Late Pleistocene and Holocene environments of the Southeastern United States from the stratigraphy and pollen content of a peat deposit on the Georgia Coastal Plain

A 5.4 m peat core from the Sandy Run Creek (SRC) valley in the upper Coastal Plain of Georgia shows that before 30 ka the valley had an aggradational sandy floor with shallow swales and low ridges of 1–2 m amplitude suggesting a braided stream pattern and a low water table. The climate from 30–25 ka was cool and dry and the vegetation open grassland with stands of pine and spruce that produced few fires. At ca. 16 ka a warmer, wetter climate caused SRC to meander and incise the valley fill removing some previously deposited sediment at the site of our peat core so that sediments of 13 ka rest directly on sediments deposited at 25 ka. After ca. 13 ka higher groundwater levels initiated vertical accretion of floodplains allowing peat accumulation in shallow depressions across the valley. Pollen from the Younger Dryas period (ca. 13–11 ka) indicates a cool, moist environment of open oak woodland, mesic trees, riparian populations of alder, and reduced levels of pine. By the early to mid Holocene, tupelo and oak dominated over pine indicating wetter conditions, while sand stringers in peat record periodic heavy rains, an elevated water table, and intervals of substantial runoff. Cooling after ca. 4.5 ka brought drier and more variable conditions. Fires increased and southern pine replaced tupelo and oak. The absence of sand stringers in peat younger than 4.5 ka indicates fewer intense rainfall events.