Abstract

Since the first application of cosmogenic nuclides to the study of glacial history and processes in 1990, increasing numbers of studies have used a variety of cosmogenic isotopes to quantify the exposure age and erosion rate of glaciated landscapes. However, obtaining chronological data from glaciated landscapes once covered by cold-based, nonerosive ice is challenging because these surfaces violate assumptions associated with simple cosmogenic exposure dating. Nonerosive glacial ice fails to completely remove nuclides produced during previous periods of exposure, leaving behind rock surfaces with complex, multigenetic nuclide inventories.

Here, we constrain the glacial history, landscape evolution, and efficiency of subglacial erosion in the Pangnirtung Fiord region of southern Baffin Island using over 300 paired analyses of in situ cosmogenic 10Be and 26Al. Simple exposure ages are 6.3–160 ka for 10Be (n = 152) and 4.3–124 ka for 26Al (n = 153). Paired bedrock-boulder samples have discordant ages, simple exposure ages generally increase with elevation, 10Be and 26Al ages for the same sample disagree, and both boulders and bedrock yield multimodal age distributions—all patterns suggestive of limited subglacial erosion. Measured 26Al/10Be ratios indicate that about one third of the samples in the data set experienced at least one period of pre-Holocene exposure followed by burial with limited erosion. Modeled two-isotope minimum-limiting exposure durations are as high as hundreds of thousands of years, and minimum-limiting burial durations range up to millions of years, implying that parts of southern Baffin Island have been preserved beneath nonerosive glacial ice for much, if not all, of the Quaternary. A subset of the samples contains few nuclides inherited from prior periods of exposure and is thus useful for constraining the chronology of the most recent deglaciation. Using these samples, we infer that deglaciation of most of the landscape occurred ca. 11.7 ka and that the Duval moraines, a prominent feature of the last deglaciation, formed ca. 11.2 ka.

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