Typical basin-fill sequences and basin migration in Yanshan, North China--Response to Mesozoic tectonic transition

Basin-fill sequences of Mesozoic typical basins in the Yanshan area, North China may be divided into four phases, reflecting lithosphere tectonic evolution from flexure (T3), flexure with weak rifting (J1+2), tectonic transition (J3), and rifting (K). Except the first phase, the other three phases all start with lava and volcaniclastic rocks, and end with thick coarse clastic rocks and/or conglomerates, showing cyclic basin development rather than simple cyclic rift mechanism and disciplinary basin-stress change from extension to compression in each phase. Prototype basin analysis, based on basin-fill sequences, paleocurrent distribution and depositional systems, shows that single basin-strike and structural-line direction controlling basin development had evidently changed from east-west to northeast in Late Jurassic in the Yanshan area, although basin group still occurred in east-west zonal distribution. Till Early Cretaceous, main structural-line strike controlling basins just turned to northeast by north in the studied area.     

华北地台北缘花岗岩—绿岩型金矿田及盲矿体的找矿模型

花岗岩—绿岩型金矿田的找矿模型地质上是富镁铁质绿岩、韧性剪切带与重熔岩体的三体一位;物探上位于航磁高背景场的负磁异常带边缘,矿田晕分散流异常规模大、强度高,有明显的浓集中心。隐伏矿床、盲矿体的找矿模型地质上是韧性剪切带、退变质带及脆性断裂带的三体一位;物探上呈现高极化率、低电阻、位于磁异常边缘的“一高一低一边”模型;化探原生晕上呈现As、sb、F、Ag、Bi、W的找矿模型。     

Subfilter-scale Fluxes over a Surface Roughness Transition. Part I: Measured Fluxes and Energy Transfer Rates

A wind-tunnel experiment was designed and carried out to study the effect of a surface roughness transition on subfilter-scale (SFS) physics in a turbulent boundary layer. Specifically, subfilter-scale stresses are evaluated that require parameterizations and are key to improving the accuracy of large-eddy simulations of the atmospheric boundary layer. The surface transition considered in this study consists of a sharp change from a rough, wire-mesh covered surface to a smooth surface. The resulting magnitude jump in aerodynamic roughnesses, M = ln(z ₀₁/z ₀₂), where z ₀₁ and z ₀₂ are the upwind and downwind aerodynamic surface roughnesses respectively, is similar to that of past experimental studies in the atmospheric boundary layer. The two-dimensional velocity fields used in this study are measured using particle image velocimetry and are acquired at several positions downwind of the roughness transition as well as over a homogeneous smooth surface. Results show that the SFS stress, resolved strain rate and SFS transfer rate of resolved kinetic energy are dependent on the position within the boundary layer relative to the surface roughness transition. A mismatch is found in the downwind trend of the SFS stress and resolved strain rate with distance from the transition. This difference of behaviour may not be captured by some eddy-viscosity type models that parameterize the SFS stress tensor as proportional to the resolved strain rate tensor. These results can be used as a benchmark to test the ability of existing and new SFS models to capture the spatial variability SFS physics associated with surface roughness heterogeneities.     

Budapest's built environment in transition

The construction of major new buildings has been noticed in Budapest since the mid 1980s. New hotels, office blocks, housing projects and most recently shopping centres have become a prominent feature of the landscape in several districts of the city. The paper first outlines a conceptualisation of the `Transition' in terms of eastern Europe as a whole identifying internationalisation, Europeanisation and national government policies as key strands in a specific case of a process of change interpreted as the interaction of antecedent conditions and current processes. It then addresses the question of conceptualising the built environment in terms of the `Transition' and three `schools of thought' in geography stressing the urban morphogenesis approach. It thus poses the question of how radical a change has `occurred on the ground' since 1989–1990. Consequently the paper examines the transition in the built environment of Budapest under three principal headings: (a) the antecedent conditions of the built environment of Budapest by spatial structure, (b) the relationship between new buildings and current processes, (c) comparing models of the spatial structure of Budapest as a socialist city and as a post-socialist-(industrial) city or post-industrial (capitalist) city. It concludes that although the processes shaping the city's built environment have changed quite radically since 1990 the physical fabric of the city and its antecedent usage have strongly influenced the spatial impact of the current processes. Budapest is a post-socialist industrial city with capitalist forms fitted into it. The city is passing from socialist to capitalist processes in a way that suggests that morphological analysis has clear potential in theorising the relationship between the global and the local. This revised version was published online in July 2006 with corrections to the Cover Date.     

Late Pleistocene and early Holocene ecological response of Lake El Trébol (Patagonia, Argentina) to environmental changes

Stratigraphy of Lake El Trébol (41°S 71°W, 758 m a.s.l.) described from an 11 m long sediment core provided a continuous record of patecenvironmental changes occurred during the last 14,000 years in southern South America east of the Andes. Located in an ecotonal area within a strong humidity gradient, this lake offers a unique opportunity to develop paleolimnological studies. Using a geochemical approach that includes elemental analysis, bulk organic matter, major nutrients and pigments combined with chironomids and pollen analysis, three zones were identified in the sedimentary record of this take. The oldest one (between 680 and 1,100 cm) corresponds to the late Glacial period. During that time, clayish laminated sediments were formed in a proglacial environment. Low organic matter, biogenic silica and nitrogen contents and the absence of pigments, pollen and chironomids characterise this period. At the end of this period, ca. 14,000 yr BP, a sharp increase in phosphorus concentrations predates major changes in limnological parameters. The transition zone (between 560 and 680 cm) is related to major changes in the drainage system that started soon after ca. 14,000 yr BP and continued to ca. 10,500 yr BP. The chemical composition of the sediments was affected by an increase in physical weathering mechanisms almost coincident with the increase in the regional volcanic activity that produced suspended volcanic detritus. The increase of mainly coarser detritical components may indicate a reorganisation of the fluvial system by that time. Simultaneously, an increase in the productivity of the lake accompanied by a gradual replacement of open vegetation with Nothofagus, Poaceae and Ericaceae, by Nothofagusforest, was observed. In the last zone (between 0 and 560 cm) the productivity of Lake El Trébol achieves maximum values. The trends in geochemical and biological indicators observed at Lake El Trébol can be up to some extent, correlated to those registered in Lake Mascardi. The results support earlier paleoctimatic scenarios from southern South America.     

Adaptive Transitions: The Long‐Term Perspective on Humans in Changing Coastal Settings

Adaptation is a key concept in long‐term human adjustments to climate change. Despite the centrality of human decisions and actions in adaptation, much of the climate change literature is thin on humanities and social science which are the primary approaches for understanding human activity. This situation is particularly pronounced in Louisiana's discussions about its disappearing coast line where research has concentrated in understanding biophysical processes and solutions prioritize short‐term adaptations. This paper reviews the relationship of adaptation and long‐term transitions in the global change discussion and traces how disjointed adaptations in coastal Louisiana have contributed to a perilous environmental situation there. It proposes a shift from discrete adaptations to efforts that incorporate interrelated biophysical and human adaptations that can sustain long‐term transitions.