Syn-rift sedimentary response to growth folding along a rift-margin transfer zone: An example from the early Miocene of the Gulf of Suez, Egypt

Abstract

Growth folds developed at rift margin transfer zones are mostly studied for their structural style and stratal architecture. The influence of the growth of these folds on the syn-rift sedimentary facies development, however, remains less documented. To address this, we investigated the syn-rift facies of the Lower Miocene Rudeis Formation in relation to the growth of structures within the North Baba transfer zone at the eastern margin of the Suez rift. Sedimentological analysis defined seven facies associations in three successive depositional systems: (i) gravel-rich submarine fans with up-dip thinning geometry, comprising upper, middle and lower fan facies associations, (ii) a gravitationally modified Gilbert-type fan delta, with tangential foreset and bottomset. Both fan systems pass gradationally into basinal marl-dominated facies, and (iii) shoreface-to-offshore. Paleocurrent measurements and the spatial facies variability indicate that the North Baba transfer zone was acting as the main sediment fairway conveying the sediments southwards from the adjacent rift shoulder to the Baba hangingwall syncline. Mapping of key stratal surfaces and growth structures helped in distinguishing four lower Rudeis stratal units, which provide a framework for studying the spatial and vertical relationships among the recognized facies. Deposition of these stratal units was influenced by progressive steepening and localized faulting of a fault-tip growth monocline above the North Baba transfer zone and a submerged intrabasinal high. These structures controlled the hangingwall gradient, bathymetry, flow pathways and facies relations, triggered multiple gravity flows and slumps, and created terraces on which patch reefs and localized shoreface deposits intermittently developed. This study reveals that the transfer zone was still acting as growth monocline even during the rift-climax. The coeval deposits were mainly sourced from a hinterland drainage catchment rather than local footwall scarps. They form progressively tilted clastic wedges that onlap and pinch out up-dip toward the growth monocline, unlike those observed at faulted margins where the facies commonly thicken toward the fault.