Pleistocene and interdisciplinary reconstitution of lacustrine deposits in the Serra Sul de Carajás, southeastern Amazonia

• Autor(a) principal: Reis, Luiza Santos
• Data de Publicação: 2020
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/64/64134/tde-19082021-163508/
• topic: Ceras foliares; Isótopos estáveis; Late Quaternary; Paleoclima; Paleoclimate; Paleovegetação; Paleovegetation; Plant waxes; Quaternário Tardio; Stable isotopes

Several studies have been performed within the Amazon basin in order to better understand the effects of Northern Hemisphere climatic events over the rainfall regime and vegetation dynamic. However, there is no broad consensus, since most studies is based only on pollen data. Due to the limitations of this technique, a multiproxy approach is essential to obtain a better interpretation of climatic variations. In this way, molecular and isotopic analyses of plant waxes (?13C and ?D) and bulk organic matter (?13C and ?15N) together with sedimentary facies, palynological, multi-elemental geochemistry, micro- and macro-charcoal fragments analyses were performed on sedimentary cores from Lake Amendoim and revealed important environmental changes over the last ~22 ka. Low sedimentation rate and siderite precipitation episodes during the Last Glacial Maximum (LGM) and Late Glacial, besides mixed C3/C4 plant communities and enriched plant wax ?D, evidence less humid conditions at Carajás. The occurrence of cool-adapted taxa such as Podocarpus, Alnus, and Hedyosmum also reveals cooler conditions during this interval, attesting the key role of changes in temperature over vegetation composition and distribution inside the Amazon basin. During LGM, colder sea surface temperature (SST) probably caused a decrease in the Atlantic Ocean moisture supply to northern South America which led to reduced precipitation amount. The Pleistocene-Holocene transition and the beginning of the Early Holocene are characterized by the large occurrence of fire events and precipitation of siderite nodules, besides reduced detrital input into the lake basin. On the other way, the data also show a higher concentration of pollen grains from forest formation and palms as well as depleted plant wax ?D and ?13C values, indicating the onset of seasonal features. A well-marked episode of intense precipitation between 11-10 ka shows a high correspondence with the Heinrich Stadial 0 and the Holocene Thermal Maximum, evidencing their influences over the rainfall regime within Amazonia. From Early to Late Holocene, a pronounced increase in C3-dominated community together with a steady decrease in plant wax ?D and ?13C values points to an expansion of ombrophylous forest over the plateau slopes in Serra Sul de Carajás and a change to predominantly wet climatic conditions similar to the current one from the last 5 ka