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Abstract:
We report the discovery of exotic igneous, metamorphic, and sedimentary cobbles in raised beach deposits near Breiðavík, northern Iceland. These deposits consist of alternating cobble-, sand-, and silt-dominated facies. A nearby package of sands and silts, dated to the Late Antique Little Ice Age (LALIA; ca. 536−660 CE), provides age constraints for the raised terraces. While the upper terraces are composed exclusively of local basaltic material, the lowermost terraces (∼2 m above high tide) contain a mix of basaltic and nonbasaltic cobbles, including quartzofeldspathic gneiss, granitoid, rhyolite, sandstone, and serpentinite. U-Pb geochronologic analysis of zircon revealed dominant age modes of ca. 2800, 1150, 500, and 240 Ma with Lu-Hf isotopic compositions suggesting derivation from Greenland’s North Atlantic craton and Caledonian fold belt. The colder conditions of the LALIA, coupled with increased iceberg calving from the Greenland ice sheet, would have led to enhanced ice-rafted debris (IRD) transport to disparate areas south and east of Greenland. The East Greenland and East Iceland currents transported this IRD from Greenland, with deposition occurring along the Icelandic coast as the icebergs melted. This IRD was likely transported across the North Atlantic during Bond event 1. This process, along with those during other transient cooling events, may explain the age discrepancies between local bedrock and detrital zircons in the Arctic.
