Explaining the Rhyacian PaleoProterozoic Lomagundi Event

The rise of oxygen and siderite oxidation during the Lomagundi Event

Authors:

Bachan et al

Abstract:

The Paleoproterozoic Lomagundi Event is an interval of 130–250 million years, ca. 2.3–2.1 billion years ago, in which extraordinarily 13C enriched (greater than 10‰) limestones and dolostones occur globally. The high levels of organic carbon burial implied by the positive δ13C values suggest the production of vast quantities of O2 as well as an alkalinity imbalance demanding extremely low levels of weathering. The oxidation of sulfides has been proposed as a mechanism capable of ameliorating these imbalances: It is a potent sink for O2 as well as a source of acidity. However, sulfide oxidation consumes more O2 than it can supply CO2, leading to insurmountable imbalances in both carbon and oxygen. In contrast, the oxidation of siderite (FeCO3 proper, as well as other Fe2+-bearing carbonate minerals), produces 4 times more CO2 than it consumes O2 and is a common—although often overlooked—constituent of Archean and Early Proterozoic sedimentary successions. Here we propose that following the initial rise of O2 in the atmosphere, oxidation of siderite provided the necessary carbon for the continued oxidation of sulfides, burial of organic carbon, and, most importantly, accumulation of free O2. The duration and magnitude of the Lomagundi Event were determined by the size of the preexisting Archean siderite reservoir, which was consumed through oxidative weathering. Our proposal helps resolve a long-standing conundrum and advances our understanding of the geologic history of atmospheric O2.

 I think I am going to drop a note to the authors and ask if they have compared the carbon 13 isotopes in the limestones and dolostones to modern ones... or at least to Phanerozoic ones.  Just to potentially rule out this.  ;)