Different 14C ages for various fractions of peat

Since the 19th century, various authors have assigned the glacial landforms in the lower valleys of northern Italy to different ice ages (Penck and Brückner 1909). This study was part of a project that involved a broad geomorphological analysis and the first-time absolute in-situ exposure dating of erratic boulders using 10Be and 36Cl (Braakhekke et al. 2020). In addition to the cosmogenic analysis, seven radiocarbon samples were taken from a fluvial terrace outcropping 6 meters high along the Ticino River. Where possible, the samples were sieved to separate a bulk fraction (<125 μm) from the undefined organic fragments. Some samples were partly dissolved during the subsequent ABA preparation of all fractions. This way, we obtained up to four ages per initial sample: one each for the insoluble bulk fraction, the humic acid of the bulk, the organic fragments, and the humic acid of the organic fragments. The obtained radiocarbon ages vary significantly, with the extreme being thousands of 14C years between the insoluble bulk fraction and the organic fragments for the same sample. For all samples, radiocarbon analysis of the bulk fractions gave much younger ages than the hand-selected macro remains. Here, we discuss the age differences and possible sources of old and young carbon found in samples. The ages of the organic fragments showed the most consistency over the whole profile, and these fragments are least likely contaminated by younger material. Based on our results obtained on macro remains, this deposit is dated to MIS3 age. About 3 meters of fine-grained sediment were deposited here during ca. 8 ky. This could tell us more about the sediment budgets during some of the (Greenland) stadial-interstadial oscillations at the outlet of a major lake (e.g., Lake Maggiore) and the erosive power of glaciers during a phase preceding the global Last Glacial Maximum.