A tectonic context for fluctuations in late Paleoproterozoic oxygen content

Abstract

ABSTRACT Nearly all models of Earth’s oxygenation converge on the premise that the first notable rise of atmospheric oxygen occurred slightly above the Archean-Proterozoic boundary, with the second notable rise occurring just below the Proterozoic-Phanerozoic boundary. Plate tectonic–driven secular changes found above the Archean-Proterozoic boundary are thought to have been partly or wholly responsible for the initial rise in atmospheric O2 in the Great Oxidation Event; however, the role of plate tectonics in oxygen levels thereafter is not well defined. Modern plate tectonics undoubtedly play a role in regulating atmospheric O2 levels. Mountain building, for example, promotes high erosion rates, nutrient delivery to oceans, and efficient biogeochemical cycling of carbon, resulting in the net burial of organic carbon—thought to be the primary regulator of atmospheric O2 levels on geological time scales. The trajectory of atmospheric O2 and oceanic redox conditions in the Proterozoic Eon, representing almost 2 b.y. of geological history, shows a dynamic history with global trends that indicate overall high-low-high O2 levels throughout the Proterozoic Eon, with low-oxygen conditions established by ca. 2.0–1.8 Ga. This contravenes the tenet that major orogenic events (e.g., the Himalaya-scale Trans-Hudson orogen and other coeval orogens that formed the supercontinent Nuna) should yield higher O2 levels, not lower. The contrast of higher O2 early in the Paleoproterozoic with lower O2 later in the Paleoproterozoic is particularly striking, and mechanisms that might have caused this secular change remain unclear. This contribution explores feedbacks related to the tectonic evolution associated with the building of proto-Laurentia and Earth’s first supercontinent, Nuna, and how this impacted the trajectory of atmospheric O2 in the latest Paleoproterozoic Era.