Stratigraphic and paleogeographical significance of Silurian acritarchs from Saudi Arabia

Abstract

Abundant and well-preserved acritarchs of Early Silurian and late Middle to Late Silurian age have been obtained from marine subsurface sequences in seven exploratory wells drilled by the Saudi Arabian Oil Company in central and northwestern parts of Saudi Arabia. Preliminary results on their stratigraphic distribution allow an informal zonation of 9 regional acritarch assemblages zones to be proposed. Correlations are made between the different local wells studied, and with contemporaneous assemblages described elsewhere. During the Silurian, Saudi Arabia occupied an intermediate to high latitudinal position, on the eastern part of the Gondwana margin. This paleogeographic situation may explain the mixture of taxa known from Western European (Balto-Scandinavia) and North American sequences, with species that have hitherto been recorded only from North Africa or South America in the high-latitude province. A local distinctive endemic microflora is also represented. This additional record of Silurian acritarchs from Northern Gondwana is of considerable importance concerning the biostratigraphic and paleogeographic implications. The distribution of acritarchs shows distinct geographic patterns that may be attributed to climatic factors, oceanic circulation pattern, and/or related to local environmental parameters. In the systematic part, eleven new species of acritarchs, Anomaloplaisium johnsium, Baltisphaeridium diabolicum, Buedingiisphaeridium incertum, Dactylofusa horrida, Goniosphaeridium versatile, Goniosphaeridium sp. A, Leiofusa cucumis, Multiplicisphaeridium circumscriptum, Neoveryhachium carminae constricta, Veryhachium strangulatum, Visbysphaera glabra, and one new genus and species of coenobial Algae, Kahfia arabica, are described and illustrated.