BE OF HYPER-ARID SOILS IN THE ATACAMA DESERT, CHILE

Due to the hyper-aridity, soil accumulation in the Atacama is radically different from any other place in the world. The desert is rich in salt and dust deposits that have mostly been built up as layers over time through atmospheric deposition in a sedimentation process that is similar to the formation of marine sediments and ice cap build up in polar regions. Stable isotopes of oxy-anions in the Atacama soils suggest that they may be a new paleoclimate proxy that extends back to millions of years before present. In order to utilize these soil oxy-anions as paleoclimate proxies, however, new approaches need to be established to produce accurate soil chronology as a function of depth. We have utilized meteoric ³⁶Cl and ¹⁰Be to establish the age of Atacama soil as a function of depth. ³⁶Cl and ¹⁰Be were extracted from soil samples that were collected from a natural gas pipeline trench in Baquadano region of the Atacama at a soil sampling vertical resolution of ~ 5 cm. Soluble salts were leached from the soils using deionized water and geochemical and isotopic analysis as conducted on the solutes. The ³⁶Cl and ¹⁰Be abundances were determined using the Accelerator Mass Spectrometer at the Purdue Rare Isotope Measurement (PRIME) laboratory. The preliminary ³⁶Cl dating of the Atacama soil suggested that the soil age at 2 meter depth is ~670 ka. The meteoric ³⁶Cl activity seems to be affected both small amounts of aqueous leaching and by the shielding effect of the earth’s magnetic field. The less soluble meteoric ¹⁰Be was used to estimate the intensity of earth’s magnetic field and to correct for the mobility of ³⁶Cl in the Atacama soil layers. Used in concert, meteoric ³⁶Cl and ¹⁰Be can be an accurate, high resolution dating method for soils in hyper-arid regions.