The erratic boulders that largely cover the extensive clayey tidal flat adjacent to the Parc National du Bic at Saint-Fabien-sur-Mer represent a range of lithologies, shapes and sizes. During surveys conducted across the tidal flat in 2010 and 2011, 2442 mega-boulders weighing between 1 and 440 metric tons, were identified and measured. Of these, 54.7% were igneous and metamorphic Precambrian erratics from the Canadian Shield and 45.3% were Appalachian Cambro-ordovician sedimentary erratics. The Precambrian erratics present at the site are smaller than those of Appalachian origin. Precambrian and Appalachian blocks weighing between 1 and 3 tons account for 45.1% and 27.2% of the total, respectively; those weighing between 3 and 10 tons, for 8.6% and 11.8%, respectively; and those weighing over 10 tons, for 1% and 6.3%, respectively. The 2 largest Precambrian boulders weigh 63 and 69 tons, whereas the 2 largest Appalachian boulders weigh 206 and 440 tons. Most of the mega-boulders are lying on the surface of the tidal flat; the remaining are partially embedded in the Goldthwait Sea clay deposit, which at this site is dated as being over 10 000 years old. Based on their characteristics, the Precambrian and Appalachian mega-boulders were initially moved by the Wisconsinian glaciers toward the St. Lawrence valley, before being transported and released into the postglacial sea by icebergs calved from the glacier edges along the north and the south shores of the St. Lawrence estuary. The amount of mega-boulders situated along the south shore of the maritime estuary, suggests that significant concentrations of icebergs occurred in the Goldthwait Sea during the deglaciation of the St. Lawrence valley between 13 500 and 9 500 years ago. Consequently, the sedimentary role of icebergs in releasing coarse debris deserves to be clearly highlighted.