Clastic Dykes and Sills from Numidian Flysch (Sicily and Tunisia): Sandy Injection Related to a High-Density Turbidity Deposit

O. Parize, B. Beaudoin

The Numidian flysch is a thick (approximately 2,000-4,000 m) turbiditic formation (Oligocene to lower Miocene) of the southern part of the Alpine chain in western Europe. In Sicily (Geraci-Siculo) and Tunisia (Tabarka, Cap Negro, Ras El Korane), the Numidian basin paleo-current pattern is southward.

Numerous sedimentary sills and dikes cut as well as shales, argillaceous slumps, and intercalated sandstones. These sandy injections fossilize a complex network of horizontal, oblique, and vertical synsedimentary joints controlled by stratification planes, general paleoslope, differential compaction, and regional tectonic setting. The sills may exceed 5 m in thickness and 100 m in lateral extent; the dikes are less than 0.9 m wide, locally 1.2 m. Depth of penetration below the mother sand is 30 m (sills) to 150 m (dikes). The dikes are often folded in a ptygmatic fashion, and the sills and dikes show pillars; these occurrences allow quantification of a postinjection compaction ratio ranging from 1.2 to 2.8. This late compaction of the surrounding mud together with the presence of burr ws on both flanks of the dikes and through the sills, and the connection with channeling sandstone bodies, indicate the early occurrence of this injection. Sand was injected downward from high-density turbidity currents (shown by the presence of thick, structureless sandstone), filling erosive, deep, steep-walled channels or gullies.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.