HR: 14:40h
AN: PP23C-05    [Abstracts]
TI: Late Cretaceous Evolution of North Atlantic Deep Waters: Neodymium Isotopic Evidence From the Cape Verde Basin (DSDP Leg 41, Site 367) and Bermuda Rise (DSDP Leg 43, Site 386)
AU: * Jiménez, A
EM: jimeneza@missouri.edu
AF: Department of Geological Sciences, University of Missouri, Columbia, MO 65211, United States
AU: MacLeod, K G
EM: macleodk@missouri.edu
AF: Department of Geological Sciences, University of Missouri, Columbia, MO 65211, United States
AU: Martin, E E
EM: emartin@geology.ufl.edu
AF: Department of Geological Sciences, University of Florida, Gainesville, FL 32611, United States
AU: Bourbon, E
EM: elo05@ufl.edu
AF: Department of Geological Sciences, University of Florida, Gainesville, FL 32611, United States
AB: The ε_Nd values of Late Cretaceous fish teeth and fish debris have been determined for two deep- ocean sites in the North Atlantic: DSDP Site 367 in the Cape Verde Basin and DSDP Site 386 on Bermuda Rise. These samples provide the first Cretaceous ε_Nd data for sediments deposited at depths of modern deep waters. As such they provide a novel perspective on the source and circulation of deep waters during the Late Cretaceous greenhouse climate including possible changes during ocean anoxic event 2 (OAE2). The fish remains analyzed exhibit good to excellent preservation and show coherent stratigraphic trends across lithologies ranging from carbonaceous black shales to carbonate-poor gray siltstones to red claystones. Unfortunately, fish debris is rare to absent in many samples, and tests are underway to determine whether dispersed Fe-Mn coatings provide a second reliable archive of bottom water values at these sites. At the Cape Verde site (eastern tropical North Atlantic), background ε_Nd values are about -9 through most of the Late Cretaceous, and a positive excursion to -6.5 occurs during OAE2. At the Bermuda Rise site (western subtropical North Atlantic), Late Cretaceous ε_Nd values are -6 to -8 but shift to -10 by the early Paleocene. The OAE2 interval, if present, has not yet been identified at Bermuda Rise. Values of -7 to -9 have been reported for fish debris and other phosphates from shelfal deposits of NW Tethys (Pucéat et al., 2005) and central Tethys (Soudry et al., 2006) suggesting North Atlantic deep waters could have been sourced largely within the North Atlantic-Tethyan region throughout much of the Late Cretaceous. However, the difference in ε_Nd values between sites suggests that there may have been a relatively radiogenic component (e.g., Pacific waters) in deep waters on the west side of the mid-Atlantic Ridge. Further, the OAE2 excursion at the Cape Verde site indicates that at least some deep waters were affected during OAE2. Possible explanations for the ε_Nd excursion include an influx of (or mixing with) radiogenic waters sourced outside the North Atlantic or the input of relatively radiogenic Nd introduced by Caribbean LIP volcanism "upstream" from the Cape Verde Basin. Finally, Paleocene ε_Nd values at Bermuda Rise indicate local deep waters had a strong North Atlantic signature by the early Cenozoic.
DE: 4515 Deep recirculations
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4924 Geochemical tracers
DE: 9325 Atlantic Ocean
DE: 9610 Cretaceous
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting