THE CONODONTS FROM THE EL HÍGADO FORMATION AND ITS CONTRIBUTION TO THE KNOWL-EDGE OF METAMORPHISM AND ORDOVICIAN PALEOGEOGRAPHY IN THE CENTRAL CORDILLERA OF COLOMBIA
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Abstract
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.
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References
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