Paleohydrology and paleoclimate of the past 33,000 years at the Tamandua River, central Brazil

Deposits of the Tamandua River contain evidence for four major paleohydrologic stages in the last 33,000 years. A wet period between 33,000 and 20,000 C-14 yr B.P. produced a high water table that allowed organic-rich deposition in the Tamandua valley. A dry interval 17,000-10,000 C-14 yr B.P. produced sandy deposits of braided channels and alluvial fans. River aggradation during this period probably resulted from a high sediment load promoted by intense slope erosion and from hash floods. A wet period after 10,000 and before 6000 C-14 yr B.P. was marked by reduced slope erosion and by high discharge that led to erosion of the valley fill. During that time forests developed widely in Brazil. A drier climate after 6000 C-14 yr B.P. caused a reduction of discharge but allowed a high water table to be maintained. (C) 1997 University of Washington.