fl€J Stratigraphy of Middle Ordovician Rocks in the Zinc-Lead District of Wisconsin, Illinois, and Iowa SURVEY PROFESSIONAL PAPER 274-K Prepared in cooperation with the Wisconsin Geological and Natural History Survey Stratigraphy of Middle Ordovician Rocks in the Zinc-Lead District of Wisconsin, Illinois, and Iowa By ALLEN F. AGNEW, ALLEN V. HEYL, JR., C. H. BEHRE, JR., and E. J. LYONS A SHORTER CONTRIBUTION TO GENERAL GEOLOGY .>,GEOLOGICAL S URVE Y < PROFES SI ON AL PAPER 274-K Prepared in cooperation with the Wisconsin Geological and Natural History Survey UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956 UNITED STATES DEPARTMENT OF THE INTERIOR Fred A. Seaton, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price 60 cents (paper cover) CONTENTS Page Page Abstract. __________________________________________ 251 Quimbys Mill member_______________________ 282 Introduction _____________________________________ 252 Lithologic description and stratigraphic re- Purpose of the investigation____________________ 252 lations_ ______________________________ 282 Location and geographic setting__________________ 252 Distribution. _ __________________________ 283 Field work.____________________________________ 252 Fauna and correlation.__________________ 284 Acknowledgments. ______________________________ 254 Economic products______________________ 284 Regional geology and stratigraphicrelations_____ ________ 254 Distribution of facies of the Platteville and con­ Structure ______________________________________ 254 ditions of deposition__________ _____________ 284 Regional stratigraphic summary __________________ 254 Decorah formation._____________________________ 285 Stratigraphic principles._________________________ 260 General features._________---_____--___--___ 285 Stratigraphic problems. _________________________ 261 Spechts Ferry shale member _________________ 286 Platteville-Decorah boundary _ _______________ 261 Lithologic description and stratigraphic re­ Beloit dolomite.____________________________ 262 lations. ______________________________ 286 Unnamed limestone member, Decorah forma­ Distribution. ___________________________ 289 tion. _ 264 Fauna and correlation.__________________ 289 Subdivisions of Galena dolomite ______________ 265 Economic products______________________ 289 Origin and application of the names.______________ 269 Guttenberg limestone member._______________ 289 Madison sandstone-________________________ 269 Lithologic description and stratigraphic re­ Pecatonica dolomite member.________________ 269 lations. ______________________________ 289 McGregor limestone member_________________ 269 Distribution___________ _________________ 292 Quimbys Mill member _______________________ 269 Fauna and correlation __________________ 293 Stratigraphy of the mining district.___________________ 271 Economic products._____________________ 293 Pre-Platteville rocks_ ___________________________ 271 Ion dolomite member_______________________ 293 Pre-Cambrian rocks_________________________ 271 Lithologic description and stratigraphic re­ Cambrian rocks_ ___________________________ 271 lations. ______________________________ 293 Ordovician rocks____________________________ 272 Distribution, ___________________________ 295 Prairie du Chien group __________________ 272 Fauna and correlation.__________________ 295 St. Peter sandstone_ ____________________ 273 Economic products._____________________ 295 Platteville formation____________________________ 274 Distribution of facies of the Decorah and con­ General features____________________________ 274 ditions of deposition_______________________ 295 Glenwood shale member.____________________ 275 Galena dolomite._______________________________ 296 Lithologic description and stratigraphic re­ General features-___________________________ 296 lations _______________________________ 275 Cherty unit ________________________________ 296 Distribution.. __________________________ 277 Noncherty unit _____________________________ 297 Fauna and correlation.__________________ 277 Distribution. _______________________________ 298 Economic products______________________ 277 Distribution of facies of the Galena and condi­ Pecatonica dolomite member.________________ 277 tions of deposition ________________________ 299 Lithologic description and stratigraphic re- Fauna and correlation-______________________ 299 lations_ ______________________________ 278 Economic products. _________________________ 300 Distribution, ___________________________ 278 Fauna and correlation.__________________ 279 Post-Galena rocks___ ___________________________ 300 Economic products______________________ 279 Ordovician rocks—Maquoketa shale.__________ 300 McGregor limestone member.________________ 279 Silurian rocks_ ______________________________ 301 Lithologic description and stratigraphic re­ Post-Silurian deposits_ ______________________ 302 lations. ______________________________ 279 Literature cited-____________________________________ 302 Distribution. _ __________________________ 282 Fauna and correlation.__________________ 282 Stratigraphic sections._______________________________ 305 Economic products._____________________ 282 Index _____________________________________________ 311 in IV CONTENTS ILLUSTRATION Page FIGURE 31. Upper Mississippi Valley region showing general geology and location of the zinc-lead district_____ __________ 253 32. Generalized stratigraphic column for zinc-lead district__ ________________________________________________ 255 33. Bluff showing Platteville, Decorah, and Galena strata-_______________-____-__----___----_____-______--_ 256 34. Diagrammatic cross section of Platteville, Decorah, and Galena strata eastward across the mining district-___ 257 35. Map of part of upper Mississippi Valley region, showing localities cited in text.___________________________ 258 36. Generalized west-east cross section of Decorah formation and adjacent strata.____________________________ 263 37. Correlation of Platteville, Decorah, and Galena strata with units in Minnesota-__________________________ 264 38. Stratigraphic column of Platteville, Decorah, and Galena strata in zinc-lead district______-____-____________ 268 39. Classifications of Platteville, Decorah, and Galena sequence since 1906-__________________________________ 270 40. Quarry showing Prairie du Chien group.__________________________---___--__-_____------------___--_- 272 41. Crossbedded St. Peter sandstone in roadcut._______-_______________--_-_________-__--__--------__-_-_- 273 42. Pecatonica and McGregor members of the Platteville formation in roadcut______________________________ 274 43. Glenwood shale member and Pecatonica member of Platteville formation above St. Peter sandstone in roadcut__ 275 44. Suggested correlatives of Platteville, Decorah, and Galena strata._______________________________________ 278 45. Comparative stratigraphic terminology of Platteville, Decorah, and Galena rocks in the zinc-lead district----- 280 46. Type section of Quimbys Mill member of Platteville formation._________________________________________ 283 47. Type section of Spechts Ferry shale member of Decorah formation______________________________________ 286 48. Quimbys Mill member of Platteville formation and the overlying Guttenberg member of Decorah formation in a quarry at Calmine, Wis_________-________________-__________---_----_-_______---_-_--_---_-_---_ 287 49. Type section of Guttenberg limestone member of the Decorah formation__________________________________ 290 50. Decorah formation in dolomite facies, overlain by Galena dolomite and underlain by Quimbys Mill member of Platteville formation, in quarry at York Church, Wis________________________________________________ 290 51. Carbonaceous shale partings between wavy dolomite beds of Guttenberg limestone member of Platteville forma­ tion in quarry in Green County, Wis_______________________________________________________________ 291 52. Exposure in mine showing effect of mineralizing solutions on Guttenberg member of Decorah formation______ 291 53. Honeycomb weathering of Galena dolomite in a roadcut in Grant County, Wis____________________________ 297 54. Maquoketa shale and overlying Silurian dolomite in roadcut and quarry._________________________________ 301 A SHORTER CONTRIBUTION TO GENERAL GEOLOGY STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT OF WISCONSIN, ILLINOIS, AND IOWA By ALLEN F. AGNEW, ALLEN V. HEYL, JR., C. H. BEHRE, JR., and E. J. LYONS ABSTRACT Stratigraphic studies, both outcrop and subsurface, of Ordovi- The Galena dolomite is generally coarsely crystalline massive cian rocks of the zinc-lead district in Wisconsin, Illinois, and vuggy dolomite or limestone divisible regionally into two units, Iowa form the basis for a more accurate means of delimiting a cherty lower unit 105 feet thick and a noncherty upper one 120 potentially ore-bearing areas from less favorable localities. feet thick. The cherty unit is divided into four zones, A, B, C, Detailed stratigraphic subdivisions of the Platteville, Decorah, and D in descending order, based primarily upon relative chert and Galena strata have permitted the mapping of folds with content and the presence of Receptaculites. The noncherty unit structural relief of 30 feet or less in areas smaller than a quarter is divided on the basis of thinness of bedding and the amount of of a mile