Stratigraphie du Silurien du Tassili N'Ajjer

Abstract

Abstract A new lithostratigraphic nomenclature is established for the Silurian of the Tassili N'Ajjer and the mole anticlines of Essaoui Mellene in southeastern Algeria from a new series of sections examined from Tihemboka westward to Oued Amassine. The unit termed the graptolite clay formation is a homogeneous unit of plastic clays ranging from 350 to 450 meters in thickness, with thin lenticular beds of ripple-marked fine-grained sandstone. The sandstones in the upper part of the formation thicken eastward, and in the eastern half of the region the fine-grained sand gives way to coarser grained sand and grit. In the eastern third of the region, the Gara Marhet sandstone is an important member. The overlying heterogeneous Atafatafa formation comprising multiple facies of lenticular silty clays, siltstones, shaly sandstones, ferruginous oolitic sandstones, massive sandstones, and quartzites thins from a thickness of 150 meters on the west, to 80 meters on the east. Ripple marks, markings of organic origin, and tigillites are numerous.