Shallow seismic reflectors and upper Quaternary sea levei changes in the Ubatuba region, São Paulo State, Southeastern Brazil

Abstract

The relationship between shaUow seismic lIDits and Quatemary sea leveI changes in Southeastem Brazil is based on boomer profiles aild core data ftom the Ubatuba region, northem São Paulo coast. In Flamengo and Palmas bays, the interpretation of seismic lines revealed the occurrence of four sedimentary units, separated by regionally correlated reflectors. The upper two lIDits correspond to Late Pleistocene and Holocene deposits. The lowermost sedimentary units were correlated to the older Quatemary transgressive events. These deposits, which have not yet been described for this area, can present1ybe fOlIDdon the Rio Grande do Sul coastal plain. In the Boqueirão Strait, two erosional events in the sedimentary strata have been associated with the Cananéia (maximum at 120,000 yr. B.P.) and Santos (maximum at 5,100 yr. B.P.) sea-level rise events.. Resumo: A partir de registros sísmicos, obtidos por "boomer" e dados de um testemunho, foi estabelecida uma relação entre lIDidadessísmicas rasas e variações relativas do nível do mar no Quatemário, na região de Ubatuba, litoral norte do Estado de São Paulo. A interpretação das linhas sísmicas revelou a ocorrência de quatro lIDidades sísmicas, associadas a seqüências sedimentares, separadas por refletores sísmicos de expressão regional. As duas unidades superiores correspondem a depósitos do Pleistoceno Superior e Holoceno, e encontram correspondência em outras áreas do planeta. Na região do Boqueirão, dois eventos erosivos são associados com os últimos eventos de subida do nível do mar. As unidades sedimentares inferiores são correlacionáveis a eventos transgressivos mais antigos, que não haviam sido ainda referidos para a área.

Chapter 5 The southern Brazilian shelf

“…More recent data by Mahiques & Souza (1999) and Klein (2005) constitute, at this moment, the most accurate and precisely dated information on sea-level stabilization periods prior to the Holocene highstand of 5.6 ka BP. In the São Paulo state coast (23830 0 S), mollusc shells collected in a palaeo-beach sediment located 6 m below the present sea level were radiocarbon dated at 7850 + 80 cal years BP (Mahiques & Souza 1999).…”

“…In the São Paulo state coast (23830 0 S), mollusc shells collected in a palaeo-beach sediment located 6 m below the present sea level were radiocarbon dated at 7850 + 80 cal years BP (Mahiques & Souza 1999). Additionally, four beach-rock samples located 13 + 1 m below the present sea level showed an age of 8000 + 50 cal years BP.…”