Application of electromagnetic techniques in survey of contaminated groundwater at an abandoned mine complex in southwestern Indiana,U.S.A.

In part of a large abandoned mining complex, electromagnetic geophysical surveys were used along with data derived from cores and monitoring wells to infer sources of contamination and subsurface hydrologic connections between acidic refuse deposits and adjacent undisturbed geologic materials.Electrical resistivity increases sharply along the boundary of an elevated deposit of pyritic coarse refuse, which is highly contaminated and electrically conductive, indicating poor subsurface hydrologic connections with surrounding deposits of fine refuse and undisturbed glacial material. Groundwater chemistry, as reflected in values of specific conductance, also differs markedly across the deposit's boundary, indicating that a widespread contaminant plume has not developed around the coarse refuse in more than 40 yr since the deposit was created. Most acidic drainage from the coarse refuse is by surface runoff and is concentrated around stream channels.Although most of the contaminated groundwater within the study area is concentrated within the surficial refuse deposits, transects of apparent resistivity and phase angle indicate the existence of an anomalous conductive layer at depth (>4 m) in thick alluvial sediments along the northern boundary of the mining complex. Based on knowledge of local geology, the anomaly is interpreted to represent a subsurface connection between the alluvium and a flooded abandoned underground mine.     

Sedimentary record of heavy metal pollution in Lake Erie

Three cores, one kilometer apart, from each of seven locations along Lake Erie were analyzed for heavy metals and dated by ²¹⁰Pb techniques. The sedimentary record of anthropogenic inputs of heavy metals parallels the increasing intensity of cultural activity in the lake basin. On the average, pollution sources annually contribute 0.4 μg of Cd, 12 μg of Cu, 12 μg of Pb and 36 μg of Zn deposited per each cm² of the Eastern Basin sediments: 0.5, 8.8, 11 and 31 μg of Cd, Cu, Pb and Zn, respectively, deposited per cm² of Western Basin sediments and 0.7, 1.4, 2.0 and 5.6 μg of Cd, Cu, Pb and Zn, respectively, deposited per cm² of fine-grained sediments in the Central Basin. These anthropogenic flux rates exceed the pre-colonial data by 80–600%. The mean flux rates for ²¹⁰Pb into the Eastern. Central and Western Basins are 0.45, 0.07 and 0.15dpm cm^?2 yr^?1. respectively. From an inventory of sources and sinks of the metals, it is shown that about 2500 × 10³ kg of Cu. 1900 × 10³ kg of Pb and 6750 × 10³kg of Zn are delivered annually into the lake. The calculated retention in the lake sediments of 45%, 65% and 35% of the total annual inputs of Cu. Pb and Zn, respectively, agrees closely with the accumulation of data derived from sediment analyses. Sewage discharges, direct and indirect, are shown to be an important source of metal in the lake. The mean residence times in the water column are inferred to be 104 days for Cu. 180 days for Pb and 152 days for Zn.     

Plate driving forces at anomaly 23 time

A world-wide set of plate boundaries and relative velocities was calculated for anomaly 23 time (about 55 m.y. ago, at the Paleocene/Eocene boundary, just before the breakup of Australia—Antarctica). The set was used as input data for Harper's recently published model of plate driving and resisting forces for the present day. The model enabled estimates to be made for the age of the oceanic lithospheric sinking at present-day and at 55 Ma old subduction zones. Plausible ages were found for most zones. The worst relative error in any torque component for the 55 Ma reconstruction was less than 8 per cent of the largest driving torque component. This is about one and a half times the corresponding error obtained for the present-day plate driving force model. It is speculated that the transference of a subduction zone from the Indian to the Australian—Antarctic plate at about 55 Ma could have caused the breakup of Australia—Antarctica. The model was also useful when preparing the plate reconstruction, by giving physically implausible results for some regions. On closer examination, our initial data in these regions were found to be in error. The substitution of more recent data generally improved the results.     

Analysis of atmospheric flow over a surface protrusion using the turbulence kinetic energy equation

Flow over surface obstructions can produce significantly large wind shears such that adverse flying conditions can occur for aeronautical systems (helicopters, STOL vehicles, etc.) Atmospheric flow fields resulting from a semi-elliptical surface obstruction in an otherwise horizontally homogeneous statistically stationary flow are modelled with the boundary-layer / Boussinesq-approximation of the governing equation of fluid mechanics. The turbulence kinetic energy equation is used to determine the dissipative effects of turbulent shear on the mean flow. Mean-flow results are compared with those given in a previous paper where the same problem was attacked using a Prandtl mixing-length hypothesis. The diffusion and convection of turbulence kinetic energy not accounted for in the Prandtl mixing-length concept cause departures of the mean wind profiles from those previously computed, primarily in the regions of strong pressure gradients. Iso-lines of turbulence kinetic energy and turbulence intensity are plotted in the plane of the flow. They highlight regions of high turbulence intensity in the stagnation zone and sharp gradients in intensity along the transition from adverse to favourable pressure gradient.     

Unexpected hydrologic perturbation in an abandoned underground coal mine: Response to surface reclamation?

A reclamation project at the abandoned Blackhawk Mine site near Terre Haute, Indiana, lasted about four months and involved the burial of coarse mine refuse in shallow (less than 9 m) pits excavated into loess and till in an area of about 16 ha. An abandoned flooded underground coal mine underlies the reclamation site at a depth of about 38 m; the total area underlain by the mine is about 10 km². The potentiometric levels associated with the mine indicate a significant (2.7 m) and prolonged perturbation of the deeper confined groundwater system; 14 months after completing reclamation, the levels began to rise linearly (at an average rate of 0.85 cm/d) for 11 months, then fell exponentially for 25 months, and are now nearly stable. Prominent subsidence features exist near the reclamation site. Subsidence-related fractures were observed in cores from the site, and such fractures may have provided a connection between the shallower and deeper groundwater systems.     

Asthenosphere flow and plate motions

Summary. A dynamical theory of flow in the asthenosphere is developed by treating it as a thin layer of Newtonian viscous fluid, pushed horizontally by the dense sinking slabs attached to some plates and by the differences in heating under continental and oceanic crust. Two-dimensional lubrication theory is adapted to give the world-wide effects of inflow to the asthenosphere at the slabs, outflow to the plates at mid-ocean ridges, and the horizontal forces applied at the slabs. The resulting torque balance for the plates is better than any previously published, and leads one to conclude that the asthenosphere's viscosity is least at the top.     

Brachiopod survival and recovery from the latest Ordovician mass extinctions in South China

South China contains many complete sections through the upper Ordovician and lower Silurian. Brachiopod data including 130 brachiopod genera, assigned to 13 orders and 27 superfamilies from mid-Ashgill through late Aeronian intervals reveal that brachiopod macroevolution before and after the latest Ordovician mass extinction shows important changes in the diversity, composition and stratigraphical distribution of the phylum. The following six intervals are recognized: (1) a faunal plateau before the latest Ordovician mass extinction (mid-Ashgill, Rawtheyan); (2) a survival–recovery interval following the first phase of the mass extinction (late Ashgill, Normalograptus extraordinarius Zone and lower Glyptograptus? persculptus Zone; Hirnantian); (3) first survival interval following the mass extinction (latest Ashgill, upper Glyptograptus? persculptus Zone; end Hirnantian); (4) a second survival interval after the mass extinction (earliest Llandovery, Parakidograptus acuminatus Zone; early to mid-Rhuddanian); (5) a recovery interval in the Silurian (early to mid-Llandovery; late Rhuddanian to early Aeronian); and (6) a radiation interval in the Silurian (mid-Llandovery; mid- to late Aeronian). Only near-shore, low-diversity, benthic assemblages (mainly BA2), characterized by Ordovician relicts with a few Lazarus taxa and progenitors, are known from the southern marginal area of the Upper Yangtze epicontinental sea during the early to mid-Rhuddanian. They were replaced by newly established Silurian brachiopod communities (mainly BA2–3) in the late Rhuddanian to early Aeronian. These are marked by many newly evolved endemic forms and new immigrants, expressing a clear recovery within the Brachiopoda, but the recovery interval of the major brachiopod groups was heterochronous. In China the typical Silurian brachiopod fauna was mainly composed of indigenous Atrypida, Pentamerida and Spiriferida with stropheodontids derived from elsewhere, such as Baltica and Avalonia, two apparent refugia in the survival interval. The Atrypida was the first major group of Brachiopoda to diversity in the late Rhuddanian. Copyright © 1999 John Wiley & Sons, Ltd.