ALASKA AND THE YUKON 



611 



basins of accumulation, one on the north and one on the south. Examine 

 Fig. 39.4. The basin on the south collected chiefly sediments of the 

 eugeosynclinal assemblage, while the trough on the north received lime- 

 stones, sandstones, shales, and cherts of the miogeosyncline and shelf. 

 Fixed lines have not been drawn on maps to show this feature, but Mertie 

 (1930) describes it as a region of epeirogenic uplift and erosion. 



The geanticline is a parallel, except in detail, of the Cordilleran geanti- 

 cline in Canada and the United States, already described and pictured 

 in the paleotectonic maps of Plates 9 to 11. 



The columnal sections of Fig. 39.5 are characteristic of the Coast 

 Ranges. Here in southern Alaksa Mid-Jurassic time marked the begin- 

 ning of development of basins and separating geanticlines that persisted 

 through the Cretaceous. 



In the Kuskokwin region Cady et al. (1955) described the Gemuk 



group of siltstone and chert with local developments of basalt and 

 andesitic rocks to be 15,000 to 25,000 feet thick. 



The Triassic and Jurassic of the northern Brooks Range and Arctic 

 Coastal Plain consists of two formations. The Shublik of Late Triassic 

 is 300 to 1000 feet thick and is composed of interbedded dense bituminous 

 limestone, chert, shale, siltstone, Iimonite oolite, and calcareous glauco- 

 nitic siltstone. It is entirely marine. The Kin<j;ak shale spans most of the 

 Jurassic and is about 4500 feet thick. It contains graywacke, varicolored 

 bedded chert, lenses of conglomerate, and coquina limestone. 



CRETACEOUS BASINS AND GEANTICLINES 



An examination of the geologic map of Alaska and the correlation chart 

 of Professional Paper 192 shows the Lower and Upper Cretaceous strata 



Fig. 39.4. Idealized evolution in 

 | cross section of Alaska from Point 

 Barrow on the north to Kodiak 

 I Island on the south. In part after 

 | Cady ef al., 1955. Vertical scale 

 j highly exaggerated. Large dots in- 

 I dicate eugeosynclinal assemblage. 

 Blank units represent miogeosyncline 

 or shelf assemblage. Small dots rep- 

 resent elastics with dominant gray- 

 wacke content. Kl, Lower Cretace- 

 ous; K2 Upper Cretaceous. Nevadan 

 structures and batholiths not shown. 

 Mogatza arch and Kobuk basin be- 

 tween Yukon basin and Brooks gean- 

 ticline not shown. 



ARCTIC 

 OCEAN 



BARROW 

 GEANTICLINE 



RESTORED TO LATE CRETACEOUS PRE-LARAMIDE TIME 



♦ CENTRAL GEANTICLINE — 



COLVILLE 



BASIN 



BROOKS RANGE 

 GEANTICLINE 



YUKON 

 BASIN 



ALEUTIAN RANGE 

 GEANTICLINE 



KUSKOKWIM 

 BASIN 



ALASKA RANGE 

 BASIN 



ALEUTIAN 

 TRENCH 





ARCTIC 

 OCEAN 



BARROW 

 GEANTICLINE 



RESTORED TO LATE JURASSIC TIME 



CENTRAL GEANTICLINE JURASSIC AND TRIASSIC E UGEOSYNCLINE 



PACIFIC OCEAN 



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SHELF PALEOZOIC EUGEOSYNCLINE 



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PACIFIC OCEAN 



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