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At least 469 records · Page 26Linked to original sources
USGS2008

The Pleistocene eruptive history of Mount St. Helens, Washington, from 300,000 to 12,800 years before present

We report the results of recent geologic mapping and radiometric dating that add considerable detail to our understanding of the eruptive history of Mount St. Helens before its latest, or Spirit Lake, stage. New data and reevaluation of earlier work indicate at least two eruptive periods during the earliest, or Ape Canyon, stage, possibly separated by a long hiatus: one about 300-250 ka and a second about 160–35 ka. Volcanism during this stage included eruption of biotite- and quartz-bearing dacite domes and pyroclastic flows in the area west of and beneath the present-day edifice, accompanied by the deposition of set C tephras. Ape Canyon-stage rocks are compositionally similar to younger Mount St. Helens dacite. The Cougar stage, about 28-18 ka, was probably the most active eruptive stage in Mount St. Helens’ history before the Spirit Lake stage. During the Cougar stage, a debris avalanche buried the area south of the present-day edifice, and voluminous pyroclastic flows, dacite domes, tephra, and a large volume pyroxene andesite lava flow were erupted. Two tephra sets, M and K, were deposited midway through this stage. Swift Creek-stage deposits were emplaced in two phases, beginning about 16 ka and ending about 12.8 ka. During the first phase, set S tephras and three large fans and at least one smaller fan of dacitic fragmental material were deposited on the northwest, west, south, and southeast flanks of Mount St. Helens. The fans are dominated by lithic pyroclastic-flow deposits associated with dome building but include both primary and reworked material from pumiceous pyroclastic flows and lahars. One Swift Creek-age dome on the west flank of the volcano has been located, and others must have been nearby. During the second phase, set J tephras were deposited, but no pyroclastic flows or domes are known to be associated with the andesitic set J tephras. Preliminary petrographic analysis of these older rocks suggests that the volcano’s magmatic system was simpler during the Ape Canyon stage than during subsequent stages and that the magmatic system has evolved from relatively simple to more complex as the volcano matured. Compositional cycles as envisioned by C.A. Hopson and W.G. Melson for the Spirit Lake stage probably did not occur during the Ape Canyon stage but developed later during the Cougar and Swift Creek stages.

Washington↗
USGS2005

Bathymetry and vegetation in isolated marsh and cypress wetlands in the northern Tampa Bay Area, 2000-2004

Wetland bathymetry and vegetation mapping are two commonly used lines of evidence for assessing the hydrologic and ecologic status of expansive coastal and riverine wetlands. For small isolated freshwater wetlands, however, bathymetric data coupled with vegetation assessments are generally scarce, despite the prevalence of isolated wetlands in many regions of the United States and the recognized importance of topography as a control on inundation patterns and vegetation distribution. In the northern Tampa Bay area of west-central Florida, bathymetry was mapped and vegetation was assessed in five marsh and five cypress wetlands. These 10 isolated wetlands were grouped into three categories based on the effects of ground-water withdrawals from regional municipal well fields: natural (no effect), impaired (drier than natural), and augmented (wetlands with artificially augmented water levels). Delineation of the wetland perimeter was a critical component for estimating wetland-surface area and stored water volume. The wetland perimeter was delineated by the presence of Serenoa repens (the 'palmetto fringe') at 9 of the 10 sites. At the 10th site, where the palmetto fringe was absent, hydric-soils indicators were used to delineate the perimeter. Bathymetric data were collected using one or more techniques, depending on the physical characteristics of each wetland. Wetland stage was measured hourly using continuous stage recorders. Wetland vegetation was assessed semiannually for 2 1/2 years in fixed plots located at three distinct elevations. Vegetation assessments were used to determine the community composition and the relative abundance of obligate, facultative wet, and facultative species at each elevation. Bathymetry maps were generated, and stage-area and stage-volume relations were developed for all 10 wetlands. Bathymetric data sets containing a high density of data points collected at frequent and regular spatial intervals provided the most useful stage-area and stage-volume relations. Bathymetric maps of several wetlands also were generated using a low density of data points collected along transect lines or contour lines. In a comparative analysis of the three mapping approaches, stage-area and stage-volume relations based on transect data alone underestimated (by 50-100 percent over certain ranges of stage) the wetland area and volume compared to results using a high density of data points. Adding data points collected along one elevation contour below the wetland perimeter to the transect data set greatly improved the agreement of the resulting stage-area and stage-volume relations to the high-density mapping approach. Stage-area relations and routinely monitored stage data were used to compare and contrast the average flooded area in a natural marsh and an impaired marsh over a 2-year period. Vegetation assessments used together with flooded-area information provided the potential for extrapolating vegetation results from points or transects to wetlands as a whole. A comparison of the frequency of flooding of different areas of the wetland and the species composition in vegetation plots at different elevations indicated the dependence of vegetation on inundation frequency. Because of the broad tolerances of many wetlands plants to a range of inundation conditions, however, vegetation assessments alone provided less definitive evidence of the hydrologic differences between the two sites, and hydrologic changes occurring during the 2 years, than the flooded-area frequencies. Combining flooded-area frequencies with vegetation assessments could provide a more versatile and insightful approach for determining the ecological status of wetlands than using vegetation and stage data alone. Flooded-area frequencies may further provide a useful approach for assessing the ecological status of wetlands where historical vegetation surveys and stage data are lacking. Comparing the contemporary flooded-area frequencies a

Scientific Investigations Report↗
USGS2017

Element migration of pyrites during ductile deformation of the Yuleken porphyry Cu deposit (NW-China)

The strongly deformed Yuleken porphyry Cu deposit (YPCD) occurs in the Kalaxiangar porphyry Cu belt (KPCB), which occupies the central area of the Central Asian Orogenic Belt (CAOB) between the Sawu’er island arc and the Altay Terrane in northern Xinjiang. The YPCD is one of several typical subduction-related deposits in the KPCB, which has undergone syn-collisional and post-collisional metallogenic overprinting. The YPCD is characterized by three pyrite-forming stages, namely a hydrothermal stage A (Py I), a syn-ductile deformation stage B (Py II) characterized by Cu-Au enrichment, and a fracture-filling stage C (Py III). In this study, we conducted systematic petrographic and geochemical studies of pyrites and coexist biotite, which formed during different stages, in order to constrain the physicochemical conditions of the ore formation. Euhedral, fragmented Py I has low Pb and high Te and Se concentration and Ni contents are low with Co/Ni ratios mostly between 1 and 10 (average 9.00). Py I is further characterized by enrichments of Bi, As, Ni, Cu, Te and Se in the core relative to the rim domains. Anhedral round Py II has moderate Co and Ni contents with high Co/Ni ratios >10 (average 95.2), and average contents of 46.5 ppm Pb and 5.80 ppm Te. Py II is further characterized by decreasing Bi, Cu, Pb, Zn, Ag, Te, Mo, Sb and Au contents from the rim to the core domains. Annealed Py III has the lowest Co content of all pyrite types with Co/Ni ratios mostly <0.1 (average 1.33). Furthermore, Py III has average contents of 3.31 ppm Pb, 1.33 ppm Te and 94.6 ppm Se. In addition, Fe does not correlate with Cu and S in the Py I and Py III, while Py II displays a negative correlation between Fe and Cu as well as a positive correlation between Fe and S. Therefore, pyrites which formed during different tectonic regimes also have different chemical compositions. Biotite geothermometer and oxygen fugacity estimates display increasing temperatures and oxygen fugacities from stage A to stage B, while temperature and oxygen fugacities decrease from stage B to stage C. The Co/Ni ratio of pyrite depends discriminates between the different mineralizing stages in the Yuleken porphyry copper deposit: Py II, associated with the deformation stage B and Cu-enrichment, shows higher Co/Ni ratios and enrichments of Pb, Zn, Mo, Te and Sb than the pyrites formed during the other two stages. The Co/Ni ratio of pyrite can not only apply to discriminate the submarine exhalative, magmatic or sedimentary origins for ore deposits but also can distinguish different ore-forming stages in a single porphyry Cu deposit. Thus, Co/Ni ratio of pyrites may act as an important exploration tool to distinguish pyrites from Cu-rich versus barren area. Furthermore, the distribution of Cu, Mo, Pb, Au, Bi, Sb and Zn in the variably deformed pyrite is proportional to the extent of deformation of the pyrites, indicating in accordance with variable physicochemical conditions different element migration behavior during the different stages of deformation and, thus, mineralisation.

Ore Geology Reviews↗
USGS2004

A water-budget analysis of Medina and Diversion Lakes and the Medina/Diversion Lake system, with estimated recharge to Edwards aquifer, San Antonio area, Texas

In January 2001, the U.S. Geological Survey—in cooperation with the Edwards Aquifer Authority—began a study to refine and, if possible, extend previously derived (1995–96) relations between the stage in Medina Lake and recharge to the Edwards aquifer to include the effects of reservoir stages below 1,018 feet and greater than 1,046 feet above National Geodetic Vertical Datum of 1929. The principal objective of this present (2001–02) study was to estimate ground-water outflow (seepage) from Medina Lake, Diversion Lake, and from the Medina/Diversion Lake system through the calculation of water budgets representing steady-state conditions over as wide a range as possible in the stages of Medina and Diversion Lakes. The water budgets were compiled for selected periods during which time the water-budget components were inferred to be relatively stable and the influence of precipitation, stormwater runoff, and changes in storage were presumably minimal. Water budgets for the Medina/Diversion Lake system were compiled for 127 water-budget periods ranging from 8 to 78 days from daily hydrologic data collected during March 1955–September 1964, October 1995–September 1996, and February 2001–June 2002. Budgets for Medina and Diversion Lakes were compiled for 14 periods ranging from 8 to 23 days from daily hydrologic data collected only during October 1995–September 1996 and April 2001–June 2002. Linear equations were developed to relate the stage in Medina Lake to ground-water outflow from Medina Lake, Diversion Lake, and the Medina/Diversion Lake system. The computed mean rates of outflow from Medina Lake ranged from about 18 to 182 acre-feet per day between stages of 1,019 and 1,064 feet above National Geodetic Vertical Datum of 1929. The computed rates of outflow from Diversion Lake ranged from about -85 to 52 acre-feet per day. The rates of outflow from the entire lake system ranged from about 5 to 178 acre-feet per day between Medina Lake stages of 963 to 1,064 feet. It is assumed that all outflow from the lake system enters the ground-water system as recharge to the Edwards aquifer. During the time that the stage in Medina Lake was greater than about 1,040 feet, Diversion Lake gained more water than it lost to the ground-water system and the rate of ground-water outflow from Medina Lake increased sharply while its stage was between about 1,043 and 1,045 feet. The observed outflow from Diversion Lake during this time decreased sharply to the extent that a net gain resulted—indicating that a substantial amount of the additional outflow from Medina Lake returned to Diversion Lake. When the stage in Medina Lake is at the spillway elevation of 1,064 feet, Diversion Lake appears to gain as much as 40 percent of the concurrent ground-water outflow from Medina Lake. An indication of water moving from the lake system into the ground-water system and back to the surface-water system was observed in the most downstream reach of the Medina River, between Diversion Lake and the Medina River near Riomedina. During conditions of no flow over Diversion Dam, this reach of the Medina River gained from about 32 to 94 acre-feet per day, with the gain increasing with increasing stage in Diversion Lake. The average of the monthly recharge to the Edwards aquifer from the Medina/Diversion Lake system—as estimated by the present study for the October 1995–September 2002 period—is 3,083 acre-feet, or about 56 percent of recharge computed for this period with a previously used (Lowry) method. The present study’s estimates of recharge for months with rising-lake stage conditions are about 44 percent of those computed with the previously used method, compared to about 60 percent for months with steady or falling-stage conditions. For stages greater than 1,045 feet, the present study estimated recharge to be about 52 percent of that computed with the previously used method, compared to about 64 percent at stages below 1,045 feet.

Texas↗
USGS1999

The rise and fall of late Paleozoic trilobites of the United States

Based on range data and generic composition, four stages of evolution are recognized for late Paleozoic trilobites of the contiguous United States. Stage 1 occurs in the Lower Mississippian (Kinderhookian-Osagean) and is characterized by a generically diverse association of short-ranging, stenotopic species that are strongly provincial. Stage 2 species are present in the Upper Mississippian and consist of a single, eurytopic, pandemic genus, Paladin. Species of Stage 2 are much longer-ranging than those of Stage 1, and some species may have persisted for as long as 12 m.y. Stage 3 is present within Pennsylvanian and Lower Permian strata and consists initially of the eurytopic, endemic genera Sevillia and Ameura as well as the pandemic genus Ditomopyge. During the middle Pennsylvanian the very long-ranging species Ameura missouriensis and Ditomopyge scitula survived for more than 20 m.y. During the late Pennsylvanian and early Permian, a number of pandemic genera appear to have immigrated into what is now North America. Stage 4 is restricted to the Upper Permian (late Leonardian-Guadalupian) strata and is characterized by short-ranging, stenotopic, provincial genera. The main causal factor controlling the four-stage evolution of late Paleozoic trilobites of the United States is interpreted to be eustacy. Whereas Stage 1 represents an adaptive radiation developed during the Lower Mississippian inundation of North America by the Kaskaskia Sequence, Stage 2 is present in strata deposited during the regression of the Kaskaskia sea. Stage 3 was formed during the transgression and stillstand of the Absaroka Sequence and, although initially endemic, Stage 3 faunas are strongly pandemic in the end when oceanic circulation patterns were at a maximum. A mid-Leonardian sea-level drop caused the extinction of Stage 3 fauna. Sea-level rise near the end of the Leonardian and into the Guadalupian created an adaptive radiation of stentopic species of Stage 4 that quickly became extinct with the latest Permian regression.

Journal of Paleontology↗
USGS2011

2009 Spring floods in North Dakota, western Minnesota, and northeastern South Dakota

In 2009, record-breaking snowfalls and additional spring moisture caused severe flooding in parts of the Missouri River and Red River of the North (Red River) Basins in North Dakota, Minnesota, and South Dakota. There were 48 peak of record stages and 36 discharges recorded at U.S. Geological Survey streamgages located in both basins between March 20 and May 15, 2009. High water continued to affect many communities up and down the rivers' main stems and tributaries for nearly 2 months. Record snowfall for single-day totals, as well as monthly totals, occurred throughout the Missouri River and Red River of the North Basins. Additional moisture in the spring as well as the timing of warmer temperatures caused record flooding in many places in both basins with many locations reporting two flood crests. Ice jams on the Missouri River, located north and south of Bismarck, N. Dak., caused flooding. Southwest Bismarck was evacuated as rising waters first began inundating homes in low-lying areas along the river and then continued flowing into the city's lower south side. On March 24, 2009, the peak stage of the Missouri River at Bismarck, N. Dak. streamgage was 16.11 feet, which was the highest recorded stage since the completion of Garrison Dam in 1954. South of Bismarck, the Missouri River near Schmidt, N. Dak. streamgage recorded a peak stage of 24.24 feet on March 25, 2009, which surpassed the peak of record of 23.56 feet that occurred on December 9, 1976. While peak stage reached record levels at these streamgages, the discharge through the river at these locations did not reach record levels. The record high stages resulted from ice jams occurring on the Missouri River north and south of the cities of Bismarck and Mandan. At the Red River of the North at Fargo, N. Dak. streamgage, the Red River reached a record stage of 40.84 feet surpassing the previous peak of record stage of 39.72 feet set in 1997. The associated peak streamflow of 29,500 cubic feet per second exceeded the previous peak of record set in 1997 by 1,500 cubic feet per second. For the cities of Fargo, and Moorhead, Minn., and the surrounding area, the stage of the Red River remained above flood stage for nearly 2 months. In addition to high stage and flow on the main-stem Missouri and Red Rivers, peak of record stage and discharge were recorded at many U.S. Geological Survey streamgages in the Missouri River and Red River Basins. Several reservoirs and lakes in the region also experienced record stage elevations from the high flows during the 2009 spring snowmelt floods.

Scientific Investigations Report↗
USGS2002

Simulation of Fish, Mud, and Crystal Lakes and the shallow ground-water system, Dane County, Wisconsin

A new MODFLOW lake package (LAK3) that simulates ground-water/lake interaction was used in simulation of Fish, Mud and Crystal Lakes?three shallow seepage lakes located in northwestern Dane County, Wis. The simulations were done to help determine the cause of increasing lake stages and provide a tool to estimate the effect of pumping water from Fish lake on future lake stages. The ground-water-flow model was developed using a telescopic-mesh refinement of the Dane and southwestern Columbia Counties regional model previously developed by the U.S. Geological Survey and the Wisconsin Geological and Natural History Survey. The parameter estimation model, UCODE, was coupled to the steadystate ground-water model to automate and optimize the calibration procedure. The steady-state model was calibrated to measured ground-water levels, Spring Creek streamflow measured at Lodi, and Fish and Crystal Lake stages. The results of the steady-state model were used as initial conditions in a transient simulation beginning in 1966 and ending in 1998. Recharge based on annual baseflow in Black Earth Creek, runoff based on measured coefficients, and precipitation and evaporation from the lake surfaces, were varied during the transient simulation. Measured Fish Lake stage was matched to simulated stage to calibrate the transient model. Model results suggest that the increase in regional ground-water recharge resulted in increased ground-water flow to the lake, which in turn resulted in increased lake stages. Simulation results of withdrawal of water from Fish Lake at 500 gallons per minute, assuming 1990?98 climatic conditions, indicate that after 1 year of pumping the stage of Fish and Mud Lakes would be reduced more than 1 foot and the stage of Crystal Lake would be reduced by less than 0.2 foot. When pumping is stopped, the lake stages would recover to near pre-pumping levels within about 3 years. When pumping is extended to 5 years, Fish and Mud Lake stage would be reduced by a maximum of 3.8 feet and Crystal Lake stage is reduced a maximum of 0.8 feet. After 4 years of recovery, Fish and Mud Lake stages are within 0.9 foot of prepumping levels and Crystal Lake stage is within 0.7 foot.

Wisconsin↗
USGS2025

Practical application of time-lapse camera imagery to develop water-level data for three hydrologic monitoring sites in Wisconsin during water year 2020

Using camera imagery to measure water level (camera-stage) is a well-researched area of study. Previous camera-stage studies have shown promising results when implementing this technology with tight constraints on test conditions. However, there is a need for a more comprehensive evaluation of the extensibility of camera-stage to practical applications. Therefore, the aim of this study was to test a camera-stage method under a wide variety of test conditions to better understand the successes and challenges of using this technology in real-world scenarios. In this study, this approach was tested during Water Year 2020 at three existing U.S. Geological Study (USGS) stream gaging stations in south central Wisconsin that had existing USGS water-level instrumentation. The specific reference objects tested were white pipes and a concrete wall. Since successful application of camera-stage relies on use of suitable images, all captured images in this study were visually inspected to determine suitability for application of camera-stage. Camera-stage measurements were then computed only on images deemed suitable and the results were compared with ground-truth stage values to determine the accuracy. For the purposes of this study, camera-stage values within ±0.10 ft of the actual stage were considered acceptable. One major challenge highlighted was the potential difficulty in obtaining suitable imagery, with the proportion of suitable images varying greatly between the four trials from 38 % to 92 %. The results from applying camera-stage to suitable images were encouraging though, with 79 % to 99 % of evaluated camera-stage values qualifying as acceptable among the four test trials.

Wisconsin↗
USGS1977

Calcic soils and calcretes in the southwestern United States

Secondary calcium carbonate of diverse origins, 'caliche' of many authors, is widespread in the southwestern United States. 'Caliche' includes various carbonates such as calcic soils and products of groundwater cementation. The term 'caliche' is generally avoided in this report in favor of such terms as calcrete, calcic soils, and pervasively cemented deposits. Criteria for the recognition of various types of calcrete of diverse origins include field relations and laboratory data. Calcic soils provide a comprehensive set of characteristics that aid in their recognition in the field. These characteristics include a distinctive morphology that is zoned horizontally and can frequently be traced over tens to hundreds of square kilometers. The major process in the formation of pedogenic calcrete and calic soils is the leaching of calcium carbonate from upper soil horizons by downward percolating soil solutions and reprecipitation of the carbonate in alluvial horizons near the base of the soil profile. The formation of pedogenic calcrete involves many factors including climate, source of carbonate, and tectonic stability of the geomorphic surface on which the calcrete is deposited. Most of the carbonate in pedogenic calcrete is probably derived from windblown sand, dust, and rain. Calcic soils and pedogenic calcretes follow a six-stage sequence morphologic development and is based on a classification devised by Gile, Peterson and Grossman in 1966. The .six morphologic stages of carbonate deposition in soils are related to the relative age of the soil and are as follows: I. The first or youngest stage includes filamentous or faint coatings of carbonate on detrital grains. II. The second stage includes pebble coatings which are continuous; firm carbonate nodules are few to common. III. The third stage includes coalesced nodules which occur in a friable or disseminated carbonate matrix. IV. The fourth stage includes platy, firmly cemented matrix which engulfs nodules; horizon is plugged to downward moving solutions. V. The fifth stage includes soils which are platy to tabular, dense, strongly cemented. A well-developed laminar layer occurs on the upper surface. VI. The sixth and most advanced stage is massive, multilaminar, and strongly cemented calcrete with abundant pisoliths, the upper surface of which may be brecciated. Pisoliths may indicate many generations of brecciation and reformation. In general calcic soils include stages I through III and are friable to moderately indurated; whereas pedogenic calcretes include stages IV through VI and are dense and strongly indurated. In a single pedon the morphologic stage of carbonate deposition decreases downward in the profile. The stage of development may be used in local regions for correlation and determination of relative ages of soils and geomorphic surfaces. Some structures observed in pedogenic calcretes may be present in other types of calcrete but the horizontal zonation typical of deposits of soil processes is absent. Laminar structure in particular is not restricted to pedogenic deposits and is common in many varieties of calcrete. Very little chemical change occurs in the noncalcareous nonclayey fractions of calcretes with age; but clay minerals within calcretes undergo a complex history of authigenesis. There is a depletion of magnesium in the calcareous portion and an enrichment of magnesium in the clayey portion of a calcrete with age. In keeping with this relationship, montmorillonite, or mixed layer montmorillonite-illite, is common in younger calcretes; whereas the high magnesium-silicate clays, sepiolite and palygorskite, are common in older calcretes. This indicates that the magnesium depleted from the carbonate is redistributed authigenically in clay minerals. The mobility of carbonate introduces many problems in attempts to date calcretes directly. Although the relative ages of soils within a province may be determined by quant

Open-File Report↗
USGS1982

Fluid-inclusion data on samples from Creede, Colorado, in relation to mineral paragenesis

Published and unpublished data on 2575 fluid inclusions in ore and gangue minerals from the Creede, Colorado, Ag-Pb-Zn-Cu vein deposit collected in our laboratories from 1959 to 1981 have shown that the average salinity (wt. % NaCl equivalent, hereinafter termed wt.% eq.) and homogenization temperature (Th), and the ranges of these two parameters for fluid inclusions in sphalerite, quartz, fluorite, and rhodochrosite, respectively, are 8.1 (4.6 - 13.4), 239?C (195-274?C); 6.1 (1.1-10.0), 260?C (190->400?C); 10.7 (6.1-11.1), 217?C (213-229?C) and 260?C (247-268?C) (bimodal distribution of Th); and 9.9 (9.3 - 10.6), 214?C (185-249?C). Inclusions have been measured in minerals from four of the five stages of mineralization previously recognized at Creede. The few inclusions of fluids depositing rhodochrosite (A-stage, earliest in the paragenesis) yield Th and salinity values more similar to those of the low-temperature (average Th 217?C) fluids forming some of the much later fluorite (C-stage) than to any of the other fluids. Th measurements on A-stage quartz range from 192?C to 263?C and average 237?C. The early, fine-grained, B-stage sphalerites yielded Th of 214 to 241?C and salinities of 6.1 to 10.2 wt. % eq. D-stage sphalerite (late in the paragenesis) has been studied in detail (growth-zone by growth-zone) for several localities along the OH vein and reveals a generally positive correlation among Th, salinity and iron content of the host sphalerite. The deposition of D-stage sphalerite was characterized by repeated cycling through different regions of salinity/Th space, as Th and salinity generally decreased with time. Seventeen salinity-Th measurements were made on D-stage sphalerite from one locality on the Bulldog Mountain vein system, which, like the OH vein, is one of four major ore-producing vein systems at Creede. These data suggest a lower Th for a given salinity fluid from sphalerite on the Bulldog Mountain vein than on the OH vein. The very high values of Th for some quartz samples (mostly D-stage) are believed to be a result of the trapping of both gas and liquid from a boiling fluid in the upper levels of the vein system. Boiling of fluids depositing D-stage quartz is indicated by the presence of steam inclusions in quartz and the extreme variability of Th values measured on quartz. The pressure was low (< 125 kg/cm 2) throughout ore deposition. Three major growth zones in D-stage sphalerite are recognized throughout the OH vein. Deposition of the first major zone began from fluids having intermediate salinities and temperatures (7.8-9.2 wt. % eq., 240?C) but the characteristics of the fluids oscillated after that, ranging from 7.2 to 10.1 wt. % eq. and from 225?C to 270?C. Deposition of the second major, most Fe-rich zone began with the hottest, most saline fluids present during D-stage mineralization (. 270?C, 10.5-12.5 wt. % eq., 3 mole % FeS in sphalerite). The fluid then oscillated with respect to Th and salinity (213-274?C, 5.2-12.5 wt. % eq.) but showed a general decrease in both with time. Deposition of the youngest major zone began with a very Fe-poor sphalerite (0.25-0.75 mole % FeS), from the least saline, coolest fluids (5-6.5 wt. % eq., 200-212?C) and ended with a trend of increasing temperature at approximately constant salinity. The fluid-inclusion data can best be explained by a mixing model involving at least two fluids--one hot and saline, the other cool and fresher. Sudden changes in the mixing ratio, presumably from changes in the plumbing, punctuated long periods of remarkably uniform conditions of ore fluid flow and deposition. The effects of other processes such as convection and heat exchange with wall rocks must have been superimposed on this simple mixing model, however. In contrast to an earlier interpretation, several aspects of the inclusion data may be interpreted to suggest exceedingly slow ore deposition. Work in progress may resolve some of these ambiguities and refine

Open-File Report↗
USGS2008

California Cenozoic Biostratigraphy -- Paleogene: Chapter 4 in Petroleum systems and geologic assessment of oil and gas in the San Joaquin Basin Province, California

The time transgressive nature of the California benthic foraminiferal stages is in most cases the result of poor taxonomy, use of local species ranges, and a lack of understanding about the type sections. Correcting these problems allows the stages to be consistently applied and enhances their ability to identify coeval strata. Each stage is identified by the first and last appearances of selected cosmopolitan benthic foraminiferal species and of reliable local species. Although further study is needed, the stages correlate with the international time scale. The revised age interpretation of the stages suggests that the Cheneyian Stage is coeval with planktic zone P1 through P3, the Ynezian Stage is coeval with planktic zone P4, the Bulitian Stage is missing in most section but when present is coeval with zones P5 and P6a, the Penutian Stage is coeval with planktic zones P6b through early P9 (no younger than the overlap between P9 and CP11), the Ulatisian Stage is coeval with P9 (younger than CP11) through P11, the Narizian Stage is coeval with zones P12 through P15, and the Refugian Stage is coeval with zones P16 and P17.

California↗
USGS2014

Flood-inundation maps for the West Branch Susquehanna River near the Boroughs of Lewisburg and Milton, Pennsylvania

Digital flood-inundation maps for an approximate 8-mile reach of the West Branch Susquehanna River from approximately 2 miles downstream from the Borough of Lewisburg, extending upstream to approximately 1 mile upstream from the Borough of Milton, Pennsylvania, were created by the U.S. Geological Survey (USGS) in cooperation with the Susquehanna River Basin Commission (SRBC). The inundation maps, which can be accessed through the USGS Flood Inundation Mapping Science Web site at http://water.usgs.gov/osw/flood_inundation/ , depict the estimated areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgage 01553500, West Branch Susquehanna River at Lewisburg, Pa. In addition, the information has been provided to the Susquehanna River Basin Commission (SRBC) for incorporation into their Susquehanna Inundation Map Viewer (SIMV) flood warning system ( http://maps.srbc.net/simv/ ). The National Weather Service (NWS) forecasted peak-stage information ( http://water.weather.gov/ahps ) for USGS streamgage 01553500, West Branch Susquehanna River at Lewisburg, Pa., may be used in conjunction with the maps developed in this study to show predicted areas of flood inundation. In this study, flood profiles were computed for the stream reach by means of a one-dimensional step-backwater model. Calibration of the model was achieved using the most current stage-discharge relations (rating number 11.1) at USGS streamgage 01553500, West Branch Susquehanna River at Lewisburg, Pa., a documented water-surface profile from the December 2, 2010, flood, and recorded peak stage data. The hydraulic model was then used to determine 26 water-surface profiles for flood stages at 1-foot intervals referenced to the streamgage datum ranging from 14 feet (ft) to 39 ft. Modeled flood stages, as defined by NWS, include Action Stage, 14 ft; Flood Stage, 18 ft; Moderate Flood Stage, 23 ft; and Major Flood Stage, 28 ft. Geographic information system (GIS) technology was then used to combine the simulated water-surface profiles with a digital elevation model (DEM) derived from light detection and ranging (lidar) data to delineate the area flooded at each water level. The availability of these maps, along with World Wide Web information regarding current stage from USGS streamgages and forecasted stream stages from the NWS, provide emergency management personnel and residents with information that is critical for flood response activities, such as evacuations and road closures, as well as for post-flood recovery efforts.

Pennsylvania↗
USGS2016

Flood-Inundation Maps for Sugar Creek at Crawfordsville, Indiana

Digital flood-inundation maps for a 6.5-mile reach of Sugar Creek at Crawfordsville, Indiana, were created by the U.S. Geological Survey (USGS) in cooperation with the Indiana Office of Community and Rural Affairs. The flood-inundation maps, which can be accessed through the USGS Flood Inundation Mapping Science Web site at http://water.usgs.gov/osw/flood_inundation/ , depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgage 03339500, Sugar Creek at Crawfordsville, Ind. Near-real-time stages at this streamgage may be obtained on the Internet from the USGS National Water Information System at http://waterdata.usgs.gov/ or the National Weather Service (NWS) Advanced Hydrologic Prediction Service at http://water.weather.gov/ahps/ , which also forecasts flood hydrographs at this site (NWS site CRWI3). Flood profiles were computed for the USGS streamgage 03339500, Sugar Creek at Crawfordsville, Ind., reach by means of a one-dimensional step-backwater hydraulic modeling software developed by the U.S. Army Corps of Engineers. The hydraulic model was calibrated using the current stage-discharge rating at the USGS streamgage 03339500, Sugar Creek at Crawfordsville, Ind., and high-water marks from the flood of April 19, 2013, which reached a stage of 15.3 feet. The hydraulic model was then used to compute 13 water-surface profiles for flood stages at 1-foot (ft) intervals referenced to the streamgage datum ranging from 4.0 ft (the NWS “action stage”) to 16.0 ft, which is the highest stage interval of the current USGS stage-discharge rating curve and 2 ft higher than the NWS “major flood stage.” The simulated water-surface profiles were then combined with a Geographic Information System digital elevation model (derived from light detection and ranging [lidar]) data having a 0.49-ft root mean squared error and 4.9-ft horizontal resolution) to delineate the area flooded at each stage. The availability of these maps, along with Internet information regarding current stage from the USGS streamgage and forecasted high-flow stages from the NWS, will provide emergency management personnel and residents with information that is critical for flood response activities such as evacuations and road closures, as well as for post-flood recovery efforts.

Indiana↗
USGS2019

Flood-inundation maps for the Iowa River at the Meskwaki Settlement in Iowa, 2019

Digital flood-inundation maps for a 9.3-mile reach of the Iowa River along the Meskwaki Settlement, Iowa, were created by the U.S. Geological Survey (USGS) in cooperation with the Sac and Fox Tribe of the Mississippi in Iowa. The flood-inundation maps, which can be accessed through the USGS Flood Inundation Mapping Science website at https://water.usgs.gov/osw/flood_inundation/ , depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgage 05451770 on the Iowa River at County Highway E49 near Tama, Iowa. Near-real-time stages at this streamgage may be obtained on the internet from the USGS National Water Information System at https://waterdata.usgs.gov/ or the National Weather Service (NWS) Advanced Hydrologic Prediction Service at https://water.weather.gov/ahps/ , which also forecasts flood hydrographs at this site. Flood profiles were computed for the stream reach by means of a calibrated one-dimensional and two-dimensional step-backwater hydraulic model. The model was calibrated by using the current stage-discharge relation at the USGS streamgage 05451770 on the Iowa River at County Highway E49 near Tama, Iowa, and stage and discharge data from historic flooding events that were recorded at the streamgage. The hydraulic model was then used to compute eight water-surface profiles for flood stages at 1-foot intervals referenced to the streamgage datum and ranging from the NWS “action stage” of 11 feet (ft) to 18 ft, the stage exceeding the estimated 0.2-percent annual exceedance probability (500-year recurrence interval) flood, as determined at the USGS streamgage 05451770. The simulated water-surface profiles were then combined with a geographic information system digital elevation model to delineate the area flooded at each flood stage (water level). In addition, potential modifications to hydraulic structures within the flood plain were modeled so any effects from the potential modifications could be evaluated. Four comparison points, which were along the flood plain, showed little to no change (less than 0.1 ft) in flood elevation from the existing conditions within the flood plain for the 11- to 16-ft stages as referenced to the USGS streamgage 05451770. There were greater changes (more than 0.1 ft) in flood elevation for the 2 comparison points that were closest to the modified hydraulic structure for the 2 highest modeled stages of 17 and 18 ft. The availability of these maps, along with internet information regarding current stage from the USGS streamgage and forecasted high-flow stages from the NWS, will provide emergency management personnel and residents with information that is critical for flood-response activities such as evacuations and road closures, as well as for postflood recovery efforts.

Iowa↗
USGS1997

The chemical evolution and paragenesis of uranium minerals from the ruggles and palermo granitic pegmatites, New Hampshire

A study of the chemical evolution and paragenesis of the uranium minerals at the Palermo No. 1 and Ruggles granitic pegmatites, Grafton County, New Hampshire, revealed four stages of secondary mineralization. A total of eight uranium minerals were identified in the four stages. The first stage is a mixture of uranyl oxide hydroxide-hydrates represented by mineral "A", which surrounds and replaces a uraninite core. The second stage is a carbonate stage found only at the Palermo No. 1 pegmatite, and is represented by rutherfordine. The third stage is represented by uranyl silicates. At the Palermo No. 1 pegmatite, this stage consists of ??-uranophane, and at the Ruggles pegmatite, it consists of soddyite and ??-uranophane. A final fourth stage is a phosphate stage represented by phosphuranylite and meta-autunite I. The first three stages of mineralization developed from hydrothermal and meteoric processes. With dropping temperatures, hydrothermal fluids reached meteoric temperatures and acquired the characteristics of meteoric water. The pH shifted from acidic (pH less than about 6 at 100??C) to alkaline (pH > 7 at 25??C). Since mineral "A" contains hydroxyl and a low amount of molecular water, it probably formed at a temperature greater than 100??C in the acidic environment. After the first stage, the hydrothermal fluids likely reached the temperatures of meteoric water. The initial pH of the meteoric water was acidic (pH less than about 6 at 25??C) and then slowly shifted to alkaline. The mineralizing fluids became oversaturated in CO3, Ca, K, and Si. Uraninite and mineral "A" became unstable and were replaced by rutherfordine and uranyl silicates. The fourth or phosphate stage developed from the introduction of groundwater. The uranyl phosphate minerals precipitated from an acidic fluid (pH < 7 at 25??C) that was oversaturated with Ca, K, U, and P.

Canadian Mineralogist↗
USGS2021

Geology, mineralogy, and cassiterite geochronology of the Ayawilca Zn-Pb-Ag-In-Sn-Cu deposit, Pasco, Peru

The Ayawilca deposit in Pasco, Peru, represents the most significant recent base-metal discovery in the central Andes and one of the largest undeveloped In resources globally. As of 2018, it hosts an 11.7 Mt indicated resource grading 6.9% Zn, 0.16% Pb, 15 g/t Ag, and 84 g/t In, an additional 45.0 Mt inferred resource grading 5.6% Zn, 0.23% Pb, 17 g/t Ag, and 67 g/t In, and a separate Sn-Cu-Ag inferred resource of 14.5 Mt grading 0.63% Sn, 0.21% Cu, and 18 g/t Ag. Newly obtained U–Pb dates for cassiterite by LA-ICP-MS (22.77 ± 0.41 and 23.05 ± 2.06 Ma) assign the Ayawilca deposit to the Miocene polymetallic belt of central Peru. The polymetallic mineralization occurs as up to 70-m-thick mantos hosted by carbonate rocks of the Late Triassic to Early Jurassic Pucará Group, and subordinately, as steeply dipping veins hosted by rocks of the Pucará Group and overlying Cretaceous sandstones-siltstones of the Goyllarisquizga Group. Relicts of a distal retrograde magnesian skarn and cassiterite (stage pre-A) were identified in the deepest mantos. The volumetrically most important mineralization at Ayawilca comprises a low-sulfidation assemblage (stage A) with quartz, pyrrhotite, arsenopyrite, chalcopyrite, Fe-rich sphalerite, and traces of stannite and herzenbergite. Stage A sphalerite records progressive Fe depletion, from 33 to 10 mol% FeS, which is compatible with the observed transition from low- to a subsequent intermediate-sulfidation stage (B) marked by the crystallization of abundant pyrite and marcasite. Finally, during a later intermediate-sulfidation stage (C) sphalerite (up to 11 mol% FeS), galena, native bismuth, Cu-Pb-Ag sulfosalts, siderite, Mn-Fe carbonates, kaolinite, dickite, and sericite were deposited. This paragenetic evolution shows striking similarities with that at the Cerro de Pasco Cordilleran-type polymetallic deposit, even if at Ayawilca stage C did not reach high-sulfidation conditions. The occurrence of an early retrograde skarn assemblage suggests that the manto bodies at Ayawilca formed at the transition between distal skarn and skarn-free (Cordilleran-type) carbonate-replacement mineralization. Mineral assemblages define a T- f S 2 evolutionary path close to the pyrrhotite-pyrite boundary. Buffering of hydrothermal fluids by underlying Devonian carbonaceous phyllites of the Excelsior Group imposed highly reduced conditions during stage A mineralization (log f O 2 < − 30 atm). The low f O 2 favored efficient Sn mobility during stages pre-A and A, in contrast to other known ore deposits in the polymetallic belt of central Peru, in which the occurrence of Sn minerals is minor. Subsequent cooling, progressive sealing of vein walls, and decreasing buffering potential of the host rocks promoted the shift from low- (stage A) to intermediate-sulfidation (stages B and C) states. LA-ICP-MS analyses reveal significant In contents in Fe-rich sphalerite (up to 1.7 wt%), stannite (up to 1908 ppm), and chalcopyrite (up to 1185 ppm). The highest In content was found in stage A sphalerite that precipitated along with chalcopyrite and stannite, thus pointing to the early, low-sulfidation assemblage as prospective for this high-tech metal in similar mineral systems. Indium was likely incorporated into the sphalerite crystal lattice via Cu + + In 3+ ↔ 2 Zn 2+ and (Sn, Ge) 4+ + (Ga, In) 3+ + (Cu + Ag) + ↔ 4 Zn 2+ coupled substitutions. Indium incorporation mechanisms into the stannite and chalcopyrite crystal lattices remain unclear.

Pasco↗
USGS2004

Textural, compositional, and sulfur isotope variations of sulfide minerals in the Red Dog Zn-Pb-Ag deposits, Brooks Range, Alaska: Implications for Ore Formation

The Red Dog Zn-Pb deposits are hosted in organic-rich mudstone and shale of the Mississippian Kuna Formation. A complex mineralization history is defined by four sphalerite types or stages: (1) early brown sphalerite, (2) yellow-brown sphalerite, (3) red-brown sphalerite, and (4) late tan sphalerite. Stages 2 and 3 constitute the main ore-forming event and are volumetrically the most important. Sulfides in stages 1 and 2 were deposited with barite, whereas stage 3 largely replaces barite. Distinct chemical differences exist among the different stages of sphalerite. From early brown sphalerite to later yellow-brown sphalerite and red-brown sphalerite, Fe and Co content generally increase and Mn and Tl content generally decrease. Early brown sphalerite contains no more than 1.9 wt percent Fe and 63 ppm Co, with high Mn (up to 37 ppm) and Tl (126 ppm), whereas yellow-brown sphalerite and red-brown sphalerite contain high Fe (up to 7.3 wt %) and Co (up to 382 ppm), and low Mn (<27 ppm) and Tl (<37 ppm). Late tan sphalerite has distinctly lower Fe (< 0.9 wt %) and higher Tl (up to 355 ppm), Mn (up to 177 ppm), and Ge (426 ppm), relative to earlier sphalerite. Wide ranges in concentrations of Ag, Cu, Pb, and Sb characterize all sphalerite types, particularly yellow-brown sphalerite and red-brown sphalerite, and most likely reflect submicroscopic inclusions of galena, chalcopyrite and/or tetrahedrite in the sphalerite. In situ ion microprobe sulfur isotope analyses show a progression from extremely low ??34S values for stage 1 (as low as -37.20???) to much higher values for yellow-brown sphalerite (mean of 3.3???; n = 30) and red-brown sphalerite (mean of 3.4; n = 20). Late tan sphalerite is isotopically light (-16.4 to -27.2???). The textural, chem ical, and isotopic data indicate the following paragenesis: (1) deposition of early brown sphalerite with abundant barite, minor pyrite, and trace galena immediately beneath the sea floor in unconsolidated mud; (2) deposition of yellow-brown sphalerite during subsea-floor hydrothermal recrystallization and coarsening of preexisting barite; (3) open-space deposition of barite, red-brown sphalerite and other sulfides in veins and coeval replacement of barite; and (4) postore sulfide deposition, including the formation of late tan sphalerite breccias. Stage 1 mineralization took place in a low-temperature environment where fluids rich in Ba mixed with pore water or water-column sulfate to form barite, and metals combined with H2S derived from bacterial sulfate reduction to form sulfides. Higher temperatures and salinities and relatively oxidized ore-stage fluids (stages 2 and 3) compared with stage 1 were probably important controls on the abundances and relative amounts of metals in the fluids and the resulting sulfide chemistry. Textural observations and isotopic data show that preexisting barite was reductively dissolved, providing a source of H2S for sulfide mineral formation. In stage 3, the continued flow of hydrothermal fluids caused thermal alteration of organic-rich mudstones and a build-up of methane that led to fluid overpressuring, hydrofracturing, and vein formation. Barite, red-brown sphalerite, and other sulfides were deposited in the veins, and preexisting barite was pervasively replaced by red-brown sphalerite. Hydrothermal activity ceased until Jurassic time when thrusting and large-scale fluid flow related to the Brookian orogeny remobilized and formed late tan sphalerite in tectonic breccias. ?? 2004 by Economic Geology.

Economic Geology↗
USGS1990

The Ag-Mn-Pb-Zn vein, replacement, and skarn deposits of Uchucchacua, Peru; studies of structure, mineralogy, metal zoning, Sr isotopes, and fluid inclusions

Uchucchacua is an Ag-Mn-Pb-Zn vein, replacement, and skarn mineral district in the central Andes of Peru. Host rocks are massive Jumasha Formation shelf limestones of Turonian age that have been folded into an asymmetric northeast-verging anticline of Andean trend. Strata near the fold crest are cut by minor dacitic intrusions and have been displaced by a conjugate set of steep wrench faults that strike northwest-southeast and northeast-southwest. Most ore occurrences are restricted to host rocks that lie below marly limestone at the top of the middle Jumasha Formation. Vein ores located along the fracture system have formed by fissure infill and by replacement of limestone wall rocks. Larger sheetlike replacement orebodies are parallel and adjacent to a large fault. Replacement is in zones of brecciation adjacent to fault bends which were dilatent during sinistral slip of the master fracture. Such fracture belts may have been subject to paleokarst solution processes before mineralization.Four paragenetic stages have been identified. Fe, Mn, and Si were introduced at the exoskarn stage (I) as the anhydrous silicates ferroan tephroite, johannsenite, rhodonite, and bustamite. During the early main stage (II) ferroan tephroite was replaced by friedelite and magnetite under oxidizing conditions at a relatively low pH. Pb, Zn, Fe, Cu, and B were introduced; principal sulfides are pyrrhotite, Fe-rich sphalerite, Mn-rich wurtzite, alabandite, galena, chalcopyrite, and tetrahedrite. Pyrrhotite was replaced by other sulfides during later stage II. Main gangue minerals were calcite, kutnohorite, rhodochrosite, and quartz. Ag, As, and Sb were introduced during the late stage (III) in the form of sulfosalts, principally pyrargyrite. Redistribution of metals introduced at stage II resulted in the growth of Fe-poor sphalerite and alabandite accompanied by calcite gangue. Decreasing Fe contents of alabandite and sphalerite during late stage II and stage III, together with the appearance of pyrite, indicate an increase in sulfur fugacity and/or decrease in temperature over this period. The supergene stage (IV) affects the upper 30 to 150 m of most veins and involves the growth of Mn hydroxides, goethite, orpiment, marcasite, cerussite, and siderite.Distribution patterns of metal ratios and high metal values define ore bands, with a succession of antiforms and synforms. Ore-band locations are determined by vein width, itself a function of wall-rock reactivity, and fracture permeability. Metal ratio distributions in the Luz vein show symmetric dispersion of metals at right angles to the ore-band axis. Ag shows the least dispersion with progressively greater dispersion of Pb and Zn.Geologic considerations indicate mineralization at a minimum depth of 1,600 m. Most primary fluid inclusions in calcite of probable stage II origin were trapped over a temperature range of about 200 degrees to 337 degrees C (hydrostatic pressure) or about 225 degrees to 362 degrees C (lithostatic). Fluid inclusions from late stage II quartz were trapped at about 165 degrees to 205 degrees C (hydrostatic) or 190 degrees to 230 degrees C (lithostatic). Salinity ranged from 0.5 to 29.7 equiv wt percent NaCl-CaCl 2 with little relation to temperature. Calcite 87 Sr/ 86 Sr values of 0.70743 to 0.71122 extend well outside the range of values both determined for magmatic rocks of the region and estimated for the host limestones but are probably compatible with older sedimentary rocks of the mine district. Salinity levels and NaCl/CaCl 2 ratios are similar to basinal brines associated with Mississippi Valley-type deposits. It is concluded that basinal brine, expelled from the deforming Mesozoic sequence, was a significant component of the ore fluid. This fluid was probably heated by dacitic magmas or cooling dacitic intrusions; a polygenetic high-salinity magmatic-basinal fluid then rose along existing strike-slip fractures toward the mineralization site where it mixed with heated low-salinity ground water.

Uchucchacua↗