HR: 12:05h
AN: PP52B-08    [Abstracts]
TI: Timing is everything: ecological vs. evolutionary pacing of Triassic-Jurassic carbon cycle disruptions
AU: * Whiteside, J H
EM: Jessica_Whiteside@Brown.edu
AF: Brown University, 324 Brook Street, Box 1846, Providence, RI 02912, United States
AU: Olsen, P E
EM: polsen@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Eglinton, T I
EM: teglinton@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, United States
AB: Eruption of Earth's largest flood basalt, the Central Atlantic Magmatic Province (CAMP) has been proposed as the trigger for a major carbon cycle disruption at the Triassic-Jurassic mass extinction interval at ~201 Ma. Inferred from negative excursions in the carbon isotopic composition (δ¹³C) of carbonate and organic matter, this perturbation has been linked to massive dissociation of isotopically light, methane-rich gas hydrates caused by volcanogenic CO₂-induced global warming. However, both the sequence and duration of the CAMP eruptions relative to the carbon cycle perturbation remain circumstantial and indirect, because the data have been from stratigraphic sections far from the flood basalts and without accumulation rate constraints. Here we use a record of atmospheric (δ¹³C) from specific molecules (nC₂₅ - nC₃₂ n-alkanes) diagnostic of terrestrial plant leaf waxes from astronomically-paced cyclical lacustrine strata in which CAMP flood basalts are interbedded to directly examine the relationship between the (δ¹³C) excursions and their durations. We show that the flood basalts postdate the abrupt start of a ~400 ky negative excursion coincident with the initiation of the mass extinction event, but predate a protracted 1.5 m.y. negative excursion. Based on a modified BLAG carbon cycle model, the timing and long durations of our (δ¹³C) excursions are incompatible with CAMP-triggered gas hydrate release. Instead, we suggest that the (δ¹³C) pattern is more consistent with a catastrophically-triggered functional reorganization of the biosphere, part of which involved the ascent of dinosaurs to ecological dominance, playing out over evolutionary time.
DE: 0420 Biomolecular and chemical tracers
DE: 1055 Organic and biogenic geochemistry
DE: 4914 Continental climate records
DE: 4950 Paleoecology
DE: 8408 Volcano/climate interactions (1605, 3309)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting