ORIGIN AND DEPOSITIONAL MODEL OF WADI AL-BATIN AND ITS ASSOCIATED ALLUVIAL-FAN, SAUDI-ARABIA AND KUWAIT

Wadi Al-Batin alluvial fan, which extends northeastward from Hafar Al-Batin in Saudi Arabia to cover parts of Kuwait and southwestern Iraq, represents the largest of several other non-active fans in central and south Arabia. Evidence put forward suggests that, like other comparable deposits of varying age in the Arabian Peninsula, the Al-Batin fan was deposited following downdip breaching of a scarp barrier by a large paleoriver further to the west which once flowed southward down the full length of the Arabian Peninsula. The downdip breaching model offers an explanation of how the Dibdibba gravels were introduced into Kuwait. It is postulated that the present southeasterly course of Tigris-Euphrates rivers to the head of the Arabian Gulf was the last of the easterly diversions of the lower courses of the southward-flowing paleoriver, as its southern end shifted progressively by a sequence of lateral breaches through the Central Arabian scarplands. It is the postulated existence of this huge former drainage system which is seen as the fundamental explanation for the occurrence of the Dibdibba Formation in Kuwait and comparable gravels elsewhere on the eastern flank of the Arabian Peninsula. After the initial phases of deposition of Al-Batin alluvial fan, its surface was dissected by floods from a reduced catchment area, no longer carrying the same sediment load and, therefore, capable of eroding the fan. Dissection of the fan surface continued until the present Wadi Al-Batin became sufficiently incised into the underlying Tertiary bedrock to serve as a permanent outlet. This led to the transport and secondary concentration of post-dissection gravels along the perimeter of the ancient fan.