SEQUENCE STRATIGRAPHIC ARCHITECTURE OF LOWER AND MIDDLE EOCENE CARBONATE PLATFORM, SIRTE BASIN, NORTH CENTRAL LIBYA

Extensive carbonate platforms covered the northern part of the African Plate during the Cenozoic. Carbonate sediments accumulated by aggradation and progradation, and show a complex, not “layer-cake,” internal stratigraphic architecture. The lower and middle Eocene carbonate sequences developed on an isolated platform within the continental rift Sirte Basin and are being studied using core, well log, and 3-D seismic reflection profiles. They are bounded by unconformities and their correlative conformities at the base and top. Four stratigraphic surfaces have been recognized on the basis of reflection termination patterns (truncation, toplap, onlap, and downlap). These surfaces divide the Eocene strata into three systems tracts, transgressive systems tracts (TST), highstand systems tracts (HST), and lowstand systems tracts (LST). These systems tracts differ in thickness and development of depositional systems. The TST is developed at the base of the sequence and contains lagoonal deposits with seismic mounds, interpreted as patch reefs. The HST is the thickest and contains well-developed slope system with an overall progradational stacking pattern. The LST is the thinnest and composed of middle ramp deposits developed during the lowest position of the sea level. The interplay of accommodation space and sediments supply is responsible for the variation in thickness and development of depositional systems. The thickness is determined by the accommodation space available during the development of each systems tracts, while the spatial distribution and temporal evolution of depositional systems are determined by sediment supply. This study establishes a carbonate sequence stratigraphic framework to help improve our understanding of depositional processes, facies relationships, and development of carbonate platforms in a rift setting. Additionally, the established methodology will provide a contribution to the sequence stratigraphic analysis of rift basin fills and can be applied to similar sedimentary basins worldwide.