thought best to include all these formations under the term post-Tuscaloosa for the following reasons: 



1. Originally these formations were named for surface deposits that were mappable units in updip 

 areas of the Coastal Plain. Subsequently, as a result of a search for oil and fresh-water aquifers, it was 

 learned that the majority of these formations, owing to downdip facies changes, tended to lose their identi- 

 ties in the subsurface. Similarly, east of Ocmulgee River, even the updip surface outcrops of these forma- 

 tions have undergone facies changes in an easterly (along the strike) direction, causing the entire Upper 

 Cretaceous Series to grade laterally to a lithology identical with that of the Tuscaloosa Formation. 



2. In addition to facies changes, faunal changes have also taken place in a downdip direction. Certain 

 foraminiferal species have been found to persist over more and more of the vertical subsurface strati- 

 graphic section thus increasing their vertical ranges and at the same time lessening, to some extent, 

 their value as guide fossils. A good example of this is Anomalina pseudopapillosa Carsey, a foraminifer 

 that is a reliable index fossil for the Ripley Formation in some updip areas. Down the dip, however, this 

 foraminifer has been found higher in the section, appearing (in wells) in the lower, or marine, part of 

 the geologically younger Providence Sand for which it has become one of its guide fossils. Thus, these 

 formational names, particularly as regards the Providence and Ripley Formations, cannot be used over 

 the greater part of the subsurface of the Coastal Plain of Georgia. An exception to this is the Eutaw Forma- 

 tion, which extends from outcrops to downdip areas, overlying the Tuscaloosa Formation as a fine to 

 medium, phosphatic, glauconitic, shelly, somewhat indurated sand. 



The subsurface areal extent of the post-Tuscaloosa is next to the largest of all the stratigraphic units 

 making up the Coastal Plain of Georgia, being second only in size to the underlying and geologically older 

 Tuscaloosa Formation (see fig. 14.) Thus, this unit, except for a narrow strip immediately south of the 

 Fall Line, underlies the entire Coastal Plain. The greatest surface exposures of the post-Tuscaloosa are 

 found just east of the Chattahoochee River Valley, in Stewart and Chattahoochee Counties. Northeast of this 

 area, however, this unit is progressively overlapped as far as the Ocmulgee River, east of which the post- 

 Tuscaloosa is completely covered by geologically younger sediments. Except for southeastern Georgia 

 the post-Tuscaloosa consists of elastics throughout its subsurface areal extent in Georgia. In the updip 

 parts of the Coastal Plain this unit is composed of light-gray to dark-bluish-gray to dark-brown (mottled 

 in surface exposures), blocky to laminated, sandy, abundantly, micaceous, locally lignitic and kaolinitic, 

 pyritiferous, glauconitic, fossiliferous clay and marl. These clays are interbedded with numerous tongues 

 of fine to coarse-grained, subangular to subrounded, pyritiferous, lignitic, micaceous, arkosic, locally 

 glauconitic and fossiliferous sand, and some relatively thin beds of gray, dense, sandy, coarsely glauconitic 

 micaceous, somewhat phosphatic, fossiliferous limestone. In downdip areas these elastics gradually change 

 to light-bluish-gray, chalky, micaceous, pyritiferous, fossiliferous marls which are interbedded with beds 

 of sand or limestone, the latter similar to those of updip areas. In extreme southeastern Georgia, the upper 

 part of the post-Tuscaloosa, of Navarro age, is composed of somewhat chalky, much calcitized, granular, 

 locally gypsiferous, fossiliferous limestones, the latter representing the limestone facies of this unit in 

 Georgia. The greatest thickness of the post-Tuscaloosa, or depocenter, occurs in central and coastal 

 areas of the Coastal Plain (see fig. 15), attaining a total thickness of more than 1,400 feet. South of the cen- 

 tral part of the Coastal Plain the post-Tuscaloosa in extreme south Georgia thins to 800 feet or less. 



A few of the more important contributions to the paleontology of the Upper Cretaceous include articles 

 by Carsey (1926), Plummer (1931). Cushman (1940), and Cole (1944). The post-Tuscaloosa represents 

 the lowest stratigraphic unit in Georgia with abundant and characteristic Foraminifera. Some of the 

 diagnostic fossils occurring in the upper division of Navarro age are Gaudryina rudita Sandidge, Robulus 

 spisso-costatus Cushman, Vaginulina webbervillensis Carsey, Guembelina globulosa (Ehrenberg), 

 Loxo stoma plaitum (Carsey), Epistomina caracolla (Roemer), Anomalina pseudopapillosa Carsey, and 

 Cibicides harperi (Sandidge). In the middle division, or Taylor, one should mention such species as 

 Robulus stephensoni Cushman, Robulus muensteri (Roemer), Bolivinoides decorata (Jones), Globotrun- 

 cana area (Cushman), Planulina texana Cushman, and Planulina t aylorensis (Carsey). Likewise Kvphopvxa 

 christneri (Carsey) and Vaginulina texana Cushman are considered diagnostic of the lower division of 

 Austin age of this stratigraphic unit. The faunal lists in table 10 show in greater detail the more important 

 smaller Foraminifera that have been observed in the post-Tuscaloosa of Georgia. 



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