Creation and fill of an Eocene incision on a leeward margin of an isolated carbonate platform, northeast Sirte Basin, Libya

Abstract

The recognition of incised valleys and the reconstruction of their filling history are significant for defining unconformity surfaces and their stratigraphic framework, particularly when detailed petrographic data are missing. However, little of such research is published so far on the characterization and factors influencing the development of incised valleys using three-dimensional seismic and well data. Thus, this work aims to examine and analyze the geometry and factors controlling the formation and sediments filling of an Eocene incised valley in a sequence stratigraphic frame using an integration of three-dimensional seismic and well data from NE Sirte Basin, Libya. The Eocene incised valley is defined by an unconformable sequence boundary underneath and contains sediments of the lowstand systems tract of Sequence 6. The incision deposits are thick limestones intercalated by thin shales and show a low-order stacking of serrated log motif. The thickness of the incised valley is 118 m and has an aerial extension of ~ 3.2 km in a southwest-northeast direction. Its uppermost width was found to be ranging between 950 and 1100 m and displays a moderately sinuous geometry with asymmetrical meanders occurring each 1 to 1.8 km. The amplitude of these meanders ranges from 500 to 700 m. No distinguishable tributaries are observed in the studied incised valley, indicating the formation of a singular stream or possibly the seismic data resolution not capable to identify small size tributaries. The geometry and stratigraphic architecture of the incised valley suggest a fluvial rather than tidal incisions. The incision primarily formed as a result of a falling sea-level that led to a subaerial exposure, while a successive rising sea-level caused the development of the lowstand deposits and infilling of the incised valley.