Provenance of basement erratics in Quaternary coastal moraines, southern McMurdo Sound, and implications for the source of Eocene sedimentary rocks

Abstract

This paper summarizes fieldwork conducted in 2007 and presents results of petrographical analyses of basement rocks that occur along with fossil-rich Eocene sedimentary erratics in moraines along the north-east flank of Mount Discovery in southern McMurdo Sound. The Eocene rocks are significant as they provide a rare glimpse into greenhouse environments at high southern latitudes. Basement erratics recovered from the moraines are petrographically similar to metamorphic and igneous rocks exposed in the Transantarctic Mountains at locations between the Carlyon and Skelton glaciers and/or within the drainage catchments of Mulock and Skelton glaciers. These new clast provenance data imply that the Eocene sedimentary erratics are most likely derived from outcrops that are currently located beneath the Ross Ice Shelf south and/or immediately east of Minna Bluff. The suite of basement and sedimentary erratics were transported to their present location by ice that flowed north-eastwards from the Skelton-Mulock region and was pushed westwards into southern McMurdo Sound by grounded ice flowing north from West Antarctica. Results from this study support prior reconstructions of ice flow during peak glacial intervals during the Miocene-Pleistocene including the Last Glacial Maximum.

Cosmogenic nuclide exposure age scatter in McMurdo Sound, Antarctica records Pleistocene glacial history and processes

“…1). These incursions of grounded ice into McMurdo Sound transported and deposited lithologies from the Transantarctic Mountains, including Granite Harbor Intrusives, Ferrar Dolerite, Koettlitz Group metamorphic rocks, Beacon Sandstone, as well as other rocks from the East Antarctic interior (Christ and Bierman, 2020;Denton and Marchant, 2000;Talarico et al, 2012Talarico et al, , 2013) (Fig. 1B).…”

“…1B). Specifically, lithologies present in the AND-1B drill core and erratics in McMurdo Sound correspond primarily to rocks found along the Mullock and Skelton Glaciers (Talarico et al, 2012(Talarico et al, , 2013. The diversity of lithologies in glacial sediments in McMurdo Sound provides targets for multiple cosmogenic nuclides to calculate exposure ages; yet, previous efforts yielded a complex exposure history (Anderson et al, 2017;Brook et al, 1995;Joy et al, 2017).…”

“…2, 3) (Christ and Bierman, 2020;Hall et al, 2015;Hall and Denton, 2000;Jackson et al, 2018;Stuiver et al, 1981). The diversity of lithologies in glacial sediments in McMurdo Sound provides targets for multiple cosmogenic nuclides by which to calculate exposure ages and the different lithologies in glacial sediments from McMurdo Sound can be tied to their bedrock sources in the Transantarctic Mountains (Talarico et al, 2012(Talarico et al, , 2013. By examining a compilation of new and previously published (Anderson et al, 2017;Brook et al, 1995) exposure ages of different lithologies in Ross Sea drift, we are able to quantify the magnitude of exposure age scatter and investigate surface processes that contribute to, prevent, or reduce nuclide inheritance in Antarctic terrestrial glacial sediments.…”

“…Due to ice cover, no cosmogenic nuclide studies from Mullock Glacier exist. Although Hatherton and Darwin glaciers transport less material into McMurdo Sound during glacial periods (Talarico et al, 2013), there is also no evidence of MIS 8 glacial sediments preserved along the margins of those glaciers (Joy et al, 2014;King et al, 2020;Storey et al, 2010). In general, exposure ages of pre-LGM glacial sediments above outlet glacier margins record glacial high-stands during MIS 6 and earlier, but there is no apparent evidence for elevated outlet glaciers during MIS 8 (Anderson et al, 2020;Bromley et al, 2010;Hillenbrand et al, 2014;Joy et al, 2014;Staiger et al, 2006;Storey et al, 2010).…”

Cosmogenic nuclide exposure age scatter records glacial history and processes in McMurdo Sound, Antarctica

“…the decay of radioactive nuclides -can produce results that are difficult to interpret in surface exposure dating samples. Nuclide inheritance affects nearly all geomorphologic settings: it complicates the interpretation of alluvial fan ages in deserts (Owen et al, 2011), river terrace exposure ages used to determine canyon incision rates (Cook et al, 2009), shore platform erosion rates in coastal settings (Trenhaile, 2018), and glacial chronologies using exposure ages of boulders on moraines or glacially sculpted bedrock (Briner et al, 2014;Corbett et al, 2016;Davis et al, 1999;Young et al, 2016). Inherited nuclides are prevalent in glacial sediments, from alpine glacier moraines (Briner et al, 2005;Heyman et al, 2011) to glacial erratics transported by polar ice sheets (Brook et al, 1995;Corbett et al, 2019;Hein et al, 2014).…”