School Of Environment And Earth Sciences

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    Landscape and Climate Changes in Southeastern Amazonia from Quaternary Records of Upland Lakes
    (MDPI, 2023-03-27T00:00:00) Guimar�es, Jos� Tasso Felix; Sahoo, Prafulla Kumar; e Souza-Filho, Pedro Walfir Martins; da Silva, Marcio Sousa; Rodrigues, Tarc�sio Magevski; da Silva, Edilson Freitas; Reis, Luiza Santos; de Figueiredo, Mariana Maha Jana Costa; Lopes, Karen da Silva; Moraes, Aline Mamede; Leite, Alessandro Sab�; da Silva J�nior, Renato Oliveira; Salom�o, Gabriel Negreiros; Dall�Agnol, Roberto
    The upland lakes (ULs) in Caraj�s, southeastern Amazonia, have been extensively studied with respect to their high-resolution structural geology, geomorphology, stratigraphy, multielement and isotope geochemistry, palynology and limnology. These studies have generated large multiproxy datasets, which were integrated in this review to explain the formation and evolution of the ULs. These ULs evolved during the Pliocene�Pleistocene periods through several episodes of a subsidence of the lateritic crust (canga) promoted by fault reactivation. The resulting ULs were filled under wet/dry and warm/cool paleoclimatic conditions during the Pleistocene period. The multielement geochemical signature indicates that the detrital sediments of these ULs were predominantly derived from weathered canga and ferruginous soils, while the sedimentary organic matter came from autochthonous (siliceous sponge spicules, algae, macrophytes) and allochthonous (C3/C4 canga and forest plants and freshwater dissolved organic carbon) sources. Modern pollen rain suggests that even small ULs can record both the influence of canga vegetation and forest signals; thus, they can serve as reliable sites to provide a record of vegetation history. The integrated data from the sedimentary cores indicate that the active ULs have never dried up during the last 50 ka cal BP. However, subaerial exposure occurred in filled ULs, such as the Tarzan mountain range during the Last Glacial Maximum (LGM) and the Boca�na and S11 mountain ranges in the mid-Holocene period, due to the drier conditions. Considering the organic proxies, the expansion of C4 plants has been observed in the S11 and Tarzan ULs during dry events. Extensive precipitation of siderite in UL deposits during the LGM indicated drier paleoenvironmental conditions, interrupting the predominantly wet conditions. However, there is no evidence of widespread forest replacement by savanna in the Caraj�s plateau of southeastern Amazonia during the late Pleistocene and Holocene. � 2023 by the authors.
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    A Holocene record of floodplain development in the northernmost portion of the Araguaia Belt, southeastern Amazonia
    (Elsevier B.V., 2021-11-01T00:00:00) Tasso Felix Guimar�es, Jos�; Kumar Sahoo, Prafulla; Monteiro Pontes, Paulo R�genes; Negreiros Salom�o, Gabriel; Ribeiro da Costa, Francisco; Maria Queiroz de Melo, Adayana; Sousa da Silva, Marcio; Oliveira da Silva J�nior, Renato
    This work aimed to understand the drivers of landscape evolution and floodplain formation in a Precambrian Shield area of southeastern Amazonia. This area evolved during the Quaternary into a denudational system with strong structural control, which produced valley side slopes between the Araguaia Belt (AB) and the topmost Parna�ba basin and narrow floodplains in the lower Vermelho River. These floodplains developed at approximately 11215�11410 cal yr BP with the deposition of muds on the weathered basement rocks of the Couto Magalh�es Formation in the Ab (CMF) long before sea-level stabilization on the Amazon coast. The chondrite- and upper continental crust-normalized patterns, along with Al/Ti and La/Th ratios, clearly indicate that muds were derived from the CMF-AB. The strong positive correlation of most of the trace elements and rare earth elements (REEs) with Al and Ti indicates their control by aluminous clay phases and a similar transport process. Overbank flows of the Vermelho River resulted in the deposition and vertical accretion of sands from the fluvial channel over the floodplain, forming discontinuous marginal levees after 4520�4710 cal yr BP. The accreted sands with the predominance of Si, Zr, and Hf and the depletion of most of the major and trace elements are likely associated with quartz enrichment and a strong sorting of heavy minerals, which is also supported by Al2O3/SiO2 vs Fe2O3/SiO2. The tributaries of the lower Vermelho River were active until 3890�4095 cal yr BP, and subsequently, the channel was abandoned as a result of the filling process. At approximately 3440�3560 cal yr BP, the floodplain was influenced by prolonged and severe droughts that fully exposed the muddy deposits and caused the enrichment of Fe-Mnoxyoxide phases. The affinity of most of the potentially toxic elements with Al signifies that these floodplain deposits are a natural record for geochemical background studies. � 2021 Elsevier B.V.