INSTITUTO DE GEOCRONOLOGIA Y GEOLOGIA ISOTOPICA
Unidad Ejecutora - UE
congresos y reuniones científicas
Sedimentology and paleontology of the Puesto Almada Member (Upper Jurassic, Cañadón Asfalto Formation), Fossati sub-basin, Patagonia, Argentina
CABALERI, NORA; BENAVENTE, CECILIA; MONFERRAN, MATEO; NARVÁEZ, PAULA; VOLKHEIMER, WOLFGANG; GALLEGO, OSCAR F.; SILVA NIETO, DIEGO; ARMELLA, CLAUDIA; PAEZ, MANUEL
Simposio; V Simposio Argentino del Jurásico; 2013
Museo Paleontológico Egidio Feruglio
A sedimentological and paleontological study of the Puesto Almada Member at the Cerro Bandera locality (Fossati sub-basin, Cañadón Asfalto Basin) is presented. Six facies associations were found: lacustrine limestones, palustrine limestones, wetland-lacustrine, eolian sandstones, fluvial sandstones, and alluvial fan; included in a lacustrine carbonate depositional setting with lakes surrounded by shallow flooded areas in a low-lying topography. The facies associations constitute four cycles defined by local exposure surfaces: 1) a shallowing upwards succession of lacustrine-palustrine-pedogenic facies with a conchostracan-ostracod association; 2) a palustrine facies association representing a wetland sub-environment, and yielding conchostracans, insect ichnofossils and body remains, fish scales, and palynomorphs (cheirolepidiacean species and ferns growing around water bodies, and other gymnosperms in more elevated areas); 3) an alluvial fan facies association indicating drop of the lake level; and 4) a lacustrine facies association representing a second wetland episode, and yielding conchostracans, insect ichnofossils, and a palynoflora mainly consisting of planktonic green algae associated with hygrophile elements. The presence of wetlands and lacustrine facies could indicate high humid conditions with a precipitation rate greater than evaporation, adequate for the development of biota and stable aquatic systems. The rivers and alluvial facies probably represent the presence of seasonal rains, with higher levels of water agitation preventing the development of stromatolites. The sedimentary features of the Puesto Almada Member are in accordance with an arid climatic scenario across the Upper Jurassic, and they reflect a strong seasonality with periods of higher humidity represented by wetlands and lacustrine sediments.