(.2oD) 

E 

/140. I~ 

Stratigraphy and Lithocorrelation of the 

Snowslip Formation 

(Middle Proterozoic Belt Supergroup), 

Glacier National Park, Montana 

By JAMES W. WHIPPLE and SUE N. JOHNSON 

U.S. GEOLOGICAL SURVEY BULLETIN 1833 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U. S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade names is for descriptive purposes only and does not imply 

endorsement by the U.S. Geological Survey. 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Whipple, James W. Uames Wilburn) 

Stratigraphy and lithocorrelation of the Snowslip Formation (Middle Proterozoic Belt Supergroup), Glacier National Park, Montana. 

(U.S. Geological Survey bulletin; 1833) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1833 

1. Geology, Stratigraphic-Precambrian. 2. Stratigraphic correlationMontana-Glacier National Park. 3. Snowslip Formation (Mont.) 

4. Glacier National Park (Mont.) I. johnson, Sue N. II. Title. Ill. Series. 

QE 75.B9 no. 1833 [QE653] 551.7' 16 87-600454 
CONTENTS 

Abstract 1 

Introduction 1 

Geologic setting 1 

Purpose 2 

Stratigraphy 2 

Hole-in-the-Wall reference section 2 

Member 1 5 

Member 2 5 

Member 3 5 

Member 4 6 

Member 5 6 

Member 6 7 

Lithocorrelation 8 

Member 1 9 

Member 3 9 

Member 5 10 

Arenite composition 11 

Discussion 11 

Depositional setting 11 

Tectonic setting 13 

Sedimentation 15 

Regional correlation 19 

References cited 20 

Appendix: Reference section 23 

FIGURES 

1. Chart showing stratigraphy and approximate age of younger Middle Proterozoic rocks of Glacier National Park 2 

2. Generalized map showing distribution of the Snowslip Formation, location of measured sections, and major structures in Glacier National 

Park 3 

3. Schematic fence diagram showing lithofacies correlation between 

measured sections of the Snowslip Formation, Glacier National Park 4 

4. Photograph of Hole-in-the-Wall basin showing location of reference 

section 6 

5. Diagrammatic stratigraphic column of the Snowslip Formation at Holein-the-Wall reference section 7 

6. Photomicrograph of member 1 ooliths 8 

7. Photograph of pinkish stomatolitic limestone in member 2 9 

8. Photograph of mud chips (rip-up clasts) in member 1 10 

9. Photograph and diagrammatic sketch of cyclic fining-upward sequences 

in member 5 11 . 

10. Photomicrograph of arenite fabric and composition, member 5 12 

11. Diagrammatic representation of the Purcell Lava at Hole-in-the-Wall 12 

12. Photograph of large pillow in the pillow lava facies at the base of the 

Purcell Lava 13 

13. Geologic map showing location of the type section of the Snowslip 

Formation 14 

Contents Ill 
14. Photograph of Lunch Creek measured section 14 

15. Photograph of Huckleberry Ridge measured section 15 

16-20. Photomicrographs of: 

16. Ooliths in member 1 16 

17. Armored spherule, upper part of member 1, Lunch Creek 

section 16 

18. Abraded and impinged quartz overgrowth on quartz grain in 

member 3, Huckleberry Ridge section 16 

19. Bimodal clast size in arenite bed of member 3, Hole-in-theW all reference section 16 

20. Typical interlocking grain texture and quartz overgrowths in 

member 5 16 

21. Ternary QFL diagram showing the compositional plots of 43 arenite 

samples 17 

22. Ternary QmFLt diagram showing inferred provenance of suites of 43 

arenite samples 18 

23. Photomicrograph of inherited quartz overgrowth in member 5 19 

24. Regional stratigraphic correlation chart 19 

25-30. Photographs of: 

25. Typical bedding style of member 6 25 

26. Incomplete fining-upward sequences in member 5 26 

27. Syneresis cracks on bedding plane surface, typical of members 

2, 4, and 6 27 

28. Desiccation cracks and traces of fluid-escape structures on 

bedding plane surface, typical of members 1, 3, and 5 28 

29. Syneresis cracks and wave-generated ripple marks on bedding 

plane surfaces, typical of members 2, 4, and 6 29 

30. Pink stromatolitic limestone, typical of members 2 and 4 30 

CONVERSION FACTORS 

For readers who wish to convert measurements from the metric system of units to the inch-pound 

system of units, the conversion factors are listed below. 

Metric unit 

millimeter (mm) 

centimeter (em) 

meter (m) 

kilometer (km) 

IV Contents 

Multiply by 

0.03937 

0.3937 

3.281 

0.6214 

To obtain inch-pound unit 

inch 

inch 

foot 

mile 
Stratigraphy and Lithocorrelation of the 

Snowslip Formation 

(Middle Proterozoic Belt Supergroup), 

Glacier National Park, Montana 

By James W. Whipple and Sue N. Johnson 

Abstract 

The Snowslip Formation is in the upper part of the Middle Proterozoic Belt Supergroup; it is exposed in the central 

and western parts of Glacier National Park and composed mostly of fine-grained, terrigenous clastic rocks that were deposited 

about 1,200 Ma in a paralic, mixed siliciclastic-carbonate environment. In the northern part of the Park, the Snows/ip Formation contains the Purcell Lava, which is a series of thin mafic 

flow units that are absent from the type section in the southern 

part of the Park. Because of the importance of the Purcell Lava 

as a time line in the Belt, a reference section is established at 

Hole-in-the-Wall in the northern part of the Park and subdivided 

into six informal members. The uppermost member (member 

6) encloses the Purcell Lava. 

Lithocorre/ation of members exposed in the reference section, the type section, and two other sections of the Snowslip 

in Glacier National Park indicates a northward thinning of 

stratigraphic units. Compositional analysis of framework grains 

in arenite units suggests that Snowslip sediments were 

multicyclic and had a cratonic source. Based on changes in 

mineralogy and facies and limited paleocurrent measurements, 

sediment transport direction was northwest with minor directional components west and southwest. 

Deposition of the Snowslip Formation was preceded by 

a period of erosion, interrupted by extrusion of the Purcell Lava, 

and punctuated by two episodes of fluvial sedimentation. These 

interruptions are interpreted to be related to periods of active 

tectonism during sedimentation. A polarity reversal is coincident with a disconformity at the base of the Snowslip. 

INTRODUCTION 

The Snowslip Formation is the lowermost stratigraphic unit in the Missoula Group of the Middle Proterozoic Belt Supergroup (fig. I). In Glacier National 

Park, the Snowslip is exposed along the Akamina 

syncline, in the Apgar Mountains, and in the downthrown 

block of the Blacktail fault (fig. 2). It mostly consists of 

terrigenous clastic rocks that were deposited in a mixed 

siliciclastic-carbonate environment. In the northern part 

of the Park, the upper part of the Snowslip encloses the 

Purcell Lava, a series of thin mafic flow units that were 

emplaced in part subaqueously and in part subaerially 

(McGimsey, 1985). The type section of the Snowslip, 

which was named and described by Childers (1963), is 

on the flank and ridges of Snowslip Mountain in the 

southernmost part of Glacier National Park (fig. 2); here, 

it rests with apparent conformity rather sharply on the 

Helena Formation, does not contain the Purcell Lava, 

and is overlain conformably by the Shepard Formation. 

The age of the Snowslip is uncertain. Hunt (1962) 

dated a hornfels below the Purcell Lava in Canada at 1,075 

Ma; however, glauconite from the overlying Shepard Formation has been recently dated (Rb/Sr) at 1,170 ± 20 Ma 

(Obradovich, Peterman, and Zartman, reported by Harrison, 1984). A U/Pb date on zircon from a metabentonite 

bed about 65 m below the base of the Snowslip (in the 

Helena Formation) at Logan Pass in Glacier National 

Park yielded an age of about 1,350 Ma, although the 

zircon was observed to contain a possible detrital core 

(Harrison, 1984). Age correlation based on paleomagnetic 

pole positions of Belt strata on Proterozoic polar wandering paths (Elston and Bressler, 1980) suggests that the age 

of the Missoula Group is no younger than 1,200 Ma and 

that the Snowslip is about 1,375 Ma (Elston, 1984). A 

major polarity reversal, known to occur at or near the base 

of the Snowslip in most parts of the Belt basin (Evans 

and others, 1975; Elston and Bressler, 1980), has not been 

correlated with polarity zonation of other Proterozoic 

sequences in the North American Cordilleran, and so, 

regional age correlation using polarity zonation is not 

possible at this time. Considering these various dates, we 

feel the Snowslip was probably deposited somewhere between 1,350 and 1,170 Ma (fig. 1). 

Geologic Setting 

The geology of Glacier National Park consists 

mainly of allochthonous Belt Supergroup strata that have 

been subjected to lowermost greenschist-facies metamorphism (Maxwell, 1973) and have a maximum thickness 

Introduction 
MIDDLE PROTEROZOIC ROCKS OF AGE* GLACIER NATIONAL PARK 

Top not exposed 

McNamara Formation ca. 1 165 Ma 

Bonner Quartzite 

0. 0. Mount Shields ::::! ::::! Lava 0 Formation 

0 <!i ~ ..!!! 

::::! 

CJ) 0 

(/) Shepard Formation ca. 1 170 Ma (/) ~ 

Q) ~ 

0. Snows lip 

::::! Purcell Lava CJ) 

++++++++++++ 

..... Formation 

- ><+++ 

Q) " " " ca. 1350 Ma IJJ ..... " Q)_$ " " " IJJ "' ++++++" Q) c: - 0 Helena ""0.0 

""0 ~ 

·- "' 2: u Formation 

Figure 1. Stratigraphy and approximate age (based on 

lithostratigraphic correlation) of younger Middle Proterozoic 

rocks of Glacier National Park. Crosses, mafic sills. *As 

presented at Belt Symposium II, October 1983 (Obradovich 

and others, 1984). 

of about 5,200 m (Whipple and others, 1984). For the 

most part, Proterozoic sedimentary rocks of the Park 

were deposited on or near a continental shelf and consist 

of terrigenous clastic rocks in succession with platformal 

carbonate units. Belt strata in Glacier National Park form 

the upper plate of the Lewis thrust fault, a major lowangle, west-dipping fault of early Tertiary age that has 

at least 40 km of northeast-directed transport (Dahlstrom, 

1970). Consequently, all sections of the Snowslip that 

were studied in the Park have been transported northeastward by the Lewis thrust fault from their original sites 

of deposition, and some are separated by upper-plate 

structures that have uncertain geometries and amounts 

of displacement (figs. 2 and 3). Nevertheless, we feel that 

lithocorrelation of the Snowslip Formation in and adjacent to Glacier National Park is possible amidst these 

structural complexities. 

Purpose 

The objectives of this study are: (1) to establish a 

reference section of the Snowslip Formation that contains 

the Purcell Lava; (2) to subdivide the formation into informal members or lithostratigraphic units; and (3) to correlate lithofacies between measured sections in Glacier 

National Park. In addition, discussion here will touch on 

depositional setting, tectonics and sedimentation, and 

regional correlation. By elucidating the stratigraphy and 

lithocorrelation of the Snowslip Formation in Glacier National Park, we hope to gain a better understanding of 

the tectonic and time-stratigraphic significance of the 

Purcell Lava and polarity reversal at the base of the 

Snowslip, and consequently, of the correlation and interpretation of equivalent lithofacies across the northern 

part of the Belt basin. Also, the correlation of Missoula 

Group rocks of the Belt basin with rocks of similar age 

in the northern Canadian Cordilleran is linked to an 

understanding of the tectonosedimentary setting of the 

Snowslip Formation. 

Data for this report were gathered as part of a comprehensive geologic study of Glacier National Park from 

1979 to 1985. We wish to acknowledge the enthusiastic 

assistance of James C. Sample who helped us with the 

tedious chore of measuring sections. 

STRATIGRAPHY 

Four sections of the Snowslip Formation (fig. 2) 

were selected to examine changes that occur throughout 

the Park across facies or structural boundaries; one of 

these is the type section revisited. In the Park, the 

Snowslip is characterized by alternating reddish and 

grayish-green clastic rocks that are locally calcareous. Its 

thickness ranges from a maximum of 636.3 m at the 

Huckleberry Ridge section to a minimum of 357.5 m at 

Hole-in-the Wall; these two sections contain the Purcell 

Lava. 

Because the type section of the Snowslip Formation does not contain the Purcell Lava, we feel that a 

reference section containing the lava should be established. The Hole-in-the-Wall section was selected for this 

purpose because it is accessible and well exposed and contains good exposures of the Purcell Lava and its contacts 

with enclosing sedimentary rocks. 

Hole-in-the-Wall Reference Section 

The reference section is in the northern part of 

Glacier National Park, just east of Boulder Pass, in the 

east-facing wall of the Hole-in-the-Wall cirque (fig. 4). 

Access is gained by well-maintained trails either from 

lower Kintla Lake (24 km), Bowman Lake (21.5 km), or 

the upper end of Waterton Lake (16 km). The Snowslip 

is well exposed in the cirque basin and can be traced 

laterally around the headwall, although some parts of the 

formation are inaccessible because of cliffs. 

2 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
114"00' 113°30' 

49°00' BRITISH COLUMBIA ALBERTA CANADA 

-\~- --~--------uNiTED STATES 

--0 f 

48.30' 

0 Whitefish 

5 

MAP LOCATION 

Kalispell 0 

Mountain 

/. . 

/ 

10 20 MILES 

\ 

( 

j 

0 

East 

Glacier 

Park 

Figure 2. Generalized map showing distribution of the Snowslip Formation and younger strata (shaded), location of measured 

sections, and major structures in Glacier National Park. HR, Huckleberry Ridge; HTW, Hole-in-the-Wall; LC, Lunch Creek; 

SM, Snowslip Mountain. 

At this locality, the Snowslip is subdivided into six 

informal members that are designated, from oldest to 

youngest, 1 through 6 (fig. 5); the uppermost member, 

6, encloses the Purcell Lava. Upper and lower contacts 

of the formation are exposed, and the Snowslip appears 

to be conformable with adjacent stratigraphic units. The 

total thickness of the Snowslip, the Purcell Lava, and an 

enclosed diabase sill is 357.5 m. 

Terms used in the following description of 

lithostratigraphic units come from a variety of sources. 

Lithologic terms are used in accordance with definitions 

from the second edition of the AGI Glossary of Geology 

(Bates and Jackson, 1980) or Pettijohn and others (1973). 

Rock color, where determined in the field, is expressed 

in alphanumeric units from the Geologic Society of 

America rock-color chart (Goddard and others, 1948); 

other color terms are subjective. Lamination and bedding 

style and thickness are from Campbell (1967), and 

Stratigraphy 3 
HR 

-<,.. . "I,_ . 

"\- "\- ~.-:::\ 

i-

"';.. . ,_ 

___ ____,_ N 

METERS 

400 

350 

300 

250 

200 

150 

100 

50 

2L5 _____ ----~15----~1o----~----~ 0 

KILOMETERS 

4 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
EXPLANATION 

® ® ® ® ® ® ® Interbedded oolitic arenite, lithic arenite, and siltite 

and argillite couplets 

~ l1"t, '"' """ """ ~ (R., Stromatolitic limestone and interbedded calcareous 

siltite 

• • • • . • • Lenticular beds of arenite 

<XXXXXW 

HTW 

HR 

LC 

SM 

u 

D 

ROOSEVELT 

FAULT 

Calcareous, fining-upward couplets of siltite and argillite; minor thin lenticular beds of calcareous arenite 

Fining-upward sequences of ripple cross-laminated 

arenite, siltite, and mud-cracked argillite 

Diabase sill 

Basalt; Purcell Lava 

Hole-in-the-wall 

Huckleberry Ridge 

Lunch Creek 

Snowslip Mountain 

Upthrown side of fault 

Downthrown side of fault 

HR 

FLATHEAD 

FAULT 

STRUCTURAL 

SETTING 

Figure 3(above and facing page). Schematic fence diagram 

showing lithofacies correlation among sections of the Snowslip 

Formation, Glacier National Park. Inset diagram shows structural setting of measured sections and relative fault movements. 

descriptive terms of grain size are those of the Wentworth 

size classification. 

Member 1 

Interbedded calcareous siltite and argillite are the 

principal lithologies of member 1. They are typically arranged as wavy nonparallel, fining-upward couplets less 

than IO mm thick, and they vary in color from reddish 

hues (5 R 5/4, 5 RP 6/2) to grayish green (10 G 6/2, 5 

G 6/1). Although siltite and argillite are the most abundant lithologies, the member is characterized by thin (less 

than 3 em thick) lenticular beds of poorly sorted, fineto coarse-grained calcareous arenite. Clasts are dominantly rock fragments, quartz, and oolites, many of which 

are partially replaced and coated by hematite (fig. 6). 

Arenite beds are commonly light gray and weather tan. 

Mottling is common among the red and green strata such 

that rock color changes along strike. Sedimentary structures include syneresis and desiccation cracks, numerous 

thin laminae of mud-chip breccia, fluid-escape structures, 

some flaser lamination, and some small-scale crosslamination in oolitic arenite beds. The lower contact is 

placed between the uppermost bed of pink to gray oolitic 

limestone of the Helena Formation and lowermost bed 

of poorly sorted calcareous arenite of member 1. Member 

1 is 25.91 m thick. 

Member 2 

Member 2 is mostly composed of greenish-gray 

siltite (5 G 6/1) and olive (10 Y 5/2) argillite couplets. 

The siltite fraction is commonly two-thirds the couplet 

thickness. Couplets are as much as 4 em thick but generally are only 10-20 mm thick. Outcrops, which generally 

weather recessively, are poorly exposed and are yellowish 

gray or brown because of local calcite and dolomite 

cements. Interbedded in member 2 are beds of pink, red, 

and cream-colored stromatolitic limestone as much as 

15 em thick (fig. 7). The distinct reddish color is the result 

of several laminae that contain fine-grained hematite 

(Horodyski, 1975). Commonly associated with stromatolites are beds as thick as 10 em of pyritic flat-pebble conglomerate and poorly sorted lithic arenite. Clasts are 

mostly rock fragments (including limestone), quartz, and 

minor feldspar that are cemented by calcite and dolomite. 

Syneresis cracks are common in argillite laminae. Ripple 

cross-lamination occurs in most beds of arenite. The 

lower contact is placed at the base of a stromatolitic 

limestone which is underlain by reddish strata of member 

1. Member 2 is 69.85 m thick. 

Member 3 

Member 3 consists of interbedded arenite, siltite, 

Stratigraphy 5 
Figure 4. Hole-in-the-Wall basin, looking west at location of reference section. Dotted line is measured section. 

and argillite that are arranged locally as fining-upward 

sequences less than 2 m thick. Arenite beds are white to 

greenish gray, less than 10 em thick, and lenticular, and 

have erosional bases. Arenite grains are fine to medium 

sized, moderately sorted, and mostly composed of quartz, 

feldspar, and some rock fragments. Siltite and argillite 

in fining-upward sequences are grayish red and reddish 

purple (5 RP 5/2). Apart from fining-upward sequences, 

beds of siltite and argillite are greenish gray and locally 

dolomitic, similar to beds in member 2. Mud-chip breccias and mud chips aligned on foresets of cross-laminated 

arenite beds are present locally, particularly at the base 

of fining-upward sequences (fig. 8). Mud-draped ripples, 

shrinkage cracks, and fluid-escape structures are common. The lower contact is placed between calcareous, 

greenish-gray rocks of member 2 and beds of quartz and 

subfeldspathic arenite of member 3. Member 3 is 16.6 m 

thick. 

Member 4 

Member 4 is similar to member 2 in all respects, 

and differentiating the two in isolated exposures is 

difficult. The dominant lithologies of member 4, as in 

member 2, are greenish-gray siltite and argillite that are 

arranged as thin, wavy fining-upward couplets or 

rhythmic sequences as much as 25 em thick. Argillite composes 80 percent of the interbedded and interlaminated 

lithologies in the lower part of the member but decreases 

to about 25 percent near the top. Stromatolitic limestone, 

pyrite, carbonate cement, and limonitic stain occur locally. In the upper part of the member, thin lenticular beds 

of very fine grained, calcareous arenite and gray dolomite 

are present. Syneresis cracks, fluid-escape structures, and 

mud-chip breccias are abundant. Arenite beds are typically ripple cross-laminated. The lower contact is placed on 

top of the uppermost reddish argillite of member 3. 

Member 4 is 79.6 m thick. 

Member 5 

In the Hole-in-the-Wall reference section, as 

elsewhere in the Park, member 5 is the most distinct and 

easiest to recognize subdivision of the Snowslip. It is 

resistant to weathering and forms bold outcrops. Beds 

of white, pink, and greenish-gray arenite are overlain 

6 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
METERS 

350 

-" 

v 

/ (\ 

> 

\ 

300 7' 

[' \ 7 

\ 

'-1 t... 

250 

1/ 

...J 

\ ..., 

..J 

-1 

..J 

..., > 

..J 

/ 

"1 "1 

/ 

/ 

Purcell 

Lava 

[' 

EXPLANATION 

--=.-= Argillite 

"-·-v Wavy nonparallel 

couplets of siltite 

and argillite 

"'-·--' Calcareous couplets 

of siltite and 

argillite 

· ··· · · Arenite 

::r::r::u Dolomitic limestone 

'\::C:t:t Ripple cross· 

laminated arenite 

1'=:?-=:~~~;:r -==""'--.---t @ @ Stromatolites 

20~ 

150 z 

0 

~ ~ 

0: 

0 

u. 

r="-'::'=::c'-:'""-'-=\ ------1 ~ 

(f) 

s M ember 3 

100 ~~~~~rT ---------t~ 

7'- -1.....-~....=. 

;. ::;~ -:.;~ 

,....-<.. . ....,..... .. .. 

-i.._ ~ ~ -::;..._-:--

···· . --- ~=--

?- -<...- 7'-' 

. . --r--·-'-

50 -~~~~~~ --~~-~;_ ...,._ ..... __ .. : .. :·:...__~---'7'-'~ 7- · ,.J..._ • ·;.,..:_· • ..,.. 

(f) 

M ember 2 

M ember 1 

Upper part of 

Helena Formation 

- Cryptalgal lamination 

0 0 Oolites 

/,/..: Diabase sill 

"r"" Basalt lava 

Figure 5. Diagrammatic stratigraphic column of the Snowslip 

Formation at Hole-in-the-Wall reference section; section includes Purcell Lava and diabase sill. 

successively by reddish beds of inter laminated arenite and 

siltite, siltite and argillite, and finally argillite; this arrangement of lithologies forms distinct fining-upward 

successions that range in thickness from a few centimeters 

to as much as 3.5 m (fig. 9). Arenite beds are locally 

calcareous and commonly lenticular, and, in order of 

abundance, are composed of quartz, rock fragments, and 

feldspar (fig. 10). Siltite beds are grayish red (5 R 5/2); 

argillite beds are reddish purple (5 RP 5/2) and have very 

thin, wavy discontinuous laminae. Sedimentary structures 

abound in this member, and most are indicative of 

shallow water and subaerial exposure. These structures 

include a wide variety of ripple marks, raindrop impressions, wrinkle marks, desiccation cracks, mud-draped ripples, mud-chip breccias, and some fluid-escape structures. 

The lower contact of the member is placed at the base 

of the lowest bed of arenite where that bed and overlying reddish strata form a fining-upward sequence. 

Member 5 is 39.82 m thick. 

Member 6 

The uppermost member, 6, encloses facies of the 

Purcell Lava and is compositionally similar to members 

2 and 4. It mainly consists of greenish-gray siltite and 

argillite couplets that are less than 1 em thick. Thin lenticular beds of arenite (less than 10 em thick), stromatolitic limestone, and thinly laminated dark-green argillite 

are present below the lava. Similar beds occur above the 

lava, but many are grayish red to reddish purple. One 

laterally continuous bed of red siliceous arenite just below 

a sill commonly contains pyrite and chalcopyrite. 

Sedimentary structures in the member include ripple 

cross-lamination in arenite beds, syneresis cracks, fluidescape structures, and mud-chip breccias. 

Although the lower contact of the Purcell Lava with 

member 6 is very irregular (probably due to loading by 

the basalt), no evidence of an unconformity was observed. 

No erosional surface was discovered at the upper contact; 

McGimsey (1985, p. 67) described the upper surface of 

the Purcell Lava at Hole-in-the-Wall as, "*** scoriaceous 

and/or smooth and ropy with a 1 to 5 em pinkish-red oxidized horizon:' Strata of member 6 appear to have been 

deposited conformably onto surface irregularities of the 

lava, and so at this locality, member 6 is interpreted to 

enclose the lava conformably. The stratigraphy of the 

Purcell Lava, which is shown in figure 11, was superbly 

described by McGimsey (1985). Of particular note, is 

about 12 m of pillow lava at the base of the Purcell, which 

suggests flowage into or under water (fig. 12). 

Below the extrusive facies of the Purcell Lava and 

separated from them by 5 m of member 6, is a diabasic 

sill that is as thick as 20m in many places. The sill, which 

locally intrudes the base of the pillow lava, is interpreted 

to be cogenetic with the Purcell Lava (McGimsey, 1985). 

Stratigraphy 7 
Figure 6. Photomicrograph (plain light) of member 1 ooliths showing hematite replacement and rims. 

Upper and lower contacts of member 6 are conformable. The lower contact is placed between reddish 

argillite and siltite of the uppermost part of member 5 

and thinly laminated greenish-gray argillite and interbedded arenite of member 6. The contact of member 6 

with the Shepard Formation is placed at the top of the 

uppermost bed of argillite, where overlying beds of the 

Shepard, in order of abundance, consist of yellowish-gray 

weathering couplets of calcareous siltite and argillite, ripple cross-laminated dolarenite, and limestone. At the 

reference section, the total thickness of member 6, the 

Purcell Lava (99.6 m), and the diabase sill is 125.72 m 

(fig. 5 and Appendix). 

LITHOCORRE LA liON 

In addition to the reference section at Hole-in-theW all and the type section, two other sections were 

measured so that four sections in all could be used for 

lithocorrelation in Glacier National Park. The type section at Snowslip Mountain (fig. 13) was revisited, and 

stratigraphic units that had been measured and described 

by Childers (1963) (total thickness reported, 489.6 m) 

were recast in terms compatible with this report. The 

Lunch Creek section is 458.4 m thick and is in the central part of the Park on the west-facing flank of Piegan 

Mountain (fig. 14). The farthest west section of the 

Snowslip was measured on the west-facing side of 

Huckleberry Ridge in the Apgar Mountains (fig. 15), 

where this formation is 636.3 m thick. Although not well 

exposed, the Huckleberry Ridge section provides data 

west of and normal to the regional strike of sedimentary 

units, whereas the other three sections are positioned 

essentially along depositional strike. 

The Snowslip Mountain, Lunch Creek, and 

Huckleberry Ridge sections can be subdivided into six informal members using the same lithostratigraphic criteria 

that were established at the reference section. The Purcell 

Lava is absent in sections at Lunch Creek and Snowslip 

Mountain, and all members thin to the north. Figure 3 

is a schematic fence diagram that shows correlation and 

changes in lithofacies among the four measured sections. 

Differences other than thickness exist among the 

four sections and are most noticeable in the mineralogy 

of the arenite beds and in the sedimentary structures. 

Because of numerous arenite beds, members 1, 3, and 

5 best illustrate differences in lithofacies and are the focus 

8 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
Figure 7. Pinkish stomatolitic limestone in member 2; knife is 8 em long. Photo by O.B. Raup. 

of the following discussion. Differences in lithofacies 

among sections in members 2 and 4 are not apparent, and 

in member 6 the major difference among sections is the 

presence or absence of the Purcell Lava (fig. 3). 

Member 1 

Most arenite beds in member 1 at all sections contain abundant dolomite clasts and ooliths and varying 

amounts of quartz and feldspar. All beds are poorly 

sorted and cemented by calcite and dolomite. Many 

ooliths are broken and deformed, some ooliths form 

aggregate spherules, and in the lowermost arenite beds, 

most ooliths are hematitic (figs. 6, 16). Small armored 

spherules are commonly intermixed with the ooliths 

(fig. 17). 

Arenite beds are most abundant in the Lunch Creek 

section, where they are thicker and more feldspathic and 

contain more ooliths than at other sections. Arenite beds 

in the Huckleberry Ridge section contain the least feldspar 

and fewest oolite beds. Mineralogy, fabric, and texture 

of arenite beds in member I suggest that the source for 

most clasts was the dolomite and oolitic limestone beds 

of the uppermost part of the underlying Helena 

Formation. 

Member 3 

Red beds that contain several sedimentary structures indicative of subaerial exposure distinguish member 

3 from the enclosing green beds of members 2 and 4. 

Member 3 is composed of rhythmic, fining-upward sequences that began with sand deposition and ended with 

silt and clay deposition. These sequences indicate cyclic 

sedimentation by waning-current flows and are thickest 

and most complete (in other words, resemble an ideal sequence; see fig. 9B) in the Lunch Creek section where 

they are 1-3m thick. In the Snowslip Mountain section 

and to some extent in the Hole-in-the-Wall succession, 

incomplete, fining-upward sequences commonly consist 

of rhythmic arenite and argillite paired beds. The 

Huckleberry Ridge section contains only a few beds of 

arenite, and distinct fining-upward sequences are rare. 

Interbedded greenish-gray siltite and argillite, similar to 

Lithocorrelation 9 
Figure 8. Mud chips (rip-up clasts) aligned on foresets of cross-laminated bed of arenite, member 3. 

strata of member 2, are common in member 3 of the 

Huckleberry Ridge section. 

Beds of arenite in all sections of member 3 are 

similar mineralogically; they mostly consist of quartz 

grains in both clast- and matrix-supported fabrics. All 

arenite units contain some carbonate and hematite as well 

as silica cement; at Huckleberry Ridge, dolomite clasts 

are common. Degree of clast rounding is the same in all 

sections and appears to be a function only of grain size 

and not of distance of transport. Quartz grains commonly 

have overgrowths, and at Huckleberry Ridge some of 

these overgrowths are abraded (fig. 18). At Hole-in-theWall some coarse-grained arenite clasts are intermixed 

with very fine grained clasts in such a manner as to suggest that the fabric and bimodal clast size are the result 

of eolian processes (fig. 19). 

Member 5 

Member 5 is the most distinct member of the 

Snowslip Formation and is present throughout Glacier 

National Park. Red beds that compose the member have 

lithofacies similar to those of member 3 except that finingupward sequences are generally thicker and complete sequences are more abundant. The sequences are rhythmic 

and vary in thickness among sections. The thickest and 

greatest number of fining-upward sequences occur at 

Lunch Creek, where they are typically 7-8 m thick. Sequences at Snowslip Mountain and Huckleberry Ridge 

are commonly incomplete and distinctly thinner (35-85 

em thick) than those at Lunch Creek and Hole-inthe-Wall. 

Beds of arenite in the lower parts of fining-upward 

sequences in member 5 vary in thickness, sedimentary 

structures, and mineralogy between sections. Where sequences are best developed, the lowermost arenite beds 

are as much as 30 em thick, cross-bedded, and lenticular. 

Unidirectional trough cross-bedding and herringbone 

cross-bedding are commonly intermixed. Large assymetrical ripples are common and display wave lengths and 

amplitudes of as much as 14 em and 1.4 em, respectively. These lowermost beds contain numerous mud chips 

derived from the top of the underlying sequence and 

several varieties of rock fragments, particularly in the 

Snowslip Mountain, Lunch Creek, and Hole-in-the-Wall 

10 Stratigraphy and lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
METERS 

2.0 

1.5 

1.0 

0.5 

Dark-red arg illite; 

shrinkage cracks 

Brick-red 

siltite 

and very fin e grained 

arenite; rippl e cr

oss-

lamination ; interlaminated argillite 

Pink subfeldspathic 

arenite; very fin e 

grained; even 

parallel lamination 

W hite quartz arenite, 

fine- to mediumgrained, cross -bedd

ed; 

mud chips on erosional base 

sections. Beds of coarse siltite and very fine to fine 

grained arenite, which overlie the coarser grained basal 

beds, are typically even-parallellaminated or ripple crosslaminated. Arenite beds of member 5 in all sections contain a wide assortment of lithic clasts, but most clasts are 

composed of monocrystalline quartz. At Snowslip Mountain, Lunch Creek, and Hole-in-the-Wall, assorted clasts 

consist of dolomite, ooliths (Hole-in-the-Wall), porphyritic diorite, chert, quartzite, and polymineralic grains 

of K-feldspar and quartz that range in size from very fine 

to coarse. At Huckleberry Ridge, clasts are dominantly 

medium-grained or finer quartz. Quartz grains and some 

K-feldspar have syntaxial overgrowths in all sections (fig. 

20). Quartz and hematite cements are common in all 

arenite units, and calcite/dolomite cements are common 

in the Snowslip Mountain, Lunch Creek, and Hole-inthe-Wall sections. 

Arenite Composition 

A ternary QFL plot (fig. 21) of quartz, feldspar, 

and lithic fragment abundance for 43 arenite samples collected from the four measured sections of the Snowslip 

Formation and member 1 along Going to-the-Sun-Road 

shows range of framework-grain composition and some 

sediment distribution patterns. The mean composition of 

framework grains for the suite is Q64F13L

23 and is 

classified as a sublithic arenite (Pettijohn and others, 

1973). The distribution of arenite samples from 

Huckleberry Ridge indicates that they are distinctly low 

in feldspar relative to other sections, whereas several of 

the Lunch Creek and Going-to-the-Sun Road samples are distinctly feldspathic. Hole-in-the-Wall samples show 

about equal amounts of feldspar and lithic fragments, 

regardless of quartz content. Such sketchy patterns and 

trends for arenite samples in the Snowslip need to be 

substantiated by additional and more complete sampling 

before they can independently support any interpretation 

of distance from source, transport direction, or compositional differences between sections. Nevertheless, when 

used in conjunction with other sedimentologic data, they 

corroborate the interpretations that are expressed in the 

following section of this paper. 

DISCUSSION 

Depositional Setting 

Lithofacies of the Snowslip Formation in Glacier 

National Park were deposited primarily in a mixed 

Figure 9. A, Cyclic fining-upward sequences in member 5 of 

the Snowslip Formation at Hole-in-the-Wall. 8, Diagrammatic 

sketch of an ideal, complete fining-upward sequence in 

member 5. 

Discussion 11 
Figure 10. Photomicrograph (crossed nicols) of arenite fabric and composition, member 5 of the Snowslip Formation at Holein-the-Wall reference section. 

siliciclastic-carbonate environment. We believe that this 

environment was marine and that the majority of sediments were deposited in a peritidal setting. At the close 

of Helena time, numerous beds of oolites and stromatolites formed on a prominent carbonate shelf that had extensive shoals. Oolite beds in the upper part of the Helena 

commonly display herringbone cross-lamination which 

suggests that the environment was influenced by tides. 

The environment of deposition for the lower part of the 

Snowslip was still in an area of carbonate production as 

evidenced by interbedded calcareous siltite and oolite and 

stromatolite beds, particularly in members 2 and 4. 

Members 3 and 5 represent a widespread influx of 

terrigenous clastic material that was probably caused by 

uplift in the source area, or increased basin subsidence, 

or both. Fining-upward sequences in these members are 

interpreted to be sheet-flood deposits that were formed 

by unrestricted, waning currents which flowed across an 

alluvial apron, adjacent to the peritidal environment. At 

times, these sediments were probably deposited in standing water, because several sedimentary structures indicate 

alternating periods of submergence and emergence. 

Fining-upward cycles that are thin, incomplete, or 

intercalated with green beds are thought to indicate deposition in more distal parts of the alluvial environment. 

METERS 

Pahoehoe facies 

Vent facies 

Pillow lava facies 

Figure 11. Diagrammatic representation of the Purcell Lava 

at Hole-in-the-Wall (McGimsey, 1985). 

12 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
Figure 12. Large pillow in the pillow lava facies at the base of the Purcell Lava at Hole-in-the-Wall. 

The Purcell Lava is interpreted to have been 

deposited in a peritidal environment. The lowermost lava 

flows (pillow facies) of the Purcell were extruded subaqueously (subtidal environment), and McGimsey (1985, 

p. 26) interpreted thickness of the pillow facies as indicating water depth that ranged from 9 to 15 m at the 

time of emplacement and probably during deposition of 

member 6. Subsequent lava flows were emplaced in a 

subaerial environment and formed positive, emergent 

areas during continued sedimentation of the Snowslip 

Formation in adjacent parts of the Belt basin. In some 

areas, upper surfaces of the last flows remained exposed 

long enough to oxidize before being inundated by marine 

waters. 

Tectonic Setting 

Deposition of the Snowslip Formation was preceded by a period of erosion, interrupted by the extrusion of the Purcell Lava, and punctuated by two episodes 

of fluvial sedimentation. These interruptions in the stratigraphic record of the Snowslip in Glacier National Park 

are interpreted as indicating an active period of tectonism. 

Because of numerous dolomite clasts and broken 

oolites that are rimmed by hematite in the lowermost beds 

of member I of the Snowslip, we suggest that a period 

of uplift, exposure, and erosion followed the shoalingupward phase of the Helena Formation and preceded the 

deposition of Snowslip sediments. The erosional event 

and influx of terrigenous material, which is most evident 

along the eastern margin (shelf) of the basin, was probably caused by increased basin subsidence, or uplift of 

source terrane, or both. On a regional scale, Harrison 

(1972) suggested that a major period of tectonic adjustment preceded deposition of the Missoula Group; his suggestion was based on a study of isopach maps and 

changes in basin geometry. Although no megascopic 

features that might suggest a disconformity at the contact between the Helena and Snowslip Formations are obvious, the contact is sharp and changes in lithofacies and 

depositional environment between the two are abrupt. 

During deposition of member 6 of the Snowslip, 

a magmatic event resulted in the extrusion of the Purcell 

Lava, which we believe accompanied basin growth 

faulting in the northern part of the Belt basin. In Glacier 

Discussion 13 
113"30' overlain by the Shepard Formation (Whipple, 1984). n---,--,--------~----~-.---,,---~-n 

1

h MILE 

5 KILOMETER 

EXPLANATION 

hn 

Shepard Formation 

Snowslip Formation 

Helena Formation 

- - -- Contact-Dashed where approximate 

~ Fault-Bar and ball 

on downthrown 

side 

20 Strike and dip of 

beds 

Figure 13. Geologic map showing the location of the type section of the Snowslip Formation (stippled) established by Childers 

(1963) in the southern part of Glacier National Park. 

National Park, oxidation of the uppermost flows suggests 

that a diastemic period followed the emplacement of the 

Java in the Snowslip Formation. In parts of the northern 

Whitefish Range, west of Glacier National Park, uppermost flows are intercalated with member 6 lithofacies, 

overlain by beds of intraformational conglomerate, or 

Thus, locally (outside of Glacier National Park), 

an unconformity is present at the top of the Purcell 

Lava. 

Members 3 and 5 of the Snowslip represent a rapid 

progradation of fluvial deposits into a peritidal setting. 

Events that caused this progradation were episodic and 

probably tectonically controlled. No unconformities between members 3 and 5 and adjacent members are evident in the sections studied, and members 3 and 5 are 

known to pinch out northwestward and westward from 

the Park (Whipple, unpublished mapping). 

A polarity reversal that occurs at or near the base 

of the Snowslip Formation represents the first such reversal following a long period of normal polarity for the 

subjacent parts of the Belt Supergroup (Evans and others, 

1975; Elston and Bressler, 1980) and forms a convenient 

magnetostratigraphic time line. This polarity event may 

correlate with a period of tectonic activity that we suggested at the close of Helena sedimentation. 

Figure 14. Lunch Creek measured section, looking east at the 

.west-facing side of Piegan Mountain; member 5 at top of photo; 

dotted line is measured section. 

14 Stratigraphy and lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
Figure 15. Huckleberry Ridge measured section, looking east. North Fork of Flathead River at toe of slope; dotted line is measured 

section. 

Sedimentation 

Only limited data are available to suggest provenance and sediment transport directions for the Snowslip 

Formation in Glacier National Park. Figure 22 is a ternary QmFLt diagram that shows inferred provenance for 

the suite of arenite samples from the four measured sections and from expos~res along Going-to-the-Sun Road. 

The mean framework mode of detrital grains in the suite 

falls in the compositional field that is characteristic of 

sediments derived from recycled orogens (Dickinson and 

others, I983). Within this field, the mode lies in the 

quartzose recycled subdivision, which denotes recycled 

sediments whose ultimate source was cratonic (Dickinson and others, I983, p. 224). This interpretation is supported by the fact that many quartz grains in arenite 

samples of the Snowslip have inherited overgrowths (fig. 

23), which is thought to indicate that the grains have been 

recycled (Sanderson, I983). 

Although the compositional data for construction 

of the provenance fields on the QmFLt diagram come 

largely from Phanerozoic rocks (Dickinson and others, 

I983), the plots and interpretation of Snowslip samples 

suggest that the diagram is useful for determining provenance and tectonic setting of Proterozoic arenites. The 

plot of detrital framework modes for members I, 3, and 

5 shows a strong cratonic sediment source for members 

3 and 5, whereas a mixed provenance is indicated for 

member I sediment. The mixed provenance of member 

I, where at least part Of the arenite composition is derived from carbonate rocks of the underlying Helena Formation, suggests that these sediments are multicyclic, had 

a cratonic source, and were recycled through platformal 

successions (Dickinson and Suczek, I979, p. 2I78). 

Sediment transport direction and paleoslope for the 

Snowslip Formation can be determined from changes in 

grain size among sections, limited paleocurrent measurements, facies changes in the Purcell Lava, and changes 

in feldspar content. In members 3 and 5, decrease in grain 

size of arenite beds, decrease in stratigraphic thickness, 

and changes in facies of fining-upward sequences are interpreted as indicating that Snowslip strata of the 

Huckleberry Ridge and Hole-in-the-Wall sections were 

deposited downslope from the Lunch Creek and Snowslip 

Discussion 15 
Figure 16. Photomicrographs (plain light) of ooliths in member 1 of the Snowslip Formation: A, Broken and deformed ooliths 

partially replaced and rimmed by hematite. 8, Oolith aggregate spherule. 

Figure 17. Photomicrograph (plain light) of an armored 

spherule showing armor of dolomite fragments, upper part of 

member 1, Lunch Creek section of the Snowslip Formation. 

Figure 18. Photomicrograph (crossed nicols) of an abraded 

and impinged quartz overgrowth on quartz grain in member 

3 of the Snowslip Formation, Huckleberry Ridge section. 

Figure 19. Photomicrograph (crossed nicols) of bimodal clast 

size in arenite bed of member 3, Hole-in-the-Wall reference 

section, which is interpreted to be the result of eolian processes. 

Figure 20. Photomicrograph (crossed nicols) of typical interlocking grain texture and quartz overgrowths in member 5 

of the Snowslip Formation. 

16 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
0 

F 

25 

0 

• 

Feldspathic 

arenite 

Q 

' .... 

• • 

• ' Subfelaspathic 

arenite 0 

+ .... 

50 

.... . 

• • 

8 + 

Sublithic 

arenite 

@ 

• 

0 • 

• 

0 

25 

+ 

• 

+ 

• 

+ 

0 

Lithic 

arenite 

+ 

• 

EXPLANATION 

+ Huckleberry Ridge 

• Hole-in-the-Wall 

.a. Snowslip Mountain 

e Lunch Creek 

0 Going-to-the-Sun Road 

@ Mean composition 

Figure 21. Ternary QFL diagram showing the compositional plots of 43 arenite samples from the Snowslip Formation in Glacier 

National Park. Samples with more than 25 percent carbonate framework grains are not included (modified from Pettijohn and 

others, 1973, p. 158, fig. 5-3). Q, quartz; F, feldspar; L, lithic fragments. Crosses, Huckleberry Ridge; solid squares, Hole-inthe-Wall; solid triangles, Snowslip Mountain; solid circles, Lunch Creek; open circles, Going-to-the-Sun Road; circle with dot, 

mean composition. 

L 

Discussion 17 
Om 

- - __ -__-_-__ :-_--__ - _:_-_.;:;--- --------- ------··--- ~------

--------- .-<!-- - ·-- -- -- -- -·- -- / -- ·- -- -- Member 1• -=-~~-:;.-.;..:-:::::..=-_--=-~--=-·-= _ --- /_:_~----_ --__ -:.:.-:_--__ -

Mixed 

" -_ -- Transitional _-;_-

-;_=- recycled - -

F 23 

EXPLANATION 

INFERRED PROVINCE 

FIELDS 

' 

Continental block 

Recycled orogen 

, Magnetic arc 

Mixed 

13 Lt 

Figure 22. Ternary QmFLt diagram showing inferred provenance for terrigenous framework modes of members 1, 3, and 5 

of the Snowslip Formation and the mean mode for a suite of 43 arenite samples from the Snowslip in Glacier National Park. 

Samples with more than 25 percent carbonate framework grains are not included. Numbers on sides of diagram are divisions 

in percent from nearest apical point (from Dickinson and others, 1983, p. 223, fig. 1 ). Qm, monocrystalline quartz; F, monocrystalline 

feldspar; Lt, lithic fragments. 

18 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
Figure 23. Photomicrograph (crossed nicols) of inherited 

quartz overgrowth (double overgrowth) in member 5 of the 

Snowslip Formation. 

CLARK FORK PURCELL WHITEFISH GLACIER CLARK 

IDAHO MOUNTAINS RANGE NATIONAL RANGE 

(Harrison and (Me Meeha n and (Whipple and PARK (Price, 1964) 

Jobin, 1963)' others, 1 980) others, 1984) (Th is report) 

Member 

4 Sheppard Shepard Shepard Sheppard 

Formation Formation Formation Formation 1-----

c / 6 6 

0 Nichol Creek c Formation 0 - Purcell Purcell Purcell ·-

- Lava - Lava Lava 

"' "' 6 E 

E /--- ~ 1------

Member < 5 0 5 ~ 

3 "----- u.. 1------

0 

4 c. 4 

u.. ·- Siyeh 

Van Creek - ------ Formation 

Formation <:3 "' 3 

!; ------ upper 

" 0 member 

u 2 c: 2 (/) 

"' 

- ------ / 1 - /1 

1---- /"'- ~?""-?/'... -------

"' 

s Wallace Soyeh 

Member Kitchener and Helena Formation 

2 Formation Helena Formation middle 

Formations member 

*Correlat•on from Lemo1ne and W1nston ( 1968) 

Figure 24. Regional stratigraphic correlation chart of the 

Snowslip Formation, northern part of the Belt basin. 

Mountain sections. In this respect, sediment transport 

directions were primarily northwest with minor components to the west and southwest. Limited paleocurrent 

measurements of cross-bedded arenite units in members 

I and 5 show bimodal, bipolar directions about trends 

of 50° NW-SE and 83° NW-SE. Assuming that the 

thickness of the pillow lava facies of the Purcell Lava 

reflects water depth, emplacement of the lavas and synchronous deposition of sediments of member 6 in Glacier 

National Park must have occurred on a surface that 

sloped gradually downward to the northwest, west, and 

southwest (McGimsey, I985, p. 27). Strata of the Snowslip observed north and east of Hole-in-the-Wall near 

Mount Rowe in Alberta, Canada (Cameron Lake area, 

fig. 2), were deposited downslope from Hole-in-the-Wall 

if the same criteria used above are applied. 

Feldspar content may or may not reflect distance 

from source (Pettijohn and others, I973; Blatt and others, 

I972), but the small amounts of feldspar in the Hole-inthe-Wall and particularly the Huckleberry Ridge sections 

are consistent with the sediment transport direction 

being downslope to the northwest and west-southwest. 

That is, these two sections were further down the 

sediment-dispersal system and therefore have a diminished feldspar content. In summary, the principal direction of sediment transport for terrigenous clastics of the 

Snowslip Formation in Glacier National Park appears to 

have been northwest with minor components to the west 

and southwest. 

·· Regional Correlation 

The Snowslip Formation is recognized in many 

parts of the Belt basin outside Glacier National Park. 

Probable facies of the Snowslip have been identified in 

parts of southwest and west-central Montana (Mudge and 

others, I982; Wallace and others, I984) and northern 

Idaho (Burmester, I985) (fig. 24). Stratigraphically 

equivalent units are known to occur in the Purcell 

Supergroup of southeast British Columbia and southwest 

Alberta (Price, I964; McMechan and others, I980). In 

the northern parts of the Whitefish Range and near 

Libby, Mont., the Snowslip rarely contains any red-bed 

sequences or carbonate, and arenite beds are few in 

number. In these areas, the Snowslip is composed of 

thinly laminated, dark-grey to green siltite and argillite. 

We suggest that this fine-grained, green-bed lithofacies 

of the Snowslip was deposited in deeper water than those 

lithofacies of the Snowslip in Glacier National Park and 

represents the coalescing of members 2, 4, and 6 as 

members I, 3, and 5 pinch out basinward (see fig. 24). 

If this suggestion is correct, these facies changes would 

also indicate that the paleoslope was down to the northwest and west from the Park. 

The Snowslip Formation is not recognized in the 

Purcell Supergroup of Canada. In southeast British Columbia, the Van Creek and Nichol Creek Formations are 

approximately equivalent to the Snowslip and Purcell 

Lava in stratigraphic position and closely resemble the 

Discussion 19 
green-bed lithofacies of the northern Whitefish Range 

(McMechan and others, 1980; Whipple, 1984). In the 

Clark Range of southwest Alberta, equivalent lithofacies 

of the Snowslip are called the upper part of the Siyeh 

Formation, which is overlain by the Purcell Lava (Price, 

1964). In Waterton Lakes National Park, north of 

Cameron Lake (fig. 2), member 5 of the Snowslip 

Formation is easily recognized but is only 20-30 m thick, 

and member 3 is only a few meters thick. These equivalent lithofacies demonstrate the continued thinning of the 

Snowslip as well as the increase in interstratified greenbed lithofacies northwest from Glacier National Park. 

Lastly, we agree with Lemoine and Winston (1986) 

that rock units mapped as the upper part of the Wallace 

Formation near Clark Fork, Idaho Oower part of Wallace 

3 as described by Harrison and Jobin, 1963), are probably 

equivalent to the green-bed lithofacies of the Snowslip 

found elsewhere west and northwest of Glacier National 

Park. 

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Sanderson, I.D., 1983, Recognition and significance of inherited 

quartz overgrowths in quartz arenites: Journal of Sedimentary Petrology, v. 54, p. 473-486. 

20 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
Wallace, C.A., Harrison, J.E., Whipple, J.W., Ruppel, E.T., 

and Schmidt, R.G., 1984, A summary of stratigraphy of 

the Missoula Group of the Belt Supergroup and a preliminary interpretation of basin subsidence characteristics, 

western Montana, northern Idaho and eastern Washington, 

in Hobbs, S.W., ed., The Belt; Abstracts with summaries, 

Belt Symposium II, 1983: Montana Bureau of Mines and 

Geology Special Publication 90, p. 27-29. 

Whipple, J.W., 1984, Geologic map of the Ten Lakes 

Wilderness Study Area, Lincoln County, Montana: U.S. 

Geological Survey Miscellaneous Field Studies Map 

MF-1589-B. 

Whipple, J.W., Connor, J.J., Raup, O.B., and McGimsey, 

R.G., 1984, Preliminary report on the stratigraphy of the 

Belt Supergroup, Glacier National Park and adjacent 

Whitefish Range, Montana, in McBane, J.D., and 

Garrison, P.B., eds., Northwestern Montana and adjacent 

Canada: Montana Geological Society Guidebook, 1984 

Field Conference and Symposium, p. 33-50. 

References Cited 21 

APPENDIX: REFERENCE SECTION 
Reference Section 

Hole-in-the-Wall reference section of the Snowslip Formation, 

Glacier National Park; section includes Purcell Lava and diabase 

sill (figs. 1 and 4) 

[Section is just east of Boulder Pass in the north part of the Park; base 

of section at lat 48"57' 53" N., long 114'1:>4' 11 • W. Measured by James 

W. Whipple and James C. Sample] 

Snowslip Formation (Middle Proterozoic); contact with overlying Shepard Formation conformable: 

Member 6: 

11. Si!tite and argillite couplets, grayishgreen; wavy nonparallel lamination; 

locally calcareous; some beds of siltite 

as thick as 10 em; interstratified white 

quartz arenite with thin, lenticular 

ripple cross-laminated beds less than 

3 em thick; mud-chip breccia, fluidescape structures, and limonite stain 

abundant ..................... . 

10. Si!tite and argillite; pink, pale-purple, 

and grayish-green siltite and dark-red 

argillite; wavy discontinuous to wavy 

nonparallel lamination; siltite locally calcareous; mud-chip breccia and 

fluid-escape structures common ... 

9. Siltite and arenite; green to dark-green 

siltite and pink to light-orangishbrown-weathering calcareous arenite; 

arenite is very fine grained and ripple cross-laminated and forms broad 

cut-and-fill structures; color mottling 

occurs locally ................. . 

8. Siltite and argillite couplets; same as 

unit 11 ....................... . 

7. Purcell Lava; basalt ............. . 

6. Argillite, pale-green; abundant limonite 

stain; thinly laminated; interlaminated siltite and argillite couplets less 

than 1 em thick; intensely deformed, 

some hornfels and quartz veinlets 

5. Diabase sill; irregular base; projects up 

and down section .............. . 

4. Argillite; same as unit 6 .......... . 

3. Arenite, dark-red, lenticular; silicified 

red argillite clasts; mixed quartz and 

calcite cement; pyrite and chalcopyrite common (fig. 25) .......... . 

2. Argillite; same as unit 6 .......... . 

1. Stromatolitic limestone, grayish-green; 

weathers orangish brown; laterally 

linked heads 30 em across, 10 em 

high; interstratified dark-brown 

cryptalgal limestone ............ . 

Total thickness of member 6 .. . 

Total thickness of Purcell Lava 

Total thickness of diabase sill .. 

Thickness 

Meters Feet 

8.1 

1.85 

1.45 

5.3 

95.0 

5.2 

4.6 

1.75 

.08 

1.89 

.5 

26.12 

95.0 

4.6 

26.6 

6.1 

4.8 

17.4 

311.6 

17.1 

15.1 

5.7 

.3 

6.2 

1.6 

85.7 

311.6 

15.1 

Member 5; contact with overlying member 6 

conformable: 

6. Lithic arenite, pale-green to white, fineto coarse-grained, poorly sorted; beds 

less than 10 em thick; interstratified 

argillite and siltite; limonite stain 

common . . . . . . . . . . . . . . . . . . . . . . . 3.8 12.5 

5. Lithic arenite and argillite, grayish-red 

(5 R 5/2) to dark-red; fining-upward 

cycles 15-20 em thick (fig. 26); lithic 

arenite at base of cycle, very coarse 

to very fine grained, poorly sorted; 

beds are lenticular and crosslaminated. Dark-red argillite at top of 

cycle; wavy discontinuous lamination; raindrop impressions . . . . . . . 17.1 56.1 

4. Lithic arenite and argillite; grayish-red 

to dark-red; fining-upward cycle; 

40-cm-thick unit of arenite at base; remaining part interstratified arenite, 

siltite (5 R 512), and argillite (5 RP 

512); ripple cross-lamination common 

in beds less than 5 em thick, ripples 

draped by argillite; desiccation 

cracks, wrinkle marks, raindrop impressions, and mud-chip breccias 

common ...................... . 

3. Lithic arenite and argillite; same as unit 

4 ............................ . 

2. Lithic arenite and argillite; same as unit 

4; lower beds of arenite grayish green 

1. 

and mottled .................. . 

Lithic arenite, grayish-green, gray, 

grayish-red, and pale-pink, very fine 

to fine grained; beds as much as 10 

em thick, ripple cross-laminated; interbedded thinly laminated, red and 

green siltite; minor argillite ..... . 

Total thickness of member 5 .. . 

Member 4; contact with overlying member 5 

conformable: 

6. Siltite and argillite; greenish-gray (5 G 

6/1) siltite and pale-grayish-olive (10 

Y 5/2) argillite; rhythmic, wavy nonparallel fining-upward beds as much 

as 20 em thick where siltite is 25 percent of bed thickness; siltite is locally calcareous and weathers light 

brown; syneresis cracks (fig. 27) and 

fluid-escape structures; pyritic and 

6.8 22.3 

3.52 11.5 

6.4 21.0 

2.2 7.2 

39.82 130.6 

limonite stained . . . . . . . . . . . . . . . . 6.9 22.6 

5. Calcareous arenite, greenish-gray, very 

fine grained, ripple cross-laminated .1 .3 

4. Dolomite, gray, brown-weathering; 

abundant syneresis cracks filled with 

sparry calcite, weathers to form miniature molartooth structures; thin bed 

of arenite at base . . . . . . . . . . . . . . . 1.0 3.3 

3. Siltite and argillite; same as unit 6; interbedded brown-weathering dolomite 

occurs locally . . . . . . . . . . . . . . . . . . 55.7 182.7 

24 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
Figure 25. Typical bedding style of member 6 showing red, mineralized arenite bed at level of hammer head. 

2. 

1. 

Stromatolitic limestone, pink to creamcolored; small irregular heads and 

cryptalgal laminae; minor interlaminated green argillite, thin deformed laminae ....... . . . ... . . . 

Siltite and argillite; same as unit 6 . . 

Total thickness of member 4 .. . 

Member 3; contact with overlying member 4 

conformable: 

4. Siltite, grayish-red; interlaminated darkred argillite; poorly developed finingupward sequences less than 2 m thick; 

mud-chip breccia and desiccation 

Thickness 

Meters Feet 

.8 

15.1 

79.6 

2.6 

49.5 

261.1 

cracks common (fig. 28) . . . . . . . . . 7.0 23.0 

3. Siltite and argillite, grayish-green; wavy 

nonparallel couplets as much as 4 em 

thick; siltite locally calcareous . . . . 3.8 12.5 

2. Arenite and siltite; light-gray arenite and 

grayish-green to dark-green siltite; 

fining-upward cycles with argillite (5 

RP 512) at top; arenite beds ripple 

cross-laminated, lenticular, and less 

than 10 em thick; cycles are less than 

2 m thick; mud-draped ripples, desiccation cracks, and fluid-escape structures common ................. . 

1. Quartz arenite, white to pinkish-gray (5 

YR 8/1), fine- to medium-grained, 

well-sorted; cross-laminated at base 

with green mud-chips on foresets; lenticular; grades upward into unit 2 

Total thickness of member 3 ... 

Member 2; contact with overlying member 3 

conformable: 

8. Siltite and argillite; greenish-gray (5 G 

6/1) siltite and pale-grayish-olive ( 10 

Y 512) argillite; siltite locally 

calcareous and weathers brown; wavy 

nonparallel couplets as much as 4 em 

thick; interbedded calcareous, very 

fine to fine grained arenite beds as 

thick as 10 em and ripple crosslaminated; syneresis cracks, fluidescape structures, and mud-chip breccias common (fig. 29); pyritic and 

locally stained by limonite ...... . 

5.73 

.07 

16.6 

2.1 

18.8 

.2 

54.4 

6.9 

Appendix: Reference Section 25 
Figure 26. Incomplete fining-upward sequences in unit 5, member 5 of the reference section of the Snowslip Formation. 

26 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
Figure 27. Syneresis cracks on bedding plane surface, typical of members 2, 4, and 6 of the Snowslip Formation, Glacier National Park; knife is 8 em long. Photo by O.B. Raup. 

Appendix: Reference Section 27 
Figure 28. Desiccation cracks and traces of fluid-escape structures on bedding plane surface, typical of members 1, 3, and 

5 of the Snowslip Formation, Glacier National Park. Photo by 

O.B. Raup. 

7. Stromatolitic limestone, pink to gray; 

small laterally linked heads and cryptalgal laminae (fig. 30) .. .. ...... . 

6. Siltite and argillite; same as unit 8, less 

arenite; some siltite beds as thick as 

20 em; cryptalgal lamination local 

5. Stromatolitic limestone; same as unit 7 

4. Siltite and argillite; same as unit 8 .. 

3. Stromatolitic limestone, pink to gray; 

laterally linked heads 10 em high; 

underlain by mud-clast conglomerate, 

elongate limestone and green calcareous argillite clasts as long as 5 em, 

Thickness 

Meters Feet 

.15 .5 

45.95 150.7 

.25 .8 

.8 2.6 

supported by coarse-grained lithic 

arenite; pyritic ................ . .4 1.3 

2. 

1. 

Siltite and argillite; same as unit 8 .. 

Stromatolitic limestone; same as unit 7 

Total thickness of member 2 ... 

18.9 62.0 

1.3 4.3 ------

69.85 229.1 

Member 1; contact with overlying member 2 

conformable: 

6. Siltite and lithic arenite; interlaminated 

grayish-green to moderate-red (5 R 

5/4) siltite and pale-reddish-purple (5 

RP 6/2) to medium-gray (N 5) 

arenite; locally calcareous; bleaching 

and mottling of rock color common; 

lenticular arenite laminae less than 5 

mm thick; some interlaminated darkred argillite; abundant mud-chip breccia; mud-draped ripples and desiccation cracks common . . . . . . . . . . . . 6.8 

5. Si1tite, greenish-gray (5 G 6/1), 

calcareous; some interlaminated, 

poorly sorted, coarse-grained, calcareous lithic arenite; all beds weather 

light brown; fluid-escape structures, 

syneresis cracks, and abundant mudchip breccia present . . . . . . . . . . . . . 4.4 

4. Siltite and argillite, pale-green (10 G 

6/2); thin wavy nonparallel to wavy 

discontinuous couplets less than 10 

mm thick; locally calcareous; some 

fluid-escape structures and mud-chip 

breccia present . . . . . . . . . . . . . . . . . 1.4 

3. Siltite and lithic arenite; same as unit 6; 

beds of arenite 3 em thick or less; 

much bleaching of colors along joints 

and on bedding surfaces . . . . . . . . . 12.61 

2. Oolitic arenite, medium-gray (N 5) to 

light-pinkish-gray, calcareous, ripple 

cross-laminated . . . . . . . . . . . . . . . . . .1 

1. Siltite and argillite; grayish-green to tanweathering, calcareous siltite and 

pale-pink argillite; wavy discontinuous lamination; syneresis cracks, 

mud-chip breccia, and fluid-escape 

structures common . . . . . . . . . . . . . .6 

Total thickness of member 1 . . . 25.91 

Total thickness of the Snowslip 

Formation . . . . . . . . . . . . . . . . . 257.9 

Total thickness of Purcell Lava 95 .0 

Total thickness of diabase sill . . 4.6 

Helena Formation (Middle Proterozoic); not 

measured; contact with overlying member 1 

of the Snowslip Formation probably disconformable. 

22.3 

14.4 

4.6 

41.4 

.3 

2.0 

85.0 

845.9 

311.6 

15.1 

28 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 
Figure 29. Syneresis cracks and wave-generated ripple marks on bedding plane surfaces, typical of members 2, 4, and 6 of 

the Snowslip Formation, Glacier National Park; knife is 8 em long. Photo by O.B. Raup. 

Appendix: Reference Section 29 
Figure 30. Pink stromatolitic limestone, typical of members 2 and 4 of the Snowslip Formation, Glacier National Park; knife 

is 8 em long. Photo by O .B. Raup. 

30 Stratigraphy and Lithocorrelation, Snowslip Fm., Glacier National Park, Montana 

* U.S. GPO: 1988 573-{)47 /66,058