PALEOGEOGRAPHY & BIOGEOGRAPHY IN THE NEOPROTEROZOIC: SOME HINTS ABOUT RODINIA

The configuration, assembly and breakup of the supercontinent Rodinia is contentious. The positioning of nearly every element described in the original ‘Rodinia Papers’ is controversial. Paleomagnetic studies can provide important constraints with regard to the latitudinal position of landmasses, but because of longitudinal indeterminancy, other data are necessary to validate/refute a particular reconstruction. Precambrian reconstructions attempt to balance the paleomagnetic data with structural, sedimentologic, isotopic and geochronologic data in order to reach a consensus view on paleogeography. Biogeographic analysis, while not totally ignored, is seldom used to constrain Neoproterozoic paleogeography. Here we attempt to combine vicariance analysis of trilobites with proposed paleogeographies in an effort to resolve some issues with regard to the breakup history of Rodinia and its vestiges. The vicariance trees indicate that the evolutionary history of trilobites extends back to the late Neoproterozoic. Most notable in this analysis is that Australian and Antarctic trilobite faunas show a close relationship, but are distinct from the rest of the studied regions. This is consistent with recent notions of a piecemeal assembly of East Gondwana and an early separation of Australia-Antarctica from Laurentia. Although primary South American trilobites could not be included in the analysis, new paleomagnetic data from Amazonia place it near the southwestern margin of Laurentia. Vicariance patterns suggest a close affinitiy between Siberia, Morocco/S. Europe, SW Laurentia and Avalonia. Parts of modern South America may have formed a bridge between Laurentia and these cratons. Baltic trilobites show close affinity with eastern northwestern Laurentian trilobites and this relationship is supported by the paleomagnetic data from both continents. We present several possible Neoproterozoic paleogeographies based on the distribution of trilobites and also consider some of the problems with these paleogeographies.