Survey of the Araripe Basin S-SE Border with the use of gamma spectrometry and magnetometry

Abstract

The Araripe Basin is located on the border between the states of Pernambuco, Piauí and Ceará in Northeast Brazil, and presents a evolutionary classic model for understanding the Gondwana breakup events during the Cretaceous Period. Additionally, the basin also contains units of great paleontological and economic relevance. Most of the geological and paleontological studies conducted in the basin have focused on the northeastern margin of the basin, while the south and west still lack research. This study tested the application of gamma spectrometry and magnetometry for mapping the units in part of the south-southeastern border of the Araripe Basin. Three main units were identified in the region: the alluvial sandstones of the Exu Formation, the fossil-rich sandstones of the Missão Velha Formation, and the shales rich in fossiliferous calcareous concretions of the Romualdo Formation. It was possible to identify and individualize the Romualdo and Exu formations, and the basin contact with the basement with the support of geophysical data. Anomalies observed in radiometric data were used to map the lagerstatten unit, presenting a replicable model for other contexts and basins. Finally, the detailed geological survey showed that the Romualdo Formation is more extensive to the south than previously estimated, extending along the foot of the plateau with approximate E-W orientation.