Oxygen isotopic composition of the Luna 20 soil     

Robert N Clayton 《Geochimica et cosmochimica acta》1973,37(4):811-813

The Luna 20 soil (< 125 μm fraction) has a relatively low δO¹⁸ (5.7%.), compared to other lunar soils (5.8 to 6.3%.). This implies either a low-O¹⁸ source material or an unusually small O¹⁸ enrichment in the processes of soil formation and maturation.  相似文献   

Chronology of late wisconsinan glaciation in middle North America     

Lee Clayton  Stephen R. Moran 《Quaternary Science Reviews》1982,1(1):55-82

We propose a chronology of late Wisconsinan glacial fluctuations in middle North America, from Alberta to Wisconsin, based on radiocarbon dates derived solely from wood. Previous chronologies of the southwestern margin of the North American Continental Ice Sheet have depended to a considerable degree on radiocarbon dates from fine-grained organic sediment. This material is commonly contaminated with older carbon, resulting in chronologic confusion. By using only dates from wood, much of the confusion disappears. However, because of the scarcity of wood dates, only four of the sixteen identified fluctuations are accurately dated: an advance into Iowa about 14,000 to 13,500 BP, an advance into South Dakota and Iowa about 12,300 BP, an advance into the Lake Michigan basin about 11,700 BP, and an advance into the Lake Superior basin about 9900 BP. In addition, the beginning of late Wisconsinan glaciation, before 20,000 BP, is fairly well documented. None of the fluctuations in the western part of the region are accurately dated.  相似文献   

Calculation of Uncertainty in the Variogram   总被引：6，自引：0，他引：6  

Julián Ortiz  Clayton V. Deutsch 《Mathematical Geology》2002,34(2):169-183

There are often limited data available in early stages of geostatistical modeling. This leads to considerable uncertainty in statistical parameters including the variogram. This article presents an approach to calculate the uncertainty in the variogram. A methodology to transfer this uncertainty through geostatistical simulation and decision making is also presented.The experimental variogram value for a separation lag vector h is a mean of squared differences. The variance of a mean can be calculated with a model of the correlation between the pairs of data used in the calculation. The data here are squared differences; therefore, we need a measure of a 4-point correlation. A theoretical multi-Gaussian approach is presented for this uncertainty assessment together with a number of examples. The theoretical results are validated by numerical simulation. The simulation approach permits generalization to non-Gaussian situations.Multiple plausible variograms may be fit knowing the uncertainty at each variogram point, . Multiple geostatistical realizations may then be constructed and subjected to process assessment to measure the impact of this uncertainty.  相似文献   

Deriving Constraints on Small-Scale Variograms due to Variograms of Large-Scale Data     

Hans Kupfersberger  Clayton V. Deutsch  André G. Journel 《Mathematical Geology》1998,30(7):837-852

The application of kriging-based geostatistical algorithms to integrate large-scale seismic data calls for direct and cross variograms of the seismic variable and primary variable (e.g., porosity) at the modeling scale, which is typically much smaller than the seismic data resolution. In order to ensure positive definiteness of the cokriging matrix, a licit small-scale coregionalization model has to be built. Since there are no small-scale secondary data, an analytical method is presented to infer small-scale seismic variograms. The method is applied to estimate the 3-D porosity distribution of a West Texas oil field given seismic data and porosity data at 62 wells.  相似文献   

A Field and Laboratory Investigation of Air Fingering During Air Sparging   总被引：2，自引：0，他引：2  

Wilson S. Clayton  Ph.D.  P.G. 《Ground Water Monitoring & Remediation》1998,18(3):134-145

Since the rejection of the bubble flow conceptual model for in situ air sparging, most practitioners have adopted the conceptual model of air channeling, which generally implies the development of widely spaced, discreet air channels that bypass large regions of the subsurface. While air channeling clearly develops in response to stratigraphic heterogeneity, the universality of widely spaced air channels in homogeneous media is not supported by available evidence. Air channeling results in low bulk air saturation due to bypassing, and field and laboratory measurements of air saturations and previously published studies were used to evaluate if air channeling is realistic. The results indicated that homogeneous coarse sands are prone to the development of air channeling, and that homogeneous fine sands show higher air saturations and are not prone to air channeling. Breakthrough air saturations, which represent the minimum air saturations, that will conduct air flow, of approximately 0.02 to 0.04 were observed in coarse sands. In contrast, breakthrough air saturations of 0.10 to 0.13 were observed in fine sands and medium sands. The transition between these behaviors falls at about 15 to 20 cm water air entry pressure. These result indicate that, at both the field and laboratory scale, coarse sands are more prone to air channeling and bypassing than fine sands. Additionally, the larger air gradients and capillary pressures in fine sands result in a less buoyancy-dominated flow pattern, with a larger lateral extent of air flow.  相似文献   

Resistance of quartz silt to isotopic exchange under burial and intense weathering conditions   总被引：1，自引：0，他引：1  

Robert N. Clayton  M.L. Jackson  K. Sridhar 《Geochimica et cosmochimica acta》1978,42(10):1517-1522

Oxygen isotopic compositions of quartz from silty sediments buried to 5400 m depth from two wells in the Gulf of Mexico each showed δ5¹⁸O variations of less than 1.7%. Clay diagenesis has been reported within this depth. The observed variations in the quartz do not appear to be primarly diagenetic effects, but rather are mainly depositional features reflecting variations in the sources of the sediments. Sources may be influenced by the variation of distance from the shore at different depths in a given sampling location and by sediment production by continental glaciations. Stability of the oxygen isotopic composition of quartz in the 10–20 μm size range under long-time humid, temperate weathering conditions was studied by analysis of saprolites formed from Pennsylvanian to Precambrian crystalline rocks. In four of the five cases, the 10–20 μm fraction was found to have only 0.1–0.5%. greater δ¹⁸O than the corresponding 20–50 μm fraction. This increase may be attributable either to a slight oxygen isotopic exchange with ambient ground waters or original differences within the rock since the saprolites were sufficiently coherent to make an influx of extraneous detrital silt unlikely. The amount of oxygen isotopic exchange in silt size quartz over periods of many million years of shallow burial or weathering appears to be small enough to permit the use of the oxygen isotopic ratio of quartz in tracing the origin of eolian and fluvial additions of minerals to continental soils and pelagic sediments.  相似文献   

Oxygen isotope studies of the geothermal system at Wairakei,New Zealand     

R.N. Clayton  A. Steiner 《Geochimica et cosmochimica acta》1975,39(8):1179-1186

Volcanic rocks in the Wairakei geothermal field have undergone extensive oxygen isotope exchange with the thermal waters, resulting in an O¹⁸-depletion averaging about 4%. A lower limit on the ratio of the mass of water to rock in the exchange system is 4·3, at least ten times greater than the corresponding figure for the Salton Sea geothermal system. Carbonates, present as alteration products in most samples, are found to be in equilibrium with waters at present-day temperatures in some wells, and to record higher ‘fossil’ temperatures in others. Quartz phenocrysts and xenocrysts remain unexchanged, and only new hydrothermal quartz is in isotopic equilibrium with geothermal solutions.  相似文献   

Oxygen isotope cosmothermometer revisited     

Naoki Onuma  Robert N. Clayton  Toshiko K. Mayeda 《Geochimica et cosmochimica acta》1974,38(1):189-191

A previously published estimate of the oxygen isotopic composition of the gas of the early solar nebula must be revised in light of the discovery of non-chemical isotope effects in carbonaceous chondrites. The solids which accreted to form the Earth, Moon and ordinary chondrites probably did not equilibrate isotopically with the gas below 1000 K.  相似文献   

RAGLAND,AN LL3.4 CHONDRITE FIND FROM NEW MEXICO     

S.I. Recca  E.R.D. Scott  K. Keil  R.N. Clayton  T.K. Mayeda  G.I Huss  E. Jarosewich  K.S. Weeks  F.A. Hasan  D.W.G. Sears  R. Wieler  P. Signer 《Meteoritics & planetary science》1986,21(2):217-229

The Ragland, New Mexico chondrite was found in 1978, and consists of a single stone of 12.16 kg that broke into three pieces. The stone is moderately weathered and has a pronounced chondritic texture. Bulk composition favors an LL classification, and modal analysis and oxygen isotopic composition are consistent with this. The thermoluminescence sensitivity of 0.056 ± 0.020 normalized to Dhajala, compositional variability of olivine (mean Fa 18.3, σ = 10.1) and low-Ca pyroxene (mean Fs 14.6, σ = 6.7), and Ca concentrations in olivine indicate metamorphic subtype 3.4 ± 0.1. The isotopically heavy oxygen composition, which is characteristic of subtypes 3.0–3.1, may be a primary characteristic and not a result of weathering. Low concentrations of radiogenic ⁴⁰Ar and planetary ³⁶Ar suggest noble gas loss.  相似文献   

A Multiple Training Image Approach for Spatial Modeling of Geologic Domains     

Daniel A. Silva  Clayton V. Deutsch 《Mathematical Geosciences》2014,46(7):815-840

Characterization of complex geological features and patterns remains one of the most challenging tasks in geostatistics. Multiple point statistics (MPS) simulation offers an alternative to accomplish this aim by going beyond classical two-point statistics. Reproduction of features in the final realizations is achieved by borrowing high-order spatial statistics from a training image. Most MPS algorithms use one training image at a time chosen by the geomodeler. This paper proposes the use of multiple training images simultaneously for spatial modeling through a scheme of data integration for conditional probabilities known as a linear opinion pool. The training images (TIs) are based on the available information and not on conceptual geological models; one image comes from modeling the categories by a deterministic approach and another comes from the application of conventional sequential indicator simulation. The first is too continuous and the second too random. The mixing of TIs requires weights for each of them. A methodology for calibrating the weights based on the available drillholes is proposed. A measure of multipoint entropy along the drillholes is matched by the combination of the two TIs. The proposed methodology reproduces geologic features from both TIs with the correct amount of continuity and variability. There is no need for a conceptual training image from another modeling technique; the data-driven TIs permit a robust inference of spatial structure from reasonably spaced drillhole data.  相似文献