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A host of unusual geological features, collectively known as Carolina Bays, hints at the cataclysm's location, says team member George A. Howard, a wetland manager at Restoration Systems, an environmental-restoration firm in Raleigh, N.C. Around 1 million of these elliptical, sand-rimmed depressions, measuring between 50 meters and 11 kilometers across, scar the landscape from New Jersey to Florida. In samples taken from 15 of the features, Howard and his colleagues found iridium-rich magnetic grains and carbon spherules with tiny diamond fragments similar to those found at Clovis archaeological sites.

The long axes of the great majority of the Carolina Bays point toward locations near the Great Lakes and in Canada—a hint that the extraterrestrial object disintegrated over those locales, says Howard.

Because scientists "haven't discovered a large, smoking hole" left by the event, the object that blew up in the atmosphere probably was a comet, says West.

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This image is from a pdf file here.

Here is another report. Quote:

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Evidence for an extraterrestrial impact 12,900 years
ago that contributed to the megafaunal extinctions
and the Younger Dryas cooling
R. B. Firestonea,b, A. Westc, J. P. Kennettd, L. Beckere, T. E. Bunchf, Z. S. Revayg, P. H. Schultzh, T. Belgyag, D. J. Kennetti,
J. M. Erlandsoni, O. J. Dickensonj, A. C. Goodyeark, R. S. Harrish, G. A. Howardl, J. B. Kloostermanm, P. Lechlern,
P. A. Mayewskio, J. Montgomeryj, R. Poredap, T. Darrahp, S. S. Que Heeq, A. R. Smitha, A. Stichr, W. Toppings,
J. H. Wittkef, and W. S. Wolbachr
aLawrence Berkeley National Laboratory, Berkeley, CA 94720; cGeoScience Consulting, Dewey, AZ 86327; dDepartment of Earth Sciences and eInstitute of
Crustal Studies, University of California, Santa Barbara, CA 93106; fNorthern Arizona University, Flagstaff, AZ 86011; gInstitute for Isotope and Surface
Chemistry, H-1525, Budapest, Hungary; hDepartment of Geological Sciences, Brown University, Providence, RI 02912; iDepartment of Anthropology and
Museum of Natural and Cultural History, University of Oregon, Eugene, OR 97403; jEastern New Mexico University, Portales, NM 88130; kSouth Carolina
Institute of Archaeology and Anthropology, University of South Carolina, Columbia, SC 29208; lRestoration Systems, LLC, Raleigh, NC 27604; mRozenstraat
85, 1018 NN, Amsterdam, The Netherlands; nBureau of Mines and Geology, University of Nevada, Reno, NV 89557; oClimate Change Institute, University
of Maine, Orono, ME 04469; pUniversity of Rochester, Rochester, NY 14627; qDepartment of Environmental Health Sciences, University of California,
Los Angeles, CA 90095; sP.O. Box 141, Irons, MI 49644; and rDepartment of Chemistry, DePaul University, Chicago, IL 60614
Communicated by Steven M. Stanley, University of Hawaii at Manoa, Honolulu, HI, July 26, 2007 (received for review March 13, 2007)
A carbon-rich black layer, dating to
12.9 ka, has been previously
identified at
50 Clovis-age sites across North America and appears
contemporaneous with the abrupt onset of Younger Dryas (YD)
cooling. The in situ bones of extinct Pleistocene megafauna, along
with Clovis tool assemblages, occur below this black layer but not
within or above it. Causes for the extinctions, YD cooling, and
termination of Clovis culture have long been controversial. In this
paper, we provide evidence for an extraterrestrial (ET) impact event
at
12.9 ka, which we hypothesize caused abrupt environmental
changes that contributed to YD cooling, major ecological reorganization,
broad-scale extinctions, and rapid human behavioral shifts at
the end of the Clovis Period. Clovis-age sites in North American are
overlain by a thin, discrete layer with varying peak abundances of (i)
magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal,
(iv) soot, (v) carbon spherules, (vi) glass-like carbon containing
nanodiamonds, and (vii) fullerenes with ET helium, all of which are
evidence for an ET impact and associated biomass burning at
12.9
ka. This layer also extends throughout at least 15 Carolina Bays, which
are unique, elliptical depressions, oriented to the northwest across
the Atlantic Coastal Plain. We propose that one or more large,
low-density ET objects exploded over northern North America, partially
destabilizing the Laurentide Ice Sheet and triggeringYDcooling.
The shock wave, thermal pulse, and event-related environmental
effects (e.g., extensive biomass burning and food limitations) contributed
to end-Pleistocene megafaunal extinctions and adaptive
shifts among PaleoAmericans in North America.
comet  iridium  micrometeorites  nanodiamonds  spherules
A carbon-rich black layer, dating to
12.9 ka (12,900 calendar
years B.P.) (1), has been identified by C. V. Haynes, Jr. (2), at
50 sites across North America as black mats, carbonaceous silts,
or dark organic clays [supporting information (SI) Fig. 5]. The age
of the base of this black layer coincides with the abrupt onset of
Younger Dryas (YD) cooling, after which there is no evidence for
either in situ extinct megafaunal remains or Clovis artifacts. Increasing
evidence suggests that the extinction of many mammalian
and avian taxa occurred abruptly and perhaps catastrophically at
the onset of the YD, and this extinction was pronounced in North
America where at least 35 mammal genera disappeared (3), including
mammoths, mastodons, ground sloths, horses, and camels,
along with birds and smaller mammals. At Murray Springs, AZ, a
well known Clovis site, mammoth bones and Clovis-age stone tools
lie directly beneath the black layer where, as described by Haynes
(4): ‘‘[T]he sudden extinction of the Pleistocene megafauna would
be dramatically revealed by explaining that all were gone an instant
before the black mat was deposited.’’

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