Late-Quaternary paleoecologic, geomorphic, and paleoclimatic history of Flat Laurel Gap, Blue Ridge Mountains, North Carolina

Flat Laurel Gap, Haywood County, North Carolina, is a high-elevation (1,500 m) heath bald and bog. Colluvial and fluvial deposits, together with the sequence of fossil pollen spectra and plant macrofossils, provide a late-Quaternary record of landscape evolution for the Southern Appalachian Mountains.

Colluvial fans and periglacial block deposits (i.e., blockstreams, blockfields, and talus) were mapped in the bog and its watershed in the vicinity of Mt. Pisgah. Thermoluminescence (TL) analysis at Flat Laurel Gap provides the first absolute-age determinations available for periglacial deposits in the Southern Appalachian Mountains. A TL date of 10,100±95G yr BP was obtained for sediments of a colluvial fan situated at the head of the bog. The colluvial fans represent late-Quaternary solifluction lobes, possibly related to episodic release of water and saturation of regolith that v/ould accompany the collapse of discontinuous permafrost within the watershed during late-glacial and early-Holocene climatic amelioration, The TL date of 11,9Q0±1,500 yr BP for a fluvial terrace in Flat Laurel Bog records the initial incision of late-glacial and early-Holocene dissection of the solifluction lobes and the formation of the modern alluvial-glade environment. A TL date of 7,400±1,000 yr BP for sediments within a blockstream entering the bog indicates reworking of Pleistocene periglacial material during a cool episode of the Hoiocene. A pegmatite dike exhumed during early-Holocene dissection of the colluvial valley fill anchors the local base level for alluvial ponding and for Holocene deposition of organic sediments in the bog.

Three geomorphic surfaces are mapped within Flat Laurel Gap. Each surface is occupied by characteristic heath-bald plant communities: (1) topographically high colluvial fans with high-heath communities (Rhododendron and Kalmia shrubs more than 3 m in height); (2) dissected colluvial and alluvial terraces with low-heath communities (Kalmia and Vaccinium shrubs up to 3 m in height); and (3) active floodplain and stream channels with glade and wet-meadow communities (Sphagnum and Cyperaceae). A 3,340-year pollen record from an open alluvial glade indicates that heath shrubs have been the dominant extralocal vegetation at Flat Laurel Gap Bog for the late-Holocene interval, and documents the antiquity of some heath bald communities in the Southern Appalachians. The paleoecologic record also records the persistence of relict, boreal plant species at high-elevations of the Southern Blue Ridge through the late-Holocene interval. Abies fraseri, previously thought to have been extirpated from the Flat Laurel Gap/Mt. Pisgah area during the mid-Holocene Hypsithermal grew at Flat Laurel Gap in the late-Holocene until it was eliminated at the site during logging of the upland forests in the late nineteenth century (circa AD 1880).