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 co
mpared with that of the Northern Gondwana. In general, the chitinozoan
faunas belong to the Gondwanan realm but latest Ordovician chitinozoa
ns seem to have been distributed in a more cosmopolitan manner. Ranges
of the species encountered have been established, and new forms are l
eft under open nomenclature until a future publication. These microfos
sils provide a fairly good indication of the age of the investigated L
ower Palaeozoic succession and, therefore, allow an accurate definitio
n of the lithostratigraphic units, which has led to the revision of th
e chronostratigraphy of this area. These biostratigraphic data demonst
rate the occurrence of an important stratigraphical gap in some areas
at the end of the Ordovician.