Field guide to lacustrine and related nonmarine depositional environments in tertiary rocks, Uinta Basin, Utah

journal articleThe lower part of the Tertiary System in the Uinta Basin of northeastern Utah and northwestern Colorado (fig. 1) reflects a series of very complex and variable forms of continental sedimentation in a basin of internal drainage. These complex forms represent the disruption of the Cretaceous depositional regime and the initiation of lacustrine sedimentation that began in a freshwater environment, evolved into a more saline regime and returned to a fresher water stage before the lake became extinct in the Tertiary. Figures 2 and 3 illustrate the relation of rock facies, stratigraphic nomenclature, and many of the important stratigraphic marker units of the upper part of the Cretaceous and the lower part of the Tertiary Systems. A complete discussion of the characteristics and evolution of the environments in which the rocks were deposited is presented by Ryder, Fouch, and Elison (1976), and terms used to identify and designate depositional environments are adopted from their work and from Cashion (1967) . Oil, gas, and bitumen-bearing (including "tar sands") siliciclastic and carbonate units are a product of this nonmarine depositional regime as are oil shale and certain saline minerals. In addition, coal is present in rocks of both alluvial and lacustrine origin. Many of the rocks deposited in fresh water contain abundant and diverse mollusk and charophyte assemblages, and palynomorphs and ostracodes are recovered from much of the sequence. J. H. Hanley and R. H. Tschudy of the U.S. Geological Survey identified the mollusk and palynomorph specimens respectively, and contributed insight into paleoenvironmental interpretation

Conservation Models and Ecological Concerns of the Community: A Case-Based Biology Lesson Plan

In this activity, students will design a conservation model that will address the ecological concerns of a community. Students will obtain topographical map of an area and related data; research and analyze appropriate data as to deforestation; survey and select area for removal of trees and landscape according to water flow; and build and produce an ecologically balanced model that will address the concerns of the community. This case will involves the use of botany, environmental science, animal biology, ecology, forestry and mathematics

Understanding the Biodiversity Contributions of Small Protected Areas Presents Many Challenges

Small protected areas dominate some databases and are common features of landscapes, yet their accumulated contributions to biodiversity conservation are not well known. Small areas may contribute to global biodiversity conservation through matrix habitat improvement, connectivity, and preservation of localized ecosystems, but there is relatively little literature regarding this. We review one database showing that the average size of nearly 200,000 protected areas in the United States is ~2000 ha and the median is ~20 ha, and that small areas are by far the most frequent. Overall, 95% and 49% of the records are less than the mean (1648 ha) and median (16 ha), respectively. We show that small areas are prevalent features of landscapes, and review literature suggesting how they should be studied and managed at multiple scales. Applying systematic conservation planning in a spatially hierarchical manner has been suggested by others and could help insure that small, local projects contribute to global goals. However, there are data and financial limitations. While some local groups practice ecosystem management and conservation planning, they will likely continue to protect what is “near and dear” and meet site-based goals unless there is better coordination and sharing of resources by larger organizations

Preliminary results on the characterization of Cretaceous and lower Tertiary low-permeability (tight) gas-bearing rocks in the Wind River Basin, Wyoming

The Wind River Basin is a structural and sedimentary basin in central Wyoming (Figure 1) that was created during the Laramide orogeny from Late Cretaceous through Eocene time. The objectives of the Wind River Basin tight gas sandstone project are to define the limits of the tight gas accumulation in the basin and to estimate in-place and recoverable gas resources. The approximate limits of the tight gas accumulation are defined from available drillhole information. Geologic parameters, which controlled the development of the accumulation, are studied in order to better understand the origins of tight gas accumulations, and to predict the limits of the accumulation in areas where little drillhole information is available. The architecture of sandstone reservoirs are studied in outcrop to predict production characteristics of similar reservoirs within the tight gas accumulation. Core and cuttings are used to determine thermal maturities, quality of source rocks, and diagenetic histories. Our work thus far has concentrated in the Wind River Indian Reservation in the western part of the basin

Tomographic and Depth Phasing Imaging of Mantle Structure beneath the Southern Africa Seismic Array

The Southern Africa Seismic Experiment was designed specifically to image the deep structure of cratonic roots. It is part of a multidisciplinary research project by Carnegie Institution, MIT, southern African academic institutions and industry collaborators to study the structure, composition, and evolution of the cratons and adjacent Proterozoic belts of southern Africa. An array of fifty five portable broadband REFTEK/STS-2 seismic stations was deployed from April, 1997 to July, 1999 along a NNE-SSW transect about 1800 km long by 600 km wide in southern Africa. Approximately half the station were redeployed to new sites in April/May, 1998 for a total of eighty two stations. The PASSCAL telemetered array of 30 REFTEK/STS2 stations was deployed in the region of Kimberley, South Africa, for a period of about 6 months early in 1999. Teleseismic P-wave and S-wave delay times from the broadband array have been analyzed to obtain tomographic images of mantle structure beneath southern Africa to depths in excess of 1000 km. Crustal time delay corrections have been applied to the data based on receiver function and surface wave inversions. Mantle velocities beneath the craton are significantly higher than those beneath the adjacent Proterozoic belts, with shear velocity constrasts disproportionately large. Mantle velocities vary across the craton itself at about the 1 percent level, with the highest velocities found beneath the southern part of the Kaapvaal craton and in the region of the Zimbabwe craton of NE Botswana and SW Zimbabwe. Clear evidence for deep cratonic root structures is observed to at least 200--250 km depth, with the most prominent root structures typically underlying diamondiferous regions. Very preliminary results from depth phasing images of P-S conversions across the PASSCAL broadband telemetered array near Kimberley, indicate a possible velocity reversal at a depth of about 300 km. Tomographic images for greater depths in the mantle indicate a prominent low velocity feature in the mantle below about 700 km, in the general region beneath the Bushveld province and north. The Bushveld province within the Kaapvaal craton is marked by relatively lower velocities in the mantle root. While the velocity contrast with adjacent undisturbed craton is comparatively small, it does correlate also with slightly greater crustal delay times (Nguuri et al., this meeting) and with a zone of null SKS splitting (Gao et al., this meeting). The seismic results coupled with evidence of younger Re/Os model ages of mantle nodules suggests possible cratonic disruption during formation of the Bushveld

Lithospheric Structure beneath Southern Africa: Implications for the Formation and Evolution of Cratons

The southern Africa seismic experiment, a collaboration involving Carnegie Institution, MIT, southern African academic institutions and industry collaborators, has provided detailed information on the tectospheric structure of the southern Africa cratons, and, by inference, on processes of early continental formation. A buoyant and geochemically distinct tectospheric mantle keel beneath the Kaapvaal and Zimbabwe cratons of southern Africa is known from the study of mantle xenoliths to extend to at least 200 km (the maximum depth for xenoliths). P-wave and S-wave tomographic results from the southern Africa array are remarkably consistent with xenolith results and show irregularly shaped high velocity roots extending locally to depths of at least 250-300 km beneath undisturbed parts of the Kalahari craton. Roots are thinner beneath the 2.1 Ga Bushveld terrane and adjacent Proterozoic provinces and are notably less distinct beneath the Proterozoic fold and thrust belt that overlies the Archean of the western Kaapvaal. The Limpopo Belt, an Archean collision zone between the Kaapvaal and Zimbabwe cratons, is characterized by a root structure indistinguishable from that of undisturbed craton. Mantle contacts between Archean terranes and adjacent younger provinces are typically vertical. Crustal thickness in southern Africa is uncorrelated or anticorrelated with elevation. Regions of high elevation within the undisturbed Kalahari craton tend to be characterized by thin crust (35-40 km), whereas the crustal thicknesses beneath the Proterozoic provinces, the Bushveld, and the Limpopo Belt are typically around 45 km. The absence of a correlation between crustal thickness and Bouguer gravity anomaly indicates isostatic balance is achieved by lateral density contrast in the upper mantle and/or in the crust. In regions of undisturbed craton, the Moho is sharp with a clear velocity contrast, whereas it is much more poorly defined in off-craton and disturbed craton regions. The character of the Moho beneath the craton suggests that the process of crustal formation: (1) was highly efficient at separating crust from mantle; and (2) produced a horizontally planar first-order Moho. Such simple Moho structure is typical of cratons, but far less common in younger continental crust. Intermediate crustal discontinuities are rarely observed in the Kalahari craton, indicating little or no layered differentiation of the crust. Models for cratonic formation and processes of cratonic disruption are considered in light of the seismic results obtained from the experiment to date