Chronology and stratigraphy of the Magdalen Islands archipelago from the last glaciation to the early Holocene: new insights into the glacial and sea‐level history of eastern Canada

The Magdalen Islands (Quebec, 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-Entree 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.

[1]  A. Murray,et al.  Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts , 2008 .

[2]  G. Fader,et al.  A conceptual model of the deglaciation of Atlantic Canada , 2006 .

[3]  A. Seaman,et al.  Chapter 48 – The Appalachian Glacier Complex in Maritime Canada , 2011 .

[4]  W. Peltier,et al.  Forms, response times and variability of relative sea-level curves, glaciated North America , 2000 .

[5]  C. Clark,et al.  Ice streams in the Laurentide Ice Sheet: Identification, characteristics and comparison to modern ice sheets , 2015 .

[6]  G. Duller.  Distinguishing quartz and feldspar in single grain luminescence measurements , 2003 .

[7]  David J. A. Evans,et al.  Subglacial till: Formation, sedimentary characteristics and classification , 2006 .

[8]  R. Chalmers.  Report on the surface geology of eastern New Brunswick, north-western Nova Scotia and a portion of Prince Edward Island , 1895 .

[9]  V. K. Prest,et al.  Late Wisconsinan and Holocene History of the Laurentide Ice Sheet , 2008 .

[10]  J. Shaw,et al.  Late Quaternary sedimentation and the postglacial sea-level minimum in Port au Port Bay and vicinity, west Newfoundland , 1993 .

[11]  K. Pye,et al.  GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments , 2001 .

[12]  J. Prescott,et al.  Cosmic ray contributions to dose rates for luminescence and ESR dating: Large depths and long-term time variations , 1994 .

[13]  R. Mott,et al.  Quaternary stratigraphy, paleoecology, and glacial geology, Îles de la Madeleine, Quebec , 1992 .

[14]  J. Shaw,et al.  The postglacial relative sea-level lowstand in Newfoundland , 1995 .

[15]  H. Josenhans.  Atlas of the marine environment and seabed geology of the Gulf of St. Lawrence , 2007 .

[16]  R. Folk,et al.  Brazos River bar [Texas]; a study in the significance of grain size parameters , 1957 .

[17]  A. Wintle.  Future Directions of Luminescence Dating of Quartz , 2010 .

[18]  J. Shaw,et al.  A new late-glacial sea-level record for St. George's Bay, Newfoundland , 2003 .

[19]  G. Fader,et al.  Morphology and seismic stratigraphy of the inner continental shelf off Nova Scotia, Canada: Evidence for a −65 m lowstand between 11,650 and 11,250 C14 yr B.P. , 1994 .

[20]  J. Vandenberghe,et al.  Pleistocene cryopediments on variable terrain , 2008 .

[21]  R. Stea.  The appalachian glacier complex in maritime canada , 2004 .

[22]  L. Owen,et al.  Luminescence dating of glacial and associated sediments: review, recommendations and future directions , 2008 .

[23]  A. Murray,et al.  The single aliquot regenerative dose protocol: potential for improvements in reliability , 2003 .

[24]  J. Rose,et al.  Till fabric patterns and significance: particle response to subglacial stress , 2003 .

[25]  J. Richardson.  Report of a geological exploration of the Magdalen Islands , 1881 .

[26]  J. Shaw,et al.  Palaeogeography of Atlantic Canada 13–0 kyr , 2002 .

[27]  G. St‐Onge,et al.  Quartz OSL dating of late Holocene beach ridges from the Magdalen Islands (Quebec, Canada) , 2015 .

[28]  J. Shaw,et al.  Late Quaternary Relative Sea-Level Change on the West Coast of Newfoundland , 2007 .

[29]  D. Nota,et al.  Sea-Floor Conditions Around the Magdalen Islands in the Southern Gulf of St. Lawrence , 1966 .

[30]  D. Belknap,et al.  Coastal and Terrestrial Impact of the Isostatically Forced Late Quaternary Drainage Divide Shift, Penobscot and Kennebec Rivers, Maine, USA , 2011 .

[31]  A. Murray,et al.  Luminescence dating of the PASADO core 5022-1D from Laguna Potrok Aike (Argentina) using IRSL signals from feldspar , 2013 .

[32]  Norbert Mercier,et al.  Dose-rate conversion factors: update , 2011 .

[33]  P. Dunlop,et al.  The subglacial imprint of the last Newfoundland Ice Sheet, Canada. , 2016 .

[34]  J. W. Goldthwait.  The occurrence of glacial drift on the Magdalen Islands , 1915 .

[35]  A. Murray,et al.  A review of quartz optically stimulated luminescence characteristics and their relevance in single-aliquot regeneration dating protocols , 2006 .

[36]  A. S. Dykea,et al.  The Laurentide and Innuitian ice sheets during the Last Glacial Maximum , 2001 .

[37]  Paul Martin,et al.  Analysis for naturally occuring radionuclides at environmental concentrations by gamma spectrometry , 1987 .

[38]  D. M. Mark.  Analysis of Axial Orientation Data, Including Till Fabrics , 1973 .

[39]  A. Murray,et al.  Modelling the effect of salinity on radium desorption from sediments , 1995 .

[40]  J. Wallinga,et al.  Selection of integration time intervals for quartz OSL decay curves , 2010 .

[41]  M. Bennett.  Ice streams as the arteries of an ice sheet: their mechanics, stability and significance , 2003 .

[42]  A. Murray,et al.  A new irradiated quartz for beta source calibration , 2015 .

[43]  P. Giles.  Windsor Group (Late Mississippian) stratigraphy, Magdalen Islands, Quebec: a rare eastern Canadian record of late Visean basaltic volcanism , 2009 .

[44]  P. Bernatchez,et al.  The Drift des Demoiselles on the Magdalen Islands (Québec, Canada): sedimentological and micromorphological evidence of a Late Wisconsinan glacial diamict , 2013 .

[45]  K. Thomsen,et al.  Review of optically stimulated luminescence (OSL) instrumental developments for retrospective dosimetry , 2010 .

[46]  A. Murray,et al.  Luminescence dating of quartz using an improved single aliquot regenerative-dose protocol , 2000 .

[47]  A. Murray,et al.  Identifying well-bleached quartz using the different bleaching rates of quartz and feldspar luminescence signals , 2012 .

[48]  G. St‐Onge,et al.  Chronology and palaeoenvironmental implications of the ice‐wedge pseudomorphs and composite‐wedge casts on the Magdalen Islands (eastern Canada) , 2015 .

[49]  C. Beaumont,et al.  A comparison of observed and theoretical postglacial relative sea level in Atlantic Canada , 1981 .

[50]  D. Godfrey-Smith,et al.  Optical dating studies of quartz and feldspar sediment extracts , 1988 .

[51]  W. Barnhardt,et al.  Late Quaternary relative sea-level change in the western Gulf of Maine: Evidence for a migrating glacial forebulge , 1995 .

[52]  G. Fader,et al.  WISCONSINAN GLACIAL AND SEA-LEVEL HISTORY OF MARITIME CANADA AND THE ADJACENT CONTINENTAL SHELF : A CORRELATION OF LAND AND SEA EVENTS , 1998 .

[53]  C. Buck,et al.  IntCal13 and Marine13 Radiocarbon Age Calibration Curves 0–50,000 Years cal BP , 2013, Radiocarbon.