This work aims to identify the mangrove dynamics in the North coast of Espírito Santo State, close to São Mateus (ES), during the Late-Holocene, using the depositional identification of paleoenvironments and the paleoflora, further a characterization of the sources of sedimentary organic matter and chronological determination of the events in the study area. In order to perform an integrated analysis of the palynological, C-14 data, sedimentological and geochemical data (δ13C, δ15N, C:N and C:S ratio), two sediment cores (MBN and LI-34) were sampled with a peat core sampler. The sedimentary profiles were extracted from mangroves close to the mouth of São Mateus and Barra Seca rivers. The deposits age was around ~2662 cal yr BP, characterized by sand cross laminations (facies Sc), lenticular heterolithic deposits (facies Hl), sand with parallel lamination (facies Sp), wavy heterolytic deposits (facies Hw), flaser heterolithic deposits (facies Hf and Sf), massive sand (facies Sm), sand parallel laminations (facies Smh facies), and mud with parallel laminations (facies Ml), with shells and vegetal fragments. The first facies association (A) consists of an estuarine point bar (~2662 and ~2215 cal yr BP), the second (B) consists of a tidal flat with mangrove/herbs vegetation, since at least ~2215 cal yr BP, and finally the third (C) such as an inlet, a typical distal estuarine channel (~1337 cal yr BP). The geochemical results indicate a mixture of C3 and C4 plants, near the basal portions, with a subsequent predominance of C3 plants towards the top of the samples, besides the presence of organic matter of marine/estuarine. The C:N ratio indicates an oscillation between the aquatic and terrestrial influences, corroborating the values of the C:S ratio (0.02-5.18), which also revealed a mixture of organic matter with marine/aquatic and terrestrial influence. The pollen results showed that the mangrove in this region has been present for at least 2662 cal yr BP, however, changes in its biodiversity have been observed, since currently this ecosystem is colonized mainly by the genus Laguncularia in the region of the mouth of the Barra Seca river, different from previous periods, where there was full development of Rhizophora and Avicennia trees. However, on the mouth of São Mateus river, the genus Rhizophora beginning the mangrove and after Avicennia. Thus, through of this study, it is possible to infer that there were no significant climatic oscillations in this region, however, the stabilization of the relative sea-level during the late-Holocene, as well as the sedimentary dynamics may be controlling the expansion/contraction process of these mangroves.
|
