Ancient Coastlines in the Continental Shelf of the State of Ceará, Northeast Brazil: Evidence from Sediment Chemistry and Stable Isotopes

Abstract

Continental shelf sediments from the state of Ceará, northeastern Brazil, have been studied to investigate meteoric diagenesis of marine sediments of previously defined ancient coastal lines. Major elements for 131 samples of carbonate sediments and C and O isotopes for 51 carapace samples of benthonic foraminifers of the Amphistegina radiata and Peneroplis planatus species were analyzed. Geochemical signatures of δ 13 C, δ 18 O, SiO 2 (stoichiometrically calculated as quartz %), Sr and Mn, and XRD document the impact of meteoric diagenesis on relict sediments from current depths of 25-30 m, 45 m, and 80 m. Morphologies of the marine shelf at these depths, interpreted from previous bathymetric profiles, correspond to holocenic marine terraces. Despite a recent sedimentary cover, it was possible to confirm that these terraces possess relict detrital, biogenic, and continental material, that resulted from erosional reworking of ancient coastlines during the Flandrian transgression.

Air-sea CO2 flux in an equatorial continental shelf dominated by coral reefs (Southwestern Atlantic Ocean)

“…Specifically for the PRM region, the annual average of SST is about 27 � C, whereas for SSS the annual average is about 36 (Soares et al, 2019). The region presents a semi-arid equatorial climate, with a small and sparse fluvial drainage (Marques et al, 2008). The ocean circulation in the region is dominated by the North Brazil Current (NBC), which originates from the bifurcation of the South Equatorial Current (SEC) between 2 � S and 12 � S (Silveira et al, 1994).…”