1990; Mens & Pirrus 1997) and possibly to the Asteridium tornatum-Comasphaeridium velvetum acritarch
Zone (Moczydlowska 1991).
9b), and acritarch
assemblages restrict the age of the Lumsden Dam Formation to the early to middle Tremadocian (White et al.
As an acritarch
assemblage typical of the Agnostus pisiformis Zone has not been recorded in the Petseri Formation (Paalits 1992; Mens et al.
Environmental control in the distribution of acritarchs
in the Lontova Stage of Estonia.
in Cambrian and Ordovician rocks of Nova Scotia and New Brunswick, Canada: new constraints on correlation and palaeogeography.
A metacarbonate bed near the top of the group yielded Middle Cambrian, Acado-Baltic trilobite fragments (Pratt and Waldron 1991), and graptolites and acritarchs
in the upper part of the overlying Halifax Group indicate an Early Ordovician age (Cumming 1985; White et al.
excystment and surface ultrastructure with descriptions of some Ordovician taxa.
The age of the Kotlin sandstone is rather loosely constrained (< 570 Ma), whereas the Lontova Formation is represented by the sub-trilobitic acritarch
assemblage of Asteridium tornatum-C.
It is worthy of note that the acritarch
assemblages discovered in the studied succession include besides the typical Siberian taxa several representatives of different Ordovician microphytoplankton 'provinces' (Servais et al.
and the acritarch
assemblage found from two levels in the Maekalda section near the centre of Tallinn (15 km west of the Ulgase section) allow tentative correlation of the Ulgase Formation in Tallinn and its environs with the Olenus trilobite Biozone (Mens et al.
The only published source on the Ordovician sequence in the vicinity of Shahrud is a paper by Ghavidel Syooki (2006), where he reported for the first time on the presence of Tremadocian deposits north of the Kalat-e Molla village and subdivided the Cambrian (Furongian)-Ordovician sequence into six acritarch
He and other paleontologists have suspected for some time that a fraction of the known acritarch
species represent predecessors of modern dinoflagellates.