Detrital record unveils the role of topography in the Antarctic Ice Sheet growth

The East Antarctic Ice Sheet is the largest ice-sheet on the planet, developed since the Late Eocene upon a puzzle made of cratonic plateaus, mountain belts and intracontinental basins. The flow pattern of the waxing Ice Sheet is controlled by the preexisting landscape, mainly where high-relief topography was already developed. On the eastern limit of the East Antarctic Ice Sheet facing the Ross Sea, the Transantarctic Mountains acted as a barrier limiting the early growth of the ice sheet. Outlet glaciers drained ice flows across the high elevation rift flank enlarging fjord-like valleys by selective erosion, whose efficiency changed also as a consequence of the variable Oligocene-Miocene climate. 

Uncertainty exists whether or not high-relief topography predates major ice growth in the Transantarctic Mountains. Here, landscape is expected to play a critical role, modulating flow directions over a preexisting drainage network. In addition, pre-Cenozoic tectonic inheritances controlled the location of highs and lows in the topography contributing to focus the glacial flow. The southern Victoria Land is the sector of the Transantarctic Mountains which offer the most complete bedrock exposition in deglaciated areas, and offshore drill cores reaching depths of up to 850 m below sea floor just off the margin. The detrital record from 36 to 18 Ma corresponds to the Eocene-Oligocene Transition and the onset of the Ice Sheet growth.   

In this study, we applied a multi-analytical approach to constrain sediment provenance using new datasets of detrital apatite fission-track thermochronology and detrital zircon U-Pb geochronology from CIROS-1 drill core. New data are coupled with petrographic description of gravel and sand fractions, facies analysis and revised age model. The source-to-sink analysis of CIROS-1 sediments is compared with Cape Roberts Project core record to reconstruct the environmental conditions and geomorphic setting of the two main valleys draining ice through Dry Valleys. The comparison between detrital signals and bedrock information suggests a change in the erosive style and the elevation of the sediment source through the Eocene-Oligocene. The Eocene catchment area located along the coast was reorganized by the overriding outlet glaciers sourced from the inner Transantarctic Mountains. The topographic divide retreated in Dry Valleys where glacial erosion was more efficient as recorded in provenance data. Results highlight how the preexisting mountainous landscape conditioned ice flow during early EAIS expansion and provide new constraints on the timing and magnitude of landscape modification along the TAM rift flank.