John M. Sharp, Jr. - Academia.edu (original) (raw)

Papers by John M. Sharp, Jr.

Ground Water, 2008

This research integrates data procedures for the delineation of regional ground water flow system... more This research integrates data procedures for the delineation of regional ground water flow systems in arid karstic basins with sparse hydrogeologic data using surface topography data, geologic mapping, permeability data, chloride concentrations of ground water and precipitation, and measured discharge data. This integrative data analysis framework can be applied to evaluate arid karstic aquifer systems globally. The accurate delineation of ground water recharge areas in developing aquifer systems with sparse hydrogeologic data is essential for their effective long-term development and management. We illustrate the use of this approach in the Cuatrociénegas Basin (CCB) of Mexico. Aquifers are characterized using geographic information systems for ground water catchment delineation, an analytical model for interbasin flow evaluation, a chloride balance approach for recharge estimation, and a water budget for mapping contributing catchments over a large region. The test study area includes the CCB of Coahuila, Mexico, a UNESCO World Biosphere Reserve containing more than 500 springs that support ground water-dependent ecosystems with more than 70 endemic organisms and irrigated agriculture. We define recharge areas that contribute local and regional ground water discharge to springs and the regional flow system. Results show that the regional aquifer system follows a topographic gradient that during past pluvial periods may have linked the Río Nazas and the Río Aguanaval of the Sierra Madre Occidental to the Río Grande via the CCB and other large, currently dry, upgradient lakes.

$Research paper thumbnail of Three-dimensional measurement of fractures in heterogeneous materials using high-resolution X-ray computed tomography$

Geosphere

When present, fractures tend to dominate fl uid fl ow though rock bodies, and characterizing frac... more When present, fractures tend to dominate fl uid fl ow though rock bodies, and characterizing fracture networks is necessary for understanding these fl ow regimes. X-ray computed tomography (CT) has long been successfully used to image fractures in solid samples, but interpretation of CT data is complicated by the inevitable blurring that occurs when fractures are thin compared to the data resolution. This issue is particularly acute when attempting to quantify fi ne fractures in scans of larger samples, as typically required for characterizing fl ow systems on a meaningful scale. A number of methods have been proposed to account for CT blurring, but do not include the ability to account for material inhomogeneity and fracture orientation. We here propose an improved method for fracture measurement that consists of characterizing the blurring as a point-spread function (PSF), and using it, in combination with a calibration for the CT number for void space, in an iterative procedure to reconstruct the fracture and material confi guration; we call this the inverse PSF (IPSF) method. Tests on CT scans of homogeneous natural samples show that the IPSF method provides more precise results than others. Further testing demonstrates that it can also recover accurate measurements in heterogeneous materials, although particularly severe inhomogeneities may lead to a locally noisy signal. The accuracy, generality, and adaptability of the IPSF method make it very well suited for characterizing fractures and fractures surfaces in natural materials. The principles behind the IPSF method also apply to the reverse problem of measuring thin features that are denser than their surroundings, such as veins or membranes, when they have one dimension that is small compared to CT data resolution.

Journal of Hydrology, 1979

AAPG Bulletin, 2012

ABSTRACT Our hydrogeologic model tests the effectiveness of brine reflux as the mechanism for ear... more ABSTRACT Our hydrogeologic model tests the effectiveness of brine reflux as the mechanism for early dolomitization of the Permian San Andres Formation. Brine circulation is constrained by sequence-stratigraphic parameters and a heterogeneous distribution of petrophysical properties based on outcrop data. The model simulates accumulation of the San Andres platform and calculates fluid flow and solute transport in response to relative sea level fluctuations. It tracks porosity loss caused by compaction and the concomitant permeability feedback. The amount of dolomite potentially formed is calculated by means of a magnesium mass balance between brine and rock. Results show that (1) brine reflux is an effective mechanism to deliver magnesium to dolomitize large carbonate successions; (2) relative sea levelcontrolled transient boundary conditions result in intricate flow and salinity patterns that can generate irregular dolomite bodies with complex spatial distributions; (3) pervasive dolomitization can result from several short-lived reflux events by the amalgamation of brine plumes sourced in different locations and times; and (4) the model successfully recreates the dolostone and limestone patterns observed in San Andres outcrops.

Journal of Hydrology, 1977