# Presentation: 185164

##                Evidence for an Extraterrestrial Impact Event 12,900 years ago that Contributed to the Megafaunal Extinctions and the Younger Dryas Cooling

**MAGNETIC MARKERS**

**              **** ****Evidence for an Extraterrestrial Impact Event 12,900 years ago that ****Contributed to the Megafaunal Extinctions and the Younger Dryas Cooling**

**Carbon spherules **(0.15-2.5 mm) are black, highly vesicular, low-density, subspherical-to-spherical objects found only in the YD impact layer at 18 widely distributed sites in concentrations up to ~1500/kg. SEM analysis shows that these spherules have cracked and patterned surfaces, sponge-like interior textures, and occasional hollow cores. SEM/EDS analysis shows the spherules are dominantly carbon with no evidence of vegetative origin, such as seed-like morphology or the cellular structure of charcoal. The objects appear identical to those reported by Rösler et al. [*68th Annual Meterological Society Meeting,* paper 5114 (2005), *First International Conference on Impact Cratering in the Solar System ESTEC*, Noordwijk, The Netherlands, 08 - 12 May (2006).] from across Europe, containing nanodiamonds and fullerenes.

**CARBON MARKERS**

**INTRODUCTION: ****The Younger Dryas event boundary (YDB) is a thin sedimentary layer of 12.9 ka age, which contains an assemblage of materials formed by an extraterrestrial impact centered over northern North America. The YDB layer contains peaks in magnetic grains, magnetic microspherules, and iridium, in addition to charcoal and soot that resulted from extensive wildfires. Two impact-related carbon-rich markers, glass-like carbon and carbon spherules, have not been reported previously in North America. The carbon-rich material contains fullerenes enriched in ET helium and nanodiamonds, suggesting an ET origin for the material. The event coincided with the megafaunal extinctions and the Younger Dryas cooling episode; we propose that neither would have occurred in the absence of this impact.**

- R.B. Firestone1, A. West2, J.P. Kennett3, L. Becker4, T.E. Bunch5, Zs. Revay6, P.H. Schultz7, T. Belgya6, O.J. Dickenson8, J.M. Erlandson9, A.C. Goodyear10, R.S. Harris7, G.A. Howard11, D.J. Kennett9, J.B. Kloosterman12, P. Lechler13, J. Montgomery8, R. Poreda15, T. Darrah15, S.S. Que Hee16, A.R. Smith1, A. Stich18, W. Topping17, J.H. Wittke5, and W.S. Wolbach18
- 1Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, 2GeoScience Consulting, P.O.Box 1636, Dewey, AZ, 85327, 3Dept. of Earth Sciences, U. of California Santa Barbara, CA, 93106, 4Institute of Crustal Studies, U. of California, Santa Barbara, CA, 93106, 5Northern Arizona U., Flagstaff, AZ, 86011, 6Institute for Isotope and Surface Chemistry, Budapest, Hungary, 7Department of Geological Sciences, Brown U., Providence, RI, 02912, 8Eastern New Mexico U., Portales, NM, 88130, 9Dept. of Anthropology and Museum of Natural and Cultural History, U. of Oregon, Eugene, OR, 97403, 10SC Institute of Archaeology and Anthropology, U. of South Carolina, Columbia, SC, 29208, 11Restoration Systems, L.L.C., Raleigh, NC, 27604, 12Amsterdam, Netherlands, 13Bureau of Mines and Geology, U. of Nevada, Reno, NV, 89557, 15U. of Rochester, Rochester, NY, 14627, 16Dept. of Environmental Health Sciences, U. of California, LA, CA, 90095, 17Gladwin, MI, 18Department of Chemistry, DePaul U., Chicago, IL, 60614.

**Magnetic grains** (1-500mm) are irregularly shaped and often sub-rounded, are more abundant than microspherules, show a distinct peak in the YDB at all 25 sites, and have lower abundances at other stratigraphic levels. They are mostly dark brown or black, and some are silicates with magnetite inclusions. Magnetic grain abundances vary greatly between YDB sites, averaging 3.4 g/kg, with higher grain abundances at sites in northern North America. Lower grain abundances were found in the southern United States. The highest concentration of magnetic grains (17.1 g/kg) was found at one site in North Carolina, along with other event markers. YDB magnetic grains from the southern sites are enriched in titanomagnetite.

**Magnetic microspherules **(10-250 mm) peaked in or near the YDB at 8 sites analyzed, spanning parts of North America and Europe from Alberta, Canada to Arizona to Belgium; none were found at two sites. Several sites also provided a few microspherules that appear to be silicate but require further analysis. Magnetic spherule abundances average 390/kg and are highest in the north, ranging up to 2144/kg. Microspherules analyzed from Michigan, New Mexico, and Canada are enriched in titanomagnetite. Copal (Amber) spherules (center)  were found at several sites.

**Vesicular, glass-like carbon **pieces up to several cm in diameter were found in the YDB at 22 sites with concentrations ranging from 0.01 to 16 g/kg. Their glassy texture suggests melting during formation, with some fragments grading into charcoal. Preliminary analysis by 13C NMR indicates the presence of nanodiamonds at 3% by weight.

**IMPACT SITES**

- An **impact ejecta layer** dated to 12.9 ka BP has been identified directly below the **black mat** at Murray Springs (arrow left), nine other Clovis-age sites from California to Belgium and throughout the rims of fifteen Carolina Bays (right). No megafaunal remains or Clovis artifacts are found within or above the black mat.  The **Carolina Bays** are a suite of 500,000, often overlapping, highly elliptical, depressions extending from New Jersey to Florida on the Atlantic Coastal Plain. They are up to 15 meters deep with parallel long axes that are from 60 m to 11 km in length. The bays have elevated, poorly stratified, sandy rims, higher on the southeast side, ranging in height up to 7 m.  Various impact ejecta markers shown on the right were also found throughout the 1.5-5 m depth of the bay rims.

- Sediment profiles from A) Murray Springs, AZ, B) Blackwater Draw, NM, C) Lake Hind, MB Canada, D) Chobot, AB Canada, E) Topper, SC, F) Morley drumlin, AB Canada, G) Gainey, MI (no picture available), H) Lommel, Belgium, and I) S. Carolina Bay M31. The depth scale is relative to the base of the YDB. Graph legends are color coded to match the respective curves, and graph points correspond with sampling locations on the photo. The bottom of the black mat is the YDB, the interval marking the extinction of the North American megafauna, and onset of Younger Dryas cooling. Magnetic grains and spherules, Ir and Ni concentrations, charcoal, and carbon spherules peak in a very narrow stratigraphic section spanning less than several hundred years. Open circles in the Ir curves indicate values that were below the detection limit, typically 0.5-1 ppb. Double peaks may have resulted from reworking in a fluvial environment.  Fullerenes, enriched in 3He, are found in the YDB at Blackwater Draw and Murray Springs. The Blackwater Draw image is a composite of three photos of strata presented in the Interpretive Center, South Wall.

| Microspherules | %FeO | %TiO2 |
| --- | --- | --- |
| Blackwater-1 | 74 | 13 |
| Blackwater-2 | 37 | 53 |
| Gainey-1 | 92 | 0 |
| Gainey-2 | 18 | 2 |
| Gainey-3 | 25 | 68 |
| Gainey-4 | 7 | 25 |
| Gainey-5 | 64 | 29 |
| Morley-1 | 44 | 47 |
| Morley-2 | 50 | 40 |
| Morley-3 | 84 | 0 |
| Morley-4 | 84 | 0 |
| Lommel-1 | 16 | 74 |
| Lommel-2 | 11 | 54 |
| Lommel-3 | 16 | 74 |
| Spherule Ave. | 44 | 34 |
| Bulk Ejecta Ave. | 30 | 22 |

**PGAA/NAA analysis** of the YD magnetic grains and microspherules shows that they have a common composition highly enriched in titanium with elemental concentrations (right) and REE depletion in Eu (below) comparable to lunar Procellarum KREEP Terrane. Magnetic grains contain up to 117 ppb iridium, over 5000 times terrestrial abundance.

- Distribution of microspherules, magnetic grains, magnetite, silicates, ilmenite/rutile, and water content at various sites.  High concentrations of terrestrial ejecta near Gainey suggest a nearby impact site.  High ilmenite/rutile concentrations away from Gainey suggest projectile-rich ejecta.

| Composition of Carbon Markers |  |  |
| --- | --- | --- |
| Element | Carbon Spherules | Glassy Carbon |
| H20 | 34% | 22% |
| B | 14 ppm | 2.6 ppm |
| C | 61% | 71% |
| N | 1.5% | 0.13% |
| F | --- | 2.5% |
| Al2O3 | 1.3% | 0.45% |
| SiO2 | 1.6% | 3.7% |
| S | 0.11% | --- |
| Cl | 540 ppm | 142 ppm |
| K2O | 840 ppm | 96 ppm |
| CaO | 0.36% | 0.38% |
| TiO2 | 700 ppm | 520 ppm |
| Co | 40 ppm | --- |
| Cd | 0.40 ppm | 0.15 ppm |
| Sm | 0.44 ppm | 0.13 ppm |
| Gd | 0.57 ppm | 0.15 ppm |

**Magnetic grains **from Gainey have terrestrial composition and grains from other sites have many signatures chemical signatures very comparable to lunar Procellarum KREEP. This suggests that the impact was an airburst near the Great Lakes depositing mostly terrestrial ejecta near  the impact site and projectile eject further away.  The uniquely KREEPy composition is surprising.