BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 32, pp. 385-394 DECEMBER 1, 1921 



SOME CONCLUSIONS IN EEGARD TO THE ORIGIN OF 



GYPSUM ^ 



BY FRANK A. WILDER 



{Read before the Society December 29, 1920) 



CONTENTS 



Page 



Prevailing opinion in regard to origin of gypsum .385 



Difficulties of generally accepted theory .386 



The lime carbonate problem •. 386 



Nature of present-day deposits 389 



Concentration of disseminated gypsum 389 



Alteration of carbonate 390 



Alteration of anhydrite 392 



A classification suggested 394 



Prevailing Opinion in regard to Origin of Gypsum 



The prevailing opinion seems to be tliat most of the important gypsum 

 deposits of the world have been formed under "salt-pan" conditions. 

 This opinion is held, even though many persons have pointed out the 

 difficulties which the theory involves. 



The classical illustration of the "salt-pan" theory for gypsum deposits 

 is found in certain nearly detached basins at the eastern end of the Cas- 

 pian Sea and elsewhere. Conditions in these basins, however, in at least 

 one important particular, differ from those that characterize gypsum 

 deposits. Myriads of organisms are drawn into the basin from the Cas- 

 pian Sea and perish in its denser brine. Gypsum deposits, on the other 

 hand, are generally devoid of fossils. To avoid this difficulty, certain 

 students of the problem have postulated a second, or inner, basin in which 

 the brine reaches the gypsum-depositing stage. According to this con- 

 ception, the remains of organic life would be deposited in the intermediate 

 basin, together with some of the lime carbonate. 



1 Revised manuscript received by the Secretary of the Society May 2, 1921. 



(385) 



