Quaternary stratigraphy, paleoecology, and glacial geology, Îles de la Madeleine, Quebec

Abstract

On the Îles de la Madeleine, a rock platform as much as 20 m asl, locally with clam borings, is correlated to the regional interglacial surface at 2–8 m; its anomalous height may be a consequence of salt tectonics. Overlying lagoonal and paludal organic beds, one with Th/U ages of 89–101 ka, record the Sangamonian climatic optimum (substage 5e), which culminated in forest more thermophilous than that of the Holocene optimum. Overlying littoral gravel and sand, considered analogous to sediments in present-day tombolos, and organic beds with less temperate pollen types were deposited during the marine transgressive climax of substage 5e and thus indicate that sea level remained high after the thermal optimum, as in Holocene time. Cold-based Early Wisconsinan ice, probably centred on the Magdalen Shelf, tectonized bedrock and interglacial beds and deposited till upon them. Periglacial features indicate a subsequent long cold period. An organic bed dating from 11.3 to 10.6 ka records a warm interval followed by cooling. Buried peat, a submerged fossil sea cliff, and barrier beaches record a marine transgression during the late Holocene.