Landscape evolution and climate changes in the Late Pleistocene–Holocene, southern Pampa (Argentina): Evidence from palynology, mammals and sedimentology

The landscape evolution of the southwestern part of Buenos Aires Province (southern Pampa) is a good example for the understanding of continental deposits in arid–semiarid regions. In Buenos Aires Province, the last 9–3 Ma record is described as sequences composed of alternating loess and palaeosol units indicating climatic fluctuations between arid and cold (loess deposition), and warm and humid intervals (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 evolution of 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 the development of a vegetation community characteristic of coastal dunes. Sea level was still lower than today. Temperature and humidity reached its maximum during the mid-Holocene when the high diversity and abundance of marine dinocysts and acritarchs indicate a transgression. 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 steppe development, as well as mammals, suggests arid to semiarid conditions. An interval of higher humidity is inferred at approximately 2000 years BP based on the development of gramineous steppe communities. A relative rise of temperature may be inferred by the southward expansion of the Brazilian mammal fauna.