Recent Carbonates-Evaporites of Southern Arabian Gulf: An Analogue to the Jurassic Reservoirs Peri-Tidal and Evaporite Cycles of Arabian Basin
The coastal areas of southern Arabian Gulf are protected by widespread seaward accreting coral reefs and prograding tidal deltas flanked by barrier islands, protected lagoons, tidal flats, and coastal sabkhas. These settings are characterized by shoaling upward cycles of Holocene carbonates and evaporites that include accumulations of ooid and grapestone grainstones, bioclastic remains, lime mud, cyanobacterial mats, gypsum and anhydrite, and halite crusts. This evolving province of Holocene sedimentary facies matches similar Jurassic sedimentary associations from the subsurface of the Arabian Basin & is used to build conceptual depositional models that, combined with a “framework” of sequence stratigraphic “flooding” surfaces bounding the lithology, explain the deposition & diagenetic settings of these ancient carbonates & evaporites. These include components of the Marrat, Arab, Gotnia & Hith Formations. The Lower Marrat contains thin, aggrading & shoaling-upward cycles capped by massive salina-type anhydrites & thin nodular, sabkha-type anhydrites. The Middle Marrat is characterized by carbonate-evaporite cycles of predominantly salina palisade & stromatolitic anhydrites & occasional supratidal sabkha enterolithic anhydrite & chicken-wire fabric anhydrite. The Upper Marrat is characterized by thin cycles of alternating sabkha & saline evaporites & carbonates. Anhydrite textures are predominantly nodular, with scattered laminated to occasionally silty dolomudstones, microbial laminites. & wavy bedded mudstones & wackestones. The Arab evolved from bioturbated brecciated mudstones & laminated bioclastic wackestones of low to moderate energy, to oolitic peloidal dolomitized packstones-grainstones of moderate to high energy setting. Sabkha anhydritic intercalations correspond to the top of each Arab member & define the regressive cycles of the formation with shallowing upward trends. The Gotnia is represented by four cycles of marine carbonate, mixed anhydrite & carbonate sabkha & salina fill, & halite that form the Gotnia basin sedimentary fill. The more than 80% of massive halite, interbedded with anhydrite, accumulated in subaqueous salina & sabkha enterolithic settings. The Hith is characterized by a thick sequence of predominantly massive anhydrite with thin interbeds & lenses of microbial & peloidal (thrombolitic), planar laminated & stromatolitic carbonates, deposited in sabkha to shallow subtidal settings.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017