AAPG Bulletin, vol. 87(11), November 2003: 1799-1822.

Burial history and thermal evolution of the Southern and western Saharan basins: synthesis and comparison with the eastern and northern Saharan basins

M. Makhous*, Y.I. Galushkin**

*Departement de Geologie Sedimentaire, Laboratoire de Stratigraphie, Université Pierre et Marie Curie-Paris VI, Tour 15/16, 4ième étage, C 117-4, place Jussieu, 75252 Paris Cedex 05, France; present address: 35, place des saisons, Paris-La Défense 1, 92400 Courbevoie, France; makhous@mail.com

**Museum of the Earth Sciences, Moscow State University, Vorobjevy gory, 119 899, Moscow, Russia; gal@geodyn.pvt.msu.ru

    Abstract

 A quasi-two-dimensional analysis of burial history and thermal evolution was carried out along eight profiles for sedimentary sections in 24 wells in the southern and western Saharan basins with the aid of one-dimensional nonsteady numerical reconstructions.
The modeling shows that thermal activation during the Permian–Triassic–Jurassic was most intense in the Timimoun basin and the northern part of the Ahnet and Mouydir basins, with a heat flow of about 70–80 mW/m2 and a lithosphere thickness of 40–50 km.
Activation was more moderate in the Sbaa subbasin and Reggane basin, with a heat flow of approximately 63–67 mW/m2 and a crustal thickness of 55–60 km. These values are comparable to those for the eastern Saharan basins, where the intensity of the Triassic activation decreased considerably from north to south. The
present-day thermal regime of the Ahnet and Reggane basins and the central part of the Timimoun basin is comparable to that of the Illizi basin, where the present-day lithosphere is as thin as 25 km, and recent volcanism has occurred. Moderate extension of the lithosphere with a maximum total amplitude of about 1.16 during
the Cenozoic is assumed in our modeling in the Reggane basin and the southern half of the Timimoun basin, as well as in the central and eastern part of the Illizi basin. Thermal analysis of the Saharan basins has shown that the Hercynian erosion can account for only a minor part of the jumps observed in the vitrinite profiles (Ro).
Intrusive activity and the associated hydrothermal heat transfer during the Triassic and Early Jurassic accurately explain the steplike character of maturation profiles in the Saharan basins. In particular, the lower level of catagenesis and conservation of oil deposits in the relatively hot Sbaa subbasin are the result of less-intensive
hydrothermal-intrusive heating of the basin during the Jurassic as compared to that in neighboring basins. This could also be ascribed to a deeper location of the lithosphere and probably deeper intrusions in the Sbaa subbasin. This relatively moderate thermal regime of the Sbaa subbasinmight be connected to its structural position of, as it was, a ‘‘shoulder’’ to neighboring deeper depressions.