Non-detrital Gallium and Aluminum in Early Precambrian Marine Chemical Sediments and the Potential Use of the Ga/Al Ratio as a Geochemical Proxy for Metal Sources and Relative Fluxes to the Early Ocean

• Applicant: Professor Dr. Michael Bau
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 404681630

In the proposed project "Non-detrital Gallium and Aluminum in Early Precambrian Marine Chemical Sediments and the Potential Use of the Ga/Al Ratio as a Geochemical Proxy for Metal Sources and Relative Fluxes to the Early Ocean" research will focus on the trace element gallium (Ga) and its geochemically similar „pseudo-isotope“ aluminium (Al). While these two metals are rather closely coupled in igneous and clastic sedimentary rocks, they may be fractionated from each other in natural waters, such as river water, seawater and hydrothermal fluids. Hence, Ga/Al ratios increase substantially from continental rocks via river water to seawater. Highest Ga/Al ratios, however, characterize marine high-temperature hydrothermal fluids. Assuming this systematic relationship was the same in the Early Precambrian oceans, the Ga/Al ratio in geoarchives such as Precambrian marine chemical sedimentary rocks (e.g., banded iron formations, cherts, lime- and dolostones) should be a geochemical proxy for the sources and relative fluxes of these metals to ambient Precambrian seawater. Hence, Ga-Al systematics may be used to verify the results derived from other geochemical proxies such as rare earth elements (REE) and Ge-Si relationships. In the proposed project, the focus will be on the Ga-Al distribution in ultrapure (i.e. detritus-free) samples from geologically well-characterized marine chemical sediments which will be studied in close collaboration with research groups which focus on isotope proxies. While sample sets that originate from sedimentary rocks with depositional ages from 3.8 to 0.6 Ga will provide information on the evolution of the Ga-Al systematics of seawater through time, data determined for samples deposited contemporaneously but at different locations will provide information on the spatial heterogeneity of the Ga/Al ratios in the Early Earth’s oceans. This will not only expand our knowledge of metal sources and fluxes in the Early Earth’s surface system, but will also improve our understanding of the potential and the limits of other geochemical proxies.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1833: Building a Habitable Earth