HR: 14:10h
AN: PP32C-03 INVITED     [PDF]
TI: Glacioeustatic Changes in the Early and Middle Eocene (51-42 Ma) Greenhouse World Based on Shallow-Water Stratigraphy from ODP Leg 189 Site 1171 and Oxygen Isotope Records
AU: * Pekar, S F
EM: pekar@ldeo.columbia.edu
AF: Queens College, School of Earth and Environmental Sciences, CUNY, 65-30 Kissena Blvd., Flushing, NY 11367 United States
AU: * Pekar, S F
EM: pekar@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, Route 9W, Palisades, NY 10964 United States
AU: Hucks, A
EM: audreyh@rice.edu
AF: Rice University, Department of Earth Science, Houston, TX 77005 United States
AU: Fuller, M
EM: MFU3961215@aol.com
AF: University of Hawaii at Manoa, Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, 1618 East-West Road, POST Bldg., Honolulu, HA 96822 United States
AU: Li, S
EM: sfl34@columbia.edu
AF: Columbia University, Department of Earth and Environmental Engineering, New York, NY 10027 United States
AB: Sequence boundary ages identified in shallow-water sediments obtained from ODP Leg 189 Site 1171 compare well with other stratigraphic records (New Jersey USA and Northwest Europe) and oxygen isotope increases, indicating that significant global sea-level changes ($>$10 m) occurred during the late early to middle Eocene (51-42 Ma). Six sequence boundaries were identified and dated using lithology, water-depth changes, age control (bio- and magnetostratigraphy), and CaCO$_{3}$ content and physical properties (e.g., photospectrometry). Benthic foraminiferal biofacies and planktonic/benthic foraminiferal ratios were used to estimate water-depth changes. Glauconitic clays and silts occur above the basal surface with increasing water depths indicated by foraminiferal studies (transgressive systems tracts). This is overlain by decreasing glauconite silt and maximum nannofossil percents, and an increase in CaCO$_{3}$ content (condensed section), which is followed by a decrease in CaCO$_{3}$ content as clays then silts increase up section as water depths decreased (highstand systems tracts). A comparison of sequence boundary ages from Site 1171 (50.9, 49.2, 48.5, 47.8, 47.1, 44.5 and 42.6 Ma) to oxygen isotope increases shows a good correlation. Additionally, sequence boundaries identified in Eocene studies from Leg 150X onshore boreholes (New Jersey, USA) and NW Europe compare well with the timing of sequence boundary development at Site 1171. The synchronous nature of sequence boundary development from globally distal sites and oxygen isotope increases indicates a global control. The only mechanism that can explain these large rapid changes is glacioeustasy. This is supported by modeling studies (Deconto and Pollard, 2003) and CO$_{2}$ estimates (Pearson and Palmer, 2000) showing that the first time CO$_{2}$ levels decreased below a threshold that would support the development of an ice sheet in Antarctica was at $\sim$51 Ma. Estimates of sea-level amplitudes range from ~20$\pm$7 m for the early Eocene (51-49 Ma) and $\sim$25$\pm$8 m to $\sim$45$\pm$14 m for the middle Eocene (48-42 Ma) using constraints established for the Oligocene oxygen isotope records.
DE: 4556 Sea level variations
DE: 4870 Stable isotopes
DE: 9310 Antarctica
DE: 9330 Australia
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting