Holocene Environmental Changes from the Rio Curuá Record in the Caxiuanã Region, Eastern Amazon Basin

Abstract

Holocene environments have been reconstructed by multiproxy studies of an 850-cm-long core from Rio Curuá dating to >8000 14C yr B.P. The low-energy river lies in the eastern Amazon rain forest in the Caxiuanã National Forest Reserve, 350 km west of Belem in northern Brazil. Sedimentological, mineralogical, and geochemical dates demonstrate that the deposits correspond to two different environments, sediments of an active river before 8000 14C yr B.P. and later a passive river system. The pollen analytical results indicate four different local and regional Holocene paleoenvironmental periods: (1) a transition to a passive fluvial system and a well-drained terra firme (unflooded upland) Amazon rain forest with very limited development of inundated forests (várzea and igapó) (>7990–7030 14C yr B.P.); (2) a sluggish river with a local Mauritia palm-swamp and similar regional vegetation, as before (7030–5970 14C yr B.P.); (3) a passive river, forming shallow lake conditions and with still-abundant terra firme forest in the study region (5970–2470 14C yr B.P.); and (4) a blocked river with high water levels and marked increase of inundated forests during the last 2470 14C yr B.P. Increased charcoal during this last period suggests the first strong presence of humans in this region. The Atlantic sea level rise was probably the major factor in paleoenvironmental changes, but high water stands might also be due to greater annual rainfall during the late Holocene.

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

“…Similar environment was found for the Calado lake located 150 km far way (Behling et al 2001). Nevertheless variable environmental condition were detected in the Amazonia during the time, drier in the central portion between 4000 and 3500 14 C yr BP and 2100 and 700 yr 14 C BP (Absy 1979) and in 4000 14 C yr BP (Moreira et al 2009) but also humid in 6000 and 2500 yr 14 C yr BP in the east (Behling and Costa 2000), in the west since 8280 14 C yr BP (Behling et al 2001) and in the central Amazonia in 4600 14 C yr BP (Irion et al 2006). These insights suggest that the evolution of both lakes may reflect autogenic processes under humid rainforest condition and their geochemical and palynologic history are consequence of local environmental conditions.…”

Dinâmica do ecótono floresta-campo no sul do estado do Amazonas no Holoceno, através de estudos isotópicos e fitossociológicos

“…Estudos palinológicos (Absy & Van der Hammen, 1976;Absy, 1985;Sanford et al, 1985;Ledru, 1992Ledru, , 1993Behling & Costa, 2000, geomorfológicos (Servant et al, 1981), sedimentológicos Turcq et al, 1993;Sifeddine et al, 1994Sifeddine et al, , 2001Sifeddine et al, , 2003 e isotópicos (Victoria et al, 1995;Desjardins et al, 1996;Pessenda et al, 1996aPessenda et al, ,b,c e 1998aPessenda et al, , 2001Pessenda et al, , 2004Gouveia et al, 1997Gouveia et al, , 1999Gouveia et al, , 2002Freitas et al, 2001) indicam a ocorrência de variações paleoclimáticas na Bacia Amazônica e em outras áreas do Brasil e da América do Sul, durante o Quaternário tardio. Paleoclimas mais secos que o atual, provavelmente, dominou algumas áreas da Bacia Amazônica, favorecendo a substituição da floresta tropical por vegetação do tipo campo.…”

Holocene history of a lake filling and vegetation dynamics of the Serra Sul dos Carajás, southeast Amazonia

“…During the late Holocene, arboreal vegetation became more prominent due to the return of wetter climate, most likely similar to those prevailing today (Pessenda et al 1998, Behling and Costa 2000, Freitas et al 2001, Bush et al 2007, Mayle and Power 2008. The upland lakes of the Serra dos Carajás, southeast Amazonia, also registered this drier period, as indicated by the lower lake levels based on low detrital input into the lake basins associated with enrichment of Hg, Se, organic carbon and evaporite minerals (Sifeddine et al 2001, Cordeiro et al 2008, Turcq et al 2002, Guimarães et al 2016.…”