Detailed palynological study of subsurface sections in the Algerian Sahara (boreholes Nl-2 and Uc-101) and southern Tunisia (boreholes Sn-1 and St-1) enables precise dating and intrabasinal and extrabasinal stratigraphic correlation. Most of the study samples proved palyniferous, yielding abundant, well preserved acritarchs (148 species) together with infrequent prasinophytes (2 species). Seven acritarch assemblage zones are recognizable, ranging in age from late Cambrian to late Ordovician (Ashgill) as follows: Timofeevia lancarae-Cristallinium randomense (Late Cambrian), Timofeevia phosphoritica-Dasydiacrodium caudatum (latest Cambrian), Acanthodiacrodium simplex-Arbusculidium destombesii (basal Tremadoc), Acanthodiacrodium angustum-Vulcanisphaera britannica (early Tremadoc), Arbusculidium filamentosum-Coryphidium bohemicum (late Arenig), Frankea sartbernardensis-Vogtlandia ramificata (Llanvirn), and Evittia remota-Villosacapsula setosapellicula (Ashgill) zones. Lower Tremadoc assemblages appear to be at least partially affected by environmental factors; as a consequence, the Tunisian assemblages differ somewhat from the Algerian ones. Notably, the important index species Acantodiacrodium angustum is not present in the Algerian Tremadoc suites. Two important regional hiatuses are recognizable in the study area: one corresponding to the upper Tremadoc through upper Arenig, and the other to the entire Caradoc. The Tremadoc and Llanvirn represent periods of maximum abundance and diversity of the microphytoplankton.