Plant remains, alluvial chronology, and cave speleothem isotopes indicate abrupt Holocene climatic change at 6 ka in midwestern USA

Sediments along 1st-5th-order streams in Midwestern USA contain excellent r ecords of abrupt climatic change in the Holocene. Cutbank exposures provide "snapshots" of areal paleovegetation based on assemblages of well-preserve d pollen and plant macrofossils; when these sites are radiocarbon dated aci d arranged chronologically, a detailed picture of Holocene vegetational cha nge emerges that is consistent with regional patterns. Lithologically disti nct alluvial sediments and periods of rapid change from aggradation to entr enchment occur at intervals of rapid vegetational change, and are coeval wi th changing values of carbon isotopes from both cave speleothems and stream alluvium, indicating Brat climate is the major forcing function. (C) 2001 Elsevier Science B.V. All rights reserved.