1 research outputs found
Neogene tectonic and climatic evolution of the Western Ross Sea, Antarctica â Chronology of events from the AND-1B drill hole
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 40Ar/39Ar 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 wellâdated regional volcanic events through direct recognition of interlayered volcanic deposits as well as by inference from flexural loading of preâexisting strata. The combined age model implies relatively rapid (1 m/2â5 ky) accumulation of sediment punctuated by hiatuses, which account for approximately 50% of the record. Three of the longer hiatuses coincide with basinâwide 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 (1275â1220 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 glacialâinterglacial succession (1220â760 mbsf) bounded by two unconformities correlated with basinâwide reflectors associated with early development of the terror rift;
3. A late Miocene volcanigenic succession (760â596 mbsf) terminating with a ~1 my hiatus at 596.35 mbsf
which spans the MioceneâPliocene boundary and is not recognised in regional seismic data;
4. An early Pliocene obliquity-controlled alternating diamictite and diatomite glacialâinterglacial succession
(590â440 mbsf), separated from;
5. A late Pliocene obliquity-controlled alternating diamictite and diatomite glacialâinterglacial succession
(440â150 mbsf) by a 750 ky unconformity interpreted to represent a major sequence boundary at other
locations;
6. An early Pleistocene interbedded volcanic, diamictite and diatomite succession (150â80 mbsf), and;
7. A late Pleistocene glacigene succession (80â0 mbsf) comprising diamictite dominated sedimentary cycles deposited in a polar environment