Implicaciones ambientales de las trazas fósiles de la Formación Ixtaltepec, Carbonífero de Oaxaca, México

Abstract

One of the most complete successions of paleozoic rocks is located at the Santiago- Ixtaltepec area, in Oaxaca State, southern Mexico. In this succession, Carboniferous rocks are formed by the Santiago (Tournaisian-Serpukhovian) and the Ixtal tepec (Serpukhovian-Moscovian) formations. The Ixtaltepec Formation has been divided into eight units (API-1 to API-8) characterized by fossil associations of corals, trilobites, bivalves, gastropods, brachiopods, bryozoans, ophiuroids, crinoids and plant fragments, with different proportions. API-4 unit is composed of sandstone and shale, and their lower and medium layers contain few body fossils and show moderate bioturbation. The present study describes nine ichnotaxa collected in this unit: Cochlichnus anguineus, Cochlichnus isp., Lockeia siliquaria, Lockeia isp., Planolites isp., Protovirgularia isp., Rhizocorallium commune, and other traces, tentatively assignable to ?Gordia isp. and ?Rhizocorallium isp., which are grouped into three associations. These ichnoassociations correspond to a Cruziana icnofacies and indicate that the deposit occurred in the intertidal zone, in a tidal plain between mudflat and mixed flat, representing a shallowing stage in this area during the Serpukhovian-Bashkirian.