Análise de espículas de esponjas como indicadores paleoambientais em sedimentos lacustres no oeste da Bahia.

Abstract

The use of sponge spicules in sediments as proxy data has been successful in paleoenvironmental reconstructions. We recovered two sedimentary cores in two ponds located in San Francisco lowland in Western Bahia to understand the paleoclimatic and the lacustrine system dynamics. Sedimentary facies and granulometric analysis were perfomed. Also, organic matter content and presence of diatoms frustules were studied, besides the identification and quantification of sponge spicules detected in sediments, which were dated by 14C. The sediment age ranged between 8410 to 3929 yrs cal BP, corresponding to the Holocene. Sponge spicules of the following species were found: Dosilia pydanieli, Heterorotula fistula, Metania spinata, Oncoslera sp., Radiospongilla inesi and Tubella variabilis. Analysis of the results suggest that the two lakes have a standardized climate pattern alternating between drier and wetter climates in relation to the current climate condition. However, the two lakes differ regarding the sedimentation rate and the microfossil content the pond of the northern portion showed lentic and lotic alternated phases, indicating a paleodrainage at the beginning of the upper Holocene, while the evidences in the southern pond of the lake system there are only lentic phases. Such evidences suggest that other physiographic factors and climate influenced the dynamics of these lakes, such as structure, litholog and tectonics of the ponds substrates.