Paleoenvironmental Interpretation of pre-rift sediments (Usfan Formation in Haddat Ash-Sham)‎ in the central Red Sea margin, Jeddah region, Saudi Arabia

الملخص EN

Field work in the Jeddah region beside sedimentological investigation added some information about the depositional history of onshore rift in the central coast of western Saudi Arabia.

The general sedimentary sequences croping out in the central Red Sea coastal area.

Jeddah region are subdivided into two major sedimentary phases: prerift and syn-rift.

The pre-rift sequence (Usfan Formation) essentially of Upper Cretaceous to Early Eocene age unconformably overlies the Precambrian crystalline basement.

II is represented by succession of continental fluviatile sandstones and siltstones (Nubia type).

grades upward into littoral marine facies (phosph ate and carbonate ledge) and supratidal sequence (dolomitic marl and shale with gypsum veins).

The pre-rift succession mostly represents a regression of the sea due to uplifting.

Study of heavy and clay minerals in the pee-rift sediments shed light on the paleogeography.

paleoclimatology and source rocks.

Opaques.

tourmaline and rutile with lesser amounts of staurolite, hornblende and epidote indicate an igneous- metamorphic ancient sedimentary province, While kaolinite is the only recorded clay mineral pointing out to an intensive leaching, strong chemical weathering and flat topography.-