Neogene tectonic and climatic evolution of the Western Ross Sea, Antarctica - Chronology of events from the AND-1B drill hole

Abstract

Stratigraphic drilling from the McMurdo Ice Shelf in the 2006/2007 austral summer recovered a 1284.87 m sedimentary succession from beneath the sea floor. Key age data for the core include magnetic polarity stratigraphy for the entire succession, diatom biostratigraphy for the upper 600 m and Ar-40/Ar-39 ages for in-situ volcanic deposits as well as reworked volcanic clasts. A vertical seismic profile for the drill hole allows correlation between the drill hole and a regional seismic network and inference of age constraint by correlation with well-dated regional volcanic events through direct recognition of interlayered volcanic deposits as well as by inference from flexural loading of pre-existing strata. The combined age model implies relatively rapid (1 m/2-5 ky) accumulation of sediment punctuated by hiatuses, which account for approximately 50% of the record. Three of the longer hiatuses coincide with basin-wide seismic reflectors and, along with two thick volcanic intervals, they subdivide the succession into seven chronostratigraphic intervals with characteristic facies: 1. The base of the cored succession (1275-1220 mbsf) comprises middle Miocene volcaniclastic sandstone dated at approx 13.5 Ma by several reworked volcanic clasts; 2. A late-Miocene sub-polar orbitally controlled glacial-interglacial succession (1220-760 mbsf) bounded by two unconformities correlated with basin-wide reflectors associated with early development of the terror rift; 3. A late Miocene volcanigenic succession (760-596 mbsf) terminating with a similar to 1 my hiatus at 596.35 mbsf which spans the Miocene-Pliocene boundary and is not recognised in regional seismic data; 4. An early Pliocene obliquity-controlled alternating diamictite and diatomite glacial-interglacial succession (590-440 mbsf), separated from; 5. A late Pliocene obliquity-controlled alternating diamictite and diatomite glacial-interglacial succession (440-150 mbsf) by a 750 Icy unconformity interpreted to represent a major sequence boundary at other locations; 6. An early Pleistocene interbedded volcanic, diamictite and diatomite succession (150-80 mbsf), and; 7. A late Pleistocene glacigene succession (80-0 mbsf) comprising diamictite dominated sedimentary cycles deposited in a polar environment