Siliciclastic Deposits of the Messinian Nile Canyon, Herodotus Basin, Eastern Mediterranean

Abstract

During the Messinian era, the closure of Gibraltar’s straits, which resulted from the northern tectonic movement of Africa, transformed the Mediterranean into a semi-closed evaporitic basin. The deposition of Messinian evaporites, dated to 5.97-5.33 Ma ago, terminated with the sudden re-opening of Gibraltar’s straits and the restoration of normal marine conditions. The decline of the sea level in the Mediterranean during the Messinian Salinity Crisis (MSC) was unprecedented and rivers were the first geomorphological systems forced to adjust to this new base level. As a result, deep canyons were formed in the areas of preexisting deltas. The Nile starts its activity in the late Eocene-early Oligocene, in parallel with the rifting of Suez; Egypt tilted northward and extensive siliciclastic sediments began accumulating in the Herodotus and Levantine basins. During the Tortonian, a substantial delta complex had already been formed, which was severely eroded during the Messinian moderate change of the base level. During the MSC the Nile created an enormous canyon, measured at a depth of more than 4000m below sea level in the offshore area of the delta. This drainage system transferred substantial quantities of sand-prone sediments, mainly from the red sea rift shoulders and Nubia sandstone outcrops. Representative deposits of the Nile canyon at the north delta are the Qawasim and Abu Mandi formations. One of the main reservoir plays of the Eastern Mediterranean Basin is the Messinian low-stand delta, comprised from Messinian sands of equivalent age to the Abu Mandi formation, deposited as a complex deltaic in shallow hypersaline setting, or as turbiditic currents in front of major fluvial canyons. This study focuses on the deposition of these potential reservoir targets at the base of the Messinian salt. These clastic accumulations may represent the Messinian basin floor fan of the Nile canyon. The present research aims to provide insights in the development of the source to sink system of the Messinian Nile, highlighting the potential prospects of the Messinian mass transport deposits (MTD’s) into the deep Herodotus Basin. For this purpose 2D seismic data were used, covering the western part of the Eratosthenes Sea Mount to the Herodotus basin, offshore Cyprus. For the seismic interpretation, signal processing attribute trace AGC (iterative) was used in grey scale, from which virtual attributes (with different window length and different number of iterations) were created for more detailed and smoother outcome. The results from seismic interpretation suggest that during the early stages of the MSC, Messinian clastic units derived from the Nile were deposited at the deepest hypersaline area of the Herodotus basin, probably simultaneously to the massive halite precipitation. In the seismic data set, high amplitude reflectors (HAR’s) have been identified at the base of the Messinian megasequence and interpreted as sinuous channel-levee deposits. North of these channel-levee deposits the HAR’s are characterized by mounded seismic facies, geometries with bidirectional downlap and chaotic internal reflections. These mounded formations are about 20 kilometers wide and have a significant thickness of about 1-1.5 km. These structures probably represent the channel/lobe complex and distal sheet lobes of the Messinian Nile canyon. The Nile transported vast quantities of clastics (up to 1.5 km thickness) in the south-west part of the Cyprus exclusive economic zone. These deposits may have similar petrophysical properties with those found at the northern Nile Delta. Due to the character and origin of the clastics, they could accommodate potential hydrocarbon reservoirs.

AAPG Datapages/Search and Discovery Article #90341 ©2019 AAPG Geoscience Technology Workshop, Exploration and Development of Siliciclastic and Carbonate Reservoirs in the Eastern Mediterranean, Tel Aviv, Israel, February 26-27, 2019