Stratigraphic Relations of the Ipubi Formation: Siliciclastic-Evaporitic Succession of the Araripe Basin

Abstract

The Ipubi Formation represents the Aptian-Albian siliciclastic-evaporitic succession of Araripe Basin, NE Brazil. This succession comprises siliciclastic rocks (bituminous shales and claystones) and evaporites (gypsum and secondary anhydrite) and represents part of the lacustrine-shallow marine post-rift phase I. This study used sequence stratigraphy concepts to define the relations between changes in the relative lake level and the formation of Ipubi deposits. Results show that the organic-rich shales of the Ipubi Formation formed during a transgressive pulse that covered large areas of the proximal domains. These deposits overlie a regional unconformity that marks the end of the deposition of the underlying Crato Formation. A High Stand stage that followed the transgression influenced the formation of evaporitic deposits. Climate conditions played a major role in influencing the triggering and stopping of evaporite deposition. Thus, a new relative lake level fall event caused the exposure of the Ipubi Formation deposits, and created another regional subaerial unconformity accompanied by widespread karstification of evaporite beds. A posterior transgression caused the deposition of siliciclastic rocks of the Romualdo Formation over the Ipubi Formation strata, and also promoted a new event of karstification of the Ipubi upper evaporite beds.

The first theropod dinosaur (Coelurosauria, Theropoda) from the base of the Romualdo Formation (Albian), Araripe Basin, Northeast Brazil

“…A layer of dark fossiliferous shale with about 50 cm is found below the conglomerate and, regarding macrofossils, has yielded so far only coprolites, small fishes, plant material (macrocharcoal), and one turtle 35,36,37,38 . Some 2.5 m above the conglomerate, at the base of the Romualdo Formation, another fossiliferous horizon is found.…”

“…A layer of dark fossiliferous shale with about 50 cm is found below the conglomerate and, regarding macrofossils, has yielded so far only coprolites, small fishes, plant material (macrocharcoal), and one turtle 35 , 36 , 37 , 38 .…”

Age of the Post-rift Sequence I from the Araripe Basin, Lower Cretaceous, NE Brazil: implications for spatio-temporal correlation

“…The depositional setting of the Ipubi Member has been interpreted as a coastal environment, susceptible to the relative sea level changes, under arid to semi-arid climatic conditions. The mineralogy, dimensions, nature and geometry of the layers indicate a depositional system similar to those of modern coastal sabkha in South Australia (Assine, 2007;Assine et al, 2014;Bobco et al, 2017;Fabin et al, 2018;Goldberg et al, 2019).…”

Paleoambiente Deposicional E Origem Da Matéria Orgânica Dos Folhelhos Betuminosos Da Formação Ipubi, Porções Leste E Sudeste Da Bacia Do Araripe, Ne Do Brasil: Evidência De N-Alcanos E Isoprenoides

“…O paleoambiente deposicional da Formação Ipubi foi preteritamente discutido por alguns autores (e.g. Neumann, 1999;Assine, 2007;Assine et al, 2014;Arai, 2014;Castro et al, 2017;Bobco et al, 2017;Fabin et al, 2018;Goldberg et al, 2019;Lúcio et al, 2020). Entretanto, ainda existem divergências a respeito da contribuição (ou não) de águas marinhas durante a deposição dos mesmos.…”

“…Destaca-se a localização das minas de gipsita, onde foram coletadas as amostras de folhelhos betuminosos da Formação Ipubi. Modificado deAssine (2007),Fabin et al (2018).PALEOAMBIENTE DEPOSICIONAL E ORIGEM DA MATÉRIA... Estudos Geológicos v 30(1) https://periodicos.ufpe.br/revistas/estudosgeologicos/indexFigura 2: Diagrama estratigráfico da Bacia do Araripe. Adaptado de Neumann (1999); Neumann & Assine (2015); seguindo novos intervalos cronoestratigráficos obtidos por Lúcio et al (2020) na Formação Ipubi e por Arai & Assine, (2020) na Formação Romualdo.…”