Michael S. Lico

Chemical Geothermometers Applied to Formation Waters, Gulf of Mexico and California Basins: ABSTRACT

Twelve chemical geothermometers based on the concentrations of silica and proportions of Na, K, Ca, and Mg in water from hot springs and geothermal wells are used successfully to estimate the subsurface temperatures of the reservoir rocks. These 12 geothermometers together with a new geothermometer based on the concentrations of Li and Na were used to estimate the subsurface temperatures of more than 200 formation-water samples from about 40 oil and gas fields in coastal Texas and Louisiana and the Central Valley, California. The samples were obtained from reservoir rocks ranging in depth from less than 1,000 m to about 5,600 m. Quartz, Na-K-Ca-Mg, and Na-Li geothermometers give concordant subsurface temperatures that are within 10°C of the measured values for reservoir temperatures higher than about 75°C. Na-Li, chalcedony, and a modified Na-K geothermometers give the best results for reservoir temperatures from 40°C to 75°C. Subsurface temperatures higher than about 75°C calculated by chemical geothermometers are at least as reliable as those obtained by conventional methods. Chemical and conventional methods should be used where reliable temperature data are required. End_of_Article - Last_Page 588------------

Exceptionally fast growth rate of <100-yr-old tufa, Big Soda Lake, Nevada: Implications for using tufa as a paleoclimate proxy

Large tufa mounds (>3 m tall, with a basal circumference of 5 m) have been discovered on the margin of Big Soda Lake, Nevada, USA. These tufa mounds are rooted at a maximum of 4 m below the current lake surface and are actively forming from groundwater seepage, which can be seen emanating from the top of the tufa mounds. Big Soda Lake is a volcanic crater lake whose water level is maintained exclusively by groundwater. The age of the tufa mounds is well constrained because prior to the development of the Newlands Irrigation Project in 1907, the water level was ∼18 m lower than the current lake level. The vertical columnar nature of the tufa mounds indicates that they formed under the lake and not subaerially. Thus, the tufa mounds are <100 yr old and have grown at a rate ≥30 mm/yr. Stable oxygen and carbon isotope analyses of tufa carbonate compared to isotopic analyses of groundwater and lake water and hydrochemical data indicate that the fluids responsible for their precipitation are a simple mixture of modern groundwater and lake water and do not reflect a recent climate signature. The exceptionally fast growth of the tufa mounds indicates that large tufa deposits may form almost instantaneously in geologic time. Given this potential for rapid growth and the fact that variations in isotopic compositions of tufa deposits have been interpreted in terms of changes in paleoclimate and changes in the composition of recharge water over thousands of years, care should be taken when trying to determine the significance of variations in isotopic or chemical compositions of tufas that may have been caused by mixing with groundwater.

Radionuclides in ground water of the Carson River Basin, western Nevada and eastern California, U.S.A.

Abstract Ground water is the main source of domestic and public supply in the Carson River Basin. Ground water originates as precipitation primarily in the Sierra Nevada in the western part of Carson and Eagle Valleys, and flows down gradient in the direction of the Carson River through Dayton and Churchill Valleys to a terminal sink in the Carson Desert. Because radionuclides dissolved in ground water can pose a threat to human health, the distribution and sources of several naturally occurring radionuclides that contribute to gross-alpha and gross-beta activities in the study area were investigated. Generally, alpha and beta activities and U concentration increase from the up-gradient to down-gradient hydrographic areas of the Carson River Basin, whereas222Rn concentration decreases. Both226Ra and228Ra concentrations are similar throughout the study area. Alpha and beta activities and U concentration commonly exceed 100 pCi/l in the Carson Desert at the distal end of the flow system. Radon-222 commonly exceeds 2,000 pCi/l in the western part of Carson and Eagle Valleys adjacent to the Sierra Nevada. Radium-226 and228Ra concentrations are Alpha-emitting radionuclides in the ground water originated from the dissolution of U-rich granitic rocks in the Sierra Nevada by CO2, oxygenated water. Dissolution of primary minerals, mainly titanite (sphene) in the granitic rocks, releases U to the water. Dissolved U is probably removed from the water by adsorption on Fe- and Mn-oxide coatings on fracture surfaces and fine-grained sediment, by adsorption on organic matter, and by coprecipitation with Fe and Mn oxides. These coated sediments are transported throughout the basin by fluvial processes. Thus, U is transported as dissolved and adsorbed species. A rise in the water table in the Carson Desert because of irrigation has resulted in the oxidation of U-rich organic matter and dissolution of U-bearing coatings on sediments, producing unusually high U concentration in the ground water. Alpha activity in the ground water is almost entirely from the decay of U dissolved in the water. Beta activity in ground water samples is primarily from the decay of40K dissolved in the water and ingrowth of238U progeny in the sample before analysis. Approximately one-half of the measured beta activity may not be present in ground water in the aquifer, but instead is produced in the sample after collection and before analysis. Potassium-40 is primarily from the dissolution of K-containing minerals, probably K-feldspar and biotite. Radon-222 is primarily from the decay of226Ra in the aquifer materials. Radium in the ground water is thought to be mainly from alpha recoil associated with the decay of Th in the aquifer material. Some Ra may be from dissolution (or desorption) or Ra-rich coatings on sediments.

Gasoline-Related Organics in Lake Tahoe Before and After Prohibition of Carbureted Two-Stroke Engines

ABSTRACT On June 1, 1999, carbureted two-stroke engines were banned on waters within the Lake Tahoe Basin of California and Nevada. The main gasoline components MTBE (methyl tert-butyl ether) and BTEX (benzene, toluene, ethylbenzene, and xylenes) were present at detectable concentrations in all samples taken from Lake Tahoe during 1997–98 prior to the ban. Samples taken from 1999 through 2001 after the ban contained between 10 and 60 percent of the pre-ban concentrations of these compounds, with MTBE exhibiting the most dramatic change (a 90 percent decrease). MTBE and BTEX concentrations in water samples from Lake Tahoe and Lower Echo Lake were related to the amount of boat use at the sampling sites. Polycyclic aromatic hydrocarbon (PAH) compounds are produced by high-temperature pyrolytic reactions. They were sampled using semipermeable membrane sampling devices in Lake Tahoe and nearby Donner Lake, where carbureted two-stroke engines are legal. PAHs were detected in all samples taken from Lake Tahoe and Donner Lake. The number of PAH compounds and their concentrations are related to boat use. The highest concentrations of PAH were detected in samples from two heavily used boating areas, Tahoe Keys Marina and Donner Lake boat ramp. Other sources of PAH, such as atmospheric deposition, wood smoke, tributary streams, and automobile exhaust do not contribute large amounts of PAH to Lake Tahoe. Similar numbers of PAH compounds and concentrations were found in Lake Tahoe before and after the ban of carbureted two-stroke engines.

Lower Permian sediment-gravity-flow sequence, eastern California

Abstract The Lower Permian (middle Wolfcampian) Zinc Hill sequence, a 65- to 110-m-thick series of beds in the Owens Valley Group in east-central California, comprises sediment-gravity-flow deposits consisting of carbonate sediment that originated on, and siliciclastic sediment that may have been generally ponded behind, a carbonate shelf to the east and northeast. Thickness patterns and paleocurrent indicators show that the sediment forming this sequence was transported primarily southeastward and deposited in a southeast-trending, lobe-shaped body. Evidently, the sediment was carried from the shelf by sediment-gravity flows that travelled westward down the slope and then turned southeastward upon reaching a southeast-trending basin at the base of the slope. Data derived from the study of this basin, which paralleled the shelf edge and is thought to have formed parallel to a southeast-oriented segment of the Early Permian continental margin, constitute one of the most important arguments favoring a Pennsylvanian to Early Permian age of truncation of the western North American continental margin.

Subsurface Temperatures Calculated by Chemical Geothermometers Applied to Formation Waters from Northern Gulf of Mexico and California Basins: ABSTRACT

Twelve chemical geothermometers based on the concentrations of silica and proportions of sodium, potassium, calcium, and magnesium in water from hot springs and geothermal wells are used successfully to estimate the subsurface temperatures of the reservoir rocks. These twelve geothermometers together with a new geothermometer based on the concentrations of lithium and sodium were used to estimate the subsurface temperatures of more than 200 formation-water samples from about 40 oil and gas fields in coastal Texas and Louisiana and the Central Valley, California. The samples were obtained from reservoir rocks ranging in depth from less than 1,000 m to about 5,600 m. Quartz, Na-K-Ca-Mg, and Na-Li geothermometers give concordant subsurface temperatures that are within 10°C of the measured values for reservoir temperatures higher than about 75°C. Na-Li, chalcedony, and a modified Na-K geothermometers give the best results for reservoir temperatures between 40°C to 75°C. Subsurface temperatures higher than about 75°C calculated by chemical geothermometers are at least as reliable as those obtained by conventional methods. Chemical and conventional methods should be used where reliable temperature data are required. End_of_Article - Last_Page 1361------------