Análisis composicional y procedencia de la Formación Pe？as Coloradas, Grupo Río Chico (Paleoceno Superior-Eoceno?), en la región oriental de la cuenca del Golfo San Jorge, Chubut, Argentina

this work describes the sandstone composition and provenance of the pe？as coloradas formation (late paleocene-eocene?) located in the eastern sector of the golfo de san jorge basin, in the chubut province. sandy sections in the unit from the profiles of the localities of punta peligro, estancia la rosa and ca？adón hondo (fig. 1) were analyzed petrographically, together with the diffractometric analysis of sandy and shale levels. the obtained data were used to define detritic modes, classify sandstones, differentiate petrofacies, and to infer the possible source of materials, in a warm and humid paleoclimatic context. in this part of the basin, the pe？as coloradas formation is composed of thin bedded conglomerates and sandstones of variable grain sizes (fine to coarse) with intercalated mudstone beds, which show evidences of pedogenesis. they are composed by grey to reddish epiclastic and volcaniclastics, with an average thickness of 80 m and representing a fluvial system of high to moderate energy (fig. 2). the paleontological record is represented by fossil woods suggesting a warm and humid weather (brea et al., 2004, brea and zucol, 2006 and raigemborn et al., 2006) and mammals remnants of late paleocene age belonging to the carodnia fauna (simpson, 1935). the golfo san jorge extensional basin was developed during the jurassic and cretaceous in a cratonic setting (hechem and strelkov, 2002). an extensive marine flooding took place from maastrichtian to early paleocene, when the salamanca formation was deposited (uliana and legarreta, 1999). during the late paleocene, the sedimentation evolved into a continental environment with the deposition of the río chico group: pe？as coloradas, las flores and koluél kaike formations was characterized by recurrence of lacustrine and fluvial conditions (legarreta and uliana, 1994). contemporarily, a bimodal calcoalcaline volcanism developed in the pilcaniyeu belt (rapela and kay, 1988). medium to coarse sandstones with matrix <