BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA

VOL. 66. PP. 857-882. 9 FIGS.. 1 PL. SEPTEMBER 1964

FRANCONIA FORMATION OF MINNESOTA AND WISCONSIN

By ROBERT R. BERG

ABSTRACT The Upper Cambrian Franconia formation in southeast Minnesota and west-central Wisconsin consists of glauconitic, quartzose sandstones that average 175 feet in thick- ness. Previous subdivision of the Franconia resulted in faunal zones to which geographic member names were given. These zones are not rock units and cannot properly be called members. In this paper, members are based on rock type. They are, in ascending order, the Wood- hill member—medium- to coarse-grained sandstone; the Birkmose member—fine-grained, glauconitic sandstone; the Tomah member—sandstone and shale; and the Reno member —glauconitic sandstone. A fifth unit, the Mazomanie member—thin-bedded or cross- bedded sandstone, forms a nonglauconitic facies that interfingers with and replaces the Reno member. Faunal zones are independent of the lithic units. The Woodhill member was deposited in the transgressing Franconia sea. Birkmose greensands formed in shallow waters far from shore, while Tomah sand and shale and Mazomanie thin-bedded sand were deposited nearer shore. Later, Reno greensands formed offshore, Mazomanie thin-bedded sand was deposited shoreward, and cross-bedded Ma- zomanie sand accumulated nearest the strand line.

CONTENTS TEXT Page Measured sections 877 Page General statement 877 Introduction 857 Taylors Falls 877 Franconia problem 857 Hudson 877 Previous studies 858 Arkansaw 878 Proposed nomenclature 859 Franklin 878 Acknowledgments 859 Maynard Pass 879 Regional stratigraphy 860 Goodenough Hill 880 General character 860 Lone Rock 880 Woodhill member 861 References cited 881 Birkmose member 862 Tomah member 863 ILLUSTRATIONS Reno member 864 Mazomanie member 866 Figure Page Paleontography 867 1. Comparison of attempts to subdivide the Local stratigraphy 869 Franconia formation 858 2. Index map 860 St. Croix Valley 869 3. Conaspis zone thickness and facies 868 Dunn County 870 4. St. Croix Valley cross section 872 Mississippi Valley 871 5. Dunn County cross section 872 Buffalo River Valley 871 6. Mississippi Valley cross section 872 Houston to Adams counties 871 7. Houston to Adams counties cross section.... 873 Baraboo area 874 8. Buffalo Valley cross section 873 Wisconsin River Valley 874 9. Wisconsin Valley cross section 873 Paleogeographic speculations 875 Facing Significance of lithic types 875 Plate page Depositional history 876 1. Franconia outcrops. 864

INTRODUCTION tinent-wide extent and to a lithostratigraphic unit of local importance in the Upper Missis- Franconia Problem sippi Valley. Studies of the Franconia during The term Franconia has been applied to an the past 50 years have been concerned chiefly Upper Cambrian biostratigraphic unit of con- with the faunally defined unit, now called the 857

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Franconian Stage (Howell et al., 1944). The In Wisconsin, Franconia was applied to the Franconia as a rock unit has been neglected, entire sequence of glauconitic sandstones be- and the subdivisions of the formation now in tween the Dresbach formation below and the use in Minnesota and Wisconsin are faunal St. Lawrence dolomite above. Such was the

TWENHOFEL and ULRICH, 1924 TWENHOFEL, RAASCH, THIS PAPER THWAITES, 1919 and THWAITES, 1935

Rock Units Rock and Faunal Units Faunal Units Rock Units

BAD AXE MEMBER UPPER MAZOMANIE GREENSAND Dikelocephalus FORMATION postrectus fauna RENO !>

YELLOW SANDSTONE Prosaukia fauna HUDSON X^MAZOMANIE MEMBER \. MEMBER Ptychaspis-Prosaukia LOWER fauna MEMBER J> GREENSAND FRANCONIA FORMATION GOODENOUGH MICACEOUS MEMBER TOMAH ^v SHALE (subdivisions as Conaspis MEMBER Twenhofel and fauna Thwaites, 1919) BASAL BIRKMOSE BEDS MEMBER IRONTON MEMBER DRESBACH IRONTON MEMBER Camaraspis WOODHILL WORMSTONES Camaraspis fauna fauna MEMBER FIGURE 1.—COMPARISON OP ATTEMPTS TO SUBDIVIDE THE FRANCONIA FORMATION

units that fail to describe the nature and dis- usage of Twenhofel and Thwaites (1919, p. tribution of sedimentary rock types. The 623) derived from Ulrich's earlier tentative Franconia problem can be solved independently classification published by Walcott (1914, p. of faunal study, and only a knowledge of rock 354). This constituted a redefinition of the types can lead to an understanding of deposi- three formations involved. tional history. The present study was made Twenhofel and Thwaites (1919, p. 616) first during 1949 and 1950 in an attempt to dis- subdivided the Franconia in their study of the criminate lithic units within the Franconia Tomah-Sparta area of Monroe County, Wis- formation and to trace these units throughout consin; they described lithic units but did not the outcrop area. name them. This and the most important sub- sequent classifications are compared in Figure Previous Studies 1. Ulrich introduced two names: Iron ton Berkey (1897, p. 373) defined the formation member for the basal Camaraspis-besn'mg sand- from outcrops at the village of Franconia just stone of the Franconia (Ulrich, 1924, p. 93- south of Taylors Falls on the St. Croix River. 94), and Mazomanie formation for sandstone Berkey's Franconia consisted of 100 feet of in central Wisconsin containing the Prosaukia fine-grained sandstone containing fossils later fauna (Ulrich, 1920, p. 73-75). Although both assigned to the Conaspis fauna, and he re- these units were defined on rock characters, stricted the term Dresbach to underlying Ulrich relied on fossils for their identification, greensands and shales. Subsequent usage of and he believed that the Mazomanie sandstone Franconia in Minnesota followed the original was younger than the Franconia. The present definition, and glauconitic sandstone overlying study concludes that the Mazomanie sandstone the Conaspis beds elsewhere in the State were represents a nonglauconitic fades that inter- assigned to the St. Lawrence formation. fingers with Franconia greensands. Trowbridge

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and Atwater (1934, p. 48) obversely suggested characters. A faunal zone may pass from a this possibility when they disagreed with highly glauconitic sandstone to a nonglauco- Ulrich and stated that the Mazomanie is the nitic sandstone within a short distance. Further- same age as the Franconia. more, two faunas may be found in the same Twenhofel, Raasch, and Thwaites (1935) type of sandstone in one outcrop, necessitating denned faunal units of the Franconia in Wis- complete fossil collections to draw a "member" consin, and the zones received geographic names boundary. Such "members" then consist of and were called members. The Wisconsin no- not one, but two or more rock types, and they menclature was firmly established by the may be identical in their variability of lithic "Conference Classification" published for the characters. Ninth Annual Field Conference of the Kansas The present subdivision of the Franconia Geological Society (Trowbridge, 1935). This establishes units of uniform lithic character, was essentially the same scheme given unofficial based entirely on rock type instead of con- sanction by the U. S. Geological Survey tained faunas. Rock units (members) are (Bridge, 1937, p. 234). The use of member separated from biostratigraphic units (faunal names for faunal units is carried in the Cam- zones), and both are recognized as important brian Correlation Chart of the National Re- but distinct entities. When the stratigraphic search Council (Howell et al., 1944). and geographic characteristics of the two Uniformity between Minnesota and Wis- are established, they are superimposed to consin usage was established in 1939 when the produce a better understanding of depositional Minnesota Geological Survey adopted the history. Conference Classification (Stauffer, Schwartz, For the Franconia, this procedure requires and Thiel, 1939). The Minnesota classification the rejection of previous member names. The differed only in the use of "Taylors Falls former members do not now designate, nor were member" for beds containing the Conaspis they intended to designate, rock types in the fauna. Upper Mississippi Valley. They were defined Attempts to recognize lithic members in by faunal criteria and have become established Minnesota were begun in 1946 under the direc- by usage as biostratigraphic terms. tion of W. C. Bell. Nelson (1951) and Bell, Feniak, and Kurtz (1952) describe persistent A cknowledgments rock types along the St. Croix and Mississippi rivers, and in the present study the rocks were Special acknowledgment is due Professor W. traced from these regions into the main Fran- C. Bell, who originally recognized the problem conia outcrop area. and method of solution, and under whose guid- ance the study was completed at the University Proposed Nomenclature of Minnesota. Field expenses were defrayed by the Geological Society of Minnesota, a group The inherent difficulty in the member whose enthusiastic and generous response made nomenclature of the Conference Classification the project financially possible. In September is apparent. The use of geographic member names implies the definition of rock units, but 1950 a number of geologists concerned with the authors (Twenhofel, Raasch, and Thwaites, Cambrian problems accompanied the writer in 1935, p. 1691) say that in their Croixan sub- the field. For many helpful suggestions and a division. critical review of the stratigraphic conclusions, I am indebted to Christina Lochman Balk, V. "The different members ... are not sharply sepa- rated from each other on the basis of lithologic E. Barnes, Josiah Bridge, E. A. Frederickson, changes.... Where lithologic and faunal characters B. F. Howell, G. O. Raasch, and J. L. Wilson. are not mutually coincident, the latter have been considered decisive." The manuscript was read and criticized by W. C. Bell of the University of Texas, J. W. Low Indeed, the Franconia formation is charac- of The California Company, and V. E. Barnes terized by a noncoincidence of lithic and faunal of the Texas Bureau of Economic Geology.

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92

Copos j_ CROSS SECTIONS < MdfTrie | A A'- St. Croix Volley BB1 - Dunn County CC'- Mississippi Volley 45 DD'- Buffalo Volley EC.'- Houston to Adorns counties FF'- Wisconsin Volley

. , Measured Section IrM -j !°iftrkonsow jD-Drom Precambrian Rocks

IMisha .Mokwo

^ > I japuriy^ Citv I A • H shoh e VACROSSEJ ! fay** •»"«" )ADAMSfi °Bffi, VVoeresceiti i MON!RO" .Hj)^^ I ^j>o!fyMiyHilll Mount Toi ,E iGoodenough I H 0 U ST 0 N\»}Brownsville reek ! Hell Hollow 1j.._ . -jjjjj^V— VERNON «fronton i i J ISAUK- IRICHLANO; CRAWFORDI

92 90 FIGTJEE 2.—INDEX MAP

REGIONAL STRATIGRAPHY the Conference Classification. However, a re- definition of the formation based on rock type General Character results in a different interpretation of the lower The Franconia formation consists of quartz- and upper contacts and adds as much as 30 ose sandstones that range from ISO to 210 feet to its total thickness. The basal Franconia feet thick within the outcrop area (Fig. 2). On member consists of coarse-grained sandstone the north and east margins of this area the that lies disconformably above the uniformly Croixan Series rests on the Precambrian of the medium-grained Galesville member of the Superior Uplands, and to the south and west, Dresbach formation. The basal coarse sands it lies beneath Ordovician and younger rocks. become finer-grained toward the top and are The Franconia is well exposed in the St. Croix overlain by a sequence of highly variable sand- River \ alley and Dunn County, Wisconsin, in stones characterized by the presence of glau- the Mississippi River Valley of southeast conite grains. These fine-grained sandstones Minnesota, and throughout a broad area in may be highly glauconitic or sparingly glauco- west-central Wisconsin. Outcrops also occur nitic, thinly laminated, cross-bedded, or massive. farther south in the Baraboo region and along Flat-pebble conglomerates are distinctive beds the Wisconsin River. at several horizons, and the top of the formation The Franconia as here defined constitutes is generally marked by a dolomitic conglomer- essentially the same rocks as the Franconia of ate. Above the Franconia is a nonglauconitic

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unit of dolomite, dolomitic siltstone, and very Wood Hill in southwest Juneau County (G. 0. fine-grained sandstone, first named St. Law- Raasch, personal communication). Although rence in Minnesota and later named Trem- defined as a lithic unit overlying an erosion pealeau in Wisconsin. St. Lawrence will be surface, "Ironton member" came to mean all used because of priority. beds containing the Elvinia fauna. As thus used In spite of the variable nature of the Fran- by Twenhofel, Raasch, and Thwaites (1935, conia greensands, several distinct lithic units p. 1699), Bridge (1937, p. 234), Stauffer and can be recognized. These members are dis- Thiel (1941, p. 37), and Howell et al. (1944), tinguished primarily on the basis of glauconite the "member" incorporates heterogeneous content and to a lesser extent on such features sandstones, including not only the nonglauco- as grain size, bedding, and the presence of car- nitic and coarse-grained sandstone so designated bonate or shale. They are, in ascending order, by Ulrich, but highly glauconitic and fine- the Woodhill member—coarse-grained sand- grained sandstone above. Moreover, this usage stone, the Birkmose member—glauconitic eliminated underlying coarse-grained beds sandstone, the Tomah member—sandstone and which are strikingly different from the finer shale, and the Reno member—glauconitic Galesville sandstone. sandstone. A fifth member, the Mazomanie, Because "Ironton member" has become a represents a nonglauconitic sandstone facies synonym of "Elvinia zone", the basal sandstone that interfingers with and replaces the green- should be given a new name that does not carry sands to the north and east. a faunal connotation. Therefore, the name The Franconia, then, is characterized region- Woodhill member is proposed. An excellent ally by facies change and a moderate degree of exposure still exists at Ulrich's secondary type heterogeneity in rock type, but the most strik- locality, and a detailed description of this ing changes in rock type occur at the base and section follows: top. The formation is defined above and below by distinct lithic changes representing change in Road cuts on State Highway 80 at Wood Hill, SE%, sec. 3, T.15 N., R.2 E., Juneau Co., sedimentary environment, and, although some Wis. variability is evident within the formation, the Birkmose member -0.5 foot exposed Feet conditions of sedimentation were maintained 8. Clay, red-brown, glauconitic 0.5 without significant break throughout the period Woodhill member—30.5 feet of its deposition. 7. Sandstone, gray to brown, medium- grained, cross-bedded, glauconitic. Cama- Woodhill Member raspis plana 3.0 The basal unit of the Franconia was first 6. Sandstone, yellow-brown, medium- named by Ulrich. He defined (Ulrich, 1924, p. grained, bedding indistinct. Camaraspis 93) the Ironton member as coarse-grained comiexa 1.5 sandstone that lies disconformably on the 5. Sandstone, white, medium- to fine- Dresbach formation and carries the Camaraspis grained, cross-bedded, few vertical bor- (Elvinia) fauna. In the type area the presence ings 13.0 of Camaraspis convexa is essential in determin- 4. Sandstone, yellow, coarse- to fine-grained, ing the thickness of the Ironton, for fossils poorly sorted, horizontal bedding marked by silt laminae, two 6-inch beds of brown, occur in a 2- to 8-foot bed almost indistinguish- medium-grained, cross-bedded sandstone. 9.0 able from the underlying barren Dresbach. Both sandstones are medium-grained and well 3. Sandstone, brown, coarse- to medium- sorted, but the Ironton lacks well-defined grained, cross-bedded 1.5 bedding, has the larger grain size, and is some- 2. Sandstone, gray, coarse-grained, horizon- what better-sorted. The differences are small tal bedding, sharp contact with bed below 2.5 and not readily apparent on the outcrop. A more unfortunate choice of type locality could Dresbach formation not have been made to demonstrate a Dres- Galesville member—41.0 feet measured bach-Franconia disconformity. Subsequently, 1. Sandstone, white, medium-grained, well Ulrich demonstrated the contact at outcrops on sorted, some gentle cross-bedding 41.0

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The Galesville sandstone is uniformly bedded at the top of the member with 1- to 2- medium-grained and well sorted for a consider- foot ledges of medium-grained, brown, cross- able distance below the contact, whereas the bedded sandstone similar to the upper beds at lower 13 feet of the Woodhill member increases Wood Hill. In the absence of interbedding, the in gram size and decreases in degree of sorting. brown, cross-bedded sandstone forms a single The contact is easily recognized and denotes bed up to 15 feet thick overlying the middle the beginning of Franconia deposition by a unit (PI. 1, fig. 1). The upper bed may contain significant change in rock type. The change may Camaraspis at the top, but, where trilobites are be abrupt, as at Wood Hill, or may be grada- lacking, inarticulate brachiopods are abundant tional through a thickness of 1 or 2 feet, as in along the cross beds. This sandstone also con- outcrops along the Mississippi River. The upper tains scattered vertical borings and was called 17 feet of the Woodhill member is a medium- "wormstone" by Twenhofel and Thwaites grained and well-sorted sandstone that carries (1919, p. 622). Camaraspis at the top. The uppermost 3 feet The dominant heavy accessory minerals in contains 20 per cent glauconite, giving the the Woodhill member are tourmaline, zircon, sandstone a greenish-gray or, on weathering, a and garnet. In central Wisconsin, the lack of brown color. Glauconite also occurs at other garnet in the upper Dresbach and its first oc- localities in the upper Woodhill, usually as currence in the basal Franconia are charac- scattered grains along cross laminations. The teristic of these sands (Pentland, 1931). Along amount is generally small, but, where it occurs the Mississippi River, however, there is no in sufficient quantity to color the rock, the change in heavy minerals across the Dresbach- coarser grain size distinguishes the upper Franconia contact; garnet is common in both Woodhill from the fine-grained, highly glauco- the Galesville and Woodhill members. nitic sandstones of the overlying Birkmose member. The type outcrop of the Woodhill is inter- Birkmose Member mediate in regional expression of the member. Eastward in Adams County and southward in Overlying the Woodhill member are fine- Juneau County the member thins to IS or 20 grained, glauconitic sandstones ranging in feet, and the lower shaly and horizontally thickness from half a foot to nearly 40 feet. bedded portion is missing. The member there This unit is named the Birkmose member from consists of one unit of brown, cross-bedded exposures north of Birkmose Park in the town sandstone carrying Camaraspis in the upper few of Hudson, Wisconsin. A description of the feet, but the coarse grain size and poor sorting type section follows: are evident at the base. Immediately north of the Baraboo region, the typical character of Section along State Highway 35, center sec. 25, T.29 N. the Woodhill is lost, as shown in the Ironton R.20 W., St. Croix Co., Wis. type area. Westward from Wood Hill the member thickens with an attendant change in Tomah member—27.0 feet Feet 7. Sandstone, buff, very fine-grained, mica- character. The lower shaly and upper cross- ceous, with interbedded gray shale. Conas- bedded divisions are maintained, but the mid- pis fauna in basal foot, Plychaspis fauna dle portion develops into a distinctive unit. above 27.0 The lower unit, 6 to 10 feet thick, is coarse and Birkmose member—27.0 feet poorly sorted; the middle unit is also coarse- 6. Dolomite, red-brown, conglomeratic, thin- grained but is better sorted and without definite bedded, glauconitic, sandy, flat pebbles of buff siltstone up to 3 inches in diameter, bedding. From the Tomah area in Monroe upper half with dolomitic siltstone laminae County and westward the middle unit is white Taenicephalus altus teilzone 2.5 and mottled with more or less linear orange patches that represent worm borings. This 5. Greensand, fine-grained, cross-bedded, with several laminae of gray shale and characteristic rock makes up a considerable buff silt, dolomitic lenses at top contain part of the member and is commonly inter- Elvinia roemeri 5.5

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4. Greensand, fine-grained, cross-bedded, that has a fusiform outline and suggests an with abundant worm borings, few thin beds of wormstone 3.5 organic origin. Calcite forms a clear cement between dolomite grains. The bed may contain 3. Wormstone, buff to orange, very fine- scattered flat pebbles of siltstone up to 6 grained, glauconitic, with cross-bedded greensand in middle and at base 7.5 inches in diameter, or the pebbles may be con- centrated to form a conglomerate as much as 2 2. Wormstone, buff, moderately glauconitic, laminae of greensand in middle below a feet thick. The conglomerate is placed in the 6-inch bed of medium-grained sand- Birkmose member because of its glauconite stone 8.0 content and cross-bedding. In rock type it is most similar to the Birkmose greensands rather Woodhill member—18.0 feet 1. Sandstone, yellow to brown, medium- to than to the thinly interbedded sandstone and coarse-grained, cross-bedded, lower part shale of the overlying Tomah member. It is a poorly sorted, pebbles and granules in basal foot 18.0 "terminal conglomerate" formed at the end of the period of deposition characterized by the Birkmose greensand is a fine-grained, quartz- accumulation of sand and glauconite in current- ose, glauconitic sandstone that commonly is agitated water. cross-bedded and poorly cemented. A typical The Birkmose in the northern half of the area sample (bed 5 above) has about 60 per cent is similar to that of the type section in which of the grains in the ^ mm grade size. Glauco- wormstone is the dominant rock. To the south nite grains constitute 45 per cent of the sand- hi the Mississippi Valley wormstone is less stone and color the rock light to dark green. common, and the upper half of the member Wormstone is a convenient field term applied becomes shaly and irregularly dolomitic. In to very fine-grained sandstone containing Houston County, Minnesota, the member con- abundant linear masses of gray shale represent- sists of greensand and dolomitic, siltstone con- ing filled borings of benthonic animals (PI. glomerates, and the thickness ranges from 9 to 1, fig. 2). The worm borings may be cylindrical 18 feet. The conglomerates occur in lensing beds and vertical, a quarter of an inch in diameter that are replaced laterally by thinly interbedded and up to 2 inches in length, but generally they greensand and siltstone. The member thins are irregular gray patches in the surrounding eastward in Wisconsin. Dolomite is persistent light-colored matrix. Freshly exposed worm- through Monroe County, but only 1 foot or stone is massive, all traces of the bedding having less of greensand and shale is assigned to the been destroyed by burrowing. A typical sample Birkmose in Adams and Juneau counties. (bed 3 above) contains nearly 50 per cent of the The friable sandstones of the member rarely grains in the Ms mm grade size. Quartz is the yield fossils, but locally trilobites are preserved dominant mineral, glauconite constitutes 16 in the dolomitic portions. At most localities the per cent of the sand, and a small percentage of boundary between the Elvinia and Conaspis the grains are composed of alkalic feldspar. zones lies within the member, and according to Because of the fineness of grain size, glauconite the Conference Classification this uniform rock seldom colors the rock. unit must be divided between the Ironton and A bed of conglomeratic dolomite at the top Goodenough "members". of the member is typically reddish brown, coarsely granular, and cross-bedded. Laminae Tomah Member or thin beds of buff, dolomitic siltstone are present in the upper half. Chemical analysis of The Tomah consists of interbedded sandstone a sample from the type section gives the follow- and shale and is essentially a nonglauconitic ing composition: dolomite, 39 per cent; calcite, unit. The name is derived from the Tomah 9 per cent; acid-soluble unknown, 17 per cent; quadrangle of Wisconsin in which Twenhofel sand and silt, 20 per cent; and glauconite, 15 and Thwaites (1919) first described this rock as per cent. Thin sections show that many of the the "micaceous shale." An excellent exposure of large, rhombic dolomite grains have at their 28 feet at Maynard Pass is selected as the type centers a regular network of opaque material section:

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Road cuts on U. S. Highway 16, 6 miles west of size particles; hydromuscovite (illite) is the Tomah, NWy4 sec. 22, T.17 N., R.2 W., Monroe Co., Wis. chief component of the clay. Reno member (part) Feet The sandstone is unique in its high content 3. Greensand, gray to brown, fine-grained, of authigenic feldspar, and it is referred to as a moderately glauconitic, mostly cross- feldspathized sandstone. Chemical and mineral- bedded. Maustonia nasuta teilzone 1 and 4 feet above base 15.0 ogical analyses (Berg, 1952) give the following composition (per cent): orthoclase, 48; quartz, Tomah member-28.0 feet 2. Sandstone, buff to gray, very fine-grained, 44; glauconite, 5; muscovite, 2; cellophane, 0.5; micaceous, thin-bedded with interbedded leucoxene, 0.4; and traces of zircon, tour- gray-green shale, upper 3 feet with worm borings and some glauconite. Paraboli- maline, and garnet. The authigenic orthoclase noides palatus teilzone at 1 and 3 feet, and occurs as rhombic overgrowths on quartz Maustonia nasuta teilzone at 16.5 feet grains and as cement. above base 28.0 Well-preserved fossils are common in nearly Birkmose member—0.5 feet exposed all outcrops. Trilobite molds are scattered on 1. Greensand, weathered and poorly ex- posed in ditch 0.5 the bedding planes or clustered in thin, non- laminated lenses. Species of the Conaspis zone Tomah sandstone is light gray to yellow, very occur in the member in most areas, and ac- fine-grained, micaceous, and laminated. It is cording to the Conference Classification the characteristically thin-bedded with beds 1 to 6 micaceous sandstone is the dominant rock type inches thick separated by laminae or partings of the "Goodenough member." of gray-green, micaceous shale (PL 1, fig. 3). In some fresh exposures 1- to 2-inch shale beds Reno Member are present. Small-scale interference ripple The Reno member is composed chiefly of marks are preserved locally in the sandstone, wormstones and greensands that constitute and shaly partings are marked by filled trails over half the total thickness of the Franconia or "worm tubes". Flat-pebble conglomerates in much of the outcrop area. Complete ex- are rare and have been observed at only two posures are rare because of the incoherence of localities. In some areas thin beds of wormstone the rock, but the sequence of beds is well occur in the Tomah member, but generally the known in Houston County and is illustrated by member is remarkably uniform. Contact with the type section near the town of Reno: the overlying Reno member is placed at the highest occurrence of interbedded shale. Section in Hell Hollow, 1.3 miles north of Reno, Textural analysis of a sandstone sample from SEy± sec. 23, T.102 N., R.4 W., Houston Co., Maynard Pass shows that it is very fine-grained Minn. to silty with 40 per cent of the grains in the St. Lawrence formation Feet He mm grade size and 30 per cent in the ^2 17. Siltstone, dolomitic, thin-bedded, some very fine-grained sandstone; basal 2 feet mm size. The interbedded shale consists of dolomite, gray, dense, thin-bedded, approximately equal amounts of silt- and clay- glauconitic 61.0

PLATE 1— FRANCONIA OUTCROPS FIGURE 1.—WOOBHILL MEMBER Cross-bedded sandstone overlying soft, worm-bored sandstone. Blair, Wis. FIGURE 2.—BIRKMOSE MEMBER Cross-bedded greensand grading upward to massive wormstone. Arkansaw, Wis. FIGURE 3.—TOMAH MEMBER Thinly interbedded sandstone and shale. Sparta, Wis. FIGURE 4.—RENO MEMBER Ripple marks preserved on silt laminae in greensand. Maynard Pass, Wis. FIGURE 5.—RENO MEMBER Greensand conglomerate with flat pebbles of underlying wormstone. Near Menomonie, Wis. FIGURE 6.—MAZOMANIE MEMBER Thin-bedded sandstone of Berkey's (1897) type Franconia. Taylors Falls, Minn.

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FRANCONIA OUTCROPS

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Franconia formation Wormstone is the dominant rock type of the Reno member—116.0 feet member, and although it resembles Birkmose 16. Conglomerate, matrix of buff, fine- grained, sandy dolomite with glauconitic wormstone it contains considerably more laminae, pebbles of siltstone, small and glauconite, up to 30 per cent. Reno greensand rounded or discoid up to 5 inches in is fine- to very fine-grained and cross-bedded. diameter 6.0 The color grades from light gray to dark green 15. Greensand, dark greenish gray, moder- with about 25 per cent of disseminated glauco- ately glauconitic, thin-bedded, cross- nite grains producing a salt-and-pepper texture. bedded, with interbedded laminae of buff silt 4.0 In addition to wormstone and greensand, the member usually contains fine-grained, micace- 14. Sandstone, brown or light gray, fine- grained, micaceous, laminated, gently ous, laminated sandstone in fossiliferous beds cross-bedded. Dikelocepkalus postrectus 6 inches to 3 feet thick. It is similar to that of fauna 2.0 the Tomah member but has more glauconite. 13. Wormstone, brown, some interbedded Oscillation ripple marks up to 3 inches in buff silt, several 6-inch beds of cross- length are present in the greensands (PL 1, bedded greensand 13.0 fig. 4), and mud cracks may occur on silt 12. Greensand conglomerates, two 6-inch laminae but are incomplete and somewhat beds separated by wormstone 2.5 irregular. Thin beds of flat-pebble conglomerate occur 11. Wormstone, gray brown, glauconitic, several 3-inch beds of green sand and within the upper 40 feet of the member. The greensand conglomerates 14.5 highly glauconitic sandstone matrix contains pebbles that are discoid, rarely exceed 6 inches 10. Greensand, dark gray to green, fine- in diameter, and are composed of glauconitic grained, thin-bedded, cross-bedded, laminae of buff silt and gray shale, some sandstone and wormstone, usually identical orange wormstone near base 14.0 to the underlying rock (PI. 1, fig. 5). Ordinarily several 3- to 6-inch beds of greensand conglom- 9. Wormstone, dark green gray, moder- ately glauconitic 11.5 erate occur within a short vertical distance, but beds range up to 2 feet thick. The greensand 8. Sandstone, gray, fine-grained, micaceous, conglomerates may thin and disappear in a laminated, glauconitic, much interbedded gray shale. Prosaukia miss fauna 2.5 single outcrop. The top bed of the member is a siltstone conglomerate having a matrix of 7. Wormstone, green-gray, glauconitic. ... 3.5 glauconitic, sandy dolomite. In Houston and Vernon counties the conglomerate forms a 6. Sandstone, gray-brown, fine-grained, micaceous, laminated. Prosaukia misa continuous bed 6 feet thick, but in other areas fauna 1.5 it is lenticular and 6 inches to 2 feet thick. According to the Conference Classification 5. Greensand, highly glauconitic, weathered (Twenhofel, Raasch, and Thwaites, 1935, p. to red or brown, two beds separated by shaly wormstone 1.5 1705) this bed is included in the "basal con- glomerate and greensand" member of the 4. Greensand, dark gray to green, fine- Trempealeau (St. Lawrence) formation, but in grained, abundant gray shaly worm borings 9.0 rock type the bed is most similar to the Reno member. 3. Sandstone, gray, fine-grained, micaceous, Fossils are found only in the laminated sand- moderately glauconitic, shaly 2.5 stone beds of the Reno member, and species of 2. Wormstone, with thin beds of greensand the Ptychaspis-Prosaukia zone ("Hudson mem- and gray sandstone. Ptychaspis striata ber") are common. The Dikelocephalus pos- fauna 20 feet above base 28.0 trectus fauna occurs within a few feet of the Tomah member—9.5 feet top, and the base of the "Bad Axe member" 1. Sandstone, gray to brown, fine-grained, usually was placed at one of the several green- micaceous, slightly glauconitic, thin- bedded with much interbedded gray sand conglomerates by Twenhofel, Raasch, shale. Conaspis fauna 9.5 and Thwaites (1935, p. 1734).

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Mazomanie Member 13. Covered. At Mazomanie this interval is cross-bedded, moderately glauconitic greensand, with buff silt laminae and a Ulrich (1920, p. 73-76) introduced the name 6-inch bed of greensand conglomerate... 18.5 Mazomanie for "a more or less decidedly cal- careous sandstone formation, approximately Mazomanie member—116.5 feet 12. Sandstone, white to yellow, friable, and 100 feet in thickness" exposed along the Wis- yellow brown, dolomitic sandstone in consin River south of the Baraboo Range. alternating beds 2 to 3 feet thick, fine- grained, cross-bedded, flat pebbles in After a study of sections in central Wisconsin, several dolomitic beds 52.0 Ulrich (1924, p. 79) concluded that the Mazo- manie is "a distinct formation that wedges in 11. Sandstone, white to yellow, fine-grained, cross-bedded, some beds slightly glau- from the east in Wisconsin between the top of conitic 14.0 the Franconia and the base of the St. Lawrence limestone." Ulrich differentiated the Mazo- 10. Covered 6.0 manie from the Franconia by the presence of 9. Sandstone, yellow, fine-grained, cross- dolomite and the relatively small amount of bedded, partly dolomitic above, slightly glauconite, but his principal criterion was the glauconitic in lower 4 feet 20.5 "Mazomanie fauna", the Prosaukia subzone of 8. Dolomite, brown, coarsely granular, very present usage. He postulated that the Fran- sandy, glauconitic, cross-bedded. Orthid brachiopod near top 7.5 conia was deposited first in western Wisconsin followed by deposition of the Mazomanie in 7. Conglomerate, 3-inch pebbles of white central Wisconsin, partially overlapping the sandstone in matrix of brown, medium- to coarse-grained, glauconitic, dolomitic Franconia. Twenhofel, Raasch, and Thwaites sandstone 1.0 (1935, p. 1702) rejected the name Mazomanie 6. Sandstone, yellow-brown, medium- because the "Mazomanie [fauna] continues grained, slightly glauconitic, cross- westward to the Mississippi River and beyond", bedded, somewhat dolomitic 11.5 and, therefore, the sedimentary relations de- 5. Sandstone, yellow brown, medium- scribed by Ulrich do not exist. grained, cross-bedded, with streaks of From the Mississippi eastward into Wis- greensand up to 3 inches thick 4.0 consin, interbedded nonglauconitic sandstone Birkmose member—1.0 foot exposed hi the Franconia greensands thicken until in 4. Greensand, dark greenish gray, fine- to central Wisconsin the entire Franconia above medium-grained, cross-bedded 1.0 the Tomah member is composed of nonglauco- Dresbach formation nitic anddolomitic sandstone. It is proposed here Galesville member—27.0 feet exposed to revive the name Mazomanie for this facies 3. Covered 6.0 that intertongues with the Reno member. In the type area along the Wisconsin River, 2. Sandstone, white, medium- to coarse- grained, gently cross-bedded, conglomer- the Mazomanie sandstone constitutes more atic at base with pebbles of quartz and than three-fourths of the Franconia thickness. rock fragments 20.0 It is best exposed at Ferry Bluff, a locality 1. Sandstone, white, medium- to fine- mentioned by Ulrich (1920) and situated across grained, horizontally bedded, silty near the river from the town of Mazomanie. top 7.0 Typical Mazomanie consists of quartzose, Section at Ferry Bluff, SWU sec. 20, T.Q N., R.6 E., fine-grained, well-sorted sandstone that has Sank, Co., Wis. nearly 80 per cent of the grains in the M mm St. Lawrence formation Feet grade size. The sandstone is yellow to white and cross-bedded. Glauconite grains are usually 15. Siltstone, buff, thin-bedded, dolomitic... 2.0 lacking and never exceed 5 per cent. Brown Franconia formation cross-bedded, dolomitic sandstone beds 1 to 3 feet thick are commonly interbedded with Reno member—24.5 feet 14. Greensand, gray to brown, moderately yellow sandstone, and the contact between glauconitic, poorly exposed 6.0 the beds is everywhere gradational. Coarse-

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grained dolomite constitutes about 40 per cent and case-hardened boulders of cross-bedded of the most highly dolomitic beds with 10 per sandstone have yielded excellent specimens of cent calcite cement and 50 per cent detrital Prosaukia subzone species. This fauna, on which quartz. Garnet is the dominant heavy acces- Ulrich's Mazomanie definition was founded, is sory mineral (Pentland, 1931). characterized by species different from those Another type of nonglauconitic sandstone in the Reno greensands (Berg, 1953, p. 557). included in the member is fine- to very fine- grained and thin-bedded (PI. 1, fig. 6). Bedding Paleontography is generally horizontal, but long, gently in- clined cross laminations are common. It is The sequence of faunas of the Franconian similar to Tomah sandstone but lacks inter- Stage in the Upper Mississippi Valley was bedded shale. The thin-bedded sandstone in outlined by Twenhofel, Raasch, and Thwaites central Wisconsin overlies the Tomah member (1935) and based on the work of G. 0. Raasch. and underlies the cross-bedded, dolomitic With only a minor change in nomenclature, Mazomanie; in the northern St. Croix Valley the zonation is that published in the Cambrian it replaces both the Tomah and Reno members, Correlation Chart (Howell et al, 1944). Fran- and cross-bedded Mazomanie is confined to conian trilobites from Minnesota and Wisconsin the top of the formation. The relationship be- were described by Owen (1852), Hall (1863), tween thin-bedded and cross-bedded Mazo- Whitfield (1880), and Ulrich and Resser (1933), manie is not clearly demonstrable throughout with lesser contributions by Resser (1937; the outcrop area because of poor exposures. It 1942) and others. The recent papers by Nelson does seem that the lateral and upward change (1951), Bell, Feniak, and Kurtz (1952), and is from Franconia greensand (including Tomah Berg (1953) complete the illustration of im- sandstone) through thin-bedded Mazomanie portant species. As now recognized the sub- to cross-bedded Mazomanie, and that cross- divisions of the Franconian Stage are, in de- bedded Mazomanie represents the nearest-shore scending order: phase of the nonglauconitic fades. Dikdocephalus postrectus zone Berkey's type Franconia section is composed Ptychaspis-Prosaukia zone Prosaukia subzone of thin-bedded Mazomanie sandstone; it is the Prosaukia '• misa-Prosaukia longicornis bio- section to which the Minnesota Geological facies Survey (Stauffer, Schwartz, and Thiel, 1939) Ptychaspis subzone Ptychaspis striata teilzone applied the name "Taylors Falls member," Ptychaspis granulosa teilzone but with a faunal definition. If it were possible Stigmacephalus oweni and Psalaspis faunules in most areas to outline the stratigraphic dis- Conaspis zone Taenicephalus subzone tribution of the thin-bedded Mazomanie, this Taenicephalus altus teilzone unit would deserve recognition as a member, Maustonia nasuta teilzone Parabolinoides palatus teilzone and the name "Taylors Falls" might be re- Eoorthis subzone vived. Iningdla major zone The Mazomanie member, then, consists of Elvinia zone two rock types: a cross-bedded, dolomitic sand- The Briscoia zone (Howell et al., 1944) has stone dominant in the type area, and a thin- not been identified in the present study. bedded sandstone well exposed only in the The EMnia fauna is widespread, and its St. Croix Valley. The thin-bedded Mazomanie species are fully described by Nelson (1951, is a distinct type distinguished from the Tomah p. 767) and Bell, Feniak, and Kurtz (1952, p. by the absence of interbedded shale, but the 177). Elvinia roemeri is rare, and the zone is regional relationships between the two Ma- characterized by Camaraspis convexa, which is zomanie rock types cannot be determined in most abundant in the uppermost Woodhill detail. The term Mazomanie has been expanded member. to include all sandstones that constitute a non- The Irvingella major zone (Wilson and glauconitic facies to the north and east. Frederickson, 1950), formerly the Ptycho- Well-preserved fossils are rare, but weathered pleurites zone, is restricted to central Wisconsin.

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Species identified are Irvingella major Resser, in more than one member. The zone trans- Comanchia amplooculata (Frederickson), Sid- gresses lithic boundaries and occupies succes- cocephalus cf. 5. candidus (Resser), and Lingu- sively higher stratigraphic positions from the lepis n. sp. The zone has been found in the basal area in which the Reno greensands dominate

Measured section 3 Thickness in feet Dominant Rock Type Mazomonie member

FIGURE 3.—CONASPIS ZONE THICKNESS AND FACIES Diagrammatic cross section, AA' shows the relation of Conaspis zone subdivisions to members: E-Eoort/ris subzone, P-Parabolinoides palatus teilzone, M-Mauslonia nasuta teilzone, T-Taenicephalus altus teilzone.

Tomah member at four localities: Friendship into the area in which the Mazomanie facies is Mound, Horseshoe Bluff, and Springville prominent. The "climb" of the faunas from Township in Adams County, and Dellona west to east is illustrated by selected sections Township in Sauk County. If the zone does from the Mississippi River to central Wisconsin occur farther west, it probably is within the (Fig. 3). In the west Eoorthis sp. has been found lower Birkmose member where fossils are in a Birkmose conglomerate near Brownsville, rare. and Parabolinoides palatus occurs near the top Species of the Conaspis zone have been de- of the Birkmose at Galesville. The Maustonia scribed (Berg, 1953, p. 555), and three teilzones nasuta teilzone has not yet been found along of local importance are recognized in the the Mississippi, but the holotype of Kendallia Taenicephalus subzone. The Conaspis fauna, as eryon of that assemblage is from this area. The well as the other Franconian faunas, is present Taenicephalus altus teilzone is common in the

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Tomah in Houston County. In the centrally Mazomanie, whereas the Prosaukia longicornis located sections, Franklin and Hustler, Eoor- biofacies is restricted to the cross-bedded this occurs in dolomite at the top of the Birk- Mazomanie sandstone (Berg, 1953, p. 557). mose, P. palatus and M. nasuta in the Tomah, The Dikelocephalus postrectus fauna in Min- and at Franklin T. altus is found in the basal nesota has been described by Bell, Feniak, and Reno. In the east Eoorthis occurs in the basal Kurtz (1952, p. 177) and occurs only in the Tomah overlying the Irvingella major fauna at uppermost part of the Reno member near Horseshoe Bluff, M. nasuta occurs in thin- Reno and at Winona. In Wisconsin the fauna bedded Mazomanie at Cooley Hill, and the T. has been reported by Twenhofel, Raasch, and altus teilzone is represented by Croixana sp. in Thwaites (1935, p. 1732,1734) from the Victory cross-bedded Mazomanie at Friendship Mound. and Tunnel City sections, and the holotype of There is no apparent sedimentary control on D. postrectus comes from the Mazomanie the distribution of the teilzones, and it is as- member near Reedsburg, Sauk County. sumed that each represents a unit of essentially The limits of the Franconian Stage were contemporaneous deposition. Thus, Tomah defined to coincide with the Franconia forma- sand and shale were deposited in the east during tion, and this has resulted in artificial faunal the formation of Birkmose greensand and con- boundaries. The greatest faunal change takes glomerate in the west, and Mazomanie sand place between the Ptychaspis and Prosaukia was deposited in the east at the same time as subzones. Saukinid trilobites first appear in the Tomah sand and shale in the west, with an Prosaukia subzone, and together with species intermediate area of Reno greensand deposition. of Dikelocephalus they form the dominant group The Ptychaspis subzone is divided into a in the overlying Trempealeauan Stage, Re- lower Ptychaspis granulosa teilzone and an definition of stage boundaries would place the upper Ptychaspis striata teilzone, assemblages contact at the more obvious faunal change of importance in the Mississippi Valley (Bell, within the Reno and Mazomanie members. Feniak, and Kurtz, 1952, p. 176). The P. granulosa teilzone has two local assemblages in LOCAL STRATIGRAPHY its basal part: the Stigmacephalus oweni faunule which is dominant in the Mazomanie facies of St. Croix Valley the St. Croix Valley (Nelson, 1951, p. 768), Franconia sections in the St. Croix Valley and the Psalaspis faunule in the Tomah mem- include the type section of the formation. The ber in the area between Arkansaw and Reads cross section (Fig. 4) illustrates the lithic and (Bell, Feniak, and Kurtz, 1952, p. 176). The faunal correlation of exposures that extend from Ptychaspis subzone faunas also exhibit a Taylors Falls, Chisago County, to Afton, stratigraphic climb from the Mississippi valley Washington County, Minnesota. to the St. Croix Valley (Figs. 4, 6). There is The Franconia is best exposed in the Hudson- some evidence of environmental control on the Afton area where its estimated thickness is 190 distribution of these faunas. The Stigmaceph- feet (indicated at top of formation in Fig. 4). alus oweni faunule is best developed in thin- The Woodhill apparently maintains a uniform bedded Mazomanie sandstone but has never thickness of 18 feet. At Hudson the base is been found in Reno greensands, whereas the marked by a thin bed of very coarse sandstone reverse is true of the Ptychaspis striata teilzone. studded with small pebbles and is overlain by The climb of the teilzones is interrupted by alternating beds of cross-bedded sandstone and apparent truncation beneath the overlying poorly sorted beds with worm borings. At Prosaukia subzone, a condition perhaps in- Franconia the Woodhill consists of cross-bedded, dicative of rapid change of environment not medium-grained sandstone with quartz pebbles expressed in the sediments. in the upper half. In the town of Taylor Falls, 1 The Prosaukia subzone shows an environ- mile north of the Taylors Falls section, a mental segregation of species. An assemblage boulder conglomerate containing the Elvinia called the Prosaukia misa biofacies occurs in fauna rests on Precambrian diabase. This is the the Reno greensands and the thin-bedded Mill Street conglomerate of Berkey (1897) and

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represents a shore phase of the Woodhill to those in the St. Croix Valley. Outcrops ex- member. tend from Dallas in southern Barron County, The Birkmose member is nearly 30 feet thick through Dunn County, to Arkansaw in north- and consists of wormstone and greensand. At ern Pepin County, Wisconsin. Taylors Falls there is no terminal conglomerate, The Woodhill is 34 feet thick at Arkansaw. but more than half the upper portion is dol- Three divisions are well developed: a lower omitic with interbedded buff siltstone and coarse-grained and poorly sorted sandstone 6 greensand. The Tomah is 28 feet thick at feet thick, a middle coarse-grained but well- Hudson and thins rapidly to the north. Only 8 sorted sandstone 22 feet thick, and upper beds feet is exposed at Marine, and the member of cross-bedded and worm-bored sandstone 6 pinches out between there and Franconia. feet thick. The Birkmose has a maximum thick- Above the Tomah a tongue of thin-bedded ness of 38 feet at Panther Hill where local Mazomanie sandstone is slightly glauconitic at thickening is due to the dominance of cross- Hudson but nonglauconitic to the north. The bedded greensand. In other sections wormstones tongue thickens northward, and at the Fran- and conglomerates are most common. The conia type section it constitutes the entire Tomah is completely exposed only at Wheeler; exposure above the Birkmose member. A tongue it is 23 feet thick and contains some interbedded of Reno greensand and wormstone extends laminae of dolomitic siltstone. north from Hudson and interfingers with white Reno-Mazomanie intertonguing is identical Mazomanie sandstone at Copas. The upper to that of the St. Croix Valley. Thin-bedded or Mazomanie tongue consists of thin-bedded very gently cross-bedded, white sandstone con- sandstone below and cross-bedded, dolomitic stitutes the lower Mazomanie tongue. At the sandstone above. base of the Reno tongue an unusual greensand Dashed lines in Figure 4 show the approxi- conglomerate contains pebbles of white and mate boundaries between faunal zones, and the brown sandstone carrying a mixed fauna of indicated fossil collections were made by Nelson Conaspis parvafrons and species of the Ptychas- (1951). The Elvinia zone occurs in both the pis granulosa teilzone. This is the only Reno Woodhill and Birkmose members, and above conglomerate with pebbles sufficiently in- Elvinia the zones climb to the north. The durated to preserve fossils. The upper Mazom- Conaspis zone at Hudson is represented by the anie tongue is thin-bedded in the lower half Taenicephalus altus teilzone in 3 feet of upper with several beds of nonglauconitic wormstone, Birkmose conglomerate and basal Tomah whereas the upper half is cross-bedded sand- sandstone. The zone thickens rapidly north- stone partially leached of its dolomite. No ward, and at Taylors Falls it becomes more than complete exposure of the Franconia exists, but 90 feet thick by the addition of the Eoorthis the correlation of sections indicates a maximum subzone and Maustonia nasuta teilzone beneath thickness of about 210 feet at Ridgeland. the expanded T. altus teilzone. Similarly in the Ptychaspis subzone, the Stigmacephalus oweni The contact between the Elvinia and Con- faunule expands into the lower Mazomanie aspis faunas falls within the upper Birkmose tongue, and the occurrence of Ptychaspis member except at Panther Hill. The Maustonia granulosa is restricted to Arcola and Hudson. nasuta teilzone is present in the basal Tomah, Ptychaspis striata is not found in the St. Croix and the Taenicephalus altus teilzone extends Valley. In the Prosaukia subzone, the Prosaukia through the Tomah and into the lower Ma- misa biofacies is present in the Reno member at zomanie tongue at Wheeler. Rock containing Afton, Hudson, and Arcola, and in thin-bedded the Ptychaspis granulosa fauna probably was Mazomanie sandstone at Copas. The Prosaukia eroded soon after its deposition, and the zone longicornis biofacies is confined to cross-bedded appears to pinch out northward. At Ridgeland Mazomanie sandstone at Hudson and Marine. the Prosaukia misa biofacies occurs in Reno and thin-bedded Mazomanie sandstones, and the Dunn County highest collection contains the Prosaukia longi- Incomplete exposures in the Dunn County cornis biofacies in cross-bedded Mazomanie area (Fig. 5) show member relationships similar sandstone.

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Mississippi Valley subzone is represented by the Prosaukia misa biofacies near the middle of the Reno member, Exposures along the Mississippi (Fig. 6) and the Dikelocephalus postrectus fauna occurs show a uniformity of the Franconia in an area near the top of the formation at Winona, Hell not reached by the Mazomanie facies. In addi- Hollow, and Victory. tion to illustrating rock types, the cross sec- tion locates the stratigraphic position of fossil collections from southeast Minnesota referred Buffalo River Valley to by Bell, Feniak, and Kurtz (1952, p. 179- Three incomplete sections in the Buffalo 181). River Valley of Wisconsin show an unusual The Woodhill thickens from 33 feet at phase of the Franconia (Fig. 8). At Praag, Arkansaw to a maximum of 44 feet at La Buffalo County, the Birkmose has cross-bedded, Crescent. Here the basal 6 feet is coarse-grained red-brown dolomite at the top and is overlain and horizontally bedded with laminae of gray by wormstones of the Reno member. The worm- silt, the middle 25 feet coarse-grained and mot- stones are glauconitic and shaly, but some beds tled with orange borings, and the upper 13 preserve the lamination found in Tomah feet medium-grained, well sorted, and cross- sandstone. The beds probably were formed by bedded. The Birkmose consists of wormstone organic reworking of Tomah sandstone. Thin and thin greensand beds at Arkansaw, and the beds of laminated and glauconitic sandstone dominance of wormstone is maintained as far interbedded with the wormstone contain fossils south as Minneiska. At Winona and Galesville of the Taenicephalus altus and Ptyehaspis most of the member is silty, dolomitic, and striata teilzones. Near Mondovi in northeast studded with large glauconite grains. This Buffalo County, the Birkmose member has only phase represents a change to the thinner unit 1 foot of red-brown dolomite at the top and is of greensands and lenticular dolomite conglom- overlain by worm-bored, laminated sandstone erates found in Houston County. The Tomah and glauconitic wormstone of the Reno mem- contains beds of wormstone from Arkansaw to ber. The section also includes a 4-foot non- Minneiska. The wormstone was derived from glauconitic bed. In Dramman Township, Tomah-type sandstone, and many beds still southwest Eau Claire County, the Birkmose is retain lamination and shaly partings. From 30 feet thick but lacks dolomite at the top. The Galesville south, the Tomah contains more in- Birkmose and Reno members are separated by a terbedded shale than is common in other areas. 15-foot bed of white sandstone, probably a Glauconitic wormstones dominate in the tongue of thin-bedded Mazomanie sandstone. Reno member, and the Reno itself forms over half the total thickness of the formation. Fossils Houston to Adams Counties are obtained from thin beds of pink to gray laminated, micaceous sandstone. Thicker, cross- The Franconia is best exposed from Houston bedded greensands occur in the upper half of County in southeast Minnesota through La the Reno, and at the top of the member the Crosse, Monroe, and Juneau counties to Adams terminal dolomite conglomerate ranges from 1 County in central Wisconsin (Fig. 7). to 6 feet thick. Three divisions of the Woodhill, as described The boundary between the Elvinia and above, can be recognized from La Crescent to Conaspis zones is in the upper Birkmose from Tunnel City, but in the type area only two Arkansaw to Minneiska but is near the middle occur, the lower coarse-grained and poorly of the member at Galesville and Brownsville. sorted and the upper medium-grained and well The lowest Conaspis collections contain Para- sorted. At Friendship Mound only a single unit bolinoides palatus at Galesville and Misha of cross-bedded sandstone with a basal grit is Mokwa and Eoorthis at Brownsville; all other present. The Birkmose in Houston County collections represent the Taenicephalus altus ranges from 9 to 18 feet thick and consists of teilzone. The Ptyehaspis granulosa teilzone and interbedded greensand, siltstone, and lenses of its basal faunules are present in the north, dolomite conglomerate. It thins eastward to 4 whereas only the Ptyehaspis striata teilzone feet of greensand and dolomite conglomerate, occurs south of Minneiska. The Prosaukia but at Brush Creek the member is unusually

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TAYLORS COPAS | ARCOLA | FALLS I MARINE HUDSON | FRANCONIA AFTON DALLAS WILSON I I WHEELER " MENOMONIE I RIOGELANO PANTHER HILL ARKANSAW FIGURE 4.—ST. CROIX VALLEY CROSS SECTION FIGURE 5.—DUNN COUNTY CROSS SECTION NORTH SOUTH 1 : I80 i-^"^ ^ -^"- TE|AI Q/iiefoctptiatos posfrtctus zone Ei 1 > E? /I i '7 i 1 Prosatikio subzone t^ i ^ri; / 1

LAKE READS LA CRESCENT BROWNS- I CITY , I VILLE | MISHA MAPLE MOUNT HELL MOKWA SPRINGS TOM HOLLOW FIGURE 6.—MISSISSIPPI VALLEY CROSS SECTION Victory section from Twenhofel, Raasch, and Thwaites (1935, p. 1733).

low in glauconite content and consists of sand- shaly greensand. This clay constitutes the entire stone conglomerate and silt. At Hustler a dense, Birkmose at Wood Hill and Goodenough Hill, red-mottled dolomite is overlain by dark red, At Horseshoe Bluff the member consists of 1 glauconitic clay that represents a weathered foot of greensand and shale. Although the B irk-

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I I I I I FRIEND- HORSE- BRUSH TUNNEL HUSTLER WOOD SHIP SHOE I LA CRESCENT I I CREEK | CITY I HILL MOUNO | BLUFF | BROWNSVILLE FRANKLIN SPARTA MAYNARO OOOOENOU6H COOLEY HELL HOLLOW PASS HILL HILL FIGURE 7.—HOUSTON TO ADAMS COUNTIES CROSS SECTION Upper half of Tunnel City section from Twenhofel, Raasch, and Thwaites (1955, p. 1732).

KEY S*--nofl-glauconitlc > -dolomilic | Sl.-highl-moderately glouconitiy glouce. Wormstone I Grttniand conglom. I Dolomite conglom. I CovereSs.-thind bed, shoty RENO • Fotsils SCALE 100-1

WOODHILL I I BLUi E LONi E FERRY BLACK RIVER | ROCK | BLUFF EARTH SEXTON- SPRING DRAMMAN MONDOVI PRAAB Milet VILLE GREEN FIGURE 8.—BUFFALO VALLEY CROSS SECTION FIGURE 9.—WISCONSIN VALLEY CROSS SECTION Upper half of Lone Rock section from Twenhofel, Raasch, and Thwaites (1935, p. 1726)

mose is thin and somewhat variable, the con- The Reno and Mazomanie interfinger centration of glauconite at this horizon makes throughout the central area. Two feet of yellow it a useful key bed. The Tomah is 28 feet thick Mazomanie sandstone is present in the Frank- at the type locality, Maynard Pass, and thins lin section, but at Brush Creek yellow sandstone to a minimum of 9 feet both to the east and to is thinly interbedded with greensand and worm- the west. stone. Only the basal 6 feet of the Mazomanie

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is now exposed at Maynard Pass and Tunnel cephalus oweni faunule is present in the Ma- City, but Twenhofel and Thwaites (1919, p. zomanie member of Adams County. In the 625) give a maximum thickness of 50 feet of Prosaukia subzone, the P. misa biofacies is yellow sandstone. They described the member present in the Reno member, and the P. as "thick-bedded, horizontal and cross-lam- longicornis biofacies in the Mazomanie member. inated yellow and gray sandstone" and observed The Dikdocephalus postrectus zone occurs at some greensand that indicates interfingering Hell Hollow and was reported from the Tunnel with the Reno member. Goodenough Hill City section by Twenhofel, Raasch, and shows two tongues of Mazomanie sandstone Thwaites (1935, p. 1732). separated by 5 to 10 feet of Reno greensand. The lower tongue is 15 feet thick, cross-bedded, Baraboo Area and friable. The upper tongue is 56 feet thick and, in the lower half, is thin-bedded with shaly Outcrops in Sauk County immediately north worm borings in some beds. The upper half is of the Baraboo Range demonstrate a thinning white to brown, cross-bedded, and dolomitic. of all members except the Mazomanie. At Twenhofel, Raasch, and Thwaites (1935) Ironton the Woodhill sandstone is 2 to 8 feet denned a "basal conglomerate and greensand" thick and is distinguished from the underlying member of the Trempealeau formation, 14 feet Galesville only with difficulty. At Dellona the thick as identified at Goodenough Hill (Twen- Galesville is medium-grained and well sorted hofel, Raasch, and Thwaites, 1935, p. 1729). and is overlain by 1 foot of coarse, red-brown This unit is Reno wormstone and greensand, Woodhill sandstone. The Birkmose consists of and the half-foot basal conglomerate is one of 1 foot of glauconitic red day. Above the Birk- three greensand conglomerates near the top mose is thin-bedded sandstone that contains of the member here and at other localities. the Irvingella major and Eoorthis faunas. Al- The Franconia in Adams County is poorly though weathered and poorly exposed, the unit exposed in erosional outliers. On Friendship appears to contain the interbedded shale of the Mound the Mazomanie member is medium- to Tomah member. Elsewhere in Sauk County coarse-grained sandstone, completely leached of the major portion of the Franconia consists of dolomite. The character of the member is well cross-bedded Mazomanie sandstone, but a shown in fresh exposures at Cooley Hill where complete exposure was not found. a small quarry at the base of the section has 6 Wanenmacher, Twenhofel, and Raasch feet of thin-bedded Mazomanie, and a road cut (1934) and Raasch (1935) have described the higher in the section exposes cross-bedded Franconia within the Baraboo Range. Accord- Mazomanie with alternating beds of white ing to them, the formation is about 60 feet friable sandstone and brown dolomitic sand- thick and contains coarse basal beds of con- stone. At the top of Horseshoe Bluff a 2-foot glomerate and grit that lie on Precambrian bed of brown sandstone contains scattered quartzite or on finer-grained Dresbach sand- glauconite grains; it suggests a tongue of Reno stone. The basal beds, probably a shore phase greensand at the top of the formation. The of the Woodhill, are succeeded by 15 feet of contact with the St. Lawrence has not been brown, sandy dolomite containing Eoorthis observed in Adams County, but a minimum remnicha and Billingsella major. Above the thickness of 150 feet for the Franconia is sug- dolomite is white to yellow, medium- to coarse- gested. grained, cross-bedded Mazomanie sandstone The rise of faunal zones to the east is charac- containing the Ptychaspis, Prosaukia, and teristic above the Elvinia zone, and the climb Briscoia faunas. The uppermost 10 to 15 feet of teilzones of the Conaspis fauna is described of the formation is fine- to medium-grained above (Fig. 3). The Irvingella major fauna is Reno greensand. found only in Adams County in the basal Tomah member. Ptychaspis granulosa occurs Wisconsin River Valley in the Reno member in the Mississippi Valley, Exposures south of the Baraboo Range and but only Ptychaspis arcolensis of the Stigma- along the Wisconsin River (Fig. 9) show the

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relationship between Mazomanie of the type glauconite coats detrital quartz and forms dis- area and Franconia greensands to the west. At seminated green dust in some of the silty or Ferry Blufi the lowest Franconia bed is 1 foot shaly sandstones. Birkmose greensand usually of cross-bedded greensand of the Birkmose contains the highest percentage of glauconite member. Above, the Mazomanie is 116 feet grains (up to 50 per cent), whereas Reno green- thick, cross-bedded, and dolomitic. A 7-foot sand contains about 20 to 30 per cent. bed of brown, sandy dolomite near the base, The distribution of glauconite indicates a containing an orthid brachiopod, is equivalent sedimentary environment in accord with that to the dolomite of the Baraboo area described previously suggested for glauconitization (Had- by Wanenmacher, Twenhofel, and Raasch ding, 1932; Galliher, 1935; Takahashi, 1939). (1934). A Reno tongue of moderately glauco- That the accumulation of glauconite takes place nitic greensand about 25 feet thick occurs at under conditions of slow sedimentation is in- the top of the formation. dicated by the greater thickness of the Conaspis At Lone Rock and Sextonville the Woodhill zone in the Mazomanie member than in the member is absent. The Birkmose consists of 3.5 Birkmose greensand. The facies relationship feet of sandy dolomite, greensand, and a basal between the Reno and Mazomanie suggests that conglomerate including fragments of Camaras- glauconite formed at a considerable distance pis sp. The Tomah contains the Parabolinoides from shore. However, ripple marks and, more palatus and Maustonia nasuta teilzones and, at rarely, mud cracks found along silty laminae in Lone Rock, has two conglomerates composed the Reno greensands prove that they were of shale and silt pebbles in a glauconitic matrix. formed in shallow water and were sometimes Above the Tomah, Reno greensands interfinger exposed to desiccation on tidal flats. Glauconite with thin-bedded Mazomanie sandstone, and occurs essentially at the site of origin. Glau- at Sextonville species of the Ptychaspis striata conitization took place in fine-grained, neritic teilzone occur in the Reno. The outcrop at Blue sediments, which were built up to the level of River exposes 7 feet of medium-grained Wood- effective wave base. Fine particles were win- hill sandstone carrying Camaraspis convexa. nowed out leaving cross-bedded greensand. The Reno greensands presumably replace the Franconia glauconite offers no clue as to the Mazomanie member in the west to form a source materials from which it was derived. The Franconia section similar to that farther north. Tomah sandstone contains 2 per cent muscovite, No complete exposures are known between some of which appears to be stages of alteration Sextonville and the Mississippi, for outcrops to glauconite. Most of the muscovite is clear, show only the upper part of the Reno. but some flakes show irregular light-green stains on the edges, others are yellow green and PALEOGEOGRAPHIC SPECULATIONS isotropic, and a few show scattered, granular aggregates of glauconite but still preserve the Significance of Lithic Types micaceous form. No gradation was found be- Glauconite formed in place is rare but does tween glauconitized muscovite and the typical occur as scattered grains in thin beds of dol- rounded glauconite grains. The green muscovite omitic silt and shale in the Birkmose at Gales- suggests glauconitization along the cleavage ville and Sextonville. The grains are dark green, planes because of structural similarity, with no smooth, ovoid, and average 1 mm in length, but alteration of the muscovite (J. W. Gruner, a few are tabular and range up to 3 mm long. personal communication). They probably were not transported with the Two types of flat-pebble conglomerates are surrounding fine-grained particles. Transported common in the Franconia, siltstone and green- glauconite is most common and occurs in sub- sand conglomerates, and both indicate local, spherical grains, light yellow green to dark subaqueous fragmentation. Lensing beds of green, with irregular lobate surfaces marked dolomitic siltstone conglomerate occur at or by cracks. The grains are concentrated in near the top of the Birkmose and Reno. Silt- cross-bedded greensands, and they are never stone pebbles are gently to steeply inclined with larger than the associated quartz grains. Much respect to the bedding planes and fall into two

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size classes: either ovoid, rounded, and 1 to 3 sition of Galesville sandstone in fresh water, inches in longest diameter, or thin, discoid, and following the retreat of a shallow inland sea. 4 to 6 inches in diameter. The matrix is com- With the return of marine waters to the area, posed of glauconitic, sandy to silty, fine-grained the basal coarse-grained and poorly sorted dolomite. A second type of conglomerate occurs Woodhill sandstone was rapidly deposited in most commonly in thin beds within the upper the littoral environment by an influx of detritus 10 to 40 feet of the Reno member. Discoid and possibly reworked Galesville sand. The up- pebbles of soft sandstone range up to 6 inches per Woodhill, cross-bedded and well sorted, was in diameter and 1 inch in thickness and are deposited more slowly in shallow water. The scattered in a greensand matrix. Pebbles are Franconia sea transgressed from the southwest rarely abundant and lie nearly parallel to the in the area of maximum Woodhill thickness and bedding planes. The greensand conglomerates progressed northward and eastward to the are not persistent laterally. The occurrence of Taylors Falls and Baraboo islands where both conglomerate types with greensands indi- conglomerates formed by intensive wave action. cates they formed in shallow water but at a After the period of rapid transgression, sea considerable distance from shore, probably by level remained relatively stable, and a near fragmentation of partially indurated sediment balance was maintained between sedimenta- during periods of strong wave action. The silt- tion and depression of the area. Glauconite of stone conglomerates represent terminal deposi- the Birkmose member formed in fine-grained tion of the underlying cross-bedded greensands sediments that were intermittently agitated and rather than the initial deposits of the overlying washed by wave action, thus forming cross- fine-grained and thinly laminated sediment. bedded greensand. Partially indurated silt was Highly dolomitic beds of the Birkmose and fragmented, and flat pebbles accumulated in Mazomanie members are clastic rocks, and their bottom depressions to form lensing dolomite allochthonous origin is clearly indicated by conglomerates. In the northern half of the area cross-bedding, occasional flat pebbles of silt- greater thicknesses of sediment slowly ac- stone, and gradation into beds of quartzose cumulated and were thoroughly burrowed by sandstone. Only the red-brown glauconitic benthonic animals. It may be assumed that the dolomite of the upper Birkmose contains organic lower part of the Birkmose was formed offshore, debris, rare cystoid (?) columnals. The sandy while the upper Woodhill was deposited nearer dolomite of the Mazomanie consists of large the strand line, for both members carry the dolomite grains of irregular or rhombic outline Elvinia fauna. cemented by clear calcite. Dolomite grains and In early Conaspis time the site of Birkmose rounded quartz grains alternate in relative deposition may have been a shoal area that abundance in successive laminae. These dol- provided a partial barrier and protection from omites were deposited in very shallow water; wave action for the waters to the east in which the dolomite probably was derived by diagenetic the interbeddded shale and sand of the Tomah alteration of calcite after deposition of calcite member was deposited (Fig. 3). Tomah deposi- fragments and detrital quartz. tion moved westward and reached the Missis- sippi Valley in late Conaspis time. In areas to Depositional History the north, Tomah sediments formed during Pre-Franconia deposits of the Dresbach middle and upper Conaspis time or through part formation exhibit a single transgressive-regres- of Ptychaspis subzone time. Tomah deposition, sive cycle; the fine-grained, fossiliferous sand- then, was confined to an environment of quiet stone of the Eau Claire member forms a marine water that was areally restricted and occurred wedge that pinches out eastward in central in several places at different times. While Wisconsin and is enclosed by the coarser, cross- Tomah sand and clay continued to be deposited bedded sandstones of the Mt. Simon and offshore, thicker Mazomanie sands, thin-bedded Galesville members. Twenhofel, Raasch, and and without clay, accumulated in shallow water Thwaites (1935, p. 1715) postulated that to the north and east (Fig. 3). Tomah deposi- Dresbach sedimentation closed with the depo- tion ended at any given place by decrease in rate

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of sedimentation that favored glauconitization Taylors Falls and permitted extensive burrowing by ben- Road cut on U. S. Highway 8 and section along thonic animals. Finally, greensand and worm- Pine Point Trail, 1 mile south of Taylors stones formed over the entire offshore portion Falls, Chisago Co., Minn. Fossils after Nelson of the outcrop area, and Tomah deposition, if (1951). it persisted, was confined to the area farther Franconia formation—110.5 feet exposed south and west. Intertonguing of the Reno and Mazomanie Mazomanie member—81.0 feet exposed Feet 7. Sandstone, as below, alternating with reflects variation in sediment supply and, sandstone, brown, fine, thin-bedded, perhaps, some fluctuation in depth of water. slightly glauconitic laminae, beds 3 to 6 feet thick. Conaspis paroafrons, C. tumidus, Nonglauconitic, cross-bedded sands were de- Croixana bipunctata, Wilbernia halli 48.0 posited nearest the shore, and thin-bedded sands offshore, while glauconitic wormstones 6. Sandstone, white, fine to medium, massive or gently cross-bedded, few coarse and greensands formed still farther from the laminae, thin beds of dolomite and silt- strand line. Increase of detritus extended stone near base. Conaspis perseus, Taeni- cephalus shumardi, Billingsella sp 26.5 tongues of nonglauconitic sands and displaced the environment of glauconitization to the 5. Sandstone, gray to brown, fine, massive to thin-bedded. Maustonia nasuta, Taeni- south and west. The Taylors Falls and Baraboo cephalus sp., Billingsella sp 6.5 islands were submerged and eventually covered Birkmose member—29.5 feet exposed by Mazomanie sands. The final phase of 4. Greensand, interbedded gray silty dolo- Franconia deposition was marked by decrease mite. Eoorthis remnicha 3.5 in supply of detritus that resulted in extensive 3. Siltstone, dolomitic, greensand laminae. glauconitization, the spread of greensand over Parabolinoides contractus, Eoorthis sp. . . . 1.5 the entire area, and the formation of dolomite 2. Greensand and thinly interbedded dolo- conglomerates. There is no evidence for regres- mitic siltstone 14.5 sional sedimentation. 1. Greensand, abundant gray shaly worm Island areas contributed sediments to the borings 10.0 littoral zone only during early Franconia dep- osition. For the most part sediments were Hudson derived from the Precambrian terrane far to the Section in south part of Hudson along State High- north and east. That the most important way 35 and on adjacent hill, SE% sec. 25, T. source rocks were older sediments is indicated 29 N., R. 20 W., St. Croix Co., Wis. Fossils by the dominance of subrounded quartz and after Nelson (1951) the presence of well-rounded grains of only the Franconia formation—171.5 feet exposed most durable heavy accessory minerals, garnet, Mazomanie member—10.0 feet exposed Feet tourmaline, and zircon. 18. Sandstone, white to brown, fine, friable, cross-bedded, upper dolomitic with white sandstone pebbles 10.0 Reno member—5.0 feet exposed MEASURED SECTIONS 17. Wormstone, buff, with cross-bedded greensand 5.0 General Statement 16. Covered 7.5 Mazomanie member—8.0 feet exposed The location of nearly all measured sections 15. Sandstone, white to brown, fine, friable, is given by Nelson (1951 p. 770), Bell, Feniak, upper dolomitic, cross-bedded. Chario- cephalus whitfieldi, Prosaukia sp. at and Kurtz (1952 p. 178-181), and Berg (1953 top 8.0 p. 557-559). Seven sections are selected to Reno member—32.5 feet exposed illustrate typical rock types in local areas; they 14. Wormstone, buff, glauconitic, with sev- are arranged geographically from northwest to eral beds of greensand. Prosaukia cf. P. dubia, Ptychaspis miniscaensis, Stigmas- southeast. pis hudsonensis near base 24.5

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13. Greensand, fine, cross-bedded, few thin 13. Wormstone, with beds of greensand con- shales 5.5 glomerate 6 inches thick 25.0 12. Wormstone, orange, glauconitic 2.5 12. Greensand, fine, moderately glauconitic, cross-bedded 4.0 11. Covered 17.0 11. Covered (estimated) 60.0 Mazomanie member—20.0 feet 10. Sandstone, yellow to buff, fine to me- Tomah member—26.5 feet dium, thin-bedded or gently cross 10. Sandstone, buff, fine, micaceous, thin- bedded, slightly glauconitic, micaceous. bedded, few worm borings. Idahoia (Psal- Idahoia wisconsensis, Monocheilus ana- aspis) marginata, I. hera, Monocheilus tinum, Ptychaspis gramdosa 20.0 anatinum, Ptychaspis gramdosa, Wilber- nia explanata, Pseudagnostus josepha, Tomah member—27.0 feet BiUingsetta pepina at base, and Idahoia 9. Sandstone, yellow to buff, very fine, thin- (Psalaspis) pattersoni at top 6.0 bedded, micaceous, with interbedded gray shale. Taenicephalus altus, Wil- 9. Wormstone, buff, micaceous, glauconitic. 2.0 bernia halli, Pseudagnostus josepha at 1 foot, Stigmacephalus oweni, S. oweni var. 8. Sandstone, gray, fine, micaceous, inter- A, Idahoia hera, Monocheilus anatinum, bedded shale. Idahoia (Psalaspis) mar- Ptychaspis arcolensis, Wilbernia explanata ginata, Monocheilus anatinum, Wilbernia W. pero at 3 to 12 feet, Monocheilus ana- hudsonensis 3.0 tinum, Ptychaspis gramdosa at 14 to 23 feet above base 27.0 7. Wormstone, gray, micaceous, glauconi- tic. 1.5 Birkmose member—27.0 feet 8. Dolomite, red-brown, conglomeratic. 6. Sandstone, like bed 8. Stigmacephalus Taenicephalus altus, Wilbernia sp., Bil- oweni, Taenicephalus cf. T. altus, Wil- lingsella cf. B. pepina, Huenella sp. in bernia explanata, Pseudagnostus josepha, upper half 2.5 Billingsella cf. B. pepina, 6 feet above base 14.0 7. Greensand. Elvinia roemeri at top 9.0 Birkmose member—27.5 feet 6. Wormstone with thin beds of green- 5. Conglomerate, red brown, dolomitic, sand 15.5 glauconitic, flat pebbles of siltstone, laminae of buff siltstone 4.5 Woodhill member—18.0 feet 5. Sandstone, yellow, medium to coarse 4. Wormstone, buff to orange, glauconitic, cross-bedded, inarticulate brachiopods, with thin cross-bedded greensands 23.0 thin wormstone bed in middle 3.5 Woodhill member—33.0 feet 4. Sandstone, yellow to white, fine to 3. Sandstone, brown, medium, cross- coarse, cross-bedded 7.0 bedded, lower part white silty with orange worm borings, ripple marks at top 5.5 3. Sandstone, yellow to gray, medium to very coarse, cross bedded, pebbles and 2. Sandstone, white to brown, medium to granules in basal foot 7.5 very coarse, massive 22.0 Dresbach formation 1. Sandstone, brown, medium to coarse, Galesville member—21.0 feet horizontal bedding with gray shale 2. Sandstone, white to yellow, medium, laminae 5.5 gently cross-bedded 3.0 Franklin 1. Sandstone, white, medium to coarse, some cross-bedding and interbedded shale, bed now covered 18.0 Road cuts and shale pit on County Road C, sec. 2, T. 20 N., R. 6 W., Franklin Town- Arkansaw ship, Jackson Co., Wis. Composite of road cuts just north of Arkansaw St. Lawrence formation Feet and along U. S. Highway 10 1 mile north and 19. Sandstone, buff, very fine, thin-bedded, slightly glauconitic, dolomitic siltstone 2.5 miles west of Arkansaw, sec. 2 land 24,T. in lower 3 feet. Osceolia osceola 13.0 25 N., R. 14 W., Pepin Co., Wis. Franconia formation—182.0 feet Franconia formation—182.0 feet Reno member—55.5 feet Reno member—95.0 feet Feet 18. Conglomerate, small siltstone pebbles in 14. Conglomerate, dolomitic, glauconitic, highly glauconitic, sandy, dolomitic siltstone pebbles 2 inches in diameter. .. 6.0 matrix 3.0

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17. Greensand, fine highly glauconitic 4.0 Maynard Pass 16. Wormstone, buff, glauconitic, 1-foot greensand conglomerate in middle 9.5 Road cuts on U. S. Highway 16, 6 miles west of Tomah, NWy sec. 22, T. 17 N., R. 2 W., 15. Greensand, light to dark gray, moder- 4 ately glauconitic, cross-bedded, ripple Monroe Co., Wis. marks on silty laminae 32.0 St. Lawrence formation Feel 14. Wormstone, buff, glauconitic 7.0 Mazomanie member—2.0 feet 11. Sandstone, brown, very fine, thin bedded, 13. Sandstone, white to yellow, fine, thin- slightly glauconitic 12.0 bedded 2.0 Franconia formation—184 feet Reno member—61.0 feet 12. Wormstone and greensand 6.5 Reno member—38.5 feet exposed 10. Conglomerate, flat pebbles of sandstone 11. Covered 21.5 in sandy, glauconitic dolomite 2.0 10. Greensand, gray to brown, medium- grained, moderately glauconitic, cross- 9. Wormstone, buff to orange, glauconitic, bedded to thin-bedded, 3-foot beds of thin beds of greensand and greensand wormstone at middle and top. Kendallia conglomerate 18.5 eryon, Taenicephalus shumardi at 4 feet, Stigmacephalus similis, Taenicephalus 8. Greensand, slightly to moderately glau- altus at 8 feet above base 29.0 conitic with glaucpnite concentrated along cross laminations, 2-foot bed of 9. Wormstone, buff, 3-inch greensand near greensand conglomerate near top 18.0 top 4.0 7. Covered 33.0 Tomah member—18.0 feet 8. Sandstone, gray to buff, fine, micaceous, interbedded shale, greensand laminae at Mazomanie member—6.0 feet exposed top. Parabolinoides palatus, Kendallia 6. Sandstone, white to yellow, fine to me- biforota, Taenicephalus shumardi at base, dium, cross-bedded 6.0 Conaspis perseus, Maustonia nasuta, Taenicephalus shumardi, Billingsella cf. Reno member—45.5 feet B, perfecta, 9 and 12 feet above base 18.0 5. Wormstone, buff to orange, slightly glau- conitic, two beds of greensand in lower Birkmose member—4.0 feet half. Ellipsocephaloides curtus, Idahoia 7. Conglomerate, dolomitic, glauconitic, flat cf. /. wisconsensis, Ptychaspis tuberosa 7 pebbles of sandstone, laminae of green- feet above base 19.0 sand and siltstone. Eoorthis sp 1.0 4. Greensand, fine to medium, highly glau- 6. Dolomite, red brown, glauconitic, coarse, conitic, cross-bedded, ripple marks on sandy. Camaraspis sp 1.0 silty laminae 11.5 5. Greensand, cross-bedded 2.0 3. Greensand, gray to brown, fine, mod- Woodhill member—42.0 feet erately glauconitic, mostly cross-bedded, 4. Sandstone, brown, coarse, cross-bedded, thin greensand conglomerate at top. upper half slightly glauconitic. Camaras- Kendallia eryon, Maustonia nasuta, pis convexa, C. plana, Elvinia roemeri, Taenicephalus shumardi, WUbernia ed- Housia varro, Iddingsia aff. I. crassimar- wardsi, Billingsella cf. B. perfecta 1 and ginata in upper half 6.0 4 feet above base 15.0 3. Sandstone, white to yellow, very fine to Tomah member—27.5 feet coarse, massive, and 1-foot beds of 2. Sandstone, buff to gray, very fine, mica- brown, coarse, cross-bedded sandstone.. 21.0 ceous, interbedded shale. Kendallia bi- forota, Parabolinoides palatus, Taeni- 2. Sandstone, white to brown, fine to very cephalus shumardi, Billingsella cf. B. coarse, thin horizontal bedding 15.0 perfecta 1 and 3 feet, Conaspis perseus, Maustonia nasuta, Taenicephalus shu- mardi, WUbernia edwardsi 16.5 feet Dresbach formation above base 27.5 Galesville member—13.0 feet 1. Sandstone, yellow, medium to coarse, Birkmose member—0.5 feet exposed well sorted, some cross-bedded 13.0 1. Greensand, poorly exposed in ditch.... 0.5

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Goodenough Hill Birkmose member—1.5 feet 6. Clay, yellow green, studded with large grains of glauconite 1.0 Road cuts on State Highway 71, 6 miles southwest of Mauston, NEy± sec. 13, T. 15 N., R. 2 E., 5. Clay, deep purplish red, many large Juneaw Co., Wis. In part from Twenhofel, grains of glauconite. Billingsella. abun- dant 0.5 Raasch, and Thwaites (1935, p. 1729) Woodhill member—32.5 feet St. Lawrence formation Feel 4. Sandstone, brown, medium to coarse, 19. Siltstone, buff, dolornitic, in lower 2 feet, well sorted, glauconitic. Camaraspis con- and brown, very fine, slightly glauconitic vexa 3.5 sandstone 8.0 3. Sandstone, brown, medium to coarse. Franconia formation—168.0 feet Camaraspis sp. at top 12.0 Reno member—34.0 feet 2. Sandstone, yellow to white, fine to coarse, 18. Greensand, moderately glauconitic, horizontally bedded with laminae of gray laminae of buff silt, thin lens of con- shale, few beds of coarse, cross-bedded glomerate at top 3.0 sandstone 17.0 17. Wormstone, buff, glauconitic, laminae Dresbach formation of silt, greensand bed in middle. ... 8.0 Galesville member—60.0 feet 16. Greensand conglomerates, three half-foot 1. Sandstone, white to brown, medium to beds separated by wormstone 3.0 coarse, cross-bedded 60.0 IS. Wormstone, gray, glauconitic, with several greensands 20.0 Lone Rock Mazomanie member—56.0 feet 14. Sandstone, white to brown, fine, cross- Road cuts on State Highway 137, 1.5 miles south bedded, vertical borings, mostly friable, of Lone Rock, SE\i sec. 13, T.8 N.,R. 2 E., few thin brown dolomitic beds. Prosau- Iowa Co., Wis. Beds 16 and 17 after Twenhofel, kia longicornis 13.0 Raasch, and Thwaites (1935, p. 1726). 13. Covered 19.0 Franconia formation—130.0 feet 12. Sandstone, brown, fine, borings numer- ous. Idahoia wisconsensis, Monocheilus Reno member—20.0 feet Feet anatinum, Ptychaspis sp 7.0 17. Greensand, pebbles near base 20.0 11. Sandstone, white, fine, worm borings. El- Mazomanie member—61.5 feet lipsocephaloidcs curlus, Idahoia hem, I. 16. Sandstone, yellow, friable, alternating wisconsensis, Ptychaspis granulosa, Wil- with beds of brown, medium, dolomitic bernia pero 17.0 sandstone, some conglomeratic 39.0 Reno member—5.0 feet 15. Covered 9.0 10. Greensand, fine, moderately glauconitic, many brown borings. Ellipsocepha- 14. Sandstone, white, fine, friable, gently loides curtus, Ptychaspis granulosa 5.0 cross-bedded 13.5 Mazomanie member—15.0 feet Reno member—18.5 feet 9. Sandstone, white to brown, fine to me- 13. Greensand, moderately to highly glau- dium, cross-bedded, friable. Conaspis conitic, cross-bedded, pebbles of white sp., Taenicephalus sp 15.0 sandstone near base 4.5 Reno member—15.0 feet 8. Greensand, moderately glauconitic, 12. Wormstone, buff, glauconitic, many horizontal and cross-bedded, micaceous thin beds of white sandstone, some inter- near base. Conaspis sp., Taenicephalus bedded shale 14.0 sp., Wilbernia sp 15.0 Mazomanie member—7.0 feet Tomah member—9.0 feet 11. Sandstone, white to yellow, slightly 7. Sandstone, buff to gray, very fine, mica- glauconitic, fine, friable, flat pebbles of ceous, interbedded gray shale. Kendallia greensand throughout 7.0 biforota, Parabolinoides palatus in lower 3 feet, Conaspis perseus, Maustonia na- Reno member—8.5 feet suta, Taenicephalus shumardi, Wilbernia 10. Wormstone, with thin beds of greensand, cf. W. edwardsi, Billingsella cf. B. perfecta greensand conglomerate at top 8.5 at top 9.0 Tomah Member—11.5 feet

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/65/9/857/3431659/i0016-7606-65-9-857.pdf by guest on 25 September 2021 MEASURED SECTIONS 881

9. Sandstone, gray, very fine, micaceous, St. Croix Valley: Jour. Paleontology, v. 25, p. laminated, much interbedded gray 765-784. shale. Kendallia eryon, Mausotnia nasuta, Owen, D. D., 1852, Report of a geological survey of Taenicephalus shumardi, WUbernia ed- Wisconsin, Iowa, and Minnesota: Phila., Lip- wardsi at base 4.0 pincott, Grambo, & Co. Pentland, Arthur, 1931, The heavy minerals of the 8. Conglomerate, glauconitic sand with 4- Franconia and Mazomanie sandstones, Wis- inch pebbles of bed below 1.0 consin: Jour. Sed. Petrology, v. 1, p. 23-26. Raasch, G. O., 1935, Paleozoic strata of the Baraboo 7. Sandstone, like bed 9. Mausotonia nasuta area: Kans. Geol. Soc. Guidebook 9th Ann. at base 4.5 Field Conf., p. 405^14. Resser, C. E., 1937, Third contribution to nomen- 6. Conglomerate, gray glauconitic shale clature of Cambrian trilobites: Smithsonian with flat pebbles of sandstone 0.5 Misc. Coll., v. 94, no. 22. 1942, New Upper Cambrian trilobites: Smith- 5. Sandstone, like bed 9. Parabolinoides pala- sonian Misc. Coll., v. 103, no. 5. tus, Taenicephaliis shumardi, WUbernia Stauffer, C. R., and Thiel, G. A., 1941, The Paleo- cdwardsi, Billingsdla cf. B. perfecta at top 1.5 zoic and related rocks of southeastern Minne- sota: Minn. Geol. Survey Bull. 29. Birkmose member—3.5 feet Stauffer, C. R., Schwartz, G. M., and Thiel, G. A., 4. Greensand conglomerate, 4-inch flat 1939, St. Croixian classification of Minnesota: pebbles of siltstone 1.0 Geol. Soc. America Bull., v. 50, p. 1227-1244. Takahashi, Jun-ichi, 1939, Synopsis of glauconiti- 3. Dolomite, red to gray, granular, glauco- zation, in Recent Marine Sediments: Am. nitic, sandy, thins eastward 1.5 Assoc. Petroleum Geologists, p. 503-512. Trowbridge, A. C., 1935, Guidebook ninth annual 2. Conglomerate, flat pebbles of white sand- field conference: Kans. Geol. Soc., Fig. 1. stone in coarse, glauconitic, dolomitic Trowbridge, A. C., and Atwater, G. I., 1934, sandstone, some quartz pebbles, frag- Stratigraphic problems in the Upper Missis- ments of Camaraspis sp 1.0 sippi Valley: Geol. Soc. America Bull., v. 45, p. 21-79. Dresbach formation Twenhofel, W. H., and Thwaites, F. T., 1919, The Paleozoic section of the Tomah and Sparta Galesville member—31.0 feet exposed quadrangles, Wisconsin: Jour. Geology, v. 27 1. Sandstone, white, medium to coarse, p. 614-633. cross-bedded, rather well sorted but with Twenhofel, W. H., Raasch, G. O., and Thwaites, laminae of very coarse grains and gran- F. T., 1935, Cambrian strata of Wisconsin- ules 31.0 Geol. Soc. America Bull, v. 46, p. 1687-1743. Ulrich, E. O., 1920, Major causes of land and sea oscillations: Wash. Acad. Sci. Jour., v. 10, no REFERENCES CITED 3, p. 57-78. Bell, W. C., Feniak, O. W., and Kurtz, V. E., 1952, • 1924, Notes on new names in table of forma- Trilobites of the Franconia formation, south- tions and on physical evidence of breaks be- east Minnesota: Jour. Paleontology, v. 26, p. tween Paleozoic systems in Wisconsin: Wis. 175-198. Acad. Sci., Arts, Letters Trans., v. 21 n Berg, R. R., 1952, Feldspathized sandstone: Jour. 71-107. Sed. Petrology, v. 22, p. 221-223. Ulrich, E. O., and Resser, C. E., 1933, The Cam- • 1953, Franconian trilobites from Minnesota brian of the Upper Mississippi Valley, part H, and Wisconsin: Jour. Paleontology, v. 27, p. Trilobita: Saukiinae: Milwaukee Pub Mus' 553-568. Bull., v. 12, p. 123-306. Berkey, C. P., 1897, Geology of the St. Croix Dalles: Walcott, C. D., 1914, Dikelocephalus and other Am. Geologist, v. 20, p. 345-383. genera of the Dikelocephalinae: Smithsonion Bridge, Josiah, 1937, The correlation of the Upper Misc. Coll., v. 57, p. 345-412. Cambrian sections of Missouri and Texas with Wanenmacher, J. M., Twenhofel, W. H., and the section in the Upper Mississippi Valley: Raasch, G. O., 1934, The Paleozoic strata of U. S. Geol. Survey Prof. Paper 186-L, p. 233- the Baraboo area, Wisconsin: Am. Jour Sci 237. v. 28, p. 1-30. Galliher, E. W., 1935, Glauconite genesis: Geol. Whitfield, R. P., 1880, Descriptions of new species Soc. America Bull., v. 46, p. 1351-1365. of fossils from the lower geological formations Hadding, Assar, 1932, The pre-Quaternary sedi- of Wisconsin: Wis. Geol. Survey Ann. Rept mentary rocks of Sweden, IV. Glauconite and 1879, p. 43-71. glauconitic rocks: Lunds Univ. Arssk., N.F., Wilson, J. L., and Frederickson, E. A., 1950, The Avd. 2, Bd. 28, Nr. 2, p. 79-82, 144-160. Irvingdla major ("Ptychopleurites") faunizone Hall, James, 1863, Preliminary notice of the fauna of the Upper Cambrian: Am. Jour. Sci., v 248 of the Potsdam sandstone: Cab. Nat. History, p. 891-902. New York 16th Ann. Rept., p. 119-226. Howell, B. F. et al., 1944, Correlation of the Cam- THE CALIFORNIA COMPANY, P. O. Box 1769, CAS- brian formations of North America: Geol. Soc. PER, WYOMING America Bull., v. 55, p. 993-1003. MANUSCRIPT RECEIVED BY THE SECRETARY OF THE Nelson, C. A., 1951, Cambrian trilobites from the SOCIETY, APRIL 6, 1953

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