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 records of abrupt climatic change in the Holocene. Cutbank exposures provide “snapshots” of areal paleovegetation based on assemblages of well-preserved pollen and plant macrofossils; when these sites are radiocarbon dated and arranged chronologically, a detailed picture of Holocene vegetational change emerges that is consistent with regional patterns. Lithologically distinct alluvial sediments and periods of rapid change from aggradation to entrenchment occur at intervals of rapid vegetational change, and are coeval with changing values of carbon isotopes from both cave speleothems and stream alluvium, indicating that climate is the major forcing function.