A stable isotope and macro-charcoal sediment record spanning the Pleistocene-Holocene transition from Maple Pond in the southern Shenandoah Valley, Virginia, USA

Abstract

This study presents a paleoenvironmental analysis of a 147-cm sediment core from Maple Pond, a sinkhole pond within the Shenandoah Valley Sinkhole Pond complex at the base of the Blue Ridge in central Virginia. The results document more than 15,000 years of continuous sediment accumulation, fire history, and environmental variability from the Late Pleistocene to the present. Stable carbon isotope ratios (δ13C: -29‰ to -27‰) and atomic C:N ratios (11-36) indicate terrestrial C₃ vegetation as the primary source of organic matter during the Late Pleistocene and early Holocene (15,000–8,000 cal yr BP), followed by a transition toward nitrogen-rich aquatic and wetland inputs during the mid-to-late Holocene. Loss-on-ignition analysis records organic content rising from ~10% in basal sediments to 35–40% in the upper core, reflecting a transition from minerogenic deposition to sustained organic accumulation. Macroscopic charcoal concentrations reveal a mid-Holocene maximum (40–49 cm depth; ~6,000–5000 cal yr BP), attributed to increased regional fire activity, possibly related to warmer drier conditions during the Mid-Holocene Maximum and a shift to fire-adapted forest (oak, hickory, pine). A smaller charcoal peak between 120 and 130 cm may relate to rapid warming at the end of the Younger Dryas, a shift back to cold conditions around 12,000 years ago. The predominance of lower charcoal abundance (<100 fragments/cm3) characterizing the majority of the sequence suggests a long record of frequent, low-intensity fire regimes characteristic of presettlement fire-adapted Appalachian forests. Geochemical and fire history patterns at Maple Pond demonstrate broad consistency with paleoenvironmental reconstructions from nearby sites (Browns Pond, Spring (aka Hack) Pond, Twin Pond and Cranberry Glades), supporting the interpretation that sinkhole ponds and wetlands throughout the Shenandoah Valley underwent similar environmental evolutions across major Late Quaternary climatic transitions.