Stable isotopic response to the late Eocene extraterrestrial impact events

• Main Author: Pusz, Aimee E.
• Format: Text
• Language: unknown
• Published: No Publisher Supplied 2007
• Subjects: Southern Ocean; Pacific
• Online Access: https://dx.doi.org/10.7282/t36d5tcv; https://rucore.libraries.rutgers.edu/rutgers-lib/23860/

Two large and near synchronous late Eocene (~35.4 - 35.5 Ma based on radiometric ages) impact events (Popigai and Chesapeake Bay) produced well-preserved structures, yet the environmental response to these impacts is poorly understood. Impact events generate ejecta deposits that surround source craters creating characteristic strewn fields. The Chesapeake Bay and Popigai impactors produced strewn fields that serve as stratigraphic markers for these impact events and the late Eocene. The late Eocene global temperature history and carbon budget are poorly constrained because of sparsely sampled ??18O and ??13C records. In this thesis: 1) the Chesapeake Bay microtektite layer is shown to be stratigraphically younger than the Popigai cpx-bearing (or microkrystite) layer, by ~ 4 kyr; 2) a first order correlation of the late Eocene ejecta layers identified in ODP Site 1090 to the geomagnetic polarity timescale in Chron C16n.1n (279 mbsf) is provided with a corresponding magnetochronologic age of 35.43 Ma, consistent with published radiometric ages; 3) new stable isotopic data is presented from Site 1090 and DSDP Site 612 that show a large and transient ??13C excursion (~0.5 0/00) associated with the impacts. At Site 1090, late Eocene benthic foraminifera are well preserved, the identified ejecta horizon is marked by an Ir anomaly (~950 pg/g), and the published magnetostratigraphic age control is excellent. Site 1090 ??13C and ??18O records of benthic foraminifera across the ejecta layer from 34.6 - 35.8 Ma (8 kyr sampling) and 33.7 - 36 Ma (16 kyr sampling) and a high-resolution (2 kyr sampling) bulk-carbonate record (278 - 279.5 mbsf) are presented. Coeval benthic foraminiferal records show a ??13C excursion from: 1) new benthic data from Southern Ocean Site 1090 show a 0.5 0/00 anomaly; 2) new benthic data from New Jersey slope Site 612 show a 0.5 0/00 change, though this record is partially truncated by an unconformity; 3) Southern Ocean Site 689 published data shows a 1.0 0/00 excursion; and 4) Pacific Ocean Site 1218 published data shows a 0.4 0/00 anomaly. The ??13C excursion is suggested to reflect a perturbation in the global carbon cycle and to be directly related to the late Eocene impactor(s).