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TitleThe morphosedimentary record of glacial to postglacial environmental changes in fjord-lake Mékinac and adjacent areas (southeastern Canadian Shield)
AuthorTrottier, A -P; Brouard, E; Lajeunesse, P; Normandeau, AORCID logo
SourceGeomorphology vol. 376, 107565, 2020 p. 1-13,
Alt SeriesNatural Resources Canada, Contribution Series 20200035
PublisherElsevier B.V.
Mediapaper; on-line; digital
File formatpdf; html
NTS31I/15; 31P/02
AreaLake Mékinac; Du-Milieu River; Laurentian Mountains
Lat/Long WENS -72.7500 -72.5000 47.2500 46.8833
Subjectsmarine geology; surficial geology/geomorphology; sedimentology; stratigraphy; environmental geology; geophysics; Nature and Environment; Science and Technology; glacial history; glaciation; deglaciation; ice margins; tectonic history; isostatic rebound; earthquakes; coastal environment; basins; fiords; surface waters; lakes; paleoenvironment; paleoclimates; geophysical surveys; acoustic surveys; bathymetry; topography; glacial landforms; glacial deposits; proglacial deposits; postglacial deposits; landslide deposits; mass wasting; deltas; Canadian Shield; Laurentide Ice Sheet; St. Lawrence Ice Stream; Mars-Batiscan Event; Younger Dryas; Champlain Sea; alluvial sediments; Phanerozoic; Cenozoic; Quaternary
Illustrationslocation maps; geoscientific sketch maps; geophysical images; tables; profiles; geophysical profiles; schematic cross-sections
Released2020 12 09
AbstractFjords can transition from marine embayments to lacustrine waterbodies under glacio-isostatic change following their deglaciation. However, little is known on how a transition from fjord to lake is influenced by glacial dynamics and how it influences sedimentation in and around the basin. Here, we analyse swath bathymetry imagery and subbottom profiles pri in Lake Mékinac (southern Québec) as well as glacial landforms from LiDAR imagery around the lake to document the evolution of a fjord basin into a lacustrine body during the transition from the Late Pleistocene to the Holocene. These analyses helped refine local glacial history and show that the study area was probably under the up-ice reach of the St. Lawrence Ice Stream during full glacial conditions. The mapping of moraines in and around Lake Mékinac shows that deglaciation of the study area was marked by stabilization of the ice-margin during the Mars-Batiscan Event, which is traditionally correlated to the climate deterioration at the end of the Younger Dryas. The architecture of acoustic facies in the lake indicates a transition from glacial conditions (U1), to proglacial-paraglacial (U2) and to postglacial conditions (U3). The bottom of Lake Mékinac also contains multiple mass movement deposits related to progradation of the Du-Milieu River delta and probably to late-Holocene earthquakes. The acoustic architecture of sediments within the lake indicates that the sedimentation regime was most dependant on the sediment input regime and that the transition from fjord to lake did not significantly influence sedimentation during deglaciation of the watershed. Further work on dating the mass movement deposits that characterise the sediment architecture should provide a better assessment of natural hazard associated with seismological events.
Summary(Plain Language Summary, not published)
The study of the transition of fjords from a marine to a lacustrine environment provides insight into ice-margin geometry, ice dynamics, glacio-isostatic adjustment, and paraglacial slope activity of southern Québec.

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