DIAGENETIC HISTORY AND SOURCE-ROCK POTENTIAL OF THE UPPER JURASSIC DIYAB FORMATION, OFFSHORE ABU-DHABI, UNITED-ARAB-EMIRATES

The Upper Jurassic Diyab Formation is a highly argillaceous dolomitic limestone unit underlying one of the most prolific hydrocarbon reservo irs in the world: the Arab Formation. The Diyab is thought to be the p rimary source for the Arab in the United Arab Emirates. Thin sections from cores in offshore Abu Dhabi show the Diyab to contain dolomitized grainstones at the base with associated glauconitization and chertifi cation grading upward to olive-green, argillaceous, organically-rich d olomitic limestones in the upper third of the Diyab, creating a marry texture which persists through to the top of the section. Late diagene tic calcite (and subordinate anhydrite) cement, which include coarse s par as well as blocky and poikilotopic fabrics, occlude much of the se condary porosity and are interpreted to have occurred during burial di agenesis. Dolomite is in the form of euhedral rhombohedra which primar ily replace the matrix of the limestones. Allochemical grains, which i nclude peloids, intraclasts and bioclasts, have recrystallized to low Mg-calcite and are partially glauconitized in the lower part of the se ction. Pressure solution has caused fracturing and stylolitization, fr actures being filled by sparry calcite and stylolites by a bituminous residue.