Resumen de Distribution of selected Silurian Acritarchs: An account of the palynostratigraphy and paleogeography of selected Silurian Acritarch taxa
An account is given on the information presently available of a group of Silurian phytoplancton, the acanthomorphitic acritarchs. The data presented are integrated from two sources: (i) the results of eight man years of research and (ii) a literature compilation and evaluation. The following formgenera are treated: Baltisphaeridium; Comasphaeridium; Dactylofusa; Deflandrastrum; Deunffia; Domasia; Estiastra; Eupoikilofusa; Hemibaltisphaeridium; Leiofusa; Leoniella; Micrhystridium; Neoveryhachium; Polydeunffia; Pulvinosphaeridium; Solita; Tunisphaeridium; and Veryhachium.
Samples were processed following the conventional acid dissolution/ heavy liquid flotation method; the method is outlined in Chapter 3.
A comparison of the composition of the acritarch assemblages from localities in the Silurian epicontinental seas at both sides of the Atlantic Ocean shows the existence in this area of several clearly differentiated contemporaneous acritarch provinces. The assemblage composition differences are not controlled by lithofacies boundaries; the biofacies boundaries might well shift through time in a regular way, independent on lithologic changes.
The palinspastic configuration of the biofacies appears to be congruent with the averaged position of the Silurian paleolatitudes as reconstructed from paleomagnetic and paleoclimatic evidence. The regular shift of acritarch biofacies over time as observed along a section from Florida to Lake Erie, is in the same general direction, paleolongitudinally, as the direction of Gondwana Pole movement as extrapolated from the average Ordovician and Lower Devonian Gondwana positions. By consequence, the acritarch biofacies in the Silurian epicontinental seas are interpreted as climate determined. The position of the biofacies belts is then: (i) «empoverished» N. carminae association: nearest to the Gondwana Pole, from 70 to 40 degrees longitudinally; (ii) N. carminae association from 40 to 20 degrees; (iii) a mixed biofacies belt containing elements of the N. carminae association and the Do. elongata association (iv) between 20 and 10 degrees; the Do. elongata association biofacies grades into the poorly delineated «Baltic» biofacies (v), situated farther towards the equator. A sixth type of association which is similar to the Baltic, was found in the Canadian Arctic and is probably also present on the Siberian shelf. These assemblages could not be studied prior to the completion of the manuscript of this paper.
In the taxonomic part the taxa discussed in the first chapters of this paper are succinctly treated. Of each species the geographic distribution and the stratigraphic ranges are given.
