Calcareous Nanofossils in the Upwelling Area of Cabo Frio, Brazil

Abstract

Calcareous nannofossils are a group of microfossils with living representatives and an abundant fossil record in marine sediments. The majority of researches focused on these fossils are centered in deep-sea regions (slopes and ocean basins), and are of interest for the oil industry for their application in biostratigraphy sections of high resolution and in paleoenvironmental reconstructions. In Brazil, efforts are still incipient on the study of nannofossils in the coastal and the continental shelf areas. Thus, this article aims to characterize the assembly of calcareous nannofossils present in cores of the coastal upwelling area of Cabo Frio and evaluate their potential as a paleoenvironmental indicator in the region. For this purpose, blades with the material of the core CF02-01B (23º16'S and 41º48'W) were prepared, corresponding to 268 cm of the sedimentary profile of the Cabo Frio shelf. Twenty-seven calcareous nannofossil species were found, with an abundant predominance of the taxa Emiliania huxleyi, Florisphaera profunda and Gephyrocapsa oceanica. Based on the distribution profile of these taxa and their paleocology, it became possible to subdivide the first 151 cm of the sedimentary profile into four intervals: 1 (~2800 to ~2300 AP years) and 3 (~1800 to ~1000 AP years) representative of strenghtening periods of the upwelling system in the area with predominand action of the ACAS, as well as lower temperatures of the superficial waters, higher rates of nutrients and growth in productivity; and 2 (~2300 to ~1800 AP years) and 4 (~1000 to ~700 AP years) representative of the weakening of the upwelling system in Cabo Frio, with predominant influence of the CB, as well as warmer superficial waters, with few nutrients and low productivity. Therefore, this research confirmed the importance and efficiency of the study of calcareous nannofossils in coastal regions for paleoenvironmental reconstructions.