Abstract

ASENSIO, Marcos A et al. The Río Foyel Formation, Oligocene- Ñiriuhau Basin: The Pacific Transgression in the Northern Patagonian Andes. Rev. Asoc. Geol. Argent. [online]. 2010, vol.66, n.3, pp.399-405. ISSN 0004-4822.

The strong extensive tectonics caused by the negative roll-back of the subduction zone between the Farallón and Southamerican plates due to their relative velocity of convergence, from the Eocene until the early Oligocene, generated diverse marine depocenters connected with the Pacific Ocean, originating marine deposits of dominant deep facies. The restricted circulation and the dysoxic and even anoxic prevailing conditions were a consequence of the morphology of these depocenters; these conditions are inferred for the Río Foyel Formation. Crystalline gypsum internal moulds, of both specimens and isolated chambers of the foraminifera Transversigerina cf. transversa, from apparent basal samples of this formation; suggest a Pacific connection and deep water settings. Palynomorphs are scarce in the basal levels; in the upper levels, the abundance and diversity of dinocysts and the predominance of amorphous organic matter with abundant framboidal pyrite suggest anoxic marine environments relatively distal from the continental source area. The sporomorphs indicate the presence of template-humid forest with subordinate open areas and a remarkable input from the coastal environment.

Keywords : Foraminifera; Palynology; Río Foyel Formation; Oligocene; Ñirihuau Basin.

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