Análisis taxonómico y morfológico de los amonites de la Formación Napo colectados en el cantón Gonzalo Pizarro, provincia de Sucumbíos.

Abstract

This study was developed on the southwest of the city of Lago Agrio, next to the Hydroelectric Project Coca Codo Sinclair, located in the northwest of the Oriente Basin between the Sub-Andean System and the Sacha-Shushufindi Corridor. The Napo Formation is composed of sequences of Shales, Sandstone and Limestone; accumulated in a marine environment, with presence of ammonites. The high content of ammonites in the area of study, allowed a taxonomic study of 149 specimens deposited in the Casa de la Cultura Ecuatoriana Núcleo Sucumbíos and 4 specimens in the analyzed area. Previous studies describe the presence of fossiliferous levels with ammonites. Through the morphological analysis of ammonites associated with the stratigraphy of the Napo Formation, it was contributed to the taxonomic update of the previously described genera. On the other hand, currently the Napo Formation does not have a physical record of fossil specimens cataloged in paleontological museums in the country, with specific descriptions in ammonites. This study helped to determine and discriminate taxa which were located at different stratigraphic levels deposited during the Late Cretaceous. A total of 153 specimens of ammonites corresponding to the genera Knemiceras, Engonoceras, Brancoceras, Oxytropidoceras, Dipoloceras, Mortoniceras associated with the Napo Basal shale were described; Mantelliceras associated with Limestone "B" belonging to the Middle Napo Member; Benueites described for the first time in Ecuador and Mammites associated with the first sequence of Limestone "A" belonging to the Middle Napo Member, Peroniceras associated with the Upper Napo shales; and the Vascoceratidae family associated with Limestone "U" in the Lower Napo member. The most abundant genus in the analyzed collection is Oxytropidoceras with 64 identified specimens; the genders scarcer are Dipoloceras, Mammites and Mantelliceras with one specimen identified for each genus. It was ratified presence of some genres that allow discriminating ages within the Napo Formation such as: Brancoceras indicating the end of the Middle Albian, Mortoniceras indicating the end of the Upper Albian, Mantelliceras indicating the beginning of the Lower Cenomanian, Benueites indicating an age from the Lower Turonian to the Middle Turonian, Peroniceras indicating the Lower Coniacian.