tht'ie is less dilution because the influx of fine 

 grained materials is less; consequently gravel 

 concentrations are higher. Toward the west the 

 relict gravel should be at some depth below the 

 prisent sea floor as suggested by diving observa- 

 tions (Reimnitz and others, 1972). Its presence in 

 ihc surface sediments is due to reworking by ice 

 i^niiging. The surficial gravel at the shelf edge is 

 an enigma in this scheme. 



I At depths below the shelf break, finer sedi- 

 ments are found which are structurally charac- 

 terized by bioturbation and faint horizontal linea- 

 tidus (fig. 15). The almost complete absence of 

 gravel is perplexing. If sedimentation were dilut- 

 ing the gravel contribution from ice rafting, the 

 hidlugical activity as indicated by bioturbation 

 ^huuld probably not be so well developed. 

 Another possibility is a paucity of ice rafting, 

 lither now or in the past, beyond the shelf break. 

 However, at present, there is no reason for believ- 

 ing that ice rafting halts or slows abruptly at the 

 iheU break. It also might be argued that the 

 deeper deposits are slumped sediments which are 

 ?ommon on the slope (Arthur Grantz, oral com- 

 munication, 1973). If this is the case the sedi- 

 ments might be representative of a period when no 

 ice rafting occurred. 



The above discussion indicates that our under- 

 standing of shelf sedimentology is far from com- 

 plete. Materials are present that must have been 

 ice rafted, judging from the dichotomy of sizes 

 present and the angular shapes of some of the 

 clasts. What is unclear is whether or not these 

 result from contemporary processes or reflect 

 agents ojjerating some time in the past, perhaps 

 fluring a lower stand of sealevel. Any interpreta- 

 tion will have to consider that this shelf experi- 

 ences intensive ice-bottom interaction, and 

 radiogenic dates from such an area must be inter- 

 preted with great care. 



It follows that the absence of information on 

 sedimentary stnjctures and an incomplete know- 

 ledge of the year-round influence of ice in most 

 other regions investigated make a comparison of 

 the sedimentary environment of the Alaskan 

 Beaufort shelf with other arctic shelves prob- 

 lematical. Creager and Sternberg (1972, p. 361), 

 in an excellent review article on the problems of 

 understanding continental shelf sedimentation, 



noted: "A lack of [measurements] of the envi- 

 ronment in which the sediments exist. We can no 

 longer interpret the environment from a vague 

 knowledge of the nature and distribution of the 

 sediments." Nevertheless, tentative comparisons 

 can be made between textural parameters of sev- 

 eral shelf areas. 



It appears that the sediments found on the 

 Alaskan Beaufort shelf are remarkably similar to 

 those reported by the University of Washington 

 group for the sediments off northern Siberia (Sil- 

 verberg, 1972; Holmes, 1967; Naugler, 1967). 

 Observations on this shelf are similar even to the 

 point of noting the occurrence of a grey stiff silty 

 clay, ascribed as pre-HoIocene, which we also 

 have found on the inner shelf (Sidoryenko, 1970). 

 Silverberg notes puzzling mixtures of surficial 

 fine silts and underlying sands which he ascribes 

 to bioturbation, but which, if it occurred in our 

 area of study, would most likely result from ice 

 gouging. 



A major difference between these two shelves 

 is in their width: The Siberian shelf is 350-400 

 km wide, the Alaskan shelf 50-100 km. Presum- 

 ably as a result of this, and the poor ice condi- 

 tions, the Siberian outer shelf has only been 

 sparsely sampled and reported on in the open 

 literature. Thus a comparison of our coarsening of 

 sediments along the shelf break is not possible. 

 However, a comparison with the limited Cana- 

 dian data would suggest that the sediments of the 

 Mackenzie embayment coarsen along the shelf 

 break as do the sediments of the Alaskan shelf 

 (Wagner, 1972; Yorath and others, 1971). 



CONCLUSIONS 



The primary observation that has resulted from 

 this study is that both ice and water significantly 

 influence geologic processes and products. In 

 contrast to temperate latitudes, where movement 

 of water is the primary agent, along the northern 

 coast of Alaska ice (gouging, rafting, as perma- 

 frost) and water trade off in time of year and 

 geographic location as the most significant agent. 

 The result is a complex environment which we are 

 just beginning to understand. The following 

 specific observations should be considered tenta- 

 tive: 



193 



