An Upper Ordovician acritarch and prasonophyte assemblage from Dawango, XinJiang, northwestern China: Biostratigraphic and paleogeographic implications

A moderately well-preserved and moderately diverse acritarch and prasinophyte assemblage was recovered from four Upper Ordovician formations of the Dawangou section, Xinjiang, northwestern China (Tarim Block). The palynomorph assemblage consists of 27 species assigned to 17 genera (24 species and 16 genera of acritarchs and three species and one genus of prasinophyte). One new acritarch species, Navifusa tarimensis is proposed in addition to one new combination, Leiosphaeridia caradocensis (= Dichotisphaera caradocensis Turner, 1984). The palynomorph assemblage is dominated by acanthomorphic acritarchs (particularly species of Baltisphaeridium), followed by netromorphs, represented by Navifusa. Leiosphaeridia is the only prasinophyte present. Palynologic and sedimentologic evidence indicates a transgressive and regressive sequence occurred during deposition of the Dawangou section sediments. Comparison of the palynomorph assemblage with correlative age assemblages elsewhere supports the observation that there was little faunal or floral provincialism during the Late Ordovician. In addition, 13 species recovered from the Dawangou section are restricted to the Caradoc–Ashgill, and have a wide geographic range making them useful biostratigraphic taxa.