Boulder, CO, USA – The June issue of GEOSPHERE, published by the Geological Society of America, is now available online. Topics of interest include common ground in the disagreement between mantle plume and lithospheric mantle–lower crust delamination models; a USGS Great Basin Paleontological Database filled with 150 years of fossil data; laser rangefinders versus terrestrial laser scanners and digital cameras in three-dimensional modeling; and contaminant sources of northern Mexico's Rio Conchos, including the effects of human activities.
A plume-triggered delamination origin for the Columbia River Basalt Group
Victor E. Camp, Dept. of Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, California 92182-1020, USA; and Barry B. Hanan.
Continental flood-basalt provinces are the source of a vigorous ongoing debate in the geological sciences. The traditional model to explain these vast outpourings of basaltic lava is to attribute their origin to the rapid melting of large plumes derived from the Earth's deep mantle. The efficacy of this model has been questioned recently by nonplume advocates, many of whom prefer to attach the origin of these provinces to a model of delamination of the Earth's lithospheric mantle and lower crust. The two models, however, are not mutually exclusive. Here, we describe a model of plume-triggered delamination for the origin of the Columbia River Basalt Group, the youngest, best preserved, and mostly intensely studied flood-basalt province on Earth. We demonstrate that such a model satisfies primary constraints on source melting, generating a chronological sequence of melting events consistent with the stratigraphic record of chemical change through time. The tectonic environment of melting is similar to that of recent numerical models that generate a cross-section of surface uplift and deformation that is identical to that in the Columbia River Basalt Group source area of eastern Oregon and adjacent Washington states.
Great Basin Paleontological Database
Ning Zhang et al., GeoInformation Consulting, 2650 NW Roosevelt Drive, Corvallis, Oregon 97330, USA.
This paper summarizes the philosophy and structure behind the recently established Great Basin Paleontological Database, which can be served over the World Wide Web for data entry, queries, displays, and retrievals. The legacy data being entered is derived from internal U.S. Geological Survey fossil reports and publications generated over the past 150 years. Once fully populated, this database should prove to be an invaluable tool for future geologic mapping, paleontological research, inventory of fossils on public lands, and mineral and oil exploration in the Great Basin.
Laser rangefinders and ArcGIS combined with three-dimensional photorealistic modeling for mapping outcrops in the Slick Hills, Oklahoma
Mohammed Alfarhan et al., Center for Lithospheric Studies, Dept. of Geosciences, University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080-3021, USA.
For detailed mapping of geologic outcrop features such as contacts and terrain, especially on steep slopes and cliffs, it is effective to map digitally and obliquely at relatively close range using handheld reflectorless laser rangefinders ("guns"). The module three-dimensional laser tool (3DLT) has been written to combine the ESRI ArcGIS module ArcMap using Visual Basic application language and the ArcObjects components in order to provide a simple, yet sophisticated platform for mapping, visualizing, and analyzing outcrops with a field computer. It integrates a relatively inexpensive laser rangefinder and any type of global positioning system (GPS) and assigns attributes defined by the user or from an extensive geologic dictionary. It uniquely allows for real-time display and analysis in 3-D space as points, lines, and polygons (and therefore strikes, dips, etc.)—the 3-D model of the geology. This is applied in Slick Hills, Oklahoma, USA, comparing and integrating it with conventional mapping. Another approach that captures an entire exposure, 3-D photorealistic modeling derived from terrestrial laser scanners and digital cameras, is also applied for comparison and contrast. The scanner approach captures the entire exposure, but this is demonstrated to be an expensive and complicated process. The laser "gun" approach, particularly when using 3DLT, has distinct advantages in cost, ease of use, speed, logistics, and real-time analysis, with competitive accuracy, and it is at least complementary to other methods.
Visualization of folding in marble outcrops, Connemara, western Ireland: An application of virtual outcrop technology
K.J.W. McCaffrey et al., Earth Sciences Dept., Durham University, Durham, DH1 3LE, UK.
In this paper, McCaffrey et al. discuss the use of laser scanning (LiDAR) and three-dimensional visualization technologies to produce virtual outcrops for student instruction purposes. We present two case studies in which students used virtual outcrop datasets to gain an understanding of marble outcrops in Connemara, western Ireland. Our work suggests that these methods have the potential to become a valuable aid to student learning.
Geochemical processes contributing to the contamination of soil and surface waters in the Rio Conchos basin, Mexico
Mélida Gutiérrez et al., Geography, Geology and Planning, Missouri State University, Springfield, Missouri 65897, USA.
The spatial distribution of geochemical sediment data (540 sampling sites) was analyzed to identify possible contaminant sources of the Rio Conchos in northern Mexico. The study focused on the two contaminants posing the largest threat to water quality: salts and toxic metalloids. The results show their most likely sources and their association with local geology and hydrology within the basin, and provide background levels that are needed to predict the effects human activities, such as urbanization and the disposal of wastes and irrigation drain returns, may have on the river.
Revisiting silicate authigenesis in the Pliocene–Pleistocene Lake Tecopa beds, southeastern California: Depositional and hydrological controls
Daniel Larsen, Dept. of Earth Sciences, University of Memphis, Memphis, Tennessee 38152, USA.
The Pliocene-Pleistocene Lake Tecopa beds have long been identified as a type-example of the concentric distribution of low-temperature sedimentary minerals, such as zeolites and feldspars, that are believed to have formed in and help identify ancient saline, alkaline lake deposits. In the present study, the sedimentary and hydrologic process controls on the formation of these low-temperature mineral zones are investigated through detailed mineral and sedimentology studies, as well as conceptual hydrologic modeling. The results indicate that ancient lake-level or, more specifically, lake-surface area and sediment composition are the most important controls on the type of sedimentary mineral formed along the lake basin margin. However, sediment grain-size and vertical migration of salty brines control the sedimentary mineral formation in the center of the basin. These results provide some guidance as well as caution to interpretation of paleohydrology and paleoclimate of ancient lake beds based on cores from the center of saline, alkaline lake basins.
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Journal
Geosphere