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Research Interests |
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My research efforts are directed toward better understanding relationships between the distribution of fossil organisms and variations in paleoclimate/paleoceanography across a wide range of temporal and spatial scales. Current projects include examination of Late Cretaceous paleoceanography and the Cretaceous/Tertiary (K/T) boundary, the Permian/Triassic (P/T) boundary, and the measurement and interpretation oxygen isotopic ratios in phosphates. Cretaceous projects focus on the
extinction of inoceramid bivalves and the ecology of planktic foraminifera
in relation to deteriorating Cretaceous greenhouse climate conditions
and to the K/T asteroid impact. In addition to fossil data, oxygen,
carbon, and strontium isotopes are used to assess changing paleoenvironmental
conditions and to test the fidelity of the stratigraphic record. Exciting
recent results show that there was a pulse of intense weathering immediately
after the K/T boundary
event, that the subtropical Atlantic was warming
while mid- to high latitudes cooled, and suggest demonstrable
links among climate, continental weathering, oceanic productivity,
and foraminiferal assemblages. The P/T boundary work concerns the timing and tempo of faunal turnover among terrestrial vertebrates in South Africa. Carbon isotopic results suggest that extinctions among therapsids (P/T boundary) in the interior of Pangea were synchronous with extinctions in the shallow marine of China and coastal regions of Australia. More importantly, our data show that the event was rapid, but not instantaneous. This rate of change argues against several potential causal mechanisms commonly invoked to explain the P/T event. Current work is focused on possible changes sulfur isotopic ratios across the boundary. The phosphate efforts are motivated by a desire to better evaluate estimates of paleotemperature. The oxygen isotope paleothermometer applied to measurements on carbonate fossils is widely used in paleoceanographic studies, but the estimates made can be compromised by diagenetic alteration. Biogenic phosphate is relatively resistant to alteration and provide a second phase that can be used to test conclusions based on carbonates (and to make estimates for results that lack carbonate fossils). Work to date has been centered on Early Ordovician conodonts, but pilot studies are underway on material from several other intervals. |
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last revised: fall 2007 |
