Pre-Pliocene History and Depositional Facies, Nile Delta, Egypt

J. C. Harms, John L. Wray

The Nile delta area has a long history of subsidence and deposition that is inferred to extend back to Jurassic or earlier times. Depositional environments, rates of subsidence, and structural events are quite varied during this time span. Deposition was dominated by platform-to-basin carbonate facies from Jurassic to Eocene time and by detrital sediments from the Oligocene onward. Deposits are truly deltaic, in the sense of representing focused deposition at the shoreline by a large integrated river, only from latest Miocene time onward.

A probable transition from continental to oceanic crust typical of the southern Mediterranean margin is overlain in the delta area by Mesozoic platform carbonates that appear to change on seismic data northward into slope and basinal facies. This platform margin, which trends east-west through the central delta, is reflected in later stratigraphic and structural characteristics; very thick Tertiary deposits, bathyal facies of Oligocene to Pliocene age, and large rotated fault blocks of Miocene strata occur only north of this margin.

Regional structural movements and sea level fluctuations influenced Tertiary deposition. The middle Oligocene and much of the earliest Miocene were times of low sea level and uplift in much of the delta area. Accumulation rates were low during Aquitanian, but the eastern delta subsided more rapidly during Burdigalian, when sea level was high and marine environments extended far to the south. The early middle Miocene had major rotational faulting in the northern delta, followed by lowered sea level and an extensive erosional unconformity. This Serravallian-Tortonian hiatus lasted 6 m.y. in the southern delta, diminishing basinward to 2 m.y. During late Tortonian and early Messinian, rapid subsidence (650 m/m.y.) occurred in the eastern delta. During this time a 1-3 km-thick clinoform s quence prograded northeastward from the central delta and perhaps reflects the first major integrated Nile River. This period of rapid sedimentation was followed by the large sea level fall in late Messinian. A valley was entrenched, and a thick Pliocene to Pleistocene deltaic wedge was deposited after sea level was restored to near-present heights.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.