Icnologia e sedimentologia das formações Oriximiná e Faro (Carbonífero) da Bacia do Amazonas

Abstract

The Monte Alegre Dome region, located in the western part of the State of Pará, shows the different deposits that make up the Paleozoic units of the Amazon Basin. These deposits include the Oriximiná and Faro formations, which represent the Mississippian subsystem of the basin and are present in the study area. These Carboniferous units have a significant number of preserved trace fossils, the occurrence of which has not yet been recorded in this interval of the Amazon Basin. In this context, the research aimed to reveal the existence of this assemblage of trace fossils in the outcrops of the Oriximiná and Faro formations, as well as to integrate sedimentary data to refine the paleoenvironmental aspects that influenced the formation of these units in the study area. The trace fossils were described taxonomically, assigned to the level of ichnogenus or ichnospecies, and interpreted ethologically, according to the behavior of the producing organism. Thirteen different ichnotaxons were identified, including 3 ichnogenera (Arenicolites isp., Planolites isp. and Spirophyton isp.) and 10 ichnospecies (Asteriacites lumbricalis, Chondrites intricatus, Cochlichnus anguineus, Cosmorhaphe lobata, Diplocraterion parallelum, Palaeophycus striatus, Palaeophycus tubularis, Thalassinoides suevicus, Zoophycos brianteus and Zoophycos villae). A lithofacies analysis was performed which, together with the trace fossil analysis, allowed to establish the presence of the distal Cruziana and the archetypal Cruziana ichnofacies. The integration of these data contributed significantly to the paleoenvironmental interpretation of the study area, indicating that the rocks were formed in a deltaic depositional context characterized by low energy conditions and low physical and chemical stress. These conditions favored the colonization of different organisms that moved, inhabited, grazed and fed on the substrates of this environment.