A SEDIMENTAÇÃO NA BAIA DE ARATU, BAHIA

ABÍLIO CARLOS DA SILVA PINTO BITTENCOURT, ARNO BRICHTA, ENRICO DI NAPOLI

Resumo


The bay of the Aratu is formed by four parts: the principal water body, the channel zone, the margins and the rivers'mouth. The sedimentation is mostly greyish-olive, silty-clay, containing few shell debris characterizing, in general, a weak energy sedimentary environment. In the margins and mouths of rivers the sediments are coarser and are constituted by fine sand and silt, always mixed with clay. In the narrower part of the channel the clay content (10-30%) is smaller than in the other areas. Biogenic deposits are found mostly in shallow water, with predominant molluscs, some of which are considered to be relics. Drilling data allowed the reconstruction of the Quaternary events in two parts: 1 - transgressive phase during the "Flandrian" (6.000-5.000 years) up to 2.83 m above the present mean sea level. It is characterized by bluish-grey, silty-clay sediments, with shell debris, reaching up to 30m. in thickness; in this phase there were developments of biogenic deposits related to climatic variations; 2 - regressive phase with continuous lowering until the present sea level with the rivers carrying coarse materials to their mouths.

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