BARRED BASINS - A MODEL FOR EASTERN OCEAN-BASIN CARBONATE PLATFORMS

Areally and volumetrically extensive carbonate platforms are conspicuo usly absent from most modern eastern ocean basins where surface circul ation brings cool waters from high latitudes and atmospheric circulati on induces coastal upwelling. Carbonate platforms fail to develop in s uch settings as a consequence of sea-surface temperature instability, nutrient excess resulting in high biotic surface productivity, and oxy gen-depleted conditions associated with upwelling and oceanic surface circulation. In contrast to modern patterns, extensive Paleozoic carbo nate platforms developed along the eastern boundary of the paleo-Pacif ic Ocean (western margin of North America). Tectonic and sedimentologi c evidence suggests that marginal oceanographic barriers (island arcs, thrust belts, suspect terranes) existed during much of this interval. These barriers effectively protected landward carbonate platforms fro m the adverse conditions typical of open eastern ocean basins. Without these barriers such extensive platforms may not have developed. In re gions that lack evidence for structurally or tectonically controlled h ighlands, the existence of eastern ocean basin carbonate platforms may serve as an important clue in paleogeographic reconstructions of the continental margin.