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 AraripeBasin, deposited under the context of the Afro-Brazilian Depression in the West Gondwana Early RiftStage. The Missão Velha Formation stands out in the Araripe Basin mainly due to the occurrence of anassembly of silicified coniferous trunks. Although theMissão 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 theearly 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 artand delimitation, tectonoestratigraphic conditions, and itsgeological and paleontologicalsettings. The unit presents an internal unconformityand its lower and upper sequences present a distinction in the paleocurrentspatternsthat change from S-SE to NW, respectively; the facies association change from riverbeds with interdigitated floodplaindepositsto high-energy braided channelsdeposits with the presence of silicified trunks. The assignment of the silicified trunks to the Dadoxylon-Araucarioxylontaxonshould be discouraged,since this denominationis outdated accordingly the rules of theInternational Code of Botanical Nomenclature