Geology/Samples

1. PP43A-03 Is There Evidence for Impact-Triggered Fires at the End Pleistocene?Wendy S. Wolbach1, Adrienne Stich1, J.B. Kloosterman2, Luann Becker3, James Kennett3, Richard B. Firestone4, Allen West51DePaul University, Department of Chemistry, Chicago, IL 60614 (wwolbach@condor.depaul.edu); 2Amsterdam, Netherlands (jbkloosterman@gmail.com);3Institute of Crustal Studies, University of California, Santa Barbara, CA 93106 (lbecker@crustal.ucsb.edu); 4Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (rbf@lbl.gov); 5GeoScience Consulting, Dewey, AZ 86327 (Allen7633@aol.com) Background: Soot at the KTB Geology/Samples Data Results and Conclusions Since 1985, significant quantities of reduced, elemental carbon and soot have been found at 13 KT boundary (KTB) sites [1-4]. Because of the wide geographic distribution of these sites, these data were interpreted to indicate that deposition of soot was a global phenomenon, coincident with the Ir-rich fallout layer [5]. The likely source of the global soot deposit is eolian deposition from extensive (or global) wildfires directly associated with the KT impact event. An estimate of the amount of soot distributed globally from the KTB fires was 2.2 ± 0.7 mg/cm2 [3]. The figure below indicates the carbon-rich, dark layer (“Black Mat”) at Murray Springs, AZ, which coincides with the abrupt Younger Dryas (YD) cooling ~12.9 ka ago. Other Impacts/Extinctions Soot has been found at just two other non-KTB sitesassociated with impacts or extinctions.z The magnitude and location of the End Pleistocene bolide is unknown and so it is impossible to predict the magnitude of any fires triggered by the impact. The presence of significant soot, however, especially the large amount at the Carolina Bay, suggests that significant burning at the very least occurred near that location ~12.9 ka ago. The fire that produced the observed soot might have been regional, or perhaps soot was initially deposited at additional sites but simply not preserved. These questions will be addressed by analyzing more End Pleistocene samples. Thirty-eight samples from the following North American sites were studied: Carolina Bays at Blackville and Myrtle Beach, SC; Murray Springs, AZ; Chobot Site, Alberta, Canada; Blackwater Draw, Clovis, NM; Glacial Lake Hind, Manitoba, Canada. Four samples from the Usselo Horizon in Schleswig-Holstein, one sample from Lommel, Belgium, and one sample from Klein Nordende, Germany, were also analyzed. End Pleistocene [1] Wolbach W. S. et al. (1985) Science 230, 167-170. [2] Wolbach W.S. et al. (1990) In: Global Catastrophes in Earth History (eds. V.L. Sharpton and P. Ward). Geol. Soc. Amer. Spec. Pap. 247, 391-400. [3] Kyte, F.T. et al. (1996), In: The Cretaceous-Tertiary Event and Other Catastrophes in Earth History (eds. G. Ryder, D. Fatovsky, and S. Gartner) Geol. Soc. Amer. Spec. Pap. 307, 389-401. [4] Wolbach W.S. and Anders E. (1989) Geochim. Cosmochim. Acta 53, 1637-1647. [5] Alvarez, L.W. et al. (1980) Science 208, 1095-1108. [6] Firestone R.B. et al., Proceedings of the National Academy of Sciences, submitted. [7] Wolbach W.S. et al. (1988) Nature 334, 665-669. Recent evidence suggests an extraterrestrial contribution to the End Pleistocene extinctions. Sediments at the base of a carbon-rich, dark layer dating to ~12.9 ka contain magnetic grains, microspherules, elevated Ir, and fullerenes with abundant 3He, all evidence consistent with extraterrestrial impact [6]. To test the possibility that combustion of the impactor, carbon-bearing rocks, or biomass could have been triggered by the impact, we searched for soot in a variety of Clovis-age sites marked by this dark layer in North America, Germany, and Belgium. Soot Isolation Method Two samples contained significant quantities of soot: Murray Springs, AZ, 20 ± 5 ppm soot and Carolina Bay, Blackville, SC, with 2000 ± 200 ppm soot. None of the remaining End Pleistocene samples studied showed visible or significant soot contents. Negative results do establish that surface contamination by soot was not a problem, even though some sample locations were undoubtedly close to automobile traffic or possible natural biomass fires. The procedure is based on that used successfully at the KTB [2, 4, 7]. Reduced C was isolated from sediments using HCl and HCl/HF. Elemental C was separated from organic C by acidic dichromate oxidation. Soot was identified using SEM imaging and quantified by weighing and particle size analysis.