干旱区生态环境知识资源中心

A high-resolution Quaternary chronostratigraphy for the Saharan region provides the most detailed Earth history record in which the response of aeolian and related systems to external forcing factors can be evaluated, and against which aeolian sequence-stratigraphic theory can be tested. Saharan environmental change follows relative arid/humid cycles and subcycles that are in part explained by Milankovitch forcing and climatic models. Aeolian sequence stratigraphy predicts the generation and preservation of accumulations and their bounding surfaces based upon the type of aeolian system, the sediment supply cycle, the sediment budget of the system, and the gain and loss of preservation space. The overall scenario for the Sahara is one of a time-lagged sediment influx to dry aeolian systems through deflation of alluvial/lacustrine sediment produced during humid times, with accumulation occurring in topographic basins because of flow deceleration. Surfaces bounding the accumulations may originate during arid-period cannibalization of bedforms and accumulations, and continue to form with stabilization during subsequent humid periods. Within the continental interior, preservation is sparse in spite of basin subsidence because of the cyclic fall of the continental water table, which allows for deflation of accumulations. Along the continental margin, preservation of the last aeolian accumulation is favored because of a rise in sea level. The Saharan surface, therefore, is one of profound reworking, and overlies a laterally discontinuous amalgamation of strata. Major imprinting of the surface may occur during 100 k-yr glacial maxima, in which sand seas form and then persist as templates for lesser cycles. Major sourcing of terrigenous sand occurs during tectonic pulses, the last of which for the Saharan interior was during the Neogene.