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Transverse and Axial Submarine Fans in a 3.2 Ga Rift Basin, Pilbara Craton

Session: Evolution of Orogenic Belts Through Time: Insights from Sedimentation, Deformation, Magmatism, and Metamorphism, Part I

Presenting Author:

Emily Stoll

Authors:

Stoll, Emily¹, Drabon, Nadja²

(1) Harvard University, Earth and Planetary Science, Cambridge, MA, USA, (2) Harvard University, Earth and Planetary Sciences, Cambridge, MA, USA,

Abstract:

Understanding when plate tectonics operated is key to understanding the Earth’s crustal evolution and habitability. One way to address the tectonic setting is through basin analysis, as basins are shaped by the uplift and subsidence of the geodynamic regime. The 3.2 Ga Corboy Formation in the Pilgangoora Basin is proposed to be the first rift basin in the Pilbara Craton, marking a shift from non-uniformitarian to modern-style plate tectonics in that region. We conducted detailed stratigraphy and facies analysis combined with updated correlations based on a high-resolution provenance analysis. The Pilgangoora Basin’s sedimentology reflects a progressive deepening and a shift from proximal, transverse to distal, axial sediment routing, consistent with progressive rift evolution. Sediment influx initially came from the present-day north, forming small submarine fans composed of high-density turbidite deposits, with up-to-meter scale, poorly sorted conglomerates and massive sandstone. These deposits reflect localized, transverse sediment delivery from nearby uplifted sources. Influx then transitioned to present-day westward flow, forming two stacked submarine channel complexes. The first complex (~600 m thick) has on- to near-axis, slope valley infill, with overall fining upwards pattern. The second complex, preserved for at least 250 m, begins with renewed conglomerate influx, and has smaller clast sizes and a higher sand:clast ratio, consistent with deeper water deposition further down the slope valley. This transition from small, coarse, proximal fans to thick, sandier, more distal axial systems, coupled with evidence for progressive basin deepening, aligns with rift basin evolution. These results provide new sedimentologic support for a modern-style plate tectonic regime in the Pilbara Craton by 3.2 Ga, refining earlier interpretations with greater detail on the basin’s stratigraphic and tectonic development.