When Sea Level Is Trumped by Tectonics and Autocylcic Processes: a Field Study of from Evolving Deep Marine Syn-Rift Basin, Sinai, Egypt

Strachan, Lorna ¹; Rarity, Frank ²; Gawthorpe, Rob ²; Wilson, Paul ^2
1 Geology, SGGES, University of Auckland, Auckland, New Zealand.
² School of Earth, Environment and Atmospheric Sciences, University of Manchester, Manchester, United Kingdom.

The link between rift tectonics, surface tilting, depositional processes and resultant deposits has been investigated from a range of environmental settings including non-marine and marine. This link is particularly keenly felt in deep marine syn-rift systems dominated by sediment gravity flow processes during rift climax times, i.e. when there is maximum displacement on the bounding fault.

Conceptual tectono-stratigraphic models for marine rift basins during rift climax, predict that subsidence will outpace sedimentation resulting in mudstone-dominated systems, controlled by sea level. While useful in driving forward our understanding of such basin types, these conceptual models are yet to be validated by outcrop studies and oversimplify the structural and sedimentological evolution of rift basins.

The aim of this presentation is to use a stunning 100% exposure, three-dimensional (3D) outcrop, to document the vertical and lateral evolution of deep marine sedimentary processes and architectures in a developing hanging wall slope and basin floor system, during rift climax.

The area of study is the Early Miocene Baba Basin, located on the western Sinai Peninsula, Egypt. The syn-rift sediments within the Baba Basin have undergone significant large scale (>300m) syn-depositional deformation and rotation, forming an archetypal example of monoclinal folding above a blind normal fault.

Integrated field mapping, detailed sedimentological analysis and terrestrial Light Detection And Ranging (LiDAR) data reveals a complex sedimentary succession dominated by coarse-grained turbidites and debrites. Turbidite channels, levees and lobes are recognised and together with debrites record evidence of evolving bathymetry resulting in flow deflections, relocation of depocentres, changing flow types and clustering of remobilization events. Markov chain analysis reveals the absence of widespread vertical trends in grain size, as might be anticipated from a sea level control. Instead the variety of bed transition types and architectures is more readily explained by tectonic and autocyclic process controls.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009