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 8 50-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 Fores t Reserve, 350 km west of Belem in northern Brazil. Sedimentological, miner alogical, 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 ind icate four different local and regional Holocene paleoenvironmental periods : (1) a transition to a passive fluvial system and a well-drained terra fir me (unflooded upland) Amazon rain forest with very limited development of i nundated forests (varzea and igapo) (>7990-7030 C-14 Yr B.P.); (2) a sluggi sh 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 l ake conditions and with still-abundant terra firme forest in the study regi on (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 prese nce of humans in this region. The Atlantic sea level rise was probably the major factor in paleoenvironmental changes, but high water stands might als o be due to greater annual rainfall during the late Holocene. (C) 2000 Univ ersity of Washington.