matter of speculation. Several possible origins — 

 fluvioglacial, glacial, ice-rafting or residual — 

 may be suggested. There is also the possibility 

 that these gravels were laid down under high 

 energy conditions, similar to those prevalent in 

 many littoral environments. On the basis of avail- 

 able data (Coulter et al., 1965; and Hopkins, 

 1967) it is most improbable that, during the 

 height of the last two major glaciations (Illinoian 

 and Wisconsin), the continental glacial advances 

 extended into and beyond the northern coastal 

 province of Alaska. As such, a glacial and/or 

 fluvioglacial origin for the shelf gravel seems un- 

 likely. No rock outcrop on the present shelf has 

 ever been reported and, therefore, any possibility 

 that the gravel is a contemporary marine residual 

 deposit is ruled out. Earlier it was observed that 

 there is an absence of size-density relationship in 

 the heavy mineral distributions in the sand-sized 

 particles of the Beaufort Sea shelf (Naidu and 

 Sharma, 1972). It is concluded from this that 

 these sands were patently not deposited, either 

 now or in the past, under high energy conditions, 

 and most likely similar depositional conditions 

 prevailed when the gravel associated with these 

 sands was laid down. 



By a process of elimination, it is surmised that 

 the bulk of the gravel on the shelf of the Beaufort 

 Sea is an ice-rafted paleo deposit. Substantiating 

 this conclusion McCulloch (1967) has stated that 

 some gravels on the edge of the northern coastal 

 plain of Alaska were transported by ice-rafting 

 during the mid-Wisconsin (Woronzofian) trans- 

 gression, about 25,300 ± 2,300 years ago. It is 

 suggestive that these ice-rafted gravels together 

 with those on the shelf, and inferred as paleo 

 deposit, apparently did not originate either in the 

 Brooks Range or in other bedrock of northern 

 Alaska. This conclusion is based on inferred 

 sea-level position (McCulloch, 1967, p. 93 and 

 p. 109), and the extent of the last two glaciations 

 in the region (Coulter et al., 1965; and Hopkins, 

 1967), as well as from the exotic lithology of the 

 Woronzofian gravels of north arctic coastal 

 Alaska (MacCarthy, 1958; Black, 1964). Most 

 probably these gravels were deposited by 

 icebergs similar to the present-day "ice islands" 

 that have originated from ice shelves of Elles- 

 mere Islands in Canada (Hopkins, 1967, p. 81). 



Our preliminary mineralogic and petrographic 

 studies of 56 specimens of gravel fragments of 

 the Beaufort Sea shelf, together with several 

 hundred samples of bedrock materials from the 

 Brooks Range, seem to further substantiate this 

 concept, although we do plan to pursue further 

 work along these lines. 



It is concluded that most of the paleo gravel has 

 remained exposed on the middle and outer shelf 

 regions, and has not been blanketed by modern 

 deposits, presumably because of relatively low 

 rates of subsequent sedimentation of sand and 

 mud. 



The present study has shown that no single 

 environment has characteristic sediment sorting, 

 skewness or kurtosis values (Table 1). As such, 

 grain-size parameters should be considered with 

 great caution in attempted interpretation of dep- 

 ositional environments of high latitude paleodel- 

 taic sediments. Mean size of sediments seems to 

 be the only size parameter that is different for the 

 various environments (Table 1), and presumably 

 this is determined by the varying contents of 

 gravel and sand. Scatterplot diagrams of various 

 grain size parameters (Figures 4 and 5), however, 

 do appear to have a potential use in paleogeo- 

 graphic studies. The trends of plots in Figure 4 

 suggest that, except in the fluvial channel of the 

 Colville River, the sorting of sediments in each 

 environment is a function of the Phi Mean Size. In 

 both the scatter-plot diagrams some overlapping 

 of field of the plots for deltaic, nondeltaic shelf 

 ( <64m), and extrashelf ( >64m) sediments is dis- 

 cerned. This may be explained on the basis that 

 some sediments perhaps somewhat arbitrarily 

 classed under a certain environment in actuality 

 do not belong to that environment. The other 

 possibility could be that such plots represent sed- 

 iments that were deposited at the transitional zone 

 between discrete environments. 



Heavy Mineral Studies 



The low concentrations of heavy minerals in 

 the deltaic sediments under investigation (Table 

 2) may be related to: (i) low concentrations of 

 heavy minerals in Colville River sands (Dygas et 

 al., 1972), which presumably are an important 

 primary source of the deltaic sands, and/or (ii) 

 lack of prolonged hydraulic conditions sufficient 



246 



