CGRG Bibliography of Canadian Geomorphology
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Author : Boyer-Villemaire, U.; St-Onge, G.; Lajeunesse, P.; Locat, J.; Bernatchez, P.; Hillaire-Marcel, C.; and Sanfaçon, R.
Date : 2006.
Title : Quaternary chronostratigraphy and climatic changes in the Sept-Îles area, Gulf of St. Lawrence: preliminary results.
Publication : Joint Annual Meeting of the Geological Association of Canada and the Mineralogical Association of Canada. University of Quebec in Montreal (UQAM) May 14-17, 2006.
Issue :
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Abstract
Recent multibeam bathymetric surveys uncovered a ~4 km diameter submarine circular structure offshore Sept-Îles, Gulf of St. Lawrence. Acoustic subbottom profiles carried out in 2005 onboard the Coriolis II revealed a sedimentary accumulation of a few tens of meters in the center of the structure. Our initial hypothesis is that the sediments in the structure may have escaped glacial erosion and therefore could represent several continuous glacial/interglacial episodes. The main objective of this collaborative research is thus to study the Quaternary stratigraphy and climatic changes from seismic and sedimentary data collected inside and around the submarine structure. Preliminary coring was performed in 2005 on board the Coriolis II. Three Lehigh gravity cores (COR0503-SEPT01-07LH, COR0503-SEPT02-08LH and COR0503-SEPT04-09LH) were collected within the structure, while a witness core (COR0503-SEPT07-11LH) was taken outside the structure about 2 km eastwards. Preliminary CAT-Scan and Multi-Sensor Core Logger (MSCL) results show that sedimentary sequences within and outside the structure are different. In all the cores collected within the structure, two main lithostratigraphic units are observed. The top unit is 25 to 50 cm thick. It is laminated, bioturbated and characterized by relatively high density and magnetic susceptibility. The lower unit is more than 2 meter-long and is relatively homogeneous and massive. It presents relatively low density and magnetic susceptibility and contains ice-rafted debris (IRD). On the other hand, the witness core comprises a similar laminated top unit, while the bottom homogeneous unit is strongly bioturbated with relatively low density and magnetic susceptibility. Downcore CT numbers (pixel intensity) extracted from the CAT-Scan images are also consistent with these observations, showing a strong correlation with bulk density. Detailed visual description of the cores, grain size and isotopic analysis (210Pb and 137Cs) are presently being performed to help develop a chronostratigraphy for the area. Finally, piston coring in the submarine structure is scheduled in the summer 2006. The magnetic properties of the collected cores will be measured on u-channel samples for the establishment of a high resolution magnetostratigraphy.
Bibliography of Canadian Geomorphology