Phytolith and Carbon Isotope Evidence for Late Quaternary Vegetation and Climate Change in the Southern Black Hills, South Dakota

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Abstract
Analyses of phytoliths and carbon isotopes document change in late Quaternary grasslands in the Red Valley of the southern Black Hills. Late Pleistocene grassland composition was equivalent to the C3grass parklands of modern central Alberta. The rise of mixed grassland occurred rapidly between 11,000 and 9000 yr B.P. Early Holocene mixed grasslands included both short and tall C4grasses. A mid-Holocene erosional unconformity (ca. 8000 to 4500 yr B.P.) precludes phytolith or isotope analysis, but suggests lack of vegetation and landscape denudation caused by a drier climatic. Basin-wide stability and soil development followed the erosional episode (ca. 4500 to 3600 yr B.P.). Mesic-adapted C4panicoid grasses increased during this period of soil development. Low-magnitude fluctuation in the C4-dominated mixed grassland occurred throughout the late Holocene (3600 yr B.P. to present). Rise in δ13C values during the last 1000 yr without corresponding change in phytoliths may indicate a decrease in woodlands caused by increased fire frequency.