Provenance, Geochemistry and Grain-Sizes of Glacigene Sediments, Including the Sirius Group, and Late Cenozoic Glacial History of the Southern Prince Albert Mountains, Victoria Land, Antarctica

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The southern Prince Albert Mountains, between David and Mawson Glaciers (75°30' to 76°S) in Victoria Land, Antarctica, comprise a series of nunataks with elevations ranging from 800 m near the coast to 2300 m ~ 130 km inland. Geochemical and grain-size analyses of tills from these nunataks reveal three major groups of deposits: (1) coarse to medium sandy tills, found on glacially streamlined summit plateaus of Kirk-patrick Basalt above 2000 m a.s.l., with geochemical compositions very similar to those of the underlying Jurassic Kirkpatrick Basalt; (2) bimodal silty and sandy tills of the Sirius Group with Ferrar/Beacon-dominated geo-chemical compositions, at elevations of 1300-1600 m a.s.l. on striated summit plateaus and high-elevation terraces; (3) fine-grained tills with high SiO2 contents from ice-cored moraines at the lee sides of large nunataks. The geochemical composition of sandy tills from the highest summit plateaus suggests that valleys had not yet cut through the Kirkpatrick Basalt and into Beacon and Ferrar rocks at the time of deposition. These tills represent a phase of temperate glaciation prior to deposition of diatom-bearing Sirius Group tills. The latter were deposited after a first phase of landscape dissection as inferred from geochemical data. The fine-grained ice-cored moraines are late-Pleistocene basal tills. The presence of pre-Pliocene glacial deposits on high mountain summits in the Prince Albert Mountains has implications for the interpretation of high-elevation Sirius Group sediments in other areas of the Transantarctic Mountains. It is possible that the 'Sirius debate' has its origin in interpretations of both thin, barren pre-Pliocene deposits on high mountain summits and thick sequences of diatom-bearing deposits in valleys elsewhere in the Transantarctic Mountains. Both types of deposits are associated with the Sirius Group, but they belong to separate glacial episodes.

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