INVESTIGADORES
ORTIZ JAUREGUIZAR Edgardo
artículos
Título:
Paleoenvironmental evolution of southern South America during the Cenozoic
Autor/es:
ORTIZ-JAUREGUIZAR, EDGARDO; CLADERA, GERARDO A.
Revista:
JOURNAL OF ARID ENVIRONMENTS
Editorial:
Elsevier
Referencias:
Año: 2006 vol. 66 p. 498 - 532
ISSN:
0140-1963
Resumen:
Southern South America (SSA) has today a high diversity of climates, environments, biomes, and
biotas, as a result of the complex interaction through time of plants and animals with the geological
forces (e.g. plate tectonics, sea-level changes, glaciations) that modulated the geography of the
continent. Arid biomes are well represented in SSA today, but were arid biomes similarly important
in the geologic past? How long in time can be found major arid biomes in SSA? With the aim of
replaying these questions, in this paper we summarized the paleoenvironmental changes of SSA
through Cenozoic, emphasizing the relationships between biomes and the geological forces that,
through different climatic-environmental factors, have driven its evolution. We define SSA the south
of the 151S area. We prefer this geographical delimitation because with it we can see and follow the
history of the biogeographic (historic and ecologic) relationships of Patagonian biota with the rest of
the South American biota. Additionally, with this delimitation we possess the most complete
Cenozoic South American land-mammal fossil record. We use biomes because biomes are taxon-free
analytical units, and their pattern of change can be traced through time independently of the taxa
present at different geological periods. Data on plate tectonics, volcanism, sea-level changes, marine
paleotemperatures, and glaciations were taken from literature. To analyse the pattern of change of
southern South American climates and environments through the Cenozoic, we used the fossil record
of land-mammals as information source. When available, the record of vascular plants were used to
contrast the inferences derived from land-mammals. Finally, we used standard geologic divisions (i.e.
Epochs) as chronological units. The main conclusion of this paper is that from Early Paleocene to
Late Pleistocene, southern South American climatic conditions changed from warm, wet, and nonseasonal, to colder, dryer, and seasonal. Concomitantly, biomes changed from tropical forest to
steppes, across a sequence constituted by subtropical forests, woodland savanna, park-savanna, and
grassland savanna. During the Quaternary, and as a consequence of glacial cycles, cold and dry
conditions were interrupted by warmer and wet periods. Accordingly, several pulses of expansion and retraction of steppes (and, concomitantly, advances and retreats of the northern tropical forests)
are recorded. This cyclic pattern of changes produced the provincialism that has characterized the
South American biota from Early Pleistocene to the present.