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Geology topics

B.B. Hanshaw

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

At least 19 recordsLinked to original sources
USGS2010

Relation of carbon 14 concentrations to saline water contamination of coastal aquifers

Naturally occurring stable or radioactive isotopes may be used in some places to identify the origin of saline water that contaminates some coastal aquifers. In a recent study to determine the origin of saline water in the Ocala Limestone aquifer near Brunswick, Georgia, the following sources were analyzed for C 14 and deuterium concentrations: potable water from the Ocala Limestone, contaminated water from the Ocala Limestone, saune water from the underlying Claiborne Group, and nearby ocean water. The chloride concentration of the groundwater ranges from about 25 ppm in the potable water to more than 2000 ppm in the deeper part of the Claiborne Group. From an interpretation of piezometric maps and other hydrologic data, previous investigators had concluded that the source of the contaminating water was the Claiborne Group and not the nearby ocean. The essentially uniform range of low values of −965 to −987‰ of the modern standard (National Bureau Standard C 14 oxalic acid) for the C 14 activity of the groundwater samples (regardless of the degree of contamination) is in agreement with this conclusion. If recent ocean water, which had a C 14 value of +285‰, were the source of contamination, the contaminated water would have had a C 14 activity higher than the activity of the fresh water. Deuterium analyses are not inconsistent with the interpretation that water from the Claiborne Group, rather than recent ocean water, is the source of the contaminating water. The concurrence of the hydrologic and the isotopic data in this area where the hydrology is well known suggests that isotopic analysis may be used to identify the origin of water in different portions of a hydrologic environment.

Georgia↗
USGS2010

Geochemical Modeling of the Madison Aquifer in Parts of Montana, Wyoming, and South Dakota

Stable isotope data for dissolved carbonate, sulfate, and sulfide are combined with water composition data to construct geochemical reaction models along eight flow paths in the Madison aquifer in parts of Wyoming, Montana, and South Dakota. The sulfur isotope data are treated as an isotope dilution problem, whereas the carbon isotope data are treated as Rayleigh distillations. All reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the Madison Limestone. The geochemical reaction models indicate that the dominant groundwater reaction in the Madison aquifer is dedolomitization (calcite precipitation and dolomite dissolution driven by anhydrite dissolution). Sulfate reduction, [Ca 2+ + Mg 2+ ]/Na + cation exchange, and halite dissolution are locally important, particularly in central Montana. The groundwater system is treated as closed to CO 2 gas from external sources such as the soil zone or cross‐formational leakage but open to CO 2 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer. The computed mineral mass transfers and modeled sulfur isotopic composition of Madison anhydrites are mapped throughout the study area. Carbon 14 groundwater ages, adjusted for the modeled carbon mass transfer, range from modern to about 23,000 years B.P. and indicate flow velocities of 7–87 ft/yr (2.1–26.5 m/yr). Most horizontal hydraulic conductivities calculated from Darcy's Law using the average 14 C flow velocities are within a factor of 5 of those based on digital simulation. The calculated mineral mass transfer and adjusted 14 C groundwater ages permit determination of apparent rates of reaction in the aquifer. The apparent rate of organic matter oxidation is typically 0.12 μmol/L/yr. Sulfate and, to a lesser extent, ferric iron are the predominant electron acceptors. The (kinetic) biochemical fractionation of 34 S between sulfate and hydrogen sulfide is approximately −44‰ at 25°C, with a temperature variation of −0.4‰ per °C. The rates of precipitation of calcite and dissolution of dolomite and anhydrite typically are 0.59, 0.24, and 0.95 μmol/L/yr, respectively. This paper is not subject to U.S. copyright. Published in 1990 by the American Geophysical Union.

Montana, Wyoming, South Dakota↗
USGS2009

Deciphering hydrological systems by means of geochemical processes

Interpretation of geochemical reactions and isotopic composition of groundwater provides a method to determine hydrological parameters such as porosity, hydraulic conductivity, and groundwater flow rates. This geochemical method is largely independent of the more conventional approach of determining these parameters by an evaluation of physical properties of aquifer systems. -from Authors

Hydrological Sciences Journal↗
USGS1987

Hydrogeological concepts in the United States: a historical perspective.

Reviews the development of hydrogeological concepts in the USA from 1879 to 1987, from early qualitative reconnaissance investigations to modern qualitative and multi-disciplinary studies involving predictive analytical techniques and a consideration of management practices. The authors present a sampling of historical milestone papers in US hydrology in the form of an annotated bibliography.-Authors

Episodes↗
USGS1986

Geochemical evaluation of the geothermal resources in the San Marcos region, Guatemala

The chemical and isotopic compositions of hot springs in the San Marcos region of Guatemala are internally consistent with a hydrologic model in which a deep 240°C reservoir and one or more shallow 195–200°C reservoirs are present. Variations in hot-spring water compositions results from a combination of boiling, mixing with cold, dilute water, and chemical re-equilibration with decreasing temperature. The recharge water for the deep 240°C reservoir is isotopically heavier than the local meteoric water and probably comes from many kilometers to the west or southwest. The water in the shallow reservoir is a mixture of the 240°C water with about 20 ± 5% of cold, locally derived meteoric water. After mixing, the water in the shallow reservoir re-equilibrates with reservoir rock at 195–200°C. In some places additional mixing with cold water occurs after water leaves the shallow reservoir.

San Marcos region↗
USGS1982

Regional ground-water flow concepts in the United States: Historical perspective

A number of important ideas, developed during the past 100 years, form the framework of the present understanding of regional ground-water flow. The most important of these ideas are: Differences in topographic elevation provide the principal driving force for regional flow. Flow through confining layers forms an essential element of regional flow systems. Chemical evolution within the flow systems can be used to understand the flow. Moving ground water is an efficient transport mechanism for heat within the Earth. We trace the evolution of these ideas in the United States and demonstrate their influence on the present-day understanding of flow systems with examples taken primarily from the American literature.

Special Paper of the Geological Society of America↗
USGS1980

Chemical mass-wasting of the northern Yucatan Peninsula by groundwater dissolution

The northern part of the Yucatan Peninsula is a relatively flat, low-lying carbonate terrane with no geomorphic expressions of stream channels. It is estimated that mean annual recharge to the groundwater system is 150 mm. For the 65,500 km 2 study area, mean annual discharge (equivalent to recharge) is 9.8 × 10 9 m 3 , or 8.6 × 10 6 m 3 for each 1 km of the 1,100-km-long coastline. In the interior of the peninsula, the recharging water annually dissolves about 37.5 t (metric tons) of calcite per 1 km 2 . When the groundwater has become saturated with calcite, little additional water-rock interaction occurs until the active mixing (dispersion) zone is reached near the coastline. Theoretical calculations and laboratory experiments have shown that when two waters, each calcite saturated and with different salinities, are mixed, the resulting solution generally becomes undersaturated with calcite and, therefore, is capable of dissolving additional calcite. On the basis of our study of the Xel Ha lagoon on the east coast of Yucatan, we calculate that as much as 1.2 mmol/L additional calcite can be dissolved in the brackish groundwater zone of dispersion. This indicates that if the total solution potential of the amount of water discharging at Xel Ha has focused within the lagoon area, the lagoon could be chemically incised in less than 3,000 yr. We postulate that chemical mass wasting by dissolution in the zone of groundwater mixing is an important geomorphic process in coastal areas of limestone terranes.

Yucatan Peninsula↗
USGS1978

Oxygen isotope composition of subglacially precipitated calcite: Possible paleoclimatic implications

Isotopic analyses of subglacially precipitated calcite from near a modern temperate glacier show that the δ 18 O (= 18 O/ 16 O relative to standard mean ocean water) of the calcite records the δ 18 O of the ice from that glacier. It may therefore be possible to determine the δ 18 O of Pleistocene ice sheets on the basis of isotopic analyses of calcite formed under that ancient ice. This, in turn, would allow estimation of the δ 18 O of Pleistocene oceans and correction of the paleotemperature scale based on foraminiferal oxygen isotopic analyses. Copyright

Science↗
USGS1973

Ultrafiltration by a compacted clay membrane-I. Oxygen and hydrogen isotopic fractionation

Laboratory experiments were carried out to determine the magnitude of the isotopic fractionation of distilled water and of 0.01 N NaCl forced to flow at ambient temperature under a hydraulic pressure drop of 100 bars across a montmorillonite disc compacted to a porosity of 35 per cent by a pressure of 330 bars. The ultrafiltrates in both experiments were depleted in D by 2.5%. and in O 18 by 0.8%. relative to the residual solution. No additional isotopic fractionation due to a salt filtering mechanism was observed at NaCl concentrations up to 0.01 N. Adsorption is most likely the principal mechanism which produces isotopic fractionation, but molecular diffusion may play a minor role. The results suggest that oxygen and hydrogen isotopic fractionation of ground water during passage through compacted clayey sediments should be a common occurrence, in accord with published interpretations of isotopic data from the Illinois and Alberta basins.

Geochimica et Cosmochimica Acta↗
USGS1973

Ultrafiltration by a compacted clay membrane-II. Sodium ion exclusion at various ionic strengths

Several recent laboratory studies and field investigations have indicated that shales and compacted clay minerals behave as semipermeable membranes. One of the properties of semipermeable membranes is to retard or prevent the passage of charged ionic species through the membrane pores while allowing relatively free movement of uncharged species. This phenomenon is termed salt filtering, reverse osmosis, or ultrafiltration. This paper shows how one can proceed from the ion exchange capacity of clay minerals and, by means of Donnan membrane equilibrium concept and the Teorell-Meyer-Siever theory, develop a theory to explain why and to what extent ultrafiltration occurs when solutions of known concentration are forced to flow through a clay membrane. Reasonable agreement between theory and laboratory results were found. The concentration of the ultrafiltrate was always greater than predicted because of uncertainty in values of some parameters in the equations. Ultrafiltration phenomena may be responsible for the formation of some subsurface brines and mineral deposits. The effect should also be taken into consideration in any proposal for subsurface waste emplacement in an environment containing large quantities of clay minerals.

Geochimica et Cosmochimica Acta↗
USGS1971

A geochemical hypothesis for dolomitization by ground water

Most modern disordered dolomite has been found in dynamic environments. However, solutions associated with modern dolomite formation do not have a common Mg/Ca ratio; the ratio ranges from about 3 to 100. Ground-water circulation may have a significant role in formation of regional dolomites; one of the primary requirements for regional dolomite formation is a large supply of magnesium ions. An X-ray study of well cuttings from the Tertiary limestone aquifer of central Florida indicates that it is composed primarily of calcite and dolomite with minor amounts of quartz and apatite. The magnesium content of the calcite is slightly lower (0-2 percent MgC03) in the recharge areas than in the deeper confined parts of the aquifer system (2-4 percent MgC03). Our data support other recent work and indicate an equilibrium constant for dolomite of 2 X 10-17. Inasmuch as this value is exactly the square of the calcite equilibrium constant (10~8-35), the Mg/Ca ratio must be unity for the three-phase equilibrium, calcite-dolomite-water. The Mg/Ca ratio in water from the aquifer is as low as 0.05 in the recharge area where the water is also undersaturated with respect to both calcite and dolomite. With time and length of travel path in the system, the water increases systematically in Mg/Ca ratio, which approaches unity; saturation with respect to the two carbonates also increases downgradient until the solution apparently becomes over-saturated with respect to both carbonates. In Tertiary limestones of the Yucatan Peninsula, the Mg/Ca range in water is similar to that for Florida. The small amount of magnesium available from the solution of magnesium calcites and dolomite in the potable zone of active circulation is insufficient to provide the amount required for extensive dolomitization unless enormous quantities of rock are available for dissolution. However, dolomite may be forming in the zones of brackish water that underlie the Florida and Yucatan Peninsulas. The required magnesium may be derived from the readily available ocean water or reflux brines as the hydrologic regimen is changed because of relative fluctuations of sea level.

Florida↗
USGS1970

Comparison of chemical hydrogeology of the carbonate peninsulas of Florida and Yucatan

Aquifers of the peninsulas of Florida and northern Yucatan are Tertiary marine carbonate formations showing many lithologic and faunal similarities. In addition, the tropical to subtropical climates of the two areas are similar, each having annual rainfall of about 1000 to 1500 mm. Despite similarities in these fundamental controls, contrasts in the hydrologic and geochemical systems are numerous and striking. For example, Florida has many rivers; Yucatan has none. Maximum thickness of fresh ground water in Florida is about 700 meters; in the Yucatan it is less than 70 meters. In Florida the gradient of the potentiometric surface averages about 1 meter per kilometer; in the Yucatan it is exceedingly low, averaging about 0.02 meter per kilometer. In Florida the chemical character of water changes systematically downgradient, owing to solution of minerals of the aquifer and corresponding increases in total dissolved solids, sulfate, calcium, and Mg-Ca ratio; in the Yucatan no downgradient change exists, and dominant processes controlling the chemical character of the water are solution of minerals and simple mixing of the fresh water and the body of salt water that underlies the peninsula at shallow depth. Hydrologic and chemical differences are caused in part by the lower altitude of the Yucatan plain. More important, however, these differences are due to the lack of an upper confining bed in Yucatan that is hydrologically equivalent to the Hawthorn Formation of Florida. The Hawthorn cover prevents recharge and confines the artesian water except where it is punctured by sinkholes, but sands and other unconsolidated sediments fill sinkholes and cavities and impede circulation. In the Yucatan the permeability of the entire section is so enormous that rainfall immediately infiltrates to the water table and then moves laterally to discharge areas along the coasts.

Florida Peninsula, Yucatan Peninsula↗
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↗