INVESTIGADORES
MEHL Adriana Ester
congresos y reuniones científicas
Título:
Late Quaternary alluvial sequences in the arid piedmont of Cordillera Frontal (33°-34° S) Mendoza, Argentina
Autor/es:
MEHL, ADRIANA E.; ZÁRATE, MARCELO A.
Lugar:
Tucumán
Reunión:
Conferencia; IX International Conference on Fluvial Sedimentolgy; 2009
Institución organizadora:
Instituto Miguel Lillio
Resumen:
The piedmont of Cordillera Frontal, between 33°-34° S, is located within the domain of the South American Arid Diagonal (AD), an area climatically sensitive to the Late Pleistocene-Holocene climate changes. Within this setting, nearly 600 metres of Late Quaternary deposits are deposited in the Tunuyán tectonic basin from which only the uppermost 30 metres crop out, mainly along the bankfulls of arroyo La Estacada basin and its tributary arroyo Anchayuyo. The exposed deposits, including four main facies and two facies associations, make up three geomorphological units, an aggradational plain (Late Pleistocene- Early Holocene), a fill terrace (Middle to Late Holocene) and the present floodplain environment (last 400 yrs. BP). Facies A represents channel deposits, it includes lag deposits (lithofacies Gmm) and channel bars (lithofacies Gh). Its participation in the alluvial sequences is secondary, being present at the lower stratigraphic section of both the aggradational plain and the fill terrace. Facies D is composed of stacked layers (0.4 to 2.5 m) of medium to fine sand and silty sand (lithofacies Sm, Sr and Src) making up several meter high sets. It is best represented at the aggradational plain, suggesting an overbank environment affected by hyperconcentrated overflows proximal to the main stream. Facies E includes horizontal layers of sandy silts laterally continuous (lithofacies Fl and Fsm), as well as lithofacies Sm. Facies E, which represents overflows reaching distal sectors of the floodplain, is the dominant facies at the fill terrace and secondarily at the aggradational plain. Overbank areas (Facies E and D) register several alluvial buried soils (lithofacies Pa) that represent intervals of stability during the aggradation process; limnic levels (lithofacies c) are also present, being very common in the fill terrace deposits. The aggradational plain and the fill terrace units are covered by a blanket of eolian sand (lithofacies Sme) that set up Facies J. Massive silty fine sands (circa 1 meter thick) of eolian origin accumulated by the end the Late Glacial are also present at the lower stratigraphic section of the aggradational plain. The facies association (Facies A, D and J) of the aggradational plain is interpreted as a distal alluvial fan dominated by overflows and secondarily sinuous streams. The fill terrace facies association (Facies A, E and J) corresponds to a fining upward sequence of a sinuous to meandering stream. Preliminary results obtained point to a climatic control of the degradation episodes that gave way to the formation of the fill terrace and the present floodplain, sometimes during the Middle and the Late Holocene respectively.