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Geology; August 1994; v. 22; no. 8; p. 747-750; DOI: 10.1130/0091-7613(1994)022<0747:SOAGCS>2.3.CO;2
© 1994 Geological Society of America
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Sonography of a glaciated continental shelf

B. D. Loncarevic1, R. C. Courtney1, G. B. J. Fader1, P. S. Giles1, D. J. W. Piper1, G. Costello2, J. E. Hughes Clarke3 and R. R. Stea4

1 Atlantic Geoscience Centre, Geological Survey of Canada, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada
2 Canadian Hydrographic Service, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada
3 Ocean Mapping Group, University of New Brunswick, P.O. Box 4400, Fredericton, New Brunswick E3B 5A3, Canada
4 Nova Scotia Department of Natural Resources, P.O. Box 1087, Halifax, Nova Scotia B3J 2X1, Canada

Sonographs of the inner continental shelf off Halifax, Nova Scotia, show a large part of the inner shelf area consisting of exposed bedrock in which the inferred sequence of structural events is clearer than the record on land. Ribbed moraines overlie eroded drumlins and provide new information on the deglaciation history. Morphologic features allow a precise definition of the maximum postglacial lowstand of sealevel at -65 to -70 m. A 1000 km2 area in eastern Canada was surveyed with a multibeam sounder EM100, manufactured by Simrad of Norway. A 100% coverage of the sea floor was achieved with 50 to 100 m track spacing, and position control was achieved using the differential global positioning system (DGPS) with an accuracy of 1-2 m.

Data were corrected for ship motion, gridded at a 10 m spacing, and displayed as obliquely illuminated relief image. The sonograph revealed characteristics of the sea bed in detail for the interpretation of bedrock and surficial structures and processes. The bathymetric images may be more useful for geologic mapping than air photographs and satellite images on nearby land, where vegetation commonly obscures the geologic features.




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