Interpretation of210Pb profiles and verification of the CRS dating model in PIRLA project lake sediment cores     

Michael W. Binford  Jeffrey S. Kahl  Stephen A. Norton 《Journal of Paleolimnology》1993,9(3):275-296

This paper reports results and analysis of²¹⁰Pb-activity measurements in 51 lake-sediment cores from 32 lakes in the four PIRLA (Paleoecological Investigations of Recent Lake Acidification) project regions (Adirondack Mountains [New York], Northern New England, Northern Florida, and the Northern Great Lakes States). General application of the Constant Rate of Supply (Constant Flux) model for²¹⁰Pb dating is valid for lakes in the PIRLA study, although application of the model is equivocal in a few lakes.²¹⁰Pb inventories and profiles are replicable among closely spaced cores within a lake. Specific²¹⁰Pb activity in surface sediments is negatively correlated with bulk sediment accumulation rate in seepage lakes, but not in drainage lakes. Drainage lakes with lower pH have lower unsupported²¹⁰Pb inventories in sediments, but the relationship does not occur in seepage lakes.²¹⁰Pb profiles in only seven of the cores, all from either the Adirondacks or the northern Great Lakes states, exhibit exponential decay curves. Deviations from an exponential profile include a flattening of the profile in the top few cm or excursions of one or a few measurements away from an exponential curve.²¹⁰Pb dates typically agree with other chronostratigraphic markers, most of which are subject to greater uncertainty. Several hypotheses, including sediment mixing, hydrologic regime, sediment focusing, and acidification, are proposed to explain variation of²¹⁰Pb distribution among lakes and regions. Hydrologic factors exert control on unsupported²¹⁰Pb inventories in PIRLA lakes, and there is a strong focusing effect in drainage lakes but a weak focusing effect in seepage lakes.This is the third of a series of papers to be published by this journal following the 20^th anniversary of the first application of²¹⁰Pb dating of lake sediments. Dr P. G. Appleby is guest editing this series.  相似文献   

Epithermal environments and styles of mineralization: Variations and their causes, and guidelines for exploration   总被引：3，自引：0，他引：3  

Noel C. White  Jeffrey W. Hedenquist 《Journal of Geochemical Exploration》1990,36(1-3)

Epithermal precious- and base-metal deposits are diverse, reflecting the different tectonic, igneous and structural settings in which they occur, the complexities of their local setting, and the many processes involved in their formation. Most epithermal deposits form at shallow crustal levels where abrupt changes in physical and chemical conditions result in metal deposition and attendant hydrothermal alteration. The principal factors that influence the conditions prevailing in the epithermal environment, and which ultimately determine the sites and character of mineralization, include: geology (structure, stratigraphy, intrusions and rock type, which affect the style and degree of permeability and the reactivity of the host); pressure and temperature (which in the epithermal environment are related on the boiling point with depth curve); hydrology (the relationship between permeability and topography which governs fluid flow, and discharge/recharge characteristics, as well as access of steam-heated waters); chemistry of the mineralizing fluid (which determines the metal-carrying capacity, as well as the associated vein and alteration assemblage); and syn-hydrothermal development of permeability and/or changes in hydraulic gradients.Many attempts have been made to classify epithermal deposits based on mineralogy and alteration, the host rocks, deposit form, genetic models, and standard deposits. All have their strengths and weaknesses. We prefer a simple approach using the fundamental fluid chemistry (high or low sulfidation, reflecting relatively oxidized or reduced conditions, respectively) as readily inferred from vein and alteration mineralogy and zoning, together with the form of the deposit, and using comparative examples to clarify the character of the deposit.Guidelines for exploration vary according to the scale at which work is conducted, and are commonly constrained by a variety of local conditions. On a regional scale the tectonic, igneous and structural settings can be used, together with assessment of the depth of erosion, to select areas for project area scale exploration. At project area scale, direct (i.e. geochemical) or indirect guidelines may be used. Indirect methods involve locating and interpreting hydrothermal alteration as a guide to ore, with the topographic and hydrologic reconstruction of the system being of high priority. These pursuits may involve mineralogic, structural, geophysical or remote sensing methods. On a prospect scale, both direct and indirect methods may be used; however, they can only be effective in the framework of a sound conceptual understanding of the processes that occur in the epithermal environment, and the signatures they leave.  相似文献   

Local currents at a shoreface-connected ridge in the German Bight     

Holger Klein  Dr. Ekkehard Mittelstaedt 《Ocean Dynamics》1991,44(3):133-142

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Evaporation from the understorey in the Jarrah (Eucalyptus marginata Don ex Sm.) forest, southwestern Australia     

E.A.N. Greenwood  L. Klein  J.D. Beresford  G.D. Watson  K.D. Wright 《Journal of Hydrology》1985,80(3-4):337-349

Annual evaporation from groundflora, litter and soil of the jarrah forest was estimated from measurements of daily evaporation by ventilated chambers on several days over two separate 12-month periods. In the first year, when sampling ranged over 0.1 ha of forest, annual evaporation during daylight hours was estimated as 410 mm (0.32 rainfall). In the second year, sampling was more frequent, on a larger scale, and included the night hours. Annual evaporation was estimated at 360 mm (0.36 rainfall).

Similarly, in the second year, annual evaporation from two trees of the dominant middle storey species, Banksia grandis, was estimated at 7500 and 18,9001 respectively. The leaf area of these two trees was 9.6 and 22.4 m², respectively, so that annual evaporation, when expressed as mm³ per mm² leaf area, was similar for both trees (mean = 820 ± 30 mm). Applying that value to all Banksia trees in a hectare of forest, and using a measured estimate of leaf area index of 0.19, the estimated annual evaporation from the Banksia component was 155 mm (0.16 rainfall). For the upland part of the forest sampled, the combined annual evaporation from the lower and middle storeys accounted for about half (0.51) of the annual rainfall.

We conclude that reduced evaporation from the upper storey following clearing or thinning may be strongly counteracted by increased evaporation from the understorey due to increased availability of energy and water.  相似文献   

The frequency and periodicity of preserved turbidites in submarine fans as a quantitative record of tectonic uplift in collision zones     

George Devries Klein 《Tectonophysics》1985,119(1-4)

The frequency and periodicity of preserved graded turbidite cycles in submarine fans in the Coral Sea and Sea of Japan are correlated to times of tectonic uplift in response to major collisions in the Owen-Stanley Range of Papua and the Hida Range of Japan, respectively. Large frequencies and shorter-term periodicities of turbidites at DSDP Site 210 were coeval with early Pliocene maximum tectonic-uplift rates which occurred in the Owen-Stanley Range in response to obduction. Similarly, large frequencies and shorter-term periodicities of turbidites at Site 299 (Toyama Submarine Fan) were coeval with the late Pleistocene uplift in the Hida Range; this uplift of 1000 to 1500 m occurred in response to collision tectonics. In both cases, trends of increasing frequencies and towards shorter-term periodicities of preserved turbidite depositional events correlate to trends of increasing rates of tectonic uplift.The role of sea-level fluctuations on changing denudation rates in these two collision zones is secondary. At Site 210, larger frequencies and short-term periodicities of preserved turbidites were coeval with early Pliocene high stands of sea level, whereas at Site 299, Pleistocene sea-level fluctuations are considered minor because at low stands of sea level, both relief and denudation rates were increased by about ten to 14%. At Site 286 (New Hebrides Basin), Eocene turbidite deposition is coeval with high stands of sea level, whereas at Site 297 (Northern Shikoku Basin), turbidite deposition was coeval with both rising and falling sea level.Analysis of both frequency and periodicity of turbidites by fan subenvironment at Site 299 indicates a record of continuous deposition, and maintainance of frequency and periodicity trends controlled by tectonic uplift. Late Pleistocene channel and overbank deposits showed periodicity differences of less than 28% of an order of magnitude, whereas Miocene-Pliocene overbank and distal turbidite periodicities differed by a 19% order of magnitude. Greater differences in magnitude occurred between distal turbidites or early Pleistocene age and Pliocene age than between Miocene-Pliocene overbank and distal turbidite deposition with a magnitude difference of 860%. These findings suggest that shifting depocenters and differences in sedimentation history in subenvironments of submarine fans are secondary to the role of tectonic uplift in this particular case.The minimal rate of tectonic uplift required to generate deep-sea fan turbidities appears to be approximately 400 m/million years. This figure is tentative and is based on very few observation points.Frequency and periodicity of preserved turbidite cycles in submarine fans in active continental margins and ancient counterparts should provide an independent measurement of rates and timing of tectonic uplift, particularly in collision terrains. Because this sediment parameter is a record of a single process from a single source and a record of “event stratigraphy”, its usage is preferable over standard and bulk sediment accumulation rates determined from age depth curves.  相似文献   

Al depth profile in Apollo 15 drill core     

K. Nishiizumi  J. Klein  R. Middleton  J.R. Arnold 《Earth and Planetary Science Letters》1984,70(2):164-168

Cosmic-ray-produced²⁶Al (t_1/2 = 7.05 × 10⁵ years) has been measured in the Apollo 15 long core (surface to 390 g/cm²—218 cm) for study of galactic cosmic ray production profiles, using accelerator mass spectrometry. The results are in general accord with non-destructive counting data obtained earlier, but systematically lower, and significantly higher precision. From this experiment the half-attenuation length for²⁶Al production can be calculated to be 122 g/cm² (150–400 g/cm² region) after normalizing the data to average chemical composition. The⁵³Mn (t_1/2 = 3.7 × 10⁶ years) production profile in deep cores was also compiled to date. The half-attenuation length for⁵³Mn production was calculated to be 123 g/cm² (150–400 g/cm² region).  相似文献   

Some results of a diffusion experiment at a river plume front     

Dr. Hjalmar Franz  Holger Klein 《Ocean Dynamics》1986,39(3):91-112

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Recent trends of urban development and town planning in Spain     

Dr. Erdmann Gormsen  Rainer Klein Dipl. Geogr. 《GeoJournal》1986,13(1):47-57

With the socio-economic change from rural to industrial, Spain has experienced an enormous urbanisation boom during the last 20 years. This has produced a concentration of high-rise apartment blocks not only in the big cities but also in medium-sized towns and even within the medieval town centres. More astonishing, compared with Central Europe, seems however, the spatial distribution of the social classes which, with a centre-periphery gradient, still corresponds to the model of the pre-industrial town. The paper investigates the impact of town planning, house building policy, and behavioural aspects on these structural patterns.  相似文献   

Effects of soil moisture dynamics on slope failure at Hyrum Reservior,Utah     

Michael P. O'Neill  Jeffrey J. McDonnell 《地球表面变化过程与地形》1995,20(3):243-253

Field observations of shoreline conditions at Hyrum Reservoir, Utah, were conducted during the summers of 1991 to 1993. A process of bluff retreat is described for a multiple-layered bluff environment of sand and clay layers. Failure is initiated by wetting and drying of clay sediments, which produces horizontal cracks within bluff material. These cracks appear to penetrate to a depth of approximately 100-150 mm before initiating vertical cracking in the sediments. The vertical cracks are propagated by continued drying of the surface sediment, ultimately leading to failure of the bluff material. The physical dimensions of sediment blocks succumbing to this mechanism range from a few hundred millimetres up to 3 m on a side, with a depth of approximately 100-150 mm. The mechanism described here appears to operate optimally when the supply of subsurface moisture is abundant and nearly continuous throughout the spring and early summer. Reservoir draw-down, large capillary fringe effects in the bluff and periodic wetting from upslope undrained hollows are the dominant moisture controls at this site. Moisture delivery to the face is strongly influenced by anisotropy of saturated hydraulic conductivity in the alternating clay and sand layers and related differences in sediment texture.  相似文献   

Ground-Water Flow Simulation for Management of a Regulated Aquifer System: A Case Study in the North Carolina Coastal Plain     

Jeffrey W. Reynolds  Richard K. Spruill 《Ground water》1995,33(5):741-748

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