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Reconstructing conditions during dolomite formation in evaporative Triassic environments (TRIADOL)
Date du début: 1 avr. 2014, Date de fin: 31 mars 2016 PROJET  TERMINÉ 

Dolomite is besides calcite the most abundant carbonate mineral in the geological record. However, the conditions and mechanisms of its formation are poorly understood. Most dolomite is considered to have formed at elevated temperatures when sediments became deeply buried over geological time scales. Abundant dolomite occurs in shallow marine carbonate deposits of the ancient Triassic Tethys margin, which today forms part of the Eastern and Southern Alps. Hitherto evidence indicates that some of these dolomites are not of a burial origin, but are penecontemporaneous; i.e. they formed during or shortly after sedimentation. Such dolomites apparently formed in extremely shallow water under the influence of evaporative conditions, similar to modern examples of evaporation-induced dolomite formation. Nevertheless, the environmental conditions that prevailed in the Triassic environments remain poorly constrained.The proposed study aims at mapping penecontemporaneous dolomite in the field. State-of-the-art methodology at the University of Vienna, such as a scanning electron microscope with focused ion beam milling, will allow to differentiate individual dolomite mineral phases at sub-micron scale. Stable isotope ratios of oxygen, calcium, strontium, boron, carbon, and sulphur will be measured to trace past temperature, alkalinity, pH, and carbon sources. Moreover, laser ablation mass spectrometry will allow to measure calcium and strontium isotopes at the high spatial resolution required to characterize individual mineral phases.This study represents a novel approach towards the reconstruction of the environmental conditions during the formation of penecontemporaneous dolomite – a process, which probably was among the most important processes of carbonate deposition through Earth’s history. It will shed light on the past carbon cycle and, thus, result in a better understanding of global geochemical cycling and ocean and atmosphere dynamics through Earth history.