2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 8
Presentation Time: 1:30 PM-5:30 PM


CHAPMAN, Mary G., Astrogeology Team, U.S. Geol. Survey, 2255 N. Gemini Road, Flagstaff, AZ 86001, FRENCH, Bevan M., Smithsonian Institution, Washington, D.C, 20560, KILLGORE, Marvin, Southwest Meteorite Lab, P.O. Box 95, Payson, AZ 85541, LAURETTA, Dante S., Lunar and Planetary Lab, Univ of Arizona, Tucson, AZ 85721, LUCAS, Spencer G., New Mexico Museum of Nat History, 1801 Mountain Road N.W, Albuquerque, NM, MCHONE, John F., Department of Geology, Arizona State Univ, Tempe, AZ 85287, TANNER, Lawrence H., Geography and Geosciences, Bloomsburg Univ, Bloomsburg, PA 17815, WOLBACH, Wendy S., DePaul Univ, 1036 W Belden Ave, Chicago, IL 60614-3214 and ZEIGLER, Kate E., Department of Earth and Planetary Sciences, Univ of New Mexico, Northrop Hall, Albququerque, NM 87131, mchapman@usgs.gov

Extinctions near the Tr-J boundary may be due to bolide impact or effects of widespread volcanism. The age of the Snyder Quarry dinosaur die-out site in central New Mexico overlaps the radiometric age of the 100-km-diameter Manicouagan impact crater (214 ± 1 Ma). Large impacts are suggested to be associated with global fires, and the dinosaur deaths in the quarry have been attributed to a widespread paleowildfire. These intriguing associations have sparked sedimentologic, petrographic, chemical, and electron microprobe analyses to investigate the possible connections between the wildfire and dinosaur deaths at the quarry. Preliminary analyses of the main fossil bed indicate the 30-cm-thick gray mudstone sharply contacts an underlying 8-cm-thick calcite pelloidal conglomerate containing 0.2-0.5 mm long apatite laths interpreted as fossil teeth of small vertebrates. The likely fecal pellets and total lack of lithics suggest the conglomerate was formed in a sediment-deprived lake. The overlying fossiliferous mudstone contains mudclasts (rip ups), calcite pellets, small fossil teeth, pyrite spherules (< 0.02 mm), partly oxidized pyrite grains (1.0-5.0 mm), blackened (burnt) plant fragments, and black bone fragments. The matrix is micrite and cements are calcite, gypsum, and chalcedony. The matrix and rip-up clasts contain occasional silt-sized angular quartz fragments that show highly undular extinction patterns and have numerous inclusions. Several quartz grains contain potential shock-induced PDFs, but these have not been confirmed. Lithic fragments and rip-up clasts are consistent with fine-grained overbank deposition. Chemical analyses of fossil wood indicate 18.5% organic carbon, consistent with burning; tests for soot content are underway. Identical analyses of fossil bone indicate 0.36% organic carbon, 1.05% hydrogen, 0.05% nitrogen, and 1.0% manganese and are inconclusive, due to high manganese content (which can also blacken bone). However, a connection between the wildfire and dinosaur deaths is consistent with blackened, perpendicularly fractured, non-scavenged, nonarticulated, but associated bones of individual skeletons. Some bone fragments have a light bluish gray mineral coating that appeared on an EDS spectrum as a titanium oxide.