Abstract

FOIX, Nicolás; PAREDES, José M; GIACOSA, Raúl E  and  ALLARD, José O. Arquitectura estratigráfica del paleoceno en el flanco norte de la cuenca del golfo San Jorge, Patagonia central. Rev. Asoc. Geol. Argent. [online]. 2015, vol.72, n.1, pp.96-106. ISSN 0004-4822.

The deposition of the Salamanca Formation and Río Chico Group (Paleocene) in the Golfo San Jorge Basin exceeds the basin boundary of the underlying continental units of the Chubut Group (Cretaceous). These Paleocene units show major northto- south stratigraphic changes for the north flank of the basin. On one hand, the accumulation of bioclastic deposits in the base of Salamanca Formation (Bustamante Member) only took place in the northern basin boundary, where the marine sedimentation occurred overlying Jurassic volcanic rocks of the Marifil Complex. In southward direction, the initial Paleocene transgression is represented by the epiclastic deposits of the Hansen Member ("Glauconítico"), overlying the Chubut Group (Cretaceous). In this way, the bioclastic deposits of the Bustamante Member are interpreted as an evidence of development of substrate-controlled marine invertebrate colonies, in which the volcanic rocks constituted a more favorable substrate to colonization of encrusting marine biota in intertidal and subtidal environments. On the other hand, noth-to-south variations in the alluvial macro-architecture of the Río Chico Group are represented by variations in fluvial styles, in the external geometry of channelized deposits, by variable preservation of floodplain deposits, and by systematical changes in the total thickness of the unit, suggesting spatio-temporal variations in the rate of generation of accommodation space during their deposition. The changes in the Paleocene stratigraphic record are spatially overimposed with de northern basin boundary of the continental Chubut Group. The extensional reactivation of this inherited basin boundary controlled the Paleocene macro-architecture in the north flank of the basin.

Keywords : Salamanca Formation; Río Chico Group; Cretaceous basin boundary; Patagonia.

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