MIS 3 glaciation in the middle Rakaia valley, New Zealand, documented through stratigraphy and luminescence geochronology

摘要

Stratigraphy, geomorphology, and luminescence dating of ice-proximal sediments document extensive MIS 3 Rakaia valley glaciation. Basal outwash contains ice-meltout depressions filled with upward-coarsening and progressively deformed outwash, overlain by undeformed ice-proximal diamicton and outwash. The most reliable luminescence date from basal outwash is 35.2 +/- 0.7 ka, consistent with site stratigraphic evolution and overlying exposure ages. The site thus indicates MIS 3 ice of similar extent as the main MIS 3/2 advance and demonstrates that ice retreated at least a short distance up-valley between the two advances. The results correlate with similar ages on ice-proximal lake sediments 10 km up-valley, on distal outwash 65 km down-valley, and with cosmogenic radionuclide dates elsewhere in the Southern Alps. This study thus confirms independently that MIS 3 glaciation was nearly as extensive as the main LGM advances in central South Island, New Zealand.