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USGS2009

Experimental alteration of artificial and natural impact melt rock from the Chesapeake Bay impact structure

The alteration or transformation of impact melt rock to clay minerals, particularly smectite, has been recognized in several impact structures (e.g., Ries, Chicxulub, Mj??lnir). We studied the experimental alteration of two natural impact melt rocks from suevite clasts that were recovered from drill cores into the Chesapeake Bay impact structure and two synthetic glasses. These experiments were conducted at hydrothermal temperature (265 ??C) in order to reproduce conditions found in meltbearing deposits in the first thousand years after deposition. The experimental results were compared to geochemical modeling (PHREEQC) of the same alteration and to original mineral assemblages in the natural melt rock samples. In the alteration experiments, clay minerals formed on the surfaces of the melt particles and as fine-grained suspended material. Authigenic expanding clay minerals (saponite and Ca-smectite) and vermiculite/chlorite (clinochlore) were identified in addition to analcime. Ferripyrophyllite was formed in three of four experiments. Comparable minerals were predicted in the PHREEQC modeling. A comparison between the phases formed in our experiments and those in the cores suggests that the natural alteration occurred under hydrothermal conditions similar to those reproduced in the experiment. ?? 2009 The Geological Society of America.

Special Paper of the Geological Society of America↗

USGS2006

Application of carbonate cyclostratigraphy and borehole geophysics to delineate porosity and preferential flow in the karst limestone of the Biscayne aquifer, SE Florida

Combined analyses of cores, borehole geophysical logs, and cyclostratigraphy produced a new conceptual hydrogeologic framework for the triple-porosity (matrix, touching-vug, and conduit porosity) karst limestone of the Biscayne aquifer in a 0.65 km 2 study area, SE Florida. Vertical lithofacies successions, which have recurrent stacking patterns, fit within high-frequency cycles. We define three ideal high-frequency cycles as: (1) upward-shallowing subtidal cycles, (2) upward-shallowing paralic cycles, and (3) aggradational subtidal cycles. Digital optical borehole images, tracers, and flow meters indicate that there is a predictable vertical pattern of porosity and permeability within the three ideal cycles, because the distribution of porosity and permeability is related to lithofacies. Stratiform zones of high permeability commonly occur just above flooding surfaces in the lower part of upward-shallowing subtidal and paralic cycles, forming preferential groundwater flow zones. Aggradational subtidal cycles are either mostly high-permeability zones or leaky, low-permeability units. In the study area, groundwater flow within stratiform high-permeability zones is through a secondary pore system of touching-vug porosity principally related to molds of burrows and pelecypods and to interburrow vugs. Movement of a dye-tracer pulse observed using a borehole fluid-temperature tool during a conservative tracer test indicates heterogeneous permeability. Advective movement of the tracer appears to be most concentrated within a thin stratiform flow zone contained within the lower part of a high-frequency cycle, indicating a distinctly high relative permeability for this zone. Borehole flow-meter measurements corroborate the relatively high permeability of the flow zone. Identification and mapping of such high-permeability flow zones is crucial to conceptualization of karst groundwater flow within a cyclostratigraphic framework. Many karst aquifers are included in cyclic platform carbonates. Clearly, a cyclostratigraphic approach that translates carbonate aquifer heterogeneity into a consistent framework of correlative units will improve simulation of karst groundwater flow. ?? 2006 Geological Society of America.

Southern Florida↗

USGS2023

Construction and modification of debris-flow alluvial fans as captured in the geomorphic and sedimentary record: Examples from the western Sangre de Cristo Mountains, south-central Colorado

Debris-flow alluvial fans are iconic features of dynamic landscapes and are hypothesized to record tectonic and climatic change. Here, we highlight their complex formation and evolution through an exemplary suite of Quaternary debris-flow alluvial fans emanating from the western range front of the Sangre de Cristo Mountains in south-central Colorado, USA. To evaluate the constructive and modifying processes that produce fan form and the associated sedimentary signatures, we applied a combined geomorphologic and sedimentologic approach using sedimentary facies analysis, soils mapping, high-resolution topographic data, and luminescence geochronology to document timing of fan construction and modification. We explored two subsets of fans in the study area: a southern set sourced from the extensively glaciated drainages of the Blanca Peak massif, and a northern set from the unglaciated drainages south of Great Sand Dunes National Park. Both sets of fans have: (1) active and successively abandoned surfaces that show evolving degradation of primary features through modification by secondary processes, (2) associated facies that display distinct characteristics representative of primary depositional and secondary modifying sedimentary processes, and (3) evidence of primary debris flow with subsequent modification by secondary processes. We found that surface geomorphology and facies assemblages in exposed alluvial-fan deposits represent sediment transport processes on both active and abandoned lobes. The link between fan surface morphologies and the sedimentary facies of their deposits provides a basis for an evolutionary process–based interpretation of debris-flow alluvial-fan geomorphology and provides a better understanding of complexities in buried paleosurfaces (intraformational progressive unconformities), surficial deformation, and landform development as recorded in debris-flow fan deposits in the sedimentary record.

Colorado↗

USGS1992

Varied records of early Wisconsinan alpine glaciation in the western United States derived from weathering-rind thicknesses

Weathering-rind thicknesses were measured on volcanic clasts in sequences of glacial deposits in seven mountain ranges in the western United States and in the Puget lowland. Because the rate of rind development decreases with time, ratios of rind thicknesses provide limits on corresponding age ratios. In all areas studied, deposits of late Wisconsinan age are obvious; deposits of late Illinoian age (ca. 140 ka) also seem to be present in each area, although independent evidence for their numerical age is circumstantial. The weathering-rind data indicate that deposits that have intermediate ages between these two are common, and ratios of rind thicknesses suggest an early Wisconsinan age (about 60 to 70 ka) for some of the intermediate deposits. Three of the seven studied alpine areas (McCall, Idaho; Yakima Valley, Washington; and Lassen Peak, California) appear to have early Wisconsinan drift beyond the extent of late Wisconsinan ice. In addition, Mount Rainier and the Puget lowland, Washington, have outwash terraces but no moraines of early Wisconsinan age. The sequences near West Yellowstone, Montana; Truckee, California; and in the southern Olympic Mountains have no recognized moraines or outwash of this age. Many of the areas have deposits that may be of middle Wisconsinan age. Differences in the relative extents of early Wisconsinan alpine glaciers are not expected from the marine oxygen-isotope record and are not explained by any simple trend in climatic variables or proximity to oceanic moisture sources. However, alpine glaciers could have responded more quickly and more variably than continental ice sheets to intense, short-lived climatic events, and they may have been influenced by local climatic or hypsometric effects. The relative sizes of early and late Wisconsinan alpine glaciers could also reflect differences between early and late Wisconsinan continental ice sheets and their regional climatic effects.

California, Colorado, Idaho, Montana, Nevada, Oreg↗

USGS2021

Freshwater cyanotoxin mixtures in recurring cyanobacterial blooms in Voyageurs National Park

Algal and cyanobacterial blooms can foul water systems, inhibit recreation, and produce cyanotoxins, which can be toxic to humans, domestic animals, and wildlife. Blooms that recur yearly present a special challenge, in that chronic effects of most cyanotoxins are unknown. To better understand cyanotoxin timing, possible environmental triggers, and inter-relations among taxa and toxins in bloom communities, recurring cyanobacterial blooms were investigated at three recreational sites in Kabetogama Lake in Voyageurs National Park from 2016-2019. Results indicated that peak neurotoxin concentrations occurred before peak microcystin concentrations and that toxin-forming cyanobacteria were present before visible blooms, which is a serious human health concern. Two cyanotoxin mixture models (MIX) and two microcystin (MC) models were developed using near-real-time environmental variables and additional comprehensive variables based on laboratory analyses. Comprehensive models explained more variability than the environmental models and neither MIX model was a better fit than the MC models. However, the MIX models produced no false negatives, indicating that all observations above human-health regulatory guidelines were simulated by the MIX models. The results show that a model based on a cyanotoxin mixture is more protective of human health than a model based on microcystin alone. In 2019, 7 of 19 toxins were detected in various mixtures. The potential toxin producing cyanobacteria, Microcystis , was significantly correlated with microcystin-YR, while Pseudanabaena sp. and Synechococcus sp. were negatively correlated to several toxins. Jaccard and Sorenson indices indicated strong same-day similarities among the three bloom communities. Nitrogen-fixing cyanobacteria were present at every site, and when combined with internal loading of phosphorus, might explain similarities among sites, and why seasonal differences, even in samples from the same site, were stronger. Information from this dissertation adds to the body of work on recurring blooms and under-studied toxins and toxin mixtures, providing a better understanding of future research options for freshwater cyanotoxins in and outside of Voyageurs National Park.

Minnesota↗

USGS2024

Use of vehicle counters to index and evaluate potential shifts in angler effort following implementation of more restrictive panfish regulations in Wisconsin lakes

Objective: Understanding angler responses to fisheries management actions such as regulation changes have important implications for the effectiveness and efficacy of such management strategies. We examined the ability of remote vehicle counters to provide a relative index of angler effort and present a case study demonstrating use of vehicle counters to assess potential changes in angler effort associated with implementation of more restrictive panfish regulations in a subset of Wisconsin lakes. Methods: We compared vehicle counts with compulsory creel and game-camera based estimates of angler hours and number of angling parties. During 2016, a series of more restrictive panfish regulations were implemented across 132 Wisconsin lakes. We deployed vehicle counters at a subset of lakes within each regulation type during pre- (2015 and 2016) and post-regulation time periods (2021 and 2022) to assess whether the distribution of angler effort (as indexed using vehicle counters) among regulation types may have shifted in response to regulation implementation. Result: At lakes with paired vehicle counters and compulsory creel data, vehicle counts explained 57-72% of variation in daily angler effort (h) and 65-85% of variation in daily number of angling parties. Across lakes with paired vehicle counters and game cameras, vehicle counters explained 77% of variation in the number of apparent angling parties; however, effectiveness of vehicle counters for explaining variation in number of apparent angling parties varied among lakes. Vehicle counters explained 63-74% of variation in number of apparent angling parties when considering paired vehicle counter-game camera observations pooled within regulation types. We did not observe any systematic shifts in effort indicative of redistribution of angler effort in response to panfish regulations. Conclusion: Results suggest that, given appropriate validation measures, vehicle counters could be used as a cost-effective tool to index angler effort, particularly when interest lies in understanding effort dynamics over large spatial scales. Our findings suggest a localized scale for implementation of specialized regulations may be appropriate given angler behaviors and preferences for Wisconsin panfish.

Wisconsin↗

USGS2002

40Ar/39Ar ages of late Cenozoic volcanic rocks within and around the Carbondale and Eagle collapse centers, Colorado: Constraints on the timing of evaporite-related collapse and incision of the Colorado River

40 Ar/ 39 Ar dating results of 133 samples from 84 late Cenozoic volcanic rocks provide emplacement ages that constrain the timing of evaporite collapse and the incision rates of the Colorado River. Our samples are from areas in west-central Colorado, both within and outside of the Carbondale and Eagle collapse centers. Significant pulses of volcanic activity occurred in the intervals from 24 to 22, 16 to 13, 11 to 9, and 8 to 7 Ma. In addition, small flows, widely spaced in time and space were emplaced during the last 4 m.y. Although individual basaltic flows appear to be chemically and isotopically homogeneous, there are significant geochemical and isotopic differences between flows, even between some flows that apparently have the same age within the limits of analytical precision. A low-relief early to middle Miocene erosional surface has been postulated in west-central Colorado. Our studies are consistent with the existence of a low-relief paleotopographic surface that is now at a minimum elevation range of ~2.9–3.4 km outside areas of collapse. Elevation departures from this range suggest that 1000 m of subsidence due to evaporite removal has locally occurred in the Carbondale and Eagle collapse centers. 40 Ar/ 39 Ar ages from downdropped and disrupted basaltic flows in the Carbondale center constrain initial collapse to >13 Ma, the timing of much of the evaporite-related collapse to the past 10–8 m.y., and an increase in the rate of collapse during the last 3 m.y. Ages and elevations of basaltic rocks above the Colorado River in Glenwood Canyon are used to calculate average apparent incision rates for the Colorado River in Glenwood Canyon of 24 mm/k.y. from 7.8 to 3.0 Ma. The average apparent incision rate increased by an order of magnitude to 242 mm/k.y. during the last 3 m.y

Colorado↗

USGS2024

Monitoring lahars

Introduction Lahars, or debris flows that originate from a volcano (Pierson and Scott, 1985; Pierson, 1995), are among the most destructive, far-reaching, and persistent hazards on stratovolcanoes. Lahars may be triggered by syneruptive rapid melting of snow and ice, lake breakouts, or heavy rains in conjunction with large eruptive columns. Alternatively, lahars can follow eruptions, when clastic deposits are mobilized by heavy rainfall or lake breakouts, occurring sporadically for years to decades after large eruptions. Some lahars can travel many tens of kilometers in river drainages stemming from volcanoes, as during the 1980 eruption of Mount St. Helens (Washington) (for example, Janda and others, 1981), recent eruptions of Redoubt Volcano (Alaska) (fig. H1; Dorava and Meyer, 1994; Waythomas and others, 2013), and the 1991 eruption of Mount Pinatubo (Philippines) (Major and others, 1996; Pierson and others, 1996). Large lahars are less likely in the absence of eruptive activity, but still possible. The Electron Mudflow at Mount Rainier (approximately A.D. 1500), Wash., is an example of a potential noneruptive lahar, likely initiated by a spontaneous collapse of weak rock, that reached the Puget Lowland after it flowed dozens of kilometers without a recognized eruptive trigger (Sisson and Vallance, 2009). The extreme hazard posed by lahars was demonstrated tragically by the 1985 Nevado del Ruiz (Colombia) catastrophe that claimed the lives of more than 20,000 people (Naranjo and others, 1986). The potential to provide warnings of minutes to hours in advance of lahar arrival in a populated area (for example, Voight, 1990) is a strong reason to provide special monitoring attention to the hazard. Populated river valleys are located downstream from many very high threat and high threat volcanoes, and these areas could be affected by lahars (for example, Hoblitt and others, 1998). The volume and mobility of lahars are two characteristics that can influence the extent of downstream effects (for example, George and others, 2022). The flows that reach the farthest downstream are mobile and voluminous. Additionally, entrainment of material as a lahar travels downstream may increase the volume, and a lahar that starts small may grow to a destructive size under certain conditions. Increasingly, stratovolcanoes host recreational enthusiasts who could be affected by relatively localized geologic hazards, such as rainfall-induced debris flows, glacial outburst floods, rockfalls, and avalanches. These types of events can be common on many volcanoes, occurring seasonally in the case of debris flows and several times per year in the case of avalanches and rockfalls (for example, Allstadt and others, 2018). Many very high threat stratovolcanoes, especially within the contiguous United States, have low eruption frequencies (less than once per century), such that monitoring networks could be used more often for detection and characterization of small surface flows than for identification of volcanic unrest. Such information can be used to validate avalanche forecasts, inform rescue efforts, or notify other agencies of potentially damaged infrastructure (for example, roads, powerlines, or trails). Note that although many of these smaller surface flows create seismic and infrasound waves, the signals are typically highly distorted by the complex volcanic topography and geology. In general, the smaller the flow, the weaker the geophysical signals that it generates, and thus a denser geophysical network is required to study smaller flows (for example, Allstadt and others, 2018). Lahar detection may not be an appropriate or necessary monitoring capability for all volcanoes. Some very high threat volcanoes, like Kīlauea and Mauna Loa, have no lahar hazards currently, and thus no detection, tracking, and characterization capabilities for lahars are needed. At other very high threat volcanoes, such as Pavlof Volcano, Alaska, lahars might be common but pose minimal threat because the volcano is so remote. Ideally, the local observatory would understand the combination of hazard and risk associated with surface flows and assign monitoring and detection capabilities appropriately. Several volcano monitoring techniques (for example, Real-Time Seismic Amplitude Measurement [RSAM], amplitude-based locations, and infrasound array processing) can be adapted to also detect, characterize, and track debris flows, lahars, and other surface flows, so instrumentation installed for detecting volcanic unrest and eruptions can have multiple purposes. The utility of instrumentation for the purpose of monitoring unrest and lahars further justifies the importance and utility of a dense network of monitoring stations, even if the volcano remains quiescent.

Scientific Investigations Report↗

USGS2021

Integrated hierarchical models to inform management of transitional habitat and the recovery of a habitat specialist

Quantifying the contribution of habitat dynamics relative to intrinsic population processes in regulating species persistence remains an ongoing challenge in ecological and applied conservation. Understanding these drivers and their relationship is essential for managing habitat‐dependent species, especially those that specialize in transitional habitats. Limitations in the ability of natural disturbance to mediate transitional habitat dynamics have resulted in a decline in early‐ and mid‐successional vegetation structure and prompted the need for aggressive habitat management to replace natural perturbations and increase habitat structural complexity. We describe a collaborative effort with a group of independent land managers to design an adaptive management program for restoring an imperiled ecosystem and recovering declining populations of an endemic habitat specialist. We developed a set of integrated, hierarchical models to estimate management‐mediated transition rates among vegetation classes in two dominant scrub communities and the species response (local colonization and extinction probabilities) as a function of habitat state. Models were fit using a long‐term data set of habitat and occupancy observations from 361 Florida scrub‐jay territories across two Florida counties. Occupancy model results correspond closely to previous approaches of estimating differential survival and reproductive success associated with habitat conditions, with highest colonization and lowest extinction rates estimated for those habitat states found to have the highest rates of survival and reproduction. In addition to offering an innovative approach for jointly modeling habitat and species population dynamics, the program we describe will also be of interest from a management perspective by providing guidance for developing collaborative, adaptive management frameworks from the ground up. We engaged land managers via workshops to specify objectives and desired state‐variable conditions, identify management alternatives, and elicit consensus opinions on model parameters. Treating expert opinions as pseudo‐observations to define Dirichlet priors allowed us to make use of existing management knowledge. Formal learning was then accumulated by updating transition probability estimates as management activities were implemented over the study period. We believe this adaptive management framework provides a useful approach for increasing our understanding of complex ecological relationships and hope that it will be adopted by others who have interest in informing management and conservation efforts.

Florida↗

USGS2008

Scientific results from Gulf of Mexico Gas Hydrates Joint Industry Project Leg 1 drilling: Introduction and overview

The Gulf of Mexico Gas Hydrates Joint Industry Project (JIP) is a consortium of production and service companies and some government agencies formed to address the challenges that gas hydrates pose for deepwater exploration and production. In partnership with the U.S. Department of Energy and with scientific assistance from the U.S. Geological Survey and academic partners, the JIP has focused on studies to assess hazards associated with drilling the fine-grained, hydrate-bearing sediments that dominate much of the shallow subseafloor in the deepwater (>500 m) Gulf of Mexico. In preparation for an initial drilling, logging, and coring program, the JIP sponsored a multi-year research effort that included: (a) the development of borehole stability models for hydrate-bearing sediments; (b) exhaustive laboratory measurements of the physical properties of hydrate-bearing sediments; (c) refinement of new techniques for processing industry-standard 3-D seismic data to constrain gas hydrate saturations; and (d) construction of instrumentation to measure the physical properties of sediment cores that had never been removed from in situ hydrostatic pressure conditions. Following review of potential drilling sites, the JIP launched a 35-day expedition in Spring 2005 to acquire well logs and sediment cores at sites in Atwater Valley lease blocks 13/14 and Keathley Canyon lease block 151 in the northern Gulf of Mexico minibasin province. The Keathley Canyon site has a bottom simulating reflection at ???392 m below the seafloor, while the Atwater Valley location is characterized by seafloor mounds with an underlying upwarped seismic reflection consistent with upward fluid migration and possible shoaling of the base of the gas hydrate stability (BGHS). No gas hydrate was recovered at the drill sites, but logging data, and to some extent cores, suggest the occurrence of gas hydrate in inferred coarser-grained beds and fractures, particularly between 220 and 330 m below the seafloor at the Keathley Canyon site. This paper provides an overview of the results of the initial phases of the JIP work and introduces the 15 papers that make up this special volume on the scientific results related to the 2005 logging and drilling expedition.

Marine and Petroleum Geology↗

USGS2002

Palynology and palynostratigraphy of the Hell Creek Formation in North Dakota: A microfossil record of plants at the end of Cretaceous time

The Hell Creek Formation of North Dakota preserves a rich and varied palynoflora including pollen, spores, and algal cysts; this palynoflora provides insight into the nature of plant life in the region in late Maastrichtian time. This palynological record supplements extensive data from the same ancient vegetation preserved in the megafloral record, and it provides background biostratigraphic data necessary to determine the nature of the Cretaceous-Tertiary (K-T) boundary event. This study of the Hell Creek palynoflora is based upon occurrences of palynomorphs in 71 samples from 20 measured sections in Bowman and Slope Counties, southwestern North Dakota . The palynoflora documented includes 115 or more palynomorph species, 98 of which are described. Three new genera are proposed, three new species are described, and five new nomenclatural combinations are made. The new taxa are Palaeoisoetes gen. nov., Styxpollenites gen. nov., Tschudypollis gen. nov., Aquilapollenites marmarthensis sp. nov., Osmundacidites stanleyi sp. nov., Styxpollenites calamitas sp. nov., Polyatriopollenites levis (Stanley 1965) comb. nov., Palaeoisoetes subengelmannii (Elsik 1968) comb. nov., Triporopollenites triplicatus (Anderson 1960) comb. nov., Tschudypollis retusus (Anderson 1960) comb. nov., and Tschudypollis thalmannii (Anderson 1960) comb. nov. The palynofloral taxa include 67 angiosperms, eight gymnosperms, 19 pteridophytes, and three bryophytes. Of these, 33 are regarded as characteristically uppermost Cretaceous taxa (K taxa). A few of the K taxa do not range all the way to the K-T boundary. Extinction of the Hell Creek palynoflora at the K-T boundary is ∼30%. The Hell Creek Formation is within theWodehouseia spinata Assemblage Zone.

North Dakota↗

USGS1983

Electrical and magnetic properties of rock and soil

Field and laboratory measurements have been made to determine the electrical conductivity, dielectric constant, and magnetic permeability of rock and soil in areas of interest in studies of electromagnetic pulse propagation. Conductivity is determined by making field measurements of apparent resisitivity at very low frequencies (0-20 cps), and interpreting the true resistivity of layers at various depths by curve-matching methods. Interpreted resistivity values are converted to corresponding conductivity values which are assumed to be applicable at 10^2 cps, an assumption which is considered valid because the conductivity of rock and soil is nearly constant at frequencies below 10^2 cps. Conductivity is estimated at higher frequencies (up to 10^6 cps) by using statistical correlations of three parameters obtained from laboratory measurements of rock and soil samples: conductivity at 10^2 cps, frequency and conductivity measured over the range 10^2 to 10^6 cps. Conductivity may also be estimated in this frequency range by using field measurements of water content and correlations of laboratory sample measurements of the three parameters: water content, frequency, and conductivity measured over the range 10^2 to 10^6 cps. This method is less accurate because nonrandom variation of ion concentration in natural pore water introduces error. Dielectric constant is estimated in a similar manner from field-derived conductivity values applicable at 10^2 cps and statistical correlations of three parameters obtained from laboratory measurements of samples: conductivity measured at 10^2 cps, frequency, and dielectric constant measured over the frequency range 10^2 to 10^6 cps. Dielectric constant may also be estimated from field measurements of water content and correlations of laboratory sample measurements of the three parameters: water content, frequency, and dielectric constant measured from 10^2 to 10^6 cps, but again, this method is less accurate because of variation of ion concentration of pore water. Special laboratory procedures are used to measure conductivity and dielectric constant of rock and soil samples. Electrode polarization errors are minimized by using an electrode system that is electrochemically reversible-with ions in pore water.

Open-File Report↗

USGS1953

The use of soils and paleosols for interpreting geomorphic and climatic history of arid regions

The study of modern surface soils, and ancient weathering zones, which occur either buried or as surface relicts, has contributed materially to understanding the complex events of the glacial and post-glacial period both in glaciated areas and in regions not influenced by glaciation. Most work of this kind in the United States has been done by geologists. Numerous Pleistocene geologists have noted weathered zones between sheets of glacial drift or loess in the middle western United States. These include Condra, et al 5 ; Frye 7 ; Frye and Leonard 8 ; Kay and Pearce 13 ; Leighton and MacClintock 15 ; Leverett 16 , 17 , 18 ; Lugn 19 ; Peltier 23 ; Schultz and Stout 26 ; Schultz, et al 27 ; and Simonson 28 . Kay and Pearce 13 interpreted the weathered zones between sheets of glacial drift as profiles of ancient soils which they referred to as gumbotil. Hseung, Marshall and Krusekopf 10 have recently questioned the pedogenic character of gumbotil, but have failed to offer a satisfactory alternative explanation. Thorp, and coworkers 30 , in a general review of buried soils, apparently consider gumbotil a product of ancient soil-forming processes.

Research Council of Israel Special Publication↗

USGS1996

Late Pennsylvanian climate changes and palynomorph extinctions

A major floral change occurs in the Upper Pennsylvanian strata in the Midcontinent, Illinois basin, and in the northern Appalachian basin of eastern United States. Lycospora spp. (derived from arborescent lycopsids) became extinct along with some other palynomorph taxa. This investigation is concerned with the importance of this major floral change. Samples were studied from western Pennsylvania, eastern Ohio, and West Virginia (from a previous study) cover the stratigraphic interval from the Upper Freeport coal bed, uppermost part of the Allegheny Formation, to the Mahoning, Mason, Brush Creek, Wilgus, and Anderson coal beds in the lower part of the Conemaugh Formation. The floral change occurs either at or below the accepted Desmoinesian-Missourian boundary in the Midcontinent and Illinois basin, whereas in the northern Appalachians this change occurs in the lower part of the Conemaugh Formation, between the Mahoning and Brush Creek coal beds, or when the Mason is present, between the Mahoning and Mason coal beds. With the advent of late Middle Pennsylvanian time, the climate began to change from wet tropical to seasonal tropical. The Middle-Upper Pennsylvanian boundary is the culmination of this drying trend, which was marked by reduction of available water. The peat swamps are interpreted as having changed from the domed type of bog to the planar type under these circumstances. Thus, in general, the coals of the Conemaugh Formation are characteristically much thinner than those of the Allegheny Formation. This was caused by a number of factors including reduced or more seasonal rainfall, decline of arborescent lycopsids, and the increased dominance of herbaceous and fern plants. As a result, there are fewer minable coal beds in the Conemaugh Formation. The first coal bed above the extinction of Lycospora spp. is dominated by the palynomorph taxon Endosporites globiformis which is derived from a heterosporous, herbaceous lycopsid. However, Sigillaria, another arborescent lycopsid, did not become extinct at this time as evidenced by the presence of the palynomorph genus Crassispora which is derived from Sigillaria. The reason for the survival of Sigillaria is not known, but it may have been able to adapt, in a limited fashion, to some sort of specialized microenvironment. The ferns, based on palynomorph occurrence, become numerically more important throughout the balance of the Conemaugh Formation, and dominate the Pittsburgh No. 8 and Pomeroy coal beds in the overlying Monogahela Formation.

Review of Palaeobotany and Palynology↗

USGS2009

Microbial abundance in the deep subsurface of the Chesapeake Bay impact crater: Relationship to lithology and impact processes

Asteroid and comet impact events are known to cause profound disruption to surface ecosystems. The aseptic collection of samples throughout a 1.76-km-deep set of cores recovered from the deep subsurface of the Chesapeake Bay impact structure has allowed the study of the subsurface biosphere in a region disrupted by an impactor. Microbiological enumerations suggest the presence of three major microbiological zones. The upper zone (127–867 m) is characterized by a logarithmic decline in microbial abundance from the surface through the postimpact section of Miocene to Upper Eocene marine sediments and across the transition into the upper layers of the impact tsunami resurge sediments and sediment megablocks. In the middle zone (867–1397 m) microbial abundances are below detection. This zone is predominantly quartz sand, primarily composed of boulders and blocks, and it may have been mostly sterilized by the thermal pulse delivered during impact. No samples were collected from the large granite block (1096–1371 m). The lowest zone (below 1397 m) of increasing microbial abundance coincides with a region of heavily impact-fractured, hydraulically conductive suevite and fractured schist. These zones correspond to lithologies influenced by impact processes. Our results yield insights into the influence of impacts on the deep subsurface biosphere.

Virginia↗

USGS2000

Isotopic studies of authigenic sulfides, silicates and carbonates, and calcite and pyrite veinlets in the Creede Formation, San Juan Mountains, Southwest Colorado

Sulfur isotope analysis of authigenic pyrite in the Creede Formation documents its precipitation by the reaction between iron in the volcaniclastic sediments and H 2 S formed through bacteriogenic reduction of sulfate added to the lake during and immediately following repeated volcanic eruptions during sedimentation. Pyrite veinlets in the underlying Snowshoe Mountain Tuff were formed by the percolation of H 2 S-bearing pore waters into fractures in the tuff. Conventional analyses of bulk samples of authigenic pyrite range from -20.4% to 34.5% essentially equivalent to the range of -30% to 40% determined using SHRIMP microprobe techniques. Conventional analyses of bulk samples of pyrite from veinlets in the Snowshow Mountain Tiff range from -3.5% to 17.6% much more limited than the ranges of -23% to 111% and -15.6% to 67.0% determined by SHRIMP and laser ablation microbeam techniques, respectively. The extreme range of δ 34 S for the veinlets is interpreted to be the result of continued fractionation of the already 34 S-depleted pore water. Oxygen isotope analysis of authigenic smectite, kaolinite, and K-feldspar together with fluid-inclusion temperatures and oxygen isotope analysis of calcite coexisting with kaolinite indicate that the smectites formed early during burial diagenesis, in accord with petrographic observations. The 40 Ar/ 39 Ar dating of K-feldspar, concorfance of K-feldspar, kaolinite, and calcite δ 18 O values, and fluid-inclusion temperatures in calcite, indicate that the sediments at core hole CCM-1 were subjected to a hydrothermal event at 17.6 Ma. The minerals formed oxygen-shifted meteoric waters with δ 18 O values of ~-9% Smecities at CCM-1 at least partially exchanged with these waters. Carbon and oxygen isotope analysis of authigenic calcites in the Creede Formation show that they formed over a wide range of temperatures from fluids having a wide range of isotopic composition, presumably over an extended period time. Some of the cements apparently formed very late from unexchanged meteoric water. Concretions and possibly some cements at CCM-1 appear to have exchanged with the 17.6 Ma oxygen-shifted hydrothermal fluids. Such exchange is consistent with evidence that lacustrine carbonates at CCM-1 exchanged with low 18 O waters, whereas those at CCM-2 underwent little, if any, exchange. The δ 13 C-δ 18 O values for calcite veinlets in the Creede Formation are similar to those for authegenic calcites. Fluid-inclusion temperatures and δ 18 O indicate that some were deposited during the 17.6 Ma hydrothermal event and others from unexchanged meteoric water at a later date. The isotope studies confirm that part of the model of Rye et al., proposing that the barites in the southern end of the Creede Mining District were formed by mixing of the Creede hydrotermal system with Lake Creede pore of lake waters. The silicate and carbonate isotope data indicate that the pores of the Creede Formation were occupied by at least three isotopically distinct water since the time of deposition. The original pore fluids were probably shifted to lower δ 18 O values during burial diagensis as a result of the hydrolysis of the volcanic glass to for smectites and other hydrous silicates. During or prior to a 17.6 Ma hydrothermal event in the vicinity of CCM-1, the Creede Formation was flushed with oxygen-shifted meteoric water, possibly related to the breaching of the east side of the caldera wall sometime between 20 and 22 Ma. Later, the Creede Formation was again flushed, this time with unexchanged meteoric water with δD-δ 18 O values of present-day waters, possibly during the incision of the Rio Grande drainage during uplifting of the southern Rocky Mountains beginning about 5 Ma.

GSA Special Papers↗

USGS1987

Improving atlas methodology

We are studying a sample of Maryland (2 %) and New Hampshire (4 %) Atlas blocks and a small sample in Maine. These three States used different sampling methods and block sizes. We compare sampling techniques, roadside with off-road coverage, our coverage with that of the volunteers, and different methods of quantifying Atlas results. The 7 1/2' (12-km) blocks used in the Maine Atlas are satisfactory for coarse mapping, but are too large to enable changes to be detected in the future. Most states are subdividing the standard 7 1/2' maps into six 5-km blocks. The random 1/6 sample of 5-km blocks used in New Hampshire, Vermont (published 1985), and many other states has the advantage of permitting detection of some changes in the future, but the disadvantage of leaving important habitats unsampled. The Maryland system of atlasing all 1,200 5-km blocks and covering one out of each six by quarterblocks (2 1/2-km) is far superior if enough observers can be found. A good compromise, not yet attempted, would be to Atlas a 1/6 random sample of 5-km blocks and also one other carefully selected (non-random) block on the same 7 1/2' map--the block that would include the best sample of habitats or elevations not in the random block. In our sample the second block raised the percentage of birds found from 86% of the birds recorded in the 7 1/2' quadrangle to 93%. It was helpful to list the expected species in each block and to revise this list annually. We estimate that 90-100 species could be found with intensive effort in most Maryland blocks; perhaps 95-105 in New Hampshire. It was also helpful to know which species were under-sampled so we could make a special effort to search for these. A total of 75 species per block (or 75% of the expected species in blocks with very restricted habitat diversity) is considered a practical and adequate goal in these States. When fewer than 60 species are found per block, a high proportion of the rarer species are missed, as well as some of the common ones. Similarity indices based on fewer than 60 species per block reflect coverage rather than habitat affinities. Atlas blocks that are ecologically similar should have similarity indices (S) of at least 0.80 to be considered adequately covered. S = 2C/(A + B), where C is the number of species in common and A and B are species totals for each of the two blocks being compared. A series of 15 13-minutes roadside stops yielded more species than 15 off-road stops, but off-road stops always had some species not detected at the roadside stops. A series of timed stops is an excellent way to map relative abundance if the stops are standardized with respect to time of day and weather, and the counts are made by observers of comparable ability. Efforts to estimate Atlas block populations in powers of 10 (as in the French Atlas) have not gained acceptance in U.S.A. Most observers feel unqualified to make estimates. An efficient way to Atlas a block is to make at least 3 early morning visits to 15 or more specific stops. Arrive in the block early enough to check for nocturnal species on at least two days; and after completing the specific stops, search the block for other species and for confirmations.

Acta Oecologica Oecologia Generalis↗

USGS1986

The non-transferability of a Cretaceous coal model in the San Juan Basin of New Mexico and Colorado

The San Juan Basin of northwest New Mexico and southwest Colorado contains several Upper Cretaceous coal-bearing formations. The coals in these formations were deposited in environments associated with repeated transgressions and regressions of the Western Interior seaway in Late Cretaceous time. A detailed subsurface and surface study of the coal beds in one of these units, the Fruitland Formation, formed the basis for a coal-depositional model (Fassett and Hinds, 1971). This model basically shows that the thickest Fruitland coals formed landward of thickly stacked sandstone beds of the regressive-marine Pictured Cliffs Sandstone. Transferability of the Fruitland coal model was tested by comparing it to another San Juan Basin coal-bearing rock unit, the lower Menefee Formation. Lower Menefee coal deposits were formed in association with the Point Lookout Sandstone, an older regressive-marine unit. The purpose of this comparison was to see if thick lower Menefee coal beds were also concentrated adjacent to thick vertical shoreface-sandstone buildups. This comparison showed that even though thick sandstone buildups were found in the Point Lookout, no thick coal beds were found in the lower Menefee Formation adjacent to them. This test suggests that certain coal depositional models may have limited value as predictive tools and must be used with caution by coal explorationists. Even more importantly, potential coal-bearing areas should never be written off simply because they do not fit a previously described model.

Colorado, New Mexico↗