SEISMIC ARCHITECTURE AND GROWTH HISTORY OF A PALEOCENE-LOWER EOCENE ISOLATED CARBONATE PLATFORM, WEST MABRUK FIELD, NW SIRTE BASIN, LIBYA

Isolated carbonate platforms are common and contain important hydrocarbon reservoirs. This study integrates 3-D seismic and well data to investigate the architecture and growth history and interpret factors controlling growth and demise of a Paleocene-lower Eocene isolated carbonate platform in the west Mabruk Field of the tectonically complex Sirte rift basin, Libya. The platform contains nine seismic stratigraphic units bounded by sequence boundaries. Those seismic units are ~760-850 ms TWT thick and have an aerial extension of at least 112 km². Six major seismic facies (SF) show complex lithology and depositional systems. Four major depositional environments are defined, based on seismic facies and attribute analyses, as platform interior (lagoon) with mounds or patch reefs, barrier reef, slope, and intraplatform seaway. Platform growth initiated in early Paleocene as patch reefs developed on top of a Cretaceous horst block and terminated in early-middle Eocene by a subaerial exposure. The platform developed through aggradation in the interior, margins, and intraplatform seaway and progradation on the slopes. It had evolved in four stages: initiation, low-relief platform, build-up, and subaerial exposure. The easterly trade winds generate an east-west energy flux that may be responsible for the prograding leeward margin and near-vertical growing windward margin. Tectonic subsidence caused by the rifting of the Sirte Basin during Late Cretaceous, coupled with repeated eustatic sea-level changes, created the accommodation space for the platform growth. The Cretaceous horst block, created by the rifting and subsidence of the Sirte Basin, forms a shallow-water positive-antecedent topography for the nucleation of carbonate sedimentation.