School Of Environment And Earth Sciences

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    Hydroclimate and vegetation changes in southeastern Amazonia over the past ?25,000 years
    (Elsevier Ltd, 2022-04-07T00:00:00) Reis, Luiza Santos; Bouloubassi, Ioanna; Mendez-Millan, Mercedes; Guimar�es, Jos� Tasso Felix; de Ara�jo Romeiro, Luiza; Sahoo, Prafulla Kumar; Pessenda, Luiz Carlos Ruiz
    Stable isotope analysis of plant waxes (?13Cwax and ?Dwax) along with detailed pollen data provide a new perspective on vegetation and precipitation variability in Serra Sul de Caraj�s, southeastern (SE) Amazonia, over the past ?25 cal kyr BP. The ?Dwax record indicates drier conditions during the Last Glacial Maximum (LGM) and a transition to wetter conditions into the Holocene, while the ?13Cwax data reveal that vegetation did not experienced C3/C4 shifts and remained dominated by C3-plant communities. Under glacial conditions C3-savanna was prominent on the Serra Sul plateau with tropical forest areas limited to the lower slopes. Tropical forests expanded upslope and forest patches developed on the plateau as a response to more humid and warmer conditions during the Holocene. Pollen data indicate a shift towards more open landscape of savanna, woodlands, and open forests during the mid-Holocene. The ?Dwax record exhibits a distinct moisture variability during the Holocene, not always coherent with the vegetation data (pollen), especially during the mid-Holocene interval. Our study confirms the complexity and the overall lack of coherence among Holocene moisture proxy records throughout the monsoon domain in South America and suggest that Holocene local moisture conditions might not follow the regional monsoonal variability. Our data further stress the need for more multi-proxy reconstructions of hydroclimate patterns in SE Amazonia. � 2022 Elsevier Ltd
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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.