Sedimentología, estratigrafía y proveniencia de la formación Rumi Cruz de la cordillera occidental del Ecuador.

Abstract

The Rumi Cruz Formation has been the subject of few sedimentological studies. Although the stratigraphy, is well defined, the few or no sedimentological, provenance and age studies have given multiple limited interpretations of the Angamarca Group and, therefore, of the Rumi Cruz formation with respect to its origin and formation within the evolution of the Western Cordillera. In this research project, the results of the sedimentological and stratigraphic studies together with the survey of stratigraphic columns, analysis of thin sections, heavy minerals and detrital zircons ages have allowed a better understanding of the Rumi Cruz Formation and therefore the Angamarca Group depositional system. In the sedimentological analysis, 7 facies were identified, which are interpreted to have been deposited in a Fan-Delta type system developed to a deep marine environment, together with the analyzed facies of the adjacent formations belonging to the Angamarca Group. Provenance analysis in heavy minerals combined with analysis in thin sections shows that the origin of the sediments of the Rumi Cruz Formation comes from the erosion of a recycled cratonic source, metamorphic rocks and, to a lesser extent, a volcanic arc. The U-Pb ages of ~38 Ma. obtained in detrital zircons from samples collected along the Apagua-Angamarca and Zumbahua-Apagua roads represent the ages of maximum deposition and are proposed as the beginning of the deposition of the Rumi Cruz Formation. With these data, it has been possible to consider that the Rumi Cruz Formation was deposited in the late Eocene during the uplift of the Eastern Cordillera and a contemporary volcanism of the Macuchi arc.