Building a stratigraphy: the lessons of the study of the Palaeozoic in the Algerian Sahara

In the last fifty years, the geology of the Algerian Sahara has undergone a big development chiefly as the result of petroleum exploration. This has led to the construction of a stratigraphic succession, mostly Palaeozoic. A short history of this yet incomplete stratigraphic succession is presented below, together with a discussion of some of the lessons learned during this process. A number of lithostratigraphic errors are also cited and illustrated. The difficulties encountered in biostratigraphy, such as the lack of fossils, biostratigraphic zonations and the problem of identifications, are pointed out. Finally, the need for a regional chronostratigraphy in a basinal study to supplement the standard chronostratigraphy, which is more distant and less useful, is presented. In conclusion, the dangers related to a possible disappearance of Invertebrate biostratigraphy in geology are pointed out.