Geology topics

B.B. Hanshaw

Publications and source records attributed to B.B. Hanshaw.

23 records · Page 2Linked to original sources

USGS1969

Geochemistry and hydrodynamics of the Paradox Basin region, Utah, Colorado and New Mexico

The Paradox Basin region is approximately bounded by the south flank of the Uinta Basin to the north, the Uncompahgre uplift and San Juan Mountains to the east, the Four Corners structural platform to the southeast, the north rim of the Black Mesa Basin and the Grand Canyon to the south and southwest, and the Wasatch Plateau and Hurricane fault system to the west. Some of these geologic features are areas of ground-water recharge or discharge whereas others such as the Four Corners platform do not directly influence fluid movement. The aquifer systems studied were: (1) Mississippian rocks; (2) Pinkerton Trail Limestone of Wengerd and Strickland, 1954; (3) Paradox Member of the Hermosa Formation; (4) Honaker Trail Formation of Wengerd and Matheny, 1958; (5) Permian rocks. Recharge in the Paradox Basin occurs on the west flank of the San Juan Mountains and along the west side of the Uncompahgre uplift. The direction of ground-water movement in each analyzed unit is principally southwest-ward toward the topographically low outcrop areas along the Colorado River in Arizona. However, at any point in the basin, flow may be in some other direction owing to the influence of intrabasin recharge areas or local obstructions to flow, such as faults or dikes. A series of potentiometric surface maps was prepared for the five systems studied. Material used in construction of the maps included outcrop altitudes of springs and streams, drill-stem tests, water-well records, and an electric analog model of the entire basin. Many structurally and topographically high areas within the basin are above the regional potentiometric surface; recharge in these areas will drain rapidly off the high areas and adjust to the regional water level. With a few exceptions, most wells in formations above the Pennsylvanian contain fresh (< 1,000 mg/l T.D.S. 2 ) to moderately saline (< 10,000 mg/l T.D.S.) water. In only a few cases are true brines (> 35,000 mg/l T.D.S.) reported. Most water samples from strata below the Permian are brines of the sodium chloride type but with large amounts of calcium sulfate or calcium chloride type water commonly occurring. Because evaporite facies occur in the Paradox Member, this unit has brines with as much as 400,000 mg/l dissolved solids content. Previous analysis of the San Juan Basin has indicated the presence of an osmotic membrane system. The highly permeable Jurassic formations were postulated to be the outflow side of the membrane. It is also possible that the Upper Paleozoic units with known brines and with an otherwise inexplicably high potentiometric surface in the Four Corners area of New Mexico could be the outflow receptors of the San Juan membrane system.

Colorado, New Mexico, Utah↗

USGS1968

On the maintenance of anomalous fluid pressures: I. thick sedimentary sequences

Various physical and chemical processes may be envisioned which will cause anomalous pressures on an underground fluid. In order to consider the maintenance of anomalous pressure, it is necessary to consider the problem as one of nonsteady fluid flow. The time rate of pressure change and maintenance depends upon the hydrodynamics of flow through porous media and the particular boundary conditions. This paper presents a series of general solutions to hydrodynamic models which are germane to the problem of creating and maintaining excess-fluid pressures in a thick sedimentary sequence. The creation and maintenance of fluid pressures approaching lithostatic pressure through a process of continuous sedimentation was evaluated. Our results indicate that a sedimentation rate of 500 m/10 6 yr (reasonable for the Gulf Coast) will create fluid pressures approaching lithostatic in a sedimentary column that has a hydraulic conductivity of 10 -8 cm sec -1 , or lower. It is apparent that the creation of anomalous pressure and its maintenance depends, to a large degree, upon the hydraulic conductivity and, to a lesser extent, upon the specific storage of clay layers within the system. © 1968, The Geological Society of America, Inc.

Geological Society of America Bulletin↗

USGS1968

On the maintenance of anomalous fluid pressures: II. Source layer at depth

Physico-chemical mechanisms have been suggested to account for anomalous fluid pressures in the geologic environment which require a fluid source at depth. The persistence of anomalous pressure is a problem that involves nonsteady fluid flow. The hydrodynamics and particular boundary conditions control the time rate of pressure change and its maintenance. A series of mathematical solutions germane to the maintenance of anomalous pressure caused by the injection of fluids into the system from a source layer are presented. The phase change, gypsum to anhydrite plus water, is used as an example of a fluid source at depth. The thermodynamics of the gypsum-dehydration reaction indicates that conversion will probably occur at shallow depths and produce fluid at a constant rate. The dehydration of montmorillonite will also produce fluids at a constant rate under geologic conditions where the reaction can occur. If horizons of material of low permeability are missing or scarce, it is doubtful that anomalous pore pressures can be maintained for more than a geologic instant. The creation and continuation of anomalous pressure depend largely upon the hydraulic conductivity and, to a lesser extent, upon the specific storage of clay layers within the system. © 1968, The Geological Society of America, Inc.

Geological Society of America Bulletin↗

USGS1965

Radiocarbon determinations for estimating groundwater flow velocities in central Florida

Carbon-14 activity was determined from HCO 3 - in samples of groundwater obtained from the principal artesian aquifer in Florida. From these data the "age" of water obtained from a series of wells, each progressively farther down gradient on the piezometric surface, was established. Relative carbon-14 ages indicated a velocity of groundwater movement of 23 feet (7 meters) per year for about 85 miles (137 kilometers) of travel. A velocity of 23 feet per year was calculated independently from Darcy's law.

Florida↗

USGS1965

Osmotic equilibrium and overthrust faulting

The two principal suggested modes of facilitating overthrust faulting are (1) lubrication at the sole by evaporite beds or micaceous shales and (2) flotation due to anomalously high (> hydrostatic) pore-water pressures. Past rapid sedimentation and tectonic compression have been suggested as important causes of anomalously high water pressure (Hubbert and Rubey, 1959). We suggest osmosis as another important possibility. Field data on shale beds and experimental studies on compacted clays show that such material can act as semipermeable membranes that greatly retard passage of dissolved electrolytes relative to H 2 O. Equilibrium osmotic pressure, π, across an ideal membrane is given by (a, activity; V H2O 0 1 , molar volume of distilled water). At 80°C, π is 470 bars between saturated halite solution and distilled water; it is 360 bars between saturated and 10 per cent solutions. At 25°C the values are 20 per cent lower. Other dissolved components, if present in similar proportions, will enhance the effect. Anomalous water pressures of at least 400 bars above hydrostatic have been measured in oil wells; many of these wells penetrate evaporites and/or shales which separate formation waters of differing salt concentrations. These pressures are explicable by assuming osmotic equilibrium across a membrane which separates saturated halite solution from solutions up to 10 weight per cent NaCl. Thus, osmotic equilibrium may be an important mechanism for floating thrust sheets. Lubrication of thrust sheets by shales or evaporites and flotation by anomalously high pressures may be simply different manifestations of the same geologic milieu. © 1965, The Geological Society of America, Inc.

Geological Society of America Bulletin↗