The Ordovician ‘Polar Wander Path’ of the acritarch Veryhachium

VECOLI, M., SERVAIS, T., LI, J., MOLYNEUX, S. G., RAEVSKAYA, E. & RUBINSTEIN, C. V.

Paris, Francia

Simposio; First International Palaeobiogeography Symposium; 2007

CNRS - Université Pierre et Marie Curie, Paris 6

The acritarch genus Veryhachium, originally described by Deunff (1954) from the Ordovician of Britanny, western France, is one of the most frequently recorded organic-walled microphytoplankton genera. Over 250 specific and subspecific taxa are recorded from the Cambrian to the Oligocene, and the genus is generally abundant and widespread throughout the Phanerozoic. The detailed analyses of the first occurrences of Veryhachium in different localities from different palaeocontinents allow to describe the palaeobiogeographical radiation of the genus from the South Pole to all Ordovician palaeocontinents: first Veryhachium specimens appeared in the middle part of the Tremadocian (Early Ordovician), and possibly earlier in the early Tremadocian, at levels where graptolites of the R. flabelliformis group occur, in localities from North Africa, that was located at the South Pole during the earliest Ordovician.  Subsequently, Veryhachium is also present in the late Tremadocian in localities of the Gondwanan margin in North Africa and Avalonia (English Lake District and Rügen Island, Germany), which are all considered to have been located at high latitudes (> 60°) in the southern hemisphere. In China, located at intermediate latitudes (between 30° and 60° S), Veryhachium has not been recorded below the lowermost Floian (lowermost Arenig), and in Argentina, located at similar latitudes, not below the middle Floian (lower-middle Arenig). The first occurrence on another palaeocontinent, Baltica, is also recorded in the lower Floian, but the genus did not become common until the Darriwilian (Middle Ordovician). This suggests that Veryhachium first appeared in the Tremadocian at high latitudes before it radiated to lower latitudes of the Gondwanan margin (China and Argentina) and Baltica during the Floian, to become cosmopolitan by the Middle Ordovician.