Navegando por Assunto "Palinologia - Rio Grande do Norte"

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Acesso aberto (Open Access)
Detecção de mudanças paleoambientais no litoral do Rio Grande do Norte (RN) durante o Holoceno médio e superior
(Universidade Federal do Pará, 2017-08-16) BATISTA, Edson José Louzada; FRANÇA, Marlon Carlos; http://lattes.cnpq.br/8225311897488790
The vegetation dynamics during the Holocene on the coastal region of Rio Grande do Norte (RN) was characterized by mangrove establishment, expansion and contraction. The dynamics of this vegetation is mainly related to the sedimentary dynamics and to the relative sea level change (RSL) recorded for this period. During the last millennium, sedimentary process controlled the vegetation dynamics along stratigraphic profiles formed by sequences of active tidal channels, followed by abandonment. Therefore, based on grain size, sedimentary structures, pollen data, isotopic data (δ13C and δ15N), C/N ratio and 14C dating of the sedimentary organic matter of two cores (NAT 6 and NAT 8) sampled in the tidal plain, shows a paleoenvironmental model since mid- to late-Holocene (~7 k yr BP to modern), described by four facies associations: (A) estuary/channel, represented by massive sandy deposits (facies Sm) and mud deposition; (B) abandoned channel, represented by the wavy heterolithic bedding (facies Hw), lenticular heterolytic bedding (facies H1) and small intervals with massive sand (facies Sm); (C) active channel, corresponding to massive sandy deposits (facies Sm); and (D) low marsh (mangroves/herbaceous plain and palms), represented by clay deposits with lenticular heterolithic bedding (facies Hl). In this context, short-time (millennium/century) changes between mangroves and other associated vegetation in this region are not necessarily related to RSL or to the climatic changes (allocyclic process), but to the sedimentary dynamics (autocyclic process) must have controlled mainly the pollen assembly along the stratigraphic profiles studied.
Acesso aberto (Open Access)
A dinâmica dos manguezais durante o Holoceno tardio na foz do rio Ceará-Mirim, Rio Grande do Norte
(Universidade Federal do Pará, 2020-10-15) NUNES, Sérgio Patrick Dias Queiroz; FRANÇA, Marlon Carlos; http://lattes.cnpq.br/8225311897488790; 8225311897488790
This paper aims to debate the impacts of climate change on subtropical mangroves during late Holocene, on the coast of the state of Rio Grande do Norte (RN) and to discuss the environmental conditions for the establishment, expansion, and contraction of mangroves. Based on the samples collected from the cores (NAT 3 AND NAT 5) to study palynological groups, data from the optical space (Landsat), sedimentary facies and multi-proxy analysis (δ13C, δ15N, TOC, TN, C:N ratio), synchronized with three 14C dating ages. The main result of this research was the succession of mangroves, divided into three palynological phrases that suggest the development of three facies associations: (1) tidal channel and (2) vegetated plain - herbs/mangrove (3) herbaceous plain. The first phase between at least ~ 4500 and ~ 2915 cal yr BP was colonized by herbs, palms, and trees and shrubs on the bank of the estuary and by mangroves, of the Laguncularia type, followed by Avicennia and Rhizophora. With dissolved organic carbon, C3 terrestrial plants influence organic matter with δ13C values between -29.7 ‰ and -26.8‰, δ15N with x̅ = 3.8‰ and C:N values around 21.2. The second phase between ~2915 and ~660 cal yr BP characterized by the establishment of the mixed tidal plain dominated by herbaceous vegetation and by the expansion of mangroves represented by Rhizophora pollen between ~2915 cal yr BP and 2814 ± 29 cal yr BP with the increase of plants C3 and dissolved organic matter (COD) in fresh/estuarine water (δ13C x̅ = -26.9 and -29.4‰; δ15N x̅ = 3.86 and C:N around 12.3). The third phase is marked by a mangrove retraction evidenced by the decrease in Laguncularia, followed by Avicennia and Rhizophora, the dissolved organic matter had a greater influence of freshwater/estuary, and terrestrial plants (C3 plants) during the last 699 ± 35 cal yr BP. Near the surface (<15 cm) Rhizophora pollen occurs, indicating the establishment of this genus in recent decades, under modern environmental conditions (δ13C x̅ = -29 and -28.8‰; δ15N x̅ = 2.55 and C:N around 24.5 ). The data obtained in the isotopic and elementary analyzes indicate sedimentary organic matter of terrestrial origin, with the presence of C3 photosynthetic cycle plants, suffering a possible aquatic and estuarine influence, however, in the sedimentary sequences formed by lenticular heterolytic deposits to be correlated with the absence and decrease of mangrove vegetation in both cores. The data from the space-time analysis indicated an expansion of the area of mangroves, so this variation in the dynamics of mangroves can be directly linked to climate changes and the relative sea level at current levels and during the last three decades.