Spruce and tamarack logs dating from the Younger Dryas and Early Holocene (YD–EH; ∼12.9–11.3k cal a BP) were found at Bell Creek in the Lake Ontario lowlands of the Great Lakes region, North America. A 211‐year tree‐ring chronology dates to ∼11 755–11 545 cal a BP, across the YD–EH transition. A 23‐year period of higher year‐to‐year ring‐width variability dates to around 11 650 cal a BP, infers strong regional climatic perturbations and may represent the end of the YD. Tamarack and spruce were dominant species throughout the YD–EH interval at the site, indicating that boreal conditions persisted into the EH, in contrast to geographical regions immediately south and east of the lowlands, but consistent with the Great Lakes interior lowlands. This infers that Bell Creek was at the eastern boundary of a boreal ecotone, perhaps a result of its lower elevation and the non‐analog dynamics of the Laurentide Ice Sheet. This finding suggests that the ecotone boundary extended farther east during the YD–EH transition than previously thought.

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cumulation and Possible Preservation The Appalachian landscape provides an excellent opportunity to examine an environment that promotes sediment subsidence, accumulation and possible preservation: mantled karst. Mantled karst exists along the Blue Ridge-Great Valley margin from south-central Pennsylvania to central Virginia. Topographically, the mantled karst contains low-relief irregular topography with abundant surface depressions, some of which contain ponds, and in places lacks continual surface drainage and springs. Sand and gravel quarries along the valley margin expose predominantly stream flow, hyperconcentrated flow, debris flow and hillslope (colluvial) deposits that mantle karstic Paleozoic bedrock and carbonate residuum. Unconformable and sometimes erosive contacts between carbonate residuum and clastic sediments, and soft-sediment deformation features have been observed within exposures suggesting subsidence into accumulation and/or preservation space created by geochemical dissolution and collapse that continues today. The likelihood of long-term survival in the geological record is dependent upon the relationship between the subsiding sediment and geomorphic base level. The Blue Ridge-Great Valley mantled karst likely contains both short-term accumulation space that is closer to geomorphic base level, thus more prone to removal by fluvial processes, and preservation space, which occurs well below geomorphic base level, where sedimentary sequences may be stored for prolonged periods of time. Ultimately, both accumulation and preservation spaces can provide insight into depositional processes, landscapes and possibly paleoenvironmental conditions, but the geologic record becomes more distorted and fragmented further back into deep time and as this landscape evolves into the future.