Abstract

The Jurassic succession of the Arabian Gulf region represents the progressive flooding of a stable craton by a shallow sea during a major sedimentary cycle. This cycle ended in the Late Jurassic with the stagnation of sea water and the formation of an extensive evaporitic platform over much of the region. Variation in the sedimentary facies throughout the Jurassic can be explained by eustatic sea level rise or fall, as well as by epeirogenic movements and faulting in various parts of the basin.

The Lower Jurassic was dominated by a carbonate-evaporite platform with substantial clastic influx from paleo-highs in western and southern Arabia. During the Middle Jurassic a vast marine platform became the setting for a well developed carbonate ramp in which clastic sediments rimmed the western and southern parts of the shallow sea. The sediments grade into impure carbonates and finally into pure carbonate shelf deposits. During the Late Jurassic the carbonate shelf environment became dominant and was differentiated into broad shelves and local intrashelf basins. Shelf carbonate consists of broad sheets of peloidal-oolitic grainstones and packstones, commonly dolomitic and anhydritic. Intrashelf basins contain interbedded, kerogen-rich marine lime mudstones and marls. In the latest Jurassic the shelfal sea became a sabkha rimmed by an evaporitic platform.

Middle-Upper Jurassic strata are widely known for their prolific oil production in the western and southwestern Arabian Gulf region. The limits of Jurassic production coincide closely with the limits of mature Late Jurassic source rocks present in the intrashelf basins. The Tithonian Hith anhydrite effectively provides regional seals for the porous, grain-rich Middle and Late Jurassic reservoirs in the oilfields of Saudi Arabia, Bahrain, Qatar and offshore Abu Dhabi. These reservoirs were charged with hydrocarbons from underlying Late Jurassic kerogen-rich basinal sediments. It is this source-reservoir-seal combination which constitutes the world’s richest single oil deposit (e.g., Ghawar Field, Saudi Arabia).