HR: 14:15h
AN: U33A-02    [Abstracts]
TI: Global Effects Of Late Eocene Impacts
AU: * Pusz, A E
EM: aimeep@eden.rutgers.edu
AF: Dept. of Geological Sciences, Rutgers University, 610 Taylor Rd., Piscataway, NJ 08854, United States
AU: Miller, K G
EM: kgm@rci.rutgers.edu
AF: Dept. of Geological Sciences, Rutgers University, 610 Taylor Rd., Piscataway, NJ 08854, United States
AU: Kent, D V
EM: dvk@rci.rutgers.edu
AF: Dept. of Geological Sciences, Rutgers University, 610 Taylor Rd., Piscataway, NJ 08854, United States
AU: Kent, D V
EM: dvk@rci.rutgers.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964, United States
AU: Wright, J D
EM: jdwright@rci.rutgers.edu
AF: Dept. of Geological Sciences, Rutgers University, 610 Taylor Rd., Piscataway, NJ 08854, United States
AU: Wade, B S
EM: bwade@rci.rutgers.edu
AF: Dept. of Geological Sciences, Rutgers University, 610 Taylor Rd., Piscataway, NJ 08854, United States
AU: Wade, B S
EM: bwade@rci.rutgers.edu
AF: Institute of Marine and Coastal Science, Rutgers University, 71 Dudley Rd., New Brunswick, NJ 08901, United States
AU: Aubry, M P
EM: aubry@rci.rutgers.edu
AF: Dept. of Geological Sciences, Rutgers University, 610 Taylor Rd., Piscataway, NJ 08854, United States
AB: Two of the three largest impact craters found on Earth since 200 Ma (Popigai and the Chesapeake Bay Impact Structure or CBIS) are late Eocene (~35.4-35.5 Ma based on radiometric ages) and are well preserved, yet the environmental response to these near synchronous and large impacts is poorly understood. No extinction events are recorded in coccolithophorids, planktonic or benthic foraminifera at this time, and terrestrial biota appear unaffected. The late Eocene global temperature history and carbon budget are poorly constrained because of sparsely sampled δ18O and δ13C records. We present new microfauna and nannoplankton evidence and stable isotopic data that show: 1) minimal biotic and temperature response associated with the impacts; and 2) a large and transient carbon isotope excursion associated with the impacts that reflect a major change in the global carbon budget. Southern Ocean ODP Site 1090 provides an exceptional record to test if a carbon isotopic anomaly is associated with the late Eocene impacts because benthic foraminifera are well preserved, the identified ejecta horizon is marked by an Ir anomaly (~950pg/g; Kyte and Liu, 2002), and the magnetostratigraphic age control is excellent (Channell et al., 2003). A first-order correlation to the geomagnetic polarity time scale at Site 1090 places the impact ejecta horizon in Chron C16n.1n (279.01 mbsf) with a corresponding age of ~35.4 Ma, consistent with published radiometric ages. We generated a high-resolution carbon and oxygen stable isotope record of benthic foraminifera across the impact ejecta layer from 34.6-35.8 Ma (8 kyr sampling) and 33.7-36 Ma (16 kyr sampling). Our results show that a transient carbon isotope decrease (277-278 mbsf) of 0.4-0.5‰ is associated with the impact horizon. The δ13C anomaly persists for ~250 kyr; then the signal returns to ‘pre-impact' values. Following recovery from the transient excursion there were no long-term changes in global carbon isotopic values associated with the impacts. Our results show no significant changes in benthic foraminifera oxygen isotope values across the impact ejecta layers, implying that no major changes in deep-water temperatures occurred. Coeval benthic foraminiferal records also show the carbon isotopic excursion: 1) new benthic data from New Jersey slope Site 612 show a 0.5‰ change, though this record is partially truncated due to a hiatus; 2) Southern Ocean Site 689 shows a larger excursion (1.0‰) (Vonhof et al., 2000); and 3) Pacific Ocean Site 1218 shows a smaller anomaly (0.4‰) (Lear et al., 2004). We suggest this δ13C perturbation was global and directly related to the late Eocene impactor(s).
DE: 1645 Solid Earth (1225)
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 6022 Impact phenomena (5420, 8136)
DE: 8136 Impact phenomena (5420, 6022)
SC: Union [U]
MN: 2007 Joint Assembly