Sedimentology and Stratigraphy of the AND-2A Core, ANDRILL Southern McMurdo Sound Project, Antarctica

During the 2007 – 2008 austral spring season, the ANDRILL Southern McMurdo Sound Project recovered a core 1138 metres long (AND-2A) from a location in the southern McMurdo Sound near the Dailey Islands. This core contains a range of lithologies, including various types of terrigenous clastic diamictite, conglomerate and breccia, sandstone and mudrocks, volcanic lava, pyroclastic and reworked volcanic sedimentary rocks, and diatomite. The succession is divided into fourteen lithostratigraphic units (LSUs), two of which (LSUs 1 and 8) are further subdivided into three and four sub-units, respectively, based on changes in abundance of lithologies. Thirteen lithofacies are recognized, ranging from diatomite and bioturbated, fossil-bearing mudrocks (representing most ice-distal environments) through interlaminated sandstone-mudrock facies and sandstone with varying dispersed gravel components, to diamictite and conglomerate (representing most ice-proximal environments), and also lava, volcanic breccia and volcanic sedimentary rocks representing extrusion, fragmentation, fallout and reworking of material from basaltic volcanic activity. Three distinct types (‘motifs’) of vertical facies stacking patterns are recognized, recording glacial advance-retreat-advance cycles with varying degrees of facies preservation. Carbonate, pyrite and zeolites are the principal secondary mineral phases in the core. The pyrite overprint is particularly prominent in the lower half of the core, where it typically obscures stratification and sediment texture. Studies of modern aeolian sediment deposition onto McMurdo Sound sea-ice reveal that between 7600 and 24 000 kg km-2 of terrigenous clastic material is being stored on the sea-ice in this region