HOLOCENE EVOLUTION OF A WAVE-DOMINATED BARRIER-LAGOON SYSTEM IN RIO DE JANEIRO, BRAZIL

In a wave-dominated coast, most of the Jacarepagua coastal plain is occupied by buildings. During a new construction in this region at Barra da Tijuca, the subsurface area was excavated, exposing its quartzose sand nature, with a high mollusk shell concentration and in situ echinoderms at -10 m depth. The possibility to access this area encouraged us to investigate the evolution of the coastal plain. A 7.84-m-long core was recovered by percussion drilling. Stratigraphic, grain size, and geochemical analysis were undertaken. Three carbonate samples were dated by radiocarbon accelerator mass spectrometry (C-14 AMS). The revised sea-level variation curve revealed that the last postglacial marine transgression reached the present mean sea-level at 7945-7500 cal BP. The sandy deposit bottom was an ancient shoreface, with in situ echinoderms buried at 7770-7540 cal BP by the Pleistocene inner barrier reworking due to the last marine transgression. The Holocene outer barrier-lagoon and its flood tidal delta were formed from 5440-5070 cal BP. Mid-Holocene marine regression allowed the outer barrier progradation and the lagoon shallowing/infill. This paper confirms prior models proposed by other researchers for the Rio de Janeiro central coast and shows its similarity with the New South Wales coast, Australia.