ALASKA AND THE YUKON 



627 



Fig. 39.13. Geosynclines, basins, and 

 uplifts of Paleozoic age in Alaska and 

 northern Canada. The fold belt of the 

 Arctic Archipelago involves the miogeo- 

 syncline. The Wollaston, Victoria Straits, 

 and Foxe basins are of the cratonic basin 

 type. Most all Alaska appears to have 

 been emergent in Pennsylvanian time. 

 Ordovician and Silurian carbonate depo- 

 sition was extensive from the Seward 

 peninsula to the Yukon. P. P. I., Prince Patrick 

 Island; B.I., Borden Island; A.H.I., Axel Hei- 



1 berg Island; M.I., Melville Island; P.W.I., 

 Prince of Wales Island; B.I., Bathurst Island. 

 D.I., Devon Island; M.P., Melville peninsula; 



)$.!., Southampton Island. 



'open folds, rather than by faults. The area appears, therefore, to form part of a 

 separate structural zone, which separates the central parts of Richardson 



^Mountains from the essentially stable belt situated further east. 



i Largest faults trend northerly and appear to be strike-slip faults. Folds are 

 medium to small-sized, irregularly patterned, and commonly dome-like. Larger 

 folds are strongly disrupted by faults and were apparently caused by an earlier 

 orogenic phase. Smaller folds are subordinated to and were apparently caused 

 by major faults. Both thev and the major faidts were, therefore, apparently 

 caused by a later orogenic phase. 



Hauterivian, late Aptian, early Albian, and late Albian or early Cenomanian 

 (? at the Lower/Upper Cretaceous boundary) unconformities were observed 



in the area. Late Aptian unconformity is accompanied by a 5 to 10° angular 

 discordance. Others are only recognizable because of smaller or larger trans- 

 gressive overlaps. 



The above unconformities were apparently caused largely by epeirogenic 

 movements as no tectonic structures are known to be caused by them. The 

 mid-Upper Cretaceous rocks of the area were, however, constantly involved 

 in the major dislocations. The contemporary structures of the area were, 

 therefore, caused largely or entirely by the post mid-Upper Cretaceous (? earl) 

 Tertiary) orogenic movements. 



A general description of the structures by Martin ( 1959) is informative. 



