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Sediment Dispersal Pathways and Processes from a Marine Rift Margin Basin: Miocene Suez Rift, Egypt

Strachan, Lorna J.*1; Rarity, Frank 2; Gawthorpe, Robert L.3; Wilson, Paul 2; Sharp, Ian 4
(1) Geology, School of Enviornment, University of Auckland, Auckland, New Zealand.
(2) School of Earth, Environment & Atmospheric Sciences, University of Manchester, Manchester, United Kingdom.
(3) Department of Earth Science, University of Bergen, Bergen, Norway.
(4) Statoil Research Centre, Statoil, Bergen, Norway.

Evolution of an extension-induced landscape exerts a primary control on sedimentary processes and deposits by: (1) driving sedimentation; (2) controlling fluid- and gravity-flow pathways; and, (3) creating sites of deposition. Detailed reconstructions of flow processes and pathways within marine rift basins are rare, though of importance, given and that many hydrocarbons are found in syn-rift strata. Instead regional studies using low-resolution outcrop and seismic data reveal deep-marine intervals dominated by hemipelagic settling and infrequent gravity flows.

Using exceptional syn-rift exposures in the northern part of the El Qaa Fault Block located on the eastern Suez Rift margin, we have undertaken a high-resolution lithofacies study to help us understand the marine sedimentary response to rifting. More than 2 km of the Rudeis Formation has been logged (12 logs at 0.01 m scale) and a lithofacies scheme developed that includes calcarenites, pebbly sandstones, mudstones and several types of conglomerate. The Rudeis Formation is divided into two coarsening-up stratigraphic units, which themselves display parasequence and bed-scale upwards-coarsening. Texturally immature, coarse-grained (0.02 m average grainsize) deposits were sourced from pre-rift strata along the adjacent rift shoulder. Gravity flows dominate sedimentation in the form of turbidity currents, debris flows (non-cohesive and cohesive), and slumping. Bed shapes imply confined and unconfined flows, and extensive reworking of channelized sediment to form within-channel bar deposits.

Submarine drainages were dominated by multi-sourced, gravity flows that interacted with complex steep faulted terrain, and were modified by ongoing deformation. They formed coalescing deposits of channelized flows that frequently avulsed and were deflected. Proximity to the rift margin and pre-rift sedimentary units, coupled with frequent earthquakes and flood events promoted coarse-grained deposition. The upward-coarsening motifs suggest that rift-related faulting enhanced the delivery of sediment to the basin over time, by steepening slopes and exposing soft pre-rift lithologies. These results provide some of the best examples of the spatial and temporal complexities of marine sediment dispersal pathways and processes from a rift margin basin.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California