North American Silurian palynofacies and their spatial arrangement: Acritarchs

Palynomorphs recovered from seven hundred samples of Silurian sediments are discussed. The samples were collected in twenty-eight localities, all located in the eastern portion of the United States of America. Several palynomorph-biofacies can be distinguished; the five acritarch-biofacies are discussed in some detail and their chronological and spatial arrangement is analysed. The acritarch-biofacies are time-transgressive. The boundaries of these biofacies are plotted in base-Wenlockian isochron geographic coordinates. Chitinozoan-biofacies will be discussed in another paper.

The manner in which the transgression of biofacies boundaries can be used, probably, to chronologically refine the circum-Atlantic Silurian stratigraphy along the path of apparent polar wandering, the zero paleolongitude, is evaluated. Since the rate of crustal movement is 2 to 3 degrees along the zero paleolongitude per epoch, it should be possible to refine the Silurian stratigraphy of the eastern United States and western Europe using the rate of biofacies transgression (of both microplanktonic and megaplanktonic organisms) over distance.

The arrangement of North American Silurian biofacies is integrated with that of the rest of the world, and it is easily shown that the Circum-Atlantic continents must be rearranged in a Wegnerian manner for the paleogeography to fall into a logical pattern of chronological and regional homotaxis.

The taxonomy and selected bibliographic references to eighty-nine Silurian acritarchs is presented in the taxonomic portion of the paper. The distribution of acritarchs in North America is presented in Table 1.