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Cambrian and Ordovician sandstones and quartzites cover the major part of Libya. During Silurian (Gothlandian) time a generally north-south trend from Tibesti through Gargaf to Garian divided the country in two sedimentary provinces, commonly differentiated as "Western-Libya" and "Eastern-Libya."
Divided by a west-southwest--east-northeast ridge in two distinct sedimentary and structural basins which are known to some of the authorities as the "Gadames" and the "Mourzouk" basins. Marine sediments were deposited in both basins during entire Paleozoic time.
At the end of Carboniferous the Hercynic orogeny was very active in the northwestern part of the Gadames basin, where Upper Carboniferous and Permian sediments produced successive transgressions and unconformities. From Upper Carboniferous to Lower Cretaceous gentle subsidence movements governed the deposition in both of the western basins and produced gradation from shallow marine, to lagoonal and to continental deposits.
The deposition in the eastern portion of Libya was probably active for the greater part of Paleozoic time. Early Paleozoic sediments are preserved in several areas and also in the Kufra basin, to the south. From Permian to Jurassic time this part
of Libya was possibly uplifted with the exception of the Northern Cyrenaican area.
The Upper Cretaceous produced a large widespread transgression in all of the northern portion of Libya, over an eroded peneplaned surface. The deposition was thin and of a "stable shelf" type with the exception of northern Cyrenaica.
During Paleocene time Western Libya remained stable; however a tilting in the eastern part of Libya produced a large sedimentary basin in the Syrte area, which continued subsiding until Miocene time with its hinge line along the Hun-Misurata main fracture system.
Large portions of Libya are still to be tested by drilling, with the oil strikes localized in general as follows: (1) in the two western Paleozoic basins; (2) in the eastern Syrte Tertiary basin where several unconformities in Upper Cretaceous and Eocene time combined with various movements, resulted in effective favorable conditions for oil accumulation.
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