14 J. Brown et al. 



Y Biome Sites X 

 - 10]- 14 000 Footprint 8500-11,000(18,500) u.„^.,,. n'O 

 !.\ /Ice Wedge Creek 25,300 )^=?Ss 



^^^ce wedge cre« 25,300^>?^ Sed.m.n,, 2,650-4,570 



9 -10 



-20 



--I0 



HUffMrn^nir m: 



FIGURE 1-6. Idealized geologic cross section across the Barrow penin- 

 sula showing location and age of radiocarbon-dated organic materials 

 (see Figure 1-3 for the approximate location of the section). The radio- 

 carbon dates in years BP are from Brown (1965) except 18,500 from 

 Everett (unpubl.) and 12,160 from Lewellen (1972). 



Geologic History 



The general course of events over the past 25,000 years has been re- 

 constructed on the basis of local and regional stratigraphic and geo- 

 morphic data and correlations (Lewellen 1972, Sellmann and Brown 

 1973). Figure 1-6, an idealized section across the Barrow peninsula that 

 incorporates radiocarbon dates and stratigraphic information, illustrates 

 the major geologic units and surface features. The materials shown in the 

 upper part of the cross section were deposited or reworked by an inva- 

 sion of the sea that extended inland to about the current 8-m elevation. 

 This elevation is not precise, since the surface relief changed as the sedi- 

 ment refroze, producing an increase in volume due to the formation of 

 ground ice. During this transgression, which occurred approximately 

 25,000 to 35,000 years ago (mid-Wisconsinan time), the surface of the ex- 

 isting permafrost would have been lowered, but permafrost probably did 

 not disappear entirely. Subsea permafrost is currently found to depths of 

 over 100 m offshore from the present coastline (Lachenbruch and Mar- 

 shall 1977, Lewellen 1977). 



With the retreat of the sea, a gravelly beach ridge-shoal complex 

 built up north and east of the Biome research area. This ridge complex 

 currently reaches elevations of 6 to 8 m. North of the ridge, but landward 

 of the present-day active beach, an embayment formed which persists in 

 fragmented form as the lakes and sloughs from Elson Lagoon to Barrow 

 Village. Until 1945 these lakes and sloughs were connected during peri- 

 ods of high water at approximately the 2.5-m elevation. At that time. 

 Middle Salt Lagoon was artificially drained to prevent flooding around 

 NARL and the level of the slough was decreased to nearly sea level (Fig- 

 ure 1-3). 



