SEDIMENT ACCUMULATION IN SEPETIBA BAY (BRAZIL) DURING THE HOLOCENE: A REFLEX OF THE HUMAN INFLUENCE

Abstract

The nature of sedimentation and sediment accumulation rates in Sepetiba Bay, Brazil were interpreted from grain-size patterns, natural radiochemical distributions and seismic stratigraphy. The grain-size analyses showed progressive upward fining of sediment in cores, and a higher percentage of clay in surficial deposits in 1996 than observed during a previous spatial survey in the 1970s. Based on ²¹⁰Pb geochronology, accumulation rates range from 0.37 cm yr-1 to 2.0 cm yr^-1 for the last hundred years. In contrast, seismic stratigraphy indicates a range from 0.01 to 0.17 cm yr^-1 over the last 7000 years. Particularly high accumulation rates are found in the northeast part of the bay, and, as a consequence of these high rates, the shoreline in the northern part of the bay prograded approximately 400 m in the last 100 years. An apparent increase in accumulation rates and a tendency for deposits to fine upward over the last ~100 years are attributed to human disturbance and soil erosion inland, which have been accelerated with economic development since the late 1970s.

doi: 10.12957/jse.2016.21868