A proposed chronostratigraphic Archean–Proterozoic boundary: Insights from the Australian stratigraphic record

Abstract

The Mount Bruce Supergroup (MBS) in Western Australia has been central to debates surrounding Precambrian stratigraphic subdivision and is one of the few relatively conformable successions that records both the chronometric Archean-Proterozoic boundary (APB) and the Great Oxidation Event/Episode (GOE) which has previously been proposed as the most practical basis for a chronostratigraphic boundary. Current understanding of the lithostratigraphy, chemostratigraphy, and geochronology of the MBS supports the placement of a chronostratigraphic APB in the vicinity of the contact between the Hamersley and Turee Creek Groups, although a precise boundary awaits the generation and integration of more detailed chemostratigraphic records of the GOE with the physical record. The chronometric APB as presently defined at 2500 Ma will suffice until consensus is reached regarding a revised definition based on the GOE, and reconciliation of the physical and proxy records of this event. However, the Australian stratigraphic record suggests placement of the APB either at the base of the first glacial diamictite, or at the top of the last banded iron formation (BIF) below the GOE. The first option would exclude some BIF from the Siderian, which in both cases would be the terminal period of the Archean, whereas the second option places all diamictite in a new period at the start of the Paleoproterozoic. It is further proposed that this new period be named to primarily reflect this glacial influence, rather than for the influence of the GOE which relies on less obvious laboratory-based proxies for its identification.