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<p>This study integrates outcrops and subsurface data of southern and central Tunisia to constrain the stratigraphy of the Saharan evaporites, which occur between the pre-salt Upper Triassic (Carnian) siliciclastic and carbonates and the Early Jurassic (Pliensbachian) B Horizon seismic carbonate marker. These evaporites, composed of four units in the subsurface (S1–S4 from top to bottom), were deposited at the eastern edge of a mega-evaporite basin encompassing the Oued Mya-Berkine basins in Algeria and the Ghadames basin in southern Tunisia. In the subsurface, a new dolomitic marker D3 is defined above the Norian S4 unit, and correlated with the Rhaetian Zerzour dolomites outcropping in the Dahar escarpment. The S4–S3 units are attributed to the Norian-Rhaetian, and the S2–S1 units to the Early Jurassic. This revised attribution highlights a change from salt-dominated to anhydrite-dominated deposition across the Triassic-Jurassic boundary placed in this studyabove the D3 marker. Delineated on regional cross-sections and displayed in isopach and facies maps, these evaporite units are each over 200&#xa0;m thick in their depocenter and overlain by carbonate marker beds recording marine floodings. The wireline log responses between those marker beds point to lateral facies changes, from halite in the basin center, to sulfates and shales, and then carbonate deposits toward the Neo-Tethys Ocean margin to the north and east. The maps suggest that the Matmata-Medenine structural paleohigh acted during the Triassic as a sill, isolating the eastern end of the mega-evaporite basin from the open sea and promoting thick evaporite accumulation during sea-level falls. During the Jurassic, this paleohigh was intermittently flooded during sea level rises, allowing the installation of a permanent subaquatic system where sulfates and dolomites can develop.</p>

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New insights into the stratigraphy, basin configuration and development of the Upper Triassic–Lower Jurassic evaporites and carbonates of southern Tunisia, Saharan platform: integrated surface and subsurface data analysis

  • 期刊论文

  • 发表日期：

    2025年6月2日

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  • Rahma Znazen,
  • Rami Sliti,
  • Ali Khachira,
  • Mohamed Soussi,
  • Jean-Yves Reynaud,
  • Abdelhamid Bensalem,
  • Moncef Saïdi,
  • Kamel Boukhalfa

摘要

This study integrates outcrops and subsurface data of southern and central Tunisia to constrain the stratigraphy of the Saharan evaporites, which occur between the pre-salt Upper Triassic (Carnian) siliciclastic and carbonates and the Early Jurassic (Pliensbachian) B Horizon seismic carbonate marker. These evaporites, composed of four units in the subsurface (S1–S4 from top to bottom), were deposited at the eastern edge of a mega-evaporite basin encompassing the Oued Mya-Berkine basins in Algeria and the Ghadames basin in southern Tunisia. In the subsurface, a new dolomitic marker D3 is defined above the Norian S4 unit, and correlated with the Rhaetian Zerzour dolomites outcropping in the Dahar escarpment. The S4–S3 units are attributed to the Norian-Rhaetian, and the S2–S1 units to the Early Jurassic. This revised attribution highlights a change from salt-dominated to anhydrite-dominated deposition across the Triassic-Jurassic boundary placed in this studyabove the D3 marker. Delineated on regional cross-sections and displayed in isopach and facies maps, these evaporite units are each over 200 m thick in their depocenter and overlain by carbonate marker beds recording marine floodings. The wireline log responses between those marker beds point to lateral facies changes, from halite in the basin center, to sulfates and shales, and then carbonate deposits toward the Neo-Tethys Ocean margin to the north and east. The maps suggest that the Matmata-Medenine structural paleohigh acted during the Triassic as a sill, isolating the eastern end of the mega-evaporite basin from the open sea and promoting thick evaporite accumulation during sea-level falls. During the Jurassic, this paleohigh was intermittently flooded during sea level rises, allowing the installation of a permanent subaquatic system where sulfates and dolomites can develop.