Contribution to the Study of the Brazilian Quaternary
João José Bigarella, Gilberto Osório de Andrade, 1965. "Contribution to the Study of the Brazilian Quaternary", International Studies on the Quaternary: Papers Prepared on the Occasion of the VII Congress of the International Association for Quaternary Research Boulder, Colorado, 1965, H. E. Wright, Jr., David G. Frey
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After a résumé of the morphoclimatic antecedents of the Cenozoic (pediplanes Pd3 and Pd2), a classification is presented of the Brazilian Quaternary on the basis of climatic fluctuations, correlating erosion surfaces with distinct, isolated stratigraphic sequences of semiarid sediments in a large area extending from the Rio Plata (Uruguay) to northeastern Brazil.
In a period of positive epeirogenesis four well-defined periods of mechanical morphogenesis are identified, alternating with humid periods that probably correlate with the Pleistocene glacial-eustatic regressions. The first (Pd1) is the youngest and most extensive, and its correlative sediments are found in many places (Guabirotuba Formation, Graxaim Formation) including the corresponding phase of pedimentation (Alexandra Formation, Nebraskan?). These are followed by successive phases of pedimentation (P2, Iquererim II Formation, Graxaim II Formation, Kansan?; and P1, Iquererim I, Graxaim I Formation, Canhanduva-Cachoeira Beds, Illinoisan?), and a detrital pavement (Wisconsin?) may have developed much later, at the transition from Pleistocene to Holocene.
The best records of glacial-eustatic variations are probably limited to post-Wisconsin events; they may be related to Fairbridge’s curves, but they also are concerned with some sediments representing Pleistocene emergences and submergences. These records appear to be related to the Pleistocene glaciations, so that the Brazilian sequence can be compared to that found in the Colorado and the Rocky Mountains.
Because in all areas investigated traces of pediments and the correlated deposits signify extensive mechanical morphogenesis during periods of Pleistocene glaciation, it is necessary to make a new approach to the general conception that the glacial phases with lower temperatures correspond to the pluvial periods.