Title : 3D seismic geomorphology of an exposed upper sabil carbonate build-up: Evidence for slope-derived talus and flank reservoir heterogeneity, Eastern Sirt Basin, Libya
Abstract:
The Upper Sabil Formation in the eastern Sirt Basin is a major Paleocene carbonate reservoir whose upper surface records subaerial exposure and erosion at the end of platform growth. The overlying Harash Formation infills inherited Upper Sabil relief and provides a stratigraphic framework for evaluating post-exposure flank evolution. This study integrates 3D seismic geomorphological analysis with well-log correlation to characterize an Upper Sabil carbonate build-up in the southern Ajdabiya Trough and to assess evidence for slope-derived talus accumulation along its northeastern flank.
Time-structure mapping of the Upper Sabil top reveals a strongly asymmetric build-up, with a steep, high-relief southwestern margin and a lower-gradient northeastern flank marked by progressive morphological smoothing. Seismic sections across the crest show truncation and irregular reflector geometry at the Upper Sabil top, consistent with an erosional unconformity developed during subaerial exposure. Within the Harash interval on the northeastern flank, a localized seismic body is identified by discontinuous to chaotic internal reflections, a convex-up external form, and reflector terminations against its margins, in contrast to the more regular layered Harash reflections basinward. Its position directly downslope from the eroded crest and within the smoothed northeastern sector supports interpretation as a slope-derived carbonate talus or debris-accumulation body.
Recognition of a Harash cycle beneath this body indicates that debris emplacement occurred during Harash deposition rather than entirely prior to its onset, implying episodic slope failure or margin shedding intercalated with background Harash sedimentation. The preferential development of this body on the northeastern flank may reflect directional hydrodynamic influence superimposed on inherited platform morphology. This geomorphological configuration introduces a potentially significant source of reservoir heterogeneity along the build-up flank, where a debris-prone interval may interfinger with porous lower Harash facies and define an underexplored exploration target within the Upper Sabil–Harash petroleum system of the eastern Sirt Basin.
