VARIAÇÃO DA ENERGIA E SUA REPERCUSSÃO NAS CARACTERÍSTICAS COMPOSICIONAIS E TEXTURAIS EM SEDIMENTOS PRAIAIS ATUAIS: EXEMPLO DA COSTA LESTE DA BAÍA DE TODOS OS SANTOS, BAHIA, BRASIL

Abstract

ENERGY VARIATION AND ITS REPERCUSSION ON THE COMPOSITIONAL AND TEX-TURAL CHARACTERISTICS IN RECENT BEACH SEDIMENTS: EXAMPLE OF THE EAST COAST OF TODOS OS SANTOS BAY, BAHIA, BRAZIL. The beach belt on the east coast of Todos os Santos Bay shows a great variability in mechanical energy which has a strong repercussion on the compositional and textural characteristics of its sediments. In terms of composition, the energy level controls the relative amount of skeletal carbonate fragments in its sediments. Texturally, the main effect of the energy variation is to change the pattern of the cumulative grain-size curves. Based on these patterns the following zones of distinct energy levels have been identified: 1. high-energy zones, where water turbulence is strong enough to transport in suspension grain of diameter up to 0.25 mm; 2. moderate-energy zones, where the turbulence is just enough to prevent the deposition of grains smaller than 0.031 mm-the size range between 0.031 mm and 2 mm are transported by saltation; 3. low-energy zone with a weak turbulence such that the sedimentation of mud particles can also take place. Representative sedimentary parameters, such as median, standard deviation and skewness are strongly influenced by energy variations within more restrict sectors where the textural characteristics of the source rock are relatively homogeneous.