Tuscaloosa Formation • — The Tuscaloosa Formation* has been identified in the subsurface in about 

 70 wells, the majority of which are situated along the northern limit of the Coastal Plain. Sediments of 

 Tuscaloosa age underlie the post-Tuscaloosa and overlie the Lower Cretaceous(?) and are correlated with 

 the Tuscaloosa Group of Alabama and, in part, with the Eagle Ford and Woodbine Formations of Texas. In 

 subsurface areal extent the Tuscaloosa underlies the entire Coastal Plain of Georgia, hence is the largest 

 of the stratigraphic units discussed. (See fig. 16.) Geographically, this unit is bounded on the north by the 

 crystalline rocks of the Piedmont. To the south these strata merge with equivalent subsurface sediments 

 in northern Florida. The Tuscaloosa Formation consists entirely of elastics, which may be broken down 

 into three readily recognizable lithologic divisions. The upper part is composed on nonmarine, fine to 

 coarse, subangular, micaceous, arkosic, pyritiferous, locally lignitic sands that are interbedded with 

 nonmarine, gray to green (mottled in outcrop), blocky to laminated, locally iron-stained, kaolinitic and 

 lignitic, micaceous, sandy clays. The middle division is composed of interbedded sands and clays, which, 

 in updip areas, resemble those of the upper part. Downdip these deposits change to marine, dark-gray 

 to dark-brown to black, laminated, somewhat fissile, abundantly micaceous, speckled**, glauconitic, car- 

 bonaceous, fossiliferous clay and shale, that are interbedded with thin beds of fine to medium-grained, 

 micaceous sand. The lower division of the Tuscaloosa is usually composed, in its uppermost part, of 

 a fine-grained, somewhat micaceous, glauconitic, locally indurated, marine sand. Below this sand the 

 remainder of the lower division consists of interbedded nonmarine, coarsely-grained, subrounded, highly 

 arkosic, micaceous sands and red to purple, blocky, sandy, sideritic, micaceous clays. Prominent and 

 extensive inclusions of kaolin, originally derived from the weathering of crystalline rocks to the north of 

 the Coastal Plain, occur in the upper part of the Tuscaloosa Formation. These deposits are found only 

 a few miles south of the Fall Line in a belt extending from Taylor County eastward into southern McDuffie 

 and Columbia Counties in east-central Georgia. Thickness of the Tuscaloosa Formation approximates 

 that of the post-Tuscaloosa Cretaceous unit (see fig. 17) with the area of greatest thickness, or depo- 

 center, lying in an east-west, linear belt in the central part of the Coastal Plain. Southeast of this belt 

 the Tuscaloosa tends to thin to less than 300 feet in southeastern Georgia. The maximum thickness 

 in this depocenter is somewhat in excess of 900 feet. 



Literature dealing with the microfossils of the Tuscaloosa Formation and equivalent deposits is limited 

 compared with that of the previously discussed unit. This is doubtless due in part to a failure until com- 

 paratively recent times to recognize the marine character of the Tuscaloosa in downdip areas of the 

 Coastal Plain. Munyan (1943) was the first to note the marine Tuscaloosa in the subsurface of Georgia 

 and Cushman and Applin (1946) were the first to demonstrate the presence of smaller Foraminifera in 

 the marine portions of the Tuscaloosa in Georgia. A summary of the important literature dealing with 

 the Foraminifera of the Tuscaloosa Formation and equivalent deposits elsewhere in the Gulf Coast in- 

 cludes articles by Lozo (1944), Loeblich (1946), Cushman and Applin (1946 and 1947), Frizzell (1954), 

 and Applin (1955). Foraminifera have been observed by the senior author in several wells penetrating 

 marine portions of the Tuscaloosa Formation in downdip areas of Georgia. These fossils, however, are 

 not identified as to species though they clearly belonged to at least two genera, Ammobaculites and Hap- 

 lophragmoides, which make up an appreciable part of the foraminiferal faunas identified by various in- 

 vestlgators - from the Tuscaloosa of Georgia. For the sake of completeness in this report the following 

 faunal list has been prepared from the above noted articles. 



*ln this report the formational name Tuscaloosa is used in preference to Atkinson. The name Tuscaloosa 

 is considered by the authors to be more applicable to the continental deposits whereas the name Atkinson 

 is more applicable to the marine equivalents as found in extreme south Georgia and Florida. 



**Finely disseminated mica flakes impart a speckled appearance to these shales. 



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