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Barney J. Szabo

Publications and source records attributed to Barney J. Szabo.

At least 37 records · Page 2Linked to original sources
USGS1991

Crustal subsidence rate off Hawaii determined from 234U/238U ages of drowned coral reefs

A series of submerged coral reefs off northwestern Hawaii was formed during (largely glacial) intervals when the rate of local sea-level rise was less than the maximum upward growth rate of the reefs. Mass-spectrometric 234 U/ 238 U ages for samples from six such reefs range from 17 to 475 ka and indicate that this part of the Hawaiian Ridge has been subsiding at a roughly uniform rate of 2.6 mm/yr for the past 475 ka. The 234 U/ 238 U ages are in general agreement with model ages of reef drowning (based on estimates of paleo-sea-level stands derived from oxygen-isotope ratios of deep-sea sediments), but there are disagreements in detail. The high attainable precision (±10 ka or better on samples younger than ∼800 ka), large applicable age range, relative robustness against open-system behavior, and ease of analysis for this technique hold great promise for future applications of dating of 50-1000 ka coral.

Hawaii↗
USGS1990

Reef growth and volcanism on the submarine southwest rift zone of Mauna Loa, Hawaii

A marine sampling program, utilizing the PISCES-5 submersible operated by the Hawaii Undersea Research Laboratory (NOAA), has confirmed the presence of a major submerged coral reef offshore from Ka Lae (South Point), Hawaii. The top of the reef is now 150–160 m below sea level. Radiocarbon and Useries dating indicates that it drowned about 13.9 ka by the combined effects of island subsidence (2.5 mm/year) and the rapid rise of sea level at the end of the last glaciation so that the relative submergence rate of more than 10 mm/year exceeded the upward growth rate of the reef. The submerged reef caps the offshore part of the southwest rift-zone ridge of Mauna Loa, which has apparently undergone little volcanic activity offshore since 170 ka, and possibly since 270 ka. This fact suggests that rift zone activity is becoming increasingly restricted toward the upper part of the volcano, a condition possibly heralding the end of the shield-building stage.

Hawaii↗
USGS1990

Uranium-series ages of marine terraces, La Paz Peninsula, Baja California Sur, Mexico

Uranium-series dating of coral samples from raised marine terrace deposits between 1.5 and 10 m above sea level in the La Paz Peninsula area, Baja California Sur, yielded ages between 123 ka and 138 ka that are in agreement with previously reported results. The stratigraphy and ages of marine units near the El Coyote Arroyo indicate the presence of two high stands of the sea during the last interglacial or oxygen isotope substage 5e at about 140 ka and 123 ka. Accepting 5 m for the sea level during the last interglacial transgression, we calculate average uplift rates for the marine terraces of about ???70 mm/ka and 40 mm/ka. These slow rates of uplift indicate a relative stability of the La Paz peninsula area for the past 140 000 years. In contrast, areas of Baja California affected by major faultf experienced higher rates of uplift. Rockwell et al. (1987) reported vertical uplift rates of 180 to 300 mm/ka at Punta Banda within the Aqua Blanea fault zone in northern Baja California. ?? 1990 Springer-Verlag.

Coral Reefs↗
USGS1990

Relative inactivity during the last 140,000 years of a portion of the La Paz fault, southern Baja California Sur, Mexico

Uranium-series dating of corals overlying the undeformed Punta Coyote gravels indicates that the underlying La Paz fault zone has been relatively inactive in this part of the Baja California peninsula during the last 140,000 years, and possibly for a significantly longer period. However, Holocene seismic activities along extensions of the fault zone north of Cabo San Lucas suggest potential seismic hazards for the city of La Paz (population 200,000), which lies about 6 km from the fault. ?? 1990 Springer-Verlag New York Inc.

Environmental Geology and Water Sciences↗
USGS1990

Ages and stable-isotope compositions of secondary calcite and opal in drill cores from Tertiary volcanic rocks of the Yucca Mountain area, Nevada

Stable-isotope compositions of fracture-and cavity-filling calcite from the unsaturated zone of three drill cores at Yucca Mountain Tertiary volcanic complex indicate that the water from which the minerals precipitated was probably meteoric in origin. A decrease in 18 O in the calcite with depth is interpreted as being due to the increase in temperature in drill holes corresponding to an estimated average geothermal gradient of 34° per kilometer. A few of the calcite samples and all of the opal samples yielded uranium-series ages older than 400,000 yr, although most of the calcite samples yielded ages between 26,000 and 310,000 yr. The stable-isotope and uranium- series dates from precipitated calcite and opal of this reconnaissance study suggest a complex history of fluid movement through the volcanic pile, and episodes of fracture filling predominantly from meteoric water during at least the past 400,000 yr.

Nevada↗
USGS1989

Uranium-series nuclides in the Golden fault, Colorado, U.S.A.: Dating latest fault displacement and measuring recent uptake of radionuclides by fault-zone materials

Concentrations and isotopic ratios of U, Th and Ra were measured in a fault zone near Golden, Colorado where major displacement occurred between about 190 and 615 ka. Faulting created new surfaces for leaching and provided the pathways for U-rich ground water. Uranium and 230 Th, the latter produced by the decay of dissolved 234 U, are adsorbed by fault gouge, hematite-stained sand and brecciated sand- and claystones. The observed U enrichment is as much as six times baseline value and the simultaneous enrichment of 230 Th is estimated at about ninefold relative to 238 U. The adsorption of radionuclides chemically analogous to Th, such as Pu (IV) and Np, and 237 Np decay products, on fault-zone materials would contribute to the immobilization of high-level radioactive waste in the vicinity of a repository in the event of leakage from engineered barriers into fractured rock-mass.

Colorado↗
USGS1989

Uranium-series dated authigenic carbonates and Acheulian sites in southern Egypt

Field investigations in southern Egypt have yielded Acheulian artifacts in situ in authigenic carbonate deposits (CaCO 3 -cemented alluvium) along the edges of now-aggraded paleovalleys (Wadi Arid and Wadi Safsaf). Uranium-series dating of 25 carbonate samples from various localities as far apart as 70 kilometers indicates that widespread carbonate deposition occurred about 45, 141 and 212 ka (thousand years ago). Most of the carbonate appears to have been precipitated from groundwater, which suggests that these three episodes of deposition may be related to late Pleistocene humid climates that facilitated human settlement in this now hyperarid region. Carbonate cements from sediments containing Acheulian artifacts provide a minimum age of 212 ka for early occupation of the paleovalleys.

southern Egypt↗
USGS1988

A 250,000-year climatic record from Great Basin vein calcite: Implications for Milankovitch theory

A continuous record of oxygen-18 (δ 18 O) variations in the continental hydrosphere during the middle-to-late Pleistocene has been obtained from a uranium-series dated calcitic vein in the southern Great Basin. The vein was deposited from ground water that moved through Devils Hole—an open fault zone at Ash Meadows, Nevada—between 50 and 310 ka (thousand years ago). The configuration of the δ 18 O versus time curve closely resembles the marine and Antarctic ice core (Vostok) δ 18 O curves; however, the U-Th dates indicate that the last interglacial stage (marine oxygen isotope stage 5) began before 147 ± 3 ka, at least 17,000 years earlier than indicated by the marine δ 18 O record and 7,000 years earlier than indicated by the less well dated Antarctic δ 18 O record. This discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine δ 18 O chronology may need revision and that orbital forcing may not be the principal cause of the Pleistocene ice ages.

Nevada↗
USGS1986

Age of -360-m reef terrace, Hawaii, and the rate of late Pleistocene subsidence of the island

Observations from a manned submersible vehicle indicate that the −360-m reef terrace northwest of the island of Hawaii is a drowned coral reef. The preferred uranium-series age of coralline algae collected from the reef face is 120 ± 5 ka. This age agrees with the notion that the reef was drowned during the sea-level rise following the major lowstand of the sea that occurred at 145 ka (oxygen isotope stage 6). This drowning pattern is similar to the previously determined radiocarbon age of 13 ka for drowning of the −150-m reef off west Hawaii, which drowned during the sea-level rise following the last major lowstand of the sea at 18 ka (oxygen isotope stage 2). Estimated average subsidence of the reef site off northwest Hawaii is 2.7 mm/yr since final drowning of the −360-m reef.

Hawaii↗
USGS1986

Water-table decline in the south-central Great Basin during the Quaternary Period; implications for toxic-waste disposal

The distribution of vein calcite, tufa, and other features indicative of paleo-groundwater discharge, indicates that during the early to middle Pleistocene, the water table at Ash Meadows, in the Amargosa Desert, Nevada, and at Furnace Creek Wash, in east-central Death Valley, California, was tens to hundreds of meters above the modern water table, and that groundwater discharge occurred up to 18 km up-the-hydraulic gradient from modern discharge areas. Uranium series dating of the calcitic veins permits calculation of rates of apparent water table decline; rates of 0.02 to 0.08 m/1000 yr are indicated for Ash meadows and 0.2 to 0.6 m/1000 yr for Furnace Creek Wash. The rates for Furnace Creek Wash closely match a published estimate of vertical crustal offset for this area, suggesting that tectonism is a major cause for the displacement observed. In general, displacements of the paleo-water table probably reflect a combination of: (a) tectonic uplift of vein calcite and tufa, unaccompanied by a change in water table altitude; (b) decline in water table altitude in response to tectonic depression of areas adjacent to dated veins and associated tufa; (c) decline in water table altitude in response to increasing aridity caused by major uplift of the Sierra Nevada and Transverse Ranges during the Quaternary; and (d) decline in water altitude in response to erosion triggered by increasing aridity and/or tectonism. A synthesis of geohydrologic, neotectonic, and paleoclimatologic information with the vein-calcite data permits the inference that the water table in the south-central Great Basin progressively lowered throughout the Quaternary. This inference is pertinent to an evaluation of the utility of thick (200-600 m) unsaturated zones of the region for isolating solidified radioactive wastes from the hydrosphere for hundreds of millenia. Wastes buried a few tens to perhaps 100 m above the modern water table--that is above possible water level rises due to future pluvial climates--are unlikely to be inundated by a rising water table in the foreseeable geologic future. (Author 's abstract)

Open-File Report↗
USGS1986

Rock-water interaction in ash-flow tuffs (Yucca Mountain, Nevada, USA)- The record from uranium studies

Forty-eight core samples of ash-flow tuffs from Yucca Mountain, NV, were selected for comparative analysis by uranium-based methods to estimate past interaction with oxidizing water. Results aid in the selection of hydrologically isolated host rocks for radioactive waste disposal. U abundances were consistently more variable than thorium in whole rocks, suggesting some selective redistribution of U. Dissolved U correlates most strongly with dissolved manganese, indicating a predominant association of U with manganese oxides.

Nevada↗
USGS1985

Two-million-year record of deuterium depletion in Great Basin ground waters

Fluid inclusions in uranium series-dated calcitic veins from the southern Great Basin record a reduction of 40 per mil in the deuterium content of groundwater recharge during the Pleistocene. This variation is tentatively attributed to major uplift of the Sierra Nevada Range and the Transverse Ranges during this epoch with attendant increasing orographic depletion of deuterium from inlandbound Pacific storms.

Sierra Nevada Range↗
USGS1985

Uranium-series dating of fossil corals from marine sediments of southeastern United States Atlantic Coastal Plain

Extensive low-lying marine deposits border the southeastern United States Atlantic Coastal Plain. Some units are fossiliferous and contain corals as isolated fragments in sediments of a detrital character. These corals are subject to alteration processes such that suites of related samples must be examined to determine the suitability of these coral samples for reliable uranium-series dating. With the exception of those from one location, most samples appear to have remained closed systems with respect to the isotopes of uranium and thorium throughout their geologic history. Extraneous 230 Th has been detected in some of the corals due to incorporation of some detrital materials into their skeletons. For these samples, different methods are applied to correct for the initial 230 Th contamination. Continued sampling and analyses have resulted in 55 individual uranium-thorium determinations. The average 230 Th ages of samples from the Norfolk Formation, and from later- and earlier-deposited sediments of the Wando Formation are ∼71,000, 87,000, and 129,000 yr, and they appear to correlate with oxygen isotope substages 5a, 5c, and 5e, respectively. The average 230 Th age of samples from beds of the Rappahannock River, Ponzer, and Ten Mile Hill localities is ∼212,000 yr, and they correlate with oxygen isotope stage 7. The sediment of the Canepatch Formation is ∼460,000, yr old, and it is tentatively correlated with oxygen isotope stage 11. There is general agreement between uranium-series and uranium-trend dates and between the quantitative trends of the amino acid data and uranium-series dates. The amino acid values, however, ure unacceptably high in at least two groups of samples, those from localities near Charleston, South Carolina, and from central Virginia.

Geological Society of America Bulletin↗
USGS1982

Extreme fractionation of 234U 238U and 230Th 234U in spring waters, sediments, and fossils at the Pomme de Terre Valley, southwestern Missouri

Isotopic fractionation as great as 1600% exists between 234 U and 238 U in spring waters, sediments, and fossils in the Pomme de Terre Valley, southwestern Missouri. The activity ratios of 234 U 238 U "> 234U238U in five springs range from 7.2 to 16 in water which has been discharged for at least the past 30,000 years. The anomalies in 234 U 238 U "> 234U238U ratio in deep water have potential usefulness in hydrologic investigations in southern Missouri. Clayey units overlying the spring bog sediments of Trolinger Spring are enriched in 230 Th relative to their parent 234 U by as much as 720%. The results indicate that both preferential displacement via alpha recoil ejection and the preferential emplacement via recoiling and physical entrapment are significant processes that are occurring in the geologic environment.

Geochimica et Cosmochimica Acta↗
USGS1982

Age determination of late Pleistocene marine transgression in western Alaska

Dating molluscs from sediments representing the Kotzebuan marine transgression in Alaska yields an average uranium-series age of 104,000 ± 22,000 yrs B.P. This and other selected Pleistocene marine deposits of western Alaska are tentatively correlated with radiometrically dated units of eastern Baffin Island, Arctic Canada.

Alaska↗