Section IV., 1915. [27] Trans. R.S.C. 



The Cretaceous Sea in Alberta. 



By D. B. DowLiNG, B.Sc, F.R.S.C. 



(Read May Meeting 1915.) 



From a very early period the region embraced by the great 

 plains was covered by the sea. In Carboniferous times land in the 

 form of an island appeared in this sea within the limits of what is now the 

 Interior plateau of British Columbia. It was maintained and grad- 

 ually increased in area by a continental uplift and by other earth move- 

 ments, the result of tangential strains which were quite pronounced 

 during Jurassic times. This general uplift culminated in the with- 

 drawal of the sea from the mid-continental area, as is shown by deposits 

 of continental formation which occur in the early part of the Cretaceous 

 period. It was not until Middle Cretaceous times that marine deposits 

 in Alberta again appear. The re-entry of the sea was probably not 

 due to a relaxation of the crustal strains but to the weakening of the 

 arch between the western highlands and the old continent by unequal 

 loading. This had been produced by the greater deposition over the 

 submerged area which was near the newly elevated land areas or 

 islands to the west, as compared with that from the older land surface 

 which is now called the Canadian Shield. This unequal loading 

 caused a deformation of the arch and with increased tangential 

 strain, a down warping of the extreme western area commenced. 

 Through early Cretaceous time the trough thus formed was kept 

 filled and maintained as a land area by the coarse material brought 

 from the highlands to the west ; but the tangential stresses to which 

 the western part of the continent had been subjected lessened through- 

 out the latter part of Cretaceous time and subsidences of more or 

 less amount are found to have occurred — most noticeably in the 

 interior of the continent. With this subsidence, mention may be 

 made of volcanic activity in at least one area in the western part, as 

 shown in the Crowsnest volcanics near Blairmore. We have thus the 

 advent of the Cretaceous sea which covered a broad band stretching 

 from the Arctic ocean to the Gulf of Mexico. The notes herewith 

 submitted refer particularly to the western limits of this sea in the 

 province of Alberta and to a suggestive correlation of the deposits 

 there found. 



As the sea was a mere flooding of the continental shelf it cannot 

 be considered as having attained any great depth ; but even with a 

 shallow muddy sea the arrangement of the littoral deposits along its 

 margin must have conformed to the general laws of distribution 



