The Dynamics of the Late Neogene Antarctic Ice Sheets in the Central Ross Sea using a Multianalytical Approach

Abstract

With the goal of determining ice sheet history in the central Ross Sea since the late Miocene, the provenance of glacial till from IODP expedition 374 site U1522 was assessed using a suite of three analyses. A total of 3,869 zircons, between 250-63 microns in size, from sixteen different cores were measured for U-Pb isotopes via LA-ICP-MS. Zircon data was compared to neodymium isotope and clast lithology datasets from collaborators. Site U1522 shows three distinct provenance shifts from the late Miocene to the Pleistocene, two of which are coincident with Ross Sea Unconformities three and two. Late Miocene samples have abundant Cretaceous zircon populations, radiogenic neodymium values, and clasts interpreted as having a West Antarctic provenance. In latest Miocene samples, zircons are mostly Ross Orogeny age (c. 470 615 Ma) and Cretaceous zircon grains are almost absent, neodymium values are relatively un radiogenic, and dolerite clasts are present signaling a shift to East Antarctic derived ice. Above Ross Sea Unconformity 3, early to mid Pliocene samples show a shift back to West Antarctic provenance with abundant Cretaceous zircons and more radiogenic neodymium values. Late Pliocene to Pleistocene samples, deposited above Ross Sea Unconformity 2, reflect dominant East Antarctic provenance with few Cretaceous zircon dates, relatively un radiogenic neodymium values, and the presence of dolerite clasts. These data are broadly in agreement with ice sheet interpretations suggested by clast analysis from ANDRILL site AND-1B. Permo-Triassic zircon dates suggest the presence of unexposed bedrock of this age beneath the West Antarctic Ice Sheet based on their association with Cretaceous dates that have not been reported from East Antarctica. The zircon dataset also reveals two late Miocene intervals with a previously undocumented Eocene Oligocene magmatic event ~30 40 Ma. The coexistence of Cretaceous dates in these intervals suggests a likely West Antarctic source. The absence of Eocene Oligocene zircons in subsequent Plio Pleistocene sediments may be explained by substantial erosion and offshore deposition of the West Antarctic interior, including volcanic edifices following the Middle Miocene Climatic Transition.