EARLY PENNSYLVANIA FLORA FROM WEST-CENTRAL ILLINOIS 



kl 



< 



a 



3 



Namurian 

 > a? o 



Westphalian 

 > CD o o 





















Lepidodendron wortheni 











Asterophyllites 

 longifolius 















Mesocolom/tes 









Dactylotheca aspera 















^ : 





-- 











Sphenopteris preslesensis 



Rhodeopleridium 





^ m 







Polaeopteridium reus si / 









Gulpemo limburgensis 



The long and differing ranges 

 of the nine taxa (text fig. 13) 

 led to the use of the concept of 

 concurrent ranges. Six forms occur 

 together in the Namurian B, ex- 

 cluding only three. Five are pres- 

 ent in the Namurian C, excluding 

 four. The numbers of concurring 

 taxa are even lower for the Namur- 

 ian A and Westphalian A. We have 

 thus to conclude that according to 

 material and information available 

 at present, the Spencer Farm Flora 

 is regarded as belonging to the 

 Namurian B or possibly the Namuri- 

 an C. 



It follows that the range of 

 Gulpenia limburgensis would now be 

 Namurian A and B (c), the range of 

 Lepidodendron wortheni would be 



Namurian B (c) to Westphalian D, and the range of Palaeopteridium reussii 

 would be Namurian B (c) to Westphalian C. 



The plant-bearing beds at Spencer Farm are approximately equiv- 

 alent in age to the Pocahontas Formation in West Virginia. The flora 

 would therefore belong in zone k of Read and Mamay (196U). However, 

 none of the index fossils used for the definition of zone k occurs in 

 the Spencer Farm Flora because of the unusual biofacies of the flora. 

 On the other hand, the genus Megalopteris has been reported from zone 7. 

 The Spencer Farm Flora, however, occurs stratigraphically clearly below 

 the beds correlated in Illinois with zone 7. Megalopteris probably has 

 an extended range. This extension is indicated by the occurrence in 

 West Virginia of Megalopteris above the Fire Creek Coal, which lies at 

 the base of zone 5 (White, 1895 )'. 



Text fig. 13 - Stratigraphic ranges in the 

 European Carboniferous of genera and spe- 

 cies occurring in the Spencer Farm Flora. 

 (Data from Gothan and Remy (1957), Fos- 

 silium Catalogus , and other sources.) 

 Dotted outline shows time of common oc- 

 currence of the majority of forms. 



SUMMARY AND CONCLUSIONS 



1) The Spencer Farm Flora was found in the basal beds of the 

 Caseyville Formation (Pennsylvanian) . These beds were deposited in a 

 ravine eroded in Mississippian limestones. The plant-bearing beds are 

 thus the oldest rocks of Pennsylvanian age in the area and represent the 

 first deposits laid down after a hiatus. 



2) The flora contains 29 species and a few problematical forms. 

 Nine taxa are identical with or directly comparable with European forms 

 with established stratigraphic ranges. Six of these have a concurrent 

 range indicating a Namurian B (or possibly Namurian C) age. Thus, at 

 present, Spencer Farm Flora is the oldest flora of Pennsylvanian age 

 known in the Illinois Basin. 



3) The flora represents an unusual biofacies, in which generally 

 rare taxa (Megalopteris, Lesleya, Palaeopteridium , Lacoea) are common. 



