T225 From Alpine Glaciers to Ice Sheets: Understanding Glacial Dynamics, Landscapes, and Environmental Change

Wednesday, 7 November 2018
8:00 AM - 12:00 PM
Room 136-137

THE KAMES OF ROHAN: LUMINESCENCE AGES OF ICE MARGINAL ACTIVITY IN MIDDLE EARTH (RANGITATA VALLEY, NEW ZEALAND) THROUGH THE LAST GLACIATION

Paper number: T225-12
Program: Technical Sessions
Time: 10:50 AM – 11:05 AM

Authors

Abstract

A spectacular kame terrace sequence marks the middle Rangitata Valley in the Southern Alps of New Zealand, forming a prominent backdrop for the village of Edoras, Rohan, in the Lord of the Rings movie trilogy, as well as a unique record of ice volume fluctuation. The geomorphology, sedimentology, and luminescence (OSL/IRSL) geochronology of this kame terrace sequence provide an opportunity to constrain the magnitude and timing of ice marginal fluctuations through the last glaciation, with particular detail through the New Zealand glacial maximum in late MIS 3 and MIS 2. While consistent with other regional glacial chronologies, the kame terrace record provides important details of MIS 3-2 ice volume fluctuations that are not discernible in CRN-dated moraine sequences.

The kame terrace surface sediments and associated buried stratigraphy document dramatic elevational fluctuations of the ice margin, here measured relative to the modern valley floor. Ice was 540 m thick ca. 63 ka and thinned to 50 m by ca. 37 ka. Ice then thickened to a near-maximum, 480 m above the valley floor by ca. 32 ka, before thinning again to 60 m by ca. 27 ka. The final ice re-expansion to middle elevations (230 m) occurred by ca. 26.5 ka, and ice subsequently thinned slowly through the period of the Northern Hemisphere last glacial maximum.

The kame terrace record is fully consistent with and complements published chronologies of glaciation in the study area, from lithofacies analysis and OSL dating and CRN dating (Shulmeister et al., 2018), and is similarly correlative with extensive CRN chronologies from the Mackenzie Basin (e.g., Putnam et al., 2013). However, the ca. 32-27 ka ice thickness decrease (425 m) confirms substantial ice volume depletion during the early portion of the “New Zealand glacial maximum,” and identifies substantial MIS 2 ice cover, represented in most New Zealand moraine chronologies, as a clear re-expansion of ice cover. Thus, the late MIS 3 and early MIS 2 advances can be viewed as distinct events.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-321453

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