Subsidence and Inversion History of Central and Eastern Tunisia

A. W. Baird

Structural mapping, balanced cross-section construction, and geophysical and geohistory analyses in central and eastern Tunisia have generated a quantitative understanding of the complex subsidence history and subsequent inversion of the Pelagian platform and its western margin.

Central and eastern Tunisia comprise the western portion of the Pelagian platform, an area on the southern passive margin of Tethys, which has undergone complex polyphase extension and subsidence since the Late Triassic. Backstripping curves (geohistory diagrams) indicate the polyphase nature of the extension can be related to many of the well-developed sedimentary facies belts that occur within the stratigraphic sequence on the platform.

Active extension and subsidence continued until at least the middle Eocene. Alpine compressional events occurred during the middle Miocene, when the western north-south-trending portion of the basin margin was inverted to form a complex thrust belt termed the N-S axis.

West-northwest-east-southeast directed compression initially formed a set of thrusts which transported hanging wall material eastward into the basin. The transport direction subsequently reversed so that hanging wall material was carried out of the basin and some of the earlier thrusts were truncated. Many of the later thrusts reactivated portions of earlier listric extensional faults and display footwall collapse structures.

Analysis of balanced cross sections and borehole data indicates overall west-northwest-east-southeast shortening of more than 50 km on thin-skinned thrusts climbing from an Upper Triassic decollement at a depth of 3 to 4 km. Thrust-generated inversion is observed only where material overlies thrust ramps.

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