CHESTER OSTRACODES OF ILLINOIS 



BY 



Chalmer L. Cooper 



INTRODUCTION 



The first descriptions of ostracodes 

 apparently of Chester age were pub- 

 lished during the last half of the nineteenth 

 century by some of the early workers in 

 Great Britain and were based on specimens 

 collected from the Carboniferous "Lime- 

 stone Series" of England^ The first Ameri- 

 can species were described by Ulrich in 

 1890 from beds in Kentucky and Illinois, 

 but these fossils seem to have aroused little 

 interest among paleontologists until after 

 the first quarter of this century. The study 

 of well cuttings by geologists connected with 

 the petroleum industry and the recognition 

 of the value of micro-fossils as horizon 

 markers has resulted in a revival of interest 

 in Carboniferous ostracodes, and since 1927 

 the number of published studies has steadily 

 increased. The discovery of oil in the Ches- 

 ter series of the Illinois basin has recently 

 directed attention to these ostracodes, and 

 several papers have been published by Cro- 

 neis, Coryell, their students, and others. 



During this time several studies on other 

 Chester formations appeared, chief among 

 which were those of Coryell and Sohn 

 (1938) on the Reynolds (Mauch Chunk) 

 of West Virginia, Morey (1935) on the 

 Amsden of Wyoming, Harlton (1929) on 

 the Fayetteville of Oklahoma and Arkansas, 

 and Roundy (1926) on the Barnett and 

 Chappel of Texas. The Fayetteville fauna 

 described by Girty (1910) should also be 

 mentioned although it was not illustrated, 

 since two important Carboniferous ostra- 

 code genera were first described therein, one 

 of which, Amphissites, was subsequently 

 figured by Roundy. 



iFor a complete bibliography of Chester ostracodes 

 up to 1934 see Bassler, R. S., and Kellett, Betty, Biblio- 

 graphic Index of Paleozoic Ostracoda: Geol. Soc. Am., 

 Spec. Paper 1, 1934. Subsequent references will be 

 found in the various synonomies and in the list of 

 references at the end of this report. 



The present study was undertaken to de- 

 termine the stratigraphic ranges of all Ches- 

 ter ostracode species known in Illinois. It 

 is based principally upon new collections 

 obtained from outcrops, but is supplemented 

 by samples from the cores and cuttings from 

 a few wells. Many of the faunas are sur- 

 prisingly rich, and fully one-third of the 

 species recognized here are new. Although 

 it is the first complete record of the distri- 

 bution of Chester species, in so far as they 

 are now known, this study must be regarded 

 as a report of progress, because many more 

 new species will probably be recognized 

 upon the study of additional collections. 



The accompanying faunal chart lists 359 

 species of Chester ostracodes, only 35 of 

 which are not known to occur in Illinois. 

 The determined stratigraphic ranges of spe- 

 cies described from other areas, but also 

 occurring in Illinois, permits the more pre- 

 cise correlation of widely separated Chester 

 formations with the standard section than 

 was formerly possible. Few species are 

 identified with European forms, and these 

 with some hesitation and only after careful 

 study. 



RANGE OF CHESTER 



OSTRACODES 

 Chester Stratigraphy 



The Chester series^ in the Illinois basin, 

 cropping out in southern Illinois and adja- 

 cent parts of Indiana and Kentucky, con- 

 sists of eight limestone and shale formations 

 alternating with a like number of sandstone 

 or sandy shale formations. The limestone 

 and shale formations vary considerably in 

 both lithology and thickness. The sand- 

 stones are largely nonmarine although some 



2 For a recent, more complete discussion of the details 

 of Chester formations see Weller and Sutton (1940, 

 pp. 819-853), and Weller (1940, pp. 31-35). 



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