HR: 14:25h
AN: PP42C-03    [PDF]
TI: Planktic Foraminiferal Turnover and Stable Isotope Stratigraphy Across OAE1B in the Subtropical North Atlantic
AU: * Huber, B T
EM: huber.brian@nmnh.si.edu
AF: Smithsonian Museum of Natural History, Department of Paleobiology, MRC-121, Washington, DC 20560 United States
AU: Price, N A
EM: small_fzzy_mamml@yahoo.com
AF: Richard Stockton College of New Jersey, Jimmie Leeds Road, Pomona, NJ 08240 United States
AU: MacLeod, K G
EM: macleodk@missouri.edu
AF: University of Missouri, Columbia, Department of Geological Sciences, Columbia, MO 65211 United States
AB: Stable isotope data generated from glassy (diagenetically unaltered) foraminifera from the subtropical North Atlantic (ODP Site 1049) reveal abrupt paleoceanographic and faunal changes that coincide with the Aptian/Albian boundary and the onset of Oceanic Anoxic Event (OAE) 1b. At least three planktic and one benthic species per sample, selected at closely spaced intervals from the {\it Globigerinelloides algerianus} Zone (mid-Aptian) through uppermost {\it Ticinella bejaouaensis} Zone (uppermost Aptian), reveal a consistently low ($<$1.1$\permil$) vertical $\delta^{18}$O gradient, suggesting that the thermocline was weakly developed throughout this time. Benthic $\delta^{18}$O values show a slight positive increase from +0.5 $\permil$ during the mid-Aptian to +1.1% during the latest Aptian, then decrease to -0.2$\permil$ during peak Corg deposition in OAE 1b ({\it Hedbergella rischi} Zone, lowermost Albian). Assuming that the $\delta^{18}$O composition of Cretaceous seawater averaged -1.2$\permil$ and polar ice sheets were absent or very small, we estimate that middle bathyal waters at this site ranged from 7-9$\deg$C during the mid-late Aptian and warmed to 12$\deg$C during OAE 1b peak Corg deposition. Mid-late Aptian upper surface waters ranged from 11-12$\deg$C, then warmed to 20$\deg$C during OAE 1b. The simultaneous change in planktic foraminifer assemblages and stable isotope values indicates that the onset of OAE 1b involved major changes in the North Atlantic climate and oceanography.
DE: 4267 Paleoceanography
DE: 4870 Stable isotopes
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting