Salt Tectonics in Tunisia

Pierre F. Burollet

The Triassic series, especially its upper part includes large thicknesses of evaporites: halite and sulfate. Because of that the Atlasic Tunisia and a large part of the Eastern Tunisia, including its offshore, are disconnected from the basement and are folded in "plis de couverture."

Large extrusions of Triassic mixed shale, evaporite and few dolomite are observed in Atlasic Tunisia, specially in the Northern part. The outcrops are mainly insoluble cap-rocks. The few wells drilled through diapirs encountered massive salt below 200 or 300 m of gypsum.

Seismic surveys and exploration wells brought a lot of new information: shape and type of salt features, role of the salt in the sedimentary processes as inequable subsidence, salt migrations, transmission of deep movements into the Mesozoic and Cenozoic couverture.

The main extrusive bodies are: salt domes, salt walls, cushions, injected faults, nappe soles, etc.

The repartition of the salt features depends on the lithologic nature of the overlying series : in Southern Atlasic Tunisia or in the Golf of Gabes where Jurassic and Cretaceous units are generally massive carbonates, the extrusions are rare, located near main faults crossings. In Nortern Tunisia where Mesozoic series is shaly there are numerous large extrusions, trending SW-NE, the first movements beeing of Aptian to Cenomanian age.

Living anticlines above salt cushions, flower structures along strike-slip faults of the couverture, flanks and pinch-outs along salt domes and salt-walls are interesting targets for hydrocarbons and a lot of them are still undrilled.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995