Ordovician plate tectonic and palaeogeographical maps

Abstract Plate tectonic and palaeogeographical maps are presented for nine time intervals during the Ordovician: early Tremadocian (485 Ma), late Tremadocian (480 Ma), early Floian (475 Ma), earliest Dapingian (470 Ma), early Darriwilian (465 Ma), late Darriwilian (460 Ma), middle Sandbian (455 Ma), middle Katian (450 Ma) and early Hirnantian (445 Ma). A plate model was used to predict the changing age of the ocean floor and, hence, the changing volume of the ocean basins and the resulting degree of continental flooding. The maps show the locations of active plate boundaries (i.e. subduction zones, mid-ocean rifts, transform faults, island arcs, back-arc basins and collision zones) and the age of the ocean floor. During the Ordovician there were six continental plates (Gondwana, Laurentia, Baltica, Cathaysia, Avalonia and Cuyania) and six oceanic plates (Iapetus, Ran, Kipchak, and Panthallasa 1, 2 and 3), as well as several poorly constrained back-arc basins (Zealandia, Alexander and Farwell). The palaeogeographical maps also illustrate the ancient distribution of mountains, land, shallow seas and deep ocean basins. Sea level was high during the Early Ordovician, fell during the middle Ordovician and rose again during the Late Ordovician. A precipitous fall in sea level occurred at the end of the Ordovician due to the short-lived Hirnantian Ice Age.