EL DEPÓSITO DE PSEFÍTAS "EL PELADERO", EN LOS ACANTILADOS DEL LITORAL MARINO DE LA PROVINCIA DE RÍO NEGRO. ARGENTINA.

A conglomerate deposit in the top of the upper section of the Rio Negro Formation is analyzed. This conglomerate is located in the neighbourhood of the homonym lighthhouse. Samples were taken for grain-size, morphology and origin determinations by sieving and binocular microscope observation . The deposit contains about 70% gravel, 23 to 26 % sands and the rest are silts and clays. Gravel petrology shows 76% acidic volcanic rocks while 24% are basic and intermediate rocks. The gravel tend to be discoidal to spherical in shape.. The psammitic fraction shows a dominion of fine to medium sand. The grains have sub-rounded forms and rough surfaces marked by bites and/or dimples. The depositional environment would correspond to a channelled river with strong energy and irregular variations in the flow, a process that developed during the Upper Pleistocene. The area of origin of El Peladero gravel would be the accumulated and razed plains located in the NW of Rio Negro province, while the sandy levels would come from the erosion of the higher levels of the Rio Negro Formation. Moreover the age of the calcareous silt that cover the gravel is about 24.530 years BP.