Holocene environmental changes from the Rio Curua record in the Caxiuana region, eastern Amazon Basin

Holocene environments have been reconstructed by multiproxy studies of an 850-cm-long core from Rio Curua dating to >8000 C-14 yr B.P. The low-energy river lies in the eastern Amazon rain forest in the Caxiuana 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 C-14 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 (varzea and igapo) (>7990-7030 C-14 Yr B.P.); (2) a sluggish river with a local Mauritia palm-swamp and similar regional vegetation, as before (7030-5970 C-14 YI. B.P,); (3) a passive river, forming shallow lake conditions and with still-abundant terra firme forest in the study region (5970-2470 C-14 yr B.P.); and (4) a blocked river with high water levels and marked increase of inundated forests during the last 2470 C-14 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. (C) 2000 University of Washington.