Tectonostratigraphic and sedimentary evolution of the Ubur–Orabi sub-basin, southeast Nile Delta, Egypt

Core study of two wells drilled in the southeastern part of the Nile Delta reveals a sub-basin in northern Egypt from the Carboniferous–Permian up to the post-Miocene. The drilled sections are approximately 2600 m thick in the Ubur well in the east and about 3238 m thick in the Orabi well to the west. Basement rocks are recorded in the eastern side of the sub-basin, whereas drilling reached only Lower Cretaceous rocks in the west. The faulting movements played the most important factor determining the distribution, lateral facies changes and unconformities between the different rock units across the sub-basin. The reversal of the faulted blocks over time led to different thicknesses of the drilled units. During the Paleogene, the downfaulted western Orabi part of the sub-basin received up to 1163 m of Paleocene–Eocene sediments, whereas only 203 m were deposited in the eastern uplifted Ubur part. During the Miocene, reversal of the sub-basin taphonomy took place leading to deposition of a thick Miocene section (898 m) in the downfaulted Ubur eastern part, whereas minor thickness (387 m) of the Miocene sediments were laid down in the high Orabi western part of the sub-basin. The stratigraphy of sections drilled is more related to the north Eastern Desert and Sinai rather than to the Western Desert facies. During the Miocene, stratigraphy of the rock units and their facies are a continuation of the Mediterranean subsurface in northern Sinai and eastern Nile Delta facies.