Abstract The objectives of this study were the biostratigraphic and paleobiogeographic interpretations of the calcareous nannofossil records of the Romualdo Formation (Aptian-Albian) in the south-central portion of the Araripe Basin. The methods used to process the samples were decanting, smear slide, centrifugation, and ultra-thin section confection. The taxonomic and biostratigraphic interpretations were carried out through qualitative and quantitative investigations. A total of 11 genera and 17 species of calcareous nannofossils, namely, Biscutum constans, Biscutum sp., Braarudosphaera africana, Braarudosphaera sp., Calculites sp., Discorhabdus ignotus, Hayesites albiensis, Hayesites sp., Nannoconus bucheri, Nannoconus sp., Retecapsa surirella, Rhagodiscus sp., Thoracosphaera sp., Watznaueria barnesiae, Watznaueria sp., Zeughrabdotus erectus, and Zeughrabdotus noeliae were identified. The integrated analysis of three outcrops suggests two distinct marine phases: the first in the Aptian, recognized in two outcrops, and during the Albian age. The genera Hayesites and Nannoconus suggest a strong Tethyan affinity. Differently, other calcareous nannofossils such as Watznaueria, Thoracosphaera, and Braarudosphaera recorded here are considered more resistant, cosmopolitan, and/or opportunistic species. Biscutum and Zeughrabdotus are sensitive calcareous nannofossils because they are more susceptible to dissolution and cannot be surely used to define this paleobiogeography and biostratigraphic range.

ABSTRACT: The Romualdo Formation, Araripe Basin, crops out in the municipality of Exu, Pernambuco State, exposing coquinas. Fauna survey, taphonomic analysis of the macrobenthos, and identification of sedimentary facies of the outcrop were carried out to contribute to paleoenvironmental understanding of the Romualdo Formation. The association of molluscs (Cerithium sp., Tylostoma ranchariensis, Aguileria dissita, Brachidontes araripensis and unidentified cassiopids) and echinoids of the species Bothryopneustes araripensis suggests sedimentation in the marine environment. The taphonomic similarities made possible the grouping of coquinas into two types. Coquinas type 1 exhibit characteristics of transport and reworking of bioclast generated by storms in proximal setting. Coquinas type 2 demonstrates echinoids in situ and articulated with spines connected to shells, suggesting a fast sedimentation by distal tempestite. Regarding sedimentary facies, the concentrations of invertebrates would have been formed in the transitional offshore zone of siliclastic platform. The results presented here evidence a broader distribution of echinoids and expand the geographic limits of the shallow marine environment in the Romualdo Formation.

Esse estudo teve como objetivo compreender a dinâmica de evolução geológica recente do vale do Rio São Francisco, no Estado de Pernambuco. A metodologia utilizada compreende dois tipos de análises: uma geomorfológica a partir da realização de mapeamento de detalhe, identificando uma unidade morfoestrutural e suas respectivas morfoesculturas, a outra geocronológica, com idades obtidas por Luminescência Opticamente Estimulada. Os resultados mostram dois conjuntos morfoesculturais eólicos elaborados ao longo do Pleistoceno tardio, com atividade deposicional até a transição para o Holoceno. A metodologia utilizada se mostrou bastante satisfatória, contudo a região ainda muito é carente de dados paleoambientais.

This study aimed at understanding the dynamics of the recent geologic evolution in the São Francisco river valley, State of Pernambuco. The applied methodology encompasses two types of analysis, a geomorphologic one based on the elaboration of a detailed map, identifying a morphostructural unit and their respective morphosculptures. The second analysis was a geochronologic one based on Optically Stimulated Luminescence. The results pointed to the existence of two sets of eolian morphosculptures shaped along the late Pleistocene, exhibiting depositional activity until the Holocene transition. The applied methodology proved quite satisfactory in this region which is still lacking paleoenvironmental data.