Deposition and preservation of fluvio-tidal shallow-marine sandstones: A re-evaluation of the Neoproterozoic Jura Quartzite (western Scotland)     

Bruce K. Levell  Howard D. Johnson  Daniel S. Collins  Marijn van Cappelle 《Sedimentology》2020,67(1):173-206

The 2 to 5 km thick, sandstone-dominated (>90%) Jura Quartzite is an extreme example of a mature Neoproterozoic sandstone, previously interpreted as a tide-influenced shelf deposit and herein re-interpreted within a fluvio-tidal deltaic depositional model. Three issues are addressed: (i) evidence for the re-interpretation from tidal shelf to tidal delta; (ii) reasons for vertical facies uniformity; and (iii) sand supply mechanisms to form thick tidal-shelf sandstones. The predominant facies (compound cross-bedded, coarse-grained sandstones) represents the lower parts of metres to tens of metres high, transverse fluvio-tidal bedforms with superimposed smaller bedforms. Ubiquitous erosional surfaces, some with granule–pebble lags, record erosion of the upper parts of those bedforms. There was selective preservation of the higher energy, topographically-lower, parts of channel-bar systems. Strongly asymmetrical, bimodal, palaeocurrents are interpreted as due to associated selective preservation of fluvially-enhanced ebb tidal currents. Finer-grained facies are scarce, due largely to suspended sediment bypass. They record deposition in lower-energy environments, including channel mouth bars, between and down depositional-dip of higher energy fluvio-ebb tidal bars. The lack of wave-formed sedimentary structures and low continuity of mudstone and sandstone interbeds, support deposition in a non-shelf setting. Hence, a sand-rich, fluvial–tidal, current-dominated, largely sub-tidal, delta setting is proposed. This new interpretation avoids the problem of transporting large amounts of coarse sand to a shelf. Facies uniformity and vertical stacking are likely due to sediment oversupply and bypass rather than balanced sediment supply and subsidence rates. However, facies evidence of relative sea level changes is difficult to recognise, which is attributed to: (i) the areally extensive and polygenetic nature of the preserved facies, and (ii) a large stored sediment buffer that dampened response to relative sea-level and/or sediment supply changes. Consideration of preservation bias towards high-energy deposits may be more generally relevant, especially to thick Neoproterozoic and Lower Palaeozoic marine sandstones.  相似文献   

Geospatial data mining for digital raster mapping     

Bruce K. Wylie  Neal J. Pastick  Joshua J. Picotte  Carol A. Deering 《地理信息系统科学与遥感》2019,56(3):406-429

We performed an in-depth literature survey to identify the most popular data mining approaches that have been applied for raster mapping of ecological parameters through the use of Geographic Information Systems (GIS) and remotely sensed data. Popular data mining approaches included decision trees or “data mining” trees which consist of regression and classification trees, random forests, neural networks, and support vector machines. The advantages of each data mining approach as well as approaches to avoid overfitting are subsequently discussed. We also provide suggestions and examples for the mapping of problematic variables or classes, future or historical projections, and avoidance of model bias. Finally, we address the separate issues of parallel processing, error mapping, and incorporation of “no data” values into modeling processes. Given the improved availability of digital spatial products and remote sensing products, data mining approaches combined with parallel processing potentials should greatly improve the quality and extent of ecological datasets.  相似文献   

Life-cycle cost and sustainability analysis of light-frame wood residential communities exposed to tornados     

Adhikari  Pramodit  Mahmoud  Hussam N.  Ellingwood  Bruce R. 《Natural Hazards》2021,109(1):523-544

Natural Hazards - Tornadoes pose a significant threat to residential communities, causing enormous physical damage and losses to their social fabric. The dominant type of single-family residential...  相似文献   

Projected changes in diverse ecosystems from climate warming and biophysical drivers in northwest Alaska     

Mark Torre Jorgenson  Bruce G. Marcot  David K. Swanson  Janet C. Jorgenson  Anthony R. DeGange 《Climatic change》2015,130(2):131-144

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The Mount Wright Arc: A Cambrian subduction system developed on the continental margin of East Gondwana,Koonenberry Belt,eastern Australia     

J.E. Greenfield  R.J. Musgrave  M.C. Bruce  P.J. Gilmore  K.J. Mills 《Gondwana Research》2011,19(3):650-669

The Mount Wright Arc, in the Koonenberry Belt in eastern Australia, is associated with two early to middle Cambrian lithostratigraphic groups developed onto the Late Neoproterozoic volcanic passive margin of East Gondwana. The Gnalta Group includes a calc-alkaline basalt-andesite-dacite suite (Mount Wright Volcanics), interpreted to represent the volcanic component of the arc. Volcaniclastic Gnalta Group rocks now buried in the Bancannia Trough represent the continental back-arc, developed immediately behind the arc in a manner analogous to the modern Taupo Volcanic Zone of New Zealand. East of the Gnalta Group is the Ponto Group, a deep marine sedimentary package that includes tholeiitic lavas (Bittles Tank Volcanics) and felsic tuffs, interpreted as part of a fore-arc sequence. The configuration of these units suggests the Mount Wright Arc developed on continental crust in response to west-dipping subduction along the East Gondwana margin, in contrast with some models for Cambrian convergence on other sections of the Delamerian Orogen, which invoke east-dipping subduction and arc accretion by arc-continent collision.This convergent margin was deformed by the middle Cambrian Delamerian Orogeny, which involved initial co-axial shortening followed by sinistral transpression, and oroclinal folding around the edge of the Curnamona Province.  相似文献   

A conceptual framework of groundwater flow in some crystalline aquifers in Southeastern Ghana     

Sandow Mark Yidana  Samuel Ganyaglo  Bruce Banoeng-Yakubo  Thomas Akabzaa 《Journal of African Earth Sciences》2011,59(2-3):185-194

A conceptual groundwater flow model was developed for the crystalline aquifers in southeastern part of the Eastern region, Ghana. The objective was to determine approximate levels of groundwater recharge, estimate aquifer hydraulic parameters, and then test various scenarios of groundwater extraction under the current conditions of recharge. A steady state groundwater flow model has been calibrated against measured water levels of 19 wells in the area. The resulting recharge is estimated to range from 8.97 × 10^?5 m/d to 7.14 × 10^?4 m/d resulting in a basin wide average recharge of about 9.6% of total annual precipitation, which results in a basin wide quantitative recharge of about 2.4 million m³/d in the area. This compares to recharge estimated from the chloride mass balance of 7.6% of precipitation determined in this study. The general groundwater flow in the area has also been determined to conform to the general northeast–southwest structural grain of the country. The implication is that the general hydrogeology is controlled by post genetic structural entities imposed on the rocks to create ingresses for sufficient groundwater storage and transport. Calibrated aquifer hydraulic conductivities range between 0.99 m/d and over 19.4 m/d. There is a significant contribution of groundwater discharge to stream flow in the study area. Increasing groundwater extraction will have an effect on stream flow. This study finds that the current groundwater extraction levels represent only 0.17% of the annual recharge from precipitation, and that groundwater can sustain future increased groundwater demands from population growth and industrialization.  相似文献   

On the utility of identification schemes for digital earth science data: an assessment and recommendations   总被引：1，自引：1，他引：0  

Ruth E. Duerr  Robert R. Downs  Curt Tilmes  Bruce Barkstrom  W. Christopher Lenhardt  Joseph Glassy  Luis E. Bermudez  Peter Slaughter 《Earth Science Informatics》2011,4(3):139-160

In recent years, a number of data identification technologies have been developed which purport to permanently identify digital objects. In this paper, nine technologies and systems for assigning persistent identifiers are assessed for their applicability to Earth science data (ARKs, DOIs, XRIs, Handles, LSIDs, OIDs, PURLs, URIs/URNs/URLs, and UUIDs). The evaluation used four use cases that focused on the suitability of each scheme to provide Unique Identifiers for Earth science data objects, to provide Unique Locators for the objects, to serve as Citable Locators, and to uniquely identify the scientific contents of data objects if the data were reformatted. Of all the identifier schemes assessed, the one that most closely meets all of the requirements for an Unique Identifier is the UUID scheme. Any of the URL/URI/IRI-based identifier schemes assessed could be used for Unique Locators. Since there are currently no strong market leaders to help make the choice among them, the decision must be based on secondary criteria. While most publications now allow the use of URLs in citations, so that all of the URL/URI/IRI based identification schemes discussed in this paper could potentially be used as a Citable Locator, DOIs are the identification scheme currently adopted by most commercial publishers. None of the identifier schemes assessed here even minimally address identification of scientifically identical numerical data sets under reformatting.  相似文献   

When is it sensible not to use XML?     

Bruce R. Barkstrom 《Earth Science Informatics》2011,4(1):45-53

This paper considers the problem of comparing the read time for a file containing an array of one-half million one-byte data values using a direct read time with the time required to read an equivalent XML file. The XML file uses a variable-length string encoding of the identifiers associated with each of the byte values. The XML file is about 180 times larger than the original file of byte values. Because the XML file is much larger and because the XML parsing requires substantially more computational work, reading the XML file on a Windows-based PC takes about 3,700 times longer than the direct read. The experimental study shows that the XML read time increases linearly with the size of the file. Given the increased read time and the increased probability of programming errors for the XML encoding, it appears that in cases where data archives are providing simple binary or text files of data that may be readily understood and read with short programs, then XML may not be an optimal choice for serving users or for preserving data.  相似文献   

Woodland expansion’s influence on belowground carbon and nitrogen in the Great Basin U.S.     

Benjamin M. Rau  Dale W. Johnson  Bruce A. Roundy  Richard F. Miller  Todd G. Caldwell  Annmarie Lucchesi 《Journal of Arid Environments》2011,75(9):827-835

Vegetation changes associated with climate shifts and anthropogenic disturbance can have major impacts on biogeochemical cycling and soils. Much of the Great Basin, U.S. is currently dominated by sagebrush (Artemisia tridentate (Rydb.) Boivin) ecosystems. Sagebrush ecosystems are increasingly influenced by pinyon (Pinus monophylla Torr. & Frém and Pinus edulis Engelm.) and juniper (Juniperus osteosperma Torr. and Juniperus occidentalis Hook.) expansion. Some scientists and policy makers believe that increasing woodland cover in the intermountain western U.S. offers the possibility of increased organic carbon (OC) storage on the landscape; however, little is currently known about the distribution of OC on these landscapes, or the role that nitrogen (N) plays in OC retention. We quantified the relationship between tree cover, belowground OC, and total below ground N in expansion woodlands at 13 sites in Utah, Oregon, Idaho, California, and Nevada, USA. One hundred and twenty nine soil cores were taken using a mechanically driven diamond tipped core drill to a depth of 90 cm. Soil, coarse fragments, and coarse roots were analyzed for OC and total N. Woodland expansion influenced the vertical distribution of root OC by increasing 15-30 cm root OC by 2.6 Mg ha⁻¹ and root N by 0.04 Mg ha⁻¹. Root OC and N increased through the entire profile by 3.8 and 0.06 Mg ha⁻¹ respectively. Woodland expansion influenced the vertical distribution of soil OC by increasing surface soil (0-15 cm) OC by 2.2 Mg ha⁻¹. Woodland expansion also caused a 1.3 Mg ha⁻¹ decrease in coarse fragment associated OC from 75-90 cm. Our data suggests that woodland expansion into sagebrush ecosystems has limited potential to store additional belowground OC, and must be weighed against the risk of increased wildfire and exotic grass invasion.  相似文献   

Submarine hydrothermal activity and gold-rich mineralization at Brothers Volcano, Kermadec Arc, New Zealand     

Cornel E. J. de Ronde  Gary J. Massoth  David A. Butterfield  Bruce W. Christenson  Junichiro Ishibashi  Robert G. Ditchburn  Mark D. Hannington  Robert L. Brathwaite  John E. Lupton  Vadim S. Kamenetsky  Ian J. Graham  Georg F. Zellmer  Robert P. Dziak  Robert W. Embley  Vesselin M. Dekov  Frank Munnik  Janine Lahr  Leigh J. Evans  Ken Takai 《Mineralium Deposita》2011,46(5-6):541-584

Brothers volcano, of the Kermadec intraoceanic arc, is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world. It has two distinct vent fields, known as the NW Caldera and Cone sites, whose geology, permeability, vent fluid compositions, mineralogy, and ore-forming conditions are in stark contrast to each other. The NW Caldera site strikes for ??600?m in a SW?CNE direction with chimneys occurring over a ??145-m depth interval, between ??1,690 and 1,545?m. At least 100 dead and active sulfide chimney spires occur in this field and are typically 2?C3?m in height, with some reaching 6?C7?m. Their ages (at time of sampling) fall broadly into three groups: <4, 23, and 35?years old. The chimneys typically occur near the base of individual fault-controlled benches on the caldera wall, striking in lines orthogonal to the slopes. Rarer are massive sulfide crusts 2?C3?m thick. Two main types of chimney predominate: Cu-rich (up to 28.5?wt.% Cu) and, more commonly, Zn-rich (up to 43.8?wt.% Zn). Geochemical results show that Mo, Bi, Co, Se, Sn, and Au (up to 91?ppm) are correlated with the Cu mineralization, whereas Cd, Hg, Sb, Ag, and As are associated with the dominant Zn-rich mineralization. The Cone site comprises the Upper Cone site atop the summit of the recent (main) dacite cone and the Lower Cone site that straddles the summit of an older, smaller, more degraded dacite cone on the NE flank of the main cone. Huge volumes of diffuse venting are seen at the Lower Cone site, in contrast to venting at both the Upper Cone and NW Caldera sites. Individual vents are marked by low-relief (??0.5?m) mounds comprising predominately native sulfur with bacterial mats. Vent fluids of the NW Caldera field are focused, hot (??300°C), acidic (pH????2.8), metal-rich, and gas-poor. Calculated end-member fluids from NW Caldera vents indicate that phase separation has occurred, with Cl values ranging from 93% to 137% of seawater values. By contrast, vent fluids at the Cone site are diffuse, noticeably cooler (??122°C), more acidic (pH?1.9), metal-poor, and gas-rich. Higher-than-seawater values of SO₄ and Mg in the Cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water/rock interactions. Iron oxide crusts 3?years in age cover the main cone summit and appear to have formed from Fe-rich brines. Evidence for magmatic contributions to the hydrothermal system at Brothers includes: high concentrations of dissolved CO₂ (e.g., 206?mM/kg at the Cone site); high CO₂/³He; negative ??D and ??¹⁸O_H2O for vent fluids; negative ??³⁴S for sulfides (to ?4.6??), sulfur (to ?10.2??), and ??¹⁵N₂ (to ?3.5??); vent fluid pH values to 1.9; and mineral assemblages common to high-sulfidation systems. Changing physicochemical conditions at the Brothers hydrothermal system, and especially the Cone site, occur over periods of months to hundreds of years, as shown by interlayered Cu?+?Au- and Zn-rich zones in chimneys, variable fluid and isotopic compositions, similar shifts in ³He/⁴He values for both Cone and NW Caldera sites, and overprinting of ??magmatic?? mineral assemblages by water/rock-dominated assemblages. Metals, especially Cu and possibly Au, may be entering the hydrothermal system via the dissolution of metal-rich glasses. They are then transported rapidly up into the system via magmatic volatiles utilizing vertical (??2.5?km long), narrow (??300-m diameter) ??pipes,?? consistent with evidence of vent fluids forming at relatively shallow depths. The NW Caldera and Cone sites are considered to represent stages along a continuum between water/rock- and magmatic/hydrothermal-dominated end-members.  相似文献