Radiocarbon geochronology of the sediments of the São Paulo Bight (southern Brazilian upper margin)

Abstract

The aim of this work was to generate an inventory of the data on radiocarbon datings obtained from sediments of the São Paulo Bight (southern Brazilian upper margin) and to analyze the data in terms of Late Quaternary sedimentary processes and sedimentation rates. A total of 238 radiocarbon datings from materials collected using different sampling procedures was considered for this work. The sedimentation rates varied from less than 2 to 68 cm.kyr -1 . The highest sedimentation rate values were found in a low-energy (ría type) coastal system as well as in the upwelling zones of Santa Catarina and Cabo Frio. The lowest rates were found on the outer shelf and upper slopes. Our results confirm the strong dependency of the shelf currents, with an emphasis to the terrigenous input from the Río de La Plata outflow which is transported via the Brazilian Coastal Current, as well as of the coupled Brazil Current -Intermediate Western Boundary Current (BC-IWBC) dynamics on the sedimentary processes. At least three indicators of the paleo sea level were found at 12200 yr BP (conventional radiocarbon age) (103 meters below sea level -mbsl), 8300-8800 cal yr BP (13 mbsl) and 7700-8100 cal yr BP (6 mbsl).

Evidence of an Marine Isotope Stage 3 transgression at the Baixada Santista, south-eastern Brazilian coast

“…When gathering the information obtained by Mahiques et al (2011 and this work, a picture emerges (Fig. 7).…”

“…In Southeast Brazil, the papers by Mahiques et al (2011) andSilva et al (2014) are the first published references that point to the occurrence of MIS3 transgression, represented by myxohaline/lagoonal deposits, located close to the present sea-level.…”

“…Close to the area of study, Mahiques et al (2011) describes a full transition from myxohaline to terrestrial environments, based on radiocarbon datings of foraminifera and organic matter, from ca 39,000 to 24,000 yr BP in a core collected in the São Sebastião Channel, state of São Paulo. Silva et al (2014) describe the formation of a sandy barrier, dated on 45,000 yr BP, deposited over lagoonal sediments, presenting ages from 48,000 and 45,000 yr BP, at Maricá region, Rio de Janeiro.…”

“…Vicalvi et al (1978) recognized a paleo-lagoon at the Abrolhos Depression (Eastern Brazilian shelf ), dating them at 10,600 yr BP (uncalibrated). Finally, Mahiques et al (2011), presented four datings on different material from a beach-rock located at 13 mbsl São Sebastião (southeastern Brazil), which gave calibrated ages around 8,200 yr BP. Suguio and Martin (1978a) provided an interpretative profile of sedimentary deposits in the area (Fig.…”

“…Additionally, a complete set of coherent (no age reversal) radiocarbon ages in both organic matter and foraminifera, ranging from 39,000 to about 24,000 BP, marks the transition of myxohaline to freshwater conditions in a shallow-water (6 mbsl) deposit in the São Sebastião Channel (state of São Paulo) (Mahiques et al 2011). Other unpublished (thesis) data, from the Paraná state, also report MIS3 high levels in the shelf and adjacent coastal plain (Souza 2005, Veiga 2005).…”