Earth Science Seminar: "Using field studies and sulfur isotopes to constrain the Great Oxidation Event"

You are invited to attend the forthcoming Earth Science Research Seminar presented by Dr Matthew Warke (University of St Andrews) on "Using field studies and sulfur isotopes to constrain the Great Oxidation Event". The seminar will take place in Meston Lecture Theatre 2 at 13:00 on Thursday, 8th Nov. All are welcome to attend.

Abstract

Over half a century ago evidence began to emerge that suggested that Earth’s atmosphere (and oceans) may not have always contained free oxygen (O₂) in modern atmospheric concentrations (i.e. ~21 %). Field and petrographic evidence constrained the disappearance of redox-sensitive detrital minerals and banded iron-formations, and the first appearance of red beds, sulphates, and phosphates, to broadly to ~2.4 to 2.3 billion years ago. It was argued that rising O₂ concentrations were the cause and subsequently this period of the early Paleoproterozoic became known as the Great Oxidation Event (GOE).

The discovery of mass-independently fractionated quadruple sulfur isotopes (MIF-S) in Archean and early Paleoproterozoic rocks provided further evidence that the early atmosphere was radically different; these trends suggested that it lacked significant concentrations of oxygen and ozone (O₃). Conspicuously the disappearance of MIF-S signals occurred at ~2.4 to ~2.3 Ga, and this – seemingly unidirectional – transition has become synonymous with the GOE.     

However, many challenges remain in understanding this signal. What generates MIF-S and how is it transported and preserved? Is it a global or localised signal? Is it a unidirectional transition or oscillatory? This talk will explore some remaining uncertainties and potential implications of recent research using case-studies from the Transvaal Supergroup in South Africa.

In addition to interpreting MIF-S, it remains difficult to measure quadruple isotopes of sulfur due to the low abundance of ³⁶S (0.02 %) and the requirement for fluorination using fluorine gas. At St Andrews, a new state-of-the-art quadruple sulfur isotope analysis system (using Curie Point pyrolysis) has been constructed and is being tested. Eliminating the need for use of fluorine gas, this line will be the UK’s first quadruple sulfur isotope analysis facility.

Speaker

Dr Matthew Warke

Venue

Meston Lecture Theatre 2