The Laurentian Channel Tertiary-Quaternary record of climate by cil51658

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									  The Laurentian Channel: Tertiary-Quaternary record of climate change, glacio-eustatic
                     and glacio-isostatic variations and submarine landslides

                                           Daniel Lebel




Themes
Sequence stratigraphy, submarine landslides, climate change, glacial history, intracratonic
basins, major river, fluvial systems.




Geographic location
Estuary of the St. Lawrence River and Saguenay fjord between Quebec City and the Magdalen
Island.




Problematic
          The nature of the submarine geology of the estuary of the St.Lawrence River remains one
of the greatest unsolved mystery of North American Geology. Under the leadership of some
canadian university researchers (Laval, UQAM, others), a series of surveys (1984 to 1990) with
air gun and boomer have been conducted to prepare an ODP site in relation with the Holocene
stratigraphic column and the regard of catastrophic events. Following this, new surveys (1996 to
1999) with 1 and 4kJ sparker has shown that the estuary is underlain by a deeply entrenched
channel filled by up to 600 m unconsolidated Tertiary-Quaternary sediments in several stacked
Quaternary sequences. Within the IMAGE project, during the MD-99 cruise, piston coring
through the upper 51 metres (less that 10% of the section) reached the last glacial-interglacial
transition. Below this unconformity, a stacked sequence of 5 megasequences fills an underlying
rugged topography. Presumably, this deep trench may be the result of 1) opening of the
St.Lawrence River valley at a yet unproven age (syn-Atlantic Mesozoic opening during the
Jurassic; reactivation in the Cretaceous; syn-Carboniferous transtension ?); 2) or represent
erosion during shoulder uplift during the Carboniferous, Mesozoic, Tertiary or more recently
still.


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       The Laurentian channel is situated at the mouth of the St.Lawrence River, and begins
with a sharp escarpment downstream from the confluence of the Saguenay River. Piston coring
on the floor of the Saguenay Fjord and the Laurentian channel shows that several catastrophic
landslide events have occurred along the flanks of these deep troughs, within a region which are
still seismically active due to a combination of glacio-isostatic rebound and particular tectonic
conditions (Laurentian Rift?, Appalachian Front?, Mesozoic extension?, or Charlevoix
astrobleme?)
       In terms of drilling technology, the estuary poses a special problem due to strong currents
and tides, deep-water conditions (200-400 m), presence of gas hydrates, and seabed stability. It is
particularly interesting to develop technologies using robotized drills.




Objective
       The objective of an IODP (integrated ocean drilling project) drilling project in the
Estuary of the St. Lawrence would be to assess the nature and age of the stratigraphic sequence
present, evaluate the glacial-eustatic record for climate change, and assess long-term geohazards
posed by submarine landslides.
       The first campaign (2003-2004) would be a general seafloor survey aimed at assessing
the different challenges posed by the nature of the seafloor and general geomorphological
conditions. This will be done in three part: 1) a Canadian SEAMAP swath scan bathymetry of
the proposed site; 2) an American-Canadian deep seismic survey to evaluate the nature of the
basement underlying the soft sediment basin; 3) a European robotized or other type of shallow
drilling campaign to map the nature of the seafloor surrounding the proposed drilling site.
       The second part of the project would consists of a deep drill hole at the proposed site, to
sample the entire unconsolidated sediment record, determine the nature of bedrock in this
unchartered terrain. The accompanying scientific assessment will include, biochronological,
geotechnical and geochronologic work as well as sedimentological and provenance studies.




Nature of scientific team
NRCAN/GSC, INRS, DFO/IML, McGill, UQAM, Laval, Europeans, etc.



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Impact
       This project will have multiple impacts: sequence stratigraphy, submarine landslides,
climat change, glacial history, Quaternary ice streams, rapid sea level changes, intracratonic
basins, major river, major fluvial systems. Jurisdiction questions over canadian submarine
territories, hazards to navigation and coastal communities. Determining the nature of underlying
bedrock will constrain (and may revise) existing interpretations for regional tectonic packages.




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