USGS Science⌕ Search

Geology topics

M.W. Bultman

Publications and source records attributed to M.W. Bultman.

6 recordsLinked to original sources
USGS2011

Transient electromagnetic study of basin fill sediments in the Upper San Pedro Basin, Mexico

The Upper San Pedro River Basin in Mexico and the United States is an important riparian corridor that is coming under increasing pressure from growing populations and the associated increase in groundwater withdrawal. Several studies have produced three-dimensional maps of the basin fill sediments in the US portion of the basin but little work has been done in the Mexican portion of the basin. Here, the results of a ground-based transient electromagnetic (TEM) survey in the Upper San Pedro Basin, Mexico are presented. These basin fill sediments are characterized by a 10–40 m deep unsaturated surficial zone which is composed primarily of sands and gravels. In the central portion of the basin this unsaturated zone is usually underlain by a shallow clay layer 20–50 m thick. Beneath this may be more clay, as is usually the case near the San Pedro River, or interbedded sand, silt, and clay to a depth of 200–250 m. As you move away from the river, the upper clay layer disappears and the amount of sand in the sediments increases. At 1–2 km away from the river, sands can occupy up to 50% of the upper 200–250 m of the sediment fill. Below this, clays are always present except where bedrock highs are observed. This lower clay layer begins at a depth of about 200 m in the central portion of the basin (250 m or more at distances greater than 1–2 km from the river) and extends to the bottom of most profiles to depths of 400 m. While the depth of the top of this lower clay layer is probably accurate, its thickness observed in the models may be overestimated due to the relatively low magnetic moment of the TEM system used in this study. The inversion routine used for interpretation is based on a one-dimensional geologic model. This is a layer based model that is isotropic in both the x and y directions. Several survey soundings did not meet this requirement which invalidates the inversion process and the resulting interpretation at these locations. The results from these locations were rejected.

Arizona↗
USGS2007

Coccidioides niches and habitat parameters in the southwestern United States: A matter of scale

To determine habitat attributes and processes suitable for the growth of Coccidioides, soils were collected from sites in Arizona, California, and Utah where Coccidioides is known to have been present. Humans or animals or both have been infected by Coccidioides at all of the sites. Soil variables considered in the upper 20 cm of the soil profile included pH, electrical conductivity, salinity, selected anions, texture, mineralogy, vegetation types and density, and the overall geomorphologic and ecological settings. Thermometerswere buried to determine the temperature range in the upper part of the soil where Coccidioides is often found. With the exception of temperature regimes and soil textures, it is striking that none of the other variables or group of variables that might be definitive are indicative of the presence of Coccidioides. Vegetation ranges from sparse to relatively thick cover in lower Sonoran deserts, Chaparral-upper Sonoran brush and grasslands, and Mediterranean savannas and forested foothills. No particular grass, shrub, or forb is definitive. Material classified as very fine sand and silt is abundant in all of the Coccidioides-bearing soils and may be their most common shared feature. Clays are not abundant (less than 10%). All of the examined soil locations are noteworthy as generally 50% of the individuals who were exposed to the dust or were excavating dirt at the sites were infected. Coccidioides has persisted in the soil at a site in Dinosaur National Monument, Utah for 37 years and at a Tucson, Arizona site for 41 years. ?? 2007 New York Academy of Sciences.

Conference Paper↗
USGS2004

A Complex Systems Model Approach to Quantified Mineral Resource Appraisal

For federal and state land management agencies, mineral resource appraisal has evolved from value-based to outcome-based procedures wherein the consequences of resource development are compared with those of other management options. Complex systems modeling is proposed as a general framework in which to build models that can evaluate outcomes. Three frequently used methods of mineral resource appraisal (subjective probabilistic estimates, weights of evidence modeling, and fuzzy logic modeling) are discussed to obtain insight into methods of incorporating complexity into mineral resource appraisal models. Fuzzy logic and weights of evidence are most easily utilized in complex systems models. A fundamental product of new appraisals is the production of reusable, accessible databases and methodologies so that appraisals can easily be repeated with new or refined data. The data are representations of complex systems and must be so regarded if all of their information content is to be utilized. The proposed generalized model framework is applicable to mineral assessment and other geoscience problems. We begin with a (fuzzy) cognitive map using (+1,0,-1) values for the links and evaluate the map for various scenarios to obtain a ranking of the importance of various links. Fieldwork and modeling studies identify important links and help identify unanticipated links. Next, the links are given membership functions in accordance with the data. Finally, processes are associated with the links; ideally, the controlling physical and chemical events and equations are found for each link. After calibration and testing, this complex systems model is used for predictions under various scenarios.

Environmental Management↗
USGS1999

Field trip guide to selected studies of the Southwest Mineral and Environmental Investigations Project in southeastern Arizona

The Southwest Mineral and Environmental Investigations Project is designed to address issues raised by rapid urban development in the basins of the southwestern U.S. These issues require objective geoscientific data that can be used by land managers and stakeholders to develop informed land and water use strategies. The project integrates new and existing geologic, geophysical, and geochemical data, and imagery to provide three-dimensional visualizations of the basins of southeastern Arizona. Emphasis is on developing better knowledge of the aquifer systems of both the basins and the ranges, on acquiring background and baseline information, and on determining the distribution of metals related to mineralization and the fate of these metals in surface and subsurface environments. The products of the project will be used in resolving issues of water quality and quantity, in understanding environmental impacts such as riparian ecosystem maintenace, and in evaluating mineral resources beneath and within the basins. The field trip highlights three topics and areas (figs. 1 and 2): (1) geology and geophysics of the upper San Pedro and upper Santa Cruz basins (M.E. Gettings, M. W. Bultman, and B.B. Houser), (2) geology, geophysics, and mineral resource potential of the San Rafael basin (M.W. Bultman), and (3) hydrology and aqueous geochemistry of the Red Mountain and Sonoita Creek drainage system (Floyd Gray). The trip guide, which begins and ends in Tucson, Arizona, also includes commentary on the cultural and mining history of the area.

Arizona↗
USGS1999

An interpretation of the 1997 airborne electromagnetic (AEM) survey, Fort Huachuca vicinity, Cochise County, Arizona

Executive Summary -- In March of 1997, an airborne electromagnetic (AEM) survey of the Fort Huachuca Military Reservation and immediate surrounds (location map, http://geopubs.wr.usgs.gov/open-file/of99-007-b/index.jpg) was conducted. This survey was sponsored by the U.S. Army and contracted through the Geologic Division of the U.S. Geological Survey (USGS). Data were gathered by Geoterrex-Dighem Ltd. of Ottawa, Canada. The survey aircraft is surrounded by a coil through which a large current pulse is passed. This pulse induces currents in the Earth which are recorded by a set of three mutually perpendicular coils towed in a 'bird' about 100 m behind and below the aircraft. The bird also records the Earth's magnetic field. The system samples the Earth response to the electromagnetic pulse about every 16 m along the aircraft flight path. For this survey, the bulk of the flightpaths were spaced about 400 m apart and oriented in a northeast-southwest direction extending from bedrock over the Huachuca Mountains to bedrock over the Tombstone Hills. A preliminary report on the unprocessed data collected in the field was delivered to the U.S. Army by USGS in July 1997 (USGS Open-File Report 97?457). The final data were delivered in March, 1998 by the contractor to USGS and thence to the U.S. Army. The present report represents the final interpretive report from USGS. The objectives of the survey were to: 1) define the structure of the San Pedro basin in the Sierra Vista-Fort Huachuca-Huachuca City area, including the depth and shape of the basin, and to delineate large faults that may be active within the basin fill and therefore important in the hydrologic regime; 2) define near surface and subsurface areas that contain a large volume fraction of silt and clay in the basin fill and which both reduce the volume of available storage for water and reduce the permeability of the aquifer; and 3) to evaluate the use of the time domain electromagnetic method in the southwest desert setting as a means of mapping depth to water. Chapter one, written by M.E. Gettings, reports the results of the analysis of the aeromagnetic anomaly data. Depths to magnetic rocks computed from these data are in good agreement with depths from gravity anomaly models (Gettings and Houser, in prep.) and confirm and refine the location of the bedrock highs which reach to within 200 m of the surface in several parts of the study area. The highly faulted and generally shallow character of the basin within the study area deduced from the gravity studies is also evident in the aeromagnetic data. The caldera ring fault delimiting the buried structural southwest edge of the Tombstone caldera is expressed in the magnetic data and deeper intrusives extending outside the caldera to the southwest are inferred. Several magnetic bodies occur at shallow depths within the Precambrian granite of the Huachuca Mountains along the eastern foothills of the mountains. These are inferred to be Tertiary intrusives but remain to be confirmed by field work if any of their uppermost dikes or apotheses are exposed. Faults delineating the east-west trending bedrock high beneath the city of Sierra Vista appear to be shallow and should be investigated for surface expressions. Chapter two, written by Jeff Wynn, analyzes and interprets the conductivity depth transforms (CDTs) and provides a general evaluation of the data quality. He concludes that there is a good general correlation between the uppermost conductor seen in the CDTs and water table depth in many cases. Detailed comparisons between the ground-based vertical electric soundings (VES) and the CDTs are reported in this chapter. The two sets of data compare well in general for most sounding sites where the VES data are not noisy.

Arizona↗