GULF COASTAL PLAIN 



650 



g= 



S 





Fig. 41.8. Offshore salt domes 

 on the continental shelf of Louis- 

 iana as of March, 1958. After 

 Habarta, 1958. 



coast belt. Those in the interior are divided into three areas, one in 

 the Tyler basin, one in the eastern part of the Sabine uplift, and one 

 in a broad zone across south central Mississippi. 



Classification. Salt domes are classified in several ways. The divisions 

 deep, intermediate, and shallow are the most commonly mentioned. 

 Deep domes are considered those whose salt core tops are greater than 

 5000 or 6000 feet below the surface (Billings, 1942), intermediate domes 

 'between 6000 or 5000 and 3000 or 2000, and shallow domes, less than 

 3000 or 2000 feet deep. Some have reached the surface. Deep domes are 

 [divided into those whose salt has been reached by the drill and those 

 ! whose salt is below any deep wells. 



Another classification concerns the relation of the salt plug to the 

 country rock. If the salt has simply domed the overlying beds in the 

 manner of a concordant laccolith, the structure is called a nonpiercement 

 dome. If, on the other hand, the salt has penetrated through the beds, 

 the structure is said to be a piercement dome. Generally all domes are 

 now considered as piercement type, whether shallow, intermediate, or 

 deep-seated. Refer to Fig. 41.9 illustrating the origin of salt domes 

 for these types and also a number of transitional ones. 



Some salt domes have mushroomed out at the top, and the cap rock 

 and part of the salt core is said to overhang. These horizontal expansions 

 or wedges have been drilled through and their presence thus demon- 

 strated. 





irmfi/.td a/let Mu>ror 11956) 



?*&>$ I STRUCTURAL ELEMENTS 

 A i, OF 



; /GULF COASTAL PROVINCE 



*• *I/IT ZONE 



Fig. 41.9. Structures of the Coastal Plain around the Gulf of Mexico. Reproduced from 

 Atwater and Forman (1959). 



