The provenance of terrigenous mud on reefs in Royal Charlotte Bank, Bahia, Brazil

Abstract

The East Brazilian continental margin contains a large shelf sector called the Royal Charlotte Bank. It has terrigenous and carbonate sedimentation associated with coastal reefs. Studies using X-ray diffractometry (XRD) and the geochemistry of immobile elements were done in samples of these reefs to figure out the provenance of the mud that arrives there. In order to do this, samples of riverine sediment from the Jequitinhonha, Santo Antônio, João de Tiba, and Buranhém rivers as well as from the Barreiras Group’s sedimentary cliffs were taken. The Jequitinhonha River was found to be the most significant mud source. This was supported by the mineral fingerprints of smectite and biotite, the concentrations of immobile trace elements such as Zr, Hf, Nb, Ta, and Th, and the distribution and ratio of rare-earth elements. These findings are supported by the prevailing north-to-south drift that occurs in the region due to the northeasterly trade winds and waves that blow throughout the region for the vast majority of the year. The findings have significant implications for hydrographic basin management and the protection of reef benthic populations.

KEYWORDS:
sedimentary provenance; geochemistry; reefs; Royal Charlotte Bank