North-Central Section (44th Annual) and South-Central Section (44th Annual) Joint Meeting (11–13 April 2010)

Paper No. 1
Presentation Time: 8:30 AM-12:00 PM


SCRUGGS, Melissa A.1, RAAB, L. Mark1, MUROWCHICK, James1, STONE, Matthew W.1 and NIEMI, Tina M.2, (1)Geosciences, University of Missouri - Kansas City, 5100 Rockhill Road, Room 420 Flarsheim Hall, Kansas City, MO 64110, (2)Department of Geosciences, University of Missouri - Kansas City, 5100 Rockhill Road, Flarsheim Hall 420, Kansas City, MO 64110,

The YDB extraterrestrial impact hypothesis posits that one or more extraterrestrial objects exploded over the Laurentide Ice Sheet 12,900 ± 100 years ago. This event is purported to have triggered the Younger Dryas stadial and coincides with the Rancholabrean termination and disappearance of the Paleoindian Clovis culture. Evidence supporting or refuting this hypothesis has great implications for the fields of geology, paleontology, and archaeology. Geochemical markers of the YDB impact (Firestone, et al., 2007) include magnetic and carbonaceous spheroids, elevated levels of radioactivity and iridium, and nanodiamonds (lonsdaleite). The event horizon at sites across North America is often overlain by a darker layer (the "black mat").

Our field site for testing the YDB ET impact hypothesis is located on the El Carrizal fault, 38 km south of La Paz, Baja California Sur, Mexico, at 23°46'34.9" N, 110°18'41.0" W. The site is situated along the uplifted (SW) side of the fault within an arroyo exposing Pleistocene-Holocene transition sediments. The presence of in situ Rancholabrean megafauna fossils at El Carrizal was independently verified by investigators from Universidad Autonoma de Baja California Sur, La Paz; cranial and postcranial sections of Mammuthus columbi were excavated from the sampling site in 1997. Sediment samples were taken from a 3 m stratigraphic section at El Carrizal which spanned the sediments where the mammoth fossils were located. This section included an anomalous greenish clastic layer at approximately 138 ± 6 cm below road surface; this layer suggests a correlation to the “black mat” stratum noted at many other terminal sites. Preliminary laboratory analysis yielded magnetic spherical particles under 60-70x magnification, and a peak in radioactivity was found at a depth of 136-138 cm, coinciding with the lower part of the darker green layer. Elemental analyses for iridium and lonsdaleite are currently underway.

If conclusive evidence of an extraterrestrial impact is found at El Carrizal, it will be the most distal documented evidence to date. This will significantly extend the geographic range of effects for the impact event.