The writer attempts to reevaluate depositional history, diastrophism, structure, and oil productivity in the greater Persian Gulf area, and to offer additional reasons for the great petroleum richness of this area. Continuous subsidence and sedimentation through Phanerozoic time resulted in the deposition of maximum thicknesses of 25,000 ft, and possibly more than 30,000 ft under the present mountains and foothills of Iran. The zone of maximum thickness may best be regarded as one relatively thick prism within an immense compound prism of sedimentary rocks. The sedimentary prism also may be regarded as having been the site of persistent epicontinental conditions in a persistent platform environment.

The center of the prism was not greatly uplifted until near the end of Tertiary time, when the geometry of the sediments was profoundly modified. The effect of uplift in the area of study was to deform basement into a relatively simple syncline with a slightly steeper northeastern flank. Overlying sediments perhaps glided down the asymmetrical flank of the syncline to form high-frequency folds, that is, the present fold belt of Iran. The fold belt and largely undeformed platform together constitute a synclinorium, a feature which the writer regards as the most prominent characteristic of the region. The region thus is called the "Persian Gulf synclinorium" in this paper.

During the last two decades, a small amount of specific data relative to the synclinorium has been released. Nevertheless, an initial synthesis of the data into systemic isopach maps and a total-sedimentary-rock isopach map is attempted herein, with the aim of furthering a general understanding of the regional geology. Ordovician and especially Permian events appear to be important among the several marine transgressions. Thus the Permian Sea may have advanced southward from a Tethyan seaway into an ancestral Arabian Sea; this interpretation, which involves an ancestral Indian Ocean on the south, is as plausible as that of a supposed segment of Gondwanaland in the present Indian Ocean during Permian time.

Ultimate producible reserves of crude oil in the Persian Gulf synclinorium are believed to exceed 250 billion bbl, which may mean that as much as 500 billion bbl of in-place oil accumulated in major structures. The main causes previously suggested for prolific reserves were continuity of sedimentation, great total sedimentary volume, good caprocks, rich source materials, and long anticlines. The writer stresses the importance of long anticlines and the presence within them of great reservoir pore volume confined within closure. The writer further stresses the intercalation of source materials and reservoir, and the early release of oil into the reservoir where its accumulation protected initial porosity from the adverse effects of diagenesis. The important sources of the Persian Gulf ynclinorium may not be those beds that now are obviously petroliferous.