Sprecher
Beschreibung
The upper member of the Saq Formation (Sajir Member) of Saudi Arabia is characterized, in its upper part, by strongly bioturbated, medium to fine-grained sandstones with intercalations of matrix-supported conglomerates passing upwards to laminated mudstones. At outcrop, these beds are relatively rich in fossils including trace fossils, lingulids and graptolites, which indicate a Dapingian to late Darriwilian age. In the subsurface, the Sajir Member yields a distinctive palynological assemblage characterized by cryptospore dyads, monads of uncertain affinity (“sporomorphs”), and morphologically distinct acritarchs which mostly exhibit short stratigraphic ranges and are thus important as stratigraphic (and possibly paleoecological) markers. The acritarchs are dominated by non-spinose, discoidal forms exhibiting variously perforate/foveate ornamentation and by thin- to thick-walled spherical morphotypes with granulate to reticulate surface ornamentation, or exhibiting thin flanges surrounding thick-walled central bodies. As such, the acritarch assemblage contrasts with the more typical contemporaneous acanthomorphic-dominated assemblages known from many peri-Gondwanan successions. Several taxa correspond to forms previously reported from Saudi Arabia and Oman but left in open nomenclature, whereas others appear to represent undescribed morphotypes and potentially new taxa. The sporomorph component includes cryptospore dyads and other simple terrestrial palynomorphs, possibly indicating an early diversification of land-derived microfloras along the northern Gondwanan margin during the Early to Middle Ordovician. Some similarities are noted with an independently dated Dapingian palynological assemblage described from the Fossil Mountain locality in Utah, USA. The distinct taxonomic composition of the assemblage suggests deposition in a terrestrially-influenced shallow marine environment, consistently with the sedimentological context.