Geochemistry and petrography of basalt grindstones from the Karak Plateau,central Jordan     

Brandon G. Watts  Marvin E. Bennett  Otto C. Kopp  Gerald L. Mattingly 《Geoarchaeology》2004,19(1):47-69

Seventeen basalt grindstone fragments from central Jordan's Karak Plateau were studied. Most of these artifacts are vesicular or amygdaloidal with calcite as the dominant mineral filling the voids. The major minerals are olivine (with iddingsite rims), plagioclase, clinopyroxene, magnetite, and apatite. Glass is present in some samples. One basalt fragment is quite different in appearance and composition and may have come from flows closer to the Dead Sea. Grindstone fragment compositions plot in the tephrite‐basanite and basalt fields. A plot of the concentrations of niobium, zirconium, and yttrium reveal that the sample compositions plot in the “within‐plate alkali basalt” and “within‐plate tholeiite” fields. The acquisition of basalts for preparing such implements appears to have been random. Some may have been introduced through trade and migration. Archaeological and environmental studies on the Karak Plateau are urgently needed because Jordan's population growth and economic development are destroying many sites and their environmental contexts. © 2004 Wiley Periodicals, Inc.  相似文献   

Potential mechanistic causes of increased baseflow across northern Eurasia catchments underlain by permafrost     

Sarah G. Evans  Brandon Yokeley  Connor Stephens  Benjamin Brewer 《水文研究》2020,34(11):2676-2690

Warming in the Arctic is occurring at twice the rate of the global average, resulting in permafrost thaw and a restructuring of the Arctic hydrologic cycle as indicated by increased stream discharge during low-flow periods. In these cold regions, permafrost thaw is postulated to increase low-flow discharge, or baseflow, through either: (a) localized increases in groundwater storage and discharge to streams due to increased aquifer transmissivity from thickening of the freeze–thaw layer above permafrost known as the active layer or (b) long-term increases in regional groundwater circulation via enhancement of groundwater–surface water interactions due to extensive permafrost loss over decades. While increasing baseflow has been observed throughout northern Eurasia, the precise mechanistic causes remain elusive. In this study, we differentiate between where these two subsurface physical mechanisms of baseflow increase are occurring by performing a baseflow recession analysis using daily streamflow records from 1913 to 2003 for 139 stations in northern Eurasia underlain by varying permafrost areal extents. Results indicate that from 1913 to 2003, the majority of catchments underlain by continuous permafrost have an increasing trend in their recession flow intercepts, a proxy for increasing active layer thickness. Alternatively, the majority of catchments underlain by permafrost types that are less spatially extensive (e.g., discontinuous, sporadic, isolated, or no permafrost) have decreasing trends in their recession flow intercepts, indicating that a potential increase in active layer thickness is not the driving factor of baseflow variations in these catchments. This may indicate that in catchments underlain by continuous permafrost, active layer thickening correlates with increases in baseflow, whereas, in other catchments with less extensive permafrost, increases in baseflow may be caused by wholesale permafrost loss and vertical talik expansion that enhances regional groundwater circulation. The results of this work may inform our understanding of the subsurface mechanisms responsible for the changing Arctic hydrologic cycle.  相似文献   

An Ipswichian fluvial deposit at Fulbeck,Lincolnshire and the chronology of the Trent terraces     

Allan Brandon  Michael G. Sumbler 《第四纪科学杂志》1988,3(2):127-133

Mammalian fossils recently discovered near Fulbeck in Lincolnshire, include abundant hippopotamus, suggesting an Ipswichian date for the Fulbeck Sand and Gravel (new name). These deposits mark a former course of the River Witham; clasts indicate derivation from outcrops of Jurassic rocks and chalky till to the south and south-east. The relationship of the Fulbeck Sand and Gravel to the terrace deposits of the River Trent necessitates a revised chronology. The Balderton Sand and Gravel (new name), laid down by the Trent along its former course to the Lincoln Gap, is shown to be older than the Ipswichian Fulbeck Sand and Gravel, and was probably deposited during the Wolstonian Stage. The Eagle Moor Sand and Gravel (new name), probably glaciofluvial outwash from the chalky tills of the region, is considerably older than the Balderton Sand and Gravel and, together with the tills, is assigned to the early part of the Wolstonian, or the Anglian glacial Stage. It is suggested that the Balderton and Eagle Moor terraces equate with the lower and upper facets of the composite Hilton Terrace of the Middle Trent.  相似文献   

Mineralogy and petrology of the LaPaz Icefield lunar mare basaltic meteorites     

K. Righter  S. J. Collins  A. D. Brandon 《Meteoritics & planetary science》2005,40(11):1703-1722

Abstract— Five basaltic meteorites from the LaPaz ice field are paired on the basis of their mineralogy and texture, and represent a unique basalt type distinct from those in the Apollo or Luna sample collections. LaPaz Icefield (LAP) 02205, LAP 02224, LAP 02226, LAP 02436 and LAP 03632 all contain plagioclase, pyroxene, ilmenite, spinel, olivine, and minor troilite, metal, phosphate, baddeleyite and silica (cristobalite). Brown glassy melt veins are ubiquitous and cross the primary igneous texture. Plagioclase, the major mineral and occurring as laths in a subophitic texture, is of narrow compositional range, from An_85–89. Pyroxene, also a major mineral, is strongly zoned, from augite and pigeonite cores to very iron‐rich rims. Ilmenite laths comprise approximately 3–5% of the basalts. Spinels show a large compositional range, comparable to that documented in Apollo 15 basalts, indicating an early chromite‐rich stage followed by an intermediate to late stage with Cr‐rich ulvöspinel. Relatively large, subhedral to skeletal olivine crystals (Fo_46–62) are sparse, and are too Forich to be in equilibrium with the bulk rock, indicating that these are xenocrysts rather than phenocrysts. The presence of melt veins with a similar composition to the bulk rock, maskelynitized plagioclase feldspar, and metastable cristobalite indicate that these rocks underwent significant shock, between 30 and 50 GPa. Calculated oxygen fugacity, using spinel‐ilmenite‐iron metal equilibria, is within the range defined by previous studies of lunar materials. The bulk composition (low MgO) and low calculated temperatures, together with modelling calculations, indicate an origin by fractional crystallization of a more primitive low TiO₂ parent liquid similar to Apollo 12 olivine basalt.  相似文献   

Genesis and continuity of quaternary sand and gravel in glacigenic sediment at a proposed low-level radioactive waste disposal site in east-central Illinois     

Kathy Goetz Troost  B. Brandon Curry 《Environmental Geology》1991,18(3):159-170

The Illinois Department of Nuclear Safety has characterized the Martinsville Alternative Site (MAS) for a proposed low-level radioactive waste disposal facility. The MAS is located in east-central Illinois approximately 1.6 km (1 mi) north of the city of Martinsville. Geologic investigation of the 5.5-km² (1380-acre) site revealed a sequence of chiefly Illinoian glacigenic sediments from 6 to 60 m (20–200 ft) thick overlying two major bedrock valleys carved in Pennsylvanian strata. Relatively permeable buried units include basal, preglacial alluvium; a complex of intraglacial and subglacial sediment; englacial deposits; and supraglacial fluvial deposits. Postglacial alluvium underlies stream valleys on and adjacent to the site. In most areas, the buried sand units are confined by low-permeability till, lacustrine sediment, colluvium, and loess. The distribution and thickness of the most extensive and continuous buried sand units have been modified considerably by subglacial erosion, and their distributions have been influenced by the buried bedrock valleys. The most continuous of the various sand units were deposited as preglacial and postglacial alluvium and are the uppermost and lowermost stratigraphic units at the alternative site. Sand units that were deposited in englacial or ice-marginal environments are less continuous. Aquifer pumping tests, potentiometric head data, and groundwater geochemistry analyses indicate minimal interaction of groundwater across localized interconnections of the permeable units.  相似文献   

Mildly peraluminous high-silica granites in a continental rift: the Drammen and Finnemarka batholiths,Oslo Rift,Norway     

Reidar G. Trønnes  Alan D. Brandon 《Contributions to Mineralogy and Petrology》1992,109(3):275-294

The peraluminous Drammen batholith (650 km²) is the largest granite complex within the mainly alkaline province of the Permo-Carboniferous Oslo Rift, and peraluminous to metaluminous granites are also present in the southern part of the otherwise alkaline Finnemarka complex (125 km²). The emplacement of the Drammen granite, and probably most of the other biotite granite complexes, predate the alkaline syenites and granites. The eight separate petrographic types of the Drammen batholith range in SiO₂ from 70 to 79 wt.% and have experienced variable amounts of fractionation of feldspars, biotite, zircon, apatite, titanite and Fe–Ti-oxides. The initial Sr, Nd and Pb isotopic ratios and a decoupling between the variations in the SiO₂ content and the aluminum saturation index [ASI=Al₂O₃/(CaO+Na₂O +K₂O)] show that the various intrusive phases are not strictly comagmatic. The _Nd values of the southern part of Finnemarka (+3.5 to +4) and the northern part of the Drammen granite (+1 to +1.5) are high and indicate insignificant (for Finnemarka) to minor Precambrian crustal or enriched mantle contributions. The very low _Sr values of all of these samples (–1 to –12, outside the main Oslo Rift magmatic array), point to a time integrated Rb-depleted crustal contaminant or an EM1 mantle component. The earliest extruded alkali basalts along the southwestern margin of the Oslo Rift are the only other samples within this low _Sr area, but their isotopic signature may also be linked to a mantle enrichment event (involving an EM1 component), e.g. associated with the Fen carbonatite magmatism 540 Ma ago. For a given ²⁰⁶Pb/²⁰⁴Pb, the ²⁰⁸Pb/²⁰⁴Pb ratios of the Drammen and Finnemarka batholiths are distinctly lower than those of the Skien alkaline volcanics and all other magmatic Oslo Rift rocks. This may indicate that the lithosphere of the central part of the rift had a time integrated Th-depletion. The samples from the southern part of the Drammen batholith, characterized by the presence of abundant miarolitic cavities, have _Nd near 0 (–0.7 to +0.4) but strongly elevated _Sr of +35 to +67. The combined Pb isotopic ratios of all the samples analyzed indicate that the Precambrian crustal anatectic contribution is in the form of time integrated Th-and U-depleted lower crust, and the high +_Sr of the sourthern part of the Drammen granite results from shallow level wallrock assimilation or magma-fluid interactions. The remarkably low contribution of old crustal components to the Finnemarka and the northernmost Drammen batholiths may result from extensive late Precambrian intracustal differentiation in southwestern Scandinavia, leading to widespread upper crustal granites ( 900 Ma) and a correspondingly dense and refractory lower crust, in particular in a zone intersecting the central part of the rift. Liquidus phase relations and mass-balance constrainst permit derivation of the granites from mildly alkaline to tholeiitic melts by extensive crystal fractionation of clinopyroxene-and amphibole-rich assemblages. It is equally possible to form the granitic magmas by partial melting of Permian gabbros of similar composition. Either scenario is consistent with the isotopic constrainst and with the presence of dense cumulates and/or residues in the lower crust. The lack of igneous rocks of intermediate composition associated with the Drammen and Finnemarka batholiths point to an efficient upper crustal density filtering. Considerable amounts of heat would be accumulated in this region if differentiated, intermediate melts could not escape to shallower levels. Successive magma injections would therefore easily result in partial melting of already solidified mafic to intermediate melts and cumulates, and it is suggested that the peraluminous granites formed mainly by water-undersaturated anatexis of mafic material.  相似文献   

Evaluating practical macrophyte control tools on small agricultural waterways in Canterbury,New Zealand     

Kathryn E. Collins  Catherine M. Febria  Helen J. Warburton  Hayley S. Devlin  Kristy L. Hogsden  Brandon C. Goeller 《新西兰海洋与淡水研究杂志》2019,53(2):182-200

Excessive macrophytes can cause significant problems in agricultural waterways requiring active management. Conventional control techniques can have a range of adverse effects. We investigated several control tools in two experiments: firstly, we tested eight treatments at a small-scale (2?m?×?2?m). We found intensive hand weeding, weed mat and herbicide spraying to be effective treatments, reducing macrophyte cover to <5%. Hand weeding and weed mat immediately reduced cover, while dieback from herbicide took two months. Weed mat was a novel and effective control mechanism along stream banks. Secondly, we tested the impact of shading on macrophyte growth. Macrophyte growth was enhanced under partially shaded conditions, but with 80% effective shading over the entire channel, cover was reduced to 17%. Once treatments ceased, macrophytes grew back within 3–5 months. Long-term, control methods will require combinations of tools but will need to include optimal shading for the target species.  相似文献   

Orbit uncertainty propagation and sensitivity analysis with separated representations     

Marc Balducci  Brandon Jones  Alireza Doostan 《Celestial Mechanics and Dynamical Astronomy》2017,129(1-2):105-136

Most approximations for stochastic differential equations with high-dimensional, non-Gaussian inputs suffer from a rapid (e.g., exponential) increase of computational cost, an issue known as the curse of dimensionality. In astrodynamics, this results in reduced accuracy when propagating an orbit-state probability density function. This paper considers the application of separated representations for orbit uncertainty propagation, where future states are expanded into a sum of products of univariate functions of initial states and other uncertain parameters. An accurate generation of separated representation requires a number of state samples that is linear in the dimension of input uncertainties. The computation cost of a separated representation scales linearly with respect to the sample count, thereby improving tractability when compared to methods that suffer from the curse of dimensionality. In addition to detailed discussions on their construction and use in sensitivity analysis, this paper presents results for three test cases of an Earth orbiting satellite. The first two cases demonstrate that approximation via separated representations produces a tractable solution for propagating the Cartesian orbit-state uncertainty with up to 20 uncertain inputs. The third case, which instead uses Equinoctial elements, reexamines a scenario presented in the literature and employs the proposed method for sensitivity analysis to more thoroughly characterize the relative effects of uncertain inputs on the propagated state.  相似文献   

Extending NMR data for permeability estimation in fine-grained sediments     

Hugh Daigle  Brandon Dugan   《Marine and Petroleum Geology》2009,26(8):1419-1427

We combine nuclear magnetic resonance (NMR) transverse relaxation time data and gamma ray data to estimate lithology-dependent permeability in silt- and clay-rich sediments. This approach extends the utility of the Schlumberger-Doll Research (SDR) permeability equation from reservoirs to aquicludes and seals, and thus improves the value and robustness of NMR data. Data from Keathley Canyon, northern Gulf of Mexico show that NMR data can be used to define permeability from 10⁻¹⁸ to 10⁻¹⁴ m² (0.001–10 millidarcies) as calibrated and tested by direct measurements on core samples. We performed uniaxial, constant rate-of-strain consolidation experiments on sediments from Keathley Canyon to determine core-scale permeability. Permeabilities from these experiments were compared to permeabilities calculated from logging-while-drilling data. A better fit between log-derived permeability and laboratory-measured permeability was obtained using the SDR equation with a variable coefficient A, rather than a constant A as is typically used. We show how A is a function of lithology and can be modeled from gamma ray data. The relationship between A and gamma ray values suggests that variations in A are caused by platy clay minerals and the effect they have on the pore system. Our results provide improved means for permeability estimation for application in basin flow modeling, hydrocarbon migration modeling, and well completion design.  相似文献   

Multiscale mechanical properties of shales: grid nanoindentation and statistical analytics     

Du  Jianting  Luo  Shengmin  Hu  Liming  Guo  Brandon  Guo  Dongdong  Zhang  Guoping 《Acta Geotechnica》2022,17(2):339-354

Acta Geotechnica - The mechanical properties of shales, a type of heterogeneous and multiphase composite, are of multiscale characteristics in nature. A large number of indentation measurements...  相似文献