Pre-salt to salt stratigraphic architecture in a rift basin: insights from a basin-scale study of the Gulf of Suez (Egypt)
Résumé
We propose a basin-scale (~300 x 100 km) study of the pre-salt to salt sedimentary fill
from the Suez rift based on outcrop and subsurface data. This study is a new synthesis
of existing and newly acquired data using an integrated approach with (1) basin-scale
synthesis of the structural framework, (2) stratigraphic architecture characterization of
the entire Suez rift using sequence stratigraphy concepts, (3) lithologic maps
reconstruction and interpretation, (4) isopach / depocenter maps interpolation to
quantify sedimentary volumes and (5) quantification of the sediment supply, mean
carbonate and evaporite accumulation rates and their integration into the rift dynamic.
The Gulf of Suez is ca. 300 km long and up to 80 km wide rift structure, resulting from
the late Oligocene to early Miocene rifting of the African and Arabian plates. The
stratigraphic architecture has recorded five main stages of rift evolution, from rift
initiation to finally tectonic quiescence characterized by salt deposits.
Rift initiation (ca. 1-4 Myr duration): the Suez rift was initiated at the end of the
Oligocene along the NNW-SSE trend of the Red Sea with evidences of active
volcanism. Continental to lacustrine deposits only occurred in isolated depocenters.
Sediment supply was relatively low.
Rift widening (ca. 3 Myr duration): the rift propagated from south to north (Aquitanian),
with first marine incursions from the Mediterranean Sea. The rift was subdivided into
numerous depocenters controlled by active faults. Sedimentation was characterized by
small carbonate platforms and associated sabkha deposits to the south and shallow
open marine condition to the north with mixed sedimentation organized into an overall
transgressive trend.
Rift climax (ca. 5 Myr duration): the rift was then flooded during Burdigalian times
recording the connection between the Mediterranean Sea and the Red Sea. The faults
were gradually connected and reliefs on the rift shoulders were high as evidenced by a
strong increase of the uplift/subsidence rates and sediment supply. Three main
depocenters were then individualized across the rift and correspond to the Darag,
Central and Southern basins. Sedimentation was characterized by very large Gilbert-type deltas along the eastern margin and associated submarine fans and turbidite
systems along the basin axis. Isolated carbonate platforms and reefs mainly occurred
in the Southern Basin and along tilted block crests.
Late syn-rift to rift narrowing (ca. 4 Myr duration): during the Langhian, the basin
recorded several falls of relative sea level and bathymetry in the rift axis was
progressively reduced. The former reliefs induced during the rift climax were quickly
destroyed as evidenced by the drastic drop in sediment supply. Stratigraphic
reconstruction indicates that the Central Basin was restricted during lowstand period,
meanwhile, open marine conditions prevailed to the north and south of the Suez rift.
The Central Basin, Zaafarana and Morgan accommodation zones thus acted as a
major divide between the Mediterranean Sea and the Red Sea. During Serravalian
times, the Suez rift also recorded several disconnections between the Mediterranean
and Red seas as evidenced by massive evaporites in major fault controlled
depocenters. The Suez rift was occasionally characterized by N-S paleogeographic
gradient with restricted setting to the north and open marine setting to the south (Red
Sea).
Tectonic quiescence to latest syn-rift (ca. 7 Myr duration): the Tortonian was then
characterized by the deposition of very thick salt series (> 1000 m) which recorded a
period of maximum restriction for the Suez rift. The basin was still subdivided into
several sub-basins bounded by major faults. The basin with a N-S paleogeographic
gradient was totally and permanently disconnected from the Mediterranean Sea, and
connected to open marine condition via the Red Sea. The Messinian was also
characterized by a thick salt series, but the evaporite typology and sedimentary
systems distribution suggest a more humid climate than during Tortonian times.
Pre-salt to salt transition was not sharp and lasted for ca. 4 Myr (Langhian-
Serravalian). It was initiated as the result of the combined effect of (1) climatic changes
with aridization and low water input from the catchments and (2) rift dynamic induced
by plate tectonic reorganization that controlled the interplay between sea level and
accommodation zones constituting sills.
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