Tertiary Stratigraphy of the Offshore Sirt Basin, Libya

The onshore Sirt Basin, Libya, is a prolific hydrocarbon basin, with reserves of approximately 50 billion barrels OE, however comparatively little exploration activity has occurred in the offshore extension of this rift basin. In advance of drilling deepwater exploration wells in the basin, this study has been undertaken to understand the Tertiary post-rift section. Regional seismic data was used to define 8 Tertiary sedimentary packages through the observation of stratal terminations and geometries that indicate a re-organisation of sedimentation. Biostratigraphy has been used to pick formation tops and tie these 8 seismically defined packages to eight offshore wells. This has allowed the development of a chronostratigraphy. During the Eocene there is a well developed carbonate margin however, at top Eocene there is a major change in sedimentation from carbonates to clastics, which subsequently infill the basin. This is coincident with a pulse of ‘Syrian Arc’ inversion. This inversion appears to have continued through to the Early Oligocene and is postulated to have caused an initial phase of slumping. There is a dramatic second phase of slumping that is focussed on the NE basin margin and is likely to have a local tectonic cause. The Messinian event is represented as an erosional surface on the basin margins and lacustrine and evaporitic deposits in the basin centre. This is overlain by a very thin Plio-Pleistocene section.