Paleogeographic and paleoclimatic setting of Lower Cretaceous basins of East Asia and western North America, with reference to the nonmarine strata

Lower Cretaceous strata are widespread in East Asia and along the western coast of North America. In both regions, Cretaceous basins contain significant stratigraphic accumulations and can be thought of as along-strike equivalents. In East Asia, fore-arc basins were oriented parallel to and east of active magmatic arcs while in western North America extensive fore-arc successions accumulated west of the arc complexes. The greater extent of nonmarine, rift and back-arc basins in the East Asian region, and overall lower topographic development, was likely related to movement of the region away from ongoing subduction to the east. In western North America, by contrast, movement of the North American plate westwards towards the active subduction zone resulted in development of a volumetrically larger and topographically higher orogen than in East Asia.The active arc complexes in both regions exerted significant controls on paleoclimate. Interior basins of both Asia and North America, landward of arc complexes, were significantly drier than the coastal areas, due to rain-shadow phenomena in both regions. Although the proto-Pacific Ocean was likely much wider during Early Cretaceous time than it is today, we infer that similar oceanic circulation patterns existed and significantly affected climate and molluscan biogeographic assemblages of both East Asia and western North America: East Asia was dominated by warm water derived from the Tethyan regions, whereas west coast North America was influenced by cooler waters derived from high-latitudes.