Project C4

Gypsum desert & atmospheric deposition

Research areas: Geochemistry, Mineralogy, Crystallography and Geomorphology

Principal investigators: Prof. Dr. Sandro Jahn, Prof. Dr. Carsten Münker, Prof. Dr. Michael Staubwasser, Dr. Christoph Lenting, Dr. Benedikt Ritter

Project Info: Phase 2

Gypsum and other CaSO₄ phases are the most common evaporites in the hyper‐arid Atacama Desert, along with major and minor salts, such as halites and nitrates. Halite and nitrate abundance follow a combination of large‐scale gradients in moisture availability (NO₃^2‐) combined with proximity to the ocean source (Cl^‐, SO₄^2‐, Na⁺). Sulfate distribution is the most complex, as it has marine and stratospheric sources, is less prone to flushing‐out, and is redistributed by aeolian deposition and moisture‐related surface activity over probably long time‐scales. The abundance ratio of primary gypsum and secondary anhydrite seemingly depends on a complex feedback of climatic, chemical, and geomorphologic factors not yet understood. Local field observations of gypsum and anhydrite distribution in the ubiquitous thick gypsic soil show abundant nodules, wedges and polygonal patterned ground, which confirm the importance of secondary redistribution. However, our experiments indicated that anhydrite cannot directly form from primary gypsum at arid conditions in the pure H₂O‐CaSO₄ system but may occur at hypersaline wet conditions that we anticipate in a hyper‐arid environment with episodic moisture supply and high abundance of halite and nitrates.

Based on the results from the first project phase, we therefore hypothesize

that gypsum phase transitions are the key in understanding the evolution of hyper‐arid environments like the Atacama Desert,
that climatic and geomorphologic feedbacks may drive or inhibit the transformation, and
that gypsum group minerals are a unique archive of palaeo‐environmental change through time.

The main objectives of this project in the second phase are therefore, to study the abundance of Ca‐sulfates with respect to

their formation kinetics, e.g. understanding phase transformations at variable temperature, humidity and salinity,
their chemical formation environments, e.g. principal sources of salts (marine, atmospheric, hydrothermal) and environmental fractionation of salt abundances at the surface, and
their dependence on geomorphologic surface processes.

We seek to explore the timing and rates of deposition and the interplay of reactions on the atomic and chemical level with geomorphological controlled water‐driven pedogenic and landscape processes. These three key topics will be addressed in four work packages. Three of those will apply a large suite of atomistic, mineralogical, elemental, isotopic, and sedimentological analytical methods. The fourth will provide existing screening methods, fieldwork coordination and interdisciplinary scientific exchange and synthesis.