Relative abundance of heavy minerals in sediment core CIROS-2 from McMurdo Sound, Antarctica (App A)

The heavy mineral assemblages of the Lower Pliocene to Quaternary glacial sediments of the CIROS-2 drill site, situated near the mouth of Ferrar Glacier on the McMurdo Sound shelf, Antarctica, were analysed by optical means in order to reconstruct the source areas and dynamics of the late Cenozoic Antarctic ice masses. The assemblages are dominated by pyroxenes, amphiboles, altered minerals and opaque minerals. Within the pyroxene group, clinopyroxenes are most abundant; within the amphibole group, green and brown hornblendes are dominant. Other important heavy minerals present in minor amounts are zircon, titanite, epidote, garnet and apatite. The downcore distribution of the heavy minerals allows a subdivision of the sedimentary sequence into two major units, which can both be further subdivided into two subunits. The Pliocene interval between 166 and 110 mbsf is characterized by relatively high concentrations of apatite, zircon, titanite, garnet, epidote and green hornblende. This assemblage accounts for some 40–60% of the heavy minerals and points to a source to the west of the drill site, in the Transantarctic Mountains, where intrusive, metamorphic and sedimentary rocks cover large areas. The interval 166–137 mbsf (Lower Pliocene) contains additional brown hornblende and palagonite, indicative of a volcanic, probably hyaloclastitic source, which possibly has to be sought beneath the ice of the Ferrar Glacier. In contrast, the uppermost Pliocene and Quaternary interval between 110 mbsf and the top of the core is characterized by high concentrations of clinopyroxenes, altered minerals and opaque minerals. This record points to a main source area in the south or east, where large areas are occupied by basaltic rocks of the McMurdo Volcanic Group. A slight change in the composition of the pyroxene group occurs within this interval, at 48 mbsf. Thus, the heavy minerals in the sediments of core CIROS-2 document different source areas and therewith major changes in the ice dynamics. During the Pliocene the ice discharged through the Transantarctic Mountains into the McMurdo Sound. The source area shifted in the Quaternary to the south, to the region of the present-day Ross Ice Shelf.