Sedimentary Environment of Brejo Santo Formation, Late Jurassic of Araripe Basin, Brazil

Abstract

ResumoAtravés das análises litofaciológica e mineralógica dos afloramentos, foi realizada a interpretação paleoambiental para a Formação Brejo Santo, Jurássico Superior da Bacia do Araripe. Foram definidas três litofácies areníticas, uma carbonática e seis lutíticas, interpretadas como pertencentes a sistema fluvial meandrante. O predomínio de litofácies lutíticas de camadas vermelhas (red beds) evidencia a deposição em corpos d'água rasos de planície de inundação, devido às condições oxidantes, sujeitos a alta evaporação em clima árido a semi-árido, associados a momentos esporádicos de inundação fluvial (litofácies areníticas) devido ao extravasamento do canal principal em períodos de cheia. A presença recorrente de carbonato sugere que os corpos d'água eram salobros. O estudo mineralógico dos argilominerais revela mudanças de condições úmidas (presença de caulinita), na base, para condições predominantemente áridas a semi-áridas no topo, confirmada pela ocorrência mineralógica em associação de calcita, dolomita e palygorskita. Palavras-chave: Interpretação paleoambiental; sistema fluvial meandrante; planície de inundação AbstractThrough the lithofaciological and mineralogic analysis of outcrops, it was performed a depositional interpretation of Brejo Santo Formation, Late Jurassic of Araripe Basin. Three sandstone lithofacies were defined, one carbonatic and six lutitic, interpreted as pertaining to meandering fluvial system. The dominance of red bed lutitic lithofacies indicates the deposition in shallow water bodies of floodplain, due to oxidizing conditions, subject to high evaporation in arid to semi-arid climate, associated with sporadic moments of fluvial flooding (sandstone lithofacies) due to the extravasation of the main channel in periods of flood. The recurring presence of carbonate suggest that water from those water bodies was brackish. The mineralogical study of clay mineral, showed changes in the humidity conditions (presence of kaolinite) on the base, for predominantly arid to semi-arid conditions on top, confirmed by the mineralogical occurrence associated to calcite, dolomite and palygorskite.

Meshless method using fundamental solution applied to computational simulation of groundwater flow of real aquifers: study case (Guariroba’s APA and Juazeiro do Norte)

“…Polygonal Domain is located in Cariri Valley, pediplan of the Araripe sedimentary basin (an interior basin), and its geological configuration is characterized by the following sequence of sedimentary geological units: Abaiara, Missão Velha and Brejo Santo formations. They were created by deposition of materials from erosion of higher crystalline exposed regions of Borborema Province during succession of rift processes in Late Jurassic and Early Cretaceous (Assine, 1992(Assine, , 2007Maia & Bezerra, 2014;Sales & Peulvast, 2007;Lima & Ribeiro, 2012;Scherer et al, 2014;Camacho & Sousa, 2017;Melo et al., 2018). Sediments of upper layer, Abaiara formation, are composed by fine up to medium granulometry sandstones with the thickness of 400m in some areas (Figure 7) (Scherer et al, 2014).…”