The Impact of Lithology on Upland Erodibility: Source-to-Sink Sediment Transfer and Composition in the Gulf of Papua

Abstract:

Continental margin source-to-sink systems deliver a wealth of water and energy resources, as well as nutrients to agricultural lands and to various onshore and offshore ecosystems. Management of a basin’s sedimentological resources is dependent on understanding the spatial and temporal patterns of sediment deposition and mineralogical composition and the feedbacks between sediment routing processes. A focus site for the MARGINS Source-to-Sink (S2S) initiative, the Gulf of Papua is a foreland basin in southern Papua New Guinea and an ideal natural laboratory to study the landscape evolution and source-to-sink sediment transfer in a tectonically active basin. High precipitation rates (up to 10 m/yr) and uplift rates (> 600 m/Myr) produce a very high terrigenous sediment flux of ∼384 Mt/yr into the Gulf of Papua. Previous provenance analyses focus on broad mineralogical patterns across the Gulf, rather than sediment routing processes and surface evolution.

This study uses Badlands to track rock types from source to sink in the Gulf of Papua. Tectonic uplift, sediment erosion, transportation and deposition processes are simulated in Badlands, a surface evolution model (Salles, 2016). The code is capable of simulating landscape evolution at time scales of hundreds of millions of years, but in order to do so the erodibilities of the surface lithologies must first be constrained. We have constrained a range of erodibility coefficients for different lithologies in the catchments delivering sediment to the Gulf of Papua by ground truthing landscape evolution simulations with measured fluvial sediment loads. Constrained erodibility coefficients for specific lithologies range from ∼6.5 x 10⁻⁶ yr⁻¹ for metamorphics and granites to ∼13.0 x 10⁻⁶ yr⁻¹ for soft sediments. These values are then used to simulate the Late Quaternary sediment flux into the Gulf, tracking rock types from their source to marine depocentres. Simulations suggest that the sediment flux into the Gulf is dominated by sediment derived from soft sediment, mafics, metamorphics and granites in the Papuan Orogen. Our results highlight the significance of basin morphology, the distribution of lithologies in catchments and the glacio-eustatic cycle as controls on temporal and spatial patterns of sediment distribution and composition in the Gulf of Papua.