Mesophotic bioclastics and bioconstructions at the continental shelf of Santos Basin, Brazil

Abstract

The Santos Basin mesophotic zone comprises one area of 104,915 km2, occupying 78% of the entire basin. Santos Basin is one of the most under stress and sensitive marine regions in the Brazilian territory due to several major ports, Oil & Gas industry, and coastal marine environmental management areas. Scientific literature recognizes that rhodolith beds and biogenic rigid-bottom patches occur on the shelf, but because lack of high-resolution seismic data, these seabed features are not yet wholly mapped at Santos Basin. However, an unprecedented gathering of historical depth sounding points and surface sediment data collection, in conjunction with an extensive field campaign of seabed sampling and sub-bottom shallow seismic records, points out new evidence of biogenic sediment distribution reefal structures in the Santos Basin. The patches of calcareous algae crusts, terraces mounds, pinnacles, and free-living rhodolith beds compose the carbonate facies on the outer shelf. Rugged bottom relief and pinnacles up to 10 m in height correlate with carbonate gravels and sandy areas. Bioconstructions are more common northward and gradually decrease southward. Geomorphological features such as rugged bottom relief might indicate the occurrence of mesophotic bioconstructions off Paraná, and Santa Catarina State coast. The mesophotic bioconstructions have evolved through four stages: 1- LGM fully sposed shelf, 2- sea-level transgression and bioconstrutions pioneers, 3- influence of the La Plata plume at the southern sector, and 4- establishment of mud patches in the northern sector due to local input.