STRATIGRAPHIC AND PALEOGEOGRAPHIC SIGNIFICANCE OF SILURIAN ACRITARCHSFROM SAUDI-ARABIA

Abundant and well-preserved acritarchs of Early Silurian and late Midd le to Late Silurian age have been obtained from marine subsurface sequ ences in seven exploratory wells drilled by the Saudi Arabian Oil Comp any in central and northwestern parts of Saudi Arabia. Preliminary res ults on their stratigraphic distribution allow an informal zonation of 9 regional acritarch assemblages zones to be proposed. Correlations a re made between the different local wells studied, and with contempora neous assemblages described elsewhere. During the Silurian, Saudi Arab ia occupied an intermediate to high latitudinal position, on the easte rn part of the Gondwana margin. This paleogeographic situation may exp lain the mixture of taxa known from Western European (Balto-Scandinavi a) 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 i s of considerable importance concerning the biostratigraphic and paleo geographic implications. The distribution of acritarchs shows distinct geographic patterns that may be attributed to climatic factors, ocean ic circulation pattern, and/or related to local environmental paramete rs. In the systematic part, eleven new species of acritarchs, Anomalop laisium johnsium, Baltisphaeridium diabolicum, Buedingiisphaeridium in certum, Dactylofusa horrida, Goniosphaeridium versatile, Goniosphaerid ium sp. A, Leiofusa cucumis, Multiplicisphaeridium circumscriptum, Neo veryhachium carminae constricta, Veryhachium strangulatum, Visbysphaer a glabra, and one new genus and species of coenobial Algae, Kahfia ara bica, are described and illustrated.