AND YET THEY PERSIST; LIDAR BARE-EARTH DEMS ELUCIDATE CAROLINA BAY RIMS AS PALIMPSEST FEATURES CONTROLLING THEIR TOPOGRAPHIC EXPRESSION THROUGH DIFFERENTIAL WEATHERING AND EROSION

Carolina bays have long been recognized as oriented oval basins. A comprehensive survey of the bays (Survey) using LiDAR bare-earth digital elevation maps (DEMs) has documented their planforms as conforming robustly to a handful of ovoid shapes which diverge from an ellipse by subtle, yet distinctive markers. These shapes are cast as six archetypes, each found to be applicable to a specific geographic region. We note that many bays with complete circumferential planforms lack raised rims, but instead are simply basins sunken into a terrace. Using the archetype templates, the Survey has identified vast numbers of basins that echo the shape and orientation of nearby well-described Carolina bays, but are not hydraulically closed. We propose that when fluvial headward erosion succeeds in breaching into a bay basin, a "valley head basin” is formed. Carolina bay raised rims appear to the naked eye to be gently arcing embankments, yet the LiDAR DEMs show them to be robust landforms tracking precisely to the archetype planform for kilometers. We speculate that these basins possess a palimpsest structural lithology that subdues the gradualistic mechanisms seeking to eradicate them by controlling their own topographic expression through differential weathering and erosion. We discuss cases where bay perimeters seem to control the extent and paths of surficial sheet and fluvial erosion, both within and around the bay. Also, we discuss bays whose identity is hidden by burial in fluvial or marine transgressive deposits, yet the LiDAR exposes their existence as ghostly traces of their properly oriented and shaped rims. These findings suggest to us that Carolina bays are not wispy gradualistic landforms of recent age, but are perhaps medial ejecta artifacts of the same Mid Pleistocene Transition Impact event that created the Australasian Tektites as distal ejecta. Our goal is to encourage the interrogation of Carolina bay age and geomorphology through deep coring and application of cosmogenic isotope dating techniques. Metrics for ~51,000 surveyed bays are available from a Google Fusion Table: https://goo.gl/XTHKC4 . Individual bays are geospatially referenceable using a hyperlinked map to display their metrics and enable visualization of the associated DEM imagery and planforms on a virtual globe: https://goo.gl/EHR4Lf .