College of Earth Sciences��Jilin University��Changchun 130061��China

Uinta Basin was located in the northeastern Utah State of U. S. A��which was rich in oil sand resources�� The area of P. R. spring oil sand deposit was 650 km2 and the resource was 6. 76 × 108 t��whose reservior was Eocene lacustrine delta sand body in Green River Formation�� The laramide orogeny changed the basin environment from marine facies to continent facies during Late Cretaceous and Paleogene�� From the latest Paleocene to Eocene�� the Uinta lake was widespread in the basin��and two sets of thick source rocks of Green River Formation were deposited�� The middle Eocene source rock in upper Green River Formation was about 150 m thick��with rich organic matter in low maturity��so that abundant immature oil was generated since 30 Ma ago�� P. R. spring oil sand deposit was degradation on slope type��which developed five sets of delta sandstone with good physical properties�� After long-distance migration along continuous sand body��the immature oil generated from the upper source rock of Green River Formation entered the sandstone reservoir of lacustrine delta in Green River Formation of P. R. spring�� and formed oil sand deposit eventually through biodegradation and water washing��