basis for reconstructing the limnology of Searles Lake and the regional climate during late Quaternary time. Six main stratigraphic units were distinguished and informally named earlier on the basis of their dominant composition: Unit Typical thickness 14C age, uncorrected (in meters) (years B.P.) Overburden Mud 7 0 to >3,500 Upper Salt 15 >3,500 to 10,500 Parting Mud 4 10,500 to 24,000 Lower Salt 12 24,000 to 32,500 Bottom Mud 30 32,500 to 130,000 Mixed Layer 200+ > 130,000 (The age of 130,000 years for the Mixed Layer is based on extrapolated sedimentation rates.) The Lower Salt is subdivided into seven salt units (S-l to S-7) and six mud units (M-2 to M-7), the Mixed Layer into six units (A to F). For each salt unit, the areal extent, volume, shape, mineralogy, and chemical composition of the solids and brines have been determined; for each mud unit (which originally extended over much of the basin), the shape and volume within a standard area, and the mineralogy, have been determined. The bulk compositions (brines plus salts) of the combined Lower Salt units S-l to S-5 and units S-6 and S-7, and the Upper Salt, were determined so that the total quantities and ratios of ions in the initial brines could be reconstructed. The 74 published HC dates on Searles Lake core samples from all but the oldest unit are supplemented by 14 new dates (determined by Minze Stuiver) on the Lower Salt. Most of the age control comes from dates based on disseminated organic carbon; two dates are on wood; dates on carbonate minerals are less reliable. Although the probable disequilibrium between the carbon in the lake and atmosphere (because of contamination, slow equilibrium rates, and other factors) causes disseminated carbon dates to be an estimated 500-2,500 years 'too old,' the ages of the major and minor units are relatively well established. The list above indicates rounded and uncorrected ages for the contacts of major units. The age of the only salt bed in the Lower Salt which indicates desiccation (S-5) is about 28,000 years. The average uncorrected sedimentation rate in the Parting Mud is 4

Professional Paper↗
USGS1909

Geology and water resources of the northern portion of the Black Hills and adjoining regions in South Dakota and Wyoming

This paper, which supplements the report on the geology and water resources of the southern half of the Black Hills, published in 1901, is the result of studies made at intervals during the years 1899 to 1907. It relates to an area of about 7,500 square miles, situated about half in South Dakota and half in the northeast corner of Wyoming (Pl. II), and covering the northern half of the Black Hills uplift and a wide area of adjacent plains. The report describes the geology of the sedimentary rocks - their stratigraphy, structure, and history - and discusses their mineral resources, including underground water, coal, gypsum, etc. It also contains information respecting surface waters available for irrigation and stock raising, timber, climate, and the history of the topographic development of the region. The crystalline rocks of the central portion of the Black Hills area and the various igneous rocks of later age are shown on some of the accompanying maps but without differentiation, as the study of their geology was not within the scope of the investigation; neither are their mineral resources considered here, for these are treated in other publications. In the field work I have been assisted mainly by Prof. C. C. O'Harra, of the School of Mines at Rapid, who has mapped the geology of large areas about Aladdin, the Devils Tower, Belle Fourche, and Rapid. Dr. W. S. Tangier Smith has mapped portions of the Bear Lodge and Nigger Hill uplifts, and Mr. C. A. Fisher has assisted in portions of the work. The geology of the region from Sturgis to a point beyond Spearfish Canyon was mapped by Prof. T. A. Jaggar, jr., with the assistance of Mr. J. M. Boutwell, in 1898 and 1899. It is desirable to repeat here the statement made in my previous report that all who study the geology of the Black Hills must feel impressed by the remarkably clear general conceptions of the geologic relations of this region afforded by the survey made by Mr. Henry Newton over a quarter of a century ago. In one short season, with many unfavorable conditions for traveling, he determined most of the broader features and recorded many of the essential details. His posthumous report, edited by Mr. G. K. Gilbert, will always remain a standard work on Black Hills geology. Later studies have added greatly to our knowledge of the details of the stratigraphy and structure, the distribution of the rocks and minerals, and the age of the beds, and have afforded means for a more complete elucidation of the geologic history, especially the physiographic development of the Black Hills region.

South Dakota, Wyoming↗
USGS2014

Petrologic insights into basaltic volcanism at historically active Hawaiian volcanoes

Study of the petrology of Hawaiian volcanoes, in particular the historically active volcanoes on the Island of Hawai‘i, has long been of worldwide scientific interest. When Dr. Thomas A. Jaggar, Jr., established the Hawaiian Volcano Observatory (HVO) in 1912, detailed observations on basaltic activity at Kīlauea and Mauna Loa volcanoes increased dramatically. The period from 1912 to 1958 saw a gradual increase in the collection and analysis of samples from the historical eruptions of Kīlauea and Mauna Loa and development of the concepts needed to evaluate them. In a classic 1955 paper, Howard Powers introduced the concepts of magnesia variation diagrams, to display basaltic compositions, and olivine-control lines, to distinguish between possibly comagmatic and clearly distinct basaltic lineages. In particular, he and others recognized that Kīlauea and Mauna Loa basalts must have different sources. Subsequent years saw a great increase in petrologic data, as the development of the electron microprobe made it possible to routinely monitor glass and mineral compositions, in addition to bulk rock compositions. We now have 100 years’ worth of glass compositions for Kīlauea summit eruptions, which, together with expanding databases on prehistoric tephras, provide important constraints on the nature of Kīlauea’s summit reservoir. A series of chemically distinctive eruptions in the 1950s and 1960s facilitated evaluation of magma mixing and transport processes at Kīlauea. At Mauna Loa, lava compositions are distinctive only at the trace element level, suggesting that its summit reservoir is better mixed than Kīlauea’s. Most summit lavas at both volcanoes, however, lie on olivine control lines having the same olivine composition (Fo 86–87 ). Study of the ongoing East Rift Zone eruption at Kīlauea has further illuminated the complexity of magma storage, resupply, and mixing along this very active rift zone. Studies of active and closed-system lava lakes have been part of HVO’s efforts since Jaggar’s unique descriptions of the Halema‘uma‘u lava lake that existed before 1924. Detailed study of closed-system bodies, including the 1959 Kīlauea Iki, 1963 ‘Alae, and 1965 and prehistoric Makaopuhi lava lakes and the Uēkahuna laccolith, have allowed recognition and quantification of processes of basalt differentiation. Specific topics reviewed herein include the occurrence of segregation veins and related structures, overall cooling history, and patterns of crystallization and reequilibration of olivine in various lava lakes. In recent decades, study of the submarine slopes of the Island of Hawai‘i and of Lō‘ihi Seamount has revolutionized our understanding of the early history of Hawaiian volcanoes. Observations of Lō‘ihi lavas first established the existence of an early alkalic stage in the evolution of Hawaiian volcanoes. Stages of volcanic development from inception to tholeiitic shield building can be observed in Kīlauea’s submarine and subaerial sections. One distinctive feature of submarine volcanics at Kīlauea, Mauna Loa, and Hualālai is that picritic lavas are more abundant than in subaerial eruptions. Also, olivine compositions of submarine lavas are more magnesian, ranging from Fo 88 at Kīlauea to Fo 89 at Hualālai. The most magnesian glasses known from Kīlauea (MgO=14.7–15.0 weight percent) were found along the submarine part of Kīlauea’s East Rift Zone. Contributions to our knowledge of the nature of the mantle source(s) of Hawaiian basalts are reviewed briefly, although this is a topic where debate is ongoing. Finally, our accumulated petrologic observations impose constraints on the nature of the summit reservoirs at Kīlauea and Mauna Loa, specifically whether the summit chamber has been continuous or segmented during past decades.

Hawaii↗
USGS2008

Overview of the 2004 to 2006, and continuing, eruption of Mount St. Helens, Washington

Rapid onset of unrest at Mount St. Helens on September 23, 2004, initiated an uninterrupted lava-dome-building eruption that continues to the time of writing this overview (spring 2006) for a volume of papers focused on this eruption. About three weeks of intense seismic unrest and localized surface uplift, punctuated by four brief explosions, constituted a ventclearing phase, during which there was a frenzy of media attention and considerable uncertainty regarding the likely course of the eruption. The third week exhibited lessened seismicity and only minor venting of steam and ash, but rapid growth of the uplift, or welt, south of the 1980-86 lava dome proceeded as magma continued to push upward. Crystalrich dacite (~65 weight percent SiO 2 ) lava first appeared at the surface on October 11, 2004, beginning the growth of a complex lava dome of uniform chemical composition accompanied by persistent but low levels of seismicity, rare explosions, low gas emissions, and frequent rockfalls. Petrologic studies suggest that the dome lava is chiefly of 1980s vintage, but with an admixed portion of new dacite. Alternatively, it may derive from a part of the magma chamber not tapped by 1980s eruptions. Regardless, detailed investigations of crystal chemistry, melt inclusions, and isotopes reveal a complex magmatic history. Largely episodic extrusion between 1980 and 1986 produced a relatively symmetrical lava dome composed of stubby lobes. In contrast, continuous extrusion at mean rates of about 5 m 3 /s in autumn 2004 to <1 m 3 /s in early 2006 has produced an east-west ridge of three mounds with total volume about equal to that of the old dome. During much of late 2004 to summer 2005, a succession of spines, two recumbent and one steeply sloping and each mantled by striated gouge, grew to nearly 500 m in length in the southeastern sector of the 1980 crater and later disintegrated into two mounds. Since then, growth has been concentrated in the southwestern sector, producing a relatively symmetrical mound with steep gougecovered slabs on its east flank. Throughout the eruption, the position of the extrusive vent has remained more or less fixed. Lack of geodetic evidence for either volume increase or pressure increase in the deep magmatic system since about 1990 and geodetic modeling that can account for only 20 to 30 percent of the 2004-to-present dome volume puzzles geodesists. Better constraints on parameters such as magma-chamber volume, crustal properties, and magma compressibility are needed to improve the models. Development of the welt and the new dome bisected horseshoe-shaped Crater Glacier, which formerly wrapped around three sides of the 1980s dome, and fractured, compressed, and thickened the glacier’s surviving east and west arms. Doubling of ice thickness resulted in increased flow rate and advance of termini, although rapid infiltration of water into the highly porous glacier bed prevented substantial basal sliding. Overall, dome growth and disintegration has removed surprisingly little ice. The outcome of the ongoing eruption remains uncertain, but Mount St. Helens’ varied eruptive history suggests multiple possibilities. One dynamical model and several petrologic investigations regard the current eruption as an extension of 1980s dome building that may persist continuously or episodically for years to come.

Washington↗
USGS2007

Executive Summary — Assessment of undiscovered oil and gas resources of the San Joaquin Basin Province of California, 2003

In 2003, the U.S. Geological Survey (USGS) completed an assessment of the oil and gas resource potential of the San Joaquin Basin Province of California (fig. 1.1). The assessment is based on the geologic elements of each Total Petroleum System defined in the province, including hydrocarbon source rocks (source-rock type and maturation and hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). Using this geologic framework, the USGS defined five total petroleum systems and ten assessment units within these systems. Undiscovered oil and gas resources were quantitatively estimated for the ten assessment units (table 1.1). In addition, the potential was estimated for further growth of reserves in existing oil fields of the San Joaquin Basin.

California↗
USGS1916

The flora of the Catahoula Sandstone

During the progress of my studies of the fossil floras of the Gulf Coastal Plain, embracing all horizons from the Lower Cretaceous to the Pleistocene and prosecuted under the general direction of T. Wayland Vaughan, material representing the floras of all the major stratigraphic units in the area extending from western Florida to central Texas has been discovered. Field work and office studies of all these floras have proceeded more or less simultaneously, and a large amount of manuscript in various stages of completion has been accumulated. The floras of the Upper Cretaceous and Eocene of South Carolina and Georgia have been described and a report on the very large lower Eocene floras is now in press.

Professional Paper↗