The relationship between sea-level change, soil formation and stress history of a very soft clay deposit

Abstract

The paper addresses the relationship between sea-level change, soil formation and stress history of a very soft clay deposit close to the city of Rio de Janeiro (Sarapui II), permitting some conclusions on hypotheses discussed over time. Dating samples throughout the very soft organic clay profile provided values between 8590 and 2300 cal. yr BP. The average rate of deposition is 0.9 mm/yr. The very soft clay overlies a yellow clayey silt soil of Pleistocene origin (12,630–12,240 cal. yr BP). The combination of geological and geotechnical data indicates that the paleo-sea-level highstand in the Rio de Janeiro area (and possibly in the region between 8°S and 26°S in the Southern Hemisphere along the Brazilian coast) occurred around 7000 cal. yr BP. These sets of data also indicate that the lower part of the Sarapui II deposit was formed during transgression and the upper part during regression. The overconsolidation of the deposit, excluding the top 2.5 m, could be attributed to secondary consolidation.