Resumen

CASAL, Gabriel A; ALLARD, José O  y  FOIX, Nicolás. Análisis estratigráfico y paleontológico del cretácico superior en la cuenca del golfo San Jorge: nueva unidad litoestratigráfica para el grupo Chubut. Rev. Asoc. Geol. Argent. [online]. 2015, vol.72, n.1, pp.77-95. ISSN 0004-4822.

Lithologic, stratigraphic and paleontological features of the most recent record of the Chubut Group in the Golfo San Jorge Basin (Argentina), allowed us to propose the definition of a new lithostratigraphic unit in the Group: Lago Colhué Huapi Formation (nov. nom.). This unit overlies the Bajo Barreal Formation (Upper Member) and it is covered by the Laguna Palacios or Salamanca Formation. Although its base and top are transitional, this unit is sometimes limited by an erosional surface in its contact with the Salamanca Formation, and it is widely exposed in the basin. Its type locality is located in the headwaters of the Chico river and we propose a composed type-strata: the holostratotype is constituted by a stratigraphic section outcropped in the headwaters of the Chico river (53 m thick), and the parastratotype is the interval outcropped in the southeastern margin of the Senguerr river (160 m thick). Criteria for the recognition of the proposed unit are its reddish mudstones and the stratigraphic position. The Lago Colhué Huapi Fomation differs from the Bajo Barreal Formation (Upper Member) because the latter is characterized by grey mudstones. This unit also differs from Laguna Palacios Formation because of the absence of tuffaceous strata and paleosoils. In its type locality, we interpreted a fluvial paleo-environment with high-sinuosity channels and well-drained floodplains, probably developed under semiarid paleoclimatic conditions. The dinosaur record of the formation allowed us to define an age ranging between Coniacian-Maastrichtian, and faunistic affinities with the Allen Fomation of the Neuquén basin.

Palabras clave : Lago Colhué Huapi Formation; Chubut Group; Upper Cretaceous; Patagonia.

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