BIO-LITHOFACIES AND DIAGENESIS IN THE EARLY-MIDDLE OLIGOCENE OF ABU-DHABI, UNITED-ARAB-EMIRATES

The Early to Middle Oligocene is missing throughout much of the Arabia n peninsula Only in the Oman Mountains and related linear NW-SE trendi ng mountains are these sediments found. In the United Arab Emirates sh allow water carbonates of the Asmari Formation (Early to Middle Oligoc ene) range from 435-481 m (1427-1578 ft). cropping out at the Jabal Ha fit area near Al Ain. Detailed measured sections, sampling and thin se ction analysis show these carbonates comprise seven distinct facies: 1 ) Nummulitic Packstone, 2) Foraminiferal Wackestone/Packstone (non-Num mulitic forams), 3) Echinoderm/Red Algal Packstone, 4) Coral Frameston e, 5) Peloidal Packstone, 6) Mudstone/Wackestone, and 7) Dolomite. Dia genetic events which have affected the Oligocene section include early cementation, formation of micrite envelopes, inversion of original ar agonite and high Mg-calcite fabrics (i.e., biogenic tests and early ma rine cements) to low Mg-calcite, leaching of tests, dolomitization, st ylolitization and fracturing, late diagenetic coarse calcite spar ceme ntation, emplacement of bitumen within stylolitic seams and finally, h ematite and pyrite staining. A depositional model has been proposed ba sed on the fossil and lithofacies assemblages which suggests that a de ep, outer shelf, quiet water lagoon supplies peloids to the back-reef, reef and fore-reef facies as well as the shallow open marine facies o f the inner shelf. A short-lived sea level low is believed to have occ urred, where continental waters manifested their presence in rare cher tification and partial to complete dolomitization of some samples.