Holocene coastal changes in Rio de Janeiro state, Brazil

Abstract

Evidence of Holocene sea-level changes along the Rio de Janeiro State Coast, and for the evolution of coastal lagoons and barriers in response to these sea- level movements, has been examined using stratigraphical and micropalaeontological techniques, radiocarbon dating and published data. Present-day diatom death assemblages have been studied in order to facilitate the interpretation of fossil assemblages, which has inter aha permitted the development of a simple statistical technique for the evaluation of the allochthonous diatom component. Modern lagoonal tide- gauge data have been used to establish a relationship between lagoonal water levels and tidal levels on the open coast. Evidence is presented which indicates that barriers which were previously believed to date from the mid-Holocene formed during the 'Last' Interglacial. The history of true Holocene barriers has been shown to be relatively complex, with some barriers having migrated by over-stepping and others by continous shoreface retreat. The published Holocene sea-level maximum for Rio de Janeiro State of -t- 4.8 m at 5100 BP is considered to be in error (approximately 3.0 m too high at this time) and a maximum Holocene sea level of -t- 3.0 m at c. 4000 BP is preferred. The evidence for sea-level maxima in other parts of Brazil at 5150 BP and for the migration of the geoid surface during the Holocene is questioned and shown to require further study. It is tentatively suggested that there may be evidence for an interglacial sea-level high at c. 35000 BP in Rio de Janeiro State.