ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 492 



INTRODUCTION 



The study of compression-impression fossils of stems of tree 

 ferns in Illinois provides new information that helps to differentiate 

 taxa. The genera can be more easily delineated than the species, which 

 show a great variability in their characters. 



In the literature of tree ferns in Illinois, only petrifactions 

 have been systematically treated (Gillette, 1937; Morgan, 1959; Stidd, 

 1971) . The compression- impression species were illustrated in general 

 compression flora studies (Lesquereux, 1866, 1870, 1879-1884; Janssen, 

 1957; Langford, 1958, 1963). The most recent report on the stems of 

 Paleozoic tree ferns in general was given by Andrews and Doubinger (in 

 Boureau, 1970). 



Materials 



The specimens described in this study are, with a few exceptions, 

 from the same shales that have yielded large numbers of other compression- 

 impression fossils. Their positions in the stratigraphic section are 

 shown in text figure 1, their localities in text figure 2. 



The "Lower Chesterian" (text fig. 1) would be approximately 

 equivalent to the uppermost Visean in European time-stratigraphy. The 

 beds of Pennsylvanian age that have yielded stems are most probably 

 equivalent to the upper part of the Westphalian and the lower part of 

 the Stephanian. 



In the descriptions of 

 specimens from some of the col- 

 lections used, localities are not 

 precise. In some, only the name 

 of a nearby town or mine is given. 

 However, in all cases there was 

 enough information to assign at 

 least an approximate stratigraphic 

 position. 



In Illinois tree fern stems 

 are preserved both as petrifactions 

 and as compression- impression fos- 

 sils. The compression- impression 

 fossils have been found in Illinois 

 in four modes of preservation: 



1) Compression of stem as 

 a thin film of coal in 

 shale. 



2) Impression without 

 carbonaceous film in 

 ironstone nodules in 

 gray shale. Normally 

 there is only one leaf 



Text fig. 1 - Occurrence of tree fern scar per nodule, 



stems in compression floras in Illinois. 



SYS- 

 TEM 



SERIES 



FORMATION 



OCCURRENCE OF TREE FERN STEMS 

 IN COMPRESSION FLORAS 



c 

 n 



a 



> 



I 



Virgilian 



Mattoon 



^ ? Gray shale, exact position 

 | unknown 



▲ Energy Shale Member (gray 



shale above Herrin (No. 6) 

 Coal Member) 



A Francis Creek Shale Member 



(shale above the Colchester 

 (No. 2) Coal Member) 



A Gray shale above Murphysboro 

 Coal Member 



A "Lower Chesterian" 



Missourian 



Bond 



Modesto 



Desmoinesian 



Carbondale 



Spoon 



Atokan 



Abbott 



Morrowan 



Caseyville 













o. 



a. 



s 



Chesterian 





Valmeyeran 



Kinder- 

 hookian 













