CEETACEOUS DEPOSITS OF THE EASTERN GULF REGION. 



23 



Exogyra costata zone 



Exogyra yonderosa zone 



Selma chalk 

 and contem- 

 poraneous 

 beds of Rip- 

 ley and 

 Eutaw for- 

 mations 

 950 + 



Tombigbee 1 1 Mortoniceras subzone 

 sand, 

 member 

 150± 



300+ 



Tuscaloosa 

 formation 



1000 ± 



Uppermost beds of the Ripley formation 



(present locally in the region) 

 Liopistka protexta subzone 



FATJNAL ZONES AND SUBZONES. 1 



STRATIGRAPHIC RELATIONS. 



The paleontologic researches carried on in the eastern Gulf region have resulted in the 

 differentiation of several invertebrate faunal zones and subzones in the Upper Cretaceous 

 deposits. Named from the top downward, these are as follows: 



1. The Exogyra costata zone, which embraces all the typical marine beds of the Cretaceous above the Exogyra 

 ponderosa zone. Near the top a well-marked sub- 

 zone designated the Liopistka protexta subzone is 

 traceable through a part of the region. New fau- 

 nal elements appear in extreme uppermost Cre- 

 taceous beds which locally in the region intervene 

 between the Liopistka protexta subzone and the 

 base of the overlying Eocene. 



2. The Exogyra ponderosa zone, which is 

 divisible into (a) the part of the zone included 

 between the Mortoniceras subzone and the base of 

 the Exogyra costata zone, and (b) the Mortoniceras 

 subzone. 



3. The basal beds of the Eutaw formation. 



The stratigraphic positions of each 

 of these paleontologic divisions and the 

 estimated thicknesses of strata embraced 

 by them are shown, in the generalized 

 section (fig. 1). 



FOSSIL LOCALITIES. 



For convenience in discussing the 

 distribution and ranges of the eastern 

 Gulf Cretaceous fossils the localities from 

 which collections have been made have 

 been grouped into the eight areas which 

 are roughly outlined on the sketch map 

 (fig. 2) and which may be designated (1) 

 western Tennessee; (2) northern Missis- 

 sippi; (3) region of Houston, Pontotoc, 

 Aberdeen, Tupelo, etc., Miss.; (4) east- 

 central Mississippi and an adjacent por- 

 tion of Alabama; (5) region of Warrior 

 and Tombigbee rivers, Ala.; (6) region 

 of Alabama River, Ala.; (7) region of 

 Chunnenugga Ridge, etc., Ala. ; (8) Chat- 

 tahoochee River and Georgia. 



Basal beds of the Eutaw formation 



Figure 1. — Generalized section showing fossil zones and subzones in the eastern 

 Gulf Upper Cretaceous deposits. In northern Mississippi and in Tennessee 

 the top of the Eutaw formation rises to higher stratigraphic levels than in Ala- 

 bama and in east-central Mississippi, and includes the time equivalents of the 

 basal portion of the Selma chalk. Figures indicate thickness in feet. (See 

 PL X, p. 20.) 



DISTRIBUTION AND RANGE OF THE SPECIES. 



The stratigraphic ranges of the invertebrate fossils identified from the areas just named 

 are given in Tables 1 to 8, inclusive. In Table 9 the ranges as given in Tables 1 to S are sum- 

 marized, and columns are added showing the stratigraphic occurrence in the Carolinas and 

 New Jersey of such of the eastern Gulf species as are common to those States. Comparison 

 with the western Gulf Upper Cretaceous faunas is omitted from the table and in large part 

 from the text discussions, because the ranges of many of the species in that region are as yet 

 but imperfectly known. Approximate correlations are possible, but as paleontologic investi- 

 gations are now being conducted by the writer m the western Gulf region he has deemed it best 

 to postpone an attempt at exact correlation until the results of this later work are available. 



i See pp. 41-55. 



