Author's reply     

G.M. Thompson  D.N. Lumsden  R.L. Walker  J.A. Carter 《Geochimica et cosmochimica acta》1978,42(4):437-439

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Uranium series dating of stalagmites from Blanchard Springs Caverns,U.S.A.     

Glenn M. Thompson  David N. Lumsden  Raymond L. Walker  Joel A. Carter 《Geochimica et cosmochimica acta》1975,39(9):1211-1218

Because stalagmites are enriched in ²³⁴U beyond the equilibrium value at the time of deposition, they are potentially datable by measuring their progress toward equilibrium. Procedures for uranium-thorium and uranium disequilibrium dating of speleothems were developed, making use of alpha spectrometry for thorium determinations and mass spectrometry for uranium determinations. The stalagmites tested were generally beyond the age range of the U-Th age dating method and, as a result, ²³⁴U/²³⁸U ratios provided the most useful dating technique. The estimated age range for a stalagmite from Blanchard Springs is 135,000 to 785,000 years BP with an interval of slow or suspended growth from about 320,000 to 570,000 years BP.  相似文献   

The precambrian of north-western Queensland,Australia     

E. K. Carter 《International Journal of Earth Sciences》1959,47(2):510-522

Precambrian rocks, ranging in age from probable Archaean to Upper Proterozoic, crop out over an area of 25,000 square miles in north-western Queensland. They fall into four large divisions, separated by major unconformities. Little is known of the history of the Archaean rocks, which are believed to include altered acid lavas, schists, gneisses and migmatite. The Lower Proterozoic strata form part of an orogenic belt. The Lower Proterozoic lower sequence is rich in altered acid and basic lavas. It has a maximum thickness of not less than 40,000 feet and was strongly deformed by east-west pressure and probably intruded by granite before the Lower Proterozoic upper sequence was deposited. Sediments form the bulk of the Lower Proterozoic upper sequence; these accumulated most thickly to the west and north-west of the core of lower sequence belt, but overlie lower sequence strata. The greatest thickness of sediments is at least 40,000 feet. The sequence was deformed by a renewal of east-west compressive stresses, accompanied by granite emplacement. Folding is strong to moderate, but lacks well-defined linearity in the west of the outcrop area.Upper Proterozoic sediments and lavas accumulated mainly in the west and north-west of the region. They are gently to moderately folded on west to north-west axes.The Precambrian in north-western Queensland, excluding the Camooweal Dolomite, crops out over about 25,000 square miles. Systematic field work was started by joint teams of the Commonwealth Bureau of Mineral Resources and the Geological Survey of Queensland in 1950.Reconnaissance mapping of the region was completed in 1954 but check work and more detailed mapping of areas of economic interest are still in progress. Maps are being prepared at a scale of 1 inch to 4 miles (1: 253,440) and a report on the area is being written (Carter andBrooks, in preparation). The Camooweal Dolomite, of Upper Proterozoic or Lower Cambrian age, is not included. Its stratigraphic and palaeographic position is discussed byNoakes (1956).The reconstruction of the geological history of the region presented below is an interpretation of the data obtained. The evidence is not sufficiently complete to enable a unique interpretation to be made of all aspects of the region's history. In particular the history of granite intrusion has not yet been completely unravelled.Paper published by permission of the Secretary, Department of National Development.  相似文献   

Seasonal and spatial distribution of planktonic crustacea in the lower Saint John River,a multibasin estuary in New Brunswick,Canada     

J. C. H. Carter  M. J. Dadswell 《Estuaries and Coasts》1983,6(2):142-153

Five stations on the lower Saint John River, a complex multibasin estuary, were sampled semiquantitatively for zooplankton at biweekly intervals for one year, and qualitatively over a 4-year period. Planktonic Crustacea were dominated by the true estuarine copepods,Acartia tonsa andEurytemora affinis and the euryhaline marine copepodsOithona similis andPseudocalanus minutus. Atypical estuarine forms, confined to a lower fiord-like basin with salinity of 20‰, were the amphipod,Parathemisto abyssorum and the mysidErythrops erythrophthalma. River flows were highly variable from year to year. Certain basins function as lakes in some years and estuaries in other years, causing extreme zooplankton community fluctuations, and succession patterns dependent on salinity rather than season. On occasion freshwater zooplankters maintained viable populations at unusually high salinities (ca. 5‰). Vertical and horizontal distributions of zooplankters indicate that the estuary in fact comprises two systems: a true estuary in the upper reaches and the surface waters at the lower end, and a fiord in a subsidiary basin in the lower end.  相似文献   

Total oxyradical scavenging capacity responses in Mytilus galloprovincialis transplanted into the Venice lagoon (Italy) to measure the biological impact of anthropogenic activities     

Camus L  Pampanin DM  Volpato E  Delaney E  Sanni S  Nasci C 《Marine pollution bulletin》2004,49(9-10):801-808

Oxidative stress related investigations to monitor the impact of the pollutant discharges into the Venice lagoon (Italy) originating from anthropogenic activities (raw sewage water, agricultural and industrial effluents, oil tanker traffic), on marine organisms have classically been carried out by analyzing specific, single antioxidants (i.e. catalase, superoxide dismutase). In this paper, two studies are reported where the total oxyradical scavenging capacity assay (TOSC) was selected and measured toward peroxyl, and hydroxyl free radicals, and peroxynitrite in mussels (Mytilus galloprovincialis) transplanted into the Venice city and throughout the lagoon to measure the biological effects of anthropogenic activities. In the first experiment, mussels from a clean site (farm) were transplanted to the urban area of Venice for 0, 1, 2 and 4 weeks; cytosolic TOSC toward peroxyl and hydroxyl free radicals, and peroxynitrite revealed that the transplantation process caused a stress (handling stress, anoxia, oxidative burst) resulting in a reduction of TOSC in both control and urban sites, therefore, preventing clear interpretation of the data after one week. At week 2, a significant TOSC reduction (P < 0.05) toward peroxyl and hydroxyl radicals in the urban site revealed that mussels experienced oxidative pressure exerted by pollutants. Most TOSC values returned to initial levels at week 4; however, TOSC induction was noticed in the control group toward peroxyl and hydroxyl radicals while in the exposed group it was not indicating an inhibition of the oxidative metabolism. In the second experiment, mussels were deployed at seven different sites throughout the lagoon. After five weeks of exposure, significant TOSC reduction was measured (P < 0.05) toward peroxyl for Palude della Rosa, Chioggia and Valle Millecampi, toward hydroxyl radicals for Valle Millecampi and Campalto and toward peroxynitrite for Valle Millecampi. Although these data indicate a depletion of the low molecular weight scavengers, additional biomarkers are needed to draw a conclusion on the health of the mussels. TOSC was proved to be an interesting health index parameter to measure pollution impact in a transplantation study provided that the mussels are exposed for two weeks and a control is run in parallel.  相似文献   

Habitat requirements for submerged aquatic vegetation in Chesapeake Bay: Water quality, light regime, and physical-chemical factors   总被引：1，自引：0，他引：1  

W. Michael Kemp  Richard Batleson  Peter Bergstrom  Virginia Carter  Charles L. Gallegos  William Hunley  Lee Karrh  Evamaria W. Koch  Jurate M. Landwehr  Kenneth A. Moore  Laura Murray  Michael Naylor  Nancy B. Rybicki  J. Court Stevenson  David J. Wilcox 《Estuaries and Coasts》2004,27(3):363-377

We developed an algorithm for calculating habitat suitability for seagrasses and related submerged aquatic vegetation (SAV) at coastal sites where monitoring data are available for five water quality variables that govern light availability at the leaf surface. We developed independent estimates of the minimum light required for SAV survival both as a percentage of surface light passing though the water column to the depth of SAV growth (PLW _min) and as a percentage of light reaching reaching leaves through the epiphyte layer (PLL _min). Value were computed by applying, as inputs to this algorithm, statistically dervived values for water quality variables that correspond to thresholds for SAV presence in Chesapeake Bay. These estimates ofPLW _min andPLL _min compared well with the values established from a literature review. Calcultations account for tidal range, and total light attenuation is partitioned into water column and epiphyte contributions. Water column attenuation is further partitioned into effects of chlorophylla (chla), total suspended solids (TSS) and other substances. We used this algorithm to predict potential SAV presence throughout the Bay where calculated light available at plant leaves exceededPLL _min. Predictions closely matched results of aerial photographic monitoring surveys of SAV distribution. Correspondence between predictions and observations was particularly strong in the mesohaline and polythaline regions, which contain 75–80% of all potential SAV sites in this estuary. The method also allows for independent assessment of effects of physical and chemical factors other than light in limiting SAV growth and survival. Although this algorithm was developed with data from Chesapeake Bay, its general structure allows it to be calibrated and used as a quantitative tool for applying water quality data to define suitability of specific sites as habitats for SAV survival in diverse coastal environments worldwide.  相似文献   

Mid-Cretaceous uplift and erosion on the northern margin of the Ligurian Tethys deduced from thermal history reconstruction     

Jean-Baptiste Peyaud  Jocelyn Barbarand  Andy Carter  Maurice Pagel 《International Journal of Earth Sciences》2005,94(3):462-474

The paleogeography during Early Cretaceous of the northern margin of the Ligurian Tethys is poorly constrained because of deformation and erosion during Pyrenean and Alpine orogenic phases. The present-day limit between Lower Cretaceous sediments in the South–East basin, located at the northwestern margin of the Ligurian Tethys, and basement rocks is the consequence of a protracted erosion history. Lower Cretaceous sediments observed today in the basin, even close to the present-day outcropping border, are characteristic of pelagic environments. A larger extent of a Lower Cretaceous cover on the basement must then be considered. This study focuses on the western part of this margin (the Causses basin), in the South of the Massif Central (France), using several thermochronometers and geothermometers to decipher the former extent of the sedimentary cover. Apatite fission track thermochronology on basement rocks surrounding the Causses basin suggests that these rocks cooled from temperatures higher than 110°C during the mid-Cretaceous. Average fluid inclusion homogenisation temperatures between 94°C and 108°C are recorded in calcite veins from outcropping Toarcian and Aalenian shales. In the shales, Tmax values, temperature obtained by Rock–Eval pyrolysis of organic matter, are in agreement with these elevated temperatures. Different explanations for these relatively high temperatures, which cannot be explained by the present-day sedimentary serie in the basin, have been tested using a 1D thermal modelling procedure (Genex). For a 95±10-mW/m² paleoflux, thick sedimentary deposits (2.5±0.3 km) including 1.3±0.3 km of Lower Cretaceous sediments cover the South of the Massif Central; these formations have been subsequently eroded from mid-Cretaceous time onwards. This study confirms that the South of the Massif Central was a site of marine sedimentation during the Early Cretaceous where a thick sedimentary sequence was once deposited.  相似文献   

Rural diversification in Bulgaria     

F.W. Carter  D. Kaneff 《GeoJournal》1998,46(3):183-191

Agriculture has always been very important for the Bulgarian economy, but during the socialist period there was considerable progress made in the diversification of employment opportunities in rural areas. While many people commuted to non-agricultural jobs in the townships (and there was a large permanent transfer from rural to urban areas), there were additional opportunities in small factories and local services in the villages themselves. The transition has seen these opportunities much reduced, at precisely the time when full-time paid work in agriculture has declined due to market restructuring while complex problems have emerged associated with liquidating the state-run cooperatives and establishing a viable alternative. The paper discusses the general issues and presents a case study from the north-central part of the country. The rebuilding of a cooperative farming system (along with other forms of consolidation) is a positive trend which could increase spending power in the villages and help in the growth of employment in rural industries and services. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Differential rotation of relativistic superfluid in neutron stars     

David Langlois  David M. Sedrakian  & Brandon Carter 《Monthly notices of the Royal Astronomical Society》1998,297(4):1189-1201

It is shown how to set up a mathematically elegant and fully relativistic superfluid model that can provide a realistic approximation (neglecting small anisotropies due to crust solidity, magnetic fields, etc., but allowing for the regions with vortex pinning) of the global structure of a rotating neutron star, in terms of just two independently moving constituents. One of these represents the differentially rotating neutron superfluid, while the other part represents the combination of all the other ingredients, including the degenerate electrons, the superfluid protons in the core, and the ions in the crust, the electromagnetic interactions of which will tend to keep them locked together in a state of approximately rigid rotation. Order of magnitude estimates are provided for relevant parameters such as the resistive drag coefficient.  相似文献   

Clast sizes of ejecta from explosive eruptions on asteroids: implications for the fate of the basaltic products of differentiation     

Lionel Wilson  Klaus Keil   《Earth and Planetary Science Letters》1996,140(1-4):191-200

We use a simple model of the formation, growth, coalescence and migration of veins of basaltic melt generated by partial melting in chondritic asteroids to deduce the sizes of, and pressures within, the fluid-filled dikes reaching the surfaces of such bodies. The gas contents ( 1000 ppm of mainly CO and N₂) of the asteroids were high enough that bubbles of free gas trapped in the melt veins gave the basaltic melts significant buoyancy; expansion of these gases as a dike opened to the vacuum at the surface led to fragmentation of the melts into liquid droplets which were transported upwards by the accelerating gases to the surface. The sizes of these droplets and, hence, of the pyroclastic glass beads into which they cooled, are calculated to lie in the range 30 μm to 4 mm; this range is essentially independent of the size or gas content of the asteroid parent and only weakly dependent on the internal pressure of the erupting fluid. The fate of the pyroclasts, however, does depend on all of these factors. At very low internal pressures, significant separation of the gas and liquid in a rising dike may take place and not all of the liquid will be expelled from the dike when it opens to the surface. For relatively large ( 100 km radius) asteroids with relatively low ( 300 ppm) gas contents, the larger clasts are too heavy to be lifted from the level at which magma fragmentation takes place by the gas flow and so would also remain behind to form basaltic veins. The apparent absence of basaltic veins in meteorites then implies both that internal pressures in near-surface dikes were generally greater than 0.3 MPa and that low gas contents were not common. Finally, as long as pyroclasts are lofted from the magma fragmentation level, they will be accelerated to at least 90% of the final gas speed. If this speed exceeds the escape speed from the asteroid (as happens readily for high gas contents and small asteroids), the pyroclasts will be expelled into space and lost from the meteorite record. Otherwise (low gas contents or large asteroids), they will eventually fall back to be incorporated into the surface regolith, modifying the chemical and physical properties of meteorites subsequently derived from it.  相似文献