Testing the application of meteoric Be-10/Be-9 ratios on dating calcium sulphate-rich wedges from the Atacama Desert
Ms Aline Zinelabedin1, Dr. Benedikt Ritter1, Dr. Steven Binnie1, Dr. Svenja Riedesel2, Prof. Tony Reimann2, Prof. Tibor Dunai1
1Atmosphere And Ocean Research Institute, The University Of Tokyo, Kashiwa, Japan, 2Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology , Tsukuba, Japan, 3Hosei University, Chiyoda-ku, Japan, 4MALT, The University of Tokyo, Bunkyo-ku, Japan
Subsurface wedges are common geomorphological features in periglacial environments and typically associated with polygonal patterned grounds on the surface. Polygonal patterned grounds are also observed surface expressions on Mars suggesting similar wedge structures and formation conditions in the Martian subsurface. Wedges in periglacial environments show a characteristic vertical lamination being the product of cryogenic processes in the subsurface. These geomorphological features similarly occur in arid to hyperarid environments, such as in the Atacama Desert, where haloturbation and salt heave mechanisms are suggested to control wedge-polygon formation. X-ray diffraction and x-ray fluorescence analyses of the wedges from the Atacama Desert revealed various calcium-sulphate phases as potential drivers for wedge-growth activity. The wedge formation is linked to varying water activity resulting in hydration- and dehydration-induced phase transitions of calcium-sulphate phases. In combination with crystallisation pressures of (re-)precipitating salts from infiltrated solutions, these salt dynamics lead to considerable volumetric changes in the deposits and result in a stress increase in the subsurface. The stress releases upward and expresses in a microtopographic signature of the surface, such as the polygonal patterned ground.
The subsurface-wedge activity in the Atacama Desert is strongly dependent on the occurrence of water of unknown state and volume. Geochronological data of calcium-sulphate wedges are crucial to temporally resolve the wedge formation and potentially use the wedge-polygon system as a palaeoclimate indicator. We test the application of cosmogenic nuclide dating on calcium sulphate-rich wedges from the Atacama Desert by using meteoric ¹⁰Be/⁹Be ratios. During wedge formation surface material is assumed to be transported through open soil fractures into the subsurface and deposited as alternating layers. Once the sediment is deposited, the meteoric ¹⁰Be/⁹Be ratio is only dependent on the radioactive decay of ¹⁰Be, which allows us to constrain the time duration between numerous wedge samples. We also apply post-infrared infrared stimulated luminescence (post-IR IRSL) dating on the subsurface-wedge material to confirm the obtained meteoric ¹⁰Be/⁹Be data and possibly determine individual deposition ages. Our post-IR IRSL results of coarse-grain feldspars extracted from calcium-sulphate wedges indicate multiple phases of wedge formation during the Pleistocene.
My name is Aline Zinelabedin and I am PhD student at the University of Cologne. My PhD project is involved in the CRC 1211 “Earth Evolution at the dry limit” and I investigate the impact of salt dynamics on the geomorphology of the Atacama Desert.