Definição Estratigráfica Da Formação Missão Velha, Bacia Do Araripe

Abstract

The Missão Velha Formation corresponds to the fluvial deposits through the Jurassic-Cretaceous interval in the Araripe Basin, deposited under the context of the Afro-Brazilian Depression in the West Gondwana Early Rift Stage. The Missão Velha Formation stands out in the Araripe Basin mainly due to the occurrence of an assembly of silicified coniferous trunks. Although the Missão Velha Formation and the Dom João Stage deposits, in general, do not present diagnostic features of tectonism and active magmatism, a series of investigations in the last decade challenged the obviousness, seeking to understand the conditions of the early rift, through new comparative and interpretative methods. Under the sight of these new data and in order to facilitate communication between the authors, the present work proposes an objective delimitation and definition of the unit through the analysis of its state of the art and delimitation, tectonoestratigraphic conditions, and its geological and paleontological settings. The unit presents an internal unconformity and its lower and upper sequences present a distinction in the paleocurrents patterns that change from S-SE to NW, respectively; the facies association change from riverbeds with interdigitated floodplain deposits to high-energy braided channels deposits with the presence of silicified trunks. The assignment of the silicified trunks to the Dadoxylon-Araucarioxylon taxon should be discouraged, since this denomination is outdated accordingly the rules of the International Code of Botanical Nomenclature.