Geology Seminar Series - Dr. Joshua Davies

Topic: Climatic and lunar signals recorded in Paleoproterozoic Banded Iron Formations

Date and Time: Wednesday, October 26, 2022 at 4:00 PM (Saskatchewan)

Zoom link: https://uregina-ca.zoom.us/j/96326232761?pwd=UEhFalE4Vk5xZWlEaitCQ0EvZmgxUT09

Speaker: Dr. Joshua Davies, Université du Québec à Montréal

Abstract:

Banded iron formations (BIFs) were widely deposited in the Neoarchean to early Paleoproterozoic oceans, between ~2.8 and ~2.4 Ga. Their formation has typically been linked to hydrothermal plume activity, continental growth and the rise of oxygen in the ocean and atmosphere. However, very little attention has been paid to climate variability and its potential role in the formation of BIFs. Climate oscillations on the thousands to millions of years scale known as Milankovitch forcing must have been operative at that time and may explain the rhythmic layering observed in BIFs. This hypothesis has never been fully tested, partially due to the unknown depositional rate of BIF. In this study, we carried out high-precision, high-accuracy TIMS U-Pb zircon dating of ash intervals interbedded in Paleoproterozoic BIF in South Africa and Australia to precisely determine their depositional rates. We combined these results with cyclostratigraphic analysis of rhythmic alternations in the weathering profile from field exposures, and also geochemical and mineralogical changes in the BIF which are laterally consistent over hundreds of km. Based on our spectral analysis results and precise U-Pb ages, we hypothesize these patterns are related to orbital forcing. Using this new framework for interpreting the cyclical layering in BIF, we discuss the implications for our understanding of the evolution of the earth-moon system.