610 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



Thickness, Feet 



Mississippion 



Central-Western 

 district 



Canning district 



Devonian 



Colville-Noatak 

 district 



Lisburne district 

 Canning district 



Silurian 



Noatak-Kobuk 

 district 



Massive light-colored semicrystalline limestone, consid- 

 erably silicified; Lisburne limestone 4000 plus 



Sandstone, shale, thin limestone, in place chert, con- 

 glomerate; Noatak formation thousands 



Gray and black limestone, somewhat brecciated, much 



silicified, equivalent of part of Lisburne limestone 3000 



Black limestone, slate, shale and sandstone; age uncer- 

 tain; rests unconformably on highly metamorphic 

 schists ? 



Upper 

 Quartzite, sandstone, slate, subordinate conglomerate, 



grit, and limestone ? 



Middle 

 Calcareous sandstones and shale ? 



Black shale, slate, and subordinate sandstone; not dif- 

 ferentiated on map 1000 plus 



Middle 

 Massive, somewhat siliceous limestone; Skajit limestone 6000 plus 



A line separating the eugeosynclinal assemblage of sediments on the 

 south from the platform (shelf) or miogeosynclinal sediments on the 

 north follows the Yukon River approximately. 



The distribution in outcrop and the geosynclinal thicknesses where 

 known of the Paleozoic strata indicate that the whole of Alaska was a 

 region of subsidence and sedimentation in the Paleozoic, and an extension 

 of the Cordilleran geosyncline. 



An episode of granitic intrusion occurred during the early Devonian 

 in the North Fork of the Chandalar River along the south flank of the 

 Brooks Range ( Mertie, 1935 ) . This is the only Paleozoic granitic intrusive 

 so far identified in Alaska, and it is in the area of the mainland assem- 

 blage of stratified rocks. Representatives of the Lower Devonian are 

 absent, and the strata of Middle Devonian age rest unconformably on 

 those of Silurian age. The rocks below are more metamorphosed than 

 those above the unconformity. This evidence indicates crustal unrest 

 in the geosyncline, such as is found in Paleozoic beds of the Alexander 



Alopah 

 limestone 



Wochsmuth 

 limestone 



Kayak 



shale 



Kanoyut 

 conglomerate 



Unnamed 

 shale and 

 sondstone 



Stuver 

 member 



Middle 



conglomerate 



member 



Lower 

 member 



SB 



LA 



Feet 

 2000 



-1500 



- 1000 

 t 500 



- 



Verticol 

 scale 



Fig. 39.3. Generalized section of Upper Paleozoic rocks in the Shainin Lake area. Reproduced 

 from Bowsher and Dutro, 1957. 



Archipelago, although slightly more continentward than the trough of 

 accumulation of the volcanic assemblage. 



Numerous other unconformities undoubtedly exist in the volcanic as- 

 semblage. 



TRIASSIC AND JURASSIC GEANTICLINE AND ADJACENT BASINS 



During the Triassic period and persisting into the Jurassic, a great ge- 

 anticline rose from the Paleozoic geosyncline and separated two adjacent 



