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TitleDeglacial sequences and glacio-isostatic adjustment: Quaternary compared with Ordovician glaciations
AuthorDietrich, P; Ghienne, J -F; Lajeunesse, P; Normandeau, AORCID logo; Deschamps, R; Razin, P
SourceGlaciated margins: the sedimentary and geophysical archive; by Le Heron, D P (ed.); Hogan, K A (ed.); Phillips, E R (ed.); Huuse, M (ed.); Busfield, M E (ed.); Graham, A G C (ed.); Geological Society, Special Publication 475, 2018 p. 149-179, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20170106
PublisherGeological Society of London
MeetingWilliam Smith Meeting - Glaciated margins:The Sedimentary & Geophysical Archive; London; UK; June 2-3, 2016
Mediapaper; on-line; digital
File formatpdf
NTS22J/01; 22J/08
AreaSept-Îles; St. Lawrence River; North Shore; Gulf of St. Lawrence; Canada; Morocco
Lat/Long WENS -66.5000 -66.0000 50.5000 50.0000
Lat/Long WENS -7.8333 -5.2500 31.0000 29.7500
Subjectssurficial geology/geomorphology; stratigraphy; geophysics; Science and Technology; Nature and Environment; geological history; glacial history; deglaciation; depositional history; depositional environment; isostatic rebound; ice margins; ice retreat; sedimentary basins; basin analysis; basin evolution; sea level changes; eustatic submergence; postglacial emergence; glacial deposits; ice contact deposits; submarine fans; glaciofluvial deposits; deltaic deposits; moraines; raised beaches; spits; glaciomarine deposits; geophysical surveys; acoustic surveys, marine; side-scan sonar; sonar surveys; systematic stratigraphy; Goldthwait Sea; Lake Daigle Moraine; Gilbert Delta; Laurentide Ice Sheet; Corossol Bank; Corossol Impact Crater; Last Glacial Maximum; Second Bani Group; Ktawa Group; First Bani Group; Moroccan Anti-Atlas; Phanerozoic; Cenozoic; Quaternary; Paleozoic; Ordovician; Silurian
Illustrationslocation maps; geoscientific sketch maps; time series; stratigraphic columns; geophysical images; schematic cross-sections; photographs; geochronological charts; stratigraphic cross-sections; stratigraphic correlations; stratigraphic sections; schematic representations
ProgramEnvironmental Geoscience
Released2018 05 14
AbstractDeglacial sedimentary sequences recording the decay and final demise of ice sheets result from intricate interactions between the pattern of ice margin retreat, inherited basin physiography and relative sea-level (RSL) changes. A specific emphasis is here given to the glacio-isostatic adjustment (GIA), which may force postglacial local RSL fall in spite of concomitant glacio-eustatic rise. In this contribution, we characterize a Quaternary deglacial succession emplaced in such a setting, subsequently used as an analogue to interpret an end-Ordovician deglacial record. The Quaternary deglacial succession, tens of metres thick, formed under condition of RSL fall forced by the GIA in c. 10 000 years in the aftermath of the deglaciation. This sedimentary succession consists of a lower, fining-upward sequence representing the backstepping of ice-contact depocentres following the retreat of the ice margin, and an upper, coarsening-upward sequence that relates to the subsequent progradation of a glaciofluvial delta system. A very similar stratigraphic stacking pattern characterizes the Ordovician analogue, suggesting a comparable deglacial sequence. By analogy with the Quaternary succession, this ancient deglacial record would have hence been emplaced under conditions of RSL fall forced by the GIA. Moreover, it must only represent a very short time interval that could be viewed as virtually instantaneous regarding the Late Ordovician glaciation. Such a vision is at odds with commonly accepted interpretations for such successions.
Summary(Plain Language Summary, not published)
Deglacial sedimentary successions result from changes in relative sea-level, ice-sheet retreat and basin physiography. In this study, we document a Quaternary succession from the St. Lawrence North Shore (Eastern Canada) and use it as an analogue for the interpretation of a late-Ordovician deglacial record in Morocco. In the St. Lawrence North Shore, subaqueous ice-proximal depocenters are superimposed by a deltaic progradation. These two successions are separated by a glacimarine to continental surface. A similar succession is observed in the late-Ordovician record of Morocco, suggesting a similar deglacial setting. The analogy thus allows us to interpret the late-Ordovician succession as being emplaced during glacio-isostatic sea-level fall.

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