APPENDIX 1: EXTENDED SAMPLE INFORMATION.

Transcription

1 1 APPENDIX 1: EXTENDED SAMPLE INFORMATION. Location map of the giant bar between Inya and Little Jaloman (topographic map 1:50,000). The circle marks the sampling location. Giant bar boulders (location 1 see Fig. 1) Photograph Information Height above ground [m] Basal plane area [m²] IN m 23.2 m²

2 2 Photograph Information Height above ground [m] Basal plane area [m²] IN m 3.6 m³ IN m 2.8 m² IN m 5.4 m²

3 3 Photograph Information Height above ground [m] Basal plane area [m²] Boulders in the former lake basin (locations 2, 3, 4 see Fig. 1) KO m 15 m² KU m 12 m² CHU m 7.5 m²

4 4 APPENDIX 2: Analytical techniques and calculation scheme s were taken from the center of the boulder surfaces. The samples were crushed and ground and the quartz fraction was separated following the procedures described by Kohl & Nishiizumi (1992) and Ivy-Ochs (1996). BeO was extracted using a combination of column chemistry separation and selective hydroxide precipitation (Ochs & Ivy-Ochs, 1997). Apparent exposure ages were calculated from the measured 10Be nuclide concentration, the sampling depth and the site-specific production rate (Lal, 1991; Stone, 2000). The ages were corrected for topographic shielding (Dunne et al., 1999), variations in the geomagnetic field (Laj et al., 2004), erosion, snow cover and uplift, considering the following aspects: (i) The erosion rate for granitic rock in the study area was calculated from the measured nuclide concentration in a bedrock sample west of the Chuya gorge (CH-03-02). The sample was taken from glacially abraded bedrock behind a prominent moraine ridge. The moraine was deposited after the flood event and dated to 13.8±1.4 ka (Reuther, 2005). Quartz crystals on the glacially abraded granitic bedrock protruded about 2.5 cm above the surrounding rock. This grain-to-grain relief (2.5 cm) and the apparent exposure age of the surface (13 ka) were used to calculate the local erosion rate in a first order approximation (1.9 mm/ka-1). Only the sample KO was not corrected for erosion because here a quartz vein in a fine-grained schist matrix was sampled which did not protrude above the rock matrix, indicating negligible surface erosion. information: Lat / Long Altitude thickness fcorr (topo, slope)* 10 Be atom AMS error Production rate Apparent age # [ ] [m asl] [cm] [g -1 SiO 2-1 *10 5 ] [%] [atm g -1 yr -1 ] [ 10 Be kyr ] 50.2 N, CH , E * correction factor for the effect of topographic shielding and surface geometry (exponential depth profile, nucleonic attenuation length 155 g cm -2, muonic attenuation length 1510 g cm -2, coefficient m=2.3). blank-corrected. local production rate corrected for geometry, topography, sample thickness, erosion, snow cover, uplift and geomagnetic variations. # corrected only for topographic shielding, geometry and sample thickness.

5 5 (ii) The Altai mountain region is currently subject to uplift (Larroque et al., 2001). Uplift rates from the neighboring Gobi Altai are reported to be around 1 mm a-1 (Owen et al., 1997). This value is used in the age calculation. (iii) Snow cover corrections were only applied to the boulders on the giant bar in accordance with field observations. The three high-standing boulders in the basins are assumed to have not been covered by snow because it is likely they were windswept. For the other samples, a conservative value of 15 cm snow cover for 4 months per year was assumed (Onuchin & Burenina, 1996; Krenke, 1998). References: Dunne, J., Elmore, D. and Muzikar, P., 1999, Scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth of sloped surfaces: Geomorphology, v. 27, p Ivy-Ochs, S., 1996, The dating of rock surfaces in situ produced 10 Be, 26 Al and 36 Cl with examples from Antarctica and the Swiss Alps. PhD Thesis No 11763, ETH Zürich, 196 p. Kohl, C.P. and Nishiizumi, K., 1992, Chemical isolation of quartz for measurement of in-situ produced cosmogenic nuclides: Geochimica et Cosmochimica Acta, v. 56, p Krenke, A., 1998, updated 2004, Former Soviet Union Hydrological Snow Surveys: edited by NSIDC. Boulder, CO: National Snow and Ice Data Center/World Data Center for Glaciology. Digital media. Laj, C., Kissel, C. and Beer, J., 2004, High resolution global paleointensity stack since 75 kyr (GLOPIS-75) calibrated to absolute values: Geophysical Monograph Series 145, p Lal, D., 1991, Cosmic ray labeling of erosion surfaces: in situ nuclide production rates and erosion models: Earth and Planetary Science Letters, v. 104, p Larroque, C. Ritz, J.-F., Stéphan, J.-F., Sankov, V., Arjannikova, A., Calais, E., Dévercherre, J., and Loncke, L., 2001, Interaction compression extension à la limite Monglie-Sibérie: Comptes Rendue de l Academie de Sciences Paris, v. 332, p Ochs, M. and Ivy-Ochs, S., 1997, The chemical behavior of Be, Al, Fe, Ca, and Mg, during AMS target preparation from terrestrial silicates modeled with chemical speciation calculations: Nuclear Instruments and Methods in Physics Research Section B, v. B123, p Onuchin, A. A. and Burenina, T. A., 1996, Climatic and geographic patterns in snow density dynamics, Northern Eurasia: Arctic Alpine Research, v. 28, p

6 6 Owen, L.A., Windley, B.F., Cunningham, W.D., Badamgarav, J. and Dorjnamjaa, D., 1997, Quaternary alluvial fans in the Gobi of southern Mongolia: evidence for neotectonics and climate change: Journal of Quaternary Science, v. 12, p Reuther, A.U., 2005, Surface exposure dating of glacial deposits from the last glacial cycle. Evidence from the Eastern Alps, the Bavarian Forest, the Southern Carpathians and the Altai Mountains: PhD thesis, University of Regensburg, Germany (accepted for publication in the series: Relief, Klima, Paläoboden, publisher: Schweizerbart, Stuttgart/Germany). Stone, J. O., 2000, Air pressure and cosmogenic isotope production: Journal of Geophysical Research, v. 105 B10, p