Advancing speleothem petrography and geochemistry proxies using cave-analogue experiments

• Applicant: Dr. Sylvia Riechelmann
• Subject Area: Geology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 536772595

Speleothem carbonates, explored through various proxies, are among the most extensively investigated climate archives. Specifically, cave monitoring programmes and cave analogue laboratory experiments are efficient tools for understanding processes controlling the precipitation of speleothems and their geochemical properties. Among the proxies studied, however, speleothem crystal fabrics and their bearing on environmental parameters remain underexplored. This is because previous work mainly focused on isotope fractionation between drip water and carbonate and less often on crystal morphology and elemental distribution coefficients of modern cave carbonates. Cave monitoring by the proponent and colleagues documents the influence of drip water Mg/Ca ratio on the calcite crystal morphology and the distribution coefficients of Mg and Sr. Hence, we propose to perform controlled laboratory experiments under cave-analogue conditions to investigate the relation between calcite crystal morphology, elemental ratios and distribution coefficients (DMg and DSr). The experimental water Mg/Ca and Sr/Ca ratios reflect the composition of drip waters monitored during cave monitoring programmes. Experimental cave water will constantly drip onto watch glasses set in a climate cabinet under stable environmental conditions and induce the precipitation of calcium carbonate. Watch glass precipitates will then be investigated for their petrographic, crystallographic, and geochemical properties. Results of the cave-analogue experiments will be linked to data obtained during cave monitoring studies and ultimately to the corresponding stalagmites and their crystal fabric. The proposed research aims to (i) determine the threshold limits for water Mg/Ca ratio controlling crystal morphology; (ii) link water Mg/Ca ratio and crystal morphology from cave-analogue experiments and cave monitoring data to speleothem crystal fabric; (iii) determine the threshold values for water Mg/Ca ratio controlling the distribution coefficients of Mg and Sr (DMg and DSr); and (iv) link calcite crystal morphology and stalagmite crystal fabric with DMg and DSr. This contribution aims to provide a framework against which existing and subsequent work can be placed to extract quantitative science, patterns and methods for the community.

• DFG Programme: Research Grants
• International Connection: Austria
• Co-Investigator: Professor Dr. Denis Scholz
• Cooperation Partner: Professor Dr. Christoph Spötl