SPORE DISTIMU'TION — McLEANSBORO 



93 



M(. I.EANSBORO GROUP 



The McLeansboro Group is the upper- 

 most group of the Pennsylvanian in Illi- 

 nois. The base of the group is defined as 

 the base of the Anvil Rock Sandstone. The 

 group is more than 1200 feet thick and is 

 composed predominantly of shales, silt- 

 stones, and sandstones, with numerous ma- 

 rine limestones and thin lenticular coals. 

 Cady (1952) noted the presence of from 

 22 to 27 coals or coal horizons within the 

 group. Of these, the Jamestown, Danville 

 (No. 7) , Friendsville, and Trowbridge 

 Coals are of economic importance. 



The group is considered to correspond to 

 the upper third of the Desmoinesian Series, 

 the Missourian Series, and possibly to part 

 of the Virgilian Series, all of the Midconti- 

 nent region; to the upper Allegheny and 

 Conemaugh Series of the Appalachian 

 Basin (Wanless, 1 955) ; and possibly to part 

 of the Westphalian D and Lower Stephan- 

 ian of Europe (Kremp, 1955) . 



Kosanke (1950) noted a major change in 

 the flora shortly after the beginning of Mc- 

 Leansboro deposition but prior to the depo- 

 sition of the Trivoli (No. 8) Coal. No 

 species of Lycospora is known from the 

 Trivoli (No. 8) Coal nor from overlying 

 coals. The change essentially conforms to 

 the Desmoinesian-Missourian boundary of 

 the M idcontinent region and agrees with a 

 major faunal change discussed by Dunbar 

 and Henbest (1942) . 



Only 14 samples of McLeansboro coals 

 or coaly streaks, principally from six coun- 

 ties in south-central Illinois, have been ex- 

 amined. Most of the samples are from units 

 overlying the Trivoli (No. 8) Coal, or in 

 other words, occurring above the major 

 floral change discussed by Kosanke (1950) . 

 The sequence in which the units are listed 

 on the distribution chart (text fig. 9) 

 should be regarded as tentative because 

 many stratigraphic problems in the Mc- 

 Leansboro Group have not yet been re- 

 solved. 



Each of the assemblages given on the dis- 

 tribution chart represents a single sample 

 from each unit given; therefore, discussion 

 of these assemblages is unnecessary. In ad- 

 dition to the strata shown on the distribu- 



tion chart, a few slides from three other 

 units were examined. Parasporitcs, Mono- 

 letes, Triletes triangulatus, and T. glabra- 

 tus are known from the Danville (No. 7) 

 Coal. T. glabratus, Monoletes, and auricu- 

 late spores are known from the Macoupin 

 Coal. Monoletes and auriculate spores also 

 are known from the Flannigan Coal. Be- 

 cause the total assemblages from these coals 

 were not examined, they have not been 

 given on the distribution chart. 



In contrast to the occurrence of Triletes 

 mamillarius in some of the coals of the 

 Carbondale Group, the species is not repre- 

 sented in the McLeansboro Group. Neither 

 T. riigosus, except for one questionable 

 specimen, nor Cystosporites is known from 

 the Trivoli (No. 8) or younger coals. This 

 parallels the absence of the small spores of 

 Lycospora. However, lageniculate-type 

 spores, T. lev is, are very common in upper 

 McLeansboro coals. 



In general, the upper McLeansboro coals 

 — Trivoli (No. 8) and those above — seem 

 to be characterized by the presence of 

 common cuticles, seed membranes, the 

 rather small large spores of Parasporites, 

 Monoletes, Spencerisporites, and Calamo- 

 spora; megaspores of Triletes glabratus and 

 T. levis and of the auriculate type; and by 

 rather rare occurrences of the triangulate 

 megaspores. 



Discussion 

 upper mississippian 



Published studies concerning plant mega- 

 spores of Mississippian age from localities 

 in North America are few (Chaloner, 

 1954b, three samples at three localities; 

 Schemel, 1950a, one sample) . Even the 

 small spore studies have been neglected, 

 mainly for economic reasons, although not 

 to as great an extent since oil companies 

 have increased their interest in this phase 

 of paleobotany (for example, Hoffmeister, 

 Staplin, and Malloy, 1955). More pub- 

 lished studies, at least in part dealing with 

 some of the older coals, are available from 

 Europe (Dijkstra, 1952b; Nowak and 

 Zerndt, 1936; Zerndt, 1934, 1937a; Horst, 

 1955; Potonie and Kremp, 1955, 1956) be- 



