Landscape evolution and climate changes in the Late Pleistocene - Holocene of southern pampas (Argentina). Evidence from palynology, mammals and sedimentology

QUATTROCCHIO, M.; BORROMEI, A.M.; DESCHAMPS, C.; GRILL, S.; ZAVALA, C.

QUATERNARY INTERNATIONAL

Elsevier Science Ltd.

Lugar: USA; Año: 2008 vol. 181 p. 123 - 138

1040-6182

The landscape evolution of the southwestern part of Buenos Aires Province (southern Pampa) is a good example for the understandingof continental deposits in arid–semiarid regions. In Buenos Aires Province, the last 9–3Ma record is described as sequences composed ofalternating loess and palaeosol units indicating climatic fluctuations between arid and cold (loess deposition), and warm and humidintervals (palaeosol development). The present drainage system flows across the Early Pliocene–Middle Pleistocene stratigraphic units.The stratigraphy and evolutionary history are analyzed using sequence-stratigraphic criteria; the interpretation of the climatic evolutionof the area is based on pollen and mammal (mainly rodents) records. The Late Pleistocene sediments reflect arid to semiarid conditions.The Late Pleistocene/Holocene transition is characterized by development of palaeosols. The Early Holocene pollen records reflect thedevelopment of a vegetation community characteristic of coastal dunes. Sea level was still lower than today. Temperature and humidityreached its maximum during the mid-Holocene when the high diversity and abundance of marine dinocysts and acritarchs indicate atransgression. This event is associated with the gramineous steppe in the continent reflecting more temperate or local humid conditions,and with Brazilian mammal fauna. This relative rise of sea level lead to flooding the riverbeds producing deposition of gray muddy facies.Approximately at 3000 years BP the marine influence ended in the area. After 2610 years BP psammophytic herbaceous steppedevelopment, as well as mammals, suggests arid to semiarid conditions. An interval of higher humidity is inferred at approximately 2000years BP based on the development of gramineous steppe communities. A relative rise of temperature may be inferred by the southwardexpansion of the Brazilian mammal fauna.