Provenance analysis of the SMS ANDRILL core: Trends in sandstone composition

The sedimentary fill in the southern McMurdo Sound of the Ross Sea provides a unique record. There are several distinct transitions in sand grain composition in the SMS core that record the advance and retreat of local glaciers draining off the Transantarctic Mountains into the basin, volcanic eruptions associated with rifting, and perhaps the growth and collapse of the West Antarctic ice sheet. Sand grain composition in the uppermost part of the core is dominantly primary volcanic (LSU1) recording derivation from a local basaltic vent that formed as part of the Dailey Islands volcanic field. Other peaks in volcanic glass content occur between ~170-224 m and ~550-660 m indicating periods of increased volcanic activity. Basement-derived grains increase markedly at ~42m, the transition from LSU1 to 2, including quartz, feldspar, biotite, muscovite, chlorite, schist, marble, basalt, and granite lithics associated with a decrease in volcanics and olivine. These record derivation from the Granite Harbour Intrusives and Koettlitz Group metasediments, delivered via the local Blue and Koettlitz Glaciers during the height of Plio-Pleistocene glacial advances. Basement-derived grain concentrations remain high until at ~165 m, mid-way down LSU4, the marble drops out. This may correspond to the minor unconformity at the base of the Pliocene deposits in the core marking the transition to Upper Miocene glaciations. Below this, marble clasts only occur as isolated peaks which may most strongly correlate with a very large Koettlitz Glacier. At ~224 m depth (the transition from LSU4 to 5), muscovite, basalt and olivine decrease and at ~340 m (LSU6 to 7) biotite, granite and amphibole decrease. Isolated increases occur again around ~500 m and ~600 m and may correspond to advances of local glaciers. Well rounded quartz grains, some with attached cements, increase abruptly at ~224 m (LSU4 to 5) and correlate strongly with orthopyroxenes in thin section. These are derived from Beacon Supergroup sandstones and Ferrar Dolerites respectively. A second increase occurs at ~420 m (LSU7 to 8). A decrease occurs at ~580 m (within LSU8) followed by an increase at ~640 m then a decrease at ~680 m (LSU9 to 10) and another increase at ~740 m (within LSU10). Dolerite lithics follow the quartz/orthopyroxene trends. Some of these changes occur at LSU boundaries that are erosional in nature but some do not. The Beacon/Ferrar grains were most likely locally derived and delivered via the Blue and Koettlitz Glaciers. The changes in concentration may correspond to the alternating glaciations in the Miocene. The loss of Beacon/Ferrar and increasing abundance of marble and other basement-derived grains higher in the core indicate an overall unroofing sequence of the Transantarctic Mountains. Our high concentrations of Beacon/Ferrar derived grains indicate local Koettlitz/Blue derivation alternating with periods lacking them during the Miocene. This echoes the changes in basement clast compositions observed by Sandroni et al. (2010) of derivation alternating between the Koettlitz/Blue and Skelton/Mulock Glacier regions suggesting growth and collapse of the West Antarctic Ice Sheet