LOS CONODONTOS DE LA FORMACIÓN EL HÍGADO Y SU CONTRIBUCIÓN AL CONOCIMIENTO DEL LOS CONODONTOS DE LA FORMACIÓN EL HÍGADO Y SU CONTRIBUCIÓN AL CONOCIMIENTO DEL METAMORFISMO Y LA PALEOGEOGRAFÍA DEL ORDOVÍCICO EN LA CORDILLERA CENTRAL COLOMBIANA
No Thumbnail Available
Date
Advisors
Evaluators
Journal Title
Journal ISSN
Volume Title
Publisher
Universidad Industrial de Santander
Abstract
Description
En la Formación El Hígado aforante en la vertiente oriental de la Serranía de Las Minas, a 9.5 km al NW del municipio de Tarqui (Departamento del Huila), se encontró en su miembro inferior, en niveles de caliza bioclástica formados por acumulaciones lumaquélicas de braquiópodos rinconeliformes, una asociación de conodontos del Ordovícico Medio, junto con microelementos reelaborados del Ordovícico Inferior y Medio basal. El conjunto involucra una mezcla tafonómica de dos o más horizontes ordovícicos. Las formas más antiguas son de edad Tremadociano (biozonas de Paltodus deltifer a Paroistodus proteus). El rango de la asociación más moderna abarca las biozonas de Lenodus variabilis a Eoplacognathus suecicus y es de edad Darriwiliano. Otras formas retrabajadas parecen sugerir asociaciones adicionales de edades Floiano, Piso Tercero y Darriwiliano basal. El descubrimiento de estos conodontos implica que el Tremadociano llegó a depositarse en esta zona y fue erosionado prácticamente in situ en tiempos arenigianos, por lo que el Terreno Chibcha ya quedaría adyacente por aquél entonces a la cuenca pericratónica del este de Colombia. El índice de alteración del color de los co-nodontos (CAI), con valores 2 a 4, descarta el metamorfsmo regional de la Formación El Hígado, afectada localmente por hidrotermalismo (CAI 6).
Palabras clave: Conodontos, Ordovícico, Cordillera Central de Colombia, Metamorfsmo, Paleogeografía
Conodonts are rare fossils in northern South America, and this work reports their frst occurrence in the Ordovician of Colombia. The studied sample come from a thin brachiopod coquina interstratifed in storm-generated sandstone deposits, 20 m above the base of the El Hígado Formation (Darriwilian) in its type section in the Central Cordillera. The conodont assemblage contains fairly well preserved elements with different states of mechanical fragmentation, corrosion and even bacterial alteration. CAI values are between 2 and 6, in absence of regional metamorphism and with evidence of local hydrothermalism. The sample involved a taphonomic mixture of two or more Ordovician horizons. The older conodont assemblage is of Tremadocian age and range from the Paltodus deltifer to the Paroistodus proteus conodont biozones. The youngest assemblage range through the Lenodus variabilis and Eoplacognathus suecicus conodont biozones and is of Darriwilian age. A number of reworked conodont taxa seem to suggest additional assemblages of Floian, Third Stage and lowest Darriwilian intermediate ages. The studied conodonts indicate the existence of older and previously unknown Ordovician sedimentation in Central Colombia, where reworked specimens were probably winnowed from condensed successions ranging from the lower Tremadocian to the lower Darriwilian, and are indicative of a pre-Ordovician accretion fro the Chibcha terrane. Key words: Conodonts, Ordovician, Central Cordillera of Colombia, Metamorphism, Palaeogeography.
Conodonts are rare fossils in northern South America, and this work reports their frst occurrence in the Ordovician of Colombia. The studied sample come from a thin brachiopod coquina interstratifed in storm-generated sandstone deposits, 20 m above the base of the El Hígado Formation (Darriwilian) in its type section in the Central Cordillera. The conodont assemblage contains fairly well preserved elements with different states of mechanical fragmentation, corrosion and even bacterial alteration. CAI values are between 2 and 6, in absence of regional metamorphism and with evidence of local hydrothermalism. The sample involved a taphonomic mixture of two or more Ordovician horizons. The older conodont assemblage is of Tremadocian age and range from the Paltodus deltifer to the Paroistodus proteus conodont biozones. The youngest assemblage range through the Lenodus variabilis and Eoplacognathus suecicus conodont biozones and is of Darriwilian age. A number of reworked conodont taxa seem to suggest additional assemblages of Floian, Third Stage and lowest Darriwilian intermediate ages. The studied conodonts indicate the existence of older and previously unknown Ordovician sedimentation in Central Colombia, where reworked specimens were probably winnowed from condensed successions ranging from the lower Tremadocian to the lower Darriwilian, and are indicative of a pre-Ordovician accretion fro the Chibcha terrane. Key words: Conodonts, Ordovician, Central Cordillera of Colombia, Metamorphism, Palaeogeography.