The Magdalen Islands (Québec, Canada) are a key location for unravelling the glacial and sea‐level history of the Maritime Provinces of eastern Canada. Although many sedimentary sequences have been described in the literature, absolute ages are lacking, impeding an accurate interpretation of the deposits and the establishment of a precise chronological framework. This study provides a detailed description of 21 stratigraphical sequences located throughout the archipelago, as well as the first comprehensive luminescence chronology from the Last Glacial Maximum (LGM) to c. 10 ka. In addition to the five samples collected for age control purposes, 34 luminescence samples were taken from 17 different sites in glacial, periglacial and coastal deposits. The stratigraphical and chronological data reveal that the islands were at the crossroads of two icecaps during the LGM; the southern islands were glaciated by the Escuminac icecap located in the western Gulf of St. Lawrence whereas the northern archipelago was glaciated at the end of the LGM by an ice flow from Newfoundland. The glacial deposit covering the northern Magdalen Islands was associated with the Newfoundland icecap; here it is named the Grande‐Entrée till and is dated to c. 20 ka. OSL ages between c. 23 and 17 ka acquired from cryopediment and coastal deposits on the southern islands indicate that this part of the archipelago was deglaciated shortly after the LGM and was affected by a high sea level and periglacial processes. Around 15 ka, the entire archipelago was deglaciated and partially submerged until c. 10 ka. This data set is the first major contribution to a detailed chronology of the Magdalen Islands and constitutes the first step towards interpreting the glacial and sea‐level history of the central area of the Gulf of St. Lawrence; this new understanding will provide input to regional marine and glacial modelling.

The deposits identified as being the Drift des Demoiselles, which is the upper unit of the southern Magdalen Islands (Québec, Canada), belong to two units of different origin, glacial and glaciomarine. At Anse à la Cabane, the glacial deposit comprises two subunits: a glacitectonite at the base and a subglacial traction till at the top. Numerous glaciotectonic deformation structures suggest ice flow towards the southeast. The till is above an organic horizon dated to ϳ47-50 ka BP. New data presented here show that the southern part of the Magdalen archipelago was glaciated during the Late Wisconsinan. We relate this ice flow to the Escuminac ice cap, whose centre of dispersion was located in the Gulf of St. Lawrence, northwest of the islands. At Anse au Plâtre, the top of the Drift des Demoiselles is a glaciomarine deposit. At Anse à la Cabane, the till is covered by a stratified subtidal unit located at ϳ20 m above sea level. Both were deposited during the marine transgression that followed deglaciation. At Anse à la Cabane, three ice-wedge casts truncate the till and the subtidal unit, providing evidence that periglacial conditions occurred on the archipelago after deglaciation. Résumé :Les dépôts identifiés comme étant le Drift des Demoiselles, qui constitue l'unité sommitale du sud des Îles-de-laMadeleine, appartiennent à deux unités d'origine distincte, l'une glaciaire et l'autre glaciomarine. À l'Anse à la Cabane, le dépôt glaciaire comprend deux sous-unités, une glacitectonite à la base et un till de traction au sommet. Les nombreuses déformations glaciotectoniques indiquent un écoulement glaciaire vers le sud-est. Ce till repose sur un horizon organique daté de ϳ47 à 50 ka BP. Ces nouvelles données démontrent que la partie sud de l'archipel des îles de la Madeleine a été englacée durant le Wisconsinien supérieur. Nous rattachons cet écoulement glaciaire vers le sud-est à la calotte Escuminac dont le centre de dispersion était situé dans le golfe du Saint-Laurent au nord-ouest de l'archipel. À l'Anse au Plâtre, le Drift des Demoiselles correspond majoritairement à un dépôt glaciomarin. À l'Anse à la Cabane, le till est surmonté par une unité de sable stratifié infralittoral située à ϳ20 m d'altitude. Cette unité s'est mise en place durant la transgression marine qui a succédé à la déglaciation. Cette transgression est également à l'origine de l'unité glaciomarine à l'Anse au Plâtre. Trois fentes de gel fossiles recoupent le till à l'Anse à la Cabane ainsi que l'unité infralittorale qui le surmonte. Elles témoignent de conditions périglaciaires sur l'archipel après la déglaciation.

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The Magdalen Islands are a valuable terrestrial record, evidencing the complex glacial and periglacial history of the Gulf of St. Lawrence. Thirteen structures interpreted as ice‐wedge pseudomorphs or composite‐wedge casts were observed at four sites on the southern Magdalen Islands and testify to the former presence of permafrost under periglacial conditions. These features truncate Carboniferous sandstone or Last Glacial Maximum (LGM) glacial and glaciomarine diamicts, both overlain by subtidal or coastal units. Six optically stimulated luminescence (OSL) and four radiocarbon ages were obtained from both host and infilled sedimentary units. These ages provide the first absolute chronological data on these structures, shedding new light on the relationships between glacial and periglacial phases. Our chronostratigraphic data suggest that, after the deglaciation and the emersion of the archipelago, thermal contraction cracks grew during the cold period of the Younger Dryas (11–10 ka; 12.9–11.5 cal. ka BP). The Younger Dryas, which is well documented in the Maritime Provinces of Canada, occurred after a pedogenesis phase associated with the Allerød warm period evidenced by the well‐developed palaeopodzol ubiquitous on the Magdalen Islands.