CREATION AND FILL OF AN INCISION ON AN EOCENE ISOLATED CARBONATE PLATFORM, NORTHEAST SIRTE BASIN, LIBYA

The recognition of incisions and the interpretation of their fill is crucial to the delineations of unconformable sequence boundaries and their stratigraphic architecture, particularly in the lack of petrographic data. There has been little research on the geometries and controlling factors on the formation of incisions to characterize the subaerial exposure on carbonate platforms from subsurface three-dimensional (3D) seismic reflection and wire-line log data. Therefore, this study characterizes the geometry and processes controlling the creation and fill of a middle Eocene incision in a sequence stratigraphic framework from an integrated analysis of 3D seismic and wire-line log data. The middle Eocene incision is bounded by an unconformable surface below and was filled with the lowstand deposits of Sequence 6. It consists of thick limestone units interbedded by much thinner shale units and featured by a low-order serrated log stacking pattern. The incision has a thickness of ~ 118 m and extends at least for 3.2 km in a SW-NE direction. It has a maximum width of ~ 950-1100 and a moderately sinuous shape with asymmetric meanders every 1 to 1.8 km. The meanders have an amplitude of ~ 500 to 700 m. The incision has no visible tributaries, suggesting that this type of incision formed as a single stream or perhaps the tributaries are too small to be seen on seismic sections. The morphology and stratigraphic context of the incision are indications of fluvial type of incision rather than tidal channels. The creation of the incision was mainly controlled by sea-level fall, which eventually caused a subaerial exposure, whereas a subsequent sea-level rise led to the deposition of the lowstand systems tract of Sequence 6 and fill of the incision.