Late Quaternary paleoenvironmental evolution of the proximal area of the Atuel-Diamante distributary fluvial system, South America

HESSE, PAUL; WILLIAMS, RORY; MEHL, ADRIANA; ZÁRATE, MARCELO A.; TRIPALDI, ALFONSINA; LORENZO, FLORENCIA

Dublin

Congreso; 20th INQUA Congress; 2019

International Union for Quaternary Research

Distributive fluvial systems (DFS) havebeen described worldwide under diverse climatic and tectonic setting. Studyingthe deposits of present DFS contributes to understanding Quaternary landscapeevolution, doing paleoclimatic inferences, and improving facies models forinterpreting sedimentary records. The eastern Andean piedmont, southern SouthAmerica, shows several DFS, like the recently defined Atuel-Diamante DFS (Fig.1). The Atuel and Diamante rivers carry seasonal meltwater from the AndesCordillera and flow to the east. They are deeply entrenched in the San Rafaeltectonic block where, at its eastern piedmont, they generate the DFS. Thissystem has been barely studied in terms of its geomorphological,paleohydrological and landscape evolution. A doctoral thesis recently finishedand associated investigations in progress have started to expose and interpretits morphology and late Quaternary history. In this presentation wecharacterize the deposits of the proximal area of the Atuel-Diamante DFS, withthe aim of interpreting the late Quaternary paleoenvironmental evolution and toinfer paleoclimatic variability. Methodology included geomorphologic mapping byremote sensing, field survey, stratigraphic section analysis of pedosedimentaryfacies, with AMS and luminescence chronology. We studied 5 localities along a SW-NE transect (Fig. 1a) whereinformation was obtained at exposed deposits, pits and by augering. Presentclimate is temperate semiarid, influenced by the Andes rain shadow and theSouth Atlantic and South Pacific anticyclones. The fluvial drainage is, atpresent, a misfit system due to the current interglacial, the presence of agriculturalirrigation networks and hydroelectric power dams on the Atuel and Diamanterivers. The proximal area, besides thegravel-sand Atuel and Diamante streams, shows many abandoned meanderingchannels and associated floodplains, with deposits dominated by silty fine sandand silt, together with minor gravelly sand-silt, forming fining-upward successions.Stabilized dune fields restrict, to the north and south, the studied DFS, wherethe aeolian medium to fine sand was also described and sampled to decipher theaeolian-fluvial relationship. Previously obtained chronology shows, in theAtuel River, a late Pleistocene-early Holocene record in an upper most, 8 mthick, fluvial terrace, suggesting important fluvial aggradation during thelast glacial termination and a significant change in the system with extensive incisionat early-mid Holocene. OSL ages in progress will provide detail about themid-late Holocene evolution of the Atuel-Diamante DFS, and all together willoffer data for paleoclimatic inferences.