Preliminary analysis of frasnian, late devonian conodont biogeography

Abstract

Although conodont endemism was not as high in the Frasnian as in earlier Devonian intervals, analysis of a limited number of intensively collected sections in the Montagne Noire, the United States and Canada, Western Australia, and the Russian Platform demonstrates levels of endemism ranging from about 30 to 35% in three composites of two zones each. Graphic correlation of sections in these regions provides the biostratigraphic framework. Endemic species occur in both the Palmatolepisand Polygnathusbiofacies, suggesting that the Frasnian was not a time of conodont cosmopolitanism throughout Devonian tropical regions, even within the widespread Palmatolepisbiofacies. Using the Probabilistic Index of Similarity of Raup and Crick (1979), all significantly dissimilar pairs are comparisons between faunas representing different biofacies, and all significantly similar pairs are faunas of the same biofacies. Although conodont biofacies were thus a major controlling factor, the statistically significant similarity observed between the Canning Basin and the Timan‐Pechora Basin in Frasnian zones 12–13 is explicable in terms of the paleogeographic reconstruction of Heckel and Witzke (1979), according to which these areas would have been connected by equatorial currents.

Key words:

• Conodont biogeography
• Frasnian
• Late Devonian
• biostratigraphy
• biofacies
• Probabilistic Index of Similarity