Estudo da paleoprodutividade do estuário de Macuse durante o holoceno

Abstract

The present research had as main objective to understand the variations of the paleoproductivi-ty in the Macuse estuary, in a recent geological past (Holocene), through the description of: organic carbon, calcium carbonate content, origin of organic matter as well as sediment granu-lometry. Two testemhos were collected along the estuarine channel, the samples were submit-ted to geochemical and granulometric analyzes in the Laboratory. The granolometric analyzes were carried out by means of the Stock-based sedimentation method. For organic carbon, Walkey and Black methods were used, total nitrogen was determined from the Kjeldahl meth-od and, finally, calcium carbonate was determined based on the weight differences of the sam-ples before and after the reaction with hydrochloric acid. In general, values of organic carbon ranging from 0.53 to 2.1% were obtained, at the two sam-pling points, for the grain size, of the three classes obtained (silt, clay and sand), the silt was more representative at all points. The values of the Corg / Ntotal ratio ranged from 3.9 to 23%, with higher values being higher than 10, thus considering a mixture of organic matter of conti-nental and marine origin, evidencing that the estuary has received mainly organic matter of continental origin evidenced by the higher values of the Corg / Ntotal ratio, the CaCO3 values fluctuated from 2.2 to 6.0%. The results of the analyzes show evidence of variations in paleoproductivity with more productive periods characterized by high values of organic car-bon, calcium carbonate, sediments of silt class and clay. There is a moderate positive relation-ship between silt and organic carbon, which suggests a dependence on silt in the preservation of organic carbon.