Is this what you are referring too?

Author : Kennett, D.J.; Erlandson, J.M.; Braje, T.J.; and Culleton, B.J.
Date : 2007.
Title : Exploring the human ecology of the Younger Dryas extraterrestrial impact event.
Publication : Eos Transactions. American Geophysical Union, Joint Assembly. May 22-25, 2007. Acapulco, Mexico.
Issue : Supplement 88(23):
Page(s) : PP42A-02.

Abstract
Several lines of evidence now exist for a major extraterrestrial impact event in North America at 12.9 ka (the YD. This impact partially destabilized the Laurentide and Cordilleran ice sheets, triggered abrupt Younger Dryas cooling and extensive wildfires, and contributed to megafaunal extinction. This event also occurred soon after the well established colonization of the Americas by anatomically modern humans. Confirmation of this event would represent the first near-time extraterrestrial impact with significant effects on human populations. These likely included widespread, abrupt human mortality, population displacement, migration into less effected or newly established habitats, loss of cultural traditions, and resource diversification in the face of the massive megafaunal extinction and population reductions in surviving animal populations. Ultimately, these transformations established the context for the special character of plant and animal domestication and the emergence of agricultural economies in North America. We explore the Late Pleistocene archaeological record in North America within the context of documented major biotic changes associated with the YDB in North America and of the massive ecological affects

Author : Firestone, R.B.; West, A.; Revay, Z.; Belgya, T.; Smith, A.; and Que Hee, S.S.
Date : 2007.
Title : Evidence for a massive extraterrestrial airburst over North America 12.9 ka ago.
Publication : Eos Transactions. American Geophysical Union, Joint Assembly. May 22-25, 2007. Acapulco, Mexico.
Issue : Supplement 88(23):
Page(s) : PP41A-01.

Abstract
A carbon-rich black layer commonly referred to as a black mat, with a basal age of approximately 12.9 ka, has been identified at over 50 sites across North America1. The age of the base of the black mat coincides with the abrupt onset of Younger Dryas cooling and megafaunal extinctions in North America. In situ bones of extinct mammals, including mammoths, mastodons, ground sloths, horses, camels, many smaller mammals and birds, and Clovis tool assemblages occur below the black mat but not within or above it. In this paper, we provide evidence for an ejecta layer at the base of the black mat from an extraterrestrial impact event 12.9 ka ago. We have investigated nine terminal Clovis-age sites in North America and a comparable site in Lommel, Belgium that are all marked by a thin, discrete layer containing varying peak abundances of (1) magnetic grains/microspherules containing iridium concentrations up to 117 ppb, (2) charcoal, (3) soot, (4) vesicular carbon spherules, (5) glass-like carbon, and (6) fullerenes enriched in 3He. This layer also extends throughout the rims of at least fifteen Carolina Bays, unique, elliptical, oriented lakes and wetlands scattered across the Atlantic Coastal Plain whose major axes point towards the Great Lakes and Canada. Microspherules, highly enriched in titanium, were found only in or near the YD boundary (YD layer with greatest deposition rates (35 per cm2) occurring near the Great Lakes. Magnetic grains also peak in the YDB with maximum deposition near the Great Lakes (30 mg/cm2). Magnetic grains near the Great Lakes are enriched in magnetite (4 mg/cm2) and silicates (23 mg/cm2) but contain less ilmenite/rutile (1 mg/cm2) than distant sites where ilmentite/rutile deposition ranges up to 18 mg/cm2. Analysis of the ilmenite/rutile-rich magnetic grains and microspherules indicates that they contain considerable water, up to 28 at.% hydrogen, and have TIO2/FeO, TIO2/Zr, Al2O3/FeO+MgO, CaO/Al2O3, REE/chondrite, K/Th, FeO/MnO ratios and SIO2, Na2O, K2O, Cr2O3, Ni, Co, Ir, Th, U, and other trace element abundances that are inconsistent with all terrestrial and extraterrestrial sources except for Lunar Procellarum KREEP terrain (PKT). We propose that the YDB layer is the ejecta layer from an airburst over the Laurentide Ice Sheet that deposited local, low-speed terrestrial material near the airburst site and KREEP-like, high-speed projectile material farther away, leaving little or no permanent crater. The associated blast wave and thermal pulse would have contributed to the megafaunal extinctions and destabilized the Laurentide Ice Sheet, loading the atmosphere with dust, soot, NOx, and water vapor and triggered the YD cooling.