Stratigraphic architecture of the Cenozoic succession in the McMurdo Sound region, Antarctica: An archive of polar palaeoenvironmental change in a failed rift setting

The Victoria Land Basin forms part of the failed West Antarctic Rift, and preserves a Cenozoic succession up to 4km thick that records the onset of Cenozoic glaciation, and the history of Antarctic glaciation over the past 34Myr. This succession is relevant both to investigations of modern climate change and to studies of long-term palaeoclimate change in general. This study provides a sedimentological and stratigraphic review of the Victoria Land Basin succession, based on analysis of several continuous drillcores acquired since the 1970s, and supported by seismic stratigraphic analysis of a large array of seismic reflection data. An array of fifteen lithofacies is recognized within the Victoria Land Basin Cenozoic succession, including fossiliferous and diversely bioturbated mudrocks and diatomites, texturally mature sandstones and conglomerates, mixed mudstones and sandstones with dispersed gravel with restricted bioturbation, and diamictites and associated lithologies. These facies record a variety of marine, glaciomarine, proglacial and subglacial environments. Locally, volcanic and volcaniclastic deposits are interbedded in the succession. Lithofacies are arranged in repetitive vertical stacking patterns (depositional sequences) that record glacial advance-retreat cycles with attendant relative sea-level changes. Seven varieties of depositional sequences (stratigraphic motifs) are recognized within the succession as a whole, and interpreted to record a range of depositional settings from rifts unaffected by glacial ice (Motif 7), through varying degrees of glacial influence with abundant meltwater contributions (Motifs 6 to 3), to cold, polar glaciated environments such as that of today (Motifs 2 and 1). Overall, there is a gradual trend upward through the succession from Motif 7 at the base towards Motif 1 at the top, but the trend is not monotonic. A significant conclusion of this work is that a record of dynamic climate and glacial conditions is preserved through the entire 34Myr period of the Cenozoic icehouse, at least in the Victoria Land Basin. Intervals characterized by consistent stratigraphic style (motifs) are recognized throughout the Victoria Land Basin succession. These intervals are of 1 to 6Myr duration, each containing numerous depositional sequences; they are one to two orders of magnitude longer than glacial-interglacial cycles, and record periods during which environmental conditions varied in an internally consistent manner. These intervals are considered to reflect convolutions of orbital parameters that remained stable for periods of 10(6) a, and then switched to alternative configurations. Such intervals are directly analogous to 1 to 8Myr intervals characterized by glaciogenic strata that are preserved within the late Palaeozoic of eastern Australia among other areas, and may be a recurring stratigraphic response to icehouse climate regimes through geological time.