%0 Journal Article
%A López Gómez, José
%A Martín Chivelet, Javier
%A Palma Durán, Ricardo
%T Architecture and development of the alluvial sediments of the Upper Jurassic TordilloFormation in the Cañada Ancha Valley, northern Neuquén Basin, Argentina
%D 2009
%@ 0037-0738
%U https://hdl.handle.net/20.500.14352/50483
%X The Upper Jurassic Tordillo Formation at Cañada Ancha area, northern Neuquén Basin, Argentina, comprises amulti-stage suit of predominantly alluvial sediments that is heterolithic in nature. In that suit, severallithofacies, architectural elements, and bounding surfaces of different order have been identified and theirlateral and vertical distribution characterized. This analysis allowed the differentiation of 3 main units (lower,middle and upper), 20 subunits (C-1 to C-20), and the characterization of their alluvial styles.The lower unit (which comprises subunits C-1 to C-4) is mainly formed by fine- to medium-grainedsandstones, which become medium- to coarse-grained towards the top. These sandstones characterizesettings ranging from floodplains with isolated, unconfined flows, to more complex, vertically stacked, multistoreysheet sandstones of braided fluvial systems. The middle unit (C-5 to C-10) is dominated by pale browngreyfine-to coarse-grained sands and medium size subangular to angular conglomerates, which reflectamalgamated complexes of sandstone sheets and downstream accretion macroforms. Remarkably, thisalluvial sedimentation was episodically punctuated by volcaniclastic flows. The upper unit (C-11 to C-20)consists of finer sediments, mainly pink to white fine-to medium grained sandstones and red to greensiltstones. Towards the top, bioturbation becomes important, and also the presence of volcanosedimentaryflows is noticeable. Fluvial settings include braided sheet sandstones with waning flood deposits evolving toisolated high-sinuosity fluvial systems, with flash flood deposits. At the top of this unit, facies may suggestmarine influence.Vertical changes in the fluvial style result from both climatic and tectonic controls. A semiarid to arid climateand the active tectonism linked to the eastward migration of the Andean volcanic arc determined majorbounding surfaces, fluvial style evolution and the presence of the volcano-sedimentary deposits. Differentstages of high and low subsidence rates has been deduced from the vertical stacking of sediments.
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