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The Gafsa district, Central Tunisia, is subject to an exhaustive study of the series situated in both sides of the C-T limit. The study is based on outcropping series. It allowed us to identify many basins throughout the district, but moreover many high sectors separating the subsiding areas. Guided by an accurate biostratigraphical framework, the study interval is subdivided into six periods: uppermost Cenomanian-lowermost Turonian (Bahloul Fm.), middle Lower Turonian (lower Gattar Fm.), upper Lower Turonian (upper Gattar Fm.), lower part of the Middle Turonian (Annaba Clay Member), upper Middle Turonian (lower successions of the Birèno M.). The top of these successions corresponds to a regional emersion surface. Each of these periods is materialized by a bloc diagram showing the palaeoenvironments at a specific time. The vertical succession of these diagrams materialized the vertical evolution of the palaeoenvironments throughout the study series.
The basins of the Gafsa area (basins of Gharsa, Chotts, Oum Laraiès, Mèjel Belabbès, Zammour, Sidi Mansour, and Gafsa-Metlaoui) are superimposed to subsiding areas which hosted by nowadays plains that are filled by recent formations, such as the salty deposits of the Chotts Fejej and Jerid Basins. Those basins are separated by uplifted narrow sectors which are barely oriented ENE-WSW (highs of the Northern range of the Chotts, Jabal Belkhir-Jabal Chemsi, Gafsa range, Kef Ech Chogga-Oum Kecheb and Metlaoui range) or NW-SE (Jabal Bou Ramli-Ben Younès).
The architecture of the Gafsa area (basins, highs) was guided by the fault network and the Triassic movements, especially the Triassic which escapes from under the large synclines towards the narrow highs. The high sectors are uplifted by the Triassic diapirism and they are systematically tilted towards the west. The study of the Chemsi-Belkhir high permits to conclude that this high was doubly tilted: firstly, tilted towards the west; and secondly, but at the same time, twisted towards the north-west. We conclude that the Gafsa district corresponds around the C-T limit, to a succession of basins separated by tilted highs, either in a north-south or in an east-west direction. Within this framework, the connection between the Gafsa district and the Tethys was located towards the East, via Sidi Mansour basin. Actually, at this latitude, the seismic sections show horizontal reflectors, which suggest that the North-South Axis structure (high) doesn't reach this area and then ends towards the north. This is supported also by the occurrence of C/T ammonites migrated from Egypt such as the Choffaticeras group. This framework seams to be valid also at the Upper Albian time with the Knemiceras group, such as K. aegyptiacum, K. sinaiticum, which is well developed within this area. All these ammonites migrated from Egypt toward North African Tethys and entered the Gafsa area through Sidi Mansour basin.
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