HR: 0800h
AN: PP41A-0623 [Abstracts]
TI: Provenance of Ice-Rafted Debris and Icebergs Offshore of Prydz Bay, Antarctica, From the Early Miocene
to the Present
AU: * Chung, E
EM: elchung@umd.edu
AF: University of Maryland, Department of Geology, College Park, MD 20742
United States
AU: Williams, T
EM: trevor@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964
United States
AU: van der Flierdt, T
EM: tina@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964
United States
AU: Roy, M
EM: roy.martin@uqam.ca
AF: Universit‚ du Qu‚bec … Montr‚al, D‚p. des Sciences de la Terre
et de l'AtmosphŠre,
C.P. 8888, Succ. Centre-Ville, Montreal, QC H3C 3P8
Canada
AB:
Ice-rafted debris (IRD) in Southern Ocean sediments indicates the presence of ice sheets or glaciers on Antarctica through
time. The geochemical and isotopic signature of the IRD can be matched with the known signature of different sectors of
Antarctica to identify the source of the IRD, and thus the launching sites of the icebergs that carried it. Thus, IRD layers
from ODP Leg 188 Site 1165, 400 km offshore of Prydz Bay, Antarctica, provide a window into the geological past to
investigate where icebergs originated, traveled, and melted from the early Miocene to the present.
The two main potential sources of icebergs, Prydz Bay and Wilkes Land, have been found to have distinct Neodymium and Argon
isotopic signatures, and in the present day, the IRD offshore of Prydz Bay comes almost entirely from the Prydz Bay sector of
the continent (Roy et al., submitted to Geology). This study applies the same techniques back to 19 Ma, using Nd isotopes on
15 whole sediment samples, and Ar isotopes (which give the age of the last major thermo-tectonic event) on individual
hornblende grains from 8 IRD layers.
Nd isotopes vary between an epsilon-Nd of -14.5 to -20.3 but do not show any systematic trend with age or within IRD layers
of the same age. The epsilon-Nd values suggest the sediment is a mixture sourced from the Prydz Bay (-16.5 to -20.7) and the
Wilkes Land (-10.7 to -16.9) sectors. The Argon ages are predominately in the 400-600 Ma range, reflecting the metamorphism
of the Pan-African orogeny, typical of most of East Antractica. However, many of the Argon ages reflect the global Grenville
orogeny (1100-1300 Ma). This age is only preserved in the Wilkes Land area east of the drill site and is therefore indicative
of a significant influx of icebergs from Wilkes Land, contrasting with the present day. We speculate that this observation
points to a more dynamic ice sheet in the geological past. Interestingly, there seems to be no major change in provenance of
icebergs at the mid-Miocene climate transition.
DE: 0732 Icebergs
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 3022 Marine sediments: processes and transport
DE: 3036 Ocean drilling
DE: 9310 Antarctica (4207)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005