The stratigraphy, depositional environments and periods of deformation of the Wajid outcrop belt, southwestern Saudi Arabia

Abstract The Wajid outcrop belt in southwestern Saudi Arabia is an area of over 22,000 square kilometers where strata of Middle(?) Cambrian through to Jurassic crop out. The Early Palaeozoic sediments in southwestern Arabia have been placed in the Wajid sandstone. This paper elevates this unit to group status and recognizes its former members as formations. The remaining Palaeozoic successions are placed in the Qalibah and Khuff formations. The Middle(?) Cambrian through to Early(?) Ordovician Dibsiyah Formation, Wajid Group, correlates with the Saq sandstone of central and northern Saudi Arabia. The ‘lower’ Dibsiyah buries a topography developed on the Arabian shield during the Late Precambrian Pan-African and/or the late Early Cambrian periods of uplift. The late Early Cambrian period of deformation is documented in southwestern Saudi Arabia and adjacent Oman by an angular unconformity which separates the Dibsiyah Formation correlative from the underlying Late Precambrian-Early Cambrian Lower Haima Group. The ‘lower’ Dibsiyah was deposited in a northward prograding fluvial apron. The ‘upper’ Dibsiyah was deposited in intertidal to shallow subtidal marine settings during a period of coastal onlap. The Late(?) Ordovician Sanamah Formation overlies the Dibsiyah Formation in angular and/or erosional unconformity. This unconformity was developed during a period of regional uplift which began near the close of the Middle Ordovician. The Sanamah Formation was deposited in broad valley complexes excavated in fluvial settings. The Early Silurian Qusaiba Member of the Qalibah Formation unconformably overlies the Sanamah. The Qalibah Formation was deposited in shallow marine to mid-shelf settings during a major period of coastal onlap. The angular unconformity to disconformity, which separates the Qalibah Formation from underlying units, resulted from diastrophism of Late Ordovician to earliest Silurian age. The Early Devonian to Middle(?) Carboniferous Khusayyayn Formation unconformably overlies the Qalibah Formation. The Khusayyayn Formation was deposited in shallow marine, lagoonal, eolian and fluvio-deltaic settings. The unconformity separating the Khusayyayn Formation from the Qalibah Formation documents a period of regional diastrophism of late Early Silurian to late Early Devonian age. Unconformably overlying the Khusayyayn is the Middle Carboniferous through Early Permian Juwayl Formation. This unit was deposited in broad valley complexes excavated in fluvial settings. The base Juwayl unconformity was produced by the Hercynian orogeny. The Permian Khuff Formation unconformably overlies the Juwayl and the former deposited in shallow marine settings. The base Khuff Formation unconformity resulted from a period of major coastal onlap. The Early Triassic Sudair shale succeeds the Khuff and the former was deposited during a period of coastal offlap in lagoonal to coastal plain settings. Near the end of the Early Triassic the Arabian Peninsula underwent another period of tectonism. In central and southwest Saudi Arabia this event is reflected by the erosion of the Sudair shale and older units from the higher portions of reactivated fault blocks and the syndepositional thickening of the Jilh Formation on the down thrown sides of these fault blocks.