646 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



VZZA 



PreCambrian 

 platforms 



Caledonian 

 folding 



Hercynian 

 folding 



Mesozoic 

 folding 



Alpine 

 folding 



Seismicicy 



Fig. 40.9. Postulate of fold belts across the Arctic basin, by Sachs, Belov, and Lapina (1955). 

 Reviewed in English by Hope (1959a). The broad black line is the great Arctic magnetic ano- 

 maly, and the row of dots the Lomonosov Range. 



and Eurasia find an explanation in the possible shallow sea migration 

 routes bordering the once emergent and later subsiding regions. 



Continental Drift. Although two or three geologists before him had 

 suggested without much documentation the concept of horizontal shifting 



of continental fragments Taylor, in 1910, is generally given credit for 

 "specifically advocating continental drift" (Van Waterschoot van der 

 Gracht, 1928). Wegener first addressed the subject in 1912 but it was 

 not until his comprehensive study, Die Enstehung der Kontinente unci 

 Ozeane, was published in 1922, that the theory became of international 

 concern. Although many European geologists supported the concept of 

 continental drift in one form or another, most American geologists con- 

 tinued to favor the Dana-Schuchert concept of permanency of the con- 

 tinents and ocean basins. The theories of continental drift, however, 

 focused attention on the Arctic Ocean basin, and Taylor in particular 

 dwelt specifically on it. He postulated drift toward the equator and 

 away from the North Pole. Figure 40.10 illustrates the general concept 

 and his view of the origin of the Arctic Ocean depression as a "dis- 

 junctive basin." Eurasia and North America were once together over the 

 North Polar region as one great continent, but pulled apart leaving the 

 Arctic basin as one of the disjunctive depressions. Greenland was con- 

 sidered a fragment left between the Baffin Sea basin and the Greenland 

 Sea depression as Europe drifted away from North America. The ap- 

 proximate extent of the continental shelves and the deep basin in the 

 Arctic had been established by Nansen and other explorers but no detail 

 of the bottom topography was known at this time. 



Wegener gave more attention to the southern hemisphere and 

 Antarctica than to the Arctic Ocean basin, and we are left to examine his 

 maps to discern his thoughts about the origin of the Arctic basin. The 

 maps show an existing ocean there, although small, before the breakup 

 occurred. In a major publication in 1924, however, Koppen and Wegener 

 show the small basin to enlarge appreciably as North America, hinging 

 in the North Polar region drifted westward and away from Europe. 



By the time of Wegener's major publications the concept of a layered 

 crust had become established. The continents were made up of a silicic 

 and lighter upper layer, the sial, resting on a mafic and heavier layer, 

 the sima, and when a continent broke and its parts drifted away from 

 each other, it was the sial that parted and drifted over the sima, leaving 

 a crust made up only of the sima. This, for isostatic reasons, was also a 

 basin. Hence, according to Koppen and Wegener, the Arctic Ocean 



