Evidence for a Western Extracontinental Land Source During the Devonian Period in the Central Andes
A large intracratonic sedimentary basin of mid-Paleozoic age in the central Andes apparently received sediments from a western land source. Lithofacies and isopach data show a thickening and general textural coarsening to the north and west in the Devonian rocks of Bolivia. Early to early Middle Devonian onlap and offlap are recognized. Rate of subsidence in the basin was only slightly exceeded by rate of sedimentation, because the youngest Devonian beds recognized are either very shallow marine (in southern localities) or nonmarine (in at least one northern locality). Devonian brachiopod community studies suggest that a shallow marine environment persisted in the region throughout the time of deposition of the Devonian rocks. An absence of bedded carbonate rocks indicates a cold-climate environment of deposition. It is suggested that the source area yielded abundant muscovite. Outcrops of sialic basement relicts in the Cordillera Occidental are concluded to be portions of a buried land mass.