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991.
Matthias?AuerEmail author Gerhard?H.?Eisbacher 《International Journal of Earth Sciences》2003,92(2):210-227
The Northern Calcareous Alps (NCA) of southern Bavaria and northern Tyrol constitute a carbonate-dominated polyphase fold-thrust wedge; together with its Grauwacken Zone Basement, it is the northernmost part of the far-travelled Upper Austroalpine thrust complex of the Eastern Alps. The present geometry developed in several kinematic stages. Jurassic extensional faults that affected large parts of the NCA and their basement originated when the main part of the NCA was still located southeast of the Central Alpine Ötztal-Silvretta complex. These faults and related facies transitions influenced the later style of detachment of the NCA thrust sheets. Mid to Late Cretaceous detachment, thrust-sheet stacking and motion over the Central Alpine complex are registered in clastic deposits of syntectonic basins. The latest Cretaceous to Cenozoic NNE- to N-directed motion of the NCA towards Europe in front of the Central Alpine complex created another set of significant contraction structures, which at depth overprinted all previous structures. During Cretaceous to Cenozoic deformation, the NCA experienced about 80 km of shortening, i.e., about 73% along the TRANSALP Profile. The European basement and autochthonous Mesozoic cover beneath the allochthonous NCA thrust sheets and flysch complexes seem to have remained relatively undeformed. 相似文献
992.
Gerd?RantitschEmail author Thomas?Rainer 《International Journal of Earth Sciences》2003,92(2):195-209
Vitrinite reflectance was measured in Late Carboniferous to Triassic shales, siltstones and marls of the Karawanken Range. Thermal models of the central South-Karawanken Range were calibrated on the basis of these data. They suggest an eroded overburden of more than 3,200 m of Jurassic to Cretaceous sediments and a heat flow in the range of 42 to 60 mW m?2 during the time of maximum subsidence. Because the reconstructed thermal history of the South-Karawanken Range is very similar to the thermal history of the Generoso basin (western Southern Alps), these data provide strong evidence for a deep basinal position of the Southern Karawanken Range during Jurassic to Cretaceous times. A vitrinite reflectance anomaly at the northern margin of the South-Karawanken Range is explained by advective heat transport during the Oligocene. The heat source for the anomalies at the western margin of the Seeberg Rise and in the area between the Periadriatic Lineament and the Donat Fault Zone is unknown. Vitrinite reflectance in Late Triassic sediments indicates the South-Karawanken Range and the South-Zala Unit of the Pannonian basement as exotic blocks in the Sava Composite Unit. This is explained by Miocene displacement of structural units, which were derived from different paleogeographical segments of the Permo-Mesozoic western Tethyan margin. 相似文献
993.
鄂尔多斯盆地白垩系含水层沉积学初探 总被引:21,自引:5,他引:16
“含水层沉积学”是沉积学、水文地质学、油气储层地质学、地球化学等相互交叉综合的产物,是以沉积学、水文地质学理论为基础,以沉积含水层为主要研究对象,以查明地下水赋存和循环条件、地下水系统结构特征、地下水水质成因与分布以及地下水富集规律为主要研究内容,最终服务于地下水资源勘查评价的一门边缘分支学科。含水层沉积学及水文地质综合研究表明,受到沉积相类型及其空间展布的明显控制,鄂尔多斯盆地白垩系地下水赋存、循环、富集条件以及地下水水质分布总体具有北好南差、盆地南部具有下好上差的宏观规律。 相似文献
994.
Richard?G.?LathropEmail author Lisamarie?Windham Paul?Montesano 《Estuaries and Coasts》2003,26(2):423-435
We assess the probability and importance of different spatial distributions ofPhragmites australis (Trin Ex Steud) within brackish tidal marshes of the mid-Atlantic United States coast. The comparative impact ofPhragmites expansion on the larger coupled marsh-estuary system may partially be a function of the landscape area dominated byPhragmites, the landscape position occupied byPhragmites, the landscape pattern created byPhragmites expansions, and the resulting impact on tidal drainage networks. We find evidence thatPhragmites establishment can occur at many landscape positions, and thatPhragmites spread within a marsh can occur via colonization (new patches), linear clonal growth (along a preferred axis), or circular clonal growth (non-directional, random spread). Early intervals ofPhragmites spread were dominated by colonization for all sites except for Piermont Marsh (which appeared to be dominated by linear clonal growth) and Lang Tract (which appeared to be dominated by circular clonal growth). Although 46–100% of new patches ofPhragmites occurred within 5 m of drainages, at only one site (Piermont Marsh, New York) didPhragmites populations remain concentrated along creek banks. Except for Iona Island, New York, which appears to be in an early stage ofPhragmites invasion, patch dynamics at all sites showed an increase followed by a decrease in patch number, as independent patches became established, expanded, and coalesced. We also found some evidence for a loss of first order streams at later stages ofPhragmites invasions in several sites (Hog Island, Lang Tract, Silver Run). 相似文献
995.
We linked a 2-dimensional water quality model of the Patuxent River with a spatially-explicit model of fish growth to simulate how changes in land use in the Patuxent River Basin would affect the growth rate potential (GRP) of Atlantic menhaden (Brevoortia tyrannus). Simulations of three land-use patterns that reflected current nutrient loadings, increased nutrient loadings, and decreased nutrient loadings were used to drive the water quality model. Changes in nutrient loadings caused changes in the timing and intensity of phytoplankton concentrations and the region of hypoxia increased during summer with increased nutrient loading. The spatial distribution of menhaden GRP was highly correlated with phytoplankton concentrations and localized in the middle on third of the Patuxent River. Menhaden growth rate was highest in early June and late summer. During June, menhaden GRP (and phytoplankton concentration) was lowest at the lower nutrient loading simulation. During late summer, mean menhaden growth rates were inversely proportional to nutrient loading rates and menhaden grew best when nutrient loadings were the lowest. Upriver to mid-river phytoplankton patches drove overall mean calculations. Model results suggest that more research is needed on water quality model predictions of phytoplankton levels at a high level of spatial and temporal resolution, menhaden foraging, and menhaden habitat selection. 相似文献
996.
Per?WestmanEmail author Johanna?Borgendahl Thomas?S.?Bianchi Nianhong?Chen 《Estuaries and Coasts》2003,26(3):680-689
This study corroborates the hypothesis that nitrogen-fixing cyanobacteria have probably occurred as an important component
of the phytoplankton community in the Baltic Sea at least since brackish water conditions were initiated 8,50014C yr BP. Pigment analyses indicate that extensive occurrences started prior to a sharp increase in nutrient levels dated to
7,10014C yr BP. The cyanobacteria could have functioned as a natural trigger for eutrophication in the Baltic Sea by importing nitrogen.
This is also verified by a contemporaneous drop in the δ15N values from 4‰ to around 2‰. We further conclude that the spreading of cyanobacteria was probably caused by a decrease in
nitrogen∶phosphorus (N∶P) in the water mass that resulted from the intrusion of oceanic water with high P levels. The fractionation
of P in sediments indicated that iron-bound P was efficiently sequestered under anoxic conditions that occurred as a consequence
of the establishment of a stable stratification caused by the marine intrusion. This pool only showed minor variations around
3 μmol g−1 at the freshwater-brackish water transition. All P pools except the CaCO3 fraction showed a distinct increase around 9,30014C yr BP prior to the transition. We interpreted this increase as a change in preservation of organic matter or in the source
of the sediment. Slightly after 4,00014C yr BP there was a dramatic drop in all P pools without any corresponding decreases in total N and carbon. Total P decreased
from around 75 to 25–30 μmol g−1. The most dramatic drop occurred in the organic bound and the detrital apatite fractions, which decreased by a factor of
3–4. We explain this as a preferential regeneration of P, especially organic P, compared to other nutrients due to more prevalent
anoxic conditions. 相似文献
997.
Joanna?M.?RankinEmail author Geoffrey?A.?E.?Wright 《Astronomy and Astrophysics Review》2003,12(1):43-69
The purpose of this paper is to suggest how detailed single-pulse observations of slow radio pulsars may be utilized to construct an empirical model for their emission. It links the observational synthesis developed in a series of papers by Rankin in the 1980s and 90s to the more recent empirical feedback model of Wright (2003a) by regarding the entire pulsar magnetosphere as a non-steady, non-linear interactive system with a natural built-in delay. It is argued that the enhanced role of the outer gap in such a system indicates an evolutionary link to younger pulsars, in which this region is thought to be highly active, and that pulsar magnetospheres should no longer be seen as being driven by events on the neutron stars polar cap, but as having more in common with planetary magnetospheres and auroral phenomena.Received: 8 May 2003, Published online: 14 November 2003
Correspondence to: Joanna M. Rankin. On leave from: Physics Department, University of Vermont, Burlington, VT 05405, USA 相似文献
998.
关于我国土地利用分类问题的讨论 总被引:62,自引:8,他引:54
在分析了我国于2002年1月起试行的最新土地利用分类系统所存在的问题之后,提出了生态用地的概念,并提出了将我国土地利用划分为农用地、建设用地和生态用地这三大类用地的设想,同时尝试提出了另一个土地利用分类方案。 相似文献
999.
Jean-Fran?ois?DeconinckEmail author Stephen?P.?Hesselbo Nicolas?Debuisser Olivier?Averbuch Fran?ois?Baudin Julian?Bessa 《International Journal of Earth Sciences》2003,92(2):255-266
We present a dataset including clay mineralogy, gamma-ray spectrometry, organic matter content and magnetic susceptibility of the Hettangian to lowest Sinemurian successions of Dorset and Somerset, southern UK (Blue Lias Formation, Bristol Channel and Wessex basins). In both areas, the clay assemblages comprise predominantly detrital illite, kaolinite and illite/smectite mixed layers. Clays probably originated from the erosion of the Hercynian massifs, the relative proportions of kaolinite and illite being modulated by arid-humid climatic fluctuations. The organic matter (OM) content (types II to IV) ranges up to 12% in both areas. A clear stratigraphical trend in clay mineral assemblages is apparent in Somerset, whereas in Dorset sharp contrasts between adjacent horizons and a greater dilution by carbonate mask the long-term evolution. Correlations between both areas based on similar vertical trends in clay mineral abundance support the suggestion of a hiatus within the angulata Zone of the Dorset succession. As expected, the kaolinite/illite ratio correlates with the Th/K ratio deduced from gamma-ray spectrometry. However, significant departures from the correlation occur in OM-rich intervals, suggesting that Th may be partly adsorbed on to OM particles. Surprisingly, high magnetic susceptibility correlates with abundant kaolinite, not with Fe-rich clays, indicating either that kaolinite is accompanied by a soil-inherited magnetisable phase (possibly iron oxide) or that illite-rich rocks are more strongly diluted by carbonate than are kaolinite-rich strata. 相似文献
1000.
The present study deals with tectonomagmatic evolution of the collision-related leucogranite located near the northwest corner of exposed basement in Sinai, Egypt. The area is composed of: (1) a gabbroic complex; (2) amphibolite; (3) post-orogenic leucogranite; (4) Feiran gneisses. The amphibolite and gabbroic suites, generated in an island arc environment, have a high Fe-tholeiitic affinity and were derived from two independent magmas. On the basis of rare earth element (REE) patterns, the gabbroic melts could have been generated from a garnet- and amphibole-bearing, enriched mantle, and were subsequently modified by fractional crystallization of pyroxene and amphibole with minor plagioclase, whereas the amphibolite melts could be derived from garnet-free depleted mantle.The leucogranite has high Al2O3 content (>13 wt%), alumina saturation index (ASI) mostly >1, and normative corundum, indicating a peraluminous nature. Chondrite-normalized REE patterns for the leucogranite show light REE enrichment (La/SmN=2.7–4.86), general flattening of the heavy REE (Gd/LuN=1.2–2), and negative europium (Eu) anomalies (Eu/Eu*=0.24–0.47). The peraluminous nature and enrichment of the incompatible elements (K, Rb, Ba and Th) in the leucogranite strongly suggest derivation from a crustal source. The most probable source for the leucogranite magmas is represented by the adjacent Feiran gneisses, which could have generated the leucogranite by dehydration melting under water-undersaturated conditions. It appears likely that the restite unmixing model is responsible for the chemical variations within the leucogranite. In accordance with this model, the chemical variation of the leucogranite can be attributed to varying degrees of separation of restitic material from the melt during its emplacement and solidification and fractional crystallization could have played a minor role during magma ascent through the crust. 相似文献