Lower Silurian-Upper Ordovician Subsurface Glacial Outwash Deposits, Northern Saudi Arabia

DOBSON, PERRY B., Northern Area Exploration, Saudi Aramco, Dhahran, Saudi Arabia

Recently acquired seismic data and reinterpreted well information in northwest Saudi Arabia extends outcropping Lower Silurian to Upper Ordovician Zarqa/Sarah glacial and periglacial deposits into the subsurface. These deposits range from northeast-trending outwash-filled channels deeply incised into the underlying Ordovician Qasim and the Cambrian-Ordovician Saq Formations in the northwest to thin sheets of sand capping the Qasim Formation in the east. A southwest source for these sediments is implied by this new data. This supports previously interpreted source directions mapped from outcrop. It also correlates with the position of the Arabian plate relative to known Gonwanaland ice caps during the Early Silurian-Late Ordovician. The recognition of glacial outwash sediments in the s bsurface provides new insight into the continuity and environments of deposition of the Qasim Formation members in northwest Saudi Arabia.

The hydrocarbon-prone Lower Silurian Qusaiba Member of the Qalibah Formation overlies the Zarqa/Sarah Formations. The Qusaiba represents a rapid transgression of the Paleo-Tethys Sea during the final melting of the Gondwanaland ice caps. The seal-source characteristics of the Qusaiba Member, combined with the good porosity and permeability of the underlying outwash deposits, suggest a prospective hydrocarbon exploration play. Gas is produced from this reservoir in the Risha field of eastern Jordan.

AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)