Nicholas Craik HBSc thesis abstract

Thesis Title: 
Exploring the Subaerial Redox Environment of the Mesoproterozoic Copper Harbour Conglomerate, Michigan, USA
The Copper Harbour Conglomerate of the Keweenaw Peninsula, Michigan is a fining upward, alluvial-fluvial-lacustrine sedimentary sequence representing the first continuous infilling of the Midcontinent Rift basin after the cessation of associated volcanic activity ~1.1 Ga. Within the formation are pervasive carbonate cement (calcrete) lenses as well as a stromatolitic horizon located within its uppermost portion. The purpose of this study was to examine the oxidative weathering products (siliciclastics), groundwater-precipitated carbonates (calcrete), and fluvial-precipitated carbonates (stromatolites) found within the subaerial Copper Harbour Conglomerate to determine the relative oxygenation of the atmosphere at the time of deposition. Past studies on atmospheric oxygen levels during the Mesoproterozoic commonly utilized deep sea shales with indeterminate and questionable weathering and hydrological pathways. In opposition to this, the Copper Harbour Conglomerate was in direct contact with the atmosphere during deposition (subaerial) and is unmetamorphosed making it a reliable proxy for atmospheric oxygen levels at the time of deposition (~1085 Ma). ICPMS and ICP-AES methods were utilized to determine the geochemistry of the rock types within the upper Copper Harbour Conglomerate. By analyzing the redox sensitive metals and rare earth elements, theoretical constructions of the hydrological pathways of these elements allows the understanding of the redox environment during deposition. Through examination of the oxidative weathering products, groundwater-precipitated carbonates, and the fluvial-precipitated carbonates using redox sensitive metals and rare earth elements, it was determined that atmospheric oxygen levels ~1085 Ma were greater than previously thought.