Basin Evolution and Geochemical Modeling
Sedimentology and Sequence Stratigraphy of Early Syn-rift Tidal Sediments; The Nukhul Formation, Suez Rift, Egypt
Research by Dr Ian Carr, Professor Rob L. Gawthorpe, Dr Christopher A.L. Jackson, Dr Ian. Sharp and Dr Ali Sadek
Introduction:
Facies and tectono-stratigraphic models for the tidally-influenced Miocene Nukhul Formation are presented, based on outcrop data from the Hammam Faraun Fault-Block, Suez Rift, Egypt.
Summary:
The Nukhul Formation can be divided into two linked depositional settings, shelf to shoreface and estuary that were deposited during the initial stages of rifting in the hangingwalls of early-formed propagating fault segments. The shelf deposits consist of offshore shelf mudstones passing gradationally upward to bioturbated shoreface sandstones. The more proximal estuary deposits can be separated into a tripartite division of estuary mouth, estuary funnel and upper estuary channel. Estuarine facies relationships generated a complex intercalation of lithologies and facies, with both gradational and sharp facies transitions. In the estuary setting tidal ravinement surfaces are typically marked by mudstones of the lower estuary funnel passing abruptly into erosionally-based tidal inlet sandstones. Maximum flooding surfaces are expressed by an abrupt erosional contact separating tidal inlet sandstones below and low estuary mudstones above. Stratigraphic development was strongly influenced by the evolving early rift structure. Depocenters were narrow (2-5 km wide) and elongate (<10 km long) parallel to the strike of normal fault segments. The shoreface shoal prevented most of the wave energy entering the estuary, increased the relative influence of the tidal currents, the elongate fault-controlled geometry of the depocenters confined the bayhead delta and further enhanced the tidal influence. Stratal geometry reflects deformation associated with low relief growth folds and surface-breaking faults that together formed part of an evolving fault array. This basin configuration and the associated Nukhul stratigraphy is markedly different to tectono-stratigraphic models for crustal-scale tilted fault blocks that are applicable to the late stages of rifting.