Evolution of the High Altitude Plains of the Southern Sierras Pampeanas During the Late Late Pleistocene-Holocene, Southern Andes, Argentina

FACINI, JOAQUIN.; CHIESA, JORGE O.; GEORGIEFF, SERGIO M.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2024

0895-9811

The eastern slope of the San Luis mountain range has a typical morphology of the Sierras Pampeanas in central western Argentina: a large extension, gentle slope gradient and remnants of paleosurfaces of erosion. These high-altitude plains, locally known as "pampas de altura", are filled with Quaternary sedimentary sequences. Geomorphological studies of the plains, sedimentological analyses and absolute dating (OSL and 14C) of the deposits were carried out and integrated into existing palaeoclimatic models. The results show two types of depressions depending on the shape, slope gradient and valley-interfluve height difference: wide-shallow valleys and narrow-deep valleys. The valley type controls the flow energy and the type, thickness, horizontal extent, age and preservation of the deposits. The sequences are described in present-day river terraces of the valleys and show fluvial-alluvial lithofacies resulting from high-energy fluvial systems associated with short sub-humid phases of the Late Pleistocene Dry Period, followed by aeolian facies of 10985 ± 655 Cal. indicating arid and dry climates during the Early Holocene. Subsequent deposits of fluid and hyperconcentrated flows of 6210 ± 325 cal. BP, massive unchannelled deposits with ages of 4519 ± 35 cal. BP and 4355 ± 270 cal. BP, and a paleosol development with an age of 3786 ± 35 cal. BP are related to the Holocene Climatic Optimum. This is followed by a hiatus extending at least to the beginning of the Upper Holocene. Finally, another paleosol associated with the Medieval Warm Period aged 1723 ± 30 cal. BP is identified, followed by alluvial aeolian sequences of 705 ± 30 cal. BP, associated with the Little Ice Age.