Resumo

MARTINEZ, Ricardo N  e  COLOMBI, Carina E. Lithofacial evolution and age of Cañon del Colorado Formation (Lower Jurassic), Eastern Precordillera, .San Juan. Rev. Asoc. Geol. Argent. [online]. 2011, vol.68, n.1, pp.96-108. ISSN 0004-4822.

The Cañón del Colorado Formation crops out in the south of Sierra de Mogna, northeast of San Juan province. The stratigraphy and age of this formation has been controversial. In this paper, the Cañón del Colorado Formation is characterized using five stratigraphic sections (P1, P2, P3, P4, P5) uniformly distributed along the outcrops. The P3 section, located in the middle of the outcrops, is defined as the type section because its integrity, and because it goes across the fossiliferous area as well. Three members were defined from the base to the top: lower, middle and upper members. Moreover, facies and facies association were defined, called: mudstone facies association (AFP), sandy-mudstone (AFPP), conglomerate-sandstone (AFCA) and conglomerate. The sequence is characterized as an alluvial piedmont system integrated by fine grain sediments of playa -lake deposits (mudstone and sandy-mudstone facies association, rarely interlayered with the conglomerate without matrix facies association) and distal to middle alluvial fan facies (Conglomerate-sandstone and conglomerate facies association). These facies form two progradant depositional sequences, the first one is integrated by the mudstone and the conglomerate facies association, while the second is integrated by the sandy-mudstone and the and the conglomerate-sandstone facies association, possibly linked to a passive border filling of a rift basin evolved along the "north Pie de Palo fault-alignment". Finally, using biostratigraphic correlation of the paleovertebrates located in middle member, a Lower Jurassic (Hettangian-Toarcian) age is suggested for the Cañón del Colorado Formation.

Palavras-chave : Lower Jurassic; Alluvial fans; Paleovertebrates; Rift; Facies.

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