Paper No. 295-9
Presentation Time: 10:15 AM
SEDIMENTOLOGY AND PROVENANCE ANALYSIS OF THE ALAMOR LANCONES BASIN, SOUTHERN ECUADOR: A LATE CRETACEOUS PRE-ACCRETIONAL FOREARC BASIN
VALAREZO, Mauricio1, VALLEJO, Cristian1, HORTON, Brian K.2, WINKLER, Wilfried3, SPIKINGS, Richard4, ESTEBAN, José5 and JACKSON, Lily J.6, (1)Departamento de Geología, Escuela Politécnica Nacional, Ladrón de Guevara E11-253, Quito, 170605, Ecuador, (2)Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712, (3)Institute of Geology, Dpt. of Earth Sciences, Swiss Federal Institute of Technology, Universitätstrasse 16, Zurich, 8092, Switzerland, (4)Section of Earth and Environmental Sciences, University of Geneva, 13 Rue des Maraichers, Geneva, 1205, Switzerland, (5)Departamento de Geodinámica, Universidad del País Vasco, Bilbao, (6)Department of Geological Sciences, University of Texas at Austin, 2275 Speedway Stop C9000, Austin, TX 78712 – 1722, mauricio.valarezo@epn.edu.ec
The Huancabamba deflection separates the north-northwest−trending Peruvian Andes from the northeast-trending Ecuadorian Andes. The Alamor-Lancones Basin is located in this region, and recorded the Cretaceous to Tertiary history of this area and its active plate margin. The basin is bounded to the west by the Amotape-Tahuín terrane and to the east by the Eastern Cordillera of Ecuador. The Río Playas sub-basin represents the upper part of the sedimentary fill of the Alamor Lancones Basin. The Alamor, El Naranjo, and Casanga Formations comprise Cretaceous sediments unconformably overlain by the Paleogene Río Playas Formation.
The geochemistry of Albian-Cenomanian volcanic/volcaniclastic rocks of the Alamor Formation indicate tholeiitic volcanism related to an extensive magmatic event in northern Peru and southern Ecuador. Coniacian to Maastrichtian El Naranjo and Casanga Formations include sandy debrites, sandy turbidites, slumps, and sandy slides. This lithofacies association suggests deposition in a submarine fan environment. Heavy mineral and QFL data from the Casanga and El Naranjo Formations show derivation from a volcanic arc. U-Pb dating of detrital zircons within the Casanga Formation indicate a dominance of zircon ages between 90 and 84 Ma. They partially overlap known biostratigraphic ages and thus corroborate contemporaneous volcanism during deposition. In addition, paleocurrents indicate sediment transport from the southeast.
Paleogene sediments of the Río Playas Formation include sandstone, sheetflood conglomerate, and red mudstone lithofacies indicating deposition in a nonmarine environment. Heavy mineral and sandstone point counts show a significant proportion of metamorphic minerals, suggesting an important tectonic event prior to deposition of the Río Playas Formation. Detrital zircon U-Pb ages include populations of 600 to 1500 Ma, implying derivation of the detritus of the Rio Playas Formation mainly from exhumed rocks of the Eastern Cordillera. Therefore, the analyzed stratigraphic section records the closure and inversion of the forearc Alamor-Lancones Basin, in response to a major tectonic event, most likely the collision of the Caribbean Plateau with the South American continental margin between 73 and 70 Ma.
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