Description of grain size, cement, and matrix in sediment core CRP-3 sandstones (Table 1).

The presence of authigenic smectite in the lower Oligocene sandstones of the Cape Roberts Project core CRP-3 from the Victoria Land Basin of Antarctica is confirmed by scanning electron, scanning-transmission electron, and light microscopy. It was emplaced as a single generation of cement within the lower portion of the Oligocene section. This section has undergone no discernible compaction since cementation. Permeabilities measured on fifty core plugs show that the lower portion of the Oligocene (from 370-766 meters below sea floor) also has systematically higher values than sediment in uppermost CRP-3 and all of CRP-2 and CRP-1.Three models for smectite authigenesis are considered as multiple working hypotheses to be tested: 1) Burial diagenesis with necessary components sourced from volcanogenic materials and heavy minerals within the drilled sequence: 2) Precipitation from hydrothermal waters associated with possible igneous intrusion(s) and nearby faults; 3) Mobilization and injection of regionally compactive 'thermobaric' fluids along a nearby fault that bounds a major graben parallel to the Transantarctic Mountain Front. The preponderance of the available evidence and Occum's Razor favors the first model, although special circumstances dictated by the position of the drill site along a rapidly subsiding rift basin require that all three models be considered equally until our analyses are complete. CC-BY Creative Commons Attribution 3.0 Unported