ABSTRACT Cretaceous System is widely represented in South America from northeast Brazil to southern Patagonia Argentina. It is characterized by having been a relatively warm climate, with rainfall and marked seasonality which allowed the development of the “conchostracan” populations.
The Cretaceous Period was a period with warm climate  , with increasingly high sea levels in the epicontinental seas. The average global temperature was near to 18˚C  . Despite the greenhouse character of the period, the cooling trend towards the Maastrichtian and the 116 Ma “cold snap” triggered the interest in possible continental Cretaceous glaciations  .
2. Cretaceous Climate and Bearing “Conchostracan” Faunas
In the Lower Cretaceous, the monsoon circulation of the Pangea culminated, due to the opening of the Atlantic Ocean  . The cool interval in the Early Cretaceous is followed by warming lasting until the late Albian  . In the continental regions there were changes in atmospheric circulation. Wetter conditions developed and paleoprecipitations increased in tropical areas  . Oceanic and continental data suggest equatorial paleotemperatures similar to the present-day  . This time was characterized by the presence of areas with prevailing microclimates. In intracratonic basins (e.g. northeast Brazil), the climate was arid with warm-hot temperatures. This type of arid climate, with heavy rainfall, generated favorable seasonal conditions for the development of a diverse “conchostracan” fauna. Wind patterns shew seasonality leading to more extreme climates over the continents. During the Upper Cretaceous warm weather prevailed, with greenhouse periods, globally averaged temperatures were 6˚C - 14˚C higher than today  . The paleoprecipitations increased as a result of the end of the monsoon circulation  . In Argentina, the conchostracan bearing units as the Lagarcito Fm. (Lower Cretaceous) was interpreted as a deposit of a shallow and perennial freshwater lake in a semi-arid climate  . The Cañadón Calcáreo Fm. (Upper Jurassic - Lower Cretaceous) was referred by  to sequences represented swampy areas, with a rich and diverse conchostracan fauna in subtropical seasonal dry climate. In Brazil-Uruguay the units are, the Botucatu Fm = Tacuarembó Fm (Late Jurassic - Early Cretaceous), indicating desert climate  . The Santana Fm. (Lower Cretaceous) represent tropical climate with highly dependent on the rainfall in the mating epoch  was, favorable to establish “conchostracan” populations. The Bauru Basin (San Carlos Fm) the climate was hot and arid  . The climate was warm and very dry, probably desert  .
Finally, the climatic characterization for the Cretaceous of South America, summarized as a warm climate with rainfall and marked seasonality, allowed the development of the “conchostracan” populations so far recorded.
This is a contribution to UNESCO-IUGS IGCP Project 679.
Cite this paper
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