2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 106-15
Presentation Time: 11:35 AM


HAYNES, Shannon J., Department of Geological Sciences, University of Missouri Columbia, 101 Geological Sciences Building, Columbia, MO 65211, MACLEOD, Kenneth G., Department of Geological Sciences, University of Missouri-Columbia, Columbia, MO 65211 and MARTIN, Ellen E., Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, FL 32611-2120

An early Maastrichtian increase in benthic oxygen isotope values (δ18O) in the equatorial Pacific and South Atlantic Oceans indicates a brief (~1-2 million year) cooling event at c. 71.5 Ma. Here, we use neodymium isotopes (εNd) from fish debris (microfossil tooth, scale, and bone fragments) to make inferences about intermediate and deep water formation and circulation patterns across the early Maastrichtian cooling event. Correlated shifts in εNd values at widely spaced sites could indicate a change in the location of bottom water formation, whereas the absence of an εNd shift could indicate cooling in the region of downwelling without requiring a change in circulation patterns. Cooling in many regions appears to correlate with changes in εNd values that are consistent with an increase in Southern Component Water (SCW). Anomalously high εNd values are reported during the early Maastrichtian cooling event at a site 525 on Walvis Ridge, but this excursion does not fit the SCW model. For Site 525, the early Maastrichtian shift was attributed to local volcanism with the correlation to widespread δ18O and δ13C excursions apparently coincidental.

At Site 525 we confirm anomalously high εNd values during the early Maastrichtian cooling event, but also observe a 2-3 εNd unit decrease 30 m above the cooling event. Further, even late Maastrichtian values at Site 525 remain ~2 εNd units above expected SCW values, but typical SCW values are found in late Maastrichtian samples in deeper sites from the northern flank of Walvis Ridge. To test whether the εNd value anomalies recorded on the top of Walvis Ridge are local and to search for a record of Southern Component Water along the bathymetric barrier between the Southern Ocean and the South Atlantic, we are analyzing samples from Site 516 (Rio Grande Rise) as well as increasing sampling density at Site 525, and Site 463 (mid-Pacific Mountains, equatorial Pacific Ocean). In addition we are analyzing spot samples from the North Atlantic Ocean, South Atlantic Ocean, and Caribbean Sea.