Libya is situated on the unstable Mediterranean foreland of the African shield. Marine strata of Paleozoic, Mesozoic, and Cenozoic ages abound in northern Libya, but continental rocks of Paleozoic and Mesozoic ages predominate in southern Libya. Several marine incursions, mainly in Silurian, Middle Devonian, Carboniferous, Late Cretaceous, and Eocene times, reached far into the country, some crossing the southern border.

Compression folds are almost wholly absent; however, uplift, subsidence, block faulting, and tilting have occurred, and angular and parallel unconformities are common. The major diastrophic disturbances include the Caledonian and Hercynian, as well as disturbances during Late Cretaceous and Oligocene through Miocene or Recent times.

The chief regional structures are the Gefara-Gabese basin, Hamada basin, Gargaf arch, Marzuk basin, Tibesti-Haruj uplift, Kufra basin, north Cyrenaican uplift, and Sirte basin. Several large flows and intrusions of Cenozoic basalt and phonolite are present. Sand and gravel conceal the bedrock in about a third of the country.

In the Sirte basin, marine sedimentation, differential compaction, reef development, subsidence, and block faulting, beginning in Late Cretaceous time, favored the development of source and reservoir rocks. Recoverable oil has been found chiefly in limestone and sandstone of Late Cretaceous and Tertiary ages, but also is reported in some knobs of lower Paleozoic sandstone and fractured Precambrian granite. In the Hamada basin, many oil accumulations have been found in sandstone beds of several Paleozoic systems. Most or all of the oil discovered to date probably is in anticlinal structures, but accumulations may exist in other types of traps.

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