systematic downstream changes in clay mineral 

 compositions in the Colville River. This is related 

 to the presence of irregularly distributed and iso- 

 lated pockets of highly saline waters (up to 40 °/oo 

 salinity) in the lower Colville River channels 

 (Schell and Hall, 1972). These pockets of water 

 are formed during winters by sealing off the shal- 

 low portions of the river by the formation of 

 bottom-fast ice and apparently have little or no 

 connection with the saline water that is reported 

 to penetrate upstream at this time (Arnborg et 

 al., 1967). The possibility does exist that some of 

 our samples, which were collected in the sum- 

 mer, within the 50-km Colville Estuary, were 

 either deposited in or were in contact at sometime 

 with such pockets of brine. In view of the assump- 

 tion that salinities of these brines would vary 

 haphazardly (Schell and Hall, 1972) it would be 

 expected, as seen in the present case, that there 

 would not be any systematic down-stream 

 changes in clay mineral types. 



The data in Table 3 show that in the <2;Lt size 

 of Colville deltaic sediments there is a notable 

 increase in the illite/smectite ratio and an atten- 

 dant decrease in smectite/kaolinite ratio, from the 

 Colville fluvial channels to the relatively more 

 saline fluviomarine and open marine regions off 

 the river mouth. These changes in clay mineral 

 assemblages are at least in part presumably due to 

 reconstitution in the more saline environment, 

 through K+ adsorption and/or cation exchange, of 

 either degraded illites and/or mixed-layered 

 illite-smectite derived from the nonsaline Colville 

 River channel. This inference is supported by our 

 detailed mineralogical studies on clay minerals 

 within subfractions of the <2/x. e.s.d. particle 

 size, and by the results of laboratory investiga- 

 tions on <2/Lt size fresh and brackish water clays 

 of the Colville River with sea water and at slightly 

 above freezing temperatures (Naidu, 1972). De- 

 tailed clay mineralogical examination (refer to 

 Appendix) shows that the Colville River clays 

 are, in fact, highly reactive. However, the 

 changes in clay minerals, especially the overall 

 significant decrease in smectite from river to open 

 sea, cannot be adequately explained solely on the 

 basis of the processes mentioned above. Consid- 

 ering results of the detailed studies by Anderson 

 and Reynolds (1966), as well as ours (refer to 



Appendix), it is difficult to envision that a smec- 

 tite such as the Umiat Bentonite will undergo any 

 significant reconstitution when passed on from 

 fresh water fluvial channel to the open marine 

 saline environment. Thus, some alternative 

 mechanism must be invoked to explain the ob- 

 served decrease in smectite in the fluviomarine 

 and marine facies of the Colville Delta. At this 

 stage of our knowledge we suspect that an apprec- 

 iable amount of the smectite in the Colville River 

 is somehow deposited at the mouth of the fluvial 

 channels. Such a conclusion is supported by our 

 detailed clay mineralogical studies on subfrac- 

 tions of clays within the <2/A e.s.d., and as well 

 by the predominance of illite and chlorite with 

 subordinate smectite in the suspensates collected 

 at sample location CR8 (Figures 1 and 2). We are, 

 however, not sure of the mechanism which brings 

 about such a deposition of smectite. On the basis 

 of experimental data gathered by Whitehouse and 

 Jeffrey (1960) differential settling of smectite over 

 illite, chlorite and kaolinite, induced by floccula- 

 tion would seem an improbable factor. However, 

 mineral sorting based purely on the primary non- 

 flocculated size of detrital particles of smectite 

 could be an important process in this context. 



Data in Table 3 bear out that there are two 

 major clay mineral zones in the shallow marine 

 facies of the deltaic complex under study. Clays 

 west of Oliktok Point have markedly lower 

 illite/smectite and illite/kaolinite ratios than 

 clays east of this point. These lateral variations in 

 clay mineral types within contiguous areas are 

 most probably attributable to differences in ter- 

 rigenous clay mineral sources and their dispersal 

 patterns, rather than to differences in deposi- 

 tional environments (Naidu and Mowatt, 1973). 

 Sedimentation in the lagoonal area east of Oliktok 

 Point is chiefly influenced by the sediment outfall 

 of the Sagavanirktok and Kuparuk rivers, 

 whereas sedimentation in Harrison Bay and the 

 offshore open marine deltaic area west of Oliktok 

 Point is largely affected by the Colville River 

 discharge. The clay mineral compositions of 

 these rivers are significantly different, inasmuch 

 as the Colville River transports far more smectite 

 and kaolinite than the Sagavanirktok River 

 (Table 3). We feel that offshore dispersal of the 

 clays discharged by the Colville River is chiefly 



248 



