Paleoenvironmental reconstruction of Quaternary valley-fill successions in summit paleosurfaces of southern Sierras Pampeanas (Córdoba Province, Argentina)

Climatic and environmental changes were inferred from the study of Late-Quaternary sequences that represent paleo-valleys filling in the summit pampas at the center-South of the Sierra de Comechingones, Córdoba Province, Argentina. A representative sedimentological section (P1) was described and sampled, and sediments age (14C), granulometric characteristics and organic matter content were determined. In the analyzed succession four main stratigraphic units were recognized and interpreted. The stratigraphic and pedological characteristics, diatom levels presence, geomorphological features and altitude conditions of the study area allow us to conclude that: 1) Valley-fill deposits are Holocene (from 8310 ± 110 yr BP to present days) and composed exclusively of loessic/loessoid material from surrounding areas. 2) The dominant transport mechanism could have been laminar and/or hyperconcentrated flows, mainly associated with slope evolution processes (sheet flow and high density flows). 3) Isolated swamps with important biological activity were the dominated environments in to the valleys. These environments suggest an alternating pedogenic cycles, were the most important was the Middle-Late Holocene, indicating a landscape stabilization tendency (4330 ± 130 yr BP). 4) Temperate-wet climatic conditions and high seasonality characterized Middle-Early Holocene (Hypsithermal period). More arid conditions dominated Late Holocene. From 1500 to 1000 BP to the present temperate-wet climatic conditions occurred, and this period was interrupted by the Little Ice Age. 5) In the mountains, both in wet and dry periods, the rainfalls were probably higher as well as the temperature must be lower than the surrounding plain, especially in winters, perhaps reaching periglacial conditions during more arid periods.