Open Access87 Sr/ 86 Sr in recent accumulations of calcium sulfate on landscapes of hyperarid settings: A bimodal altitudinal dependence for northern C hile (19.5°S–21.5°S)
Author(s) -
Cosentino N. J.,
Jordan T. E.,
Derry L. A.,
Morgan J. P.
Publication year - 2015
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2015gc005954
Subject(s) - geology , holocene , anhydrite , sulfate , gypsum , altitude (triangle) , sea level , sea salt , geochemistry , mineralogy , oceanography , chemistry , paleontology , aerosol , geometry , mathematics , organic chemistry
An elevation‐dependent relationship of the 87 Sr/ 86 Sr ratio of Holocene surface accumulations of sulfate salts is demonstrated for a continental margin hyperarid setting. In the Atacama Desert of northern Chile, gypsum and anhydrite of multiple origins exist widely on superficial materials that originated during the last 10,000 years. An important source of calcium sulfate is from offshore‐generated stratocumulus clouds that are advected onto the continent, where they generate fog that transfers water droplets to the ground surface which, upon evaporation, leaves calcium sulfate crystals. Meteorological measurements of the cloud base and top altitudes average ∼400 m and ∼1100 m above sea level (masl), respectively. The seawater ratio of 87 Sr/ 86 Sr (0.70917) is distinctively higher than that reported for weathered mean Andean rock (less than 0.70750). Samples of 28 modern surface salt accumulations for locations between 200 and 2950 masl and between ∼19°30′ and ∼21°30′S verify that 87 Sr/ 86 Sr varies as a function of site altitude. Sites below 1075 masl and above 225 masl display calcium sulfate 87 Sr/ 86 Sr of mean value 0.70807 ± 0.00004, while the ratio outside this altitudinal domain is 0.70746 ± 0.00010. Thus, the 87 Sr/ 86 Sr ratio of Holocene salt accumulations differentiates two altitudinal domains.