849 resultados para Geomorphological subdivision


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This report is a conclusion of the major research outcome during my post-doctoral residence of research and work. Its content covers the researches of the deep thermal characteristic and dynamics evolution beneath the northern margin basin of South China Sea. In this report, the each other action and effect between lithosphere ad mantle convection were regarded by the combine of deep and shallow study, subdivision from whole to part, and pay equal attention to determine the nature and fixed quantity. The investigative method we used in this report is geothermal and gravity methods. By the help of geological model and geophysics modeling, we calculated lithosphere thermal structure, rheology structure and mantle convection. Firstly, the report introduces concisely the purpose and the previous achievement to this research. Then, it analyzed the characteristic of heat flow on South China Sea. The structure of deep temperature and thermal has been calculated in some models of heat generation and conduction. The rock rheology structure also was computed by the relationship between temperature and viscosity. All these calculations were finished under the guidelines of combine with geology and geophysics. Meanwhile, the fields both deep mantle convection and small scale upper mantle convection are computed. Beside, the density and temperature disorder resulted by mantle convection were also computed with the convection field. After these, the report bring the contribution of local field of mantle convection, thermal construct and effective viscosity beneath the northern margin basin of South China Sea. And, base on the tectonic background and evolution feature, this report discussion the evolution mechanism of south China Sea and its northern margin basin. The end of this report, the main conclusion of this research was summarized and brings out.

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The past two decades have witnessed an unprecedented growth of interest in the palaeoenvironmental significance of the Pleistocene loess deposits in northern China. However, it is only several years ago that the Tertiary red clay sequence underlying Pleistocene loess attracted much attention. One of the major advances in recent studies of eolian deposits on the Loess Plateau is the verification of the eolian origin for the Tertiary red clay sediments. The evidence of the eolian origin for the red clay is mainly from geochemical and sedimentological studies. However, sedimentological studies of the red clay deposits are still few compared with those of the overlying loess sediments. To date, the red clay sections located near Xifeng, Baoji, Lantian, Jiaxian, and Lingtai have been studied, with an emphasis on magnetostratigraphy. These sections have a basal age ranging from ~4.3 Ma to ~7.0 Ma. The thickness of the sections varies significantly, depending perhaps on the development of local geomorphological conditions and the drainage system. Although the stratigraphy of the red clay sections has been recorded in some detail, correlation of the red clay sequences has not yet been undertaken. Geological records (Sun J. et al., 1998) have shown that during glacial periods of the Quaternary the deserts in northem China were greatly expanded compared with modern desert distribution. During interglacial periods, desert areas contracted and retreated mostly to northwestern China because of the increase in inland penetration of monsoonal precipitation. According to pedogenic characteristics of the red clay deposits, the climatic conditions of the Loess Plateau is warmer and wetter generally in the Neogene than in the late Pleistocene. Panicle analyses show that grain size distribution of the red clay sequence is similar to that of the paleosols in the Pleistocene loess record, thus implying a relatively remote provenance of the red clay materials. However, the quantitative or semiquantitative estimates of the distance from the source region to the Loess Plateau during the red clay development remains to be investigated. In this study, magnetostratigraphic and sedimentological studies are conducted at two thick red clay sequences-Jingchuan and Lingtai section. The objectives of these studies are focused on further sedimentological evidence for the eolian origin of the red clay, correlation of red clay sequences, provenance of the red clay, and the palaeoclimate reconstruction in the Neogene. Paleomagnetic studies show that the Jingchuan red clay has a basal age of 8.0 Ma, which is 1 million years older than the previously studied Lingtai section. The Lingtai red clay sequence was divided into five units on the basis of pedogenica characteristics (Ding et al., 1999a). The Jingchuan red clay sequence, however, can be lithologically divided into six units according to field observations. The upper five units of the Jingchuan red clay can generally correlate well with the five units of the Lingtai red clay. Comparison of magnetic susceptibility and color reflectance records of four red clay sections suggests that the Lingtai red clay sequence can be the type-section of the Neogene red clay deposits in northern China. Pleistocene loess and modem dust deposits have a unimodal grain-size distribution. The red clay sediments at Jingchuan and Lingtai also have a unimodal grain-size distribution especially similar to the paleosols in the Pleistocene loess record. Sedimentological studies of a north-south transect of loess deposits above S2 on the Loess Plateau show that loess deposits had distinct temporal and spatial sedimentary differentiation. The characteristics of such sedimentary differentiation can be well presented in a triangular diagram of normalized median grain size, normalized skewness, and normalized kurtosis. The triangular diagrams of the red clay-loess sequence at Lingtai and Jingchuan indicate that loess-paleosol-red clay may be transported and sorted by the same agent wind, thus extending the eolian record in the Loess Plateau from 2.6 Ma back to about 8.0 Ma. It has been recognized that during the last glacial maximum (LGM) the deserts in northern China had a distribution similar to the present, whereas during the Holocene Optimum the deserts retreated to the area west of the Helan Mountains. Advance-retreat cycles of the deserts will lead to changes in the distance of the Loess Plateau to the dust source regions, thereby controlling changes in grain size of the loess deposited in a specific site. To observe spatial changes in sedimentological characteristics of loess during the last glacial-interglacial cycle, the texture of loess was measured along the north-south transect of the Loess Plateau. Since the southern margin of the Mu Us desert during the LGM is already known, several models of grain size parameters versus the minimum distance from the source region to depositional areas were developed. According to these semiquantitative models, the minimum distance from the source region to Lingtai and Jingchuan areas is about 600 km during the Neogene. Therefore the estimated provenance of the Tertiary red clay deposits is the areas now occupied by the Badain Jaran desert and arid regions west of it. The ratio of the free iron to total iron concentration attests to being a good proxy indicator for the summer monsoon evolution. The Lingtai Fe_20_3 ratio record shows high values over three time intervals: 4.8-4.1 Ma, 3.4-2.6 Ma, and during the interglacial periods of the past 0.5 Ma. The increase in summer monsoon intensity over the three intervals also coincides with the well-developed soil characteristics. It is therefore concluded that the East-Asia summer monsoon has experienced a non-linear evolution since the late Miocene. In general, the East Asia summer monsoon was stronger in Neogene than in Quaternary and the strongest East Asia summer monsoon may occur between 4.1 and 4.8 Ma. The relatively small ice volume and high global temperature may be responsible for the strong summer monsoon during the early Pliocene.

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Jiyang depression is one of the most important petroleum production basins in China. The petroleum pools, found easier, have been densely explored and developed. At present, the subtle traps are becoming the main exploring aims. A lot of Tertiary sand-conglomerate body petroleum pools, as one of the important subtle pools, have been discovered recently. It is necessary and urgent to study deeply the developing characteristics and petroleum pool distribution of Tertiary sand-conglomerate bodies in Jiyang Depression. The present dissertation has concluded the main developing characteristics of the Tertiary sand-conglomerate bodies in Jiyang Depression, and studied the sand-conglomerate bodies in Chengnan Fault Zone in detail. Depending on the synthesized studies of geology, geophysics and logging data, the following conclusions have been arrived at. Four criterion layers in Member 3 of Shahejie Formation, according to the depositional cycle analyses, have been established for the subdivision of different layers of sand-conglomerate bodies and the correlation of different sand-conglomerate bodies. It indicated that the alluvial delta, delta-fan, alluvial fan, shallow water fan , deep water turbidite , fan-front turbidite are the six kinds of sand-conglomerate bodies, which have been distinguished in Jiyang Depression with the study of genetic types, characteristics and distribution of sand-conglomerate bodies. The shallow water fan, steep slope deep water turbidite and fan-front turbidite were the main types of sand-conglomerate bodies developed in Chengnan steep slope. Their identification and distribution have been described in detail. The development and distribution of sand-conglomerate bodies were resulted by fault depressing, palco-climate change and channel or trough on the uplift. The fault depressing is the most important-factor to the episodic developing of sand-conglomerate bodies. An episodic developing genetic mode has been established by the contrast analyses between episodic fault depressing and climate change cycles. The hydrocarbon accumulation in the sand-conglomerate bodies in the steep slope was correlated with fan types, depositional phases, fault depressing and diagenesis. Sand-conglomerate wedge out (include up-oblique and onlap), lithological wedge out, mud screen (for anticline), fault plugging (by mud opposite sand, mud daubing) are the 5 possible mechanisms of oil accumulation. Lithological pool, stratigraphic pool and tectonic pool and lithologic-tectonic complex pool, and 9 subtypes of petroleum pools have been detected. It is easy for different pools to be combined as a complex reservoir, which was distributed along the syn-depositional fault slopes. The sand-conglomerate bodies in deep sag were usually evaluated as pore zone for hydrocarbon accumulation before. In fact, they are potential. Because of fan-front turbidite sands were especially developed in these zones, the sands have a close connection with the oil mud, and lithological pools can be expected to find in these zones. Chengnan fault slope was main channel of oil migration, and mud screen is the principle key for the oil accumulation in the sand-conglomerate bodies. If there was no mud between the sand-conglomerate bodies or on the top of sand-conglomerate bodies, the sand-conglomerate bodies would connect each other and there would be no dense material to hold up the oil migration along the slope. As the sand-conglomerate bodies could not been taken as a screen, the mud screen is the key for developing pool in this slope. According to this principle, about 6 potential traps, such as C915 block, C913 block, C916 block, south of Y109 well block, Y104 block and Y153 block, were selected for exploration and development.

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We describe a software package for computing and manipulating the subdivision of a sphere by a collection of (not necessarily great) circles and for computing the boundary surface of the union of spheres. We present problems that arise in the implementation of the software and the solutions that we have found for them. At the core of the paper is a novel perturbation scheme to overcome degeneracies and precision problems in computing spherical arrangements while using floating point arithmetic. The scheme is relatively simple, it balances between the efficiency of computation and the magnitude of the perturbation, and it performs well in practice. In one O(n) time pass through the data, it perturbs the inputs necessary to insure no potential degeneracies and then passes the perturbed inputs on to the geometric algorithm. We report and discuss experimental results. Our package is a major component in a larger package aimed to support geometric queries on molecular models; it is currently employed by chemists working in "rational drug design." The spherical subdivisions are used to construct a geometric model of a molecule where each sphere represents an atom. We also give an overview of the molecular modeling package and detail additional features and implementation issues.

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Cook, Anthony; Mege, D.; Garel, E.; Lagabrielle, Y., (2003) 'Volcanic rifting at Martian grabens', Journal of Geophysical Research 108(E5) pp. 1-33 RAE2008

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Jednym z wyników prognoz wykonywanych z zastosowaniem globalnych i regionalnych modeli klimatycznych jest odkrycie wysokiego prawdopodobieństwa wzrostu częstości oraz natężenia ekstremalnych opadów. Poznanie prawidłowości ich powtarzalności i zasięgu przestrzennego ma oczywiście bardzo duże znaczenie gospodarcze i społeczne. Dlatego, niezależnie od wprowadzania nowych technik pomiarowych należy dokonywać analizy i reinterpretacji archiwalnych danych, korzystając z możliwości stwarzanych przez rozwój GIS. Głównym celem opracowania jest analiza prawidłowości przestrzennej i czasowej zmienności miesięcznych oraz rocznych maksymalnych dobowych sum opadów (MSDO) z lat 1956-1980, z obszaru Polski. W pracy wykorzystano nowe w geografii polskiej metody geostatystyczne. Do publikacji dołączono dysk DVD ze źródłową bazą danych i najważniejszymi wynikami w postaci numerycznej i kartograficznej.

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The aim of the studies in the Perznica River catchment were relief changes caused by the development of transportation infrastructure. This type of transformation is dependable on the state of economy and the settlements. The development of transportation network in the last two hundred years was examined through the analysis of archival cartographic materials – maps from the years 1789, 1855, 1877, 1935 – and the comparison with the situation from mid 1980s. The Perznica River catchment has an area of 249 km2 and it is located in north-western Poland in the central part of the Drawskie Lakeland macroregion, which belongs to the West Pomeranian Lakeland. The heterogeneous Perznica River catchment relief has a denivelation of 159 m and is within 60 and 219 m a.s.l. The study area is within the Parsęta River lobe. A number of subzones, whose morphological diversity and diversity of sediments lithofacies is mainly a reflection of areal deglaciation of the continental ice-sheet marginal zone, has been distinguished and these are: • subzone of the internal kame moraine – the undulated moraine upland, diversified by kame forms and kettle holes, • subzone of ice-free space forms – the uplands of kame plateaux, • subzone of melt-out lake basins – Lake Wielatowo basin with a characteristic collar ridge, • morphological levels of the northern Pomeranian sloping surface – mainly flat moraine uplands and small outwashes. The economic development of the Perznica River catchment advanced in close connection with the physical and geographical context, mainly with the relief, soils and hydrological conditions. As a result, the flat moraine uplands and marginal outflow plains, which were easiest to cultivate, have been developed and populated faster than any other. Since the early medieval period, large, compact villages, often centered around big estates, were emerging in those areas. In areas with a high relief energy–kame-melt moraines, ice-free space forms and ridges around melt-out lake basins–farming entered on a larger scale from the eighteenth century. Scattered settlements in those areas forced the creation of a dense access road network to farms and fields. In the case of anthropogenic forms of transportation with denivelation exceeding 1 m in the study area, road excavations are present for 37.3 km, road undercuttings for 43.8 km and road embankments for 38.7 km in total length. That gives a high ratio of density of such forms, equal to 2.1 km per km–2.

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Coastal processes and wildlife shape the coast into a variety of eye-catching and enticing landforms that attract people to marvel at, relax and enjoy coastal geomorphology. These landforms also influence biological communities by providing habitat and refuge. There are very few field guides to explain these processes to the general public and children. In contrast, there is a relative wealth of resources and organised activities introducing people to coastal wildlife, especially on rocky shores. These biological resources typically focus on the biology and climatic controls on their distribution, rather than how the biology interacts with its physical habitat. As an outcome of two recent rock coast biogeomorphology projects (detailed at: www.biogeomorph.org/coastal) a multi disciplinary team produced the first known guide to understanding how biogeomorphological processes help create coastal landforms. The ‘Shore Shapers’ guide (shoreshapers.org) is designed to: a. bring biotic geomorphic interactions (how animals, algae and microorganisms protect and shape rock) to life and b. introduce some of the geomorphological and geological controls on biogeomorphic processes and landform development. The guide provides scientific information in an accessible and interactive way – to help sustain children’s interest and extend their learning. We tested a draft version of the guide with children,the general public and volunteers on rocky shore rambles using social science techniques and present the findings, alongside initial results of an evaluation of a newer version of the guide and interactive workshops taking place throughout 2014.

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Studies on the flora and fauna of the Canary Islands show that this Archipelago is one of the planet’s diversity hot spots. However, an analysis of the differences in the phytogeographic characteristics of each of the islands that make up this Archipelago is lacking. This article focuses on the phytogeographic characterization of the island of Gran Canaria. This island exhibits geological and climatic characteristics resulting in a rich vascular flora, including endemic species and genera that are significantly different from the other islands of the Archipelago. These differences are verified through statistical analysis of the existing similarity between the floras of the members of the Canary Islands. This study also analyses the subdivision of Gran Canaria Island, indicating that there are three well-differentiated areas on the island itself. Finally, this study argues that these areas, themselves, should be considered biogeographic sectors.

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This article aims to propose a chronological subdivision in the history of African communication. African communication today is one of the most important axes for implementing development strategies, sustaining education, health, and schooling programmes, and so on. However, many of these programmes fail due to a lack of or ineffective communication between international organisations, local elite and lay people. The reasons for this situation must be found in Africa’s history of communication, which has undergone radical transformations in its different phases. Using the functionalist analysis drawn up by Jakobson, this article proposes a new chronological subdivision of Africa’s history of communication, reflecting on the current contradictions in contemporary communication in Africa.

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During various periods of Late Quaternary glaciation, small ice-sheets, -caps, -fields and valley glaciers, occupied the mountains and uplands of Far NE Russia (including the Verkhoyansk, Suntar-Khayata, and Chersky Mountains; the KolymaeAnyuy and Koryak Highlands; and much of the Kamchatka and Chukchi
Peninsulas). Here, the margins of former glaciers across this region are constrained through the comprehensive mapping of moraines from remote sensing data (Landsat 7 ETM+ satellite images; ASTER Global Digital Elevation Model (GDEM2); and Viewfinder Panorama DEM data). A total of 8414 moraines
are mapped, and this record is integrated with a series of published age-estimates (n = 25), considered to chronologically-constrain former ice-margin positions. Geomorphological and chronological data are compiled in a Geographic Information System (GIS) to produce ‘best estimate’ reconstructions of ice extent during the global Last Glacial Maximum (gLGM) and, to a lesser degree, during earlier phases of glaciation. The data reveal that much of Far NE Russia (~1,092,427 km2) preserves a glaciated landscape (i.e. is bounded by moraines), but there is no evidence of former ice masses having extended more than 270 km beyond mountain centres (suggesting that, during the Late Quaternary, the region has not been occupied by extensive ice sheets). During the gLGM, specifically, glaciers occupied ~253,000 km2, and rarely extended more than 50 km in length. During earlier (pre-gLGM) periods, glaciers were more extensive, though the timing of former glaciation, and the maximum Quaternary extent, appears to have been asynchronous across the region, and out-of-phase with ice-extent maxima elsewhere in the Northern Hemisphere. This glacial history is partly explained through consideration of climatic-forcing
(particularly moisture-availability, solar insolation and albedo), though topographic-controls upon the former extent and dynamics of glaciers are also considered, as are topographic-controls upon moraine deposition and preservation. Ultimately, our ability to understand the glacial and climatic history of this region is restricted when the geomorphological-record alone is considered, particularly as directly-dated glacial deposits are few, and topographic and climatic controls upon the moraine record are difficult to
distinguish.

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A key for three putative species apparently found in three geographic areas, i.e. Coregonus clupeoides (in Scotland), Coregonus stigmaticus (in England), and Coregonus pennantii (in Wales) given in a recent review was tested quantitatively using 544 individuals from nine populations. The classification success of the key was very low (27%). It was concluded that there is currently no robust evidence for the recognition of the three putative species. Furthermore, the use of phenotypic characters alone to distinguish putative species in postglacial fish species such as those of the genus Coregonus that show homoplasy in many of these traits is questioned. In the absence of further evidence, it was concluded that a single highly variable species best describes the pattern of phenotypic variation in these U.K. populations. On this basis it is argued that taxonomic subdivision of U.K. European coregonids is inappropriate and that Coregonus lavaretus should prevail as the species name applicable to all populations.

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Salt weathering is a crucial process that brings about a change in stone, from the scale of landscapes to stone outcrops and natural building stone facades. It is acknowledged that salt weathering is controlled by fluctuations in temperature and moisture, where repeated oscillations in these parameters can cause re-crystallisation, hydration/de-hydration of salts, bringing about stone surface loss in the form of, for example, granular disaggregation, scaling, and multiple flaking. However, this ‘traditional’ view of how salt weathering proceeds may need to be re-evaluated in the light of current and future climatic trends. Indeed, there is considerable scope for the investigation of consequences of climate change on geomorphological processes in general. Building on contemporary research on the ‘deep wetting’ of natural building stones, it is proposed that (as stone may be wetter for longer), ion diffusion may become a more prominent mechanism for the mixing of molecular constituents, and a shift in focus from physical damage to chemical change is suggested. Data from ion diffusion cell experiments are presented for three different sandstone types, demonstrating that salts may diffuse through porous stone relatively rapidly (in comparison to, for example, dense concrete). Pore water from stones undergoing diffusion experiments was extracted and analysed. Factors controlling ion diffusion
relating to ‘time of wetness’ within stones are discussed, (continued saturation, connectivity of pores, mineralogy, behaviour of salts, sedimentary structure), and potential changes in system dynamics as a result of climate change are addressed. System inputs may change in terms of increased moisture input, translating into a greater depth of wetting front. Salts are likely to be ‘stored’ differently in stones, with salt being in solution for longer periods (during prolonged winter wetness). This has myriad implications in terms of the movement of ions by diffusion and the potential for chemical change in the stone (especially in more mobile constituents), leading to a weakening of the stone matrix/grain boundary cementing. The ‘output’ may be mobilisation and precipitation of elements leading to, for example, uneven cementing in the stone. This reduced strength of the stone, or compromised ability of the stone to absorb stress, is likely to make crystallisation a more efficacious mechanism of decay when it does occur. Thus, a delay in the onset of crystallisation while stonework is wet does not preclude exaggerated or accelerated material loss when it finally happens.

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Defining Simulation Intent involves capturing high level modelling and idealisation decisions in order to create an efficient and fit-for-purpose analysis. These decisions are recorded as attributes of the decomposed design space.

An approach to defining Simulation Intent is described utilising three known technologies: Cellular Modelling, the subdivision of space into volumes of simulation significance (structures, gas paths, internal and external airflows etc.); Equivalencing, maintaining a consistent and coherent description
of the equivalent representations of the spatial cells in different analysis models; and Virtual Topology, which offers tools for partitioning and de-partitioning the model without disturbing the manufacturing oriented design geometry. The end result is a convenient framework to which high level analysis attributes can be applied, and from which detailed analysis models can be generated
with a high degree of controllability, repeatability and automation. There are multiple novel aspects to the approach, including its reusability, robustness to changes in model topology and the inherent links created between analysis models at different levels of fidelity and physics.

By utilising Simulation Intent, CAD modelling for simulation can be fully exploited and simulation work-flows can be more readily automated, reducing many repetitive manual tasks (e.g. the definition of appropriate coupling between elements of different types and the application of boundary conditions). The approach has been implemented and tested with practical examples, and
significant benefits are demonstrated.