Burial history and thermal evolution of the northern and eastern Saharan basins

摘要

The numerical one-dimensional reconstruction of the burial history and thermal evolution of the sedimentary section and basement was conducted for 32 wells in the East Algerian basins with the help of the Galo basin-modeling system. These reconstructions allowed the performance of a quasi-two-dimensional analysis of the burial history of the basins, changes in rock temperatures, the lithosphere thickness, and maturation conditions of organic matter during basin development along the four profiles crossing the study region. The modeling assumed that the highest thermal activation in the history of the Saharan basins, with the heat flow more than 100 mW/m2 and the thinnest lithosphere on the order of 25–35 km, took place during the Late Carboniferous to Permian in the Dahar and Oued el-Mya basins. The uplift responsible for this activation caused erosion of 2000–3000 m of Ordovician to Lower Carboniferous strata. The Ghadames and Illizi basins were subjected at the same time to more moderate erosion and thermal activation with heat flow less than 75 mW/m2. In the Triassic–Cretaceous interval, maximum subsidence occurred in the northern areas, which were characterized by maximal thermal activation and the thinnest lithosphere in the Permian. At present, the situation is opposite to that in the Permian: the highest thermal regime occurs in the southern areas of the study region and especially in the Illizi basin, where heat flow reaches and even exceeds 100 mW/m2, and the thickness of the lithosphere decreases as much as 30 km. The modeling also assumes stretching of the lithosphere in the northeastern and central parts of the Illizi basin, with maximal amplitude of about 1.16 during the Cenozoic. The analysis shows that the Hercynian erosion could account for only a few of the abrupt changes in vitrinite profiles in the Saharan basins and that Triassic and later intrusive activity and associated hydrothermal heat transfer accurately explain the steplike character of maturation profiles.