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At least 289 records · Page 16Linked to original sources
USGS2009

A formal framework for scenario development in support of environmental decision-making

Scenarios are possible future states of the world that represent alternative plausible conditions under different assumptions. Often, scenarios are developed in a context relevant to stakeholders involved in their applications since the evaluation of scenario outcomes and implications can enhance decision-making activities. This paper reviews the state-of-the-art of scenario development and proposes a formal approach to scenario development in environmental decision-making. The discussion of current issues in scenario studies includes advantages and obstacles in utilizing a formal scenario development framework, and the different forms of uncertainty inherent in scenario development, as well as how they should be treated. An appendix for common scenario terminology has been attached for clarity. Major recommendations for future research in this area include proper consideration of uncertainty in scenario studies in particular in relation to stakeholder relevant information, construction of scenarios that are more diverse in nature, and sharing of information and resources among the scenario development research community. ?? 2008 Elsevier Ltd.

Environmental Modelling and Software↗
USGS2003

Monitoring the coral disease, plague type II, on coral reefs in St. John, U.S. Virgin Islands

In July 1997, conspicuous white patches of necrotic tissue and bare skeleton began to appear on scleractinian corals in several bays around St. John, US Virgin Islands. Analysis of diseased coral tissue from five different species confirmed the presence of a Sphingomonas-like bacterium, the pathogen for plague type II. To date, 14 species of hard corals have been affected by plague type II around St. John. This disease was monitored at Haulover and Tektite Reefs at depths of 7-12 meters. The study site at Tektite Reef has >50% cover by scleractinian corals with 90% of hard corals being composed of Montastraea annular is. Monthly surveys at Tektite Reef from December 1997 to May 2001 documented new incidence of disease (bare white patches of skeleton) every month with associated loss of living coral and 90.5% of all disease patches occurred on M. annularis. The frequency of disease within transects ranged from 3 to 58%, and the area of disease patches ranged from 0.25 to 9000 cm2. The average percent cover by the disease within 1 m2 ranged from 0.01% (?? 0.04 SD) to 1.74% (?? 9.08 SD). Photo-monitoring of 28 diseased corals of 9 species begun in September 1997 at Haulover Reef revealed no recovery of diseased portions with all necrotic tissue being overgrown rapidly by turf algae, usually within less than one month. Most coral colonies suffered partial mortality. Very limited recruitment (e.g., of Agaricia spp., Favia spp. and sponges) has been noted on the diseased areas. This coral disease has the potential to cause more loss of live coral on St. John reefs than any other stress to date because it targets the dominant reef building species, M. annularis.

Conference Paper↗
USGS1969

The Cloudy Pass epizonal batholith and associated subvolcanic rocks

The Cloudy Pass batholith, one of several small epizonal Tertiary batholiths in the Northern Cascade Mountains, discordantly intrudes metamorphic rocks of pre-Late Cretaceous age. The batholith is remarkable for its chilled borders, associated porphyry plugs, and intrusive breccias. The main body of the batholith consists largely of labradorite granodiorite. Part of the northeast side of the batholith is bordered by a complex more than half a mile thick of chilled rocks of Hart Lake that consists of separately injected, contrasting layers of porphyry. At lower levels these are an early, outer layer of dacite; a younger, inner layer of dacite and labradorite-by-townite andesite; and a middle, still younger layer of autobreccia compositionally similar to the inner layer. Contacts between layers are complex and consist at lower levels of intermixed zones, suggesting that at these levels the early rocks were still molten when injected by the later rocks. At higher levels the younger rocks split into separate dikes, and contacts between younger and older rocks are sharp, suggesting that at these levels the older rocks had solidified before they were intruded by the younger rocks. The border complex is thought to have been cooled largely by expanding gases which were released from the batholith and which escaped to the surface through this zone. The contact between the labradorite granodiorite and the inner layer is gradational locally, but in most places the granodiorite intrudes the inner layer, and the contact is sharp. Where the middle and inner layers of the complex are absent, the contact of granodiorite and dacite of the outer layer is gradational. Porphyry plugs which puncture the adjacent metamorphic rocks, although more siliceous than the rocks of the complex, consist largely of dacite and are petrographically indistinguishable from dacite of the complex. Intrusive breccias are of two types: one consists of rounded fragments of batholithic rocks in a “marble cake” mixture of calcic quartz diorite and white quartz monzonite and is confined to the core of the batholith; the other consists of fragments of batholithic rocks and gneiss in a matrix of varying proportions of igneous and finely comminuted materials and is confined to the porphyry plugs and gneiss. This second type seems to have been injected explosively, probably accompanying “second boiling” of the labradorite granodiorite. Plagioclases range from high- to low-temperature varieties. The transitional and high-temperature plagioclases are confined to the deuterically least-altered parts of the chilled margins. The low-temperature plagioclase occurs in the batholithic core and the complex of Hart Lake, and is thought to have inverted from an original high-temperature form because of long-continued existence at elevated, although subsolidus, temperatures, or because of the action of volatile constituents, or both. The batholith seems to have made room for itself by lifting its roof, and the complex of Hart Lake developed along the upfaulted eastern side.

Washington↗
USGS2010

Sediment management strategies associated with dam removal in the State of Washington

Different removal strategies are described for dams in three diverse drainage basins (Wind River, White Salmon River, and Elwha River basins) in the State of Washington (USA). The comparisons between the strategies offer the opportunity to track the effects of sediment resulting from dam decommissioning in the Pacific Northwest and to determine possible effects on socio-economically important species of anadromous salmonids. Hemlock Dam, located on Trout Creek and managed by the United States Forest Service, was removed from July to September 2009. To mitigate the effect on fish downstream (specifically, salmonids) and to minimize sediment aggradation downstream in the main-stem Wind River, the Forest Service chose to excavate the approximately 42,000 cubic meters of sediment entrapped behind the dam before removal of the dam. Thus, the reach of Trout Creek downstream of the dam will not be affected by a large, released pulse of accumulated sediment. In contrast, the scheduled removal of Condit Dam, located on the White Salmon River 30 kilometers to the east of Hemlock Dam, involves a different removal strategy. Condit Dam will be breached near its base in order to mobilize the 1.7 million cubic meters of trapped sediment during the reservoir drawdown in an effort to decrease the time needed for the downstream reach to return to normal levels of suspended sediment. Finally, the much-anticipated 2011 removal of two dams on the Elwha River on the Olympic Peninsula in northwestern Washington will take place over 2 years with progressive notches cut into the dams from the top down. Although some portion of reservoir sediment will be carried downstream by the river, the specific timing of notching will be adaptively managed to mitigate the effects of raised sediment concentration on fishes and people living downstream. With improved scientific understanding from these studies, future damremoval projects can be planned and executed with approaches that mitigate deleterious effectson salmonids.

Washington↗
USGS2021

A more representative community of ecologists

Ecologists play a crucial role in providing solutions to the challenges facing the world. For most of the history of the field, however, the science of ecology has been pursued by white men, and increasingly, by white women. This lack of diversity is untenable today, not only because it is socially unjust, but also because solving environmental problems requires diversity. Ecology as a science is an extremely rewarding and fun career choice for many, but how can the field recruit a more diverse workforce to do this important and gratifying work? Attracting and retaining future ecologists of color is the focus of this Forum. How do young people choose a career in ecology and environmental sciences? For many ecologists, environmental scientists and managers, and future natural resource professionals, an early field experience provides a crucial introduction and gateway. A sojourn at a field station, an extended field trip, or field expedition has introduced many of today’s professionals to their fields, but at the same time, a growing literature documents problematic behavior, discrimination, and other forms of harassment that have been far too frequently reported, and little attention has been given to conscious or implicit exclusion of students from diverse backgrounds. In their lead article, Bowser and Cid, two leading researchers and long-time champions of diversity in ecology, build on experience in long-running programs as well as the literature to diagnose challenges facing diverse youth, and present approaches to encourage, rather than discourage, further engagement. They describe affirmative and creative measures that foster a sense of inclusion and community among young scholars; this sense of belonging and empowerment allows many to advance to studies and careers in ecology and environmental science. In the subsequent six papers, authors explore topics either responding to, or inspired by, the lead paper. They explore alternatives to a field experience as a gateway to a career in ecology or environmental sciences through, for example, data science or the social sciences. Other comment papers describe challenges faced in the next phases of an academic career, barriers faced by specific cultural groups and the approaches, challenges, and outcomes of programs aiming to increase the diversity of the environmental STEM workforce. All responses sound a clarion call for change to hear and value different voices and perspectives to be heard and valued. These include (1) structural and cultural change to our institutions and reward structures; (2) developing and nurturing personal relationships among students and their mentors, within teams and in internships; (3) making entry to ecology inviting and making advancement in ecology free from systemic barriers; and (4) broadening our vision of ecology, and the ways we learn about the world’s ecosystems. The Ecological Society of America, the home for Ecological Applications , is committed to the diversity, equity and inclusion needed to tackle environmental challenges in unity (https://www.esa.org/esablog/2020/09/24/time-for-action-esa-initiates-a-diversity-equity-inclusion-and-justice-deij-task-force/). The world needs all available talent and perspectives to meet environmental challenges today. Ecological Applications has long published occasional papers on the profession of ecology and never ones more important or timely than these. The editorial team is proud to provide an outlet for the voices of our field, in all its current, if inadequate, diversity and honored to host the passionate and committed views of our authors.

Ecological Applications↗
USGS2020

An international code comparison study on coupled thermal, hydrologic and geomechanical processes of natural gas hydrate-bearing sediments

Geologic reservoirs containing gas hydrate occur beneath permafrost environments and within marine continental slope sediments, representing a potentially vast natural gas source. Numerical simulators provide scientists and engineers with tools for understanding how production efficiency depends on the numerous, interdependent (coupled) processes associated with potential production strategies for these gas hydrate reservoirs. Confidence in the modeling and forecasting abilities of these gas hydrate reservoir simulators (GHRSs) grows with successful comparisons against laboratory and field test results, but such results are rare, particularly in natural settings. The hydrate community recognized another approach to building confidence in the GHRS: comparing simulation results between independently developed and executed computer codes on structured problems specifically tailored to the interdependent processes relevant for gas hydrate-bearing systems. The United States Department of Energy, National Energy Technology Laboratory (DOE/NETL), sponsored the first international gas hydrate code comparison study, IGHCCS1, in the early 2000s. IGHCCS1 focused on coupled thermal and hydrologic processes associated with producing gas hydrates from geologic reservoirs via depressurization and thermal stimulation. Subsequently, GHRSs have advanced to model more complex production technologies and incorporate geomechanical processes into the existing framework of coupled thermal and hydrologic modeling. This paper contributes to the validation of these recent GHRS developments by providing results from a second GHRS code comparison study, IGHCCS2, also sponsored by DOE/NETL. IGHCCS2 includes participants from an international collection of universities, research institutes, industry, national laboratories, and national geologic surveys. Study participants developed a series of five benchmark problems principally involving gas hydrate processes with geomechanical components. The five problems range from simple geometries with analytical solutions to a representation of the world’s first offshore production test of methane hydrates, which was conducted with the depressurization method off the coast of Japan. To identify strengths and limitations in the various GHRSs, study participants submitted solutions for the benchmark problems and discussed differing results via teleconferences. The GHRSs evolved over the course of IGHCCS2 as researchers modified their simulators to reflect new insights, lessons learned, and suggested performance enhancements. The five benchmark problems, final sample solutions, and lessons learned that are presented here document the study outcomes and serve as a reference guide for developing and testing gas hydrate reservoir simulators.

Journal of Marine and Petroleum Geology↗
USGS2026

Challenges and opportunities for national-scale projections of future coastal landscape change

Local to global scale projections of future coastal landscape change are essential to improve land and resource management decisions that aim to prepare for and reduce risk exposure to impending coastal hazards. However, the availability of actionable knowledge is often limited due to the complexity of drivers of change, their consequences, and uncertainties that span disciplines. Varying spatial and temporal scales of physical processes that occur on landscapes with differing levels of coastal development and modification complicate decision-making. This paper reviews advances in observational approaches, modeling, and quantification of uncertainty to support the next generation of coastal change projections. We also highlight transdisciplinary opportunities for making this information more accessible and useful to support decision-making in the coastal zone. This includes consideration of different levels of user engagement to address specific needs, as well as resources and mechanisms that can support knowledge transfer broadly. A central recommendation is the development of a coordinated framework to support research integration including three components: accounting for relevant drivers, processes, and feedbacks; working with users to identify their information needs; and generating meaningful projections and uncertainty. Actions that would support such frameworks include the evaluation of models through coordinated research approaches and multi-model comparisons; ongoing investments in observations and data-driven approaches necessary to understand this complex environment; expansion of modeling capabilities using novel techniques; prioritization of co-development efforts between researchers and users; and continued training and support for transdisciplinary research.

Alaska, California, Florida, New York↗
USGS2003

Survival and growth of Atlantic white cedar plantings in Louisiana and Missisippi

Atlantic white cedar (cedar) is a native forest dominant in isolated areas throughout the Atlantic Coastal Plain and in a portion of the Gulf of Mexico Coastal Plain. Although the range of this species extends west to southern Mississippi, stands are uncommon in this area. In addition, most of the existing Mississippi stands are privately owned and afforded little long-term protection. To examine the feasibility of planting cedar at the western edge of its range and to determine if the species is a viable replacement for pine in wet areas, one-year-old seedlings were planted at three pine plantation sites in Louisiana and wildings at two bay-head locations in Mississippi. Overall, survival was high (87%), especially in the Louisiana sites, and after 10 growing seasons the trees averaged 5.3 m in height and 6.1 cm in diameter. This growth rate compared favorably with cypress and slash pine of other studies. The results of this study have shown that cedar can be a viable choice for restoration efforts or forest product plantings.

Louisiana, Mississippi↗
USGS2017

A carbon balance model for the great dismal swamp ecosystem

Background Carbon storage potential has become an important consideration for land management and planning in the United States. The ability to assess ecosystem carbon balance can help land managers understand the benefits and tradeoffs between different management strategies. This paper demonstrates an application of the Land Use and Carbon Scenario Simulator (LUCAS) model developed for local-scale land management at the Great Dismal Swamp National Wildlife Refuge. We estimate the net ecosystem carbon balance by considering past ecosystem disturbances resulting from storm damage, fire, and land management actions including hydrologic inundation, vegetation clearing, and replanting. Results We modeled the annual ecosystem carbon stock and flow rates for the 30-year historic time period of 1985–2015, using age-structured forest growth curves and known data for disturbance events and management activities. The 30-year total net ecosystem production was estimated to be a net sink of 0.97 Tg C. When a hurricane and six historic fire events were considered in the simulation, the Great Dismal Swamp became a net source of 0.89 Tg C. The cumulative above and below-ground carbon loss estimated from the South One and Lateral West fire events totaled 1.70 Tg C, while management activities removed an additional 0.01 Tg C. The carbon loss in below-ground biomass alone totaled 1.38 Tg C, with the balance (0.31 Tg C) coming from above-ground biomass and detritus. Conclusions Natural disturbances substantially impact net ecosystem carbon balance in the Great Dismal Swamp. Through alternative management actions such as re-wetting, below-ground biomass loss may have been avoided, resulting in the added carbon storage capacity of 1.38 Tg. Based on two model assumptions used to simulate the peat system, (a burn scar totaling 70 cm in depth, and the soil carbon accumulation rate of 0.36 t C/ha −1 /year −1 for Atlantic white cedar), the total soil carbon loss from the South One and Lateral West fires would take approximately 1740 years to re-amass. Due to the impractical time horizon this presents for land managers, this particular loss is considered permanent. Going forward, the baseline carbon stock and flow parameters presented here will be used as reference conditions to model future scenarios of land management and disturbance.

North Carolina, Virginia↗
USGS2009

Plasma corticosteroid and electrolyte dynamics of hybrid striped bass (white bass x striped bass) during netting and hauling

Striped bass hybrids ( Morone chrysops female x Morone saxatilis male) confined in a net for 10 minutes had significantly elevated corticosteroid levels (24.2 † 5.4 μg/100 ml) and significant hyperchloremia (150.02 † 2.7 meq/liter), in comparison with baseline levels of 0.8 † 0.1 μg/100 ml and 132.6 † 1.5 meq/liter, respectively. Hauling hybrids for 2 hours in freshwater significantly elevated corticosteroid levels (12.2 † 1.2 μg/100 ml) and reduced chloride levels (119.8 † 1.4 meq/liter). Corticosteroid levels remained high and hypochloremia developed within 24 hours after both netting and hauling. Although netting and hauling in 25 mg/liter MS-222 3 or 10 g/liter NaCl prevented chloride depletion during the stress, hypochloremia developed within 72 hours after the fish were transferred to freshwater. The development of hypochloremia several hours after handling indicates that hybrid bass that survive the initial stress do not necessarily recover, but may die in the days following handling. Fish anesthetized in 50 mg/liter MS-222 for 15 minutes prior to handling followed by hauling in water containing a combination of 25 mg/liter MS-222 and 10 g/liter NaCl did not develop hypochloremia within 72 hours after hauling; plasma corticosteroids were elevated during transport, but returned to nearly normal levels within 24 hours. This combination of 25 mg/liter MS-222 and 10 g/liter salt was the most successful handling medium tested.

Conference Paper↗
USGS2014

USGS ecosystem research for the next decade: advancing discovery and application in parks and protected areas through collaboration

Ecosystems within parks and protected areas in the United States and throughout the world are being transformed at an unprecedented rate. Changes associated with natural hazards, greenhouse gas emissions, and increasing demands for water, food, land, energy and mineral resources are placing urgency on sound decision making that will help sustain our Nation’s economic and environmental well-being (Millennium Ecosystem Assessment, 2005). In recognition of the importance of science in making these decisions, the U.S. Geological Survey (USGS) in 2007 identified ecosystem science as one of six science directions included in a comprehensive decadal strategy (USGS 2007). The Ecosystems Mission Area was identified as essential for integrating activity within the USGS and as a key to enhanced integration with other Federal and private sector research and management organizations (Myers at al., 2007). This paper focuses on benefits to parks and protected areas from the USGS Ecosystems Mission Area plan that expanded the scope of the original 2007 science strategy, to identify the Bureau’s work in ecosystem science over the next decade (Williams et al., 2013). The plan describes a framework that encompasses both basic and applied science and allows the USGS to continue to contribute meaningfully to conservation and management issues related to the Nation’s parks and ecological resources. This framework relies on maintaining long-standing, collaborative relationships with partners in both conducting science and applying scientific results. Here we summarize the major components of the USGS Ecosystems Science Strategy, articulating the vision, goals and strategic approaches, then outlining some of the proposed actions that will ultimately prove useful to those managing parks and protected areas. We end with a discussion on the future of ecosystem science for the USGS and how it can be used to evaluate ecosystem change and the associated consequences to management of our Nation’s natural resources.

The George Wright Forum↗
USGS2014

Quantifying the predictive consequences of model error with linear subspace analysis

All computer models are simplified and imperfect simulators of complex natural systems. The discrepancy arising from simplification induces bias in model predictions, which may be amplified by the process of model calibration. This paper presents a new method to identify and quantify the predictive consequences of calibrating a simplified computer model. The method is based on linear theory, and it scales efficiently to the large numbers of parameters and observations characteristic of groundwater and petroleum reservoir models. The method is applied to a range of predictions made with a synthetic integrated surface-water/groundwater model with thousands of parameters. Several different observation processing strategies and parameterization/regularization approaches are examined in detail, including use of the Karhunen-Loève parameter transformation. Predictive bias arising from model error is shown to be prediction specific and often invisible to the modeler. The amount of calibration-induced bias is influenced by several factors, including how expert knowledge is applied in the design of parameterization schemes, the number of parameters adjusted during calibration, how observations and model-generated counterparts are processed, and the level of fit with observations achieved through calibration. Failure to properly implement any of these factors in a prediction-specific manner may increase the potential for predictive bias in ways that are not visible to the calibration and uncertainty analysis process.

Water Resources Research↗
USGS2002

Tertiary cooling and tectonic history of the White River uplift, Gore Range, and western Front Range, central Colorado: Evidence from fission-track and 39Ar/ 40Ar ages

Apatite fission-track (AFT) data from Proterozoic and Paleozoic rocks in the mountains of north central Colorado (White River Uplift, Gore Range, and western Front Range) record significant cooling that began with uplift and erosion related to the Laramide Orogeny and continued through the Tertiary to Pliocene time. The mountains immediately flanking the Blue River half graben (Williams Fork Mountains to the east and the Gore Range to the west) cooled significantly during the Neogene. The AFT ages along the flanks of the Blue River half graben are significantly younger than AFT ages farther to the east in the central and eastern Front Range and to the west in the White River uplift. In both of these areas, the apatite ages suggest Laramide cooling. The Williams Fork Mountains–Gore Range zone of young AFT ages extends southward adjacent to the axis of the Rio Grande rift through southern Colorado and New Mexico. These young ages result from a combination of elevated heat flow, uplift, and erosion along the axis of the Rio Grande rift during Neogene time. Zircons from Proterozoic rocks yield Proterozoic fission-track ages, indicating that this part of the Colorado basement has not been heated to temperatures 200 C since Middle Proterozoic time. A sanidine 40 Ar/ 39 Ar age of 27 Ma from a rhyolite tuff just above a basal boulder conglomerate of the Troublesome Formation in a tilted fault block within the Blue River half graben shows that Tertiary deposition started there in middle Oligocene time. Xenocrystic sanidine from a basalt stratigraphically higher than the rhyolite tuff has an age of 24 Ma. Thus, the basalt is significantly younger than its postulated source, the 32 Ma laccolithic complex at Green Mountain.

Colorado↗
USGS2008

Dike orientations in the late jurassic independence dike swarm and implications for vertical-axis tectonic rotations in eastern California

Analysis of the strikes of 3841 dikes in 47 domains in the 500-km-long Late Jurassic Independence dike swarm indicates a distribution that is skewed clockwise from the dominant northwest strike. Independence dike swarm azimuths tend to cluster near 325?? ?? 30??, consistent with initial subparallel intrusion along much of the swarm. Dike azimuths in a quarter of the domains vary widely from the dominant trend. In domains in the essentially unrotated Sierra Nevada block, mean dike azimuths range mostly between 300?? and 320??, with the exception of Mount Goddard (247??). Mean dike azimuths in domains in the Basin and Range Province in the Argus, Inyo, and White Mountains areas range from 291?? to 354?? the mean is 004?? in the El Paso Mountains. In the Mojave Desert, mean dike azimuths range from 318?? to 023??, and in the eastern Transverse Ranges, they range from 316?? to 051??. Restoration for late Cenozoic vertical-axis rotations, suggested by paleodeclinations determined from published studies from nearby Miocene and younger rocks, shifts dike azimuths into better agreement with azimuths measured in the tectonically stable Sierra Nevada. This confirms that vertical-axis tectonic rotations explain some of the dispersion in orientation, especially in the Mojave Desert and eastern Transverse Ranges, and that the dike orientations can be a useful if imperfect guide to tectonic rotations where paleomagnetic data do not exist. Large deviations from the main trend of the swarm may reflect (1) clockwise rotations for which there is no paleomagnetic evidence available, (2) dike intrusions of other ages, (3) crack filling at angles oblique or perpendicular to the main swarm, (4) pre-Miocene rotations, or (5) unrecognized domain boundaries between dike localities and sites with paleomagnetic determinations. ?? 2008 The Geological Society of America.

Special Paper of the Geological Society of America↗
USGS1903

The mineral resources of the Mount Wrangell district, Alaska

The Tenth Census, taken in 1880, gives the number of white inhabitants of the Territory of Alaska as 430. In the decade from 1880 to 1890 this number had increased to 4,298, and in the following decade, that between 1890 and 1900, a further increase to 30,493 is recorded. The Director of the Mint in his report for 1891 gives the value of the yield of the Territory in precious metals as $772,197. By 1900 these figures were increased to $8,265,772. These statistics of the growth in population and in mineral output of Alaska serve as an index to the general increase in the importance and· commercial value of the Territory as an integral part of the domain of the United States. The larger part of this growth began with the discovery, late in the autumn of 1896, of the placer deposits of Klondike River in Canadian Yukon territory. Soon after this discovery there was a great influx of prospectors, miners, and, business men to all parts of Alaska, but particularly to the regions tributary to the Yukon, and with this increase in population came a proportional increase in transportation facilities and business interests.

Alaska↗
USGS2018

U-Pb geochronology and tectonic implications of a Silurian ash in the Farewell Terrane, Alaska

The Farewell terrane is an exotic continental fragment in interior Alaska that during the early Paleozoic was the site of a passive margin. We report a 238 U/ 206 Pb zircon age of 432.9±3.0 Ma from a Farewell terrane ash in Mt. McKinley quadrangle, Alaska. This age overlaps with prominent detrital zircon age maxima reported from Silurian and Devonian strata from the Farewell, Arctic Alaska-Chukotka, White Mountains, Alexander, and Yreka terranes, and from parautochtonous Silurian and Devonian foreland-basin strata along the Laurentian margin in the Canadian Arctic and Alaska. These findings can be explained in terms of refinements to the extrusion model of Colpron and Nelson (2011). In the original model, the Farewell terrane was interpreted as having been extruded westward into the paleo-Pacific realm from an initial position along the Siberian margin of the Uralian seaway, that is, the early Paleozoic ocean between Siberia and Baltica. We suggest (1) that the Farewell terrane was deposited along a passive margin that faced into the Uralian seaway; (2) that the terrane more likely originated along the northern or eastern margin of Baltica (present directions), rather than Siberia; and (3) that the Silurian ash and Silurian detrital zircons were derived from a magmatic source along a convergent margin that overrode distal parts of the Farewell passive margin during the Late Ordovician and Silurian. The Farewell terrane was eventually dislodged from Baltica, began to travel with the extruding plate, and was conveyed toward the Pacific to its eventual resting place in Alaska.

Alaska↗
USGS1982

Geomorphology of New England

Widely scattered terrestrial deposits of Cretaceous or Tertiary age and extensive nearshore and fluvial Coastal Plain deposits now largely beneath the sea indicate that the New England region has been above sea level during and since the Late Cretaceous. Estimates of rates of erosion based on sediment load in rivers and on volume of sediments in the Coastal Plain suggest that if the New England highlands had not been uplifted in the Miocene, the area would now be largely a lowland. If the estimated rates of erosion and uplift are of the right order of magnitude, then it is extremely unlikely that any part of the present landscape dates back before Miocene time. The only exception would be lowlands eroded in the early Mesozoic, later buried beneath Mesozoic and Cenozoic deposits, and exhumed by stream and glacial erosion during the later Cenozoic. Many of the rocks in the New England highlands are similar to those that underlie the Piedmont province in the central and southern Appalachians, where the relief over large areas is much less than in the highlands of New England. These comparisons suggest that the New England highlands have been upwarped in late Cenozoic time. The uplift took place in the Miocene and may have continued into the Quaternary. The New England landscape is primarily controlled by the underlying bedrock. Erosion and deposition during the Quaternary, related in large part to glaciation, have produced only minor changes in drainage and in topography. Shale and graywacke of Ordovician, Cambrian, and Proterozoic age forming the Taconic highlands, and akalic plutonic rocks of Mesozoic age are all highland makers. Sandstone and shale of Jurassic and Triassic age, similar rocks of Carboniferous age, and dolomite, limestone, and shale of Ordovician and Cambrian age commonly underlie lowlands. High-grade metapelites are more resistant than similar schists of low metamorphic grade and form the highest mountains in New England. Feldspathic rocks tend to form lowlands. Alkalic plutonic rocks of Mesozoic age underlie a large area in the White Mountains of New Hampshire and doubtless are a factor in their location and relief. Where the major streams flow across the regional structure of the bedrock, the location of the crossings probably is related to some other characteristic of the bedrock, such as joints or cross faults. The course of the Connecticut River is the result of the adjustment of the drainage to the bedrock geology during a long period of time. There is no ready explanation why many of the large rivers do not cross areas of calcalkalic plutonic rock, but rather take a longer course around such areas, which tend to include segments of the divide between the streams. The presence of coarse clastic materials in Miocene rocks of the emerged Coastal Plain of the Middle Atlantic States suggests uplift of the adjacent Piedmont and of the Adirondack Mountains at that time. The Miocene rocks of the submerged Coastal Plain in the Gulf of Maine and south of New England are fine grained and contain only small amounts of fluvial gravel. Perhaps the coarse clastic materials shed by the New England highlands in late Cenozoic time are buried by or incorporated in the Pleistocene glacial deposits.

Professional Paper↗
USGS2022

Histochemical evidence for nitrogen‐transfer Endosymbiosis in non‐photosynthetic cells of leaves and inflorescence bracts of angiosperms

We used light and confocal microscopy to visualize bacteria in leaf and bract cells of more than 30 species in 18 families of seed plants. Through histochemical analysis, we detected hormones (including ethylene and nitric oxide), superoxide, and nitrogenous chemicals (including nitric oxide and nitrate) around bacteria within plant cells. Bacteria were observed in epidermal cells, various filamentous and glandular trichomes, and other non-photosynthetic cells. Most notably, bacteria showing nitrate formation based on histochemical staining were present in glandular trichomes of some dicots (e.g., Humulus lupulus and Cannabis sativa ). Glandular trichome chemistry is hypothesized to function to scavenge oxygen around bacteria and reduce oxidative damage to intracellular bacterial cells. Experiments to assess the differential absorption of isotopic nitrogen into plants suggest the assimilation of nitrogen into actively growing tissues of plants, where bacteria are most active and carbohydrates are more available. The leaf and bract cell endosymbiosis types outlined in this paper have not been previously reported and may be important in facilitating plant growth, development, oxidative stress resistance, and nutrient absorption into plants. It is unknown whether leaf and bract cell endosymbioses are significant in increasing the nitrogen content of plants. From the experiments that we conducted, it is impossible to know whether plant trichomes evolved specifically as organs for nitrogen fixation or if, instead, trichomes are structures in which bacteria easily colonize and where some casual nitrogen transfer may occur between bacteria and plant cells. It is likely that the endosymbioses seen in leaves and bracts are less efficient than those of root nodules of legumes in similar plants. However, the presence of endosymbioses that yield nitrate in plants could confer a reduced need for soil nitrogen and constitute increased nitrogen-use efficiency, even if the actual amount of nitrogen transferred to plant cells is small. More research is needed to evaluate the importance of nitrogen transfer within leaf and bract cells of plants

Biology↗