The Tremadoc to early Llanvirn is the time interval in the Ordovician
for which a global
acritarch distribution pattern can be proposed. It is possible to differentiate
a high latitude, cold- to temperate-water realm and a low latitude, warm-water
realm. The cold-water assemblages, recorded from numerous
localities at the northern border of Gondwana in the southern hemisphere,
include
some diagnostic
morphotypes, such as Arbusculidium filamentosum, Arkonia,
Aureotesta, Coryphidium-Vavrdovella,
Dicrodiacrodium, Frankea and Striatotheca.
Assemblages related to warm-water areas are described from
Canada, the United States, northern China, Australia, and Baltica. Although
a
distinction of separate
provinces within the cold-water and warm-water realms is difficult, the
differentiation between these two
units appears evident and a distinction of the assemblages from peri-Gondwana
and the microfloras from
Baltica is possible. This enables a recognition of the Trans-European Suture
Zone in the early to middle Ordovician.