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Africa’s landscape is dominated by a manifold of second-order epeirogenic structures superimposed on a first-order bimodal topography. Bivariate regression analysis of Africa’s surface topography shows that this is a complexly folded surface with regionally elevated areas in southern and eastern Africa, and a topographically low northern and western Africa. The apparent spatial relationships between these features are analysed using anomaly correlation between surface topography and free-air gravity anomalies. Occurrences of positively correlated features between gravity and topography in Africa are found to be limited to second-order epeirogenic features. Geophysical modelling and geologic evidence indicate that Africa’s bimodal topography is genetically distinct from these second-order features, and linked to sources as deep as the sublithospheric mantle. The age, measured and modelled elevation of the bimodal topography require that topographic uplift of south-central Africa be episodic. We infer from our findings together with relative sea-level changes, that the near-bimodality of Africa’s topography is an ancient feature inherited at least from upper Paleozoic times. Our reconstructed paleotopography suggests that Africa was largely a low-lying continent dominated by its cratons, and that basement distribution disregards the present-day uplift patterns of Africa. 相似文献
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鄂尔多斯盆地中部气田的储层为奥陶系马家沟组白云岩风化壳,马五１层为其主力气层,该层可分为四个小层,沉积相为分布稳定的蒸发潮坪环境,经历了表生期和浅、深埋藏期岩溶作用,天然气主要聚集在岩溶孔洞缝中。 相似文献
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Braid-delta depositional systems are widely developed in most continental basins in China. Research indicates that, for different types of braid delta, the facies sequence and association, which are cr... 相似文献
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This study deals with detailed mapping of sedimentary features within Torok Formation and Nanushuk Group in the northern part of the National Petroleum Reserve in Alsaka (NPRA). These Cretaceous units correspond to a single depositional regime of a large deltaic system. Seismic reflecting surfaces within the sequence are seen as sigmoidal traces in seismic sections. These horizons can be identified over long distances (up to 160 km) within individual seismic sections and can be correlated between intersecting sections. The study is centered in four different areas in which seismic information is relatively abundant and of good quality. One of the study areas is of special interest because of a large, now-filled ancient submarine canyon, Simpson Canyon. Reflection-time measurements were obtained by digitizing various horizons that were manually traced on seismic sections. Reflection-time measurements have been converted to depth values, corrected for postdepositional tilting, and portrayed as structure contour maps, perspective fish-net diagrams, and isopach maps prepared by computer. Computer mapping procedures are essential to obtain three-dimensional representations of reflecting surfaces. Because the northern NPRA has undergone little tectonic deformation since Cretaceous, horizons that have been mapped provide a close representation of submarine paleotopographic surfaces. A succession of these surfaces reveals progressive changes in the form of deltaic deposits from west to east, suggesting that energy of waves and currents increased as the delta prograded eastward. The succession of surfaces also suggests that Simpson Canyon was affected by at least two events of erosion and refilling. 相似文献
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