Estratigrafía y paleontología de amonites de la Formación Santiago (Jurásico inferior), en la Cordillera Cutucú, sureste del Ecuador

Abstract

The Santiago Formation presents a sedimentary marine sequence deposited during extensive events approximately 199 Ma ago, mainly due to the accumulation of ammonites at certain levels. This paper analyzes the fossil record of the ammonites of the most fossiliferous Member, the Yukianza Member, as well as taxonomic identifications and taphonomic analyzes of the sampled ammonites. As results the information is synthesized in a stratigraphic column of 850 m. of power and a geological cut in the path Patuca-Santiago. In addition to a study of sexual dimorphism of Jurassic ammonites, as well as their abundance. In this study the lower member of the Santiago Formation corresponds to limestones and calcareous sandstones called Member Rio Santiago, the intermediate Member consists of shales and sandstones rich in organic matter deposited in a turbiditic environment known as the Yukianza Member and the Upper Member consists of sandstones , limolites and black shales with basaltic intercalations deposited in a deltaic environment called Member Patuca. 355 copies of Yukianza Member ammonites characterized by distal facies were studied. Were identified: Arnioceras sp., Leptechioceras sp., Paltechioceras cf. harbledownense, Paltechioceras aff. mexicanum, Orthechioceras aff. incaguesiense, Orthechioceras cf. pauper (dimorphic species), Schlotheimia, Vermiceras sp., in the town of Chiguaza del Hettangiano al Sinemuriano.