SEDIMENTARY ENVIRONMENTS IN SUBMARINE CANYONS AND 

 ON THE OUTER SHELF - UPPER SLOPE OF GEORGES BANK 



Dr. Page C. Valentine 



U.S. Geological Survey 



Woods Hole, MA 



Sedimentary environments have been identified on the southern margin of 

 Georges Bank in the depth range of 150 to 500 m on the basis of sedimentary 

 texture, bedforms, and direct current measurements. Dominantly erosional vs. 

 depositional environments are identified for the outer shelf, upper slope, and 

 submarine canyons along the southern margin of Georges Bank. Studies 

 conducted in Oceanographer, Lydonia, and other canyons suggest that it is 

 possible to predict sedimentary environments in unstudied canyons based on 

 overall canyon morphology and by analogy with the known distribution patterns 

 of canyon sedimentary environments. 



SHELF ENVIRONMENT 



Georges Bank is an isolated shoal, separated from continental sediment 

 sources by the Northeast Channel, Great South Channel, and the Gulf of Maine. 

 The mean regional flow field is clockwise around Georges Bank. The bank 

 surface is erosional; fine sediments winnowed from the bank top are delivered 

 to bank-edge environments. Coarse sands and gravels found near-bottom current 

 maxima on the bank grade to finer sands and mud along the southern margin. 



At the shelf edge, rippled sand gives way to smoother and finer-grained 

 sand deposits as water depth increases on the upper slope. Submarine canyons 

 of varying size and wall steepness incise the Georges Bank shelf and contain 

 such sedimentary facies as pavements of ice-rafted gravel, bioeroded and 

 collapsed Pleistocene silt outcrops, mobile sands, and almost featureless 

 silty sands. 



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