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Sedimentitas marinas del Neógeno en la bahía de Tumaco, Nariño
The Eastern Foothills of Colombia
By Andrés MORA, Eliseo TESÓN, Jaime MARTÍNEZ, Mauricio PARRA, Álvaro LASSO, Brian K. HORTON, Richard A. KETCHAM, Antonio VELÁSQUEZ and Juan Pablo ARIAS–MARTÍNEZ
Here we summarize for the first time the structural geometry and evolution of the Eastern Foothills of Colombia on the basis of new and previously published cross sections. We compare shortening records of the Caguán–Putumayo and Llanos Foothills as two different end–members for thick– and thin–skinned foothills deformation along the Andean deformation front. The Caguán–Putumayo area involves thick–skinned deformation and broad basement uplifts, such as the Garzón Massif, with a simple frontal monoclinal structure expressed in folded and faulted basement rocks, similar to broad thrust–related uplifts in the eastern Rocky Mountains of North America. In contrast, the Llanos Foothills have a more complex array of structural styles, from tightly folded frontal basement structures to thin–skinned antiforms of faulted detachment folds. The main control on the style of basement deformation appears to be basement composition, which is igneous/metamorphic crystalline in the Caguán–Putumayo area and low–grade metasedimentary in the Llanos Foothills, prompting tighter basement folds. The main control for thin– versus thick–skinned deformation appears to be the thickness of the Mesozoic – Cenozoic stratigraphic units and the presence or absence of detachment horizons. The Andean Foothills of Colombia record a geometric evolution that started in the Oligocene, with similar structural styles across all segments at that time. However, the deformation styles diverged during accelerated Miocene to recent shortening, where rapid deposition of thick fluvial sedimentary units drove source rocks into the oil window and helped form efficient detachment horizons for thin–skinned deformation in deeper sectors of the basin.
Keywords: thin–skinned, thick skinned, basement, detachments.