Jay A. Raney

Mud volcanoes of the Orinoco Delta, Eastern Venezuela

Abstract Mud volcanoes along the northwest margin of the Orinoco Delta are part of a regional belt of soft sediment deformation and diapirism that formed in response to rapid foredeep sedimentation and subsequent tectonic compression along the Caribbean–South American plate boundary. Field studies of five mud volcanoes show that such structures consist of a central mound covered by active and inactive vents. Inactive vents and mud flows are densely vegetated, whereas active vents are sparsely vegetated. Four out of the five mud volcanoes studied are currently active. Orinoco mud flows consist of mud and clayey silt matrix surrounding lithic clasts of varying composition. Preliminary analysis suggests that the mud volcano sediment is derived from underlying Miocene and Pliocene strata. Hydrocarbon seeps are associated with several of the active mud volcanoes. Orinoco mud volcanoes overlie the crest of a mud-diapir-cored anticline located along the axis of the Eastern Venezuelan Basin. Faulting along the flank of the Pedernales mud volcano suggests that fluidized sediment and hydrocarbons migrate to the surface along faults produced by tensional stresses along the crest of the anticline. Orinoco mud volcanoes highlight the proximity of this major delta to an active plate margin and the importance of tectonic influences on its development. Evaluation of the Orinoco Delta mud volcanoes and those elsewhere indicates that these features are important indicators of compressional tectonism along deformation fronts of plate margins.

Native woodland loss during the mid 1900s in Cameron county, Texas

Abstract Large-scale native woodland loss in the Lower Rio Grande Valley of Texas during the 20th century has been reported in the literature. However, no detailed, quantitative study of landscape change in the area has been conducted. This paper presents an example of quantified native woodland loss within this area. Using historical topographic maps and aerial photographs, we were able to map the extent of native woodland areas in Cameron County in the 1930s. The historical native woodland areas were then compared with the 1983 extent of native woodlands as mapped on modern topographic quadrangles. Our results for Cameron County corroborate previous estimates of native woodlands loss in the Lower Rio Grande Valley, though at a slightly lower percentage (91%). Comparisons with recent land-use and land-cover mapping show that much of the loss was a result of agricultural expansion.

Experimental Study of Faulting in an Anisotropic, Inhomogeneous Dolomitic Limestone

Eighty-nine tests were run on cores of laminated dolomitic limestone from the Manlius Formation (Devonian, eastern New York) at confining pressures of 1, 200, 300, 400, 500, 600 and 800 bars, and with the angle between laminae and maximum principal stress varying from 0° to 90°. Percentage of dolomite varies markedly both between specimens and within a single specimen. Results indicate that faults will form parallel to laminae at inclinations of laminae to maximum principal stress between about 13 ° and about 51 ° , and that the laminae exert some control over fault orientation well beyond this range. Within the range tested, confining pressure does not suppress or enhance the ability of the laminae to control fault orientation. At 800 bars, the behavior of the rock is changing, with development of ductile faults or significant ductile flow. Compressive strength depends primarily on confining pressure and orientation of the laminae, but also varies significantly with Young9s modulus. The data are consistent with the Coulomb-Navier criterion of brittle fracture, assuming lower values for internal friction and cohesion parallel to the laminae than in all other directions. Observed and calculated compressive strengths agree more closely if the Young9s moduli of the specimens are taken into consideration. The significant effect of the irregular and discontinuous laminae in the test material on rock strength and fault orientation suggests caution in assuming the usual 30 ° angle between maximum principal stress and faults when conducting fracture analysis in areas of anisotropic, inhomogeneous rocks (a description that fits most sedimentary rocks).

Analysis of EO-1 ALI data to determine local impacts of Hurricane Iris on broadleaf forests in Belize, Central America

Hurricane Iris, a Category Four hurricane on the Saffir-Simpson hurricane scale with winds exceeding 200 kph, made landfall in southern Belize, Central America, on October 8, 2001. Extensive wind damage occurred, including toppled and defoliated trees, and major losses to the local banana industry. Among the regions impacted by the storm was the Monkey River area located approximately 130 km south of Belize City. Imagery acquired on December 4, 2001, from NASAs Earth Observing-1 (EO-1) Advanced Land Imager (ALI) was used to analyze impacts on land cover/land use with emphasis on broadleaf forests. Comparisons were made with pre-hurricane Landsat TM data, in which 14 land cover/land use classes, including 6 classes of forests and savannah, 5 classes of wetlands and coastal lands, and 3 classes of developed land were classified.

Preliminary evaluation of NASA EO-1 imagery through an analysis of land cover/land use in Belize, Central America

This project, funded through NASAs Earth Observing-1 (EO-1) program, is a 2-year investigation to evaluate EO-1 ALI and Hyperion in Belize, Central America. The Bureau of Economic Geology and Center for Space Research are evaluating the newly acquired data in cooperation with the Government of Belize.

Neotectonic history and geometric segmentation of the Campo Grande fault: A major structure bounding the Hueco basin, trans-Pecos Texas

The northwest-striking Campo Grande fault of trans-Pecos Texas has a surface trace of about 45km. It divides the downthrown, central part of the Hueco basin, which contains as much as 2850m of Cenozoic fill, from the shallower northeastern flank that has 150-300m of fill. This normal fault is composed of three main en echelon segments, which are composed of numerous en echelon fault strands that are 1.5-10 km long at the surface. These strands strike N25°-75°W and dip 60°-90° southwestward. Erosion-resistant calcrete (stage IV-V) at the surface aids in preserving scarp heights of between 1.5 and 11.5m and scarp slopes of between 4° and 17°. Surface analysis of faulted upper Tertiary and Quaternary units along the southeastern Campo Grande fault segment indicates that successively younger units have less displacement. The last surface rupture was late Pleistocene. On the hanging wall of one fault strand, faulted calcic soil horizons (stage III) as much as 1m thick with vertical separations of 1-2 m indicate at least five episodes of fault movement, sediment deposition, and surface stabilization since middle Pleistocene time. The maximum vertical offset during the latest surface rupture was about 1-1.5m.