Deposition and sea-level evolution models for Upper Pleistocene/ Holocene in the Sao Sebastiao Channel (SE Brazilian coast) inferred from 5th order seismic stratigraphy

摘要

In this paper, we used seismic stratigraphy for the study of deposition and sea-level evolution on the Sao Sebastiao Channel (SSC), southern Brazilian coast. About 60 km of high-resolution single-channel seismic lines were acquired to establish a 5th order seismic stratigraphy model for the area. After graphical processing for noise attenuation and enhancing of deep-reflections, we could interpret six seismic horizons and the acoustic basement which together defined six seismic units. Studying those units in a late Quaternary relative sea-level oscillations context, we propose a 4-phase deposition evolution model that took place since the Marine Isotopic Stage (MIS) 5e in the SSC area. The first phase comprises the deposition of seismic units U1 and U2 prior to MIS 4 with the deposition of one lowstand systems tract (LST) and one highstand systems tract (HST). Before the second phase, the sea-level dropped eroding the top layers of the previous units. During the second phase, after the Last Glacial Maximum (LGM), another LST (unit U3) was formed in one of the three stabilization periods of Upper Pleistocene/early Holocene sea-level rise on the Brazilian coast. Following an increase in sea-level rise velocity, we interpreted a transgressive system tract (unit U4) and another HST (unit U5) developed until the maximum sea-level of the Mid-Holocene, at 6 ky B.P during the third phase of our model. During the fourth phase, sea-level fall evolved to the present level, giving conditions to the deposition of the last HST (unit U6) interpreted in the region.