1 PRESENTATION OF DR. PAGE C. VALENTINE 



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3 DR. VALENTINE: Thank you. Today in discussing the sedimentary 



4 environments in the Georges Bank canyons, I want to focus on several 



5 areas where we have, it seems to me, fairly clear evidence for sediment 



6 erosion, transport, and deposition. 



7 The observations and interpretations are based on the distribution 



8 of sediment texture, sedimentary bedforms such as ripples and sand 



9 dunes, on measurements of the strength of bottom currents from 



10 submer-sibles, and from data reported by Brad Butman and his co-workers 



11 from long-term current-meter deployments. 



12 The results show that sedimentary patterns do exist in the canyon 



13 regions, and suggest that in part we might be able to predict 



14 sedimentary environments in areas where we have little or no data. 



15 (Slide presentation.) 



15 This is a bathymetric map of the northeastern part of the U.S. 



17 margin. It shows the isolation of Georges Bank. Unlike the New England 



18 Shelf and the Middle Atlantic Shelf, Georges Bank is completely isolated 



19 from continental sediment sources by the Gulf of Maine and by the 



20 Northeast Channel and by Great South Channel here. 



21 So, in effect, and broadly speaking, we have an erosional 



22 environment here on Georges Bank. This is a sediment texture map of 



23 Georges Bank based on John Schlee's data from the 1960s. 



24 The double-ended red arrows show the orientation of the major 



25 semidiurnal tidal flows across the bank, and the dotted arrows show the 



26 clockwise mean flow that's been alluded to previously. 



27 We see that on the top of the bank, sand and gravel predominates 



28 in areas of strong currents, the tidal currents reach up to 1 knot on 



29 the bottom in shallow areas and diminish as water depth increases 



30 towards the edges of the bank. 



31 The finer-grained sediments are being deposited around the edges 



32 of the bank shown in blue and purple colors there. The mean current is 



33 thought to transport the fine sediment that's winnowed from the coarser 



34 sediments by the strong currents and is thought to transport that fine 



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