Environmental changes in the western Amazônia: morphological framework, geochemistry, palynology and radiocarbon dating data

Abstract

The sediments from the Coari lake, a "terra firme" lake sculpted into Plio-Pleistocene deposits, and the Acará lake, a flooding-type lake developed on Quaternary sediments in the floodplain of the mid-Solimões river, in the western Amazônia, Brazil, were studied to investigate the environmental condition of their developing. This study includes mineral composition, geochemistry, Pb isotope, palinology, radiocarbon-age and morphological framework of the lakes obtained from SRTM satellite images. The geological and the environmental conditions in the two lakes are highly variable and suggest that their evolution reflect autogenic processes under humid rainforest condition. Although kaolinite, quartz, muscovite, illite, and smectite are the main minerals in both lakes, the geochemistry indicates distinct source, the Acará lake sediments have higher concentrations of Al 2 O 3 , Fe 2 O 3 , FeO, CaO, K 2 O, MgO, Na 2 O, P 2 O 5 , Ba, V, Cu, Ni, Zn, Pb, Sr, Li, Y and La and have more radiogenic Pb than the Coari lake sediments. The radiocarbon ages suggest that at 10160 yr BP the Coari lake started to be developed due to avulsion of the Solimões river, and the Acará lake was formed by the meander abandonment of Solimões river retaining its grass dominated shore at ca. 3710 yr BP.

Impact of mid- to late Holocene precipitation changes on vegetation across lowland tropical South America: a paleo-data synthesis

“…The sites from across central and western lowland Amazonia show that the HETF biome stayed largely intact in this region throughout the mid- to late Holocene. Evidence of this biome stability comes from consistent HETF pollen signals from large lake sites (reflecting regional scale vegetation signals; e.g., Behling et al, 2001c; Horbe et al, 2011) and small sites (reflecting local vegetation signals; e.g., Liu and Colinvaux, 1988; Behling et al, 1999; Bush et al, 2004b). Even if moisture levels were slightly lower during the mid-Holocene, it is clear this was not enough to cause biome turnover.…”

“…Evidence of this biome stability comes from consistent HETF pollen signals from large lake sites (reflecting regional scale vegetation signals -e.g. Behling et al, 2001c;Horbe et al, 2011) and small sites (reflecting local vegetation signals -e.g. Liu and Colinvaux, 1988;Behling et al, 1999;Bush et al, 2004b).…”

“…= pollen analysis; 2 = charcoal analysis; 3 = isotopic analysis; 4 = physio-chemical analysis. (Irion et al, 2006) 2* Acará lake1,3,4 3°39.32'S 62°42.07'W (Horbe et al, 2011) 3* Coari Lake1,3,4 4°3.85'S 63°18.11'W (Horbe et al, 2011) 4 Lago Rogaguado1,2 12°59.84'S 65°59. 16'W (Brugger et al, 2016) 5 Laguna Orícore1,2 13°20.74'S 63°31.…”

Holocene paleohydrology of Quistococha Lake (Peru) in the upper Amazon Basin: Influence on carbon accumulation

“…Floodplains are extremely complex and dynamic systems (Moreira-Turcq et al, 2004) and their constant changes are influenced by neotectonic movements and/or hydrological changes dependent on climate and vegetation cover. These changes can have great impact on the morphology of the basin, causing avulsions, newly impeded floodplain lakes, and island development (Franzinelli and Latrubesse, 1993;Mertes et al, 1996;Costa et al, 2001;Latrubesse and Franzinelli, 2002;Horbe et al, 2011).…”

Análise multitemporal do sistema fluvial Solimões-Amazonas entre os tributários Purus e Negro, Amazônia Ocidental, Brasil

“…Os terraços estão dispostos em faixas paralelas às margens do sistema fluvial Solimões-Amazonas e são contínuos por dezenas de quilômetros. A presença de paleocanais sobre os terraços (Mertes et al, 1996;Latrubesse e Franzinelli, 2002;Horbe et al, 2011;Gonçalves Júnior, 2013) evidencia períodos de avulsão e retomada da sedimentação e, juntamente com a estratificação heterolítica, ajuda a caracterizar a predominância do estilo fluvial meandrante do sistema fluvial Solimões-Amazonas no Pleistoceno Superior-Holoceno Inferior, que difere do atual estilo anastomosing-anabranching, que começou a se desenvolver a partir de 6.000 anos AP (Soares, 2007). Segundo este autor, a mudança de estilo meandrante para anastomosado foi associada à ascensão do nível de base regional, em função da subida do nível do mar e/ou movimentos tectônicos.…”