Facies Analysis and Sequence Stratigraphy of CRP-2/2A, Victoria Land Basin, Antarctica

The Oligocene to Quaternary succession encountered in CRP-2/2A is divided into twelve recurrent lithofacies (some of which have been subdivided further), reflecting a range of marine, glacimarine and possibly subglacial environments of sediment accumulation. A cyclical vertical arrangement of lithofacies was noted throughout the core, and is used as the basis for a sequence stratigraphic analysis. Twenty-four sequences are recognised, each of which begins with a Sequence Boundary (Glacial Surface of Erosion), and each is interpreted to record a cycle of glacial advance and retreat with associated changes in relative sea-level. During at least some of these cycles, ice is interpreted to have extended as far as and seaward of the drill-site. A recent reinterpretation of seismic reflection data by Henrys et al. (this volume) permits the first correlation between seismic reflection records and the stratigraphic surfaces identified herein. All but one of the reflectors recognised correspond to sequence boundaries, and most reflectors correspond to the base of thin, truncated and amalgamated sequences. Additionally, three thick and relatively complete sequences (9 to 11) are identified individually by seismic reflectors. The major surfaces of omission in CRP-2/2A, identified from a variety of evidence, correspond to changes in cross-sectional geometry in the seismic records, and in the case of the unconformity at 307 mbsf can be interpreted as recording the onset of a phase of active tectonic subsidence associated with half-graben development, bounded by periods of more uniform, slower, possibly thermal subsidence. Possible controls on cyclicity are discussed, and include long-term eustatic cycles, Milankovitch frequency cycles, and more local climatic and/or tectonic events. The analysis allows the recognition and separation of tectonic from climatic (?glacio-eustatic) controls on the Cainozoic stratigraphy of the McMurdo Sound region.