CONTROLS ON STRATIGRAPHIC ARCHITECTURE OF RIFT-MARGIN SEQUENCES: INSIGHTS FROM THE LOWER MIOCENE OF THE GULF OF SUEZ, EGYPT

The relative impact of eustasy and local tectonics on the stratigraphic architecture is still a matter of debate. The current work addresses the interplay of eustasy and deformation to control the syn-rift sedimentation at the Suez rift margin. Excellent Lower Miocene outcrops of Nukhul and Rudeis formations in Baba Syncline allow twigging such response/controls relationship through integration of field mapping of stratal geometries and surfaces, facies analysis, Sr-dating and biostratigraphy. The Sr-isotope dating is currently in progress in collaboration with LDEO.

The early syn-rift Nukhul Formation is distinguished into 5 units (N1-N5): N1 occurred as sporadic alluvial/fluvial facies infilling scours (0.5 -10m) along the prerift/synrift unconformity. N2-N5 are coarsening upward shoreface cycles (7-25m) that filled the incipient Baba sub-basin and onlapped the early-formed drag monocline above the propagating rift bounding fault (RBF). The rift-climax Burdigalian sequences of the Rudies Formation (~380 m) occurred as shallow to deep water conglomeratic fan deltas interfingering with basinal marl. Stratal geometries are represented by onlapping/convergence toward the RBF and divergence basinwards with internal downlap. Localized patches of coral reefs developed on the footwall crest indicating complete submergence. Stratigraphic cyclicity exhibits coarsening-upward stacking pattern at different hierarchical levels (3^rd to 5^th order). Preliminary Sr-isotope dating of both oyster shells and foraminifers provides results at sub-million years resolution in consistency with the biostratigraphy.

The stratal architecture is interpreted as principally influenced by growth fault propagation folding, block tilting, morphotectonics of the rift shoulder and local transpressional faulting. In the proximal fan delta sequences, eustatic-driven cyclicity is superposed by tectonic-controlled sediment influx variations during episodic fault activity/quiescence, in contrast to the distal basinal area where laterally continuous cycles developed.

Our next step is to acquire more solid Sr-dates of key stratigraphic surfaces and to correlate them to a known Early Miocene sea level signal to decipher the relative roles of eustasy and deformation in the development of such surfaces.