Late Quaternary glacial and deglacial history of eastern Vestfirdir, Iceland using cosmogenic isotope (36Cl) exposure ages and marine cores

The late glacial and deglacial history of Vestfirdir, NW Iceland is interpreted from terrestrial field‐based evidence and compared with marine cores and seismic studies. Understanding the timing of deglaciation is complicated by a lack of dateable organic material on land, uncertainties associated with interpretation of diamictons, and ambiguities in radiocarbon dating. New36Cl exposure ages of boulders and bedrock surfaces suggest that at least part of the coastal uplands were ice‐free by approximately 20 ka. Deglaciation of the valleys followed. Boulders from the crest of an end‐moraine in the Selá river valley have a mean36Cl age of 14.6 ka ± 0.8 ka (n = 4), and the outermost moraine in the valley adjacent to Kaldalónjökull has a mean36Cl age of 11.7 ka ± 0.9 ka (n = 2). Tephrochronology provides a link between the terrestrial and marine sequences around Vestfirdir. The Vedde Ash (ca. 12 k cal. yr BP) is present in some offshore cores, but it is absent from terrestrial sites, suggesting that its distribution provides a constraint on ice extent during the Younger Dryas. The Saksunarvatn Ash (10.2 ± 0.6 k cal. yr BP), confirmed by geochemical analyses and radiocarbon dating, is present in at least three terrestrial locations on eastern Vestfirdir and in many cores from the fjords and shelf, which constrains early Holocene ice extent.