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.
Tertiary planation and uplift exhumed two unconformities (paleoplains) and produced two peneplains into which Quaternary glaciation excavated submarine basins and channels. The last interglaciation deposited organic beds and cut an intertidal rock bench and
littoral gravel, now emerged 2-7 m. The nonglacial period spanned 126-47 ka BP according to 30 Th/U and 14C wood ages at 16 sites. Two temperate cycles climaxed 125 and 86 ka BP and are correlated to oxygen isotope substages 5e and 5a; the first had hardwood forest reflecting a warmer than present
climate; the second had boreal forest like today. Early-Middle Wisconsinan time is recorded by three tundra/boreal forest alternations, reflecting climatic deterioration until Wisconsinan glaciers arrived 62-47 ka BP. Several ice flow phases left crosscutting striations, superimposed drumlins and
fluting, and three main till sheets of differing lithology, colour, texture, and provenance. An ice cap began on the highlands, then an ice sheet from mainland Nova Scotia advanced eastward and deposited a red foreign till on the lowlands. South-flowing regional ice (Laurentide?) crossed the island;
it was cold-based on the highlands and preserved preglacial soil and landforms. Weathered striations beneath fresh till suggest an ice free interval. A northward flow from Scotian Shelf which introduced shell fragments may have signalled an ice rise, a flow reversal due to drawdown, or a new ice
dome on the emergent shelf. The ice divide shifted onshore forming a Bras d'Or Lake centre. Gulf of St. Lawrence ice on the west coast dammed lakes that drained northward. Climatic cooling 11-10 ka caused glacial readvance and renewed solifluction. Highland ice lasted until 8-9 ka and Neoglacial
cirque glaciers may have formed. Neotectonics tilted the bench southward and displaced it 15 m at Aspy Fault. Submerged features, geodetic relevelling, and tide gauging show a relative sea level rise of 20-70 cm/100 a due glacial forebulge collapse. Unstable slopes have landslides and sagging
cliffs.
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