Rift History of the Western Victoria Land Basin: A new Perspective Based on Integration of Cores with Seismic Reflection Data

Abstract

The results of a stratigraphic study of the western Victoria Land Basin, Antarctica, are summarized. This analysis is based on all existing seismic reflection data integrated with lithological information from fully cored drillholes in the Cape Roberts area of western McMurdo Sound. A number of subsurface seismic reflectors were recognized in the Cape Roberts area and correlated to stratal interfaces previously recognized in the cores. These events were then traced regionally throughout the southern McMurdo Sound, and form the basis for a new seismic stratigraphic subdivision of the Cenozoic section. Key reflectors define boundaries of seismic stratigraphic units, each of which shows distinctive overall cross-sectional geometry and internal reflection character/facies. On this basis, we propose a new model for the evolution of the Victoria Land Basin, invoking five phases of tectonic activity and associated sediment accumulation patterns. Phase 1 (pre-latest Eocene) involved regional uplift and erosion of the Transantarctic Mountains to the immediate west of the basin. Phase 2 (latest Eocene to Early Oligocene) was an Early Rift stage characterized by sediment accumulation in laterally restricted grabens. Phase 3 (Early Oligocene to Early Miocene) was the Main Rift stage, in which sediment accumulation was no longer confined to grabens in the west of the basin, but rather formed an eastward-thickening wedge into the centre of the basin. Phase 4 (Early Miocene) was a consequence of passive thermal subsidence, producing a relatively even blanket of sediment across the entire basin. Phase 5 (post-Early Miocene) was associated with the “Terror Rift” and gave rise to a succession contain both young magmatic rocks and young faults and which thickens markedly into a central depocentre. The new framework allows recognition of thick, post-Early Miocene stratigraphic intervals as yet unsampled by stratigraphic drilling in McMurdo Sound.