Seismic stratigraphy of trapandé bay (southern Brazil) to study sea-level changes and deposition evolution in the upper quaternary

Abstract

The Quaternary relative sea-level in the Southeastern Brazilian margin is mostly studied using a sedimentary approach. In this work, we used high-resolution seismic and bathymetric data to study the depositional evolution in the Quaternary of Trapandé Bay, in São Paulo State, Brazil. Using seismic stratigraphy, we have analyzed over 198 km of seismic sections and we interpreted 6 seismic horizons which defined 5 seismic units. The oldest unit (U1) is related to the highstand deposits developed during Marine Isotope Stages (MIS) 5. The horizon H1 represents the erosional surface formed during the regression that culminated in the Last Glacial Maximum (LGM). After that, during the first stabilization period of sea-level rise, unit U2 formed and was subsequently eroded by a rapid flood of the bay, forming the erosional surface H2. During middle and late Holocene, it was identified a transgressive tract in the unit U3 and a progradational facies in unit U4, limited to the more coastal regions. Finally, unit U5 developed in Late Holocene, with depositional characteristics similar to those of present time. We found none seismic expression of Late Holocene high-frequency relative sea- level oscillations.