Petroleum Systems of Divergent Continental Margin Basins
Progradation and Retrogradation of the Libyan Shelf and Slope, North African Continental Margin
Published:December 01, 2005
Joseph C. Fiduk, Peter B. Gibbs, Eugene R. Brush, Lynn E. Anderson, Thomas R. Schultz, Steven E. Schulz, 2005. "Progradation and Retrogradation of the Libyan Shelf and Slope, North African Continental Margin", Petroleum Systems of Divergent Continental Margin Basins, Paul J. Post, Norman C. Rosen, Donald L. Olson, Stephen L. Palmes, Kevin T. Lyons, Geoffrey B. Newton
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With the lifting of economic sanctions, western companies have come back to explore for hydrocarbons in Libya, onshore and offshore. However, virtually no modern marine seismic data has been acquired over the past twenty-five years to assist in this renewed exploration effort. During the past year, new 2D pre-stack time migrated seismic data has been acquired and used to examine the large-scale structural and depositional features of the Libyan shelf and slope. The data cover approximately 38,000 line kilometers in water depths ranging between 15 to 2200 meters.
The present day Libyan shelf margin has a demonstrably progradational character. Thick, laterally extensive deltaic deposits dominate the shallow shelf and upper slope. These deposits display classical clinoform geometries that suggest multiple phases of progradation during the past 3-5 Ma. Seismic resolution within the clinoform packages is high, as growth faulting, distributary channels, slump scars, and rotated blocks within the delta front are readily visible.
Clinoform geometries visible below, but truncated by, the Messinian unconformity indicate that the early to middle Miocene margin of Libya was also progradational at certain times.
Recent deltaic deposits sit upon and within a deeply eroded and scarred paleotopography, suggesting large-scale retrogradation of the shelf margin. The erosional surface extends for nearly 500 km along strike in the Sirt Embayment. A 65 km long portion of this erosional surface displays high relief truncated strata, healed fault scarps, and related deep-seated faults. In this area it is likely that a very large volume of shelf margin strata is missing.
The Libyan margin is tectonically active today and has been through most of the Cenozoic. Many faults penetrate from deeply underlying Mesozoic strata to the ocean bottom. The close association of active faults scarps, truncated strata, a potentially large missing section, and a laterally extensive erosional unconformity combine to suggest the possibility of catastrophic margin failure. The exact timing of margin retrogradation is uncertain at present but erosional relationships hint that margin failure occurred either coincident with or following the Messinian salinity crisis.