HEINE, CHRISTIAN J., Saudi Aramco, Dhahran, Saudi Arabia

ABSTRACT: A Continental Clastic Depositional Model for the Permian Unayzah Formation, Hawtah Field, Central Saudi Arabia

The Permian Unayzah Formation lies unconformably on the Silurian Qusaiba Member of the Qalibah Formation. The pre-Unayzah unconformity (PUU) represents a Hercynian tectonic event responsible for uplift and erosion representing 100-150 m.y. worth of missing section along the Hawtah Trend. Overlying the PUU, the Unayzah clastic sequence is comprised of locally sourced sediments from the adjacent paleotopography. Above the thin veneer of locally sourced sediments is a more regionally sourced, confined braided stream sequence, which completely backfills the existing paleotopography. Once the paleotopographic surface had been leveled, the depositional environment changed from a confined braided stream to a broad braided plain. Within this sequence of vertically stacked and laterally migrat ng braided plain sediments, the bulk of the reservoirs within the Hawtah field are contained. As the transgressive Khuff seas continue to encroach on the Unayzah depositional system, the uppermost sediments of the broad braided plane environment are reworked by transgressive coastal processes. The resulting reworked shoreface and shallow-marine facies are genetically related to the Khuff transgression and lie unconformably on the Unayzah continental clastics.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.