Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp. 298-. 308 



Patterns of deposition at the continental margin* 



By Henry C. Stetson 



Museum of Comparative Zoology, Harvard University 



and Woods Hole Oceanographic Institution. 



GENERAL STATEMENT 



The term " continental shelf and slope ", " continental terrace ", or " continental 

 platform ", as it has been used for decades in the geological hterature, connotes to 

 most geologists the submerged margin of the land masses. But with our rapidly 

 increasing knowledge of submarine geology the fact is becoming apparent that being 

 under water is about the only attribute that many of these areas have in common. 

 It is high time for a reappraisal of what these features really are, and to examine 

 their origin, and to consider critically whether the term should be applied indis- 

 criminately to the submerged margin of any large land mass, no matter how dis- 

 similar the topography and the structure may appear to be. 



A continental terrace, as the term will be used here, is a three-dimensional sedi- 

 mentary structure. The shelf is the shallow, gently sloping upper surface, and the 

 slope is the steep seaward face. It is our purpose here to trace the development of 

 such a sedimentary structure from its earliest beginnings, and to try to show that, 

 where continental margins do not exhibit this simple structure, the answer probably 

 lies in unravelling the varied events of their geologic history rather than in trying to 

 find an oceanographic interpretation. For it is on this point that much of the con- 

 fusion in the present day literature has arisen as modern marine surveying reveals a 

 bewildering variety of forms. We are fortunate in having preserved two large terraces 

 which have remained basically unaltered ever since their earhest beginnings. For 

 these two terraces, although ancient, are primitive in their structure; they are arche- 

 types, to borrow a term from biology, of many other more complex forms that have 

 evolved in other parts of the globe, whose origin has now been obscured by subse- 

 quent events. I refer, of course, to the platforms bordering the eastern and Gulf 

 coasts of the United States. And we are doubly fortunate in that these submerged 

 margins together with their emerged coastal plains have been the sites of intensive 

 geological investigation. 



Around the world today the submerged continental margins are of varying widths. 

 The extreme cases are the shelf off Siberia facing the Arctic Basin, three to four 

 hundred miles in width, in contrast to the west coast of South America where the shelf 

 is practically non-existent. At the present time all the continents are largely emergent 

 and the shallow, interior seas which have repeatedly flooded them in the past have 

 largely drained away. Consequently, the continental terraces are now the chief sites 

 where marine sediments are accumulating. There is one major exception to this: 



* Contribution No. 782 from the Woods Hole Oceanographic Institution. 



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