GEOLOGY OF THE BAMBOO DISTRICT.pdf

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Information CirculNumber 14

GEOLOGY OF THE BAMBOO DISTRICT, WISCONSIN

A Description and Field Guide IncorporatingStructural Analysis of the Precambrian RocksandSedimentologic Studies of the Paleozoic Strata

I. W. D. DalzielColumbia University, New York

andR. H. Dott, Jr.The University of Wisconsin, Madison

With Summaries of theGLACIAL GEOLOGY

R. F. BlackUniversity of Connecticut

and

PUNT ECOWGY OF THE BAMBOO HILLS

J. H. ZimmermanUniversity of Wisconsin Arboretum, Madison

Available from the Geological and Natural History Survey, 1815 UniversityAvenue, Madison, Wisconsin, 53706. Price $8.00


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GEOIQGY OF THE BARABOO DISTRICT. WISCONSINT a b l e of C o n t e n t s

FOREWORD ........................................................INTRODUCTION ( D a l z i e l an d D o t t ) ..................................

R e g i o n a l G e o l o g i c S e t t i n g ...................................H i s t o r y o f R e s ea r c h .........................................Economic Geology ............................................

PRECAMBRIAN GEOIQGY ............................................................e l a t i o n s h i p s an d Ag es o f t h e P r e c am b r i an R oc ks( D a l z i e l and D o t t )

P e t r o l o gy ( D a l z i e l ) ........................................S e d im e n t ol o g y o f t h e B ar ab oo Q u a r t z i t e ( D o t t ) ...............S t r u c t u r a l H i s t o r y ( D a l z i e l ) ..............................................................t r u c t u r a l Geom etry ( D a l z i e l ) ...................e n e s i s o f t h e B ar ab oo S y n c l i n e ( D a l z i e l ).........................................ALEOZOIC GEOIQGY ( D o t t )S t r a t i g r a p h i c Summary ............................................................ambrian Sed imen to log y and Pa leogeog raphy Impor tanc e o f Ra re Even t s ....................................

GLACIAL GEOIQGY ( B l a c k ) ..........................................I n t r o d u c t i o n ...............................................................erm inal mora in e of Late Woodfordian (Car y) Age ................e a t u r e s A s s o c i a te d w i t h t h e T e r m in a l M o ra in e....................v idence of G re a t e r Dep loyment of t h e Ic e S y n o p s i s o f G l a c i a l H i s t o r y an d E v o l u t i o n o f Some M a j o r L and-

forms ................................................ .......................LANT ECOLQGY OF THE BARABOO HILLS (Zimmerman)G e o lo g i c I n f l u e n c e s o n t h e B i o t a .............................E c o lo g i c D i v e r s i t y ...........................................Human Occupation .............................................

LIST OF REFERENCES ................................................FIELD TRIP ROAD LOG ( D a l z i e l and Do t t ) ...........................

Page1

APPENDIX .. UPPLENENTARY STOPS ( D a l z i e l and Do t t ) ...............


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ILLUSTRATIONSPage

Cover. Stanley A. Tyler by Van Hise Rock (STOP 2).Figure 1. Regional tectonic and index map of the Great Lakes Region ..

2. Orientation of cross stratification in the Baraboo Quartzite3. Cross section of the Baraboo syncline . . . . . . . . . . . . . . . . . . . . .4. Relations of main-phase mesoscopic structures..............5. Photomicrographs of cleavages in the Baraboo Quartzite.....6. Mechanical significance of main-phase cleavage accord-

ing to the isc cons in school" of structural geologists.7 . Suggested mode of origin of the longrain and the late main-

phase crenulations and cleavage (SIL) ..................8. Dynamic (stress) analysis of the Baraboo syncline .........9. Photographs of some typical Cambrian sediments .............10. Types of cross stratification recognized in this study.....11. Thickness changes within one set of trough cross beds that

produces opposite plunge directions of trough axes .....12. Cross bedding orientations north of the Baraboo Ranges .....13. Hypothetical paleogeographic map of the Baraboo islands in

Late Cambrian (Franconian) time ...................... ..14. Photographs of prominent glacial features - Late Woodfordian

(Cary) end moraine and Devils Lake ....................15. Topographic map of East Bluff, Devils Lake ................16. Sketch map of pothole area, East Bluff, Devils Lake . . . ....17. Hypothetical preglacial and present drainage maps of the

Baraboo region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .18. Route and location map for field trip road log .............19. Bedding/cleavage relations, west side of Lower Narrows

(STOP 1 and Supplementary Stop A) .....................20. Stereoplot for Precambrian rocks at Lower Narrows

(STOP 1 and Supplementary Stop A ) . . . . . . . . .. . . . . . . . . . .21. Geologic map of Upper Narrows (Rock Springs) area

(STOPS 2 and 3; Supplementary Stops B and C) . . . . . . . . . .


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.........igu re 22 . Cross se c ti o n of Upper Narrows of Baraboo Rive r 101. . . . . . . . .3 Sketch of s t r u c t u r e s i n Van Hise Rock (STOP 2 ) 10324. S t e r e o p l o t f o r Ba ra bo o Q u a r t z i t e . w e st s i d e of

Upper Narrows (STOP 2 ) ............................. 1 0 325 . St e re o p l o t f o r B arab oo Qu a r t z i t e i n t h e West J lang e

(STOP 4) ........................................... 10826 . Geologic map of D evi ls Lak e-Pa rfrey s Glen ar e a

(STOPS 5 and 11; Sup plem enta ry S to ps F and I ) ....... 11327 . S ke tc he s of f i e l d s t r u c t u r a l r e l a t i o n s a t t h e n o r th e a s t

c or n er of De vils Lake (STOP 5) . . . . . . . . . . . . . . . . . . . . . 11428. St e re o p l o t f o r Ba raboo Qu a r t z i t e of Dev i l s L ak e a r ea

(STOP 5) ....................................... .... 11529 . S t r u c t u r e i n t h e p h y l l i t i c zo ne of t h e Baraboo Q u a r t z i t e .

S k i l l e t Creek (STOP 6) ............................. 1 2130 . S t e r e o p l o t f o r Ba ra bo o Q u a r t z i t e of t h e S k i l l e t C reeka r e a (STOP 6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . 1 2331. Ge olo gic map of t h e La Rue Quarry a r e a (STOP 7) . . . . . . . . 12532 . Sketches of Cambrian-Precambrian u nc on fo mi ty i n

La Rue Qua rry (STOP 7 ) ..................... ........ 12633. S k et ch e s o f s t r u c t u r a l r e l a t i o n s i n B ara bo o Q u a r t z i t e

a t La Rue Qua rry (STOP 7 ) .......................... 12734 . Ste reo p lo t f o r Baraboo Qu ar tz i te a t La Rue Quarry

(STOP 7 ) ........................................... 12735 . Ge olo gic map of t h e Hemlock Draw-Leland a r e a (STOPS

8 and 9 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 236. Festoon cro ss bedding cu t by S co l i t hu s tu be s . Hemlock

Draw (STOP 8 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 13337 . Geologic map of Denzer ar e a showing anomalous st r u c t u r e s

i n Pa l eo zo i c s t r a t a (STOP 1 0 ) ..................... . 13738 . Disharmonic fo l d s i n Oneota Formation (STOP 10 ) ......... 13839 . Fa ulte d f o l d i n Jordan and Oneota Formations (STOP 10) .. 13840 . Sketch of e a s t f ac e of P ar fr ey s Glen (STOP 11) .......... 14241. Bedding /cleavage re la t i on s on ea s t s i d e of Upper Narrows

(Supplementary Stop B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14642 . St e re o p l o t f o r Ba rabo o Qu a r t z i t e . e a s t s i d e Uppe r Narrows

(Supplementary Stop B) ............................. . 146


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F i g u r e 4 3 .

44 .

45.

46.

47.

48 .

Map o f f l a g s t o n e q u a r r y i n Rock S p r i n g s s h o wi ng l a r g e -s c a l e t r o u g h c r o s s b e d d i n g ( S u p pl e m e nt a r y STOP C) .... 1 4 8

S k e t c h o f f a c e o f f l a g s t o n e q u a r r y ( S up p le m en t ar ySTQP C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9

S t e r e o p l o t f o r B ar ab oo Q u a r t z i t e a t N ar ro ws C re ek(Supp lemen ta ry S top D ) . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 15 0

S e c o n d a r y f o l d s a nd c l e a v a g e i n D iamond H i l l a r e a (Supp lemen ta ry S to p E) ............................... 1 5 1

S t e r e o p l o t f o r B a ra bo o Q u a r t z i t e o f Diamond H i l l a r e a(Supp lemen ta ry S to p E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

S t r u c t u r a l r e l a t i o n s i n p h y l l i t i c zone of BarabooQ u a r t z i t e a t t h e n o rt hw e st e n t r a n ce t o D e v i ls L ake....................t a t e P a r k ( S u p pl e me n ta r y S t o p F) 1 5 3

S t r u c t u r a l r e l a t i o n s i n p h y l l i t i c zone of B arabooQ u a r t z i t e a t U.S. Highway 1 2 r o a d c u t ( S u p pl e m en t a ryS t o p G ) ........................................... ... 1 55

S t e r e o p l o t f o r B ar ab oo Q u a r t z i t e a t U.S . Highway 1 2 . . . . . . . . . . . . . . .. . . . . . .o c a l i t y ( S up p le m en t ar y S t o p G ) 156S ec on da ry p ha se s t r u c t u r e s i n p h y l l i t i c z on e o f t h e

Ba raboo Qua r t z i t e nea r Happy H i l l Schoo l...............................Supplem entary S to p H) 157S t e r e o p l o t f o r B araboo Q u a r t z i t e , w e s t er n p a r t o f t h e ...out h Range (n ea r SlDP 8 and S upplemen tary St op H) 15 7S t e r e o p l o t f o r P r ec am br ia n r o c ks i n t h e e a s t e r n p a r to f t h e Sou th Range (Supp lemen ta ry S top s J , K , an d L) . 1 5 9T e ns i on g a s he s a nd c l e a v a g e i n q u a r t z i t e n e a r e a s t end. . . . . . . . . . . .. . . .f Sou th Range (Supp lemen ta ry S to p L) 1 6 1S t e r e o p l o t f o r B ar ab oo Q u a r t z i t e a t E a s t e r n C l os u re...............f t h e s y n c l i n e ( S u p pl em e nt ar y S t o p M) 162


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(Plates are in pocket)Plate I. Geologic map of the Baraboo region.

11. Cross sections of the Baraboo region.111. General structure map of Precambrian rocks of the Baraboosyncline.IV. Minorstructures map of Precambrian rocks of the Baraboosyncline.V. Structural data (stereoplots) for Precambrian rocks.

VI. Conglomerate-size data for lower Paleozoic rocks of theBaraboo region.VII. Cross bedding orientation data for the lower Paleozoicstrata of the Baraboo region.

TABLES Page.........able 1. Precambrian stratigraphy of the Baraboo District 32. Rubidium-strontium and potassium argon data used in.....................................ge calculations 93. Mesoscopic structures in the Baraboo Quartzite (summary).. 184. Comparison of terminology used for mesoscopic structures . 25. Paleozoic stratigraphy of the Baraboo region ............. 406. Major silicate minerals of sandstones of the Baraboo region 437. Principal heavy accessory minerals of sandstones of the

Baraboo region ...................................... 448. Size-distribution data for Paleozoic sandstones of theBaraboo region ...................................... 459. Estimates of Cambrian dynamic wave parameters fromboulder dimensions .................................. 510. Regional lower Paleozoic cross stratification orientation

data for western Wisconsin and northern Illinois ..... 6011. Summary of natural plant communities of the Baraboo hills 7912. Sedimentary data for Supplementary Stop C at Rock Springs(Flagstone quarry in Galesville Sandstone) ........... 14913. Key to stereoplot symbols for field trip localities ...... 164


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FOREWORDF o r m ore t h a n h a l f a c e n t u r y , t h e Ba ra bo o d i s t r i c t h a s b ee n a n

u n u su a l ly i m p or ta n t g e o l o g i c al l a b o r a t o r y t h a t h a s c o n t r i b u t e d t o t h ee d u c a t i o n o f c o u n t l e s s t h ou s an d s o f s t u d e n t s r e p r e s e n t i n g a t l e a s t 1 0 0d i f f e r e n t c o l l e g e s . The l i s t of t ea ch er s and r es ea rch worker s who havebeen drawn t o t h e Baraboo h i l l s r ea ds l i k e a "who 's who" o f Americangeo logy . Y e t , i n s p i t e of a l l o f t h e lo ng -s ta nd in g i n t e r e s t i n t h er e g i o n , a s a t i s f a c t o r y m odern g e o l o g i c map an d d e t a i l e d s y n t h e s i s o fB ara bo o g eo lo gy h a s n o t be en a v a i l a b l e . I t was t o r e c t i f y t h i s om i s si o nt h a t t h i s s t u dy was u n de r ta k en u n d e r t h e d i r e c t i o n o f t h e W is co ns inGeo log ic a l and Nat u ra l H is to r y Su rvey , t h e Univ. o f Wiscons in -Ex tens ion .W e h op e t o h a v e p r e s e n t e d new d a t a a nd i d e a s t h a t w i l l s t i m u l a t e t h ef u r t h e r i n t e r e s t of b ot h s t u d e n t s a nd p ro f e s s i o na l g e o l o g i s t s .

A t t h e same t im e t h a t t h i s g u i d e t o t h e ge ol og y o f t h e Ba ra bo o d i s -t r i c t i s p r e s e n t e d , we w is h t o v o i c e a s t r o n g p l e a t o p r e s e r v e t h e p r i c e -l ess key ou t c ro ps f rom th e ons la ugh t o f geo logy hammers i n th e hands o fe a g e r b u t u n t h i n k i n g v i s i t o r s . Rock o u t c r o p s , t o o , s om et im es r e q u i r econserva t ion -mindedness l e s t t h e h i l l s b e pe n ep l an e d by n on e o t h e r t h a ng e o l o g i s t s ! I r o n i c a l l y , - no th in g i s t o be ga in ed by hammering a t s uchl o c a l i t i e s , f o r t h e s t r u c t u r a l r e l a t i o n s h i p s a r e b e s t s e en on w ea the re ds u r f a c e s .

W e a r e most g r a t e f u l t o G eorge F. H an so n, S t a t e G e o lo g i s t , a n d t oM e re di th E. O strom , A s s o c i a t e S t a t e G e o l o g i s t , f o r t h e i r c o n t i n u a l i n t e r e s tt hr ou gh ou t t h e s t u dy and f o r t h e i r c r i t i c a l r e a d i ng s o f t h e m a nu sc ri pt .Some f i n a n c i a l s u p p o r t i n a d d i t i o n t o t h a t o f t h e S ur ve y was p r o v id e d byt h e W is c o n sin Alum ni R e s e a r c h F o u n da t io n ( r e s e a r c h g r a n t s t o R .H . D ot t, J r . ) ,t h e N a t i o n a l S c i e nc e Fo u nd a ti o n ( g r a n t GA 12926 t o I.W.D. Da lz ie l a tLamont-Doher ty Geo logi cal Ob serva tory of Columbia U ni ve rs i t y) , and ColumbiaU n i v e r s i t y ( f i e l d ex p e ns e s t o I.W.D. D a l z i e l ) .

Many o f ou r co l lea gue s a t t h e Un iv er s i ty o f Wiscons in and a t ColumbiaU n i v e r s i t y h el p e d u s i n o ne way o r a n o t h e r . I n p a r t i c u l a r w e t h a n k S tu r g e sB a i l e y ( f o r u n p u bl i s he d X-ray d a t a ) , C a r l E. Dut ton o f t h e U. S. Geo log ica lSurvey i n Madison, Campbell Craddock, Ma rsh al l Kay, Cha r les V. G u id o t t i ,G er ry L. S t i r e w a l t ( f o r p e rm i s s io n t o u s e un p u bl i s he d m i c ro s c o p i c d a t a ) ,and Richard E. B is c hk e . K en ne th 0 . S t a n l e y a s s i s t e d w i th p e t r o g r a p h i cwork and Rober t B lod ge t t and Pau l Wel l s per fo rmed some of t h e s i z e ana lys es .Unpubli shed g eo lo gi c maps by E nis Usbug, Dennis Howe, Douglas Hac kba rth,and Sharon Kreutzman were very h e lp fu l , a s was some unpu blish ed sediment-o l og ic d a t a ob ta ine d by Mary Roshard t .

D r a f t i n g was d on e i n t h e U n i v e r s i t y o f W is c o ns in C a r to g r a p h i c L a bo ra -to r y b y M. Czechanski , A.L. LeBlanc, and S.J . Thompson unde r th e d i re c t i o no f Randa l l D. S a le , i n - c h a r g e o f C a rto gr a ph y f o r t h e G e o lo g i c a l a nd N a tu r a lH i s t o r y Su rv ey . We a l s o w i sh t o t h a n k K enneth I . L a ng e, N a t u r a l i s t a tDe v i l s Lake S t a t e Park , Pe te r Monkmeyer, Un ive r s i ty o f Wiscons in Co l legeof Engin eer i ng , R ober t L. Mil le r of t h e Un ive r s i ty of Ch icago , and GrantCot tam o f t h e Un ive r s i ty of Wisconsin Departmen t of Bo tany f o r as s i s t a nc ei n c r i t i c i z i n g t h e m a nu sc ri pt .


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ISOTOPIC DATE PRO VINC ES OF THE GREAT LAKES REGION-

PROVINCE!i 5 U ~ ~ ~ \ O RJP". -. ,, 2.4-2.6 b.V.

7

WATE RLOO 140 Rb-S r date1 2 K-Ar dateR rhyoliteG granitic rocksGa gabbroic rocksGn gneissS schist

10 0 200miles

Figure 1. Regional tectonic and index map of the Great Lakes Regions, showing the Baraboo and WaterlooQuartzites with respect to major Precambrian isotopic-date and tectonic provinces. Note also limitsof Paleozoic strata. Individual isotopic dates are included in the Mazatzal Province, which encom-passes the Baraboo region. The north-south-trending Wisconsin arch is shown in southern Wisconsin.(Adapted from Goldich, et al, 1966).- -


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(Dalziel and Dott)

Regional Geologic SettingPrecambrian basement rocks are locally exposed along the axis of the

Wisconsin Arch as inliers in the flat-lying lower Paleozoic sediments. Thelargest and best known of these inliers occurs in Columbia and Sauk Counties,south-central Wisconsin, where Precambrian rocks -- mainly quartzite -- forman elongate ring of hills known as the Baraboo Ranges (Fig. 1). The hillsrise to a maximum elevation of 700-800 feet above the level of the WisconsinRiver Valley (pl. I). Sedimentary rocks of Cambrian and Ordovician agesunconformably overlie the Precambrian basement and contain spectacular basalconglomerates in many places.

The Baraboo Ranges are exhumed monadnocks of massive, pink, maroon orpurple-colored Baraboo Quartzite. This conspicuous rock unit is certainlymore than 4,000 feet thick, and appears to rest stratigraphically upon poorlyexposed acidic igneous rocks. Precambrian metasedimentary rock units over-lying the Baraboo Quartzite-have been recorded in drill and iron mining re-cords (Weidman, 1904; A. Leith, 1935; Schmidt, 1951), but have not beenpositively identified in outcrop. The Precambrian succession in the Baraboodistrict inferred from subsurface as well as surface data is shown in Table 1.

TABLE 1PRECAMBRIAN STRATIGRAPHY OF THE BAMBOO DISTRICTRowley Creek Slate (maximum known thickness 149 feet)Dake Quartzite (maximum known thickness 214 feet)

(Unconf rmity?)Freedom Formation (dolomite and ferruginous slate;

minimum thickness 1000 feet)Seeley Slate (maximum known thickness 370 feet)Baraboo Quartzite (thickness over 4000 feet)

(Unconf rmity?)Rhyolitic "basement" (thickness unknown)

Subsurface information suggests that in places the Dake Quartzite restson the lower (ferruginous slate) member of the Freedom Formation. This ledA. Leith (1935) to propose an unconformity beneath the Freedom Formation. How-


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ever, according to Leith, the records have been lost and the cores destroyed.He reported that 42 diamond drill cores in the eastern part of the basinpenetrated the Dake Quartzite, and suggested that an outcrop on a low ridgenortheast of Baraboo, and another in a railroad cut southwest of Baraboo,might be of Dake Quartzite. However, only a local pebbly unit in the for-mer is unlike typical Baraboo Quartzite, and there is no strong reason forbelieving that the Dake Quartzite, if it exists, does indeed crop out.

The entire Precambrian succession has been folded into a complexdoubly-plunging asymmetric syncline with an axial surface striking approxi-mately east-northeast-west-southwest and dipping steeply north-northwest.At the present level of erosion, the syncline is about 25 miles long andhas a maximum width of 10 miles. The north limb is nearly vertical andthe south limb dips gently northwards.

The Precambrian rocks form a structural and topographic basin infilledwith Paleozoic and Pleistocene sediments.

Historv of Research

The very existence of an inlier of metamorphic and igneous rocks inthe region probably would have attracted much attention from geologists.However, the work of C. R. Van Hise, C. K. Leith and W. J. Mead (bestknown of the isco cons in school" of structural geologists), in the latterpart of the nineteenth and early part of the twentieth centuries, hasmade the beautifully-displayed structures in the deformed metasedimentsat Baraboo famous to structural geologists throughout the world.

The earliest recorded geological observations at Baraboo were thoseof Shumard (1852) reported by Owen in his account of a survey of Minnesota,Iowa and Wisconsin. Percival (1856), in his report of geological surveycommissioned by the State of Wisconsin, remarked on the similarity of thequartzite forming the North and South ranges at Baraboo, and suggestedthat they might in fact be part of the same formation. He regarded thequartzite as the metamorphic equivalent of the lower Paleozoic sediments.Hall (1862) first correctly assigned the quartzite to the Precambrianand correlated it with the Huronian of Ontario. Winchell (1864) reportedCambrian fossils near Devils Lake, but it was left to Irving (1872) duringthe first extensive study of the area to prove the unconfomable relation-ship between the quartzite and the Cambrian sediments. Irving also madethe first detailed structural observations, recording the general attitudeof the cleavage in phyllitic lenses within the quartzite in the SouthRange (Irving, 1877). Like Chamberlin (1873) he published a tentativecross section in which he inferred the quartzite of both the North and-outh Ranges to lie on the north limb of a broad upright anticline.Irving and Chamberlin apparently were misled by the overturned north-dipping beds on the north limb of the syncline in the vicinity of theUpper and Lower Narrows of the Baraboo River (Pl. I). Salisbury andAtwood (1903) were similarly misled. Although they showed the synclinalrelations of the quartzite beds on the North and South Ranges, they in-correctly showed a tight anticline within the North Range.


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The most comprehensive account of the Baraboo Quartzite and the structuralgeometry of the Baraboo syncline is that of Weidman (1904). A. Leith (1935)later described the lithology of the overlying Precambrian units after extensivdrill records became available. Weidman also seems to have been the firstworker to record correctly the structural geometry of the quartzite; he basedhis interpretation on extensive observations of dip and strike. However, it isgenerally accepted that Van Hise was first to appreciate fully the structuralconfiguration of the quartzite on the basis of bedding/cleavage relations.Van Hise, C. K. Leith and Mead largely concerned themselves with studies ofI?rock cleavage1' nd correlation of the succession at Baraboo with Precambrianstratigraphy in the Lake Superior region to the north. As a result of thiswork they came to be recognized as the isco cons in school" of structural geolo-gists. The igneous rocks underlying the quartzite at Baraboo were assigned tothe Archean, while the metasediments were correlated with the "~uronian", ow1 ~nimikean", f the Lake Superior region (Van Hise and C. K. Leith, 1911).

Numerous University of Wisconsin theses have been written on the structureof the Baraboo Quartzite, particularly the western end. These have provedparticularly valuable in the present study for locating critical outcrops, butmost contain no information on mesoscopicl structures other than bedding. Anexception is the exhaustive study by Adair (1956) of the so-called "anomalous"structures of the syncline (secondary phase structures of this paper). Schmidt(1951) compiled a valuable synthesis of the subsurface data. Other thesesinclude those of Damm and Mees (1943) on the northwestern end of the syncline,Gates (1942) on the Baxter Hollow granite, Griesell (1937) on the west end ofthe South Range, Mayer (1934), Wenberg (1936) and Kemmer and Kovac (1937) onthe West Range, and C. K. Leith (1941) on the South Range. Ostenso (1953)and Hinze (1957) carried out magnetic and gravity surveys respectively.

An extremely valuable structural analysis of the Baraboo Quartzite, mainlyon the microscopic scale, was carried out by Riley (1947). The extensive dataobtained during his study of the deformed quartz grains has been valuable inthe interpretation of subsequent experimental work (e.g. Raleigh and Christie,1963; Friedman, 1964; Carter and Friedman, 1965).

The most recent published work on the Precambrian rocks of the area priorto the present study is that of Hendrix and Schaiowitz (1964), who studied thegeometry and field relations of mesoscopic structures in phyllitic layers nearthe top of the quartzite exposed on the south limb of the syncline.Paleozoic rocks also were observed, of course, by the earliest workers,but they received less attention than the Precambrian. Irving and Weidmanrecognized the profound unconformity between the two sequences and noted thespectacular coarse basal Paleozoic conglomerates. Weidman had a clear appre-ciation of profound mountain building and deep erosion prior to Cambriandeposition. He noted that the most resistant Precambrian rocks in Wisconsinremained as islands or monadnocks, and estimated that the Baraboo monadnocksmust have been from 1000 to 1600 feet above the surrounding plain. He alsorecognized the unusually close control of the late Precambrian-Cambrian topo-graphy upon that of the present day. The general stratigraphy and severalfossil localities became widely known among Upper Mississippi Valley geologists

1. Mesoscopic structures are those on hand specimen or single outcrop scales.


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during the first quarter of the century. Stratigraphic names borrowed fromeastern states, such as Potsdam Sandstone and Trenton Limestone, graduallywere displaced by newer Mississippi Valley terminology after 1920 (See Table 5)At the same time, the district was being used for field trips by many schools,and it figured in the great stratigraphic controversy promulgated by E. 0.Ulrich. Based upon his interpretation of some stratigraphic relationshipsaround Baraboo and Madison, as well as in Missouri, Ulrich proposed an entirenew Ozarkian System between the Cambrian and Ordovician. A bitter controversyensued between Ulrich and other stratigraphers such as Twenhofel. By 1935,the Ozarkian was discredited by the demonstration of several mis-correlationsof lower Paleozoic formations, which had resulted from erroneous age assign-ments to certain critical faunal assemblages, including some from the Baraboodistrict.

By 1930, geologists who visited the area frequently, such as W. H.Twenhofel, G. 0 . Raasch, F. T. Thwaites, A . C. Trowbridge, and J. H. Bretz,were well versed in the stratigraphy around Baraboo, but this knowledge wasnot generally available until J. M. Wanenmacher mapped and described thePaleozoic formations in detail for a Ph.D. dissertation in 1932. Publishedstratigraphic syntheses for the area appeared soon thereafter (Wanenmacher,et al., 1934; Raasch, 1935). Two Bachelor's theses done at the University--f Wisconsin (H. F. Nelson, 1940; Oetking, 1943) dealt with the Paleozoicrocks a few miles south of the syncline, and a recent Master's thesis (Usbug,1968) treated the northwestern portion of the syncline. With extensivechecking and additional mapping by Dott, maps included in these reports,that of Wanenmacher, three unpublished maps prepared as student independentstudy projects at the University in Madison by Douglas Hackbarth (south-eastern Baraboo hills), Dennis Howe (southwestern Baraboo hills), andSharon S. Kreutzman (eastern haif of syncline), and old unpublished field mapsin the files of the Wisconsin Survey were used in preparing the accompanyinggeologic map (Pl. I). Recent revisions of stratigraphic nomenclature proposedby the Wisconsin Geological and Natural History Survey (Ostrom, 1967) areadopted herein.

The origin of the Paleozoic sediments of the Baraboo area has receivedfar less attention than has the general stratigraphy, a circumstance typicalof the entire Mississippi Valley region. Comments in Wanenmacher, et al.- -1934), Raasch (1958), and Farkas (1960) are practically the only specificreferences, and they are very general. On a regional scale, however, Ostrom(1964) and Raasch and Unfer (1964) interpret Cambro-Ordovician cyclic patternsof sedimentation that should have affected sedimentation in the Baraboo area;Hamblin (1961) and hrich (1966) have provided regional paleocurrent data.Because the stratigraphy is now well known,the sedimentology is emphasized inthis monograph, for the Baraboo area offers unusual opportunities for detailedanalysis of ancient sedimentary environments and paleogeography. Results ofrecent sedimentologic investigations provide new data for interpretationspresented here.

The Pleistocene geology of the Baraboo area has received almost as muchattention as have the Precambrian rocks. The Devils Lake area, especially,provides unusually clear features easily comprehended by the neophyte, thusit has been for years a favorite for student trips; the origin of the lake isso readily demonstrable as to delight even the most casual tourist. Besides


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t h e o b v io u s t e rm i n a l m o ra i ne l o o p i n g a ro un d t h e Dev i l s L ak e v a l l ey and t h en cenor thwes tward th rough the w e s t ed ge of B arab oo , s t r i a t e d ro ck s u r f ace s , o ut washd e p o s i t s , a nd g l a c i a l l a k e s e di m en t s a r e w e l l d i sp la y ed i n t h e d i s t r i c t . Thet o p og r a p hi c c o n t r a s t b etw ee n t h e r e c e n t l y - g l a c i a t e d e a s t e r n h a l f a nd t h e w e s t e rnp o r t i o n of t h e s y n c l i n e r e gi o n i s indeed s t r i k i n g , and was no ted by ea r l yworkers ( e .g . , Weidman). Th is co n t ra s t , o f which t h e Baraboo ar ea p rov ides asample, i s o f r e g i o n a l e x t e n t , and l o n g a g o l e d t o t h e c o nc e pt o f t h e fam ousD r i f t l e s s Area o f s o u t h wes t e rn W i sco ns i n.

Comprehens ive repor t s on geomorpho logy and P le i s tocene depos i t s inc ludee ar ly one s by Sal is bu ry and Atwood (1897; 1900) and Alden (1918), wh ile l a t e rones were by Ma rti n (1932), Smith (1937), Th wai tes (1935; l 95 8) , and Powers(19 60 ). More s p e c i f i c l o c a l r ep o r t s hav e d e a l t w i t h Dev i l s L ak e (T ro wbr id ge ,1917; Twenhofel and McKelvey, 1939; and Bla ck, 1967, 1968) and wi th g l a c i a lL ak e M er ri mac, whi ch s ur ro u nd ed t h e ea s t e rn en d o f t h e d i s t r i c t (B re t z , 1 9 50 ) .B l ack ' s p ap e r i s e s p e c i a l l y d e si gn ed t o l e a d e i t h e r t h e l ayman o r p r o f e s s i o n a lt o s p e c i f i c f e a t u r e s t h a t b e a r on t h e l a t e P l e i s t oc e n e h i s t o r y of t h e D e vi lsL ak e a r e a . I t p r o v id e s a v a l u a b l e su pp le me nt t o t h e b r i e f d i s c u s s i o n ofP l e i s t o ce n e g eol og y i n t h i s g ui debo ok .

Economic GeologyThe Baraboo qu a r t z i te was used o r ig in a l l y f o r macadam aggre ga te and

p av in g b l oc k s. I t was l a t e r q u a r r i e d e xt e n s i v e ly f o r m e t a l l u r g i c a l ( re -f ra ct or y) purposes . Now t h e main use i s f o r r a i l r o a d b a l l a s t , w i th somea l s o b e in g u s ed f o r g r i n d i n g p e b b le s .

E x t en s i ve a c c o un t s o f t h e h i s t o r y o f i r o n m in in g i n t h e Ba ra bo o d i s t r i c ta r e av a i l a bl e i n Weidman (19041, Van H i s e and C. K. L ei th (1911), and Schmidt(1951). T. C. Chamberlin i s g e n er a l ly c r e d i t e d w i t h f i r s t r e co gn i zi ng t h ep o s s i b i l i t y of t h e r e b e in g i r o n o r e i n t h e Baraboo d i s t r i c t i n 1882. H eb a se d h i s s u g g e st i o n on t h e p r e se n c e o f i r o n m i n e r a l s i n q u a r t z v e i n s . I r o nfor ma tio n was di sc ov er ed i n Freedom Township (T.llN., R.5E.) i n 1887 anddur ing the per iod 1889-1899 it was mined just w e s t of La Rue fo r pa i n t p ig -ment by t h e Chicago and Northw estern Railway Company. I t was i n Ap ri l 1900t h a t W. G. La Rue s t ru ck o re-g rade i r on on t h e same p rop er ty .

Mining was confin ed t o t h e ar ea so uth of Baraboo and North Freedom. Thel o c a t i o n s o f t h e I l l i n o i s , Sauk and C ahoon m i nes , f ro m whi ch a l l t h e o re wassh ipped , a r e shown on th e geo log ic map (P l . I ) . The o r e was mined from t h elow er member of t h e Freedom For mat ion, which i s a t l e a s t 400-500 f e e t t h i c ki n p l ace s (P l . 1 1 ) . I t was m o s t ly r ed h em a t i t e w i t h a s m a l l amount of l i m o n i t e .The a v e r ag e i r o n c o n t e n t i n 1 , 5 1 7 a n a l y s e s o f s am pl es f ro m t h e I l l i n o i s m inewas 36.4% (Van H i s e and C. K. L e i t h , 1 9 1 1 ) . A t t h e end of 1909 onl y 0.06% ofa l l t h e i r o n o r e o b t a i n e d fr om P r ec am br ia n s e di m en t s i n t h e L ak e S u p e r i o r r e g i onh ad come from t h e B arab oo d i s t r i c t , b u t it was e st i m a t e d t h a t t h e r e were re-s e rv es o f 9 10 b i l l i o n t o n s o f o r e w i t h 35% o r more o f i r o n (Van H i s e and C. K .Le it h , 1911, p. 461 and 492). The I l l i n o i s mine ope rat ed from 1904-1908, the nb r i e f l y f ro m s t o c k p i l e s i n 1 91 6, f i n a l l y c l o s i n g down t h e s ame y e a r a f t e r pro-duci ng 315,350 to ns of or e. The Cahoon mine op er at ed from 1916-1925 (ex cept1919 and 1921) and produced 327,683 to ns . Records from t h e Sauk mine ar e nota v a i l a b l e . F l o od i n g a p p a r e n t l y was a m aj or f a c t o r i n c a u s i ng t h e c l o s u r e o fa l l th r ee mines (Schmidt , 1951) . Unfor tun a te ly , Weidman 's be l i e f (1904 ,p. 1 5 2) t h a t t h e d i s t r i c t would become a s i m p o r t ant a s some o f t h e a rea sa rou n d Lake Su p e r i o r was n o t f u l f i l l e d .


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PRECAMBRIAN GEOLOGYRelationships and Ages of the Precambrian Rocks

(Dalziel and Dott)The determination of the age of the Baraboo Quartzite and associated rocks

is conjectural because of isolation from the Great Lakes Precambrian rocks,wherein the standard time scale has been established for North America. Hall(1862) suggested a correlation with the Huronian of Ontario. Because of thepresence of banded iron ores closely associated with dolomite, and all under-lain by quartzite, correlation with Middle Precambrian (Animikean) rocks onthe north and south sides of Lake Superior has been generally assumed eversince. But this type of correlation is tenuous at best, hence we judged itdesirable to attempt to bracket the Baraboo sequence by establishing iso-topically the ages both of slightly older and slightly younger rocks.

Relative age relations of the plutonic rocks around Denzer (southwestside of the syncline, P1. I) to the sediments are ambiguous, so these rocksare of little value for establishing an older age limit as is borne out bythe large scatter in Rb-Sr analyses of the Baxter Hollow granite (Table 2).The rhyolite complex offers more hope, for it underlies the Baraboo Quartziteconcordantly on both limbs of the syncline, and nowhere shows offshoots pene-trating the quartzite. Local rhyolite masses alleged to overlie the quartziteare, in our opinion, glacial erratics. The rhyolite has flow-banding andfragmental textures exactly like those characteristic of extrusive tuff brecciasand rhyolitic glasses as Weidman noted many years ago (1895)) and Stark morerecently (1930; 1932). The rhyolites at Baraboo are strikingly similar towidely scattered dark rhyolites in central Wisconsin. Asquith (1964) studiedthe latter and found that several had microscopic shard and axiolitic structurescharacteristic of welded tuffs (ignimbrites). He did not detect such structuresin the more deformed Baraboo rhyolites, but we have subsequently found clearaxiolitic and faint shard-like relicts in a number of thin sections. Togetherwith megascopic textures, these features prove not only a volcanic origin ofthe rhyolite around Baraboo, but probably a welded tuff origin for much of it.

Several workers (following Weidman, 1904) have claimed that small rhyo-lite pebbles occur in the basal Baraboo Quartzite, but we have been unable toconfirm this. What Weidman referred to in 1904 as a basal rhyolite-bearing con-glomerate is in reality the breccia that he earlier had interpreted correctlyas of volcanic origin and belonging to the older rhyolite complex (see Stark,1932). Most of the small, dark pebbles in the Baraboo appear to be jasper,although in fine particles without obvious phenocrysts these can be impossibleto distinguish from red, devitrified rhyolitic glass fragments.

In spite of the lack of proven rhyolite pebbles in the quartzite, therewas no doubt in our minds that the rhyolite is older. Therefore, we had Rb-Sranalyses performed for five specimens of rhyolite from three localities aroundthe Baraboo syncline. The results (Table 2) allowed an isochron to be drawnwhose slope indicated an age of 1.54 (k0.04) b.y. The similar appearingrhyolites of central Wisconsin (Fig. 1) have yielded dates of 1.30 to 1.60(Goldich, et al., 1966), a range too large either to prove or disprove adirect age relation.


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TABLE 2: Rubidium-strontium and potassium-argon data used in age calculations.RUBIDIUM-STRONTIUM ANALYSES (by M. Halpern, The University of Texas, Dallas;

September, 1968) :

Volcanic Rocks:0-4 0.7580 0.214 0.0881 2.49

Baxter Hollow Granite:

POTASSIUM-ARGON ANALYSES (by Geochron Laboratories, March, 1968) :

Phyllite in Baraboo Quartzite:

*Norallzed to ~ r ~ / S r ~ ~10 of 0.1104. A t t of thorn -ly8e8 , n o d i z a d ~ r ~ ~ /loof tb .Ww t t 8 nrtituk of Teelmology standard SlCg (L# 82327)- a8ured arr 0.7084 20.00026 (mom of 7 analpar).ACE = 1 [,he+A@x A#" + 1 J

h e T


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A younger age limit for Baraboo Precambrian rocks first was approachedby attempting to date micaceous minerals in phyllite zones within the quartziteby the K-Ar method, which might pinpoint the date of later metamorphism. Re-sults (Table 2) indicated a date seemingly too young (760 + 50 m.y.) to relate-to the known tectonic history of the Great Lakes region, thus it is a minimalage at best. We attach no significance to it because a great excess of K-freepyrophyllite over K-bearing muscovite in the phyllites made the K percentageso small that the analyses were done to the limits of sensitivity of themethods employed.

As an alternative, we turned to the identical appearing Waterloo quartzite,which is exposed in another but smaller inlier 25 miles east of Madison (Fig. 1).Here previous dating of a pegmatite dike cutting the quartzite (1.44 b.y.;Aldrich, et al., 1959) and of a muscovite-rich phyllite zone within the quartz-ite (1.41 b.y.; Goldich,--t al., 1966) seems to limit quartzite deposition tosome time prior to 1.4 b.y. ago. By extrapolation between Waterloo and Barabooit appears that deposition occurred between about 1.45 and 1.5 b.y. ago, follow-ed by deformation that produced the fold structures and metamorphism about1.4-1.45 bey. ago.

If our admittedly circuitous interpretations are correct, and if there hasbeen no wholesale re-setting of whole-rock isotopic clocks, then the Baraboo-Waterloo Quartzite masses are younger than both the Middle Precambrian Animi-kean and Huronian rocks with which they have long been correlated. They evenappear to postdate the well-known Penokean orogeny (1.6-1.9 b.y. ago), whichaffected at least the northern half of Wisconsin. Thus one could read somesuggestion from our results of a post-Penokean orogenic event (circa 1.4-1.5;roughly Elsonian in the Canadian Survey or Mazatzal in western U. S. termin-ology) that has been suggested by several workers, but which is not yet fullyaccepted as valid (see Goldich, et al., 1966).- -

Rb-Sr analyses of the long-enigmatic Baxter Hollow granite northeast ofDenzer suggest that it will remain enigmatic somewhat longer. It has beenargued that the granite is younger than the quartzite (Gates, 1942), but thisis not certain, and Stark (1932) believed it to be older. The two are separatedby a narrow zone of sheared rock, rendering their relations rather ambiguous.Rb-Sr ratios were so similar in all samples of the granite analyzed that anisochron could not be constructed. Calculation of dates for individualsamples indicates a total possible spread of values so large (1.36-1.67 b.y.)that the rock could as well be related to the post-Baraboo orogenic event or tothe pre-Baraboo rhyolitic volcanism. Obviously "further study is indicated."

Petrology(Dalziel)

Only a brief description of the various Precambrian rock types will bepresented here. More extensive accounts of the igneous rocks and the BarabooQuartzite are given by Weidman (1904), Stark (1932) and Gates (1942), and ofthe overlying Precambrian metasediments by Weidman (1904) and A. Leith (1935).The following descriptions are partly condensed from their articles.


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Rhyolite. Much of the rhyolite is fine-grained, dark gray or red in color,crudely banded, and contains small quartz and feldspar phenocrysts. At somelocalities, however, it has the appearance of a volcanic breccia, and localtuffaceous sandstones also occur (Stark, 1930). In others compositionallayering (presumably flow banding) is well developed. It shows relict micro-scopic textures typical of welded tuffs. A number of structural surfaces,some marked by the alignment of deformed phenocrysts, can be observed.

Diorite. Two small outcrops of diorite occur near Denzer (Pl. I). No fieldrelations can be seen. The rock is massive, medium-grained, and reddish incolor. It consists largely of plagioclase (70-8590), hornblende (10-20%) andquartz; mica, apatite and iron oxide are minor constituents, and some of thehornblende is altered to chlorite.Granite. A few outcrops of granite are located on the south side of the southrange in Baxter Hollow on the main branch of Otter Creek (Pl. I). The rock ismedium to fine-grained and consists of plagioclase feldspar (50-75%), quartz20-45%), mica, hornblende and apatite. The granite is sheared adjacent to theBaraboo quartzite, and jointing is common in all outcrops.Baraboo Quartzite. The quartzite is a massive, vitreous rock, typically pink,maroon or purple, but locally white or gray. It is comprised of more than 80percent quartz, which occurs as medium to coarse sand-size grains and sporadicrounded granules and fine pebbles. There is no pronounced basal conglomerate;rather, fine pebble bands and lenses are common throughout. The pebbles arepredominantly white quartz, and rarely exceed one inch in diameter. In mostoutcrops, bedding parting parallel to pebble layers or argillaceous zones ispronounced, but in low, glaciated outcrops it may be obscure. Where suchsurfaces are well exposed, excellent ripple marks may be seen. Current bed-ding is almost universal. An intricate color banding is confusing. In somecases it follows bedding or current bedding surfaces, but commonly it is in-dependent of both (See Weidman, 1904, p. 24) and forms circular, elliptical,and irregular patterns on planar joint surfaces (Fig. 27c; STOP 5). Jointsare ubiquitous and mostly steeply dipping.

Numerous layers or lenses of more argillaceous material occur within thequartzite. Most are only a few inches thick, but some reach several feet.They have been referred to in the literature variously as argillite, slate,schist and quartz-schist. X-ray diffraction studies of specimens from anumber of localities have been carried out by S. W. Bailey of the Universityof Wisconsin-Madison. He reports that they chiefly consist of pyrophylliteand quartz with minor quantities of muscovite and hematite (personal communi-cation). They will be referred to here as phyllitic-quartzite, quartz-phylliteor phyllite because they exhibit more pronounced recrystallization and lessregular foliation than a slate, but are finer grained than a Schist.

The quartz-pyrophyllite-(muscovite)-(hematite) assemblage of the phylliticlayers indicates that the Raraboo Quartzite reached the lower greenschistfacies of regional metamorphism. Some idea of the temperature involved can beobtained from experimental data. According to Kerrick (1968) the upper stabil-ity limit of pyrophyllite is 410-430~~t 2-4 lb. water pressure. It is interesting to note that Weidman (1904, p. 49) mentions that andalusite is11probably" present in the Seeley Slate. If this could be confirmed it wouldmean that the metamorphism reached the upper greenschist facies, and the


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t em pera ture must have been h igher t han t ha t o f t he upper s t a b i l i t y f i e l d ofpy rop hy l l i t e , a t l e as t l oc a l l y . Weidman a l so m en tions t he p resence ofI f kao l in i te" i n th e Precambrian metasediments. Although t h i s could , i f con-f i rmed, in d ic a t e lower temperatures , i t should be borne i n mind t h a t th e termwas used very ge ner al ly i n Weidman's t ime; ka ol in i t e could be hydrothermal i nor ig in (se e Bai ley and Tyl er , 1960 and discu ssio n of b re cc ia zone i n UpperNarrows a t Baraboo, STOP 2 . ) An unusual , ni ck el i f er ou s phosphate min era l , l a m -l i t e ,o cc u r s i n ve i n l e t s sou theas t of Dev il s Lake (Olsen , 1962) .

A t a number of l o c a l i t i e s on th e south l imb of th e syncl ine (e .g . , nor th-ea st ent ran ce t o Devi ls Lake St a te Park, S k i l le t Creek, Highway 12 and HappyH i l l Scho ol; STOPS 5 and 6, Suppleme ntary S top s G and H r e s p e c t i v e l y ) t h e r ea r e o u tc r op s of p h y l l i t e up t o 1 0 f e e t t h i c k c o n t a in i ng t h i n q u a r t z i t e b ed s.A s t h e s e l o c a l i t i e s a l l o c cu r a t a h ig h s t r a t i g r a p h i c l e v e l i n t h e B arabooQuar tz i te and ar e roughly on s t r i k e wi th one another (P l . 111), they probablyrep resen t t he same p hy l l i t i c zone.

A b r e c c i a c o n s i s t i n g of r e l a t i v e l y c o a r s e , a n g ul a r q u a r t z i t e fr a gm e nt sin a qu ar tz mat r ix c onta in ing d ic k i te forms a prominent zone 150 yards wideon th e west s i d e of t h e Upper Narrows (Ableman's Gorge: STOP 2) i n t h e NorthRange, and has f igur ed ex tens iv ely i n th e l i t e r a tu r e (e .g . , Weidman, 1904,p. 25). A few narrower brec cia ted zones occur elsewhere, some con tain ingk a o l i n i t e i n t h e m a tr i x (S.W. Bailey, personal communicat ion).S eel ey S l a t e . The s l a t e i s described (Weidman, 1904; A. Lei th , 1935) a s grayo r g re e n i n c o l o r , c o n s i s t i n g of a l t e r n a t i n g bands v a r yi ng s l i g h t l y i n t e x t u r eand color, and being uniform in i t s appearance. A f i n e s t r a t i f i c a t i o n and aw e l l developed cle ava ge a r e both commonly pre se nt.Freedom Formation. Frequ ent ly re fe rr ed t o a s the Freedom Dolomite, t h i s forma-t i on con s i s t s of a number of d i f f e re n t rock t ypes , s l a t e , ch e r t and i ron o rei n ad di t ion t o dolomite (Weidman, 1904). Minerals pre sen t i n varyin g propor-t i on s a r e qu ar tz , do lomi te , hem at i te and c la y miner a l s . Dolomi te forms th eupper member and va rio us typ es of fe rr ug ino us r ock s form th e lower member. Af e r r u g i n o u s s l a t e i s p r e se n t a t t h e b a se r e p r e s e n ti n g a t r a n s i t i o n from t h eSeeley Sl at e. Composi tional banding i s prominent throughout th e formatio n;secondary cleavage i s poorly developed , bu t f i l l e d f ra c t ur es a re common.Dake W ar tz i t e . This i s r epo r t ed f rom d r i l l co res t o be a coa r se-g ra inedq u a r t z i t e w i t h a h ig h p ro p o rt io n of c h l o r i t e a nd s e r i c i t e a s a m a t r ix (A.Le it h, 1935). Pebbles , sometimes ang ula r , a r e common, and co ns is t only ofqua r tz and qu ar tz i t e . The mat r i x of the rock i s f e r rug inous nea r t h e base .Rowley Creek Sl a t e i s a gray quartz-chlorite-sericite s l a te . Bedding andc l eavage a re p resen t and t he rock ox id i ze s t o a r edd i sh co lo r on t hes es u r f a c e s . (A . Lei th , 1935) .

Sedimentologv of t h e Baraboo Bu ar tz it e

Composit ion and Texture. Besides qu ar tz gr ai ns (0.25-2.0 mm) the Barabooc o n ta i ns z i rc o n , r u t i l e , i r o n o x id e s, c h l o r i t e , p y r o p h y l l it e and s e r i c i t ea s a c c e s s o r i e s ( s e e Ta b le s 6 , 7 f o r compos i t ional da ta ) . Most qu ar tz sand


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grains in the formation have very thin films of iron oxide (chiefly hematite),which gives rise to the characteristic reddish color. Conglomerates consistof more than 90 percent clear to milky, well-rounded and well-sorted quartzgranules and pebbles, about 5 percent dark red jasper, and a few percent ofother dark lithic fragments, which tend to be more angular. The maximumpebble size known is about 3 centimeters, but most are less than 1.5 cm.Approximate proportions of the original lithic types within the formationare: 85% well-sorted sand; 5% argillaceous fine sand and silt; and 10%conglomerate. Finest units occur chiefly in the upper Baraboo, whereas con-glomerate is rather uniformly distributed in lenticular units a few inchesto a foot thick.Sedimentary Structures. Stratification is discernible in most Baraboo out-crops, although either secondary color banding or shearing obscures it insome cases. Over most of the syncline "master" or true bedding is revealedby essentially parallel parting planes assumed to have been originallyhorizontal; the majority of beds are from 6 to 12 inches thick. Asymmetricalripple marks occur widely on the bedding surfaces, but are especially welldisplayed in quarries along the north (vertical) limb of the syncline.

Cross stratification and associated small scour features, reflected byslight variations of color and texture, are prominent internal sedimentarystructures. Individual inclined laminae average about one-fourth inch inthickness. Roughly 60 percent of the exposed cross-stratified units arebounded by parallel, planar truncation surfaces, here termed master strati-fication or master bedding (generally abbreviated simply to bedding). Theamplitude of most inclined sets of cross laminae is from 6 to 12 inches,while small-scale cross laminae with amplitudes on the order of one or twoinches occur in some fine-grained units. The remainder of the strata showinclined truncation surfaces that produce wedge-shaped bodies with amplitudesof up to three or four feet. In the latter cases, the master bedding may beimpossible to detect, making interpretation of structural measurements some-what hazardous. Conversely, structurally-induced cleavages may be easilymistaken for cross bedding in certain cases. Typical cross stratification ismost easily studied at the U. S. Highway 12 locality (Supplementary Stop G)the Upper Narrows (Stop 2), and in the bluffs at Devils Lake (STOP 5).

Brett (1955) described the cross bedding as mostly straight in crosssection, thus with only slightly tangential bases (formerly known as theI?torrential type"). Common lack of a clearly tangential base makes top-bottom determinations difficult in many outcrops, but classic, curved,tangential bases also are well displayed. Brett noted that very rare fore-sets are as much as 7 to 10 feet long, these being low-angle types. Ingeneral, the foresets are much shorter and show angles of inclination from

0 .about 12 to as much as 54 degrees. Repose angles greater than 35 in well-sorted and rounded sandstones have been steepened structurally after deposition.Contortions clearly formed during or just after deposition are characterizedby disharmonic folding of laminae in patterns geometrically unrelated to thesyncline. In other cases, however, the origin of overturning of the tops ofcross sets is less obvious. Brett (1955) and Pettijohn (1957) have noted thatcross sets should be flattened on the north limb of the syncline and steepenedon the south by differential slip between strata during folding; Brett founda 5-degree difference between average inclinations on the two limbs. This isoversimplifying the case and, needless to say, careful structural observationsare required to separate cases of synsedimentary deformation from laterstructural deformation (see p. 16).


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Because of the induration of the quartzite, cross stratification israrely seen in three-dimensions except on talus blocks. This fact, coupledwith a limited understanding of cross stratification prior to 1960, naturallyled to an assumption that Baraboo cross bedding is practically all of the17textbook type", namely, simple uniformly inclined planes (see Fig. 10).But close examination in favorable outcrops (e.g., U. S. 12 roadcut, Supple-mentary Stop G) reveals that trough or scoop-shaped cross sets are not onlycommon, but may be the dominant form, as is typical of many sandstones.Trough shapes are especially prominent where truncation surfaces are non-parallel, producing the well-known wedge-trough or "festoon" stratification(Fig. 10).

Paleocurrent analysis by Brett showed a pronounced average preferreddip of cross strata toward the south-southeast (Fig. 2). Apparently Brettdid not recognize the possible importance of trough-type sets, which aredifficult to measure, and his number of readings per locality was small (atonly 5 of 45 localities were 10 or more readings reported). For simplicityof restoration to horizontality, he also assumed that folding had not rotatedthe foresets in the plan-view sense. In view of the fact that the strike ofthe cross-sets and the fold axis are near parallel, this seems reasonable.In spite of these possible shortcomings, Brett was able to verify the appar-ent mean foreset inclination direction with 21 asymmetrical ripple orienta-tions; there was only a 22O difference between their mean orientations, andlocally the agreement was within 5 degrees. Qualitative observation by our-selves at many localities leaves no doubt of a general north-to-south averagecurrent flow during Baraboo deposition as reported by Brett.

Sedimentary and Tectonic Environments. We have no reason to question thelong-assumed aqueous deposition of the Precambrian sediments, although cri-teria are almost totally lacking. Brett (1955) states that the ripple-markindex (amplitude divided by wave length) is characteristic for water depo-sition, but structural modifications preclude the use of cross-lamination andripple inclination for environmental determination (see Fig. 33b, STOP 7).As usual, one must argue by indirect analogy with other strata whose environ-ments are well established, which leads to the conclusion that the entirePrecambrian sequence was deposited in shallow marine water. During Baraboodeposition vigorous current agitation prevailed, as attested by texture andstratification. Mud, carbonate, iron and silica deposition followed but pre-sumably still in relatively shallow marine water.

The great purity and volume of preserved Baraboo sandstones is indeedimpressive. For example, the quartzite is 40 or 50 times thicker than themineralogically similar Ordovician St. Peter Sandstone. The contrast iseven more staggering, however, when we consider that both the Baraboo andWaterloo Quartzite are but local remnants of what was presumably a muchlarger original body of sandstone! Such pure sandstones generally have beenconsidered most characteristic of stable cratonic regions, but the Barabooapparently formed within a mobile tectonic belt, or at least was caught upin such a belt soon after deposition. Together with several other purequartzites of Middle and Late Precambrian ages in the Great Lakes region,which also occur within mobile belts, it constitutes inescapable evidenceof a long and complex history of repeated weathering and depositionalepisodes. Furthermore, such voluminous ancient pure quartz sandstoneattests to existence of still-larger volumes of quartz-bearing continental


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c r u s t a l p ar e n t r o ck s e a r l y i n e a r t h h i s t o r y ( i . e . , by 2. 0 t o 2. 5 b. y. a g o) .To w hat e x t e n t t h e q u a r t z i t e s r e f l e c t p e c u l i a r i t i e s of P re ca mb ri an w e a t h e ri n g d ue t o t h e n a t u re o f t h e ea r l y a tm o sp h ere and a l a c k of l an d v eg e t a t i o ni s n o t c l ea r . The p re s en ce o f v e ry a l um i no u s p y r o p h y l l i t e s u g g es t s ex t rem e l yt ho r ou g h w e a t he r i ng of s o i l s i n s o u r c e a r e a s .

P r e se n c e o f t h e b u t - s l i g h t l y - o l d e r r h y o l i t e co mpl ex , p l u t o n i c r o c k s ,and defo rmat ion and metamorph ism of t h e sedimen tary sequence i t s e l f , a l la t t e s t t o t h e d ev el op ment o f t h e P recamb r ian s eq u en ce wi t h i n a m o b i l et e c t o n i c b e l t t h a t ex t en d ed ea s t -wes t a c r o s s W i scon si n. The g r ea t t h i ck -n e s s o f t h e s t r a t a , w hi ch a p p a r e n t ly a l l f orm ed i n s ha l lo w -w a te r e n vi r on -m ent s , i n d i ca t e s p ro fo un d su b s i d en ce wi t h i n t h a t b e l t . B as ed upon l i t h o -l o g i c and t h ic k n es s s i m i l a r i t i e s , a s w e l l as r e c e nt i s o t o p i c d a t i n g , i ta p p e a r s t h a t t h e B ar ab oo i s p a r t o f a v e r y l a r g e q u a r t z i t e ma ss of l a t eM id dl e o r e a r l y L a t e P re ca mb ri an ag e ( c i r c a . 1 . 5 b .y . o l d ) e x t en d i ng a tl e a s t f rom Sou th Dakota t o Lake Mich igan (s ee F ig . 1 ) .

F i g u re 2. R es to re d d i p o r i e n t a t i o n s o f c r o s s s t r a t i f i c a t i o n i n t h e BarabooQu ar t z i t e s ho wi ng a n o r t h - t o - s ou t h p a l eo cu r ren t p a t t e r n . G. W. B r e t t ,JOURNAL OF GEOLOGY, 1955, F i g . 1, from p. 145. Copyright , The Un ive rs i tyof Chicago Pr es s. A l l r i g h t s r e s e r v e d ( p u bl i s he d w i t h p e r m i s s io n ) .


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S t r u c t u r a l H i s t o ry( D a l z i e l )

The Precambr ian rocks o f t h e Baraboo d i s t r i c t were t ec to n i ca l l y d e f o r medi n a Precambrian mobi le b e l t . In common wi th t h e metased iments of a l l mobi leb e l t s i n v e s t ig a t e d i n d e t a i l t o d a t e , t h ey show t h e e f f e c t s o f p ol yp ha sed u c t i l e d e f or ma t io n . Most of t h e meso s co p ic s t r u c t u r es ob s e rv ed can b ea s c r i b e d t o t h e e f f e c t s o f o n e m ain d e f o rm a t io n e p i s o de d u r i n g w hic h t h eB ara bo o s y n c l i n e was fo rm ed . O t he r s t r u c t u r e s s e e n o n l y i n t h e p h y l l i t i cl a y e r s can b e shown to h av e r e s u l t ed fro m o n e, o r p o s s ib ly two , l a t e r b utn o t n ec es s a r i l y u n r e l a t ed p h as es. The s t r u c t u r es a r e summarized i n T ab l e 3 ;i n T ab l e 4 t h ey a r e co r r e l a t ed w i th t h o s e r eco rd ed by R i l ey ( 1 9 47 ) , H end rixand Sch a iow i t z ( l 9 6 4 ) , and ea r l i e r w o rk e rs .

There i s c e r t a i n l y n o re a so n t o s up po se t h a t t h e d i f f e r e n t se t s ofs t r u c t u r e s d e s c ri b e d h e r e a r e t h e r e s u l t o f more t h a n o ne o ro ge ny . F o rexample, i n t h e Appalach ian-Caledonian o rogen , th e Taconian and th e Acadiano r o g e n i e s i n t h e A p pa l ac h ia n s, a nd t h e f i r s t a nd s ec on d p h as e s ( e a r l yO r do v ic i an an d l a t e S i l u r i a n ) o f t h e C al ed on ia n or og en y i n t h e B r i t i s hI s l e s , e ac h r e s u l t e d i n s i m i l a r s eq ue nc es o f s t r u c t u r e s ( D a l z i e l ,1969b; Dewey, 1969a and 1969b). In f a c t , whi le th e sequence o f s t r u c t u ra ld ev elop ment o u t l i n ed i n T ab l e 3 can b e d emo ns t r at ed c l e a r ly o n t h e b a s i s o fc r i t e r i a s uc h a s t h e de fo rm at io n of a s l a t y c l ea v ag e by a l a t e r c r e n u l a t i o nc l e a v a g e , t h e r e i s good r e a so n t o b e l i e v e t h a t a l l t h e e v e n ts d i s t i n g ui s h e dwere p a r t o f t h e p r o g r e s s iv e d e f o rma t io n of t h e P recambr ian s u cces s io n a tBar ab oo i n r e s p o n s e t o o n e r eg io n a l stress s ys tem. The v a r io u s s t r u c t u r esm ere ly r e c or d c e r t a i n s t a g e s w i t h i n a c o n t in u ou s s t r a i n h i s t o r y .P r e - t ec to n i c s t r u c tu r e s . M ast e r b edd ing ( S ) a nd c u r r e n t b e dd in g i n t h eq u a r t z i t e we re , t o some e x t e n t a t l e a s t , a c t i v e e l em e nt s d u r in g t e c t o n i cdeformat ion f o r bo th typ es of su r fac es ar e commonly s l i cke ns i ded . Thei mp or ta nc e of t h i s t y pe of d ef or ma ti on i n t h e o v e r a l l s t r a i n of t h eBaraboo Quar tz i te i s d i s c u s s e d l a t e r .

O ve rs te ep en in g, o v e r t u rn i n g , a nd d i s t o r t i o n of t h e c r o s s - s t r a t i f i c a t i o ni s co n s id e r ed t o b e d o min an t ly sy n s edimen ta r y . D i s to r t i o n i s c o n fi n e d t od i s c r e t e b e ds , a nd o v e r t u r n i n g of s ou th wa rd f a c i n g f o r e s e t s o c c u r s ev en i nv e r t i c a l b e ds o n t h e n o r t h l im b o f t h e s y n c l i n e wh ere i t i s u n l i k e ly t o h av er e s u l t e d from r o t a t i o n a l s t r a i n d u ri n g f o l d i n g. O v er tu rn in g of t h e f o r e s e t sa t t h e t o p of t h e be ds on t h i s l im b i s down d i p t o t h e s o u th . The r o t a t i o n a ls t r a in must h ave b een i n t h e o p p o s i t e d i r e c t i o n , t h e h ig h e r b ed s moving u pd i p t o t h e no r, th o u t of t h e c o r e o f t h e s y n c l i n e ( s e e Fi g . 3 ) .

P r e f e r r ed o r i en t a t i o n of some p eb b les i n t h e q u a r t z i t e may b e p rimar y .They l i e w i th t h e i r l o n g e st and i n t e r m e d i a t e a xe s i n t h e b ed di ng o r c u r r e n tb edd ing s u r f ace s , and i n some cas e s a l s o h av e a c r u d e , l i n e a r p r e f e r r edo r i e n t a t i o n . D im en si on al o r i e n t a t i o n of s m a l l e r q u a r t z g r a i n s i s probablyl a r g e l y t e c t o n i c .

M ig r a t i o n of s o lu t i o n s t hr o u gh t h e s ed iment s t o p ro d uce t h e complexco lo r banding was pos t-d epo si t ion al , but presumably pre dat ed metamorphismand deformat ion , a s i t i s n o t s t r u c t u r a l l y c o n t r o l l e d ( s e e F i g. 2 7c ).


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Main Phase S t r uc t u re s . Mesoscop ic s t ru c t u r es ass igned t o th e main phase ofdefo rmat ion a r e t h e most common minor s t r uc tu re s i n t h e metasediments anda r e c l e a r l y r e l a t e d t o t h e m ac ro sc op ic 2 Bara boo s y n c l i n e ( F i g . 3 ) .Cleavage and c leavage/bedd ing in te rs ec t i on s a r e be s t deve loped and mos twi d e l y r eco g n i zab l e .

There i s a g r ea t d ea l o f co n fu s i o n o v e r c l eav ag e t e rm in o l og y g en e ra l l y ,bu t th e Baraboo are a i s a s s oc i a te d i n t h e minds of a l l s t r u c t u r a l g e o l o g i s t swi t h c l a s s i c a l s t u d i e s of ro ck c l eav age . The new names ap p l i ed i n t h i sa c co u nt h a ve be en s e l e c t e d i n o r d e r t o a v o i d g e n e t i c i m p l i c a t i o n s a nd don o t c onf or m t o t h e c l a s s i c a l t e rm i no l og y .

Ear l y workers ( I rv in g , 1877; S te id tman , 1910 ; C.K. Lei th , 1913 , 1923)r ec og ni ze d " s t r i k e j o i n t s " i n t h e q u a r t z i t e ( n e a r v e r t i c a l on t h e s o ut hl im b, n e a r h o r i z o n t a l o n t h e n o r t h l i m b ) , w h ic h w er e r e f r a c t e d i n t o a n o r t hd i p pi n g " f r a c t u r e c l ea va ge " i n t h e more p h y l l i t i c be ds . I n f a c t t h e i rI l j o i n t s " a r e p a r a l l e l t o a more s u b t l e , c l o s el y - sp a c e d p a r t i n g ( S1 ' on T a b le s3 and 4; F ig s . 3 and 4 ) , which pervades th e qua r t z i t e of t h e Baraboo Ranges.T h i s i s a p p a r e n t l y c o n t r o l l e d by t e c t o n i c a l l y - f l a t t e n e d q u a r t z g r a i n s a nda l i g n e d p h y l l o s i l l i c a t e s a t l e a s t i n im pure q u a r t z i t e be ds ( F i g. 5 B). O ther-w i s e i t i s m e re ly a c l o s e l y s pa ce d p a r t i n g . The " f r a c t u r e c l ea v ag e " r e f e r r e dt o c o n s i s t s of v e ry c l o s e l y s pa c ed , b u t n o n e t h el e s s d i s c r e t e , s u r f a c e s form edby c o n c e n t r a t i o n s of a l i g n e d p h y l l o s i l i c a t e s ( S1 on T a b le s 3 and 4; Figs . 3 ,4 , and 5 a ) . Of ten s l i g h t d i s p l acem en t s can b e o b s erv ed a l o n g t h e s e s u r fac es(se e F ig . 27 , and C. K. Le i th , 1923 , F ig . 54 ) which appear t o deform( s l i g h t l y c r e n u l a t e ) p h y l l o s i l i c a t e s f or m in g a much more p e n e t r a t i v e s u r -f a c e i n t h e p h y l l i t i c b e ds , w hich i s v er y f a i n t i n t h e f i e l d b ut r e a di l yv i s i b l e i n t h i n s e c t i o n ( SI E on T ab le 3 , see Fi g s . 3 , 4 and 5 a ) .

Here t h e c l o s e l y s pa ce d p a r t i n g i n t h e q u a r t z i t e ( S i t ) i s termed simplyt h e q u a r t z i t e c le a va g e, and t h e " f r a c t u r e c le av ag e" of C. K . L e i t h a n d o t h e r si s c a l l e d p h y l l i t i c c l ea v ag e (S1). A s Ramsay (1967, p. 180) po in ts ou t ,t h e r e c an on ly b e o ne t r u e s l a t y c l e a va g e i n a t e c t o n i t e ( i . e . a c om pl et el yp e n e t r a t iv e c le a va g e, a f f e c t i n g a l l t h e p l a t y m i ne r al s i n t h e ro c k ). I n t h eB ar abo o Q u a r t z i t e t h i s i s t h e somewhat obscure SIE su rf ac e fo rmed by t h es c a t t e r e d p h y l l o s i l i c a t e s i n r a t h e r q u a rt z o se p h y l l i t e s a nd deformed by s l i pon t h e more d i s c r e t e s ur f a c e s of t h e ( ~ 1 ) h y l l i t i c c le av ag e.

2 . M ac ro sc op ic s t r u c t u r e s a r e t h o s e t h a t o c c u r on t h e s c a l e o f more t h a no ne o u t c ro p . Hence t h e i r e l u c i d a t i o n i n v o l v es ex t r ap o l a t i o n f ro m o neo u tc r op t o t h e n e x t.

3. A " p e n e t r a t i v e " s t r u c t u r e i s one which i s c l o s e l y s p aced t h ro u g h o u tt h e r oc k. The d e f i n i t i o n i s t h e re f o re d ep en d en t o n s ca l e .


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Table 3MESOSCOPIC STRUCTURES I N THE BARABOO QUARTZITE

AGE

Primary

Pos t - sediment a t on ,p r e t e c t o n i cEa r l y Main Phase

Main Phase

Late Main Phase

Secondary Phase

Late Phase

STRUCTURES

So Bedding (master bedding)( a l s o c u r r e n t b e dd i ng , andperhaps some prefer redg r a i n a n d p e b b l e o r i e n t a -t i o n )

Color banding

I z i t eSIE * Sla ty c leavage

( p h y l l i t e ) S l *Q u a r t-

A x i al s u r f a c e s of t i g h tasymmetr ic minor folds( f o ld in g So )

S1 P h y l l i t i c c l e av -a ge ( p h y l l i t e ) , d e -forming SIE

SIL F a i n t s t r a i n - s l i p o rc r e n u l a t i o n c l e a v a g e( de fo rm in g S 1 i n p h y l l i t e )

c l e a -vage( q u a r t -z i t e )

S 2 S t r a i n - s l i p o r c r e nu l a -t i o n c l e a v a g e ( c o n ju g a t e ;deforming So and, mainly,S1 i n p h y l l i t e )A x ia l su r f ac es o f m ino rchevron fo lds (deformingSo, S1, and s l * )Axia l su r f aces o f openminor fo lds (deformingSo. S1 and S2)

Ripple marks?Some pre fe r re d gr a i nan d p eb b le o r i en t a -t i o n

So /S IE n t e r -s e c t i o n( i n d i s t i n c t )S d S l i n t e r -s e c t i o n

Axes o f t i g h tasymmetricmin o r f o ld s

-o& '

i n t e r -s e c -t i o n

Longrain( m i n e r a l a l i g n -m en t) i n S 1 t r a n s -( p h y l l i t e ) i t i o n -S l i c k e n s i d e s a1on So (quar t -z i t e )Boudin axes

Axes o f f i n e cren u la-t i o n s ( d e f o r min g S1i n p h y l l i t e )Axes o f c ren u l a t io ns(deforming So and,m in ly , S 1 i n p h y l l i t e )Axes of minor chevronfo lds deforming So ,S 1 and S l * )

Axes of open minorf o l d s


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TABLE 3 (con td . )

' a r ious

-b u b t f u lJ o i n t s , some q u a r t z - f i l l e d ;quar tz "ve ins" , inc lud i ngen eche lon t ens io n gashes i nbands, some deformed ga sh esprobably post-second phase )Brecc ia zones and fau l t s (? )Local h igh ly pene t ra t ivec le a va g e i n q u a r t z i t e

Second cleavage(c l o s e l y s p aced j o i n t i n g )

i n q u a r t z i t eOther c l eavages(c l o s e l y s p aced j o i n t i n g )

i n q u a r t z i t e

Sl i ckens ides on bedd ing ,cu r r e n t b ed di ng , f r ac t u r ec l eav ag e and j o i n t s u r f ac e ,

Boudin AxesIn t e r s ec t i o n of h i g h l yp e n e t r a t i v e c l ea v ag e i nq u a r t z i t e w i t h b e dd in gIn t e r s ec t i o n of s econ dc le a va g e i n q u a r t z i t ewith beddingI n t e r s e c t i o n o f o t h e rc le a va g es i n q u a r t z i t ewi th bedding

* Fo r d e f i n i t i o n s o f c l eav ag e t e rmi no lo g y u sed h e re s e e t ex t .NNW SS E

(quartzite cleavage)

b. ,

C.

(crenulation cleavage)North limb South limb

Figure 3. Diagrammatic cros s-se ct io n of th e Baraboo sy nc l in e showing th ea t t i t u d e s and r e l a t i o n s h i p s of c l ea v a ge s .


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Table 4COMPARISON OF TERMINOLOGY USED FOR MESOSCOPIC STRUCTURES

IN THE BARABOO QUARTZITEDalziel (this paper) Riley (1947) Hendrix & Schaiowitz (19e

1

(S ) Slaty cleavage*1( S d S I E ) Bedding/slatycleavage intersection(indistinct)

(So) Bedding(master bedding)

EARLY MAIN PHASESTRUCTURES

Bedding and bedding planefoliation (principalfoliation of south limb)

MAIN PHASE STRUCTURES

I (S, ) Quartzite I I

Bedding

-

-(S ) Phyllitic1cleavage**

Axial plane foliation(north limb only)

cl&avage ***cSo/S1)~edding phylli-

I zite cleavage 1 intersection I ---

Normal rock or fracturecleavage

tic cleavage intersectionlintersectionShear fractureBedding/axial plan foliation/ ---

---Bedding/quart- I~edding/shear racture

intersectionAxial surfaces of 1 Axial planes of normaltight minor foldsLongrain (mineralelongation lineation)Slickensides onbedding

---Grain elongation (? )

---Boudin axes-

LATE MAIN PHASESTRUCTURES(SIL Faint strain-slip or crenulationcleavageAxes of finecrenulations

drag folds---a lineation on bedding-

--- l~oudin xes

------

- ----

Y


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21TABLE 4 (contd.)

(S ) S t r a i n - s l i p o r2c r e n u l a t i o n c l e a v a g e

I A x i al s u r f a c e s o f Im i n o r c h e v r o n f o l d sA xes o f c r e n u l a t i o n sand minor chev ron fo ld s

LATE PHASE STRUCI'URESA x i a l s u r f a c e s o f o pe nm i n o r f o l d sAxes of open minor fo ld sI STRUCI'URES OF VARIOUS AGESd o i n t s ; q u ar tz - f i l l e di o i n t s

Q u a r t z " v e i n s " ; q u a r t zf i l l e d t e n si o n g as he si n bands, some deformed

B r e c c i a z o n e sSTRUCTURES OF DOUBTFUL AGE

C le av ag es i n q u a r t z i t eo t h e r t ha n S i t

R eve rs e s l i p o r r oc kc l e a v a g e ; r e v e r s e

l ~ x i a l l an es of r ev e rs--- ] d r a g f o l d sIC r e s t s a nd t r o u g h s o f IAxes o f r e ve r s e d ragc he vr on o r b u c kl i ng f o l d s f o l d s

J o i n t s ; q u ar tz - f i l l e dj o i n t s

Q u a r t z v e i n s ; q u a r t zf i l l e d l a dd e r te n s io nf r a c t u r e s; deformed andS -sha ped q u a r t z f i l l e dg a s h v e i n s

J o i n t s

S l i c k e n s i d e sQ ua rtz f i l l e d j o i n t sS l i c k e n s i d e s

B r e c c i a z o n e s I ---

I

S he ar f r a c t u r e s (?)

* F o r d e f i n i t i o n s of c l e a v a g e t e rm i n o lo g y u se d h e r e s e e t e x t .** " ~ r a c t u r e l ea va ge " o f Van H i s e , C. K. L e i t h and o t h e r g e o l o g i s t s o f

t h e isc cons in school ."* " s t r i k e j o i n t i n g w of g e o l o g i s t s of t h e isco cons in school" .


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Slickensides with chatter marksfacing up dip (south ) \

s1 Crenulation cleavageFigure 4. Block diagram showing the relations of main phase mesoscopic

structures on the south limb of the Baraboo syncline.


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I t w i l l be noted th at the term "axia l p lane c leavage" has been avoided .This i s b ec au se a l l t h r e e c l ea v ag e s di sc u ss e d up t o t h i s p o in t a r e r e l a t e d t ot h e f o r ma t io n of t h e Baraboo s y n c l i n e bu t n one a r e s t r i c t l y a x i a l p l a n a r(Fig. 3 ) . The s la ty c leavage (SIE) converges on th e ax ia l surfa ce , th ep h y l l i t i c c leavage (S1), though sometimes ax ia l p lanar , i s v a r i a b l e i na t t i t u d e w i t h i n a s i n g l e b ed , and q u a r t z i t e c le a va g e ( S ' ) i s v a r i a b l e o v e rt h e s y n c l in e . I t i s everywhere nea r ly a t r i g h t ang l es i o t he m as t e r bedd ingand hence ax ia l p lana r on ly i n the h inge zones .

On t h e p h y l l i t i c c l e av a ge s u r f a c e s , a f i n e mi ne r al a l ig nm en t l i n e a t i o ncan som et im es be d i s ce rned alm os t a t r i gh t ang l es t o t he ho r i zo n t a l ( eas t -nor theast -wes t -southwes t ) S /S in te rs ec t i on (F ig . 4 ) . This i s t h e s t r u c t u r e

I t 0known a s longrain" in s la te s . ' I t i s i n ti m at e ly r e l a t e d t o t h e p h y l l i t i cc leavage a s par t of what F l in n (1965) has ca l l ed an L-S sys tem, t he l in ea t i onbe ing fo rm ed by t he l i n ea r p re fe r red o r i en t a t i on of t he c r ys t a l s t ha t formt h e S s u r f a c e . I t c an b e t r a c e d from t h i n p h y l l i t e b e ds , i n w hich S l i e s1c l o s e t o S i n t o s l i c k e n s i d e s on t h e b ed din g s u r f a c e s of t h e q u a r t z i i e

0 '(Fig . 4 ) . The gen et ic impl ica t ion s of thes e two types of l i ne at io n w i l l bed i sc u ss e d l a t e r , b ut t h e y a r e c l e a r l y r e l a t e d d i r e c t l y t o t h e S and S '1c l ea v a ge s . I n some p l a c e s a f i n e c r e n u l a t i o n of t h e p h y l l o s i l i c a t e s l y i n gi n t h e main p h y l l i t i c c l ea y ag e (S ) p a r a l l e l s t h e l o n g r a in and t h e s l i c k e n -1s id es on t he bedding su r faces (F ig . 4 ) . This can be observed, f o r example,a t t h e no r theas t end of Dev il s Lake, t he no r thwes t en t r ance t o t he De v i l ' sLake St a t e Park , and th e ea s t bank of S k i l l e t Creek (STOP 5, SupplementaryStop F , and S top 6 , res pec t ive ly) .

The c r e n u l a t i o n r e s u l t s i n a f a i n t , d is c on ti nu ou s s t r a i n - s l i p o r crenu-l a t i o n 4 c le a va g e i n p h y l l i t i c l a y e r s. I t c l e a r l y p o s t d at e s t h e f o r ma ti on oft h e ( S ) p h y l l i t i c c l e av a g e, b u t n o n e t he l e ss i s i n t im a t e ly r e l a t ed geo-1m et r i c a l l y t o t h e l ong ra in i n S land t he s l i cke ns ides on S and can be

0'g e n e t i c a l l y e x p l ai n ed on t h i s b a s i s ( s e e F i g. 7 ) . No cas e was observedw here t h e f i n e c r e n u l a t i o n i s a t a n an gl e t o e i t h e r of t ho se l i ~ l e a r t r u c t u r e s .The a s s o c i a t e d s t r a i n - s l i p o r c r e n u l a t i o n cl e av a ge i s termed S (F ig . 4 ) .1

A l l of t h e s t r u c t u r a l e l em e nt s m en tio ne d s o f a r c an be r e l a t e d d i r e c t l yt o t h e f o rm a t io n of t h e B araboo s y n c l i n e a nd r e c or d p a r t i c u l a r s t a g e s i n t h ep rog res s ive s t r a in of t he B araboo Quar t z i t e du r ing i t s main phase of deforma-t i on . Three s e t s of s t r uc tu r es r e s u l t i ng from th i s de form ation phase can berecogn ized i n t h e ph y l l i t i c l ay e r s (S S1 and S see Tab l e 31, but onlyE ' 1 ~ ;one i n t h e q u a r t z i t e ( S ' ) . The qu ar &z i te c leavage (S ' ) i s r e f r a c t e d i n t ot h e p h y l l i t i c c le av ag e 1.9 , but i t may have or ig i na te & e a r l i e r , perhaps1when S was be ing fo rm ed i n t he p hy l l i t i c l aye r s .1

Mesoscopic fo ld s r es ul t i ng from th e main phase of deformation a r e founda t o n ly two l o c a l i t i e s , b ot h on t h e s o u t h lim b of t h e s y n c l i n e i n t h e t h i c kp h y l l i t e zone c o n t a i n in g t h i n q u a r t z i t e b e ds . A t Skillet Creek (STOP 6,See F ig . 29b) and the northwest en t ran ce t o Devi ls Lake S ta te Park(Supplementary Stop F, See Fig . 48), t h e p h y l l i t ic cleava ge (S1) i s a x i a lp l a n a r t o f o l d s w it h n e a r h o r i z o n t a l a x es and a s ou h e r l y ve rg en ce ( d i r e c t i o n5of over turn ing) . These a r e th e "normal dra g fold s" of Hendrix and4. S t r a i n - s l i p o r c r e n u la t i o n c le a va g e i s u se d h e r e t o d e s c r i b e a c l o s e l y s pa ce

pa r t i ng marking an a lignment of ph yl lo s i l i ca te s r es u l t i ng f rom th e deforma-t i o n of a p r e - e x is t i n g more p e n e t r a t i v e s t r u c t u r a l s u r f a c e ( i . e . , s l a t y o rp h y l l i t i c c le av ag e.

5 . Minor fo ld s such as th ese most o f t en or i g i na te f rom processes o th er thanf r i c t i o n a l " d r a g " .


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Schaiowitz (1964) i n th a t they a r e congruent with the macroscopic geometryof t he B araboo sync l i ne . The t h in qua r t z i t e beds wi th in t he ph y l l i t i cl ay e r s have r eac t ed i n a much l e s s du c t i l e f a sh ion than t he phy l l i t e . Theyform boudins wit h east-west axes cross ed by te ns ion gashes and fr a ct ur es .Some of th e boudins a r e deformed by secondary phase s t ru ct ur es .Secondary Phase S t ru ctu res . S t ru ctu res th a t pos td ate main phase s t ru ct ur a le l emen t s, and a r e l e s s obv ious ly r e l a t e d t o t he fo rm at ion of t he B araboosy nc l in e, have been assigned t o a secondary phase of deform ation (s eeTable 3). A t a number of l o c a l i t i e s on th e south l imb of th e main syn cl in e ,and a t one l oc a l i t y on t he no r th l im b , coa r se eas t -no r theas t - west-southwests t r i k i ng c r enu l a t i on c l eavages a s soc i a t ed wi th chev ron fo ld s can be s een t odeform the main c leavage of th e ph y l l i t i c hor izons (S ) as we l l a s bedd ing1(se e F ig . 3 ) . Many of th e chevron fo lds , which have ne a rh or iz on ta l axes ,a r e ove r tu rned t o t h e no r th on t h e sou th l im b , hence t hey have l ong beenca l l ed "revers e drag fo lds" (see Hendrix and Schaiowi tz , 1964) as they ar enot congruent wi th the geometry of th e syncl ine . I t can be shown th a t the rea r e con juga t e c renu l a t i o n c l eavages on t h e sou th l im b , d ipp ing bo th nor th-northwest and south -south east (Fig. 3) .

While t h e main phase p hy l l i t i c c l eavage can r ead i l y be t r a ced i n to ac le av ag e i n t h e q u a r t z i t e , t h i s i s not t r ue of th e second phase cre nul a t io ncleavages . There ar e , however, a number of o t he r s t ru ct ur a l sur fa ce s i nthe q ua r t z i te a t some lo c a l i t i e s , one o r more of which may be equivalen tt o t h e c r e n u l a t i o n cl ea v ag e s i n t h e p h y l l i t e .Late Phase S t ructures . A t two l o c a l i t i e s on t he sou th l im b ( S k i l l e t C reek ,Stop 6, and the U. S. Highway 12 ro ad cu t, supplemen tary St op G) m inor s t ruc tu rescan be observed th a t appear t o deform th e second cre nul a t io n c leavages . Theses t ru ct ur es a re ra t he r open minor fo ld s (F ig . 29e and 49d) . They a r e ra re , andt h e i r o r i g in i s r a th e r problema tical because of th e complex geometry of th econjugate secondary cren ula t ion c leavages (F ig . 49b , c and d) .O the r S t ruc tu res . S t ruc tu res t h a t r e s u l t from b r i t t l e de fo rmation of rocksa r e more d i f f i c u l t t o r e l a t e i n ti me t h an d u c t i l e s t r u c t u r e s . F or i n s ta n c e ,two jo i n t sur fac es merely in te rs ec t i ng one another most of te n y i e l d no ev i -dence of t h e i r age r e l a t i on s , bu t a c re nu l a t i on c l eavage can be deduced un-equ ivoca ll y t o pos tda t e a s l a t y c l eavage because it deforms it.

Jo in t s a re common throughou t t he qua r t z i t e . The i r a t t i t ud e and t ec ton i cs i g n i f i c a n c e w i l l be d i scussed la te r . None ar e seen t o be deformed so theya r e a l l l i k e l y t o ha ve de ve lo pe d l a t e i n ( o r a f t e r ) t h e main ph as e of s y n c l i n a ldevelopment.

Some of t h e j o i n t s a r e f i l l e d w i t h r e c r y s t a l l i z e d w h i te o r p a l e pin kqu ar tz . Numerous en echelon bands of qu ar tz -f i l le d ten sio n gashes occu r, and a r el o c a l l y c o n ju g a te F The gashes commonly have a s igmoid shape due t o cont inueddisplacement along th e bands. The (S ' ) q u a r t z i t e c l e a v a g e i s deformed i n th e1same sense (Fig. 54b). The gashes pos tda te th e development of t h i s cleav age,which cannot be tra ce d through them (Fig. 54a ).

C e r t a in s l i c k e n s i d e s and b ou di ns c a n c l e a r l y b e r e l a t e d t o t h e mainphase o f de fo rm ation ( s ee above) , but o the r s canno t. Near ly a l l s t ru c t u r a l


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Figure 5. Photomicrographs showing the nature of cleavages in theBaraboo Quartzite.

A. Quartz-phyllite layer in quartzite at northeast corner of DevilsLake (STOP 5, see Figs. 3, 4 and 27a). Two discrete phylliticcleavage (S1) surfaces dip north (left on photograph) at a higherangle than the faint but much more penetrative slaty cleavage(S~E) hich they crenulate slightly. Plane polarized light.

B. Quartzite cleavage (~1') n specimen from the quarry on the eastside of the Upper Narrows (STOP 3). Alignment of phyllosilicateminerals and quartz grains in the cleavage is well developed, thequartzite being relatively impure. Crossed-nicols.

C. Bedding and phyllitic cleavage (almost parallel) deformed by second-ary crenulation cleavage (S2) which dips south (right on photograph).Phyllitic zone of the Baraboo Quartzite, U.S. Highway 12 roadcut(Supplementary Stop G, see Figs. 3 and 49a). Plane polarized light.

D. Phyllitic cleavage deformed by secondary strain-slip cleavage. Notecomplexity of strain-slip cleavage in detail and very faint conjugatesurfaces. East side of Upper Narrows (Supplementary Stop B, see Fig.3). Plane polarized light.


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s u r f ac es i n t h e q u a r t z i t e (mas te r b ed di ng , cu r r e n t bed di ng , j o i n t i n g , 'S1cleav age) show s l i ck en sid es . These may have formed a t d i ff er en t t imes .F i n a l l y , t h e r e a r e two ty p e s of s t r u c t u r e s whose r e l a t i o n s h i p ha s n o t

been resolved. A t a number o f l o c a l i t i e s n ea r t h e ea s t end of t h e s y n c l i n e ,a f a i n t b ut p e r s i s t e n t c le a va g e c an b e d is c er n ed i n t h e q u a r t z i t e t h a t seemst o be more p en e t r a t i v e t h an t h e S ' cleav age, and may rep re

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