UnB - Instituto de Geociências - Produção Científica
RESUMOS/ABSTRACTS
FOLHELHOS NEGROS DA FORMAÇÃO ALAGAMAR E SUA PROVENIÊNCIA BASEADA EM ESTUDOS ISOTÓPICOS Sm-Nd E SEU POTENCIAL PARA ANALISE ESTRATIGRÁFICA
DANTAS, E.
L.
PIMENTEL, M. M.
DO CARMO, D. A.
GIOIA, S.
MARUOKA, M.
Simpósio sobre o Cretáceo do Brasil y Simposio Sobre El Cretácico De America Del Sur,2, 2002, São Pedro, Estado De São Paulo. Boletim, 1: pp
Palavras chave: Alagoas, Albiano, Cretaceous, Paleoambiente, Área fonte de sedimentos
The Lower Cretaceous Alagamar Formation, northeastern Brazil is an oil source rock interval of the Potiguar basin. Different depositional environments have been proposed for the deposition of Alagamar Formation, normally involving the transition from continental settings at the base, to hipersaline lagoonal deposits at the top. Sediment provenance studies are useful to assess the source areas of detrital sediments and constrain depositional models for sedimentary basins. In this study we demonstrate that the Sm-Nd isotopic method is useful not only to investigate the sediment provenance, but also to be used as a tool for stratigraphic correlations between different drill cores and sedimentary sequences of the Potiguar Basin. Preliminary data from nine dark grey, organic-rich shale samples from distinct drill cores in the Alto de Macau (RN-6 and RN-1), Umbuzeiro graben (RN-7) and Ubarana graben (RN-9) yielded encouraging results, suggesting marked differences in source areas for distinct members of the Formation. The basal Upanema Member presents TDM model ages between 2.6-2.7 Ga, indicating provenance from Archaean to Paleoproterozoic basement. On the other hand, the upper Galinhos Member typically displays TDM model ages which are substantially younger, around 2.2 Ga. The middle layers Ponta do Tubarão shows TDM values which are roughly intermediate between the basal and upper units, with TDM values ranging from ca. 2.4 to 2.0 Ga. The isotopic variations are in agreement with biostratigraphy observations showing continuous change in palaeoenvironmental and palaeoclimatic conditions during deposition of different units. These changes were, therefore, accompanied by a shift in the source areas of the detrital sediments.