Estudios de los depósitos cuaternarios entorno a Chunchi (Chimborazo): morfoestratigrafía y caracterización petrográfica.

Abstract

Canton Chunchi is located in the Inter-Andean Valley, at the junction of the Cordillera Real and Occidental, the study area of this work is located between 2º17.3 S and 78º55.5W, at the southern of the province of Chimborazo. A detailed study of the Quaternary deposits was carried out in the area, including petrographic characterization and geological mapping at a scale of 1:25,000 to determine the spatial distribution of the lithologies and the location of the structures that appear in that area. The mapping and field work made it possible to determine the spatial distribution of the different Quaternary units, estimate their thicknesses, and interpret their origin. For this purpose, bibliography was compiled, and field trips were made to obtain samples, and carry out petrology (thin sections), stratigraphy and the geological map. Through the analysis, 6 Quaternary Units were determined in the area, and considering the estimated ages for the Cangahua Formation it was possible to establish relative ages for them. The defined units include: Old Breccia Unit (Middle and Lower Pleistocene) composed of Debris-flow consolidated breccias; Cangahua Unit (Middle and Upper Pleistocene) composed of tuffs with volcanic lithics; Debris Terrace Unit I (Middle and Upper Pleistocene); Debris Terrace Unit II (Holocene) composed of colluviums; Recent Alluvial (Holocene) deposits transported by water flows; and deposits accumulated by Recent Landslides (Holocene) produced by mass removal phenomena affecting the entire area. All these Quaternary units accumulated on paleo-valleys on the volcanic and volcanoclastic Puñay Formations (Oligocene-Miocene) and Cisarán Fm. (Miocene). In the latter Formation, the distribution of a hydrothermal alteration affecting these materials around Chunchi was mapped.