| Summary: | This thesis presents multi- method numerical ages and age estimates obtained from the previously undated Ókoli Tephra of the Vestfírôir Peninsula, NW Iceland and the Þórsmörk Ignimbrite (ÞIG), Eastern Volcanic Zone, S. Iceland. These provide unique chronological constraints for Quaternary landscape evolution, ice sheet extent and ice -sheet thickness. In addition, they allow ice -free area hypotheses in Iceland to be tested and terrestrial and marine records of palaeoenvironmental change in the North Atlantic region to be linked more securely. The 2.26±0.11 Ma fission-track age of the OÞoli Tephra is particularly important because it places a major new age restriction on glacially driven, macroscale landscape evolution processes of fjord network formation on the Vestfírdir Peninsula. The pre- radiocarbon, Quaternary era is a vital period in which current glacial /interglacial cycles developed and caused widespread environmental change. Dating controls for this era are limited because of widespread glacial erosion, but in Iceland certain tephra deposits have survived glacial overriding and can provide accurate age constraints and precise spatial correlation for stratigraphic sequences. The two tephra deposits chosen for this study are of great palaeoenvironmental significance. The 013oli Tephra rests unconformably 580 -600 m.a.s.l. near the plateau surface of Skagafjall (NW Iceland). The 100 -160 m thick sequence of ice -dammed lake deposits beneath it were thought to have formed `20- 17,000' years ago. The ÞIG (Eastern Volcanic Zone, EVZ, S. Iceland) is the largest Quaternary -age ignimbrite deposit in Iceland and glass compositions have been geochemically linked with the highly silicic (Si0₂ >68 wt %) component of North Atlantic Ash Zone-2 (NAAZ-2), 48-58 ka. Correlation, fission -track (FT) and thermoluminescence (TL) methods were used to produce ages from the glass shards that overwhelmingly dominate the highly silicic airfall and /or pyroclastic flow ash components of these deposits. Dating glass ...
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