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At least 883 records · Page 49Linked to original sources

USGS2013

Using simulated maps to interpret the geochemistry, formation and quality of the Blue Gem Coal Bed, Kentucky, USA

This study presents geostatistical simulations of coal-quality parameters, major oxides and trace metals for an area covering roughly 812 km 2 of the Blue Gem coal bed in southeastern Kentucky, USA. The Blue Gem, characterized by low ash yield and low sulfur content, is an important economic resource. Past studies have characterized the Blue Gem's geochemistry, palynology and petrography and inferred a depositional setting of a planar peat deposit that transitioned to slightly domed later in its development. These studies have focused primarily on vertical geochemical trends within the coal bed. Simulated maps of chemical elements derived from 45 measured sample locations across the study area provide an opportunity to observe changes in the horizontal direction within the coal bed. As the Blue Gem coal bed shows significant vertical chemical trends, care was taken in this study to try to select samples from a single, middle portion of the coal. By revealing spatial distribution patterns of elements across the middle of the bed, associations between different components of the coal can be seen. The maps therefore help to provide a picture of the coal-forming peat bog at an instant in geologic time and allow interpretation of a depositional setting in the horizontal direction. Results from this middle portion of the coal suggest an association of SiO 2 with both K 2 O and TiO 2 in different parts of the study area. Further, a pocket in the southeast of the study area shows elevated concentrations of elements attributable to observed carbonate-phase minerals (MgO, CaO, Ba and Sr) as well as elements commonly associated with sulfide-phase minerals (Cu, Mo and Ni). Areas of relatively high ash yield are observed in the north and south of the mapped area, in contrast to the low ash yields seen towards the east. Additionally, we present joint probability maps where multiple coal-quality parameters are plotted simultaneously on one figure. This application allows researchers to investigate associations of more than two components in a straight-forward manner useful in guiding resource exploration.

Kentucky↗

USGS1973

Effects of temperature on embryonic development of lake herring ( Coregonus artedii )

Embryonic development of lake herring ( Coregonus artedii ) was observed in the laboratory at 13 constant temperatures from 0.0 to 12.1 C and in Pickerel Lake (Washtenaw County, Michigan) at natural temperature regimes. Rate of development during incubation was based on progression of the embryos through 20 identifiable stages. An equation was derived to predict development stage at constant temperatures, on the general assumption that development stage (DS) is a function of time (days, D) and temperature (T). The equation should also be useful in interpreting estimates from future regressions that include other environmental variables that affect egg development. A second regression model, derived primarily for fluctuating temperatures, related development rate for stage j (DR j ), expressed as the reciprocal of time, to temperature (x). The generalized equation for a development stage is: DR j = ab x c x 2 d x 3 . In general, time required for embryos to reach each stage of development in Pickerel Lake agreed closely with the time predicted from this equation, derived from our laboratory observations. Hatching time was predicted within 1 day in 1969 and within 2 days in 1970. We used the equations derived with the second model to predict the effect of the superimposition of temperature increases of 1 and 2 C on the measured temperatures in Pickerel Lake. Conceivably, hatching dates could be affected sufficiently to jeopardize the first feeding of lake herring through loss of harmony between hatching date and seasonal food availability.

Michigan↗

USGS2011

Syn-extensional plutonism and peak metamorphism in the albion-raft river-grouse creek metamorphic core complex

The Cassia plutonic complex (CPC) is a group of variably deformed, Oligocene granitic plutons exposed in the lower plate of the Albion-Raft River- Grouse Creek (ARG) metamorphic core complex of Idaho and Utah. The plutons range from granodiorite to garnet-bearing, leucogranite, and during intrusion, sillimanite- grade peak metamorphism and ductile attenuation occurred in the country rocks and normal-sense, amphibolite-grade deformation took place along the Middle Mountain shear zone. U-Pb zircon geochronology from three variably deformed plutons exposed in the lower plate of the ARG metamorphic core complex revealed that each zircon is comprised of inherited cores (dominantly late Archean) and Oligocene igneous overgrowths. Within each pluton, a spread of concordant ages from the Oligocene zircon overgrowths is interpreted as zircon recycling within a long-lived magmatic system. The plutons of the CPC have very low negative whole rock ??Nd values of -26 to -35, and initial Sr values of 0.714 to 0.718, consistent with an ancient, crustal source. Oxygen isotope ratios of the Oligocene zircon overgrowths from the CPC have an average ??18O value of 5.40 ?? 0.63 permil (2SD, n = 65) with a slight trend towards higher ??18O values through time. The ??18O values of the inherited cores of the zircons are more variable at 5.93 ?? 1.51 permil (2SD, n = 29). Therefore, we interpret the plutons of the CPC as derived, at least in part, from melting Archean crust based on the isotope geochemistry. In situ partial melting of the exposed Archean basement that was intruded by the Oligocene plutons of the CPC is excluded as the source for the CPC based on field relationships, age and geochemistry. Correlations between Ti and Hf concentrations in zircons from the CPC suggest that the magmatic system may have become hotter (higher Ti concentration in zircon) and less evolved (lower Hf in zircon concentration) through time. Therefore, the CPC represents prolonged or episodic magmatism system (32-25 Ma), and the intrusions were each accompanied by sillimanite-grade deformation and extension. The Oligocene magmatism and peak metamorphism preserved in the ARG metamorphic core complex are likely related to regional trends in mantle-derived magmatism that led to protracted heating, melting and mobilization of the deeper crust.

American Journal of Science↗

USGS2001

Geological characterization of remote field sites using visible and infrared spectroscopy: Results from the 1999 Marsokhod field test

Upcoming Mars Surveyor lander missions will include extensive spectroscopic capabilities designed to improve interpretations of the mineralogy and geology of landing sites on Mars. The 1999 Marsokhod Field Experiment (MFE) was a Mars rover simulation designed in part to investigate the utility of visible/near-infrared and thermal infrared field spectrometers to contribute to the remote geological exploration of a Mars analog field site in the California Mojave Desert. The experiment simultaneously investigated the abilities of an off-site science team to effectively analyze and acquire useful imaging and spectroscopic data and to communicate efficiently with rover engineers and an on-site field team to provide meaningful input to rover operations and traverse planning. Experiences gained during the MFE regarding effective communication between different mission operation teams will be useful to upcoming Mars mission teams. Field spectra acquired during the MFE mission exhibited features interpreted at the time as indicative of carbonates (both dolomitic and calcitic), mafic rocks and associated weathering products, and silicic rocks with desert varnish-like coatings. The visible/near-infrared spectra also suggested the presence of organic compounds, including chlorophyll in one rock. Postmission laboratory petrologic and spectral analyses of returned samples confirmed that all rocks identified as carbonates using field measurements alone were calc-silicates and that chlorophyll associated with endolithic organisms was present in the one rock for which it was predicted. Rocks classified from field spectra as silicics and weathered mafics were recognized in the laboratory as metamorphosed monzonites and diorite schists. This discrepancy was likely due to rock coatings sampled by the field spectrometers compared to fresh rock interiors analyzed petrographically, in addition to somewhat different surfaces analyzed by laboratory thermal spectroscopy compared to field spectra.

California↗

USGS2022

Sedimentological and geochemical perspectives on a marginal lake environment recorded in the Hartmann’s Valley and Karasburg members of the Murray formation, Gale crater, Mars

This study utilizes instruments from the Curiosity rover payload to develop an integrated paleoenvironmental and compositional reconstruction for the 65-m thick interval of stratigraphy comprising the Hartmann's Valley and Karasburg members of the Murray formation, Gale crater, Mars. The stratigraphy consists of cross-stratified sandstone (Facies 1), planar-laminated sandstone (Facies 2), and planar-laminated mudstone (Facies 3). Facies 1 is composed of sandstone showing truncated sets of concave-curvilinear laminae stacked into cosets. Sets are estimated to be meter-to sub-meter-scale, consistent with low-height dunes. Thin stratigraphic intervals of Facies 1 and stacking patterns with Facies 2 and 3 support a wet aeolian dune interpretation. Meter-thick packages of planar-laminated sandstone (Facies 2) are interpreted to represent interfingering dune-interdune strata. Facies 3 consists of meter-thick packages of planar-laminated mudstone interpreted to represent lacustrine deposition with persistent standing water. Integration of geochemistry with each facies reveals some compositional control based on the depositional process. Models for source rock composition from Alpha Particle X-Ray Spectrometer measurements show that facies derived from a basaltic source. Alteration indices and geochemical trends provide evidence that moderate chemical weathering occurred before compositional changes due to diagenesis. Differences in wt% FeO (T) and TiO 2 between facies are minimal, though trends point to sediment sorting in transport. Comparisons to terrestrial basaltic sedimentary systems indicate that the Hartmann's Valley and Karasburg facies reflect deposition in an environment where diverse subaqueous and subaerial facies persisted adjacent to a long-lived body of water.

Journal of Geophysical Research Planets↗

USGS2012

Morphology and growth history of Delgada Fan: Implications for the Neogene evolution of Point Arena Basin and the Mendocino Triple Junction

Long-range side scan (GLORIA) sonographs and seismic reflection data acquired during a survey of the western U.S. Exclusive Economic Zone in 1984, coupled with information from Deep Sea Drilling Project sites, provide new insights into the growth and evolution of the Delgada Fan. Construction of the fan commenced in the latest Miocene (∼6 Ma) following the filling of the Neogene Point Arena Basin. The fan presently covers more than 50×10 3 km 2 of the Pacific plate and contains approximately 15×10 3 km 3 of predominantly terrigenous detritus. The large size of the fan is incompatible with the small present-day supply of sediment to the canyon system. The GLORIA data show the Delgada Fan to be a hybrid-type fan, exhibiting characteristics of both elongate and radial fans. The morphology and volume of the fan, along with evidence for a decline in accumulation rates on the lower fan during the Quaternary period, suggest that the fan experienced an early growth phase (latest Miocene and Pliocene) characterized by relatively rapid progradation of elongate fan lobes followed by a period (Quaternary) of slower growth that has featured a shift of depocenters to sites closer to the canyons and a transition to distributary channels bordered by less prominent levees and overbank deposits. We examine the growth of Delgada Fan in relation to the Neogene evolution of the North American-Pacific plate boundary using a series of paleogeographic reconstructions based on recently published time displacement histories of the Mendocino triple junction (MTJ), the San Andreas fault (SAF), and the Pacific plate, upon which the fan rests. The time displacement curves for the SAF and the MTJ suggest that the MTJ and Mendocino Fracture Zone overtook and passed Point Arena Basin at about 10 Ma when the basin lay immediately southwest of the present San Francisco Bay area. We suggest that the MTJ joined the SAF at approximately that time and location, thus making the SAF the master fault in the transform system. This interpretation is compatible with evidence from seismic reflection profiles over the fan, which demonstrate that the fan and the canyon system and therefore Point Arena Basin have moved as a unit since the inception of fan growth (∼6–7 Ma). Point Arena Basin lay southwest of the San Francisco area at 10–12 Ma, and the passage of the MTJ caused the disruption of the forearc shelf and slope and the development of local uplifted and subsiding blocks. In particular, uplift of the “bay block” immediately east of the SAF may have provided the source area for the late Miocene sediments that filled Point Arena Basin and set the stage for the growth of Delgada Canyon and Fan system. The growth rate of the fan has decreased, and the style of deposition has changed as the system was tectonically transported to its present location adjacent to the small youthful drainages of the King Range.

Journal of Geophysical Research Solid Earth↗

USGS2023

Progradational-to-retrogradational styles of Palaeogene fluvial fan successions in the San Juan Basin, New Mexico

Basin-scale outcrop analyses of fluvial architecture in the Palaeogene San Juan Basin, New Mexico, document lateral and vertical trends in channel, floodplain and palaeosol characteristics. Herein, the uppermost part of the Palaeocene Nacimiento Formation and lower Eocene Cuba Mesa and Regina Members of the San Jose Formation are identified as deposits of large fluvial fans based on trends observed across the basin. Stratigraphic trends suggest two packages originated by fluvial fan progradation. Progradation of the lower fan system provides a new explanation for the transitional nature of a disconformity at the Nacimiento–San Jose Formation contact, previously thought to be a low-angle unconformity. The two fan systems are separated by a retrogradational interval that culminates in a depositional hiatus at the contact between the Cuba Mesa and Regina Members. This, combined with poor age constraints, indicates that the duration of the disconformity at the base of the Cuba Mesa Member may have been overestimated. Furthermore, the succession is interpreted as deposits of variable-discharge rivers, based on the combined abundance of upper flow regime and high deposition rate sedimentary structures indicative of intense flooding events, preservation of in-channel bioturbation and paedogenic modification indicating periods of prolonged dryness, lack of identifiable bar strata and alternations of poorly drained and well-drained floodplain deposits with pedofacies indicating alternating wet–dry cycles. This dataset adds to a growing body of evidence linking the formation of large fluvial fans to discharge variability and thus to hydroclimates with significant inter- and intra-annual precipitation variability and intense rainfall. A long-term stratigraphic shift from poorly drained to well-drained floodplain deposits across two progradational fan successions indicates that a predictive model suggesting downstream decreases in soil drainage conditions is not encompassing of all large fan systems, and instead suggests a transition to a more arid climate across the Palaeocene–Eocene boundary.

New Mexico↗

USGS2014

Identifying the pollen of an extinct spruce species in the Late Quaternary sediments of the Tunica Hills region, south-eastern United States

Late Quaternary fluvial deposits in the Tunica Hills region of Louisiana and Mississippi are rich in spruce macrofossils of the extinct species Picea critchfieldii , the one recognized plant extinction of the Late Quaternary. However, the morphology of P. critchfieldii pollen is unknown, presenting a barrier to the interpretation of pollen spectra from the last glacial of North America. To address this issue, we undertook a morphometric study of Picea pollen from Tunica Hills. Morphometric data, together with qualitative observations of pollen morphology using Apotome fluorescence microscopy, indicate that Picea pollen from Tunica Hills is morphologically distinct from the pollen of P. glauca , P. mariana and P. rubens . Measurements of grain length, corpus width and corpus height indicate that Picea pollen from Tunica Hills is larger than the pollen of P. mariana and P. rubens , and is slightly larger than P. glauca pollen. We argue that the morphologically distinctive Tunica Hills Picea pollen was probably produced by the extinct spruce species P. critchfieldii . These morphological differences could be used to identify P. critchfieldii in existing and newly collected pollen records, which would refine its paleoecologic and biogeographic history and clarify the nature and timing of its extinction in the Late Quaternary.

Louisiana, Mississippi↗

USGS2003

Fluid flow in the resurgent dome of Long Valley Caldera: Implications from thermal data and deep electrical sounding

Temperatures of 100??C are measured at 3 km depth in a well located on the resurgent dome in the center of Long Valley Caldera, California, despite an assumed >800??C magma chamber at 6-8 km depth. Local downflow of cold meteoric water as a process for cooling the resurgent dome is ruled out by a Pecle??t-number analysis of temperature logs. These analyses reveal zones with fluid circulation at the upper and lower boundaries of the Bishop Tuff, and an upflow zone in the metasedimentary rocks. Vertical Darcy velocities range from 10 to 70 cm a-1. A 21-km-long geoelectrical profile across the caldera provides resistivity values to the order of 100 to >103 ??m down to a depth of 6 km, as well as variations of self-potential. Interpretation of the electrical data with respect to hydrothermal fluid movement confirms that there is no downflow beneath the resurgent dome. To explain the unexpectedly low temperatures in the resurgent dome, we challenge the common view that the caldera as a whole is a regime of high temperatures and the resurgent dome is a local cold anomaly. Instead, we suggest that the caldera was cooled to normal thermal conditions by vigorous hydrothermal activity in the past, and that a present-day hot water flow system is responsible for local hot anomalies, such as Hot Creek and the area of the Casa Diablo geothermal power plant. The source of hot water has been associated with recent shallow intrusions into the West Moat. The focus of planning for future power plants should be to locate this present-day flow system instead of relying on heat from the old magma chamber. ?? 2003 Elsevier B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗

USGS1997

14 C ages and activity for the past 50 ka at Volcán Galeras, Colombia

Volcán Galeras is the southernmost Colombian volcano with well-recorded historic activity. The volcano is part of a large and complex volcanic center upon which 400,000 people live. Historic activity has centered on a small-volume cone inside the youngest of several large amphitheaters that breach the west flank of the volcano, away from the city of Pasto (population 300,000). Lava flows (SiO 2 between 54.6 and 64.7 wt.%) have dominated activity for more than 1 Ma, but explosive events have also occurred. Joint studies by volcanologists from Colombia, Ecuador, Peru, Bolivia, Argentina, and the United States produced 24 new 14 C ages and more than 100 stratigraphic sections to interpret the past 50 ka of activity at Galeras, including sector collapse events. The youngest collapse event truncated 12.8 ka lava flows and may have occurred as recently as 8 to 10 ka. Tephra-fall material rapidly thins and becomes finer away from the vent area. The only widespread marker in the < 10 ka section is a biotite-bearing tephra deposited between 4.1 and 4.5 ka from a source south of Galeras. It separates cryoturbated from largely undisturbed layers on Galeras, and thus dates a stratigraphic horizon which is useful in the interpretation of other volcanoes and geotectonics in the equatorial Andes. Pyroclastic flows during the past 50 ka have been small to moderate in volume, but they have left numerous thin deposits on the north and east flanks where lava flows have been impeded by crater and amphitheater walls. Many of the pyroclastic-flow deposits are lithic rich, with fines and clasts so strongly altered by hydrothermal action before eruption that they, as well as the sector collapse deposits, resemble waste dumps of leached cappings from disseminated sulfide deposits more than volcanogenic deposits. This evidence of a long-lived hydrothermal system indicates susceptibility to mass failure and explosive events higher than expected for a volcano built largely by lava flows and modest Vulcanian eruptions. Photographs, written accounts, and our study document historic north and east flank pyroclastic flows as far as 10 km from the summit; however, none have left recognizable deposits in Pasto for more than 40 ka.

Journal of Volcanology and Geothermal Research↗

USGS2003

Actual evapotranspiration and deficit: Biologically meaningful correlates of vegetation distribution across spatial scales

Correlative approaches to understanding the climatic controls of vegetation distribution have exhibited at least two important weaknesses: they have been conceptually divorced across spatial scales, and their climatic parameters have not necessarily represented aspects of climate of broad physiological importance to plants. Using examples from the literature and from the Sierra Nevada of California, I argue that two water balance parameters—actual evapotranspiration (AET) and deficit (D)—are biologically meaningful, are well correlated with the distribution of vegetation types, and exhibit these qualities over several orders of magnitude of spatial scale (continental to local). I reach four additional conclusions. (1) Some pairs of climatic parameters presently in use are functionally similar to AET and D; however, AET and D may be easier to interpret biologically. (2) Several well-known climatic parameters are biologically less meaningful or less important than AET and D, and consequently are poorer correlates of the distribution of vegetation types. Of particular interest, AET is a much better correlate of the distributions of coniferous and deciduous forests than minimum temperature. (3) The effects of evaporative demand and water availability on a site's water balance are intrinsically different. For example, the ‘dry’ experienced by plants on sunward slopes (high evaporative demand) is not comparable to the ‘dry’ experienced by plants on soils with low water-holding capacities (low water availability), and these differences are reflected in vegetation patterns. (4) Many traditional topographic moisture scalars—those that additively combine measures related to evaporative demand and water availability—are not necessarily meaningful for describing site conditions as sensed by plants; the same holds for measured soil moisture. However, using AET and D in place of moisture scalars and measured soil moisture can solve these problems.

Journal of Biogeography↗

USGS1990

Climatic change and permafrost. Record from surficial deposits

The physical and chemical characteristics of surficial deposits and the floral and faunal remains they contain provide information that is useful for interpreting both paleoclimate and past permafrost conditions. Surficial deposits thus provide a record of climatic change and permafrost history. This record suggests that initiation of permafrost in lowland areas of the Southern Arctic Archipelago and continents of the northern hemisphere may have occurred about 2,400,000 years ago during the pronounced cooling that led to the first major glaciation of late Cenozoic time. Since then, climate has been relatively cold but cyclically variable, characterized by the growth and shrinkage of large, continental ice sheets. Permafrost has expanded and contracted in response to these climatic changes, and we can expect the present permafrost conditions to change in response to future climatic changes. To predict the response of permafrost and the landscape to future climatic change we should: (1) Define relations between climate and the modern landscape; (2) establish long‐term records of past climatic change and landscape response; and (3) determine the paleoenvironments of past warm periods as possible analogs for future global warming.

Journal of Cold Regions Engineering↗

USGS2023

Stratigraphic architecture and fluvial interpretations of the Upper Cretaceous (Turonian?) Middendorf Formation, Chesterfield County, South Carolina, U.S.A.

The Upper Cretaceous (Turonian?) Middendorf Formation is a sand-rich stratigraphic unit of fluvial origin that forms a large aquifer in the U.S. Atlantic Coastal Plain. In Chesterfield County (South Carolina), which is the site of the type locality, the formation ranges in thickness from 66.5 to > 119.7 meters. The base of the formation is an unconformity above Paleozoic metasiltstone, and the upper contact is an unconformity above which lies sand of the Quaternary Pinehurst Formation. Outcrops display the following five facies assemblages: 1) sandstone to conglomeratic sandstone (fluvial bar and channel deposits), 2) beds of alternating laminae of sandstone and mudstone (fluvial overbank or floodplain deposits), 3) ≥ 1 m-thick beds of clay (swamp deposits, floodplain deposits, and/or sediment that accumulated in abandoned fluvial channels), 4) 0.2–0.5 m-thick planar to slightly undulatory beds of framework-supported sandstone with a mud matrix (traction-dominated current deposits at the top of fluvial bars, upper-flow-regime bedform deposits in subsidiary fluvial channels, or coarse-grained overbank deposits), and 5) sandstone to conglomeratic sandstone cemented by iron (interpreted as fluvial bar and channel deposits, with the iron cement being a diagenetic “groundwater ferricrete” that formed via the circulation of shallow groundwater and the oxidation of iron-bearing minerals). Kaolinite in various forms is pervasive throughout the formation and is interpreted as an early diagenetic phenomenon that formed by prolonged postdepositional weathering and flushing by meteoric water under a warm and humid paleoclimate. The fluvial system that formed the Middendorf Formation prograded into the area from the west or northwest from uplifted margins of Mesozoic rift basins and/or the Appalachian Mountains. This progradation was a response to a base-level fall and the sediment accumulated during base-level lowstand and subsequent early transgression. In Chesterfield County, the Middendorf Formation can be subdivided into three fining-upward sequences. Each sequence consists predominantly of medium to coarse sand with a greater abundance of gravel in the lower part of the sequence and a greater abundance of clay and silt beds in the upper part. Each sequence is interpreted as either a response to autogenic processes or a response to allogenic sea-level changes, specifically a higher-order (higher-frequency) progression from relative lowstand conditions to early transgression whereby coarse sand and gravel (e.g., fluvial bar and channel deposits) were preserved during initial lowstand conditions and a greater proportion of mud and finer-grained sand (floodplain deposits) were preserved during subsequent early transgression. The Middendorf Formation is correlative with several other kaolinite-rich fluvial sandstones in North America including the Raritan Formation in New Jersey, the Tuscaloosa Formation of the eastern Gulf of Mexico (Alabama, Mississippi, Louisiana), the Woodbine Formation of the central Gulf of Mexico (Texas), and the Frontier Formation of Wyoming. The accumulation and preservation of these formations occurred in response to a Turonian eustatic sea-level fall and subsequent transgression, and the early diagenetic kaolinite in these formations is attributed to similar warm and humid paleoclimate conditions.

South Carolina↗

USGS2020

High-resolution mapping of the freshwater-brine interface using deterministic and Bayesian inversion of airborne electromagnetic data at Paradox Valley, USA

Salt loads in the Colorado River Basin are a primary water quality concern. Natural groundwater brine discharge to the Dolores River where it passes through the collapsed salt anticline of the Paradox Valley in western Colorado is a significant source of salt to the Colorado River. An airborne electromagnetic survey of Paradox Valley has provided insights into the 3D distribution of brine in the surficial aquifer. A combination of stochastic and deterministic resistivity inversions were used to interpret the top of the freshwater-brine interface and to qualitatively describe the vertical salinity gradients across the interface. Low-resistivity regions indicative of brine occur near the land surface where brine discharges to the Dolores River and increase in depth several kilometers up-gradient along the axis of the valley. The most conductive parts of the brine plume are found in the areas below and adjacent to the river, suggesting that the brine becomes shallower and more concentrated as it reaches its natural discharge location. A significant freshwater lens overlying the brine west of the Dolores River is spatially correlated to the intermittent West Paradox Creek and agricultural irrigation. Below this lens, the transition from freshwater to brine appears to occur abruptly over a few meters and correlates to available well information. However, away from these regions and particularly with distance from the river, the freshwater-brine interface appears to be more diffuse.

Colorado↗

USGS1988

Paleoecology of Middle Pennsylvanian-age peat-swamp plants in Herrin coal, Kentucky, U.S.A.

To develop a method for quantifying the vegetation of Pennsylvania-age coal beds, of four coal-ball (permineralized peat) profiles and four coal column samples from the Herrin coal bed (Kentucky No. 11) Carbondale Formation in western Kentucky were compared. An estimated 89.5% of the coal can be identified botanically. Compaction ratios for individual tissues were estimated using point counts of organic matter in coal balls. The estimated abundances of major plant groups (lycopods, ferns, sphenopsids, and pteridosperms) in coal balls differ by less than 10% compared to coal after accounting for differential compaction of plant tissues. Standard deviations in taxonomic and maceral composition among coal columns are generally less than 2%. Consistent differences in botanical composition were found between benches showing that the method is consistent when applied to sufficient thicknesses of coal. It was not possible to make fine-scale correlations within the coal bed using the vegetational data; either the flora varied considerably from place to place or the method of quantification is unreliable for small increments of coal (5 cm or less). In the coal, pteridosperm abundance is positively correlated with underlying shale partings. This correlation suggests that pteridosperms are favored either by higher nutrient levels or disturbance. In the third of four benches in the Herrin coal bed, a succession from Sigillaria -containing zones to zones dominated by Lepidophloios hallii is interpreted as a shift towards wetter conditions. In the other benches, the main factors controlling the taxonomic composition appear to have been the relative abundance of nutrients and/or the frequency of disturbance as indicated by the relative abundance of partings. Criteria for distinguishing between domed and planar swamps are discussed. These include: distribution of partings, type of plant succession, and changes in plant diversity, average plant size, preservational quality and sporinite content. The infrequency of partings in bench C suggests a peat dome developed while the peat of that bench was accumulating but other evidence either fails to support the development of a peat dome or is ambiguous. The maceral composition resembles those of other Carboniferous coals which are thought to have formed from planar peat swamps. Formation of fusain bands appears to be associated with processes occurring above the peat surface, such as burning or prolonged oxidative exposure. Oxidation of accumulated peat is unlikely because fusain bands rarely include more than a single plant.

International Journal of Coal Geology↗

USGS2002

Aftershock triggering by complete Coulomb stress changes

We examine the correlation between seismicity rate change following the 1992, M 7.3, Landers, California, earthquake and characteristics of the complete Coulomb failure stress (CFS) changes (ΔCFS( t )) that this earthquake generated. At close distances the time-varying “dynamic” portion of the stress change depends on how the rupture develops temporally and spatially and arises from radiated seismic waves and from permanent coseismic fault displacement. The permanent “static” portion (ΔCFS) depends only on the final coseismic displacement. ΔCFS diminishes much more rapidly with distance than the transient, dynamic stress changes. A common interpretation of the strong correlation between ΔCFS and aftershocks is that load changes can advance or delay failure. Stress changes may also promote failure by physically altering properties of the fault or its environs. Because it is transient, ΔCFS( t ) can alter the failure rate only by the latter means. We calculate both ΔCFS and the maximum positive value of ΔCFS( t ) (peak ΔCFS( t )) using a reflectivity program. Input parameters are constrained by modeling Landers displacement seismograms. We quantify the correlation between maps of seismicity rate changes and maps of modeled ΔCFS and peak ΔCFS( t ) and find agreement for both models. However, rupture directivity, which does not affect ΔCFS, creates larger peak ΔCFS( t ) values northwest of the main shock. This asymmetry is also observed in seismicity rate changes but not in ΔCFS. This result implies that dynamic stress changes are as effective as static stress changes in triggering aftershocks and may trigger earthquakes long after the waves have passed.

Journal of Geophysical Research B: Solid Earth↗

USGS2025

Genetic structure of an expanding population of Humpback Chub in Grand Canyon

Objective Humpback Chub (HBC) Gila cypha in Grand Canyon declined in abundance and distribution over the latter part of the 20th century but have substantially increased in abundance and distribution over the past two decades. Although previous genetic work suggested that HBC in Grand Canyon belong to one genetic group, here we evaluate the genetic structure of HBC in Grand Canyon to determine whether relic populations in western Grand Canyon may have contributed unique variation to the recent population expansion or whether differences in behavior linked to migration in eastern Grand Canyon may promote assortative mating and heretofore unrecognized population structure. Methods Using fin clips collected from 167 individual HBC representing four sampling sites within Grand Canyon, we extracted DNA and developed data sets consisting of approximately 20,000 anonymous genomic loci. We quantified patterns of genetic diversity, and we accounted for outlier single-nucleotide polymorphisms to ensure that our interpretations of genetic patterns were not misled by adaptive processes and did not mask adaptively important genetic variation. Results Despite behavioral variation and the possibility that individuals with unique genetic variation survived in isolated warmwater sites within western Grand Canyon, HBC were not differentiated by sampling site or by differences in migratory behavior. Heterozygosity and nucleotide diversity were consistently high among sampling sites, and inbreeding coefficients were close to zero. Conclusions The HBC in Grand Canyon constitute a single genetic population. Our results do not preclude a genetic basis to migratory behavior, but our data suggest that this trait does not lead to assortative mating. Furthermore, while HBC may have survived in discontiguous warmwater refugia in western Grand Canyon during decades when the main stem was too cold for spawning, our data did not reveal any noticeable spatial variability in HBC genetics in the main stem after the recent HBC population expansion.

Arizona↗

USGS2007

Accumulation of dechlorination daughter products: A valid metric of chloroethene biodegradation

In situ reductive dechlorination of perchloroethene (PCE) and trichloroethene (TCE) generates characteristic chlorinated (cis-dichloroethene [cis-DCE] and vinyl chloride [VC]) and nonchlorinated (ethene and ethane) products. The accumulation of these daughter products is commonly used as a metric for ongoing biodegradation at field sites. However, this interpretation assumes that reductive dechlorination is the only chloroethene degradation process of any significance in situ and that the characteristic daughter products of chloroethene reductive dechlorination persist in the environment. Laboratory microcosms, prepared with aquifer and surface-water sediments from hydrologically diverse sites throughout the United States and amended with [1,2- 14 C] TCE, [1,2- 14 C] DCE, [1,2- 14 C] DCA, or [1,2- 14 C] VC, demonstrated widely variable patterns of intermediate and final product accumulation. In predominantly methanogenic sediment treatments, accumulation of 14 C-DCE, 14 C-VC, 14 C-ethene, and 14 C-ethane predominated. Treatments characterized by significant Fe(III) and/or Mn(IV) reduction, on the other hand, demonstrated substantial, and in some cases exclusive, accumulation of 14 CO 2 and 14 CH 4 . These results suggest that relying on the accumulation of cis-DCE, VC, ethene, and ethane may substantially underestimate overall chloroethene biodegradation at many sites.

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