Biostratigraphy based on foraminifers from the continental rise of the northern coast of the State of Bahia, Brazil

Abstract

The Quaternary period is characterized by environmental changes, widely recorded in the ocean basins due to continuous, slow sedimentation. Considering this condition, this paper analyzes the vertical distribution of the foraminiferal microfauna in core REG-114, collected at the foot of the continental rise off the north coast of Bahia, and presents the results of biostratigraphic analysis of fossil assemblages of these organisms. The core was collected at a depth of 2,640 m in 2008. In the laboratory, eight samples extracted at intervals of 20 cm were treated according to the standard methodology for carbonate sediments. In all samples the most abundant fraction was clay (>; 75%). Along the sedimentary column 63 species of foraminifera, belonging to 35 genera, 28 benthic and 7 planktonic, were identified. The main species found were: Globigerinoides ruber (43.96%), G. trilobus (11.42%), G. elongatus (11.33%) Globigerina bulloides (6.58%), Globigerinoides saculifer (6.04%) and Globorotalia trucatulinoides (5.21%). On the basis of fluctuations in the planktonic species, it was possible to identify two biostratigraphic zones (Zones Y and Z) and two subzones (Y1 and Y2). The boundary between these subzones was established by the decline of the species Globorotalia trucatulinoides and G. crassaformis, characteristic of cold water, and an increase in Globigerinoides saculifer, characteristic of warm water, indicating abrupt warming of the water mass. Associated with this, the distribution of planktonic species, with percentages >; 90%, indicates that sediments were not remobilized on the ocean floor, thus confirming the environmental stability in this region, as characterized by the low sediment supply.