Palaeoenvironmental analysis of Archaean siliciclastic sedimentary rocks in the west-central Jack Hills belt, Western Australia with new constraints on ages and correlations

Zircons with ages between 3.05 and 4.4 Ga and hosted in conglomerates and associated sandstones in the Jack Hills belt of Western Australia have been the subject of numerous studies but none, to date, has been concerned with understanding the depositional environments of the sedimentary rocks. Intact, 250 and 320 m thick stratigraphical sections include conglomerates and sandstones that are equivalent to those at the W74 discovery site that host the ancient zircons. Facies associations are compatible with a prograding fan delta depositional setting in which alluvial fans were sourced by proximal highlands, were built directly into a lake or sea and were characterized by high gradients and high flow velocities. Locally, the succession is capped by a 20-25 m thick interval of cross-bedded quartz arenite-gritstone with a similar U-Pb detrital zircon age spectrum to the W74 discovery site, suggesting that this facies association is of comparable age and genetically related to the underlying facies associations. The quartz arenite-gritstone facies association is interpreted to record transgressive tidal reworking of the fan delta. Similar sedimentary units, including areally extensive quartz arenite successions, are widely developed elsewhere in Western Australia and on other continents, indicating that stable continental crust was widespread by 3.0 Ga.