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Extensional Basins (extensional + basin)

Distribution by Scientific Domains

Earth and Environmental Science	100%

Selected Abstracts

Dynamic modelling of passive margin salt tectonics: effects of water loading, sediment properties and sedimentation patterns

BASIN RESEARCH, Issue 3 2005
Lykke Gemmer
We investigate the evolution of passive continental margin sedimentary basins that contain salt through two-dimensional (2D) analytical failure analysis and plane-strain finite-element modelling. We expand an earlier analytical failure analysis of a sedimentary basin/salt system at a passive continental margin to include the effects of submarine water loading and pore fluid pressure. Seaward thinning sediments above a weak salt layer produce a pressure gradient that induces Poiseuille flow in the viscous salt. We determine the circumstances under which failure at the head and toe of the frictional,plastic sediment wedge occurs, resulting in translation of the wedge, landward extension and seaward contraction, accompanied by Couette flow in the underlying salt. The effects of water: (i) increase solid and fluid pressures in the sediments; (ii) reduce the head to toe differential pressure in the salt and (iii) act as a buttress to oppose failure and translation of the sediment wedge. The magnitude of the translation velocity upon failure is reduced by the effects of water. The subsequent deformation is investigated using a 2D finite-element model that includes the effects of the submarine setting and hydrostatic pore pressures. The model quantitatively simulates a 2D approximation of the evolution of natural sedimentary basins on continental margins that are formed above salt. Sediment progradation above a viscous salt layer results in formation of landward extensional basins and listric normal growth faults as well as seaward contraction. At a later stage, an allochthonous salt nappe overthrusts the autochthonous limit of the salt. The nature and distribution of major structures depends on the sediment properties and the sedimentation pattern. Strain weakening of sediment favours landward listric growth faults with formation of asymmetric extensional depocentres. Episodes of low sediment influx, with partial infill of depocentres, produce local pressure gradients in the salt that result in diapirism. Diapirs grow passively during sediment aggradation. [source]

Role of crustal anisotropy in modifying the structural and sedimentological evolution of extensional basins: the Gamtoos Basin, South Africa

BASIN RESEARCH, Issue 3 2004
Douglas A. Paton
Through the investigation of crustal heterogeneities, sedimentary basin architecture and seismic stratigraphy, we demonstrate how a crust-scale anisotropy controls the initiation of rifting and the subsequent structural and sedimentological evolution of the Mesozoic Gamtoos Basin, southern South Africa. The results demonstrate that the >90-km-long Gamtoos Fault established its length very early in its syn-rift phase (within ,5 Ma of rift initiation) before accruing over 6 s (two-way-travel time (TWT)), or >12 km, of displacement without any significant subsequent increase in length. In addition, there is no evidence at the resolution of the data of fault segmentation, isolated depocentres nor of intra-basin faults progressively coalescing during the syn-rift interval. The early establishment of length resulted in a rapid transition from a terrestrial depositional environment to anoxic, deep marine conditions. The Gamtoos Fault has a 90° bend in the fault trace that we propose is inherited from the underlying structure. Immediately adjacent to the bend the basin-fill is significantly deformed and a high-amplitude (>1.7s TWT) monoclinal fold is observed. Previous workers proposed that the fold was a consequence of a complex interplay between compression and extension. Through a restoration of the basin-fill deformation we produce a model that suggests that the fold is a consequence of the accommodation of extension by the unusual plan-view trace of the fault. The evolution of the basin does not conform to current fault growth models and it is proposed that its unusual and complex development can be attributed to the underlying crustal-scale anisotropy, a fact that is likely to be important in other areas in which crustal stretching is superimposed on heterogeneous continental crust. [source]

Tectono-sedimentary evolution of active extensional basins

BASIN RESEARCH, Issue 3-4 2000
R. L. Gawthorpe
We present conceptual models for the tectono-sedimentary evolution of rift basins. Basin architecture depends upon a complex interaction between the three-dimensional evolution of basin linkage through fault propagation, the evolution of drainage and drainage catchments and the effects of changes in climate and sea/lake level. In particular, the processes of fault propagation, growth, linkage and death are major tectonic controls on basin architecture. Current theoretical and experimental models of fault linkage and the direction of fault growth can be tested using observational evidence from the earliest stages of rift development. Basin linkage by burial or breaching of crossover basement ridges is the dominant process whereby hydrologically closed rifts evolve into open ones. Nontectonic effects arising from climate, sea or lake level change are responsible for major changes in basin-scale sedimentation patterns. Major gaps in our understanding of rift basins remain because of current inadequacies in sediment, fault and landscape dating. [source]

Heat Flow Pattern in the Mainland of China and Its Geodynamic Significance

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2000
WANG Yang
Abstract On the basis of 723 heat flow measurements in the mainland of China and over 2000 data from the global heat flow data set, the authors compiled the heat flow map of the mainland of China and its adjacent areas to exhibit the overall variation of the heat flow pattern in the mainland. The heat flow pattern of the mainland is complex, and can not be simply summarized as "low in the north and west and high in the south and east". Significant difference exists between eastern and western China in the spatial pattern of heat flow. Divided by the 105°E meridian, heat flow values in eastern China show a westward-decreasing trend; and a northward variation is observed in western China. The high-heat flow regions correspond to tectonically active belts such as Cenozoic orogens and extensional basins, where mantle heat flow is high; and the low-heat flow regions correspond to stable units such as the Tarim and Yangtze platforms. This heat flow pattern is controlled by India-Asia collision in the west and Pacific plate subduction in the east. The lateral variation in lithospheric strength corresponds to the heat flow variation, and there is a generally reversely proportional relation between heat flow and lithospheric strength in the mainland of China. The mosaic pattern of present deformation in the mainland results from lateral rheological heterogeneity. The good coincidence between weak strength domains and seismic zones demonstrates the intrinsic relation between the strength heterogeneity and regional seismicity pattern in the mainland of China. [source]