Formation of the Carolina Bays: ET Impact vs. Wind-and-Water

Details Formation of the Carolina Bays: ET Impact vs. Wind-and-Water Formation of the Carolina Bays: ET Impact vs. Wind-and-Water

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmpp43a..10k&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #PP43A-10

Other

5420 Impact Phenomena, Cratering (6022, 8136), 6022 Impact Phenomena (5420, 6240 Meteorites And Tektites (1028, 3662), 6250 Moon (1221), 9350 North America

Scientific paper

The Carolina Bays are a group of lakes, wetlands, and depressions, stretching from Florida to New Jersey along the Atlantic Ocean, and ranging up to 11 km in length and about 15 m in depth. Their distinctive elliptical shapes and common orientation towards the Great Lakes region have generated many hypotheses about their method of formation, including extraterrestrial impact (Melton and Schriever, 1933; Prouty, 1934). Another suggests that springs or groundwater dissolution of soluble minerals caused subsidence, which formed water-filled depressions that became the Bays (Johnson, D.W., 1944). One of the prevailing views is that Carolina Bays represent irregular lakes that were gradually reshaped into ellipses by circulating lake currents, generated by strong ice-age winds blowing perpendicular to the current long axes of the Bays (Kaczorowski, 1977). We report results from a suite of cores taken from within a Bay, which we have named "Howard Bay," located about 2 km north of the town of Duart in Bladen County, North Carolina. Located on the high western bluff of the Cape Fear River, the Bay is 2.7 km long, 1.6 km wide, and filled with about 9 meters of sediment with an encircling rim that is ~1-meter high. Analyses of seven cores along the long axis of Howard Bay reveal an assemblage of abundant magnetic grains, microspherules, carbon spherules, glass-like carbon, and iridium, typical of the YDB impact layer (12.9 ka) at many other sites across North America. The impact layer conforms to the basal contours of the basin, suggesting that the markers were deposited immediately or soon after the Bay formed. Further analyses of samples in complete core sequences reveal that, unlike typical, peat-rich Carolina Bays, Howard Bay essentially lacks peat, diatoms, pollen, or other organic materials, suggesting that this Bay never stored water for any sustained length of time. Furthermore, several trenches confirm that the deepest part of the Bay is filled with >6 m of cross-bedded eolian sand with no evidence of lacustrine sedimentation. This evidence calls into question prevailing hypotheses (a) that all Bays were lakes and ponds in the past and that their shapes were formed by wave action, or (b) that groundwater movement led to subsidence that formed the Bay. The presence of impact markers, including high concentrations of iridium, in a layer just above the basal sediments of this Bay that is filled with eolian sand supports the extraterrestrial impact hypothesis for Bay formation.

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