Biostratigraphy of the Ordovician chitinozoa of northwestern Saudi Arabia

Chitinozoans from water and exploratory wells located in northwestern Saudi Arabia have been investigated. A local biozonation is suggested, representing the Lower to Upper Ordovician interval in Arabia, and compared with that of the Northern Gondwana. In general, the chitinozoan faunas belong to the Gondwanan realm but latest Ordovician chitinozoans seem to have been distributed in a more cosmopolitan manner. Ranges of the species encountered have been established, and new forms are left under open nomenclature until a future publication. These microfossils provide a fairly good indication of the age of the investigated Lower Palaeozoic succession and, therefore, allow an accurate definition of the lithostratigraphic units, which has led to the revision of the chronostratigraphy of this area. These biostratigraphic data demonstrate the occurrence of an important stratigraphical gap in some areas at the end of the Ordovician.