Thesis (M.Sc.) - Cairo University - Faculty of Science - Department of Geology

The Dara area in the Northeastern Desert is an example of the Ediacaran volcano-sedimentary deposits.The latter is characterized by their diverse lithofacies and proportions within the study area. They can be classified into inter- and syn-eruptive facies that were generated by diverse depositional processes including debris flows, sheet floods, lacustrine flood flows, lava flows, pyroclastic ash falls/density currents and dike swarms. Three main sequences are recorded along the Dara up-streams area; lower, middle and upper which are represented by the latter facies. These facies correspond to alluvial fan, aeolian-fluvial, lacustrine, lava flow and pyroclastic facies associations. They reveal variations in accommodation to sediment supply (A/S) ratio.The ratios of A/S range from (>+1) through (0) to (0 to +1) for lower, middle, and upper sequences, respectively, demonstrating a significant change in depositional context. The diversity of the facies along the three sequences can be subdivided into Low-Accommodation Systems Tracts (LAST) with negative A/S (A/S ratio close to zero) and High- Accommodation Systems Tracts (HAST) with fluctuation in A/S ratio between zero and +1. The lower and upper sequences are characterized by the presence of clast-supported conglomerates and pyroclastics with fluvial sand bodies and debris flow deposits, overlain or underlain by lacustrine deposits, respectively denoting a fluctuations between a LAST (positive A/S ratio close to zero) and a HAST(A/S ratio > 1).The middle sequence is marked by lava flows facies at the base, passing to pyroclastic deposits, defining a LAST (A/S close to zero). The upper sequence sediments show sediment recycling and moderate weathering (high CIA and PIA) of the protolith near uplifted basin flank(s) under dominant semi-arid to arid conditions, if compared with those exposed at lower sequence

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