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Results for “Radiocarbon”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 109 records · Page 6Linked to original sources
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↗
USGS2016

Radiocarbon constraints imply reduced carbon uptake by soils during the 21st century

Soil is the largest terrestrial carbon reservoir and may influence the sign and magnitude of carbon cycle-climate feedbacks. Many Earth system models (ESMs) estimate a significant soil carbon sink by 2100, yet the underlying carbon dynamics determining this response have not been systematically tested against observations. We used 14C data from 157 globally distributed soil profiles sampled to 1 m depth to show that ESMs underestimated the mean age of soil carbon by more than six-fold (430±50 years vs. 3100±1800 years). Consequently, ESMs overestimated the carbon sequestration potential of soils by nearly two-fold (40±27%). These biases suggest that ESMs must better represent carbon stabilization processes and the turnover time of slow and passive reservoirs when simulating future atmospheric CO2 dynamics.

Science↗
USGS1981

Comparison of uranium-series, radiocarbon, and amino acid data from marine molluscs, Baffin Island, Arctic Canada

Uranium-series and 14 C dates and the extent of amino acid racemization are reported for 24 marine shell samples from three areas of Baffin Island, Arctic Canada. When the radiometric dates are plotted against the ratio of D-alloisoleucene:L-isoleucene in the shells, five broad age groups are recognized. The uranium-series data indicate that 231 Pa is incompletely retained in most fossil shells and that 230 Th is lost from some of the samples. Therefore, their apparent ages are minimum. However, a few dated samples in each group have yielded useful age results, and the minimum ages of the five groups of samples are estimated as 7,000 to 11,000, ≥ 70,000, ≥ 136,000, ≥ 190,000, and > 300,000 yr. Calculated integrated thermal histories based on the epimerization reaction in the mollusc Hiatella arctica Linné give paleotemperature estimates of around −5 °C, compared to the present mean annual air temperature of about −11 °C.

Baffin Island↗
USGS1980

Quaternary stratigraphic sections with radiocarbon dates, Wiseman Quadrangle, Alaska

The Wiseman quadrangle contains a rich stratigraphic record of alluvial, glacial, and periglacial events of the late Quaternary in the south-central Brooks Range. The numerous bluffs along the Koyukuk River and its tributaries expose drift sheets of the late Pleistocene Itkillik I glacial phase (table 1), and outwash and other proglacial deposits of the succeeding Itkillik II phase. During Itkillik I time, glaciers flowed south through virtually all of the valleys of the south-central Brooks Range to terminate in piedmont lobes within the Koyukuk lowland (Hamilton, 1978, 1979a). Outwash covered the Koyukuk Valley floor beyond the ice limits. Glaciers of Itkillik II age were more restricted; the largest reached positions near the south margin of the range, but many mountain valleys of the Wiseman quadrangle remained unglaciated. Lower alluvial terraces of Holocene age record alternating episodes of aggradation and soil development. Some of these events were controlled locally by mass movements and perhaps by faulting, but others may be related to regional climatic reversals and to fluctuations of cirque glaciers at valley heads.

Alaska↗
USGS1979

Subsurface stratigraphy and geochemistry of late Quaternary evaporites, Searles Lake, California, with a section on radiocarbon ages of stratigraphic units

Searles Lake is a dry salt pan, about 100 km 2 in area, that lies on the floor of Searles Valley, in the desert of southeast California. Several salt bodies of late Quaternary age lie beneath the surface, mostly composed of sodium and potassium carbonate, sulfate, chloride, and borate minerals. Mud layers separate the salt bodies, which contain interstitial brine that is the source of large quantities of industrial chemicals. The value of annual production from the deposit exceeds $30 million; total production to date exceeds $1 billion. The salts and muds were deposited during Pleistocene and Holocene times by a series of large lakes (200 m maximum depth, 1,000 km 2 maximum area) that fluctuated in size in response to climatic change. Salts were deposited during major dry (interpluvial) episodes, muds during wet (pluvial) episodes that correlate with glacial advances in other parts of North America and the world. Data based on cores from the deposit are used in this paper to establish the stratigraphy of the deposit, the chemical and mineral compositions of successive units, and the total quantities of components contained by them. These parameters are then used to determine the geochemical evolution of the sedimentary layers. The results provide a refined basis for reconstructing the limnology of Searles Lake and the regional climate during late Quaternary time. Six main stratigraphic units were distinguished and informally named earlier on the basis of their dominant composition: Unit Typical thickness 14C age, uncorrected (in meters) (years B.P.) Overburden Mud 7 0 to >3,500 Upper Salt 15 >3,500 to 10,500 Parting Mud 4 10,500 to 24,000 Lower Salt 12 24,000 to 32,500 Bottom Mud 30 32,500 to 130,000 Mixed Layer 200+ > 130,000 (The age of 130,000 years for the Mixed Layer is based on extrapolated sedimentation rates.) The Lower Salt is subdivided into seven salt units (S-l to S-7) and six mud units (M-2 to M-7), the Mixed Layer into six units (A to F). For each salt unit, the areal extent, volume, shape, mineralogy, and chemical composition of the solids and brines have been determined; for each mud unit (which originally extended over much of the basin), the shape and volume within a standard area, and the mineralogy, have been determined. The bulk compositions (brines plus salts) of the combined Lower Salt units S-l to S-5 and units S-6 and S-7, and the Upper Salt, were determined so that the total quantities and ratios of ions in the initial brines could be reconstructed. The 74 published HC dates on Searles Lake core samples from all but the oldest unit are supplemented by 14 new dates (determined by Minze Stuiver) on the Lower Salt. Most of the age control comes from dates based on disseminated organic carbon; two dates are on wood; dates on carbonate minerals are less reliable. Although the probable disequilibrium between the carbon in the lake and atmosphere (because of contamination, slow equilibrium rates, and other factors) causes disseminated carbon dates to be an estimated 500-2,500 years 'too old,' the ages of the major and minor units are relatively well established. The list above indicates rounded and uncorrected ages for the contacts of major units. The age of the only salt bed in the Lower Salt which indicates desiccation (S-5) is about 28,000 years. The average uncorrected sedimentation rate in the Parting Mud is 4

Professional Paper↗
USGS2006

AMS Radiocarbon dating of paleosols intercalated with tephra layers from Mayon Volcano, southern Luzon, Philippines: A preliminary report

This paper presents the AMS 14 C dates of paleosols intercalated with tephra layers in the vicinity of Mayon Volcano, southern Luzon, Philippines. the obtained 14 C dates are almost consistent with the stratigraphy of the Mayon tephra group. On the basis of calibrated 14 C age of soil layer directly overlying the lowest ash layer, the oldest eruptive event must have taken place shortly before 20 cal kyr BP. This age is younger than the previous estimates for Mayon.

Mayon Volcano↗