Journal of Paleontology, vol. 18, no. 4, pp. 343-354, pls. 54, 55, 2 text figs., July 1944 



SMALLER FORAMINIFERA FROM THE PORTERS CREEK 

 FORMATION (PALEOCENE) OF ILLINOIS 



CHALMER L. COOPER 



Illinois State Geological Surve^^ Urbana^ 



Abstract — A microfauna of smaller Foraminifera from the cuttings of a water 

 well in Cache, southern Alexander County, shows the occurrence of Lower Eocene 

 (Paleocene) sediments almost to the northern limit of the Mississippi embayment. 

 Six families are represented, comprising 15 genera and 30 species. More than half of 

 the species belong to the Lagenidae, with two to four species in each of the Hetero- 

 helicidae, Ellipsoidinidae, Rotaliidae, Globigerinidae, and Anomalinidae. Two new 

 species are described. 



INTRODUCTION 



THE ORIGINAL northern limit of Tertiary 

 sediments in the Mississippi embay- 

 ment is unknown. The Cretaceous deposits 

 in the Mississippi Valley probably extended 

 as far north as southeastern Minnesota 

 (Sardeson, 1898) and may have been at one 

 time coextensive with those of the Mid- 

 continent region. To a certain extent the 

 succeeding Paleocene sea flooded the same 

 areas. Therefore it is probable that the 

 earliest Cenozoic formations originally ex- 

 tended farther north than the present out- 

 crops in southern Illinois would indicate. On 

 the other hand, shore line conditions are 

 indicated by the absence of some marine 

 horizons which are present farther south. 

 In Tennessee the Ripley group is composed 

 of the McNairy sand over- and underlain 

 by the Owl Creek and Coon Creek marine 

 formations. The last two formations are 

 not recognized in Kentucky and from the 

 very sandy and glauconitic character of the 

 Ripley in Illinois it is possible that only the 

 McNairy is present here also. The possibil- 

 ity should be pointed out that the shore- 

 ward nonfossiliferous phases of these higher 

 and lower formations would take on the 

 sandy characteristics of the McNairy and 

 would therefore be indistinguishable from it. 

 The same is true of the Wilcox group. In 

 Tennessee it is composed of the Holly 

 Springs sandy formation which is over- and 

 underlain by the Grenada and Ackermann 

 marine shaly and limy formations. The lat- 

 ter is not recognized in Kentucky and from 



^ Published with permission of the Chief. 



the sandy character of the Wilcox at the 

 northern limit of its outcrop the Grenada is 

 probably also absent. This would leave the 

 Holly Springs as the sole representative of 

 the Wilcox group at the northern end of the 

 embayment, although the possible presence 

 of the sandy shoreward phase of the other 

 members of the group must not be over- 

 looked. 



The northernmost outcrop of Paleocene 

 formations shown on the geologic map of 

 the United States (Stose, 1932) is found on 

 the eastern side of the Mississippi embay- 

 ment just south of the Kentucky line in the 

 north-central part of Henry County, Ten- 

 nessee. On the west side of the embayment 

 the most northern extent of the Midway is 

 shown southeast of Newport in northeastern 

 White and southeastern Independence coun- 

 ties, Arkansas. However, Lamar and Sutton 

 (1930, fig. 1) mapped the Porters Creek for- 

 mation around the eastern and northern 

 edges of the embayment across Kentucky 

 and into Alexander County, Illinois, as far 

 west as the town of Unity where the forma- 

 tion dips beneath younger sediments. They 

 also mentioned (p. 953) the possible occur- 

 rence of the formation at Idalia and Bloom- 

 field, central Stoddard County, Missouri. 

 However, no correlation of the Porters Creek 

 of Illinois, other than with the formation in 

 Tennessee, was made by these writers. Sub- 

 sequent work has confirmed the suspected 

 occurrences and revealed others in Missouri 

 (Farrar and McManamy, 1937; Stewart, 

 McManamy, and McQueen, 1943) and 

 has shown that a number of clianges are 

 necessary in the Illinois portion of the map 

 (see text fig. 1). 



343 



