The Cretaceous System of Southern South America

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Abstract
The initial history of all Cretaceous sedimentary basins of southern South America is related to the early breakup of Gondwanaland. Along the subduction zone of the Pacific coast, Late Jurassic-Early Cretaceous marine basins were initiated in central Chile and west-central Argentina (the Andean Basin) and in southern Patagonia (the Austral Basin), with the development of volcanic arcs and ensialic troughs. South of 50° south latitude an intra-arc or back-arc marginal basin was formed. At about the same time, several isolated rift basins, formed on the continent and along its Atlantic margin, were the site of continental volcanism and sedimentation. In Barremian time the magmatic arc of the Andean Basin underwent an important eastward migration, resulting in the initial uplift of the Cordillera Principal of Argentina and Chile. This uplift caused a reversal of the regional slope, and continental basins developed. South of 50° south latitude, closure of the marginal basin that began in Late Albian time was accompanied by uplift, resulting in a foreland stage of development of the Austral Basin with deposition of turbidites within a generally regressive pattern. In Maastrichtian time, sedimentation was discontinued in the continental basins of west-central Argentina and central and northern Chile. The marine area of the Austral Basin had become more restricted. Large regions of northern Patagonia, northeastern Argentina, and Bolivia were covered by a shallow sea, and some restricted fore-arc marine basins were developed on the coast of central Chile. Marine sedimentation was also continuous throughout most of Late Cretaceous time in the Atlantic basins of southern Brazil and central Argentina. Continental deposition was restricted to central Patagonia and the intracratonic Paraná Basin. There was a correlation between diastrophism, igneous activity, and the global cycles of sea-level changes. The transgressive-regressive pattern of the Andean Basin appears to have been controlled by regional tectonics in an area in which local vertical movements were greater than global sea-level changes. In the Austral Basin a different transgressive-regressive pattern emerged, as local tectonic movements could not completely overprint the record of global changes of sea level. Widespread marine sedimentation in a series of Atlantic and Pacific basins during late Late Cretaceous time was coincident with a worldwide transgressive peak. The Cretaceous florais known mostly from Patagonia. Lower Cretaceous invertebrates are known mainly from west-central Argentina, whereas Upper Cretaceous invertebrates are known almost exclusively from southern Patagonia. Vertebrates are most common in continental Upper Cretaceous strata of central-northern Patagonia and southern Brazil. Changes in the diversity, endemism, and evolutionary rates of marine faunas appear to be related to transgressive-regressive pulses. The Cretaceous climate north of 43° south latitude was characterized by warm and extremely arid conditions. To the south of this arid belt was an area with temperate and humid climate.

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