to concentrate heavy minerals in the sand frac- 

 tion. Except during infrequent storms the conti- 

 nental margin and shallow marine environments 

 of north arctic Alaska are essentially low energy 

 depositional areas, and as such it is believed that 

 sands of these regions are not exposed to extended 

 mineral sorting by hydraulic action. 



The relatively higher percentages of heavy 

 minerals that are observed in successively finer 

 sand size grades in almost any one of the sedi- 

 ments (Table 2) show that heavy mineral distribu- 

 tions in the present deltaic environment conform 

 to the hydraulic equivalent concept (Rubey, 

 1933) and to the size-density relationships that 

 usually exist in water-laid sands (Rittenhouse, 

 1943). 



Observations made on the heavy mineral dis- 

 tributions in the offshore deltaic sediments (Table 

 2) are contrary to those made on the adjoining 

 fluvial sediments (Dygas et al., 1972) and on far 

 offshore nondeltaic shelf sediments of the 

 Beaufort Sea (Naidu and Sharma, 1972), inas- 

 much as the size-density relationship does not 

 exist in sediments from the latter two environ- 

 ments. Considering these differences, it would 

 seem that in the deltaic marine area mineral sort- 

 ing is brought about more effectively, presumably 

 because of the prevalence there of stronger and 

 prolonged hydraulic action. However, differ- 

 ences in hydraulic action can not be invoked to 

 explain the observed differences between con- 

 centrations of heavy minerals in any one size of 

 sand in the shelf and the delta. The fact that there 

 are relatively higher contents of heavy minerals in 

 sands of the shelf, in spite of the presumed lower 

 energy conditions prevailing there, suggests that 

 the bulk of the shelf sands have originated from 

 somewhere else than the delta. We hope to clarify 

 this suggestion by detailed heavy mineral studies 

 of sands from the delta and the shelf. 



The preceding conclusions seem to support the 

 earlier contention that transportation of sand from 

 the delta to the shelf by contemporary ice-rafting 

 is insigificant. If ice transport, and associated in 

 toto deposition of deltaic sands from the ice was 

 important on the shelf, then it would be expected 

 that both in the delta and on the shelf the total 

 concentrations of heavy minerals and their dis- 

 tributional patterns in various sand sizes would be 

 similar. This, as mentioned earlier, is not true. 



Causes and Significance of Clay Mineral Varia- 

 tions 



Results of our study do not show any clear cut 

 progressive downstream changes in the bulk <2fi 

 size clay mineral assemblages over the lower 

 161 -km length of the Colville River (Figure 6, 

 and Table 3). These observations run counter to 

 those made in low-latitude estuaries by several 

 investigators (Parham, 1966 for a review; and 

 Naidu, 1968), who noted clay mineral changes 

 with increased salinities of water progressively 

 downstream. These systematic downstream varia- 

 tions in clay minerals have been generally attrib- 

 uted either to: (i) gradual reconstitution of one 

 mineral to another through exchange/adsorption 

 of ions, or (ii) continuous regeneration of de- 

 graded clay minerals by an increase in interlayer 

 ion adsorption commensurate with increasing 

 salinities, or (iii) physical sorting of various clay 

 minerals because of differential settling of the 

 various species induced by changing salinities of 

 water. Thus it would seem that downstream varia- 

 tions in clay mineral assemblages in the Colville 

 River are either not influenced by hydrographical 

 factors or that there are other agents which tend to 

 overcompensate the effects of these factors. We 

 believe that clay mineral variations in the Colville 

 River are largely influenced by local influxes of 

 various detrital clay minerals, rather than to 

 changes in the depositional environment. This is 

 suggested by the abrupt increase in smectite and 

 an attendant decrease in other clay minerals in 

 samples 4 and 5 (Table 3; Figure 6). Likewise in 

 sample 8 a notable increase in kaolinite and chlo- 

 rite, and an abrupt drop in smectite concentration 

 is observed. It is relevant to note that all these 

 samples were gathered at or immediately down- 

 stream of the confluence points of the tributaries 

 Ingaluat Creek, Kogosukruk River, and Itkillik 

 River, repectively, with the Colville River. It is 

 quite obvious from this relationship that the 

 Kogosukruk River and the Ingaluat Creek flow 

 through a smectite-rich terrain (presumably the 

 Umiat Bentonite beds; Anderson and Reynolds, 

 1966), and that the Itkillik River drains a 

 terrain — perhaps the greywackes of the Torok 

 Formation — relatively enriched in kaolinite and 

 chlorite and poor in smectite. 



There is another possibility which merits men- 

 tion in attempting to explain the apparent lack of 



247 



