||20 December 2007
GSA Release No. 07-72
December Media Highlights: Geosphere
Boulder, Colo. - A special themed issue of GEOSPHERE, published in electronic format only by the Geological Society of America, is now available online. Articles focus on new digital technologies applied to multi-scale geologic models.
Highlights are provided below. Representatives of the media may obtain complimentary copies of articles by contacting Ann Cairns. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOSPHERE in articles published. Contact Ann Cairns for additional information or other assistance.
Non-media requests for articles may be directed to GSA Sales and Service, .
- Introduction: Unlocking 3D earth systems — Harnessing new digital technologies to revolutionize multi-scale geologic models
- Tim Wawrzyniec Richard R. Jones, Ken McCaffrey, Jonathan Imber, Nick Holliman, and Robert E. Holdsworth
- Curvature and fracturing based on global positioning system data collected at Sheep Mountain anticline, Wyoming
Patricia Fiore Allwardt et al., Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305.
- Keywords: fractures, folds, GPS, intensity, variance analysis.
- Fractures are heterogeneities within reservoirs and aquifers that can either enhance or disrupt fluid flow. Knowledge of the orientation, intensity, and spatial location of fractures is thus sought for economic purposes. Previous studies have suggested that the attributes of fractures developed across a surface are directly linked to the curvature of that surface. Here, the authors reinvestigate the relationship between curvature and fracturing by coupling measurements of fracture orientation and spacing with high resolution spatial data acquired across geological surfaces at Sheep Mountain, Wyoming. In the process, they define a workflow for the collection, post-processing, filtering, and analysis of global positioning system data, demonstrating how one may quantitatively understand the shapes of surfaces. Ultimately, this work reveals that although curvature correlates positively with variance in fracture orientation at Sheep Mountain, there is no apparent correlation between curvature and the intensity of fracturing. Mechanisms in addition to the flexure of surfaces have played a role in the development of the fracture pattern at Sheep Mountain and therefore the relationship between curvature and fracture intensity is not direct.
- Characterization of fluvial architectural elements using a three-dimensional outcrop dataset: Escanilla braided system, South-Central Pyrenees, Spain
Richard Labourdette, TOTAL/Montpellier 2 University, Geoscience Technologies Department of Structural Geology, Sedimentology, and Geology Laboratory, Avenue Larribau, PAU, Cedex 64 018, France; and Richard R. Jones, Geospatial Research Ltd., Department of Earth Science, University of Durham, Durham DH1 3LE, UK.
- Keywords: three-dimensional methods, laser surveys, photogrammetry, braided channels, Eocene
- Recent advances in field geology allow outcrop observations to be captured straight into three-dimensional space using laser mapping, from ground stations or helicopters. This, along with ground positioning system (GPS) and high resolution digital photography, enables geologists to build three-dimensional models integrating conventional field measurements. These virtual reality technologies applied in highly indented and inaccessible cliffs, such as the Olson area in Spain, provides the visualization and integration of geological information in three-dimensions. The resulting spatial coherence of acquired data allows geologists to capture the evolution of sedimentation either laterally or vertically in the cliffs. This vertical component of observations enables an access to the evolution of detailed sedimentary processes through time, including the past influence of climate variations, tectonic evolution and major sea-level changes. The achieved virtual models have reached such a level of detail, giving a unique opportunity to study sediment morphological variations in their depositional settings.
- Planetary science: Multiple datasets, multiple scales, and unlocking the third dimension
Paula Martin, Department of Earth Sciences, Durham University, Science Laboratories, Durham, DH1 3LE; and Ellen R. Stofan, Proxeny Research, Laytonsville, MD 20882, USA.
- Keywords: planetary, Mars, surface, subsurface.
- The aim of this manuscript is to provide a basic introduction to the available range of planetary science datasets, and the combination of these datasets over a range of scales, resolutions and techniques to address geological problems. It is hoped that this sharing of practice will facilitate successful collaborations between planetary scientists and those applying new digital technologies to multi-scale geologic models.
- Three-dimensional modeling of glacial sediments using public water-well data records: An integration of interpretive and geostatistical approaches
Erik R. Venteris, Division of Geological Survey, Ohio Department of Natural Resources, Columbus, OH 43229, USA.
- Keywords: glacial sediments, geostatistics, hydrofacies, water wells, hydrogeology.
- Three-dimensional models of glacial and surficial materials are needed for a wide range of applications from ground-water modeling to mineral resource inventory. The main source of data for such models is lithology logs from public water well records. A modeling case study was conducted for an approximately 130 square kilometer area near Lake Erie in northwest Ohio to test the usefulness of water wells in 3D modeling. Through statistical and geostatistical analysis, it was found that water well data provided reliable information for the modeling of stratigraphic units (tens of meters thick, tens of square km in area). However, the water well data provided little reliable information on smaller sedimentary structures (sedimentary facies such as sand lenses, interbedded lacustrine clay layers etc.). The accurate modeling of groundwater flow requires an accounting for facies scale structures. Alternate sources of information such as geophysical data and 3D outcrop models are needed to realistically simulate sedimentary facies in the subsurface.
- From outcrop to reservoir simulation model: Workflow and procedures
Håvard D. Enge, et al., Centre for Integrated Petroleum Research, Department of Earth Science, University of Bergen, Bergen, NORWAY.
- Keywords: outcrop analogs, laser methods, Pyrenees, sandstone, deltas, clinoforms, Canyonlands National Park, grabens, ramps, fault blocks, reservoir, modeling, analog simulation, fluid
- Subsurface hydrocarbon reservoir models are limited by available geological data. Outcrop analogs from comparable systems are commonly used to provide additional input to models of the subsurface. This paper presents new methodologies for the acquisition and utilization of digital geological 3D information generated by ground-based laser scanning (lidar) of outcrops. Selected datasets from the United States and Spain are used to illustrate the application of the workflow to geological problems at a reservoir scale.
- A method for acquiring and processing ground-based lidar data in difficult-to-access outcrops for use in three-dimensional, virtual-reality models
Florence Bonnaffe et al., Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, The University of Texas at Austin, University Station, Austin, Texas 78713-8924, USA.
- Keywords: lidar acquisition, lidar processing, outcrop
- Lidar (light detection and ranging) data provide a centimeter-scale-resolution digital outcrop model. This technology supplements and improves conventional outcrop investigations by providing geoscientists ways to digitally visit and analyze outcrops on their computers or workstations. The lidar data are converted into optimized triangulated surfaces used for photodraping or for 3D visualization and interpretation. The authors have developed a workflow that allows us to create optimized virtual reality models for difficult-to-access outcrops such as sea cliffs or outcrops where exposure is limited by trees or buildings. Vegetation and other obstacles altering the view of exposures can be digitally removed to create a perfectly continuous outcrop rendering that greatly enhances stratigraphic analysis and mapping of sedimentary bodies.
- Knowledge transfer in a digital world: Field data acquisition, uncertainty, visualization, and data management
Clare E. Bond et al., Department of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, UK, and Midland Valley Exploration, Glasgow, G2 2HG, UK.
- Keywords: uncertainty, digital, knowledge transfer, 3D visualization, data management
- Encouraging the transfer of scientific expertise between academia, industry, and the public has gained political and social momentum in the twenty-first century. In geoscience, the use of the Web combined with a move to digital data acquisition, processing, and interpretation technologies, has provided a unique opportunity for rapid progression of the science and its understanding by the public. In this paper, the authors outline the need for geoscientists to better understand the benefits and limitations of digital data acquisition, processing and interpretation to truly harness this opportunity. Like its more traditional counterpart, digital geology contains uncertainties, and these uncertainties, derived from data collection, combining data sources, presentation of data, and models in 3D visualization environments, need to be understood for effective knowledge transfer. Understanding the benefits and limitations of "digital geology" will place the geological community in a better position to represent their findings in a digital environment for effective dissemination.
Other papers in the issue:
- Uncertainties in long-term geologic offset rates of faults: General principles illustrated with data from California and other western states
Peter Bird, Department of Earth and Space Sciences, University of California, Los Angeles, California 90095-1567, USA.
- Keywords: neotectonics, faulting, statistics.
- Geologists estimate the long-term slip rates of faults by finding ancient features that have been cut and offset by the fault, and then dating these features. In the past, description of the errors and uncertainties involved has been rather cursory. This paper presents all the equations needed for determining the uncertainties in slip rate in a wide variety of cases, and applies them to data from the western United States. By contrasting rates from different offset features on the same fault, we are able to estimate the small fraction of rates that are fundamentally incorrect, and the larger fraction of rates which are inapplicable to neotectonics because rates have changed over millions of years. Such analysis helps to put estimation of future seismic hazard on a stronger statistical basis.
- Guides to understanding the aeromagnetic expression of faults in sedimentary basins: Lessons learned from the central Rio Grande rift, New Mexico
V.J.S. Grauch, U.S. Geological Survey, Federal Center, Denver, Colorado 80225-0046, USA.
- Keywords: aeromagnetic surveys, faults, faulting, sedimentary basins, rifts.
- In many sedimentary basins, mapping faults is difficult because of the extensive alluvial cover. This is true for basins that underlie the Rio Grande Valley in north-central New Mexico and the growing cities of Albuquerque and Santa Fe. These basins comprise the central Rio Grande rift, a geologic feature that began to form about 35 million years ago as plate tectonic forces pulled apart the crust. Many of the covered faults in these basins are revealed by high-resolution aeromagnetic data, geophysical data acquired in low-flying aircraft that respond to subtle variations in the magnetic properties of rocks and sediments. The fault patterns revealed suggest that faults are much more prevalent within the basin sediments than previously thought. Although most of these faults are now inactive, knowing where they are may help understand how faults partition basin aquifers and control the flow of ground water, how seismic waves from potential earthquakes might propagate underground, and how rift basins form in general. Using aeromagnetic data to map concealed faults in sedimentary basins is a new approach, so their aeromagnetic expressions are poorly understood. This paper uses lessons learned in the central Rio Grande rift to help geologists understand how to interpret and map faults in sedimentary basins from aeromagnetic data. Included with the paper is a digital compilation of interpreted faults for the central Rio Grande rift. When combined with the guides presented in the paper, the compilation should provide direction and fuel for future work in a wide variety of multidisciplinary basin-related topics.
- Stratigraphy, paleomagnetism, and anisotropy of magnetic susceptibility of the Miocene Stanislaus Group, central Sierra Nevada and Sweetwater Mountains, California and Nevada
Nathan M. King et al.; corresponding author: John W. Hillhouse, U.S. Geological Survey, Menlo Park, California 94025, USA.
- Keywords: ash-flow tuff, Miocene, California, paleomagnetism, magnetic anisotropy
- The Stanislaus Group volcanic rocks are located in the central Sierra Nevada and Sweetwater Mountains in California. Table Mountain of the Tuolumne, which is a well-known landmark near Sonora, California, is capped by lava flows of the Stanislaus Group. This group of volcanic rocks erupted ca. 9 million years ago from a now-extinct volcano named the Little Walker Caldera just north of Bridgeport, California. Magnetic properties of these volcanic rocks, preserved during cooling soon after eruption, were used to determine the flow direction from the Little Walker Caldera. Other magnetic properties were used to show how areas of Earth's crust rotate between faults. Overall, the Stanislaus Group is very useful for describing the motions of old faults and is an important tool to help geologists describe the uplift history and ancient stream valleys of the Sierra Nevada.
- Three-dimensional geologic model of the northern Nevada rift and the Beowawe geothermal system, north-central Nevada
Janet T. Watt et al., U.S. Geological Survey, Menlo Park, California 94025, USA.
- Keywords: aeromagnetics, Beowawe geothermal system, gravity, north-central Nevada, northern Nevada rift, 3-D geologic model.
- This paper describes the geology and geophysics of a part of the eastern Northern Nevada rift (NNRe) that encompasses the Beowawe geothermal system and the assumptions, extrapolations, and geophysical modeling conducted to generate a three-dimensional (3D) geologic model. The model integrates regional geologic and tectonic interpretations with local geologic, drill-hole, gravity and magnetic data, and other geophysical information. The geology of the NNRe and Beowawe geothermal system is complex and characterized by two distinct sets of fault structures (ENE-WSW and NW-SE) that play an important role in localizing mineral and geothermal resources and providing conduits for fluid flow. Based on our modeling, the NNRe is a major crustal feature that extends to at least mid-crustal depths. The 3D geologic model can be used to estimate deep geothermal reservoir geometries, identify the relative importance of fault-controlled versus distributed flow, and determine potential recharge pathways for the Beowawe geothermal system. On a more regional scale, the geophysical modeling of gravity and magnetic data identify and/or constrain the position of buried intrusive bodies, which are important features for hydrologic modeling and exploration for pluton-related ore deposits.
- Timing of sedimentation, metamorphism, and plutonism in the Helgeland Nappe Complex, north-central Norwegian Caledonides
Calvin G. Barnes et al., Department of Geosciences, Texas Tech University, Lubbock, Texas 79409-1053, USA.
- Keywords: geochronology, U-Pb, zircon, Caledonian, Norway
- Starting about 430 million years ago, the continental land masses of Laurentia (North American and Greenland) and Baltica (much of Scandinavia and Finland) began to collide. This "Caledonian" collision was comparable in scale to that of the modern collision of the Indian subcontinent with Asia. This paper presents information relating to the 70 million years of geologic time preceding the collision, and specifically to the geologic events that occurred along the eastern margin of Greenland as the Baltic collider approached. Our results show that one or more small ocean basins lay east of the Greenland margin. These basins opened, were filled with sedimentary deposits, and were then telescoped together along thrust faults during a few million years of time. Deep burial due to thrusting then caused extensive melting of the newly-formed rocks and consequent formation of granitic magmas. A similar sequence of events has been recognized in northern Scotland; our data suggest a close connection between Caledonian rocks of Scotland and those of north-central Norway.
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