An integrated geological and geophysical study of the Uinta Mountains, Utah, Colorado and a geophysical study on Tamarix in the Rio Grande River basin, West Texas.

摘要

This research consists of two parts. One part deals with an integrated analysis of the structural anomaly associated with the Uinta Mountains, Utah. The other part deals with a study on the effect of Tamarix on soil and water quality.;The Uinta Mountains are an anomalous east-west trending range of the Central Rocky Mountains and are located in northeastern Utah and northwestern Colorado. They have long been recognized as a structural anomaly that is surrounded by other Laramide structures that trend N-S or northwest. The study area extends from -112 to -108 degrees longitude and 41.5 to 39 degrees latitude and consists of three major geologic features: The Green River basin, Uinta Mountains, and the Uinta basin. This study investigates the tectonic evolution and the structural development of the Uinta aulacogen. There is a growing interest in exploration for petroleum and other hydrocarbons in the area of this study. Oil companies have been drilling wells in this area since the 1950's. The results of this study will enhance the existing knowledge of this region, and thus will help in the pursuit of hydrocarbons.;A highly integrated approach was followed for this investigation. Gravity, magnetic, drill hole, seismic and receiver function data were used in the analysis. Gravity and magnetic data were analyzed using software tools available in the Department of Geological Sciences such as Oasis Montaj and GIS. Filtered gravity maps show that the Uinta Mountains and the surrounding basins and uplifts are deep seated features. These maps also reveal a correlation between the Uinta Mountains and the regional tectonic structures. This correlation helps in understanding how the different tectonic events that this region went through contributed to the different phases of development of the Uinta aulacogen. Four gravity models were generated along four north-south trending profile lines covering the target area from east to west. Interpretations of these models give a comprehensive picture of the structures in the study area. These models show that the Uinta uplift is a single sedimentary block with numerous thrust faults on the northern and southern flanks of the uplift. These models also reveal the fact that the thickness of the crust is quite variable in the study area. This is also supported by the crustal thickness map constructed for this study from seismic and receiver function information. Magnetic maps show that the Proterozoic sedimentary package known as Uinta Mountain Group extends into the Basin and Range and indicates its link with the ancient rift margin in the Western United States.;Findings of this research are correlated to earlier studies and placed in a broader context. Finally an analogy is made between the Uinta aulacogen, the Southern Oklahoma aulacogen and the Dniepr-Donets aulacogen in Ukraine. This discussion focuses light on the mechanism that led to the Uinta's development from a failed rift to an uplift.;Part two of this research examined the effect of saltcedar (Tamarix sp) on water and soil properties in the Rio Grande River valley in West Texas. Tamarix is a woody phreatophyte (water-loving plant) common in riparian habitats. The presence of Tamarix in a river system raises concerns about its effect on water quality because it can increase the salinity of water and surrounding soil and it reduces stream flow.;Geophysical electrical techniques were used to track soil salinity and moisture changes caused by Tamarix, as well as to determine how soil salinity and moisture properties are altered when Tamarix is eradicated from the region. These techniques allowed more rapid in-situ assessment of the soil properties than the conventional method of removing soil and water samples for analysis.;This study was focused on the influence of Tamarix on soil properties and hydrology at the subsurface at four sites in the Rio Bosque Wetlands Park, El Paso, Texas Two sites had flourishing Tamarix and two others were areas where the Tamarix have either been killed with herbicides or chopped down but their stumps have been left in place. Two soil properties, namely resistivity and ground conductivity, were monitored at the sites for one year on a bi-monthly basis. Ground penetrating radar was used to investigate near surface soil stratigraphy that influences groundwater flow and soil properties. The target was to determine what role Tamarix plays in the seasonal variation of the electrical properties of the soil.;Seasonal variation in resistivity shows that resistivity primarily varies at shallow depth and this variation is more prominent away from the trees. Also this variation was higher at the dead tree site compared to the live tree sites. This suggests the trees act to maintain relatively constant salinity and moisture condition around themselves.