Assessing the origin of an early Pleistocene iron formation on Milos (Greece) using stable Fe isotopes

Project description
Banded iron formations (BIFs) are chemical sedimentary rocks that consist of alternating silica-rich and iron-rich bands (>15 wt.% Fe). The occurrence of BIFs in the rock record is mostly confined to the Archean and Paleoproterozoic, when anoxic conditions enabled the presence of abundant dissolved Fe(II) complexes in seawater. Following the oxygenation of the atmosphere and oceans, the abundance of BIFs decreases dramatically due to the lower solubility of Fe under oxidizing conditions. The discovery of an early Pleistocene banded iron-rich formation on the island of Milos (Greece) has therefore sparked debate on whether this could represent a modern analogue to Precambrian BIFs. One of the arguments used in favor of a banded iron formation is the observation of filamentous fossils that resemble photoferrotrophic micro-organisms (Chi Fru et al., 2013; Kilias et al., 2013), which is thought to be a key microbial process involved in the oxidation of Fe(II) during Precambrian BIF formation. However, another study has argued that the iron-rich formations on Milos do not represent chemical sedimentary rocks, but clastic sedimentary rocks with Fe enrichment from post-depositional hydrothermal overprinting (Sun et al, 2022).

This project will investigate the origin of Fe enrichment in the Pleistocene iron formations on Milos island using stable Fe isotopes. It specifically aims to evaluate whether iron oxidation occurred by microbial photoferrotrophy in the water column, or by high-temperature hydrothermal alteration in pore spaces. In addition, Fe isotope data will provide insight into formation pathways of individual Fe-bearing minerals from the extent at which they are in Fe isotopic equilibrium with fluids. This work will improve our understanding of the origin of a possibly unique modern analogue for Precambrian BIFs.

Proposed course plan during the master's degree (60 ECTS)
GEOV243 Environmental geochemistry (10 ECTS)
GEOV245 Geomicrobiology (10 ECTS)
GEOV300 Selected Topics in Geoscience (5 ECTS)
GEOV342 The geochemical toolbox (10 ECTS)
GEOV344 Geobiology and the evolution of life on Earth (10 ECTS)
Z-GEOV Field course on minerals for the energy transition (5 ECTS)
GEO-3130 Ore geology (10 ECTS, UiT)

Field-, lab- and analysis work
Representative rock samples will be collected on Milos during a field course in October 2024 with the co-supervisors. Rocks will be cut to remove weathered edges, and thin sections will be prepared for SEM to investigate mineralogy and microbial textures. Unweathered material will be crushed in agate crushers and sequential Fe extraction with spectrophotometry will be used to determine the abundance of different Fe phases. Based on this work, a selection of samples will be prepared for Fe isotope analyses using ion exchange chromatography and multi-collector inductivelycoupled plasma mass spectrometry (MC-ICP-MS).