Martin L. C. P., Blard P. H., Lave J., Braucher R., Lupker M., Condom Thomas, Charreau J., Mariotti V., Davy E. (2015). In situ cosmogenic Be-10 production rate in the High Tropical Andes. Quaternary Geochronology, 30 (A), p. 54-68. ISSN 1871-1014.
Titre du document
In situ cosmogenic Be-10 production rate in the High Tropical Andes
Martin L. C. P., Blard P. H., Lave J., Braucher R., Lupker M., Condom Thomas, Charreau J., Mariotti V., Davy E.
Source
Quaternary Geochronology, 2015,
30 (A), p. 54-68 ISSN 1871-1014
Continental climate change during the late glacial period has now been widely documented thanks to Cosmic-Ray Exposure (CRE) dating of glacial features. The accuracy of these CRE ages mainly relies on a priori knowledge of the production rate of the cosmogenic nuclide that has accumulated in a specific mineral. To produce unequivocal and accurate chronologies of glacier fluctuations during the late glacial period, it is crucial that the cosmogenic nuclide production rates are better constrained, particularly in the high tropics where existing spatial and temporal scaling models show significant discrepancies. Here we report a new production rate established at low latitude (19 degrees S) and high elevation (3800 alas on the Challapata fan-delta, at the edge of the Paleolake Tauca, on the flank of Cerro Azanaques (Bolivia). Sedimentological evidence for synchronicity with the Tauca Lake highstand along with U-Th and C-14 measurements established that the fan-delta is 16.07 +/- 0.64 kyr BP old. In situ-produced Be-10 concentrations measured in 15 boulders lying on the fan-delta yield a mean Be-10 concentration of 4.92 +/- 0.05 x 10(5) at g(-1). A local in situ Be-10 production rate of 30.8 +/- 1.3 at g(-1) yr(-1) is thus obtained at 3800 masl and 19 degrees S. Application of the "Lal-modified" scaling scheme to this Azanaques production rate, using a standard atmosphere and the Muscheler et al. (2005) geomagnetic reconstruction, leads to a Sea Level High Latitude (SLHL) in situ Be-10 production rate of 3.76 +/- 0.15 at g(-1) yr(-1) (1 a uncertainty). In addition, we propose a reference in situ Be-10 calibration dataset for the region that combines the production rates of this study with those of Blard et al. (2013b) and Kelly et al. (2015). This dataset of three calibration sites shows a good consistency and yields a regional in situ Be-10 production rate of 3.74 +/- 0.09 at g(-1) yr(-1) using the same scaling.
Plan de classement
Hydrologie [062]
;
Géologie et formations superficielles [064]
Description Géographique
BOLIVIE ; ANDES ; ZONE TROPICALE ; TAUCA LAC ; AZANAQUES CORDILLERE
