PLEISTOCENE DEPOSITIONAL ENVIRONMENTS ON THE EASTERN ROSS SEA CONTINENTAL SLOPE, ANTARCTICA

Abstract

In 2018, International Ocean Discovery Program Expedition 374 drilled a 208.28 m-thick sequence of Plio-Pleistocene sediments on the Eastern Ross Sea continental slope, Antarctica (Hole U1525A). In this thesis, sediments from Hole U1525A are used to reconstruct the depositional environment on the slope since 2.4 Ma, focusing on characterising instances of West Antarctic Ice Sheet (WAIS) extension to the continental margin. Late Pleistocene Ross Sea Fan deposits in Hole U1525A are also studied to identify provenance changes that may link to changing ice stream dynamics. Core images, grain size, X-ray fluorescence and physical properties datasets were used from the upper 121.05 m of Hole U1525A to create a detailed lithofacies scheme and depositional model since 2.4 Ma. Supporting grain size data from three legacy cores from the Glomar Challenger/JOIDES Basins were also used to aid comparison with continental shelf sediments. A total of nine lithofacies were identified: five between 2.4 – ~0.8 Ma and four after ~0.8 Ma, ranging from laminated to massive muds and diamict facies. Hemipelagic settling, ice-rafting and reworking/deposition by bottom currents define the 2.4 - ~0.8 Ma interval, including a switch to turbidity current deposition dominating after 1.4 Ma. This likely relates to an increased frequency of grounded ice at the margin. Evidence of warmer oceanographic conditions and glacial collapse occurred at ~1.18 Ma, possibly linking to relatively warm water masses impinging the shelf. Glacigenic debris flow deposition occurred after ~0.8 Ma as the Ross Sea Fan expanded over the core site. Variability of terrigenous-phase elements in debris flows implies a) a standard ice stream drainage configuration, b) a strong West Antarctic signature, or c) an increased southern Trans-Antarctic Mountain signature, potentially indicating asynchronous WAIS and East Antarctic ice stream dynamics. These data will support further analysis of the inception and growth of the Ross Sea Fan.