Are there thick sediments within South Pole Basin? Investigating the lithology of SPB using COLDEX airborne geophysics 

Because sedimentary basins may exert considerable control over ice sheet dynamics and basal heat flow, it is vital to constrain the extent, thickness, and level of consolidation of sediments throughout the continent and at local scales. Until recently, the South Pole Basin (SPB), situated between the Gamburtsev Subglacial Mountains, the Transantarctic Mountains, and Recovery Subglacial Highlands, has been one of Antarctica's least-explored regions. Previous studies based on seismic and machine learning models, including those by Baranov & Morelli (2023) and Li et al. (2022), have characterized SPB as a sedimentary basin with sediment thicknesses exceeding 1 km. Conversely, a seismic study conducted by Zhou et al. (2022) identifies SPB as a region with little to no sedimentary rock. A lack of dense geophysical data as well as the inherent difficulty of studying geology beneath the Antarctic Ice Sheet introduced a large amount of uncertainty into these assessments. Recent airborne radar, gravity, and magnetics data collected by the Center for Oldest Ice Exploration (COLDEX) has revealed two distinct geomorphological provinces within South Pole Basin: the southern portion of SPB which exhibits relatively smooth, reflective bedrock, while the northern SBP manifests as much rougher terrain. The abrupt boundary between Inner and Outer SPB is associated with the onset of subglacial melting, inferred from a rapid thinning of the basal layer, decreased ice sheet surface slope, and presence of subglacial lake-like features. In addition to surficial differences, these provinces are marked by distinct free-air, Bouguer, and isostatic gravity signatures. A large, arc-shaped magnetic high parallel to Recovery Subglacial Highlands cuts across SBP, facilitating a robust depth to basement analysis and providing constraints for gravity inversions. By integrating COLDEX data with previous airborne surveys and newly collected seismic data, we offer a revised geological interpretation of the South Pole Basin and discuss its tectonic history, potential for groundwater storage, and the preservation of ancient ice in this region.