View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Illinois Digital Environment for Access to Learning and Scholarship Repository °,'S ,S}*TE If/jltf GEOLOGICAL SURVEY 3 3051 00003 5240 Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/studiesofchester91illi STATE OF ILLINOIS DWICHT H. GREEN. Governor DEPARTMENT OF REGISTRATION AND EDUCATION FRANK G. THOMPSON. Director DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON. Chief URBANA CIRCULAR NO. 9: STUDIES OF THE CHESTER SERIES IN THE ILLINOIS BASIN REPRINTED FROM THE TRANSACTIONS. ILLINOIS STATE ACADEMY OF SCIENCE. VOL. 35. NO. 2. DECEMBER 1942 < 1943) PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA. ILLINOIS 19 4 3 CONTENTS PAGE USE OF THE GLEN DEAN LIMESTONE AS A STRUCTURAL KEY HORIZON IN THE ILLINOIS BASIN By George V. Cohee 5 CHESTER INDEX OSTRACODES By Chalmer L. Cooper 8 SUBSURFACE STRATIGRAPHIC SECTIONS NEAR TYPE CHESTER LOCALI- TIES IN SOUTHWESTERN ILLINOIS Bji Frank E. Tippie 9 [3] USE OF THE GLEN DEAN LIMESTONE AS A STRUCTURAL KEY HORIZON IN THE ILLINOIS BASIN 1 GEORGE V. CoHEE" Illinois State Geological Survey, Urbana, Illinois The Glen Dean formation is one of the dicating some structural movement dur- best known formations of the Chester ing late or post-Glen Dean time. series in Illinois. Since 1937 the basal The Glen Dean formation in the Illi- limestone has been used widely as a nois basin is predominantly limestone structural key horizon and as a subsur- with various amounts of shale. In many face '•marker" in drilling. The producing areas it consists of two limestone mem- formations in most of the new oil fields bers, separated by calcareous shale, which in Illinois lie below the Glen Dean lime- are designated as upper and lower or stone, so the formation is penetrated by a "massive" Glen Dean. The upper lime- great majority of the oil tests drilled stone is very erratic in its distribution within its boundary. but the lower member is persistent and The formation was first described by maintains a fairly uniform structural re- Butts" in 1917 as follows: "The Glen lationship with the underlying beds al- Dean limestone is named from Glen Dean though there may be some local variation in the southern part of Breckinridge in its thickness. Both the top and base County, Kentucky. This name is adopted of this lower member are used as key because of the excellent exposure of the horizons on which structure contour limestone along the railroad on both sides maps are based. The limestone is charac- of Glen Dean. It is composed of varying teristically coarse-grained, crinoidal, proportions of limestone and shale and oolitic, and brownish-gray. It contains a includes locally, at least, a little sand- variable amount of chert and some dolo- stone. The bottom segment of the forma- mite. In most areas it is the highest tion, at several widely separated points in limestone of the Chester series that con- Breckinridge County, is about 10 feet of tains well developed oolites. (Occasion- green and red shale lying upon the flaggy ally oolites occur in the higher Menard Hardinsburg sandstone." and Vienna formations.) In subsurface Figure 1 shows the subsurface and out- studies the top of the formation is placed crop boundaries of the Chester series and at the top of the calcareous shale over- the Glen Dean formation in Illinois and lying the uppermost limestone and the the thickness of the Glen Dean through- bottom of the formation is placed at the out its areal extent. Considerable varia- base of the calcareous shale below the tion in thickness is noted from north to basal limestone member. south. Around the north end of the Illi- The Glen Dean is usually overlain by nois basin it is from to 25 feet thick, the Tar Springs formation, generally a and in Jackson County in southwestern massive sandstone which varies from 30 Illinois it is more than 100 feet thick. A to 135 feet in thickness but in some areas short distance to the east in Union it is principally shale or sandy shale. County there is a pronounced thinning of The Glen Dean formation is underlain by the formation along the outcrop, but it the Hardinsburg formation, which gen- thickens again to almost 100 feet in John- son County. In the deep basin area in erally consists of shale and sandy shale White, Hamilton, and Wayne counties, it or siltstone and is usually from 20 to 60 is generally from 50-75 feet thick. Thin- feet thick. Locally a well developed ning of the formation occurs in areas of sandstone may occur within the Hardins- major structural features in the State, in- burg. 1 Reprinted from page.? 132-134 of the Transactions. 2 Xow Assistant State Geologist, Indiana Division of Geology, Indianapolis. * Butts, Charles. Description and Correlation of the Mississippian Formations of Western Kentucky: Kentucky Geol. Survey, 1917, p. 97. [5] Illinois State Academy of Science Transactions Fig. 1. —Thickness map of Glen Dean formation. Geology—19J/.2 Meeting Fig. 2. —North-south electric log- cross-section of New Harmony Field. In various areas in the Illinois basin stone occurs in the other wells of the certain thin persistent limestone beds, cross-section. The "massive" limestone is such as the basal Golconda limestone, poorly developed in well six. In the few have proved more satisfactory than the areas where production is limited to that Glen Dean for detailed structural in- part of the Chester series above the Glen formation. In the New Harmony field of Dean, the basal Menard or the lower Kin- eastern White County the thin basal kaid limestone, if present, are used for Golconda limestone is present throughout structural key horizons. the area and is a better structural key The Glen Dean formation is an im- horizon than the basal Glen Dean lime- portant subsurface "marker" because it is stone which is slightly variable in thick- usually recognized easily in electrical ness. Figure 2, a north-south electrical logs, in sample studies, and in drilling, log cross-section in the New Harmony and it is present over most of the area in field, shows the variation in thickness of southern Illinois where oil development the Glen Dean formation in that area. and exploration is most active. The wells represented in the cross-sec- tion are about one mile apart. In wells ACKNOWLEDGMENTS one, three, and five of the cross-section, The writer is grateful to Dr. A. H. Bell the upper Glen Dean limestone is pres- and other members of the Survey staff ent; however, it is best developed in well for helpful suggestions and criticism of one. Only the lower or "massive" lime- the manuscript. Illinois State Academy of Science Transactions CHESTER INDEX OSTRACODES 1 Chalmeb L. Cooper Illinois State Geological Survey, Urbana, Illinois The ostracodes constitute one of the which continue into the Pennsylvanian most persistent orders of microfossils. era with little or no change in the num- Although many genera are extremely ber of species represented, are Amphis- long lived, careful study reveals many sites, Bythocypris, Ectodemites, Kirkbya, species of value as index fossils. These and Paraparchites. forms have been found in all types of However, genera alone are of little marine sediments throughout most of the value as stratigraphic indices. Only eight Paleozoic era. Freshwater forms ap- of the 67 genera known to occur in the peared with the change of the sedi- Chester series are restricted to one forma- mentary conditions that resulted in the tion, and five of these are represented by deposition of alternating marine and only one species each. More diagnostic freshwater beds in the Pennsylvanian and species are found in the New Design Permian systems. The non-marine forms (lower Chester) group than in the Horn- become important only in post-Paleozoic berg (middle Chester) and Elvira (upper formations. Chester) groups. In the New Design As shown by recent work3 the Chester group about half of the known species series has furnished one of the most are restricted to one formation, whereas diversified ostracode faunas of the approximately only a third of the species Paleozoic era. Nearly 360 species are in each of the two higher groups are so known and all but 35 are found in Illi- restricted. The greatest change in the nois. This is a very marked increase ostracode faunas occurs at the Homberg- over the number of species found in the Elvira boundary, dividing the Chester lower Mississippian formations. series into an equal number of formations A few holdover genera from the De- above and below. vonian period are present, but in greatly Some of the restricted species may not decreased numbers, namely Beyrichia and be good index fossils. Many of them are Pi i in ilia. The Chester series is character- new and further work will no doubt in- ized by a great increase in the number crease their range. In some genera the of species of Bairdia, Cavellina, Glypto- species are so nearly alike that they are pleitra, Healdia, and P araparchites. readily confused, and for this reason they Genera restricted to the series are Bair- are of little value for correlation. These diolites, Chcstcrella, Deloia, Geffenites, include species of Bairdia, Healdia, Glyplopleuroides, Lochriella, Paracavel- Cavellina, and many species of the Am- Inui, Perprimitia, and Tetratylus. Genera phissitinae. 1 Reprinted from page 13.") of the Transactions. 2 Cooper, Chalmer L,., Chester ostracodes of Illinois: Illinois Geol. Survey, Rept. Inv. 77, KU pp.. 14 pis., 1941. ) Geology—191$ Meeting SUBSURFACE STRATIGRAPHIC SECTIONS NEAR TYPE CHESTER LOCALITIES IN SOUTHWESTERN ILLINOIS 1 Frank E.