PALEOZOIC CORDILLERAN GEOSYNCLINE 



B5 



tinent during Paleozoic time. That the western margin has a belt of major 

 orogeny with associated intrusive and extrusive igneous activity and 

 metamorphism needs no longer to be defended. At the time of writing 

 of the first edition of this book the profession was just accepting the view 

 and abandoning the older one of a small continental borderland, now 

 partly submerged beneath the Pacific Ocean. 



It may be stated that we have no information on conditions in Cam- 

 brian time west of northwestern Nevada. Cambrian strata are recognized 

 farther south in California in the Death Valley region, but these lie on 

 the projection of the eastern miogeosynclinal assemblage. Ordovician 

 rocks, like the Cambrian, are not known for sure west of northwestern 

 Nevada. In southeastern Alaska, however, they have been identified very 

 close to the Pacific margin of the continent, and are part of an extensive 

 eugeosynclinal assemblage. Silurian rocks have now been recognized near 

 the Pacific in the Klamath Mountains, but the paleogeography of the entire 

 region from northwestern Nevada to the Pacific is practically unknown. 

 The presence of Silurian strata in the Klamath Mountains and sequences 

 under them which might be Ordovician and Cambrian lead to the con- 

 clusion that the western margin of the continent as early as Cambrian 

 time was about where it now is; and that the continent has not grown 

 appreciably since. 



We must also postulate several phases of major orogeny together with 

 the accumulation of eugeosynclinal sequences in adjacent and associ- 

 ated basins or troughs in early Paleozoic times along the western margin 

 of the continent. The transitional zones of the eugeosynclinal and miogeo- 

 synclinal assemblages are now fairly well positioned, and the basins of 

 the miogeosyncline are beginning to take on specific shape and distribu- 

 tion in light of our present knowledge. Geanticlines, the Beltian and Raft 

 River, are postulated, and the Tooele arch seems clear. These add com- 

 plexity to what was previously considered a simple broad basin. 



A major and unsolved problem is the relation of the southwesterly 

 trending Paleozoic tectonic elements in southern Nevada, Arizona, and 

 California to the continental margin — they are distinctly discordant 

 rather than approximately concordant or unilateral. The problem has been 

 discussed in Chapter 5. 



BAYHORSE QUAD. 

 IDAHO 



LOST RIVER RANGE 

 IDAHO 





TENDOY RANGE 

 S. W. MONT. 



NORTHEASTERN 

 UTAH 



OQIIRRH MTS., 

 CENTRAL UTAH 







AMSDLN FM.» 



MANNING CAN. SH.» 



MANNING CAN. SH.' 







"BRAZER"* 



BIG SNOWY GR. 



GREAT BLUE LS. 

 HUMBUG FM. 



GREAT BLUE LS . 

 HUMBUG FM. 



MILLIGEN 









DESERET LS. 



DESERET LS. 



ARGILLITE 





z 

 o 

 to 



MISSION CAN. LS. 









MILLIGEN 

 ARGILLITE 



a 

 3 





MADISON LS. 



MADISON LS. 



LODGEPOLE LS . 



SAPPINGTON FM. + 



LEATHAM 





PARTLY L. PENNSYLVANIA 

 + OCCURS EASTWARD AS PART OF SHELF SEQUENCE 



Fig 6.16. Correlation of Mississippian formations of southwestern Montana, eastern Idaho and 

 northern Utah. 



A major orogenic belt began to develop in central Nevada in late 

 Devonian time, and through several phases of folding and thrusting con- 

 tinued development through the rest of the Paleozoic. The belt is pro- 

 jected northward through eastern Oregon and Washington into southern 

 British Columbia in Mississippian and Pennsylvanian time to the Shuswap 

 orogenic belt in British Columbia. Another orogenic belt lay to the west 

 in Pennsylvanian and Permian time, and it seems to have been separated 

 from the central Nevada belt by a basin of sedimentation. The entire 

 region including both belts and the intervening basin become involved in 

 orogeny, volcanism, and intrusive activity thereafter, starting in Permian 

 time. 



Shifting basins and the appearance of uplifts of several kinds add com- 

 plexity to the miogeosyncline and its relation to the shelf in the late 

 Paleozoic. 



The Canadian cordillera is not as wide as that of the western United 

 States, and perhaps its development is more regular. From what is known 

 it appears that a geanticline of Beltian strata developed early in Paleozoic 

 time and separated a western eugeocynclinal trough of sedimentation 

 from an eastern miogeosynclinal trough. The eugeosynclinal region was 

 subjected to repeated orogeny, metamorphism, and igneous activity. In 

 this connection it is pertinent to review Buddington's observations in 

 southeastern Alaska. 



