Acid mine drainage contaminates groundwater of a Tennessee watershed     

Christopher J. O’Bara  R. Don Estes 《Environmental Geology》1985,7(3):159-161

Water samples were collected from 18 natural springs within the West Fork of the Obey River watershed. Overton County, Tennessee, to determine if groundwater was adversely affected by runoff from abandoned surface coal mines Six springs were found to be affected severely and deemed unfit as a source of potable water Water quality of the remaining springs was essentially unaffected it appeared that proximity to surface mines, elevation at the outflow, and geology of the surrounding strata determined the quality of the groundwater The unit is jointly supported by Tennessee Technological University, the Tennessee Wildlife Resource Agency, and the US. Fish and Wildlife Service  相似文献   

Buried trees,water table fluctuations,and 3000 years of changing climate in west-central Oklahoma     

Stephen A. Hall  Christopher Lintz 《Quaternary Research》1984,22(1):129-133

A sequence of radiocarbon-dated buried trees, buried soils, a carbonate zone, and a molluscan fauna from Carnegie Canyon indicate that between 3200 and 2600 yr B.P. the climate of west-central Oklahoma was drier than today. A high water table accompanied a period of moister climate 2000 to 1000 yr B.P. The water table dropped after 1000 yr B.P. due to a change toward dry conditions.  相似文献   

Rhabdopleura hollandi, a new pterobranch hemichordate from the Silurian of the Llandovery district,Powys, Wales     

R.B. Rickards  A.J. Chapman  J.T. Temple 《Proceedings of the Geologists' Association. Geologists' Association》1984,95(1):23-28

  相似文献   

The downward continuation of aerial gravimetric data without density hypothesis     

Christopher Jekeli 《Journal of Geodesy》1987,61(4):319-329

Techniques for downward continuing gravity field data from aircraft altitude are well established if the earth's surface is either approximated by a plane or sphere, or is replaced by one of these surfaces using terrain corrections based on a density model. An alternative procedure is presented here where the continuation is analytical to a nontrivial surface, such as the actual topographic surface. Terrain elevations must be given, but density information is specifically not used.  相似文献   

14C dating and palaeoenvironment of the historic ‘little ice age’ glacier advance of Nigardsbreen Southwest Norway     

John A. Matthews  John L. Innes  Christopher J. Caseldine 《地球表面变化过程与地形》1986,11(4):369-375

Moss and grass remains associated with a well-developed in situ palaeosol buried beneath a moraine ridge in front of Nigardsbreen (Jostedalsbreen ice cap, southern Norway) have been ¹⁴C-dated. Pollen preserved with the plant remains suggests the existence of an agricultural landscape prior to the deposition of the moraine. The calibrated dates and the pollen spectra are in close accord with historically-documented evidence for the timing and palaeoenvironment of the ‘Little Ice Age’ advance of the glacier. Considerable potential is indicated for estimating the maximum ages of moraine ridges and for palaeoenvironmental reconstruction where such documentary evidence does not exist.  相似文献   

Thermal regime at the Upper Stillwater dam site, Uinta mountains, Utah: Implications for terrain, microclimate and structural corrections in heat flow studies     

Michael S. Bauer  David S. Chapman 《Tectonophysics》1986,128(1-2)

A detailed study of the subsurface thermal regime at the Upper Stillwater dam site, Uinta Mountains, northeast Utah, has been made. Temperature measurements were made in 36 drillholes located within a 1 km² area and ranging in depth from 20 to 97 m. Holes less than about 40 m deep were used only to obtain information about spatial variations in mean annual surface temperature. Several holes in or near talus slopes at the sides of the canyons have temperature minima approaching 0°C between 10 and 20 m indicating the presence of year-round ice at the base of the talus. Another set of holes show transient thermal effects of surface warming resulting from clearing of a construction site 3.5 years prior to our measurements. Most of the remaining holes show conductive behavior and have gradients ranging from 13° to 17°C km⁻¹. Measurements made on 44 core samples yield a thermal conductivity of 5.6 (std. dev. 0.35) W m⁻¹ K⁻¹ for the Precambrian quartzite present. Surface heat flow estimates for these holes range from 70 to 100 mW m⁻². However, the local disturbance of the thermal field by topography and microclimate is considerable. A finite difference method used to model these effects yielded a locally corrected Upper Stillwater heat flow of about 75 mW m⁻². A final correction to account for the effects of refraction of heat from the low conductivity sedimentary rocks in the Uinta Basin into the high conductivity quartzite at the dam site, produced a regionally corrected Upper Stillwater heat flow between 60 and 65 mW m⁻². This value is consistent with the observed heat flow of 60 mW m⁻² in the Green River Basin to the north and the Uinta Basin to the south.  相似文献   

Pressure dependence of melt viscosities on the join diopside-albite     

Mark Brearley  James E. Dickinson  Jr.  Christopher M. Scarfe 《Geochimica et cosmochimica acta》1986,50(12):2563-2570

The pressure dependence of melt viscosities on the join diopside-albite has been studied using falling-sphere viscometry. The five melt compositions investigated are: diopside, Ab₂₅Di₇₅, Ab₅₀Di₅₀, Ab₇₅Di₂₅ and albite. Experiments were performed at 1500° and 1600°C and at pressures of 5, 10, 15, 20 and 25 kbar. The positive and negative pressure dependence of the viscosity of diopside and albite, respectively, were confirmed. All intermediate compositions show an initial decrease in viscosity with increasing pressure; however, melt of Ab₂₅Di₇₅ composition passes through a minimum viscosity at approximately 12 kbar and 1600°C. This behavior is analogous to the variation in the viscosity of water with pressure at low temperature.

It is suggested that the three-dimensional, fully polymerized, albite structure dominates flow at low pressures. With increasing pressure, disruption of this structure and decrease in the average size of the flow units leads to domination by the diopside structure. The variation in viscosity with composition along the join at one atmosphere can be adequately modelled using the and (1965) configurational entropy model with an additional two-lattice configurational entropy of mixing term. The pressure dependence of viscosity in the diopside-albite system, however, cannot be predicted by the model, because there is an absence of information on the pressure dependence of the model parameters.

It is probable that relatively polymerized magmas (e.g. rhyolites to SiO₂-saturated basalts) show a negative pressure dependence of viscosity to depths where they originate in the lower crust or upper mantle. In contrast, the most depolymerized, naturally-occurring melts, such as strongly SiO₂-undersaturated basalts and picrites, may exhibit a viscosity minimum. The viscosity of these melts may be sufficiently high at depths within the upper mantle to inhibit their segregation, rise and eventual eruption at the surface.  相似文献   

Finite-difference elastic wave propagation in 2D heterogeneous transversely isotropic media1     

Christopher Juhlin 《Geophysical Prospecting》1995,43(6):843-858

The velocity-stress formulation for propagation of elastic seismic waves through 2D heterogeneous transversely isotropic media of arbitrary orientation is presented. The equations are recast into a finite-difference scheme and solved numerically using fourth-order spatial operators and a second-order temporal operator on a staggered grid. Absorbing, free-surface and symmetry boundary conditions have been implemented. Test cases compare well with other published solutions. Synthetic seismograms are calculated over two idealized models: (i) vertical fractures in granite with a dolerite sill reflector and (ii) a dipping anisotropic shale. Comparisons with the isotropic counterparts show significant differences which may have to be accounted for in seismic processing in the future.  相似文献   

Delay coordinates: a sensitive indicator of nonlinear dynamics in single charged particle motion in magnetic reversals     

Sandra C. Chapman  Nicholas W. Watkins 《Annales Geophysicae》1995,13(8):836-842

The delay coordinate technique is examined as an indicator of the regime of particle dynamics for the system of single charged particle motion in magnetic reversals. Examples of numerically integrated trajectories in both static (zero electric field) and time dependent (corresponding nonzero induction electric field) simple models for magnetic reversals are considered. In the static case, the dynamics can in principle be directly classified by constructing Poincaré surfaces of section; here we demonstrate that whilst the Poincaré surface contains the relevant information to classify the dynamics, the corresponding delay coordinate plot can provide a far more sensitive indication of the onset of nonregular behaviour. In the case of nonperiodic time dependence considered here Poincaré plots cannot in general be constructed directly. Nevertheless, delay coordinate plots can still reveal details of the phase space portrait of the system, and here are shown to indicate whether segments of stochastic motion exist in a given trajectory. It is anticipated that the delay coordinate plot technique as realized here will be a valuable tool in characterizing the behaviour in large numbers of trajectories that are evolved in time-dependent systems, thereby giving us insight into the evolution of the distribution function as a whole, either in prescribed fields or in self-consistent numerical simulations.  相似文献   

The use of bioassays as part of a comprehensive approach to marine pollution assessment     

Peter M Chapman  Edward R Long 《Marine pollution bulletin》1983,14(3):81-84

  相似文献