ko 



ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 500 



The Spotted Ridge Flora from TABLE 8 — OCCURRENCE OF IMPORTANT 

 the Lower Pennsylvanian of Oregon TAXA IN FLORAS COMPARABLE WITH 

 was described by Read and Merriam THE SPENCER FARM FLORA* 

 (19^0), Arnold (1953), and Mamay 

 and Read (1956). The flora con- 

 tains Mesocalamites and a Pecop- 

 teris (p. oregonensis) that is 

 very similar to Dactylotheca as- 

 pera. 



Ti dwell (196T) described a 

 flora from the Manning Canyon 

 Shale in Utah. This flora is of 

 early Pennsylvanian age and con- 

 tains a few forms comparable with 

 species of the Spencer Farm Flora. 



Age of the Flora 



Prior to the discovery of the 

 Spencer Farm Flora, the oldest de- 

 posits in the Illinois Basin could 

 be correlated with the Westphalian 

 A. Thus, it was assumed at first 

 that the Spencer Farm Flora could 

 be of the same age as other basal 

 beds. This was in agreement with 

 the Westphalian B age of the Baby- 

 lon Sandstone, which was in turn 

 derived from the correlation with 

 other plant-bearing beds in the 

 Illinois Basin. 



However, preliminary inves- 

 tigations of the spore flora in 



the host rock of the Spencer Farm Flora indicated a Namurian age (Russel 

 Peppers, oral communication). An analysis of the megaflora showed that 

 the flora is most likely of Namurian B age. 



The Spencer Farm Flora is difficult to date because it grew in 

 an environment that is seldom represented in the fossil record. Strati- 

 graphic ranges have been established elsewhere for only nine of the 28 

 plants occurring in the Spencer Farm Flora. All of these ranges are 

 known from European coal basins only. Thus the ranges of those nine 

 taxa were plotted against the time-stratigraphic scale of the European 

 Carboniferous (text fig. 13). At first glance, the Spencer Farm Flora 

 would seem to be a mixture of several ages. However, because all of 

 the material comes from only two very close locations, this possibility 

 can be excluded. 



If we assume that first occurrence is the most meaningful para- 

 meter in biostratigraphy, the conclusion would be that the flora is of 

 Westphalian A age and that the ranges of several Namurian forms would 

 have to be extended considerably. This conclusion would contradict the 

 overall Namurian character of the flora. 









<f 















00 















00 





m 



v£> 









~* 



m 



00 



0^ 









X 



r~- 













3 



00 













at 



r—i 



>. 



T3 







00 



S-i 





u 



m 











a) 



W 



u 



CD 







<T< 



3 



3 



0) 



Di 









W 



0) 



Jl 











W 



u 



> 



r, 





« 



a) 



<u 



X) 



<D 



< 





u 



4-1 



hJ 



1=1 



52 



a, 









•H 





< 









T-\ 



£ 













Pn 



,-J 



.. 



X 



C 









1— 1 



=c 



O 



•H 





B 













CO 





5-1 



Q 













Ct) 





C 



r. 



G 



c 





tn 



•> 



O 



<D 



3 



3 







w 



u 



H 



O 



O 





u 



•H 



>> 



rH 



4-1 



s 





QJ 



O 



ea 



•H 



w 







O 



c 





> 



00 



JZ 





C 



■H 



•u 



Xi 



c 









0) 



rH 



u 



w 



3 



4-1 





a 



H 







3 



O 



3 





CO 



1— 1 



PM 



Pi 



>-> 







Alloiopteris gracillima 



X 



X 



- 



- 



X 



_ 



Dactylotheca 



X 













Palaeopteridium reussii 



X 



X 



- 



X 



X 



X 



Lacoea seriata 



X 



X 



~ 



X 



X 



X 



Megalopteris 



X 



X 



X 



X 



- 



- 



Lesleya 



X 



X 



- 



- 



- 



- 



Alethopteris lonchitica 



X 



X 



- 



- 



- 



- 



Alethopteris 



- 



- 



X 



X 



X 



- 



Orthogoniopteris 



- 



- 



- 



X 



- 



- 



Neriopteris 



- 



- 



- 



- 



X 



X 



Eremopteris 



cf . 



- 



X 



X 



- 



- 



Sphenopteris 



X 



X 



X 



X 



- 



- 



Mariopteris 



cf . 



X 



- 



- 



- 



X 



Neuropteris 



- 



X 



- 



- 



X 



X 



The lists are not complete because they are 

 based on the literature and on a few specimens 

 consulted in old collections. 



