The Making of Antarctica's Fjords
Below is a vertically-exaggerated reconstruction of the Lambert Glacier and Prydz Bay region of East Antarctica both at the present day (a and b) and 34 million years ago (c).
This work was carried out as part of NSF Antarctic Earth Sciences award (ANT #0838722) conducted in collaboration with Peter Reiners, George Gehrels, and graduate student Clare Tochilin at the University of Arizona and Sidney Hemming at Columbia University.
Collaborative Research: Erosion history and sediment provenance of East Antarctica from multi-method detrital geo- and thermochronology
Publications and Abstracts
Work related to this project now published in Nature Geoscience
and Geochemistry, Geophysics, Geosystems
Thomson, S.N., Reiners, P.W., Hemming, S.R. & Gehrels, G.E. (2013). The contribution of glacial erosion to shaping the hidden East Antarctic landscape. Nature Geoscience, 6, p. 203-207, doi:10.1038/ngeo1722.
In the News:
Tochilin, C.J, Reiners, P.W., Thomson, S.N., Gehrels, G.E., Hemming, S.R. & Pierce, E.L. (2012). Erosional history of the Prydz Bay sector of East Antarctica from detrital apatite and zircon geo- and thermochronology multidating. Geochemistry, Geophysics, Geosystems, 13, Q11015, doi:10.1029/2012GC004364.
Thomson, S.N., Reiners, P.W., Tochilin, C.J., Hemming, S.R. & Gehrels, G.E. (2011). The Cenozoic history of East Antarctic subglacial erosion and sediment flux from the offshore detrital thermochronometric record. Eos Transactions AGU, Fall Meeting Supplement, Abstract PP33B-1934.
Thomson, S.N., Reiners. P.W., Hemming, S.R., Cox, S.E. & Gehrels, G.E. (2011). An offshore thermochronometric record of post-Eocene East Antarctic subglacial erosion and landscape evolution. 11th International Symposium on Antarctic Earth Sciences, Edinburgh, UK.
Thomson, S.N., Hemming, S.R., Reiners, P.W. & Cox, S.E. (2009). Revealing the subglacial erosion and landscape evolution history below the East Antarctic ice sheet using detrital thermochronology. GSA Abstracts with Programs, Vol. 41, No. 7, p. 52
1209 Ap U-Pb ages
2020 AFT ages
214 AHe ages
283 Zr U-Pb ages
668 ZFT ages
31 ZHe ages
151 Hornblende Ar-Ar Ages
Figure 1a: 3D vertically exaggerated representation of East Antarctic ice surface (from the Bedmap 2 data-set) showing location of Lambert Glacier and offshore cores sampled in this study
Figure 1b: 3D vertically exaggerated representation of East Antarctic subglacial topography (from the Bedmap 2 data-set, surface rebound adjusted isostatically for removal of ice) showing outline of Figure 2 and location of Prime Meridian and Antimeridian (International date-line)
Figure 2: Map showing location of core hole samples, as well as newly acquired onshore AFT ages (black text) and apatite U-Pb ages (white text with black background) from moraines of the Pagadroma Group. Published bedrock ages shown as colored circles (Arne et al., 1993; Arne, 1994; Lisker et al., 2003; Lisker et al., 2007a; Lisker 2007b)
Detrital Apatite Data Summary:
Below are figures showing a summary of all the apatite U-Pb, fission track, and (U-Th)/He data that we have obtained so far from several different cores drilled in Prydz Bay (locations shown in Figures 1 and 2 above).
Pre-34 Ma: A very slowly eroding stable craton since the Permian
1) Slow constant pre-34 Ma erosion rates of 0.005-0.03 km/Myr for over 200 Myr.
2) Accelerated cooling between ~300 and 250 Ma at >0.05 km/Myr.
Figure 5: (a) Apatite fission-track vs (U-Th)/He “double-date” plot from ODP hole 1166A hole late Eocene sandstones. Points close to the 1:1 line (green field) represent fast cooling at the time represented by the AFT and AHe ages. Points along the red line represent long-term constant erosion rates. Points below the red line (blue field) represent grains that have undergone accelerated cooling since the time represented by the AHe age. (b) AFT versus AHe “triple-date” plot with color-coded U-Pb ages from the same grains from a slightly younger early Oligocene sandstone.
Figure 6: (a) Simple thermal model of rocks in the Lambert catchment that were at different temperatures (or depths) at 35 Ma. The paths are based on thermochronologic constraints (fast cooling at end Permian followed by very slow cooling until onset of widespread glaciation at ~34 Ma). (b) Predicted AFT and AHe age-depth profiles at 35 Ma using published annealing and diffusion models incorporated into HeFTy thermal modeling software (Ketcham, 2005). The long period of slow cooling produces a diagnostic rapidly decreasing age versus depth profile. (c) Predicted AFT and AHe age-depth profiles at 35 Ma with an additional 50°C mid-Creaceous heating episode.
Post-34 Ma: Up to 3km localized glacial incision in Lambert Glacier catchment
Figure 7: AFT-AHe age pairs fitted to predicted 34 Ma age-depth profiles (from Figure 6 above) compared to Bedmap2 bedrock topography and single-dated grain age data.
Figure 8: Cartoon illustrating the concept of thermochronometric “stratigraphy”. If sudden incision occurs into an old stable landsurface where a steep age versus depth profile has developed, then ongoing incision will quickly yield apatite with younger AHe and AFT ages that previously resided at depth. The more incision that occurs, the younger the ages that will be found in detrital apatite deposited in Prydz Bay (or from the bedrock at the bottom of deeply incised troughs in the hinterland).
Implications for Cenozoic Sediment Flux Estimates
Since 34 Ma = ~32,165 km3/Myr (= ca. 90 x 106 t/yr)
If most during early Oligocene = ~218,000 km3/Myr (= ca. 625 x 106 t/yr)
For comparison Yukon River has a sediment load of ~60 x 106 t/yr; Mississippi River has a load of ~400 x 106 t/yr; and the Amazon River has a load of ~1200 x 106 t/yr
Figure 9: Plot of geophysical (local) relief (elevation difference between a smooth surface connecting the highest points in the current landscape calculated using a moving 50km radius circle, and the current topography using Bedmap2. The values agree well with the depths of incision implyed by detrital apatite thermochronometry. The total volume represented by the geophysical relief in this figure is 1,100,000 km3.
Last Modified: April 23rd, 2013