Glacial geomorphology of the Northeast Newfoundland Shelf: ice‐stream switching and widespread glaciotectonics

Abstract

Analysis of Olex bathymetry, multibeam sonar and seismic survey data, shows that, perhaps during the mid Pleistocene, grounded ice crossing the Northeast Newfoundland Shelf was topographically steered in Hawke Saddle, occupied a broad trough underlying much of Belle Isle Bank and present‐day Notre Dame Trough, and deposited ~100 m of stacked glacigenic sediment; grounded ice crossed southern Funk Island Bank and occupied Notre Dame Trough. During the Wisconsinan Stage, c. 30 cal. ka BP, flow remained topographically steered in Hawke Saddle, but due to flow switching two convergent ice streams incised the stacked sediments of the earlier phase, creating the modern Notre Dame Trough, and diverging around an erosional remnant near the shelf edge. The ice margin at the Last Glacial Maximum (c. 18 14C ka BP) was at the shelf edge in Trinity Trough but far to the west elsewhere. Retreating ice did not stabilize at fjord mouths, but halted several times within fjords. Shelf morphology was shaped by glaciotectonism. The large tectonized zone on the north flank of Notre Dame Trough was created by the northernmost of the two convergent streams. Glaciotectonism was most widespread in the enclosed St. Anthony Basin, where the Quaternary cover has been stripped away, arrays of composite ridges have formed and sediment blocks have been thrust onto the adjacent bank. A large hill‐hole pair was formed on the east side of the basin, extending onto Belle Isle Bank. A hill‐hole pair on the inner shelf was formed by ice flow from the northwest into Notre Dame Channel. Evidence of widespread glaciotectonism distinguishes this relatively deep shelf from the adjoining, relatively shallow, eastern Canadian shelves, but has strong parallels with parts of the Norwegian continental shelf where methane hydrates maybe played a role in regulating ice‐stream flow.

An updated radiocarbon-based ice margin chronology for the last deglaciation of the North American Ice Sheet Complex

“…Given the continued growth in the size and diversity of chronological data (Stokes et al, 2015) a revision of the NAISC margin chronology is overdue. For example, recent marine geophysical work and mapping of ice streams (Brouard and Lajeunesse, 2017;Shaw and Longva, 2017;Margold et al, 2018) suggests an expansion of the LGM ice margin onto the continental shelf well beyond that depicted by Dyke et al (2003). In addition, new regional reconstructions of post-18 ka ice dynamics and ice streaming have been produced (De Angelis and Kleman, 2007;Ross et al, 2012;Hogan et al, 2016;Gauthier et al, 2019) and there has been a surge in the use of non-radiocarbon dating methods (e.g.…”

Reply to the comment by H.A.J. Russell on “Converging ice streams: a new paradigm for reconstructions of the Laurentide Ice Sheet in southern Ontario and deposition of the Oak Ridges Moraine”

“…They are now widely identified on the beds of Pleistocene and pre-Pleistocene ice sheets, indicating that they too were similarly structured (Le Heron 2017; Putkinen et al 2017;Stokes et al 2016;Margold et al 2014Margold et al , 2015Margold et al , 2018Stokes 2018). Today, almost 200 ice streams are currently recognized in the last Cordilleran and Laurentide ice sheets (Clark 1993;Patterson 1997;Dyke 2008;Kleman 2005, 2007;Evans et al 2006Evans et al , 2008Evans et al , 2014Ross et al 2006Ross et al , 2009Ross et al , 2011Ó Cofaigh et al 2010aÓ Cofaigh et al , 2013MacLean et al 2010MacLean et al , 2015MacLean et al , 2017Occhietti et al 2011;Paulen et al 2017;McMartin 2017;McMartin et al 2018;Veillette et al 2017;Shaw and Longva 2017;Margold et al 2018;Eyles et al 2018a). Russell does not acknowledge this large body of work and its significance for paleo-glaciological reconstructions for Southern Ontario.…”