LOWER CRETACEOUS(?) SERIES 



Strata of Lower Cretaceous(?) age, have been identified in 18 wells that are distributed over 16 counties 

 in the Coastal Plain of Georgia. These sediments underlie the Tuscaloosa Formation and overlie older 

 rocks ranging in age from Triassic(?), to Paleozoic, to Precambrian. 



From available data the subsurface areal extent of this stratigraphic unit is considerably less than that 

 of the overlying Tuscaloosa Formation. The northern limit of recognizable Lower Cretaceous(?) begins 

 in Georgia at the Chattahoochee River in southern Chattahoochee County, trends eastward approximately 

 to central Houston County, thence southeastward to the coast of Georgia, in eastern Bryan County (see 

 fig. 18). If this interpretation is true then this unit is absent from the entire northeastern part of the 

 Coastal Plain as well as from a somewhat restricted, linear area situated immediately south of the Fall 

 Line. However, in the latter area this may or may not represent the true subsurface picutre. In this part 

 of the Coastal Plain both the Tuscaloosa and Lower Cretaceous(?) units are nonmarine in origin, hence 

 are lithologically so similar as to be practically impossible to differentiate. It is possible, therefore, that 

 beds of Early Cretaceous(?) age may have been included with the Tuscaloosa in wells situated in this 

 part of the Coastal Plain. Although these deposits were mapped by Eargle (1955, pi. l)as belonging to the 

 lower part of the Tuscaloosa Formation, some inconclusive shreds of evidence support a possible Lower 

 Cretaceous(?) age for these sediments: 1) these strata underlie conventional sediments of Tuscaloosa 

 age, 2) they overlie crystalline rocks of Precambrian age in western Muscogee County and 3) they appear 

 to be lithologically somewhat different from the usual, updip Tuscaloosa of this part of the Coastal Plain. 

 In much of the northeastern part of the Coastal Plain, wells are not deep enough to reach the Lower Cre- 

 taceous(?) hence the presence (or absence) of this unit here is not known. Many more additional data 

 are needed before this problem can be solved. The Lower Cretaceous(?) in Georgia is composed entirely 

 of elastics which consist of interbedded nonmarine, varicolored, coarse, subrounded, very arkosic, mi- 

 caceous sand and brick-red to pale-yellowish-green, blocky, abundantly micaceous, locally sideritic, 

 sandy clay. Owing to their brilliant red color these clays are often referred to by drillers as "red beds," 

 when encountered in wells. The Lower Cretaceous(?) thickens greatly in southwestern Georgia (see fig. 19) 

 where more than 2,600 feet have been logged as belonging to this stratigraphic unit. Using 

 the map of the pre-Cretaceous surface (see fig. 20) as a base, the maximum thickness in Georgia of lower 

 Cretaceous(?) may be on the order of 3,5000 feet. Such a thick series of sediments would indicate the exis- 

 tence of a possible depocenter in this part of Georgia during Lower Cretaceous(?) time. 



Due to the nonmarine nature of all the Lower Cretaceous(?) deposits found in Georgia, no microfossils 

 have been observed in the series. Further downdip in Florida, where this unit becomes marine in character, 

 these strata have been identified as being of Early Cretaceous age — the reason for assigning an Early 

 Cretaceous(?) age to this unit in Georgia. 



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