U I ~ University of Wisconsin-Extension INFORMATION CIRCULAR GEOLOGICAL AND NATURAL HISTORY SURVEY NUMBER 47 1985

A Subsurface Study of the St. Peter Sandstone In Southern and Eastern Wisconsin

by Huazhao Mai and R. H. Dott Jr.

WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY MADISON, WISCONSIN INFORMATION CIRCULAR NUMBER 47 1985

A Subsurface Study of the St. Peter Sandstone In Southern and Eastern Wisconsin

by Huazhao Mai and R. H. Dott Jr.

Published by and available from: WISCONSIN GEOLOGICAL & NATURAL HISTORY SURVEY 1815 University Avenue, Madison, Wisconsin 53705 M. E. Ostrom, Director and State Geologist

CONTENTS

PREFACE...... ••...... v

ABSTRACT...... 1

INTRODUCTION...... • ...... • . . . . . • ...... 2

METHODS OF STUDy...... 3

STRATIGRAPHY...... • • • ...... • ...... 3 Name and Age .....•••...... •...... " 3 Stratigraphic Subdivisions...... 4 Regional Distributions and Thickness Patterns .....•.•...... 6

STRATIGRAPHIC PATTERNS WITHIN WISCONSIN ....•...... 6 Overlying and Underlying strata ...... • 6 The Unconformity Surface...... 7

SEDIMENTATION OF THE ST. PETER SANDSTONE ...... •.•...... 11 Composition ...... •...... •...... 11 Texture .....•...... •..•...... , ...... 11 Grain-Surface Textures and Overgrowths ...... •.. 12 Diagenesis .....•...... •...•...... 12 Source of Sand...... 15 Depositional Processes and Environments ...... 16 Paleogeographic setting ...... •...... 18

TECTONIC IMPLICATIONS ...... •.•...... •..... 21

SUMMARy ...... ••...... •...•...... 23

ACKNOWLEDGEMENTS...... • ...... 23

REFERENCES .....••...... : ...... • . . . .. 24

iii

ILLUSTRATIONS

Figures:

1. Distribution of the st. Peter Sandstone ...... 2 2. Example of Skolithos trace fossils...... 4 3. Generalized strat igraphic column:...... 5 4. Thickness of the Ancell Group ...... 8 S. Scanning electron microphotograph of quartz grains ...... 12 6. Microphotograph of a thin section of the st. Peter Sandstone ...... 14 7. SEM photograph of an eoli an quartz grai n...... 14 8. SEM photograph of quartz grains with diagenetic coatings ...... 15 9. Facies and paleogeography for Tonti deposition ...... 16 10. Adhesian pseudo-crosslamination in the st. Peter Sandstone ...... 17 11. Climbing-ripple translatent lamination ...... 19 12. Lithologic log of the st. Peter Sandstone ... " ...... •...... 20 13. Drainage patterns on the pre-St. Peter unconformity surface ...... 21 14. Regional sub-crop map of the pre-St. Peter unconformity ...... 22

Tables:

1. Composition of selected samples of the st. Peter Sandstone ...... 9 2. Grain size data for selected samples of the st. Peter Sandstone ...... 10 3. Grain roundness estimates using the Rho scale ...... 13

Plates:

1. Structure contour map of the pre-St. Peter Sandstone eros ion surface...... ins ide back cover

2. Paleogeologic map of the pre-St. Peter Sandstone surface ...... inside back cover Thickness map of the St. Peter Sandstone

v

PREFACE

The St. Peter Formation is an important aquifer as well as a source of high­ purity silica sand in southern and eastern Wisconsin. This report summarizes the first of a series of studies planned to investigate the stratigraphy and geometry of the Cambrian and Ordovician rocks in the subsurface of Wisconsin. These rocks are the source of much of the water supply for the urban and rural communities of southeast Wisconsin, and the abundance of samples collected during construction of private and municipal wells makes such studies possible. An understanding of the thickness, depth, variability and composition of these water-bearing forma­ tions is essential to protect and manage our deep groundwater resource.

Dr. Meredith E. Ostrom Director and State Geologist

vii A Subsurface Study of the St. Peter Sandstone In Southern and Eastern Wisconsin

by 2 Huazhao Mai1and R. H. Dott, lr.

ABSTRACT The St. Peter Sandstone (or Formation) was deposited upon an exten­ sive erosion surface developed on older A subsurface study of the St. Peter Ordovician, Cambrian, and (locally) Sandstone in southern and eastern even Precambrian rocks. Drainage Wisconsin has been undertaken using patterns can be recognized from the water well samples and sample logs and structure contour map. The purity and one core. A thickness map of the St. texture of the sands tone a ttes t to a Peter Sandstone, a structure contour long history of abrasion and sorting map of the pre-S t. Peter surface, and a prior to deposi tion. There is li ttle paleogeologic map of the pre-St. Peter doubt that much of its character was surface have been constructed. Regional inheri ted by recycling of Cambrian distribution and thickness patterns, sandstones during the pre-St. Peter source of sand, tectonic implications erosional episode. Sedimentological as well as sedimentation of the St. studies have shown tha t much of the Peter Sands tone are discussed in the St. Peter in Wisconsin was depo­ text. This inves tiga tion provides a sited by eolian processes, but marine more complete picture of the subsurface transgression from the sou thwes t also geology of the St. Peter Sands tone in produced a marine facies, which is best Wisconsin than has ever been shown developed in western Wisconsin and at before. The information therefore the top of the formation farther east­ should be helpful to government ward. Both the paleo-drainage and agencies, industry, educators and the paleogeologic patterns indicate that general public, especially because the the so-called Wisconsin arch was not St. Peter is a potential aquifer and influential at this time. Instead a source of pure silica sand. It also is pre-St. Peter domal area lay beneath important as a possible avenue for the eastern Wisconsin and pre-St. Peter migra tion of toxic was tes. drainage was entirely eastward.

The Research Center of Petroleum Geology, Box 916, Wuxi, Jiangsu, China

2 Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706

1 INTRODUCTION a) thickness variations, b) configura­ tion of the basal unconformity, and c) paleogeology beneath the unconfor- In Wisconsin the St. Peter Sandstone mi ty. A fuller knowledge of these or Formation crops out along the flanks aspec ts should complement recen t of the Wisconsin arch in an arcua te detailed sedimentologic studies of belt (Fig. 1). Along the west flank, surface exposures (e. g. Mazzullo and the sandstone is more dissected, Ehrlich, 1983, Winfree, 1983; Winfree forming a belt of outliers, which and Dott, 1983) to provide an under­ includes isolated examples in north­ s tanding of the genesis of one of the western Wisconsin (St. Croix and Pierce world ' s mos t famous sands tones. Such Counties) that were not studied. The knowledge also should have considerable St. Peter Sands tone is found in the economic importance. subsurface throughout eastern and southern Wisconsin. The subsur face The Middle Ordovician St. Peter extent occupies more than three-fourths Sandstone is a classic cratonic super­ of the total area of distribution of rna ture quartz arenite composed of the St. Peter in the state. Therefore remarkably uniform and very pure, a subsurface analysis of the Sandstone rounded, well-sorted, coarse- to fine­ was undertaken primarily to establish: grained sand. The sandstone constitu-

DISTRIBUTION OF ST. PETER SANDSTONE

Outcrop

Subsurface

Probable former extent

o 100 200 Km I ! r' o 100 MI

Figure 1. Distribution of the St. Peter Sandstone

2 tes an extensive and continuous sheet central Wisconsin provided lithologic of clastic rocks overlying a widespread data comparable to that available in unconformi ty and occupying much of the outcrops. It is unfortunate that no cen tral part of the Uni ted S ta tes other cores were available. Some out­ (Fig. 1). The exceptionally widespread crops were studied to correlate the sub-St. Peter unconformity defines the surface and subsurface information. A base of the Tippecanoe stratigraphic search of the Ii terature (including a sequence of Sloss (1963). Although few gamma ray logs for the Michigan the St. Pe ter Sands tone has long been Basin) provided additional data. studied in Wisconsin, few geologists Plates 1 and 2 are the principal re-­ have availed themselves of subsurface suIts of the subsurface analysis. information available from many graphic logs prepared from detailed study of water well drill cuttings contained in the files of the Wisconsin Geological and Natural History Survey. The STRA TIGRAPHY synthesis of this vast data bank would provide much informa tion on subsurface stratigraphy and structure as well as Name and Age the tectonic history of Wisconsin and adjacent states. St. Peter is the name applied by Owen (1847, p. 170) to the sandstone The purity of the St. Peter exposed in Minneapolis and St. Paul, Sandstone makes it a sand resource for Minnesota, along the "St. Peter River", glass manufacture, abrasives, and which is now called ''Minnesota River". foundry molding. Its porosity and per­ The type section is in a bluff where meability make it a potential ground the Minnesota joins the Mississippi water and petroleum reservoir. The River at Fort Snelling in Minneapolis. St. Peter is quarried extensively for silica sand and is a major aquifer in Generally the St. Peter is non­ Illinois (lHllman et al., 1975, pp. 62- fossiliferous, except for local "worm 63); it has been similarly exploited to borings" (Skoli thos) in wes tern a lesser degree in Iowa, Minneso ta and Wisconsin and throughout southeastern Wisconsin. The St. Peter could be }Iinnesota and northern Illinois important to toxic waste movement in (Fig. 2). Sardeson (1896, pp. 70-79) the subsurfaces. described a few - species of fossils, including pelecypods, gastropods, cephalopods, brachiopods, bryozoans and METHODS OF STUDY sponges, from several horizons below the top of the formation at St. Paul, Minnesota. He also reported fossils The major sources of data were from t.'1e top of the St. Peter (probably three types of logs. These were pri­ the Glenwood Member) at Dodgeville, marily water well sample logs, some Wisconsin. Fossils have also been water well drillers' logs, and one found in sandstone considered to be core. Cuttings from selected wells St. Peter at Kentland, Indiana (Shrock were studied to gain understanding of and Mallot, 1933, p. 351). Middle the general lithology, especially Ordovician Chazyan conodonts are variations of grain size. Any apparent reported from shales in cores at St. anomalies of forma tion iden tif ica tion Paul, northwestern Iowa, and eastern on the logs were checked by examining Nebraska (Witzke, 1980) and cu ttings. A single core of the entire Blackriveran ones from the Glenwood formation from near Sheboygan in east- Member in southwestern Wisconsin

3 Figure 2. Examples of Skolithos trace fossils in the St. Peter Sandstone. A. Clear Skolithos tubes at many levels at the eastern end of S tarved Rock State Park, Illinois. B. Subtle weathered tubes in a roadcut 1.2 miles north of Pine Bluff, Wisconsin on County Highway P approximately 12 miles west of Madison.

(Clark, 1971). In Iowa and Nebraska, conglomeratic mixture of chert, shale brachiopods have also been found in and sandstone at the base, a clean, dark shales (Witzke, 1980). The exact friable sands tone in the middle, and a age span of the St. Peter Sandstone is sha1y and dolomitic sandstone and shale unclear, but the span of the Simpson at the top. The basal conglomerate was Group of Oklahoma, at least part of assigned the name Kress Member by which is considered correlative with Buschbach (1964, p. 51). Because the the S t. Peter, ranges from possible type section of the Kress Member is Early Ordovician (Beekmantownian) represented only by samples from a well through Middle Ordovician (B1ackriveran) in northern I111nois ra ther than from and is alleged to become progressively an outcrop, Ostrom (1967) renamed the younger northward (Dapples, 1955, basal conglomerate the Readstown Member p. 445). But the McLish Formation in for exposures in the vicini ty of the Simpson Group, which is considered Readstown, Wisconsin (Fig. 3). The by some to be the principle equivalent Reads town Member is very irregular in of the St. Peter, is only Chazyan. occurrence, but is easily identified in Therefore, Witzke (1980) has suggested well cuttings as well as outcrops. It that the St. Peter is mostly Chazyan may rest unconformably upon any of the and (a t the top) B1ackriveran in the underlying older formations (Pl. upper midwes t . I-Cross Section AA', BB', CC ' , DO'; Pl. 2 ). Thickness of the Reads town Member Stratigraphic Subdivisions can vary grea tly, depending upon pos i­ tion along the irregular pre-S t. Peter erosion surface. Its maximum thickness In Wisconsin the St. Peter is 275 feet in well Iw-ll in Iowa Sandstone or Formation consists of a County, where the entire formation is

4 System series Group Formation Member

Neda Cincinnatian Maauoketa Galena Sinnipee Decorah Champlainian Platteville Henne in Ancell Group Glenwood Harmony Hi 11 in st- Peter Nokomis Ordovician Illinois Tonti Readstown Shakopee Willow River Prairie New Richmond Canadian du Chien Oneota

Coon Vallev Sunset Point Jordan Van Oser Trempealeau Norwalk St- Lawrence Black Lodi Earth Cambrian St. Croixan Tunnel City Lone Rock Reno < Mazom~ Tomah Birkmose Wonewoc f- ,Ironton dalesville------Bonneterre Elk Mound 'au Claire Mt. Simon

Figure 3. Generalized stratigraphic column of Paleozoic rocks in Wisconsin (modified after Ostrom, 1978). abnormally thick (PI. I-Cross Section sands tone, commonly wi th fros ted CC'). The Readstown Member consists of grains, poorly cemented by dolomite, white to red sandstone, conglomerate and is whi te, red or yellow in color. (consisting of fragments of shale, Commonly the Tonti Member contains thin chert, sands tone and dolomi te), brown layers of pale green shale. to red shale, or any comb ina tion, all in a rna trix of fine to coarse sand or The Tonti is overlain by the clay. Glenwood Member, which consists of dolomitic poorly sorted sandstone, blue Pure, fine-to-coarse quartz sand­ green shale or a sandy dolomi te, gray stone in the middle was named the Tonti to light gray in color. The name Formation by Templeton and Willman Glenwood was introduced by Calvin (1963, p. 45), but was designated a (1906, pp. 60-61) for a 15 foot-thick member of the St. Peter Forma tion in sec tion of shale and sands tone exposed Wisconsin by Ostrom (1967). The Tonti in Glenwood Township, Winneshiek Member conformably overlies the County, northeastern Iowa. The Readstown Member, but, where the latter Glenwood was designated a separate is absent, sandstones of the Tonti formation by Templeton and Willman overlap it to rest directly upon any (1963, p. 48), but it is considered by of the underlying older forma tions the Wisconsin Geological and Na tural (PI. I-Cross Sec tion AA', CC'). In His tory Survey to be a member {)f the Wisconsin the Tonti generally forms the St. Peter. It was subdivided into the greater part or the entirety of the St. Nokomis, Harmony Hill and Hennepin Peter Sandstone. The Tonti is commonly (Fig. 3) (Templeton and Willman, 1963; 100-150 feet thick, but locally exceeds Ostrom, 1967), but these were not 260 feet. The Tonti Member is chiefly distinguished in the present study. fine-to medium-grained, well-sorted The Glenw{)od is absent in some areas,

5 such as over the Wisconsin arch, but is where sandy facies grade eas tward to distinguishable in most wells in other carbonate ones (Fig. 1) (Dapples, 1955; areas. It may be the only unit present Sloss and others, 1960, pp. 6-7; Droste in northeastern Wisconsin, where it and others, 1982, p. 6; Bricker and occurs as a very sandy dolomi te (Pl. others, 1983, pp. 6-9). The stra- I-Cross Section BB'). tigraphically equivalent Simpson Sands tone of Oklahoma grades sou thward Templeton and Willman (1963, p. 29) into shaly sandstone, shale and sandy proposed the name "Ancell Group" to limestone (Dapples, 1955, p. 446). The replace "s t. Peter Sands tone". The St. Peter's western margin, which is name was taken from Ancell in south­ erosional, is found in Nebraska, eastern Missouri, where quartz sand­ Kansas, and Minnesota (Fig. 1), but stone is intimately associated with similar Ordovician pure quartz sand­ argillaceous and sandy carbona te rocks stones also occur widely on the western (Du tch town and Joachim Forma tions) , side of the transcontinental arch from which overlie the Everton Dolomi te and Colorado to Manitoba (e.g. Harding, underlie the Platteville Group. In Winnipeg, etc.; summarized in Witzke, northern Illinois the Ancell Group 1980). The northern margin also has includes all strata previously referred been completely modified by erosion, to the St. Peter and Glenwood. The new but there are a few outliers of fossi­ group name apparently was proposed to liferous Middle Ordovician quartz encompass significant regional facies sandstone in the southern Canadian variations, which pose serious stra­ shield (Fig. 1). tigraphic problems in the subsurface of Indiana, Illinois and Iowa. In the The St. Peter mus t have once upper midwest, however, the name Ancell extended many miles farther toward the offers no advantage, so the original north and west according to the charac­ name St. Peter has persisted and is teris tics of the forma tion as seen in used in this study. the most northern outcrops of Wisconsin and Minnesota (Thiel, 1935, p. 352) as Regional Distribution well as along its wes tern subsurface limit. Thus even the impressive pre­ and Thickness Patterns served extent of the St. Peter and its correIa tive sands tones unders ta tes the Areal dis tri bu tion and stra- original vas tness of this exceptional tigraphic rela tionships of the St. clas tic forma tion. Peter Sands tone indica te that it con- sists of an extensive and continuous sheet of clastic sediment covering STRATIGRAPHIC PATTERNS large areas in Wisconsin, Minnesota, Illinois, Iowa, Missouri, and Arkansas WITHIN WISCONSIN (Fig. 1). Except for local thickening in Wisconsin (PI. 2 ) and Illinois, the St. Peter Sandstone is very uniform Overlying and Underlying Strata and shows no regular changes in thick­ ness in the upper midwes t, where it The St. Peter Sandstone is overlain averages 100-200 feet. But the thick­ conformably by carbona te rocks of the ness of the clastic sheet increases Sinnipee Group, specifically limestone progressively into southern Oklahoma or dolomite of the Platteville (the equivalent Simpson Sandstone). Formation. The St. Peter - Platteville Apparently the eas tern depositional contact is sharp both in outcrops and edge of sandstone passes through in the subsurface. In southwestern central Michigan, Indiana and Kentucky, Wisconsin - as in adjacent Iowa and

6 Illinois - the Glenwood tends to com­ feet within a distance of only 1,000 prise several feet of green shale with feet. variable proportions of quartz sand. Farther east it is characterized by The morphology of the pre-St. Peter intensely bioturba ted calcareous sand­ surface (Pl. 1, 2) suggests that both s tone and sandy dolomite. Its thick­ stream drainage patterns and karst ness varies from 0 to 60 fee t, bu t no topography were developed. As both obvious pattern of variation is evident Buschbach (1961) and Thwaites (1961) (Pl. I-cross sections). have argued, the surface could not be the resul t simply of pos t-depositional The famous basal unconformity solution and compaction as was everywhere separates St. Peter strata suggested by Flint (1956). from older ones. In much of the area studied, the St. Peter overlies the Comparison of the 3 maps and the Lower Ordovician Prairie du Chien cross sections shows that in the vici­ Group, which is dominated by cherty nity of Beaver Dam, Watertown, and dolomite (Pl. 1, 2). In many areas, Dodgeville cities, abnormally thick however, pre-St. Peter solution and/or sections of 150-400 feet of St. Peter erosion removed Prairie du Chien strata Sands tone can be traced among several to expose various Cambrian and, locally, wells as continuous channel fillings even Precambrian rocks (Pl. 1, 2). (Pl. 2). They coincide well with the pre-St. Peter topography (Pl. 1) as well as the occurrence of older rocks The Unconformity Surface exposed by erosion on the pre-St. Peter surface (Pl. 2). In Beaver Dam, such an ancient channel lies directly along The thickness· of the St. Peter the northwest flank of a paleotopo­ Sandstone ranges from 0 to about 400 graphic high of Precambrian rock (Pl. feet in Wisconsin (Pl. 2). The top 1, 2). The channel gradient is from of the St. Peter Sandstone is so flat southwest to northeast. The bottom of tha t the varia tion of more than 200 the channel reaches Upper Cambrian feet in thickness in less than 1 mile Trempealeauan strata (Pl. 1, 2). In clearly reflects the very irregular Watertown and Milwaukee, a valley pre-S t. Peter erosional surface (Pl. 1, descends in a sou theas terly direc tion. 2). I t has been complica ted by pos t-S t. Peter faulting (PI. 1, 2). Southwest On the regional scale of the entire of Dodgeville, a channel reaches Tunnel study area, the maximum relief of the City strata and contains the thickest pre-St. Peter surface is 1700 feet in section of St. Peter in the entire map eastern Wisconsin and 900 feet in area. It flowed toward the south and southern Wisconsin. The surface pre­ can be traced into northern Illinois as sently dips toward the east about 25 a tributary to a more easterly-trending feet per mile in eastern Wisconsin and channel with over 300 feet of St. Peter toward the south or southwest about 18- (Fig. 4). Also another tributary of 20 feet per mile in southern Wisconsin. this valley seems to underlie the On the scale of a few townships, the Mississippi River in southwestern maximum relief is 300-400 feet (Pl. 1). Wisconsin (Pl. 1). Contours also Variation is appreciable even on a indicate smaller, somewhat branching local scale. For example in the Pine channel patterns in the southeastern Bluff area 10 miles wes t of Madison, corner of Wisconsin (Pl. 1). maximum relief is 120 feet wi thin only 1.3 miles horizontally and the total Karst topography is strongly thickness varies from 20 feet to 140 suggested on parts of the pre-St. Peter

7 REGIONAL THICKNESS PATTERNS ~J(/OFTHE~T. PETER SANDSTONE Co"'\"'~'

'______S.P. Outlier""'0

,./

0 100 200 Km / 11--,.'-'-..",-1' ------,<5 0 100 Mi \

Figure 4. Thiekness of the Aneell Group (ineluding St. Peter Sandstone) in the northern midwest region. Thieknesses outside of Wiseonsin are modified after Dapples, 1955; Willman and others, 1975; Droste and others, 1982; and Brieker and others, 1983.

surfaee by isolated eireular areas with Member with ehert and dolomitie anomalous thiekness. Examples oeeur in fragments. Busehbaeh (1961) reeognized Dodgeville, Monroe and southeast of probable pre-St. Peter karst topography Darlington, and northwest of Green Bay on earbonate roeks in the subsurfaee of (PI. 1, 2), whieh are eons trained by northern Illinois. Where the St. Peter elosely spaeed wells. Probably many overlies Cambrian elastie roeks, more exist than eould be deteeted. however, he inferred stream-ehannel Prairie du Chien earbonate roeks topography. A similar dual origin for generally underlie the St. Peter the pre-S t. Peter surfaee is indiea ted Sands tone along the flank of the in Wiseonsin. Wiseonsin areh. Apparently these ear­ bonate roeks were subjeet to solution The paleogeologie or suberop map of by ground water in a humid, tropieal the pre-St. Peter surfaee in Wiseonsin Ordovieian elimate, whieh would also (Pl. 2) shows an eroded domalfeature aeeount for the elays of the Readstown in the vieinity of Milwaukee, whieh has

8 TABLE 1. Composition of selected samples of the St. Peter Sandstone (volume percent).

Thin Mono- Other Other Quartz C03 Other Pores Total % Section crystalline quartz grains Dver- cement cement (No. No. quartz growth. grains)

SP1219 78.8 0.6 --- 1.2 2.3 0.2 16.9 100 Sheboygan (iron) (n-485) Core SP1222 86 1.8 0.5 --- 0.2 --- 11.4 99.9 (n-437) SP1287 77 .8 0.2 --- 0.9 0.9 0.2 19.9 99.9 (iron) (n-423)

84-1SP 83.9 ------16.2 100.1 , (n-421) B4-2SP 82.5 0.4 ------17.1 100 (n-468) 84-3SP 74 ------26 100 (n-416 Pine Bluff P-7SP 69.1 -- -- 2.1 --- 1.5 27.4 100.1 Area (iron) (n-475) P-9SP 70.1 0.6 -- 1.3 13.2 --- 14.7 99.9 (n-469) SP-30 78.5 ------0.5 - --- 21 100 (n-442) SP-3L 70.3 ------0.2 --- 3.3 26.1 99.9 (clay (n-421) mineral) SP-5 73.8 ------0.2 --- 8.B 17 .1 99.9 ( iron) (n-432) Monticello 82-2ASP 78 ------0.9 --- 2.4 18.6 99.9 (feldspar (n-424) Argyle 84-5SP 75.2 0.7 --- 4.6 -- --- 19.5 100 .., (n-415) --- TABLE 2. Grain size data for selected samples of the St. Peter Sandstone. (See Table I for locations)

Thin sec tion Mean size Median size (mm) Sorting W No. (mm) (;:s)

SP1219 0.38 0.41 0.53

SP1222 0.28 0.27 0.71

SP1287 0.28 0.28 0.6

84-1SP 0.26 0.25 0.49

84-2SP 0.22 0.25 0.50

84-3SP 0.27 0.25 0.6

P-7-SP 0.21 0.21 0.47

P-9-SP 0.23 0.23 0.57

SP-30 0.41 0.44 0.67

SP-3L 0.35 0.34 0.71

SP-5 0.33 0.31 0.63

82-2ASP 0.26 0.25 0.6

84-5SP 0.55 0.57 0.61

been noted before by Ostrom (1970, zite and granite were exposed on the p. 32). This dome-like feature shows northwest flank of the dome rather than oldes t Cambrian s tra ta (M t. Simon at its center. Apparently this is Forma tion) in its center wi th younger merely one of several irregularly Cambrian formations concentrically distributed hills of Precambrian rocks distributed around the core in a west­ whose distribution bears little rela­ ward direction. The eas tern side of tion to early Paleozoic structural the dome is unknown because it lies features. Other patterns on the paleo­ beneath Lake Michigan. The dome was geologic map more directly reflect the eroded extensively during pre-St. Peter topography of the unconformi ty surface time because the St. Peter directly with areas of Cambrian rocks simply overlies the much older Mt. Simon occupying the deepest ancient valley Formation at its center. A curious floors (as in southwestern Wisconsin oval-shaped area of Precambrian quart- especially) •

10 SEDIMENTATION statistically significant difference between the mean sizes for 19 samples OF THE ST. PETER SANDSTONE each of eolian (0.22 mm) and marine (0.26 mm) sandstones. Coarse sand Composition occurs both as: 1. scattered grains making a bimodal texture, 2. very thin laminae, and 3. in small ripple lenses. The St. Peter is a remarkably pure and supermature quartz arenite con­ Dapples (1955, pp. 456-459) showed taining 99 per cent quartz sand grains no trends in regional size distribution with the majority of the remaining and stated that the mean size of the volume being cements (Table 1). The St. Peter and Simpson sands range from heavy mineral suite of the St. Peter coarse to fine. He indicated that the Sandstone makes up less than 1 per cent sands are coarser in Illinois, northern of the total grains wi th zircon, tour­ Missouri and most parts of Kansas. We maline, ilmenite and leucoxene domi­ believe that he showed the sands in nant, and rutile, garnet, anatase, Wisconsin as "too fine" (0.125-0.25 mm). apa ti te, stauroli te, ceyloni te, and pyrite occurring as traces (Tyler, Shale is almost, but not quite, 1936, p. 55). completely lacking in the St. Peter Sandstone, but increases to the south­ The St. Peter is generally very west into the Simpson Group (in poorly cemented by authigenic cementing Oklahoma) as though currents winnowed ma terials. Quartz overgrowths and carried mos t clay to the sou them ("cement") are widespread and carbonate edge of the craton (Dapples, 1955). cements are locally abundant. Feldspar occurs especially at the base of the The St. Peter Sandstone is well to St. Peter, and has been considered to very well sorted (Table 2 & Fig. 5). be syngenetic sanidine (Woodard, 1972) The standard deviations of size distri­ or simply diagenetic K-feldspar (Odom, butions in Wisconsin are generally 1974; Odom and others, 1979). Iron about 0.60 (Table 2). Dapples (1965, cements are locally abundant, and have pp. 456-459) showed no significant produced bright red, yellow and brown trend in sorting in the St. Peter, and colors. The origin and timing of these supposed tha t the sorting is uniformly latter cements are not clear, but some good throughout. Winfree (1983, probably represent oxidized pyri te or pp. 104-107) found no difference bet­ marcasi te because these sulphides are ween the eolian and marine sets of known to occur in the subsurface. Clay standard deviations. Indeed, size­ and feldspar cemen ts are presen t bu t distribution statistics have proven rare. undiagnostic for determining process or environment in either the St. Peter or similar older Cambrian sandstones. Texture The St. Peter is noted for its The size of St. Peter sands is grain roundness (Fig. 5). In general, generally characterized in mos t of the rounding decreases with decreasing literature as fine sand, but there is a grain size, as is to be expected (Table lot of medium and even some coarse sand 3), but even the finer sand grains in the forma tion, especially in tend to be better rounded in the St. Wisconsin (Table 2). The overall Peter than in most sandstones (Fig. 6). average size in Wisconsin falls near the fine/medium boundary (i.e. about Poros! ty for the samples analyzed 0.25-0.35 mm). Winfree (1983) found a in this study varies from 11% to 27%

11 Figure 5. Scanning electron microphotograph of well-rounded St. Peter Sandstone quartz grains. A. Marine grains (lOOx); B. Eolian grains (70x). Note that there is no obvious difference of rounding. (From Winfree, 1983).

(Table 1). A more extensive study by cluded that grain-surface textures do Hoholick and others (1984) shows tha t not differ significantly for the eolian porosi ty in the St. Peter varies from and aqueous strata (as established nearly 40% at the surface to nearly independently by sedimentary structures zero percent at a depth of 8,000 feet and trace fossils). The only exception in the Illinois Basin. may be a sligh tly grea ter abundance of dish-shaped concavities on eolian grains (Fig. 7). Grain-Surface Textures and Overgrowths Diagenesis Most of the grains of the St. Peter are fros ted, which was no ted long ago The St. Peter Sands tone has had a and attributed to wind abrasion. Now complex diagenetic history charac­ the fros ting of sand is generally con­ terized by several episodes of cemen­ s idered to be the resul t of chemical ta tion and dissolu tion. Quartz over­ etching (Shepard and Young, 1961, grow ths tend to be earliest, followed pp. 196-214; Kuenen, 1960, pp. 94-113; by carbonate and iron cements. Quartz Kuenen and Perdok, 1962, pp. 648-658). cement occurs at all depths, chert and chalcedony are present locally near the Wi th the scanning elec tron surface, calcite predominates at inter­ microscope Mazzullo and Ehrlich (1983) mediate depths, and dolomite and local and also Winfree (1983, pp. 87-103) anhydri te occur in the deepes t part of found upturned or broken cleavage the Illinois basin (Hoholick and others, pIa tes and dish-shaped concavi ties to 1984). In the silts and clay-size be abundant on some grains that they fractions, K-feldspar, illite, smectite regard as eolian (Fig. 7). They also and chlorite are present; kaolinite has found extensive diagenetic overgrowths, also formed where fresh water has which inhibit the interpretation of invaded (Odom, and others, 1979). origin from grain-surface textures Primary porosl ty is said to predomina te (Fig. 8) . In general, Winfree con- down to a depth of 4,000 feet; it

12 TABLE 3. Grain roundness estimates using the Rho scale (0-6) - percentage of grains in each Rho class. (See Table I for locations).

Thin sec tion Sub-angular Sub-rounded Rounded Well-rounded Total % Mean size No. (2-3) (3-4) (4-5) (5-6) (No. grains) (mm)

SP1219 2.3 26.9 43.5 27.3 100 0.38 (n=216) SP1222 21.8 42.7 27.7 7.8 100 0.28 (n-206) SP1287 --- 19.4 46.3 34.4 100.1 0.28 (n=227) 84-1SP 0.3 13.5 42.6 43.6 100 0.26 (n-289) 84-2SP 0.9 16.7 45.1 37.2 99.9 0.22 (n=215) 84-3SP 0.5 9.3 55.6 34.6 100 0.27 (n-214) P-7SP 3.0 39.1 49.8 8.1 100 0.21 (n-235) P-9SP 4.7 45.6 47.4 2.3 100 0.23 (n-215) SP-30 --- 3.9 41.1 55 100 0.41 (n=231) I SP-3L --- 4.1 40.7 55.2 100 0.35 I (n-221) SP-5 0.5 5.5 57.1 36.9 100 0.33 (n-217) 82-2ASP --- 15.6 59 25.4 100 0.26 (n-20S) 84-SSP ------15.1 84.9 100 0.55 (n-212) ,.... '" Figure 6. Microphotograph of a thin section of the St. Peter Sandstone from Pine Bluff (12 miles west of Madison) showing a bimodal size distribution (Crossed Nicols; lOx).

Figure 7. SEM photograph of an eolian quartz grain with a dish-shaped concavity with broken cleavage pIa tes to the left (200x). (From Winfree, 1983). ranges from 10 to 40%. Much of this, vadose zone. Secondary porosity domi­ however, is probably due to solution of nates from depths of 4,000 to 8,000 cements, especially carbonate, so would feet but is mostly less than 10%; it not be strictly primary. Winfree has resulted from the leaching of both recognized meniscus cements with the grains and cements (Hoholick, and SEM, which would have formed in the others, 1984).

14 A

B Figure 8. SEM photographs of quartz grains with diagenetic coatings. A. Euhedral syntaxial quartz overgrowth (300x). B. Rhombic carbonate and hexagonal platy layered silicate (lower left) (7000x). (Both from Winfree, 1983). So urce of Sand based upon inclusions in quartz. The immediate source was a sedimentary Tyler (1 936) stated that the ulti­ terrane, however. Apparently St. Peter mate source of the St. Peter sands was sand was recycled from Cambrian sand­ largely a plu tonic (grani tic) terrane, s tones during pre-S t. Peter erosion,

15 ST. PETER (TONTI) PALEOGEOGRAPHY

______S.P. Outlier~o

Large·scale croSS· bedded facies present /' Mean cross bedding orientation

o 100 200, Km I i o 100 Mi ,',.", .

Figure 9. Facies and paleogeography for Tonti deposition in the upper midwest (modified after Dapples, 1955). Inset map: E is the Ordovician equator and W locates Wisconsin.

for most of the sands of the Wonewoc sou thwes tern Wisconsin. Seemingly the and Jordan Formations are as mature as source of sand lay somewhere to the those of the St. Peter. north of southern Wisconsin (Fig. 9). Dapples (1955) postulated northeast to southwest dispersal on the basis of Depositional Processes regional facies (i.e. more shaly to the and Environments southwest in Oklahoma where the Simpson Group is located). The grada tion to The problem of deposition of the marine carbonate facies toward the east St. Peter Sands tone bas been deba ted precludes a source in tha t direction. for more than a hundred years. Early Potter and Pryor (1961) reported a mean in the present century, authors favored cross bedding dip direction toward the an eolian environment by noting the southwest in Illinois, and Dott and dominant fine grain size, excellent Roshardt (1972) showed dispersal toward sorting, rounding and frosting as well the west from cross bedding orien­ as its craton-wide extent (e.g. Berkey, tations in dominantly eolian facies in 1906; Grabau, 1913), while other

16 authors argued for a marine origin of stratification suggestive of eolian based upon reports of fossils and deposition for some of the St. Peter burrows (e.g. Dake, 1921; Dapples, southwest of Madison. Meanwhile, trace 1955). Many workers have envisioned fossils, chiefly Skoli thos, also were the sand as fluvial and eolian origi­ recognized by Dott, Byers and Winfree nally with final reworking by trans­ in other places. Winfree (1983) found gressive marine processes. Dake them widely from Starved Rock, emphasized that textural features could Illinois, throughout western Wisconsin, be inherited from one cycle to another. to southeast Minnesota (Fig. 2). In This seems clearly to be the case for Ordovician stra ta, these are taken as the exceptional rounding of medium and proof of a marine origin for sandstones coarse grains in both the St. Peter and containing them. Meanwhile, Mazzullo underlying Cambrian sandstones. A long and Ehrlich ( 1983) proposed both history of wind abrasion (Kuenen, 1960) aqueous and eolian contributions in is implied even for some of those Minnesota based upon microscopic sandstones that contain marine fossils. studies of grain shape and surface textures. I t is an interes ting bi t of Large cross-beds in sets as much as irony that the St. Peter Sandstone is 30 feet thick were found in the St. now seen to be bo th eolian and marine. Peter Sandstone in Wisconsin by Pryor Winfree (1983) and Winfree and Dott and Amaral (1971). They, and also Dott (1983) described both an eolian and and Roshardt (1972), interpreted these a marine facies in sou thwes tern as marine and probably of tidal origin. Wisconsin, and indicated that part of Such large-scale cross bedding is more the eolian facies was reworked during typical of eolian dunes, however, and the Tippecanoe transgress ion as adhesion structures (Reineck, 1959; several earlier workers proposed but Hunter, 1973) were discovered near could not actually prove. Madison by Dott and Byers in 1980. In 1981 Dott found them also in the very Hunter's (1977, pp. 361-387) stra­ large-scale cross sets at Monticello, tifica tion types together with adhesion which were illustrated by Pryor and s truc tures (Reineck, 1959; Hunter, Amaral as well as Dott and Roshardt. Subsequently Winfree (1983) discovered several other locali ties with adhesion pseudo-cross lamination and other types

Figure 10. Adhesian-ripple structures in the St. Peter Sandstone: A. Oblique view showing pseudo-crosslaminae dipping toward the right (roadcut on County Highway J, 1.8 miles southeast of Pine Bluff, Wisconsin); B. Plan view showing characteristic irregularly rippled surface (locality uncertain; specimen is 12 cm long). Wind was from the lef t in bo th cases.

17 1973) are the most convincing evidence Chien Group, the Early Ordovician for an eolian origin. Adhesion pseudo­ epeiric sea withdrew and recently­ cross lamina tion is formed by depos i­ deposited rocks were eroded throughout tion of saltating dry sands, which the area. More than 400 feet of strata adhere to a water-saturated sandy were removed in some loca tions to surface. The adhesion ripples so expose units as old as the Mt. Simon {ormed aggrade and migrate up wind if and even Precambrian rocks (PI. 1, 2). the sand supply persists. This produ­ The magni tude of the relief sugges ts ces a distinctive sort of cross lamina- that the duration of the erosion was tion (Fig. 10). Eolian climbing considerable. During erosion, streams translatent laminae are formed by the cut deep valleys to form stream migration and climbing of wind ripples drainage patterns as noted above. At during tractional deposition. The the same time, solution by ground water laminae are very thin because eolian apparently formed caves and sinkholes ripples are so low in profile (Fig. 11). in carbonate rocks, and finally deve­ Grainflow deposits are formed by non­ loped a mature karst landscape. The cohesive sands avalanching intermit- St. Peter sea advanced over this land­ tently down dune slipfaces. Grain scape, drowning many valleys but irre­ fall laminae are formed by grainfall gularly submerging other areas. Sand deposi tion rela ted to flow separa tion derived from exposed Cambrian sand­ a t a dune cres t, resulting in short stones in Wisconsin, northern Michigan, transport in suspension. Ontario, and probably also northern Minnesota was transported southwestward Bes ides the area sou thwes t of (present coordinates) by eolian and Madison (Winfree, 1983), we think mos t braided fluvial processes (Fig. 9). of the St. Peter in the Sheboygan core The Readstown Member apparently was is eolian because of identifiable deposited during the development of the translatent laminae and a lack of trace valleys and sinkholes by erosion and fossils (Fig. 12). In eastern solution, but the Tonti sands were Wisconsin, impressive large cross-bed, deposi ted long afterward; they simply climbing translatent laminae as well as filled and leveled the irregular land grain fall laminae are well exposed in surface. Finally, the eolian and flu­ the St. Peter Sands tone along a road vial deposits were reworked and/or cut west of a quarry at Ripon, buried by the advancing sea. Either Winnebago County. Those structures can medium-scale trough cross bedding or a also be found in another quarry east of complete lack of discernible stratifi­ Berlin, \Jinnebago County. cation and presence of some recogni­ zable Skoli thos traces characterize the Paleogeographic Setting marine facies.

The regional geome try of the St. The sandstone of the Tonti Member Peter and supermaturity of its grains grades upward into thin dolomi tic, imply a very stable, cratonic landscape shaly sandstone and shale of the with low relief. Moreover, no signifi­ Glenwood Member (Pl. 1), reflecting a cant land vegetation is known for near-cessation of deposition as sug­ pre-Devonian times. ges ted by the abundance of shale and, in sandy phases, of intense biotur­ Probably a eustatic fall of sea bation as well as some phosphatic nodu­ level led to forma don of the basal les and glauconite pellets. Fraser unconformi ty. The varia tion of relief (1976) postulated that the Glenwood carved on the pre-St. Peter strata formed in a large, relatively quiet indicates that, after deposition of the lagoon behind a large sand barrier in carbona te strata of the Prairie du northern Illinois. Transgression

18 Figure 11. Climbing-ripple translatent (eolian ripple) lamination in the St. Peter Sandstone. A. Roadcut on U.S. Highway IS near Blockhouse approximately 3 miles northeast of Dickeyville, Wisconsin. B. Core from Van Driest No. 1 well at Sheboygan, Wisconsin; width of core is 10 em (Sec. 12, T. l3N, R. 22E.).

19 VAN DRIEST NO.1 CORE (SB-86) - SHEBOYGAN COUNTY 12-T13N-R22E

Thin anhydrite layer and SUlphide minerals Dolomitic "wormstone" with snale lenses

Sandy dolomite and bioturbated medium sandstone; some pyrite

Tan medium sandstone with fine lamination mottled

Bimodal quartz sandstone with interstitial pyrite

Bimodal medium and coarse sandstone (grains up to 1 mm) Very thin lamination; carbonate cement Medium sandstone with some coarse grains: some overgrowths. very fine. parallel lamination with some inverse grading (eolian?) Some thin cross bed sets

Very fine (eolian trans latent?) lamination 1 em coarse sandstone

Medium sandstone with very fine (eolian trans latent?) lamination

Bimodal sandstone

Fine parallel and cro~s lamination 1 cm coarse sandstone Medium to coarse sandstone

Cross bedding (laminae 0.1 - 1.0 cm thick)

Dark (clay?) lamina

Cross lamination (aqueous?)

Bimodal medium and coarse sandstone; firmly cemented

1300 Medium sandstone with local fine lamination --= Py Bimodal medium and coarse sandstone

1310 Cross lamination

1320

1330

'-'-'-'- Medium sandstone with faint cross lamination 1340 py. '"

Contorted(?) lamination with pyrite

MediUm sandstone with dark streaks (pyrite?) SUlphide mineral veinlet (galena and sphalerite) Medium sandstone with snaIl cross lamination; quartz overgrowths Medium and coarse sands~one with thin clay streaks Readstown Heterogeneous mixture of OOlitic fragments with sandstone =-;-__~=-I-'0'"i'+-Lenses of white sandstone and dark shale ____ TUNNEL CITY Glauconite sandstone GROUP Figure 12. Lithologic log of the St. Peter Sandstone in the Van Driest No.1, Sheboygan, Wisconsin. (Sec. 12 T. 13N., R. 22E.).

20 apparently had progressed sufficiently Peter - Simpson - Harding - Winnipeg to stop the supply of sand to the mid­ sandstones attest to a very stable west. After an interval of non­ craton. Stable cratons, however, do deposition there, deposition of the show evidence of broad arches and richly-fossiliferous Platteville car­ basins. Always there is a question of bonate sediments began as transgression when such features formed. Was the con tinued to flood the cra ton. The Wisconsin arch, for example, already carbonate facies spread over the craton in existence during St. Peter time? from the southeast (Dapples, 1955). Results from the present study bear Except for local winnowing, there is no upon this issue. evidence of erosion between St. Peter and Platteville deposition in Wisconsin. At present in Wisconsin, the St. Peter dips very slightly eastward and TECTONIC IMPLICATIONS southward. A trial removal of present dip showed no significant change of Supermaturity and blanket geometry direction, so PI. 1 was not corrected (thin bu t very widespread) of the St. for present dip.

~ PRE-ST. PETER VALLEYS f)) (Arrows indicate flow directions) (,[IV \

I S.P. Outlier

~ '" ~o L-, ~ c::i MINNEAPOLlS­ ! (') \ ST. PAUL • I 11)'1; ) Ii VZ, , J ..----1'~ ! \ \ olSheboyg ~\ ) ------~ (Core \/ ( MAD'S\~--}- \ d -~---~ / ( '-'\\) \ .-" ' I ,I '~,,:;-.--;.~:::;;:?~ __ - -- 1- ----'.~

o 100 200 Km

~ 1-1 J _-,....L_-,,-I' \ ------."Y o 100 Mi

Figure 13. Drainage patterns on the pre-St. Peter unconformity surface inferred from plate 1 for Wisconsin and from Willman and others (1975) for northern Illinois.

21 The large channel in northern of Madison, and the St. Peter in the Illinois, tributaries of which are Sheboygan core, Ripon road cut, and evident in the southwestern corner of Berlin quarry appear nonmarine and a Wisconsin, cuts directly across the little coarser-grained than in western extension of the arch into Illinois, Wisconsin. Finally, the dispersal data indicating that there was no topo­ sugges ts deriva tion of the sand from graphic divide there (Fig. 13). The the north with spreading toward the paleogeologic map (Pl. 2 and Fig. 14) southwest right across the Wisconsin shows that the most deeply truncated arch (Fig. 9). ("domal") area beneath the St. Peter is not coincident with the Wisconsin arch, but lies to the east. Only the area of In summary, the lJisconsin arch uppermost Cambrian rocks south of seems not to have had any topographic Madison gives any hint of the arch. influence during Middle Ordovician time. Either, it is chiefly post-St. Facies and dispersal patterns also Peter in origin, or else it had a very bear upon arch history. Nonmarine spasmodic his tory prior to and after facies (Winfree, 1983) lie southwest that time.

PRE-ST. PETER PALEOGEOLOGY

S.P. Outlier ~~~--,.

MI

~Prairie du Chien l:irouPI EJ Upper Most Cambrian brn Elk Mound Group • Precambrian

o 100 200 Km II---.-"L-""'T'...... J' --- o 100 Mi

Figure 14. Regional sub-crop map of the pre-St. Peter unconformity. Adapted from Ostrom (1970), Buschbach (1961), Witzke (1980), and plate 2 of this study.

22 SUMMARY sents an interval of near nondeposition and intense bioturbation of uppermos t Tonti sands prior to Platteville 1. The morphology of the pre-S t. carbona te deposition across the entire Peter surface in Wisconsin reveals that cra ton during the grea tes t epeiric sea normal stream erosion and karst deve­ flood in all of Phanerozoic time. lopment both acted to shape the very irregular pre-St. Peter surface. ACKNOWLEDGEMENTS 2. The charac ter of the pre-S t. Peter surface was controlled mainly by underlying rock type. Erosional This paper is a resul t of research streams flowed on both Cambrian clastic carried out at the Wisconsin Geological and Prairie du Chien carbona te rocks, and Na tural His tory Survey while the but karst evidence is confined to the senior author was a Visiting Scholar latter. from the Peoples Republic of China at the University of Wisconsin, Madison. 3. Today the pre-S t. Peter sur- We are very gratefUl to Dr. M.E. Ostrom face dips 29 feet per mile toward the of the Wisconsin Geological Survey for east in eastern Wisconsin, and about the opportunity to pursue this projec t 18-29 feet per mile toward the south or and invaluable advice throughou t the southwest in southern Wisconsin. The course of the investigation. paleogeology and paleotopography of the Particular thanks are due Dr. Bruce basal unconformity surface, however, Brown of the Wisconsin Geological sugges t that this til ting - and thus Survey for furnishing assistance and the Wisconsin arch - post-date the St. cri tical review. Various aspects of Peter Sandstone. By implication, it geological interpretation also bene­ would also post-date the overlying fitted from discussion with Roger Platteville-Galena strata because they Peters and Kathy Massey. Drafting was are perfectly concordant with the upper done by Michael Czechanskl, John St. Peter. If the arch originated Zuiker, Brenda Haskins-Grahn, and before Middle Ordovician time, it must Deborah Patterson. Other Survey per­ have been structurally inactive during sonnel also helped conSiderably with the Middle Ordovician, for it did not the analysis of samples. produce a topographic divide. We have drawn extensively from the recent MS thesis of Keith Winfree, and 4. The St. Peter was deposited all of the SEM photos of sand grains in a variety of nonmarine and marine were taken by Winfree. The work of environments. Residual deposits of the Winfree and some of our subsequent Reads town Member probably formed more research was supported in part by or less contemporaneously with erosion Na tiona 1 Science Foundation Grants No. and karst formation. Sands of the EAR-8107729 and EAR-8312873. Tonti Member were dispersed across the central craton by fluvial and eolian processes on a vegetation-free land­ scape; they filled valleys and sink­ holes to level the landscape. Marine transgression reworked these sands to varying degrees - completely in western Wisconsin, and southeastern Minnesota, partially in south-central Wisconsin, and possibly not at all in eastern Wisconsin. The Glenwood Member repre-

23 REFERENCES CITED

Berkey, C. P., 1906, Paleogeography of St. Peter Time: Geol. Soc. Am. Bull., v. 17, pp. 229-250.

Bricker, D. M., Milstein, R. L., and Reszaka, C. R., Jr., 1983, Selected Studies of Cambro-Ordovician sediment within the Michigan Basin: Mich. Geol. Survey Rept. Inv. 26, Part I, 54 p.

Buschbach, T. C., 1961, The Morphology of the St. Peter surface of northeastern Illinois: Transactions of Ill. State Acad. Sci., v. 54, Nos. 1 and 2, pp. 83-89.

Buschbach, T. C., 1964, Cambrian and Ordovician strata of northeastern Illinois: Ill. State Geol. Survey Rept. Inv. 218, 90 p.

Calvin, Samuel, 1906, Geology of Winneshiek County, Iowa: Iowa Geol. Survey Ann. Rept., v. 16, pp. 60-61.

Clark, D. L. (editor), 1971, Conodonts and biostratigraphy of the Wisconsin Paleozoic: Information Circular No. 19, Wis. Geol. and Nat. History Survey, 151 p.

Dake, C. L., 1921, The problem of the St. Peter sandstone: Bull. Missouri Univ. Sch. Mines and Met., Tech. Ser., v. 6, 228 p.

Dapples, E. C., 1955, General lithofacies relationship of St. Peter Sandstone and Simpson Group: Am. Assoc. Petroleum Geologists Bull., v. 39, No.4, pp. 444-467.

Dott, R. H., Jr., and Roshardt, M. A., 1972, Analysis of cross-stratification orientation in the St. Peter Sandstone in southwestern Wisconsin: Geo!. Soc. Am. Bull., v. 83, pp. 2589-2596.

Droste, J. B., Abdulkareem, T. F., and Patton, J. B., 1982, Stratigraphy of the Ancell and Black River Groups (Ordovician) in Indiana: Indiana Geol. Survey Occasional Paper 36, 15 p.

Flint, A. E., 1956, Stratigraphic relations of the Shakopee Dolomite and the St. Peter Sandstone in southwestern Wisconsin: Jour. Geol., v. 64, p. 396-421.

Fraser, G. S., 1976, Sedimentology of a Middle Ordovician quartz areni te­ carbonate transition in the upper Mississippi Valley: Geol. Soc. Am. Bull., v. 86, pp. 833-845.

Grabau, A. W., 1913, Principl~s of stratigraphy: New York, A. G. Seiler and Company, 1189 p.

Grether, W. J. and Clark, D. L., 1980, Conodonts and stratigraphic relationships of the Readstown Member of the St. Peter Sandstone in Wisconsin: Geoscience Wisconsin, v. 4, p. 1-24.

24 Hoholick, J. D., Metarko, T., and Potter, P. E., 1984, Regional variations of porosity and cement: St. Peter and Mount Simon Sandstones in Illinois Basin: Am. Assoc. Petroleum Geologist Bull., v. 68, pp. 753-764.

Hunter, R. E., 1973, Pseudo-crosslamination formed by climbing adhesion ripples: Jour. Sed. Petrology, v. 43, pp. 1125-1127.

Hunter, R. E., 1977, Basic types of stratification in small eolian dunes: Sedimentology, 24, p. 361-387.

Kuenen, Ph. H., 1960, Sand: Sci. Am. v. 202, pp. 94-113.

Kuenen, Ph. H., and Perdok, W. G., 1962, Experimental abrasion,S. Frosting and defrosting of quartz grains: Jour. Geol., v. 70, pp. 648-658.

Mazzullo, J. M., and Ehrlich, R., 1983, Grain-shape variation in the St. Peter Sandstone: A record of eolian and fluvial sedimentation of an Early Paleozoic cratonic sheet sand: Jour. Sed. Petrol, v. 53, pp. 105-119.

Odom, I. E., 1974, Syngenetic sanidine beds from Middle Ordovician St. Peter Sandstone, Wisconsin: A discussion, Jour. Geol., v. 82, pp. 112-116.

Odom, I. E., Willand, T. N., and Lassin, R. J., 1979, Paragenesis of diagenetic minerals in the St. Peter Sandstone (Ordovician), Wisconsin and Illinois, in Scholle, P. A. and Schluger, P. R., Aspects of diagenesis, Special Pub. No. 26, Soc. Economic Paleontologists and Mineralogists, p. 425-443.

Owen, D. D., 1847, Preliminary report of the geological survey of Wisconsin and Iowa: U. S. General Land Office Rept., p. 170.

Ostrom, M. E., 1967, Paleozoic stratigraphic nomenclature for Wisconsin: Wis. Geol. and Nat. Hist. Survey Inf. Circ 8, 1 p.

Ostrom, M. E., 1970, Stratigraphy and sedimentation of Cambrian and Ordovician rocks in western Wisconsin: Geol. and Nat. Hist. Survey, Univ. of Wis. Info. Circ. 11, pp. 10-34.

Potter, P. E., and Pryor, W. A., 1961, Dispersal centers of Paleozoic and later clastics of the Upper Mississippi Valley and adjacent areas: Geol. Soc. Am. Bull., v. 72, pp. 1195-1250.

Pryor, W. A., and Amaral, E. J., 1971, Large-scale cross-stratification in the St. Peter Sandstone: Geol. Soc. Am. Bull., v. 82, pp. 239-244.

Reinecke, H. E., 1959, Haftrippeln and haftwarzen, ablagerungsformen von flugsand: Senckenbergiana Lethaea. v. 36, pp. 347-357.

Sardeson, F. W., 1896, The St. Peter Sandstone: Minn. Acad. Nat. Sci. Bull., v. 4, pp. 70-79.

Shepard, F. P., and Young, R., 1961, Distinguishing between beach and dune sand: Jour. Sed. Petrol., v. 31, pp. 196-214.

25 Shrock, R. R., and Malott, C. A., 1933, The Kentland area of dis turbed Ordovician rocks in northwestern Indiana: Jour. Geol., v. 41, p. 351.

Sloss, L. L., 1963, Sequences in the cratonic interior of North America: Geol. Soc. Am. Bull., v. 74, pp. 93-114.

Sloss, L. L., Dapples, E. C., and Krumbein, W. C., 1960, Lithofacies maps: an atlas of the United States and southern Canada: New York, Wiley, 108 p.

Templeton, J. S., and Willman, H. R., 1963, Champlainian Series (Middle Ordovician) in Illinois: Ill. State Geol. Survey Bull., v. 89, 260 p.

Thiel, C. A., 1935, Sedimentary and petrographic analysis of the St. Peter Sandstone: Geol. Soc. Am. Bull., v. 46, pp. 559-614.

Thwaites, F. T., 1961, The base of the St. Peter sandstone in southwestern Wisconsin: Wis. Acad. Sci., Art, and Letters, v. 50, pp. 203-219.

Tyler, S. A., 1936, Heavy minerals of the St. Peter Sandstone in Wisconsin: Jour. Sed. Petrol.. v. 6, No.2, pp. 55-84.

Willman, H. B., Atherton, E., Buschbach, T. C., Collinson, C., Frye, J. C., Hopkins, M. E., Lineback, J. A., and Simon, J. A., 1975, Handbook of Illinois stratigraphy: Ill. State Geol. Survey Bull. 95, 261 p.

Winfree, K. E., 1983, Depositional environments of the St. Peter Sandstone of the upper midwes t: Unpub. mas ter' s thes is, Uni v. of Wis. 114 p.

Winfree, K. E., and Dott, R. H., Jr., 1983, Progress on the St. Peter Sandstone of the upper midwest: in Geol. Soc. Am. Field Guide, Univ. Wis., pp. 4-11.

Witzke, B. J., 1980, Middle and Upper Ordovician paleogeography of the region bordering the transcontinental arch, in, Fouch, T. D. and Magathan, E. R. (editors), Paleozoic paleogeography oY-the west-central United States: Denver, Rocky Mt. Section of Soc. of Economic Paleontologists and Mineralogists, p. 1-18.

Woodard, H. H., 1972, Syngeneti'c sanidine beds from Middle Ordovician St. Peter Sandstone, Wisconsin: Jour. Geology, v. 80, pp. 323-332.

26 ISSN: 0512-0640 Cover photo: St. Peter Sandstone; Monticello, Wisconsin