Evolution of Upper Palaeozoic Proto-Pacific peripheral and intracratonic basins of Western Gondwana.

LIMARINO, C.O.; SPALLETTI, L.

Mendoza

Simposio; Gondwana 12 Conference; 2005

International Association for Gondwana Research

The paleogeographic evolution of Late Paleozoic basins located in southern South America is addressed in this paper. Three major types of basins are recognized: intracratonic, proto-Pacific and peripheral. Intracratonic basins (comprising Paraná, Chaco-Paraná, Sauce Grande-Colorado and La Golondrina basins) are floored by continental or cuasi-continental crust, showing low or moderate subsidence rates, and limited magmatic and tectonic activity. Proto-Pacific basins (northern and central Chile, Navidad-Arizaro, Río Blanco and Calingasta-Uspallata basins and depocenters along the Chilean Patagonia) show a very complex tectonic history, widespread magmatic activity, high subsidence rates and in some cases metamorphism of Late Paleozoic sediments. An intermediate situation corresponds to the peripheral basins (eastern Madre de Dios, Tarija, Paganzo, and Tepuel-Genoa basins) which lacked extensive magmatism and metamorphism. However, coeval tectonism and sedimentation rates were possibly more important than those in the intracratonic region.  According to the stratigraphic distribution of Late Paleozoic sediments, regional-scale discontinuities and changes in sedimentation patterns, five major paleogeographic stages are proposed. The lowermost is restricted to the proto-Pacific and peripheral basins, corresponds to the Mississippian (stage 1) and is characterized by shallow marine and transitional siliciclastic sediments. During stage 2 (Early Pennsylvanian) glacial-postglacial sequences dominated in the intracratonic and peripheral basins, while terrigenous shallow marine sediments prevailed in the proto-Pacific basins. Stage 3 (Late Pennsylvanian-Early Cisuralian) shows the maximum extension of glacial-postglacial sediments in the Paraná and Sauce Grande-Colorado basins (intracratonic region). Fluvial deposits interfingering with thin intervals of shallow marine sediments prevailed in the peripheral basins. To the West, proto-Pacific basins were dominated by coastal to deep marine conditions (including some turbiditic successions). In the Late Cisuralian (stage 4), important differences in sedimentation patterns are registered for the western proto-Pacific basins and the eastern intracratonic basins. The former were locally dominated by volcaniclastic sediments, or in other cases by marine deposits. The intracratonic basins are characterized by shallow marine conditions punctuated by several episodes of deltaic progradation. Finally, in the Late Permian (stage 5), volcanism and volcaniclastic sedimentation dominated in the basins located along the western South American margin. The intracratonic basins were, in turn, characterized by T-R cycles composed of shallow marine, deltaic and fluvial siliciclastic deposits.