Tashamingo Subdivision in Sinking Creek karst valley, a tributary of the Garretts Spring drainage basin in Jessamine and Woodford counties, Kentucky, was flooded in February 1989. To determine the cause of flooding, the groundwater basin boundary was mapped, discharge data were measured to determine intake capacity of swallets, and hydrologic modeling of the basin was conducted. Swallet capacity was determined to be limited by the hydraulic parameters of the conduit, rather than by obstruction by trash. Flooding from a precipitation event is more likely, and will be higher, when antecedent soil moisture conditions in the watershed are near saturation. Hydrologic modeling shows that suburban development of 20 percent of the southeast basin will cause a small increase in flood stage at Tashamingo Subdivision. 相似文献
In the aureole of the Beinn an Dubhaich granite, Skye, the minimum observed median forsterite-calcite-calcite dihedral angle
varies from 110° at the olivinein isograd to about 165° (the equilibrium value) at the granite-limestone contact. Laboratory
experiments were performed to investigate the kinetics of this textural change. It was found that the rate of change of the
forsterite-calcite-calcite dihedral angle followed approximately first-order kinetics with an activation energy of 48±4 kJ
mol-1 for fluid-present conditions, and 90 ±4 kJ mol-1 for fluid-absent conditions. Scanning ion imaging demonstrated that, at least in the early stages of textural change, solution-reprecipitation
of the calcite was the rate determining step in the fluid-present runs. The latter result and the value of the activation
energy are both consistent with the activation energy found by previous authors for (albeit zeroth order) silicate-aqueous
solution solution-reprecipitation reactions. The value of activation energy for the dry data does not correspond to those
for either grain boundary or volume diffusion of oxygen or magnesium in forsterite. The mechanism for textural equilibration
in the fluid-absent runs is uncertain. Application of the experimentally-derived rate equation to the Beinn an Dubhaich marbles
gave activation energies higher than those obtained experimentally. It is concluded from consideration of grain growth effects
that activation energies derived from the Beinn an Dubhaich marbles probably reflect textural equilibration under predominantly
fluid-absent conditions. 相似文献
The variation of elastic lithospheric thickness within the Canadian landmass is determined using the coherence between surface topography and Bouguer gravity anomalies. Estimates of elastic thickness (or, equivalently, rigidity) are derived by minimizing the difference between the observed coherence and that predicted by an isostatic model consisting of a thin elastic plate which is subject to surface and subsurface loading and overlies a fluid substratum (the asthenosphere).
Estimates of the elastic thickness vary from 17–18 km in coastal Labrador and Baffin Island to > 150 km near Lake Winnipeg, Manitoba. A broad correlation exists between lithospheric thickness and age. Exceptions to this correlation are areas of reduced plate thickness in North Atlantic coastal regions where magmatic activity associated with rifting and the formation of a passive margin may have been sufficient to reduce the plate strength but not enough to reset the thermal age of the basement rocks. Areas of greater plate thickness than that predicted by thermal cooling occur in the continental interior and may reflect lithospheric thickening due to the chemical and mechanical effects accompanying continental agglomeration. 相似文献
Magnetic susceptibility and its anisotropy in the Borrowdale Volcanic slates at Kentmere in the English Lake District are attributed largely to preferred orientation of a paramagnetic chlorite of diabantite-ripidolite composition. In units of 10−6 cgs/g, the principal susceptibilities for the slates are 9.61; 9.42; 8.69 and for the chlorite grains the minimum anisotropy is represented by principal susceptibilities of 11.57; 11.22 and 9.15. Because the magnetic susceptibility is carried by a tightly packed, matrix-forming mineral that has recrystallised during the deformation it is not possible to imagine simple grain rotation as being responsible for the anisotropy of susceptibility. 相似文献
Preliminary results of a seasonal study of the pelagic community at a station on the outer edge of the Cornwallis Estuary suggest that the seasonal variation in plankton community respiration (PCR) is related to organic inputs from nearby salt marshes. Annual phytoplankton production is low (<30 g C m−2 y−1) and exhibits a seasonal cycle very different from PCR. There is no indication that resuspension of benthic diatoms is an important energy input to the pelagic system. PCR, however, is quite high and exhibits a seasonal trend similar to the export of salt marsh detritus. Zooplankton densities (5–200 l−1) and biomass (<0.4 g m−3) appear to be much greater than could be supported by phytoplankton alone. The Cornwallis Estuary may be an estuarine system exhibiting a net export of organic matter to nearby offshore waters. 相似文献
The ratio and other parameters have been measured in fossil planktonic foraminifera from the Atlantic and Pacific Ocean basins in order to evaluate the ratio of seawater during the last 75 million years. Results on well-preserved samples indicate that the ratio has increased to its present value by 10–15% during the Cenozoic, and that minima occurred between 55-45 Ma and 10-5 Ma, when the ratio was 15–25% less than at present. The long-term increase may reflect either decreasing deposition of aragonite with a high ratio in shallow seas, or decreasing seafloor spreading rates and consequently decreasing hydrothermal supply of Ca during the Cenozoic. Other geologic evidence suggests that the Eocene minimum (near 50 Ma) may have resulted from increased aragonite sedimentation, while the Late Miocene minimum (between 10-5 Ma) may have been caused by an increased rate of seawater-basalt exchange when seafloor spreading rates increased on the East Pacific Rise near 10 Ma. 相似文献
Long period body waves are examined to show that the Hamran (1972.9.3), Darel (1981.9.12) and Patan (1974.12.28) earthquakes in Kohistan had focal depths of about 8–10 km. All involved high angle reverse faulting (thrusting) and had seismic moments of about 2.2 to 2.7·1025 dyne cm. These shallow depths contrast with the deeper hypocentres found in the Hindu Kush and northeast Karakoram to the north and in Hazara to the south. The Hamran and Patan shocks were assigned depths of 45 km by the ISC, indicating that even well-recorded events in this region may have focal depths in error by 30 km 相似文献