Sebastian Viehmann

• Seawater archives such as (Banded) Iron Formations (BIFs) may serve as excellent archives of geochemical proxies for the composition of Precambrian seawater to evaluate physico-chemico environmental conditions of the ancient hydrosphere-atmosphere systems. This thesis presents major and trace element analyses by ICP-OES and ICP-MS measurements and high-precision Nd (and Hf)isotope data obtained by isotope dilution technique and MC-ICPMS and TIMS analyses of chemical and clastic sediments of the Mesoarchean Witwatersrand IF, the Late Archean - Early Proterozoic Krivoy Rog IF and the Neoproterozoic Urucum IF to highlight the evolution of ancient oceans and the environmental impacts on ancient seawater chemistry during the Precambrian. The rare earths and yttrium (REY) coupled with high field strength element (HFSE) systematics are used to (I) identify the purity of each individual chemical sediment sample, but also to investigate (II) the composition of Precambrian seawater, (III) the redox conditions of ancient environments and (IV) the impact of black smoker-style, high-temperature, hydrothermal fluids on local and global Precambrian seawater chemistry. Furthermore Nd and Hf isotopic compositions of representative clastic and chemical sediments were applied as geochronological tools and were used to unravel the sources of elements in dissolved and suspended fractions of ancient seawater and to gain further insights into weathering and erosion processes on Early Earth.