Global Facies Distributions
from Late Vendian to Mid-Ordovician
Kirill B. Seslavinsky and Irina D. Maidanskaya
Global paleogeographic world maps compiled for the late Vendian, Cambrian, and Early to Middle Ordovician bring together, possibly for the first time, a systematic and uniform overview of paleogeographic and facies distribution patterns for this interval. This 150 Ma period of Earth history was a cycle of oceanic opening and closing. These processes were accompanied by formation of spreading centers and subduction zones, and systems of island arcs and orogenic belts replaced one another successively in time and space. The main features of our planet during this period were the vast Panthalassa Ocean and several smaller oceanic basins (Iapetus, Rheic, Paleoasian).
A VARIETY OF plate tectonic reconstructions has been proposed for the Neoproterozoic and early Paleozoic (e.g., Zonenshain et al. 1985; Courjault-Radé et al. 1992; Kirschvink 1992; Storey 1993; Dalziel et al. 1994; Kirschvink et al. 1997; Debrenne et al. 1999). Some of these are reproduced elsewhere in this volume (Brasier and Lindsay: figure 4.2; Eerola: figure 5.4). However, none of them wholly satisfies current data on paleobiogeography, facies distributions, and metamorphic, magmatic, and tectonic events. Pure paleomagnetic reconstructions often ignore paleontologic data and contain large errors in pole position restrictions. Paleobiogeographic subdivisions developed for single groups, mainly trilobites and archaeocyaths, do not fit either each other or paleomagnetic data, and they ignore the possibility that Cambrian endemism may have been a result of high speciation rates rather than basin isolation (e.g., Cowie 1971; Sdzuy 1972; Jell 1974; Repina 1985; Zhuravlev 1986; Shergold 1988; Pillola 1990; Palmer and Rowell 1995; Gubanov 1998). Furthermore, terrane theory suggests even more-complex tectonic models due to inclusion of multiple “suspect” terranes and drifting microcontinents (Coney et al. 1980). Such terranes are now recognized in a large number of Cordilleran and Appalachian zones of North America (Van der Voo 1988; Samson et al. 1990; Gabrielse and Yorath 1991; Pratt and