Stratigraphic Cross Sect~On of Paleozoic Rocks of South Idakota
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\.';1;; STRATIGRAPHIC CROSS SECT~ON OF PALEOZOIC ROCKS OF SOUTH IDAKOTA BY R. A. SCI!IOON Reprinted, from Stratigraphic Cross Secti~n of Paleozoic Rocks OKLAHOMA TO SASKATCHEWAN I PUBLISHED BY THE AMERICAN ASSOCIATION <i>FPETROLEUM GEOLOGISTS TULSA, OKLAHOMA, U.S.A. 19(j~ SOUTH DAKOTAl (SectionD-E, Plate 4) R. A. SCHOON" Vermillion,South Dakota INTRODUCTION ded locally with white siltstone or sandstone,and an The cross section of Paleozoicrocks of South Dakota upper gray, argillaceous dolomite. The member con- extends generally northwestward through the western formably overlies the Red River Formation in the vi- half of the state. Data obtained from cuttings and elec- cinity of well 13 and northward. The Gunt'Onis brown- tric logs of 17 wells wer(~used in the preparation of the ish-gray, finely crystalline dolomite. South of well 13 report. both members are more sandy and are unrecognizable STRATIGRAPHY in the Upper Ordovician-Devoniansandstone section. The Deadwood Formation of Cambrian to Early Or- The Stonewall Formation, the youngest Ordovician dovician age is predominantly white to reddish-orange, formation shown on the cross section, is pale-red to fine- to medium-grainedquartz sandstone,and dolomite. light-tan dolomite that is finely crystalline and locally The sandstoneranges from dolomitic to orthoquartzitic sandy. Dark-green shale and gray sandstoneare com- mon variants in the base of the Stonewall. and contains green shale and locally abundant glauco- nite. The Interlake Group, which is treated as a formation by the South Dakota Geological Survey, includes all The Ordovician Winnipeg Formation consists of a strata depositedduring the Silurian Period. The rock is lower fine- to medium-grainedquartz sandstone,green splintery to subwaxy shale with small, vitreous, black light-tan to brown dolomite with a fine-grained clastic zone at the base. Its age is believed to be Early and phosphate nodules, and an upper slightly argillaceous Middle Silurian. siltstone interbedded \\.ith green shale. From well 7 southward the formation is not recognized.The Winni- The Souris River Formation unconformably overlies the Interlake Group and includes the oldest deposits of peg is probably of Black River-Trenton age and is the Devonian Period. The rocks, chiefly varicolored regionally unconformable on the DeadwoodFormation. shale and red dolomitic sandstone,may representan an- The Bighorn Group, of Middle to Late Ordovician cient zone of weathering that is partly equivalent in age age,is divided into the Red River and Stony Mountain to Devonian rocks in the deeperparts of the Williston Formations. In North Dakota the Stonewall Formation basin. also is included in the Bighorn Group. The Upper Devonian Duperow Formation is predom- The Red River Formation consists of light-brown to pale-red limestone that is in part dolomitized, and light- inantly light-brown, fine-grained to lithographic lime- stone and dolomite interbedded with gray shale. Ac- colored chert. In South Dakota there is a thre~fold sub- cording to Sandberg (1962, Fig. 6), the Duperow con- division of the formation (Agnew and Tychsen, 1965, formably overlies the Souris River; however, if the p. 156) that is more apparent on electric logs than in Souris River representsa local weathering profile, the cuttings. Pending further study, the subdivisions have contact is at least partly unconformable. been designated"C," "B," and "A," in ascendingorder. The basal Mississippian Englewood Formation con- Wells in the Buffalo field, Harding County, produce sists of tan to pale-red, dolomitic siltstone and vari- from porous zones at the top of unit B and near the colored shale. Sample studies indicate that the Engle- middle of unit A. wood-Lodgepolecontact is transitional. Thus, the Engle- At the north end of the cross section the Stony wood appearsto be a beginningshaly phaseof the Lodge- Mountain Formation is divided into two members,the pole Formation. Stoughton belowand tile Gunton above.The Stoughton Most Mississipp;anstrata in South Dakota are part consists of a lower green, waxy shale that is interbed- of the Madison Group, which includes the Lodgepole, 1 Manuscriptreceived, June 26,1967. Mission Canyon, and Charles Formations. .South DakotaGeologicltl Survey. In northern South Dakota the Lodgepoleis light-gray to brown, sparselyoolitic limestone that is progressive- The authorswho composedthe crosssections of the ad- jacent statesare thanked for their constructivecomments ly more dolomitic southward. At the southern end of concerning the subsurface correlations in the areas com- the cross section the rock is a light- to medium-brown mon to the stateboundaries. dolomite with pinhole porosity. South of well 5 is a do- to SOUTH DAKOTA lomite section that has a maximum thickness of 190 ft thick known as the "third Leo sand." (wells 3 and 4). T'his sequenceis referred to the Ordo- The Wendover-MeekFormation is chiefly yellowish- vician by many geologists,but data from recent drilling brown anhydrite and dolomite. Sandy zonesat the base indicate that it may be of Mississippianage. In this re- and near the top are known as the "second" and "first port the dolomite section south of well 5 is designated Leo sands," respectively. At the top of the formation is as "Lodgepole." a red clay bed called the "red marker" that has been The Englewood-Lodgepolecontact is conformable in designated as the Pennsylvanian-Permian boundary the north. South of well II Lodgepole rocks overlap (Agatston, 1954, p. 534; McCauley, 1956, p. 163). older formations and may lie 10C1l.llyon the Precam- Variations in the thickness of the Wendover-Meekare brian surface betweenwells 6 and I. probably the result of pre-Permian erosion. Oil is pro- The Mission Canyon Formation is predominantly duced from the "second Leo sand" at Barker Dome in light-brown, partly lithographic limestone with irregular the southern Black Hills and showshave been reported zones of fragmental to reefoid limestone and minor in the "first Leo" in the samearea. quantities of anhydrite. The formation conformably The Broom Creek Formation is the basal Permian overlies the Lodgepole and offiaps northward. South of unit. At the northern end of the cross section these well 7 the Mission Canyon is absentbecause of post- rocks are predominantly dolomite and dolomitic sand- Mississippianerosion. stone; southward from well 15 they grade to partly The Charles Formation is a sequenceof anhydrite, sandydolomite and anhydrite. light-brown to gray limestone and doJomite,and some The Cassa Formation, the uppermost unit of the chert. The Charles offiaps in a northward direction and Minnelusa Group in South Dakota, consists of reddish, conformably overlies the Mission Canyon. silty claystone or sandstone with some impure anhy- The Big Snowy Group is representedin South Dako- drite. The thickness is irregular because of the uncon- ta by only the lowermost subdivision,the Kt"bbeyFor- formity at the top of the Broom Creek Formation. mation. In wells 16 and 17 the Kibbey consists of South of well 6 the CassaFormation is absentbecause white, medium- to coarse-grainedsandstone, and light- of post-Permianerosion. The Cassa includes the "Con- brown dolo,mite. versesands" of the Black Hills. Rocks of the Minnelusa Group include five Pennsyl- The Opeche Shale is red to pale maroon, and lies vanian formations-the Fairbank Reclamation Round- conformably on the CassaFormation. South of well 7 it top, Hayden, and Wendover-Meek-and two E~rly Per- is absentbecause of post-Permianerosion. mian formations-the Broom Creek and Cassa(Condra The Minnekahta Formation is pink to light-purple, et aI., 1940). ~ r. fine-grained limestone with some anhydrite locally. It The Fairbank Formation consists of white, fine-~ appearsto be conformable with the underlying Opeche, grained sandstone and varicolored clay and shale. It ~ and according to Goldsmith (1959) is possibly of appearsto be a time-transgressivesandstone and laterit- Leonard age. ic deposit formed on the surface of Mississippianand ~ In neighboring states the Spearfish Formation is di- older rocks. Numerous oil showshave, been reported in ~ vided into Permian and Triassic subdivisions. At pres- the Fairbank. An interval from 4,805to 4,814 ft in wel~ ent, the South Dakota GeologicalSurvey does not make I I had good oil stains in tightly cementedsandstone. -..this distinction. Therefore, the Minnekahta Limestone The Reclamation Formation is light-colored, sublitho- is consideredthe youngestPaleozoic unit in this report. graphic limestone interbedded with varicolored shale. STRUCTURE Minor dead oil stains have been reported in the lime- stone. The South Dakota crosssection is approximately par- The Roundtop Formation is the most reliable marker allel with the axis of th~ Williston basin. ~o m~jor bed in the PaleozoicIsection. From well 5 northward it s~ructuralfeatures are eVId~n.t-the w~st-trendmg SIOUX is predominantly green,waxy shale with scatteredsand ndge (well 5) and the Williston basIn. .Farther north grains; south of well 5 it is medium- to coarse-grained (.wells 9 a~d ~o), the absenceof the Fairbank Fo~a- sandstonecemented with greenclay. The Reclamation- tl.on ~ay Indicate the presence of a subdued anCIent Roundtop contact appearsto be transitional and region- hl~h.m west-centra! ~o?th. Dakota. The pronounced ally conformable, although there are local unconformi- thmmng?f .post-Mlsslsslpplan'beds between.wells 15 ties between wells 16 and 17 and south of well 5. and 17 I?d~cates that t~e nor.iliwest-trendmg.Cedar The Hayden Formation is mainly yellowish-brown, C~eek .antlclme was growIng dunng Pennsylvaman-Per- lithographic to oolitic limestone interbedded with black Inlan time. radioactive shale, minor quantities of anhydrite, and GEOLOGIC HISTORY fine-grained sandstone. At the base of the Hayden in Paleozoic depositionbegan with the Cambrian to Or- most places is a dolomitic sandstonebed about 15 ft dovician clastic sedimentsof the Deadwood Formation PALEOZOIC ROCKS, OKLAHOMA TO SASKATCHEWAN in the Williston basin, parts of the Chadron arch, and areas,and possibly in the area.of the Cedar Creek anti- the Black Hills area.