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Sedimentitas marinas del Neógeno en la bahía de Tumaco, Nariño

 Volume 3 Chapter 11

Chapter 11

Oligocene – Miocene Coal–Bearing Successions of the Amagá Formation, Antioquia, Colombia: Sedimentary Environments, Stratigraphy and Tectonic Implications

By Juan Carlos SILVA–TAMAYO, Mario LARA and Ana Milena SALAZAR–FRANCO

Pages 233–245

Manuscript accepted October 29, 2018


The Amagá Formation is an upper Oligocene – middle Miocene tropical siliciclastic succession that was deposited along several semi–isolated intramontane (pull–apart) sedimentary basins in the northernmost part of the Colombian Andes. Despite the fact that these coal–bearing sedimentary records constitute one of the most complete upper Oligocene – middle Miocene continental successions deposited along the hinterland of the northern Andes convergent margin, limited geologic information is available in the literature about their sedimentology and stratigraphy. In this contribution, we report new detailed stratigraphic information from the Amagá Formation in the Santa Fe de Antioquia–San Jerónimo Basin and integrate it with previously published sedimentologic, sequence stratigraphic, biostratigraphic, geochronologic and thermochronologic information about the sedimentary successions in this formation, which crop out along the Amagá–Venecia, Fredonia–La Pintada–Valparaíso and Santa Fe de Antioquia–San Jerónimo Basins. This integrative approach allows us to assess the mechanisms controlling the sedimentologic evolution of tropical hinterland/intramontane successions along Andean–type convergent margins. 

 Our approach allows us to subdivide the Amagá Formation into two members, i.e., the lower and upper members. Regionally, the lower member records a change in sedimentary environments from a braided river system to a meandering river system. This change occurred during a period of increasing sediment accommodation space, which coincides with the late Oligocene (28–25 Ma) break–up of the Farallón Plate into the Nazca and Cocos Plates. The upper member of the Amagá Formation displays a facies association typical of braided river systems, and it was deposited during a period of decreasing sediment accommodation space. This decrease in sediment accommodation space likely resulted from a major regional uplift event associated with the early Miocene change from oblique to orthogonal convergence between the Nazca and South American Plates and the early Miocene (23–21 Ma) docking of the Panamá–Chocó Block to northern South America.

Keywords:  Amagá Formation, sequence stratigraphy, northwestern Andes, Oligocene – Miocene tectonics, PanamáChocó Block.