Early Paleozoic sediments of NE Africa and Arabia: Products of continental-scale erosion, sediment transport, and deposition

The extensive Early Paleozoic platformal sediment blanket of NE Africa and Arabia accumulated over a ca. 2000 km wide platform with a subdued topography that formed along the periphery of Gondwana when the continent was stabilized in the aftermath of the Pan-African orogeny. The sediments consist largely of far-traveled mature clastics. In the long run, sediment thickness was controlled by the subsidence of the platform. The sediment blanket displays a transition from sandstones, often pebbly, deposited in braided rivers to very shallow marine sandstones with trace fossils, while in more peripheral parts of the platform finer marine clastics become increasingly abundant. As time passed, transgressions reached further inland, so generally marine beds become more abundant up-section. The area of deposition gradually expanded-from a belt several hundred kilometers wide in the Early Cambrian, to well over 1000 km in the Ordovician and Silurian. Deposition over such a wide region, including very wide epeiric seas, required the operation of a continental-scale system of sediment transportation and dispersal. Bypassing of sediments and efficient sorting occurred over long distances. Deposition occurred in many discrete events, so sediment transport involved temporary storage and subsequent reworking and further transportation. Thus, much of the finer-grained fraction derived from the interior of the continent accumulated on the outer parts of the platform. This must be taken into consideration in estimates of the bulk composition of the sediments that were supplied to the platform. Most of these deposits appear to be first-cycle sediments derived by thorough chemical weathering of metamorphic and plutonic rocks of the Pan-African basement. However, recycled sediments derived from more distant sources may well also be present.