Detrital zircons from Late Paleozoic Ice Age sequences in Victoria Land (Antarctica): New constraints on the glaciation of southern Gondwana

Abstract

The Lower Permian tillites of the Beacon Supergroup, cropping out in Victoria Land (Antarctica), record climatic history during one of the Earth’s coldest periods: the Late Paleozoic Ice Age. Reconstruction of ice-extent and paleo-flow directions, as well as geochronological and petrographic data, are poorly constrained in this sector of Gondwana. Here, we provide the first detrital zircon U-Pb age analyses of both the Metschel Tillite in southern Victoria Land and some tillites correlatable with the Lanterman Formation in northern Victoria Land to identify the source regions of these glaciogenic deposits. Six-hundred detrital zircon grains from four diamictite samples were analyzed using laser ablation−inductively coupled plasma−mass spectrometry. Geochronological and petrographic compositional data of the Metschel Tillite indicate a widespread reworking of older Devonian Beacon Supergroup sedimentary strata, with minor contribution from Cambro-Ordovician granitoids and meta-sedimentary units as well as Neoproterozoic metamorphic rocks. Euhedral to subhedral Carboniferous−Devonian zircon grains match coeval magmatic units of northern Victoria Land and Marie Byrd Land. This implies, in accordance with published paleo-ice directions, a provenance from the east-southeast sectors. In contrast, the two samples from northern Victoria Land tillite reflect the local basement provenance; their geochronological age and petrographic composition indicates a restricted catchment area with multiple ice centers. This shows that numerous ice centers were present in southern Gondwana during the Late Paleozoic Ice Age. While northern Victoria Land hosted discrete glaciers closely linked with the northern Victoria Land-Tasmania ice cap, the west-northwestward flowing southern Victoria Land ice cap contributed most of the sediments comprising the Metschel Tillite.

A “Local First” Approach to Glacigenic Sediment Provenance Demonstrated Using U-Pb Detrital Zircon Geochronology of the Permo-Carboniferous Wynyard Formation, Tasmanian Basin

“…Based on flow directions, the Wynyard Fm is proposed to have been deposited by an ice mass centered in North Victoria Land (NVL), Antarctica, with contributions from ice masses located adjacent to the Dundas Trough (Fig. 1;Hand, 1993;Henry et al, 2012;Veevers, 2006;Zurli et al, 2022). Prior provenance work has demonstrated that most Wynyard Fm clast lithologies are attributable to pre-Permian source rocks in western Tasmania (Banks, 1981;Hand, 1993), and not NVL sources.…”

“…flowed generally from south to north through the Dundas Trough (Fig. 1A; Hand, 1993), 2. had a warm (temperate) thermal regime (Henry et al, 2012;Ives, 2021;Powell, 1990), and 3. was part of, possibly an outlet glacier or ice stream of, a larger ice sheet that was centered over North Victoria Land (e.g., Ives, 2021;Veevers, 2006;Zurli et al, 2022).…”

“…Constraining the provenance of glacigenic sediments from past ice ages is a key tool in determining the size and distribution of ancient ice centers (e.g., Griffis et al, 2019;Martin et al, 2019;Zurli et al, 2022). The inferred characteristics of these ice centers are lynchpins in understanding climate through geologic time, including the Late Paleozoic Ice Age (LPIA; Isbell et al, 2012).…”