Permian marine sedimentation in northern Chile: new paleontological evidence from the Juan de Morales Formation, and regional paleogeographic implications

Permian marine sedimentary rocks that crop out in northern Chile are closel y related to the development of a Late Paleozoic magmatic are. A study of U pper Paleozoic units east of Iquique (20 degreesS) identified three members within the Juan de Morales Formation, each of which were deposited in a di fferent sedimentary environment. A coarse-grained terrigenous basal member represents alluvial sedimentation from a local volcanic source. A mixed car bonate-terrigenous middle member represents coastal rind proximal shallow m arine sedimentation during a relative sea-level rise related with a global transgression. Preliminary foraminifer biostratigraphy of this middle membe r identified a late Early Permian (late Artinskian-Kungurian) highly impove rished nodosarid-geinitzinid assemblage lacking fusulines and algae, which is characteristic of temperate cold waters and/or disphotic zone. The upper fine-grained terrigenous member represents shallow marine siliciclastic se dimentation under storm influence. The Juan de Morales Formation consists o f continental, coastal and shallow marine sediments deposited at the active western margin of Gondwana at mid to low latitudes. A revised late Early P ermian age and similar paleogeography and sedimentary environments are also proposed for the Huentelauquen Formation and related units of northern and central Chile, Arizaro Formation of northwestern Argentina, and equivalent units of southernmost Peru. (C) 2000 Elsevier Science Ltd. All rights rese rved.