The Stratigraphy and Sedimentology of the Middle Proterozoic Snowslip Formation in the Lewis Whitefish and Flathead Ranges Northwest Montana

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Graduate Student Theses, Dissertations, & Professional Papers Graduate School

1988

The stratigraphy and sedimentology of the Middle Proterozoic Snowslip Formation in the Lewis Whitefish and Flathead Ranges northwest Montana

Brad C. Ackman The University of Montana

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Stratigraphy and Sedimentology of the Middle Proterozoic

Snowslip Formation in the Lewis, Whitefish and Flathead

Ranges, Northwest Montana

Brad C. Ackman

B.S., Southern Methodist University, 1986

Presented in partial fulfillment of the requirements

for the degree of

Master of Science

University of Montana

1988

Approv^d-hy

Chairman, Board of Examiners

Dean, Graduate School

i j S ' S Date

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ackman, Brad C., M.S. December 1988 Geology

Stratigraphy and Sedimentology of the Middle Proterozoic Snowslip Formation in the Lewis, Whitefish and Flathead Ranges, Northwest Montana

Director: Don Winston ' ^ ^

The Snowslip Formation is the lowermost formation of the Missoula Group in the Middle Proterozoic Belt Supergroup. It is well exposed in Glacier National Park (Lewis Range) and the adjacent Flathead and Whitefish ranges. The type Snowslip Formation is composed dominantly of fine grained, red and green terrigeneous clastic rocks that were deposited into the broad, shallow, northwest trending Belt basin approximately 1250 Ma. Large alluvial aprons flanked the uplifted southwestern source terrain and sloped northward into the Belt "sea". The toes of these alluvial aprons graded basinward into vast sand and mudflats which were periodically inundated by the shallow waters of the Belt "sea". Throughout much of the study area the Snowslip Formation is divided into six informal members. Each member contains distinctive suites of sediment types which are defined by grain size, sedimentary structures and original mineralogy. These sediment type suites provide the basis for interpreting the depositional environment of each Snowslip member. Members 1, 2, k and 6 are dominated by the even and lenticular couplet, tabular silt and coarse sand and intraclast sediment types interpreted to characterize distal sand and mudflats. Members 3 and 5 are considerably coarser grained and are characterized in the southern sections by thick sequences of the flat-laminated sand sediment type which pass northward to thinner flat-laminated sand beds and even couplets. Members 3 and 5, like the Snowslip Formation in general, thin and become finer grained basinward. These members record the tectonically or climatically induced basinward progradation of alluvial aprons. The Snowslip Formation is conformably bound by the Helena Formation below and in the north by the Purcell Lava above. In the southern portion of the Belt basin, where the Purcell Lava is absent, the top of member 5 generally marks the top of the Snowslip Formation. The possibility of the Tertiary Flathead and Nyack fault systems representing reactivated Laramide thrust faults was qualitatively evaluated by comparing sedimentologic differences in the Snowslip Formation across the fault zone. Sedimentologic variations are attributable to the spatial separation of the sections and minor shifts in the source terrane, and tectonic foreshortening across the fault is not apparent.

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Page

Abstract ii

Table of Contents iii

List of Figures vi

List of Tables vii

Acknowledgements viii

1. Introduction 1

Geologic Setting 5

Purpose 5

Regional Correlation 6

2. Sediment Types 7

Introduction 7

Crossbedded Sand Sediment Type 8

Flat-Laminated Sand Sediment Type 12

Even Couple Sediment Type 13

Even Couplet Sediment Type 15

Lenticular Couplet Sediment Type 17

Tabular Silt Sediment Type 19

Microlamina Sediment Type 20

Coarse Sand and Intraclast Sediment Type 21

Discontinuous Layer Sediment Type 23

Carbonate Mud Sediment Type 25

3. Description of Type Section and InformalMembers 27

Introduction 27

111

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Manber 1 28

Member 2 29

Member 3 30

Member 4 32

Member 5 33

Manber 6 34

4. Northern Whitefish Range Reference Section 35

5. Stratigraphie Boundaries of the Snowslip Formation 38

Lower Boundary 38

Upper Boundary 39

6. Generalized Depositional Model for the Snowslip Formation 46

7. Correlation of Informal Members 53

Introduction 53

Member 1 56

Member 2 57

Member 3 59

Member 4 60

Member 5 62

Member 6 65

8. Sedimentologic Interpretations of the Snowslip Formation 68

Introduction 68

Source Areas of the Snowslip Formation 68

Progradation of Member 3 and 5 70

Marine Versus Lacustrine Controversy 71

9. Evaluation of Possible Thrusting Along Roosevelt and 74 Nyack Faults

Introduction 74

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Comparison of Sections 76

Interpretations 78

10. Summary 82

References 85

Appendix A. Measured Section Locations and Profiles 90

Snowslip Mountain 92

Paola Creek 110

U.S. Highway 2 Roadcut 133

Hidden Lake 137

Granite Park 154

Red Meadow Creek 165

Bluebird Creek 179

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. List 9t Fi«yrgg

Figure Page

1. Generalized stratigraphie column of the Belt Supergroup. 2

2. Inferred outline of the Belt basin. 3

3. Map of the study area and locations of measured sections. 4

4. Sediment types of the Snowslip Formation. 9

5. Idealized fining-upward, single sheetflood sequence from 31 members 3 and 5 of the Snowslip Formation.

6. Generalized stratigraphie section of the Snowslip Formation 41 showing informal members and various interpretations of formation boundaries.

7. Hypothetical block diagram showing distribution of 47 sediment types in the Missoula Group.

8. Diagramatic sediment type cross section of a single flood 49 deposit from the proximal alluvial apron to the distal, submerged mudflats.

9. Stratigraphie correlation of the Snowslip Formation. 54

10. Fence diagram showing thickness of Snowslip m«nber 5 63 throughout the study area.

11. Diagram showing inferred Proterozoic structure 69 of the Belt basin during Missoula Group deposition.

12. Generalized structure map. 75

13. Schematic diagram showing possible tectonic history 80 of the Flathead and Nyack fault systems.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. List of Tables

Table Page

1. Thicknesses of the Snowslip Formation throughout 53 the study area.

Vll

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Acknowledgements

First and foremost I thank my father for his generous financial

support throughout my years in school.

I thank my wife, Teresa, for her help in preparing this work and

also for her unwavering ability to cope.

My thanks to Don Winston, Gray Thompson and Dr. Keith Osterheld for

their academic suppoi± and thoughtful criticism of this work.

My thanks to Jim Whipple for his superior publications and

enlightening conversations; both of which proved vital to this thesis.

Finally, I thank "Grizzly" Rob Thomas for his field assistance and

his inspiring love for the fauna of Glacier National Park.

Vlll

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Snowslip Formation is the lowermost formation in the Missoula

Group of the Middle Proterozoic Belt Supergroup (Figure 1). It mostly

consists of terrigenous clastic rocks that were deposited in a broad,

shallow, northwest trending basin. The Belt basin occupies eastern

Washington, northern Idaho, western Montana and southern British

Columbia where it is known as the Purcell Basin (Figure 2). The Belt

"sea" has been interpreted as marine by Whipple and Johnson (1988) and

as an intracratonic lake by Winston (1986 b). Childers (1963) named and

described the Snowslip Formation from exposures near Snowslip Mountain

in the southernmost portion of Glacier National Park (Figure 3). Here

the Snowslip Formation is conformably bound by the Helena Formation

below and the Shepard Formation above. In the northern portions of the

Belt basin, the Snowslip Formation is conformably overlain by the

Purcell Lava, a series of thin mafic flows.

Whipple and others (1986) divided the Snowslip Formation of Glacier

National Park into six informal members based on major sedimentologic

differences. These members are also identifiable in the northern

Flathead and southern Whitefish ranges and are useful in correlating and

analyzing the Snowslip Formation.

The Snowslip Formation is approximately 1600 feet thick at Snowslip

Mountain (Childers, 1963) and thins dramatically to the northwest toward

the northern Whitefish Range (Smith, 1963; Whipple and others, 1984).

Alternating red and green units at the type section pass northwestward

to finer grained, entirely green rocks in the northern Whitefish Range.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Pilcher Formation

Garnet Range Formation

McNamara Formation 1 s Bonner Formation iC 1— 4

(A§ Mount Shields Formation (A as Shepard Formation

Purcell L a v a ^ ^ ^

& Snowslip Formation 1 S g o■p i (D c: Helena Formation 0) CD S C->

Empire Formation CD1 •H Grinnell Formation r H 1 Appekunny Formation

«—4•p

Altyn Formation 1

Figure 1. Generalized stratigraphie column of the Belt Supergroup.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CRATO N BASINBELT

HELENA EM8AYMENT

PERRY INFERRED

WESTERN DILLON BLOCK CRATON

50 100 Ml 50

lift* IIZ* no*

Figure 2. Inferred Middle Proterozoic outline of the Belt basin in the United States and southern Canada. Partly restored along its eastern margin to its pre-thrust position, but not structurally restored along its western margin. From Winston (1986 b).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. BRITISH COLUMBIA ( ALBERTA INTERNATIONAL I BOUNDARY Bluebird Creek GLACIER NATIONAL PARK Eureka Red Meadow Creek Granite ParkO

O Hidden Lakel

Hwy. 2 Roadcut

Whitefish Paola Creek

©Snowslip Mountain

O Measured Sections

10 20 30 MILES

Figure 3. Map of the study area and locations of measured sections.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. This facies change has lead to confusion concerning placement of the

upper boundary of the Snowslip (Winston 1984, 1986 a).

The age of the Snowslip Formation is uncertain. Harrison (1984)

reported a Rb/Sr date on a glauconite from the overlying Shepard

Formation at approximately 1170 Ma. A U/Pb zircon date from the Helena

Formation about 200 feet below the Snowslip Formation yielded an age of

approximately 1350 Ma (Harrison, 1984). Considering these ages, the

Snowslip Formation was probably deposited approximately 1250 Ma.

Geologic Setting

Glacier National Park and the adjacent Whitefish and Flathead ranges

lie within the late Cretaceous to Paleocene thrust belt of northwestern

Montana (Winston, 1986 d). Belt rocks in Glacier National Park form the

relatively undeformed upper plate of the Lewis thrust and have been

subjected to lowermost greenschist facies metamorphism (Maxwell, 1973).

The Whitefish and northern Flathead ranges are structurally separated

from Glacier National Park by the northwest trending Flathead and Nyack

fault systems (Figure 12; Mudge, 1970; Constenius, 1981). This series

of Tertiary, listrie normal faults cuts the upper plate of the Lewis

thrust. Whipple (personal communication, March 1987) believes the

extensional Flathead and Nyack fault systems may represent the Tertiary

reactivation of earlier Laramide thrust faults.

Purpose

The objectives of this study are; 1) to provide a stratigraphie

description and sedimentologic interpretation of the Snowslip Formation

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in Glacier National Park (Lewis Range) and adjacent Whitefish and

northern Flathead ranges, 2) to help resolve confusion concerning the

placement of the upper boundary of the Snowslip where it changes facies

and 3) to evaluate qualitatively the possibility of structural

foreshortening across the Roosevelt and Nyack faults which separate

Glacier National Park and the northern Flathead Range. In order to

fulfill these objectives, seven stratigraphie sections of the Snowslip

Formation were measured with a Jacob’s staff and Brunton compass and

described at the scale of 1" = 10* (Appendix A). Figure 3 shows the

locations of the measured sections.

Regional Corelation

West of the study area toward Clark Fork, Idaho, Lemoine and Winston

(1986) correlate the Snowslip Formation with the lower part of the

Wallace Formation member 3 as described by Harrison and Jobin (1963).

North of the Whitefish Range in the Purcell Supergroup of British

Columbia, the Snowslip Formation passes to the Van Creek Formation

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

southwest Alberta, the Snowslip Formation correlates with the upper part

of the Siyeh Formation (Price, 1964). South of the study area, the

Snowslip Formation has been mapped by Mudge and others ( 1982 ), Wallace

and Lidke (1980), Wallace and others (1981) and Harrison and others (1981)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Sediment Types

Introduction

Winston (1986 d) chose to abandon rock type terminology and proposed

a sediment type classification for stuying Belt rocks. Several problems

exist with the rock type terminology which is based mostly on grain

size, mineralogy and color. First, rock types are often considered

thick, mappable units of rock. Therefore, a particular rock type may

contain several different types of sedimentary structures and represent

several sedimentary processes and depositional environments. Secondly,

diagenesis and metamorphism commonly influence lithology and color. For

example, since reducing diagenetic fluids migrated extensively through

Belt rocks (Rye and others, 1984), many depositionally different

sediments have been classified as the same rock type because they are

green. Diagenetic environments do not necessarily parallel depositional

environments and the two should be studied separately. Also, the

raetamorhic rock type "argillite" has created difficulty. Should

"argillite" refer strictly to slightly metamorphosed clay or more

specifically to slightly metamorphosed silt and clay mixtures common in

Belt sediments? Because rock type terminology is confusing, it is not

appropriate for detailed analysis of Belt rocks, including their

depositional processes and environments.

Winston (1986 b, d) proposed sediment type terminology to alleviate

problems encountered with the older rock type terminology. Grain size,

sedimentary structures and original mineralogy are the criteria for

defining each sediment type. Rock color is commonly determined by

diagenetic alteration of the original mineralogy and is therefore not a

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. criterion for defining sediment types.

Fourteen sediment types are now recognized; gravel, crossbedded

sand, flat-laminated sand, tabular silt, even couple, even couplet,

pinch-and-swell couple, pinch-and-swell couplet, lenticular couplet,

microlamina, coarse sand and intraclast, discontinuous layer,

desiccated mud and carbonate mud.

In the study area, the Snowslip Formation contains the crossbedded

sand, flat-laminated sand, tabular silt, even couple, even couplet,

lenticular couplet, microlamina, coarse sand and intraclast,

discontinuous layer and carbonate mud sediment types (Figure k). The

following sediment type descriptions and interpretations are modified

from Winston (1986 b, p. 90-104 and 1986 d, p. 89-92).

Crossbedded Sand Sediment Type

The crossbedded sand sediment type consists of fine to medium

grained, crossbedded, subfeldspathic quartz sand. Beds range in

thickness from 5 to 40 centimeters. Two kinds of crossbeds occur in

this sediment type in the Snowslip:

(1) Trough crossbeds with tangential toes above scoured lower

bounding surfaces, recording down current migration of dunes or

megaripples.

(2) Planar crossbeds that have planar foreset beds above unscoured

surfaces, recording down current migration of bars or sand waves.

Trough crossbeds range up to 20 centimeters thick and are

occasionally arranged in cosets, forming beds up to 40 centimeters

thick. In some beds the trough crossbed scale decreases upward from

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. S£DiM£NT Type R a n g e in Compositional Gr a in s i z e SEDIMENTARY STRUCTURES VARIETIES N a m e TERRIG- c a l c a r CARBONA- £NQ US COUS ceous CROSSBEDDED S a n d

F l a t - l a m in a t e d S a n d

Ta b u l a r S i l t

E V E N Co u p l e

E v e n C o u p l e t

LENTICULAR

C o u p l e t

MICROLAMINA

C o a r s e S a n d AND /NTRACLAST

Discontinuous L a y e r

Figure k . Sediment types of the Snowslip Formation. From Winston (1986 b).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. decimeters to centimeters. Planar crossbeds range up to 30 centimeters

thick. At some locations they are interstratified with trough

crossbeds, but in many outcrops they are the dominant foim of cross

stratification. Trough and planar crossbeds exhibit well defined,

unidirectional modes.

The crossbedded sand sediment type occurs most commonly in members 3

and 5 as the basal portion of fining-upward sequences up to 1 meter

thick (Figure 5). Trough and planar crossbeds commonly rest on gently

scoured bases. Above the medium grained crossbeded sand sediment type is

the fine grained flat-laminated sand sediment type, which in turn passes

up to the mud-rich discontinuous layer sediment type.

These fining-upward sequences record individual sheetfloods that

surged down the alluvial apron toward the Belt "sea”. Each flood

deposit thins and fines basinward down the apron. The crossbedded sand

at the base of fining-upward flood sequences was deposited during

maximum discharge, but water depth and grain size were sufficient to

maintain lower flow regime conditions. Trough and planar crossbeds

commonly overlie scoured bases. This crossbedded sand is generally

medium grained and contains abundant mudchips, especially near the

base. As the flood waned and became shallower, upper flow regime

conditions deposited flat-laminated, fine grained sand over the medium

grained crossbedded sand. This shift from lower to upper flow regime

has been explained by Winston (1973 a, b, 1977, 1978) as the result of

decreasing water depth to the point where large scale bedforms were

washed out, therefore shifting flow to the upper regime even though flow

velocity decreased. As the flood continued to wane, water velocity

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. dropped until lower flow regime conditions were again achieved producing

climbing-ripple cross laminations near the top of the flat-laminated

sand. When flow ceased and localized ponding occurred, clay settled

from suspension capping the fining-upward sequence. This mud-rich upper

portion of the sequence is characterized by the discontinuous layer

sediment type. Wind generated waves commonly reworked the uppermost

mud-rich sediments and oscillation ripples are therefore abundant. When

flood waters evaporated, these uppermost units were intensely

desiccation cracked. The resulting mudchips were often incorporated in

the next flood deposit. Fining-upward sequences ccwnpare closely with

those of the Precambrian Moodies Group (Eriksson, 1978).

At a regional scale the crossbedded sand sediment type characterizes

the sourceward facies of large sand wedges. The crossbedded sand

sediment type as a whole passes basinward to the flat-laminated sand

sediment type which characterizes Snowslip members 3 and 5. Rare beds

of crossbedded sand, isolated fr

members 3 and 5 and are interstratified with flat-laminated sand beds.

Isolated beds of crossbedded sand record low sinuosity flow of broad

flood channels down the alluvial apron in the lower flow regime.

Thickening and thinning of some beds indicates the channels were floored

by medium grained dunes and bars. The scale and patterns of these

trough and planar crossbed sets closely correspond to the crossbeds of

m o d e m braided stream channels (Smith, 1970). Thus, the rare beds of

crossbedded sand within thick sequences of flat-laminated sand record

flood channels that flowed out over more distal portions of the alluvial

apron.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Flat-Laminated Sand Sediment Type

The flat-laminated sand sediment type consists of even, continuous,

fine to medium grained sand beds, 10 centimeters to 1 meter thick.

Flat-laminated sand beds rest either on planar depositional surfaces or

undulating, scoured surfaces. Mudchips commonly overlie scoured

surfaces and are concentrated in the lower parts of the sand bed.

Mudballs, formed by the accretion of mudchips, are also common along the

base of beds. Mudballs are up to 6 centimeters in diameter and are

remarkably well rounded. The lower and middle portions of beds are

flat-laminated while climbing-ripple cross laminae commonly occur in the

upper parts. Both types of lamination are outlined by diagenetic

hematite or thin placers of heavy minerals. Tops of some beds exhibit

straight crested, symmetrical, oscillation ripples and are overlain by

thin, desiccation cracked mud drapes.

As described above, the flat-laminated sand sediment type also

occurs within fining-upward sequences in members 3 and 5. In thick sand

wedges, such as Snowslip member 5, the flat-laminated sand sediment

type dominates intervals that are basinward from of the crossbedded sand

sediment type. It is in this stratigraphie position that the flat-

laminated sand sediment type is most fully developed, forming

characteristic tabular, flat-laminated beds. These beds continue as

resistant layers across most outcrops, interstratified with recessive

beds of the discontinuous layer and even couplet sediment types. In

the southern sections, Snowslip members 3 and 5 are characterized by the

flat-laminated sand sediment type.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The flat-laminated sand sediment type records deposition from

sheetfloods moving only fast enough to transport fine to medium grained

sand, yet flowing mostly in the upper regime. During the initial flood

stages, soft, sticky mudchips from the underlying desiccation cracked

mud drape or discontinuous layer sediment type, were accreted into

mudballs by gentle rolling downslope. Occasional climbing-ripple cross

laminae record periodic shifts to the lower flow regime. Oscillation

ripples and thin mud drapes indicate ephemeral standing water following

floods.

The shift from deeper water lower flow regime dunes and bars to

shallower and slower upper regime sheetflow recorded in fining-upward

sequences also explains the basinward facies change from medium grained

crossbedded sand to fine grained flat-laminated sand. Shallow channels

which deposited the crossbedded sand sediment type broadened downslope

into sheetfloods from which tabular beds of the flat-laminated sand

sediment type were deposited. As sheetfloods spread basinward, they

deposited the thinner flood deposits of the even couple sediment type.

As individual floods waned, velocity and depth decreased progressively

up the alluvial apron, and beds of the discontinuous layer sediment type

were deposited over the flat-laminated sand and even couple sediment

types. These basinward thinning and fining sequences compare closely

with sandstone beds of the Devonian Trentishoe Formation, also

interpreted to be ephemeral sheetflood deposits (Tunbridge, 1981).

Even Couple Sediment Type

Sharply based, even, continuous beds 3 to 10 centimeters thick that

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. grade upward from fine grained sand and silt to silt mixed with clay

characterize the even couple sediment type. The sandy and silty lower

parts of even couples are mostly flat-laminated or occasionally

climbing-ripple cross laminated and some contain mudchips. The upper

muddy portion of the couples are ccmmonly desiccation cracked and some

exhibit oscillation ripples. Color ranges from red and green in purely

terrigenous couples to yellowish green in calcareous couples.

The flat-laminated sand, characteristic of members 3 and 5 in the

southern sections, passes northward to even couples and thinner flat-

laminated sand beds.

Tabular beds with sharp, locally scoured bases dominated by flat-

laminated, fine grained sand and silt grading up to mudcracked and

occasionally oscillation rippled silt and clay, record sheetflood

deposition of fine sand and mud. FIat-laminations in the basal, sandy

portion of even couples record upper flow regime deposition. As

velocity slowed, conditions occasionally shifted to the lower flow

regime, forming climbing-ripple cross laminations. The muddy upper

portion of couples was deposited by settle out as the sheetfloods waned.

When flow ceased, shallow ponds formed and small, wind generated waves

reworked the upper portion of the couples into straight crested,

symmetrical ripples. The ponds eventually evaporated and the couples

were desiccation cracked. Mudcrack ploygons were then picked up by the

next flood and incorporated into the succeeding sediments as mudchips.

In the Snowslip, a basinward fining and thinning sequence is

recorded in members 3 and 5 by the progression from flat-laminated sand

to even couples to even and lenticular couplets. Thus, even couples

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. record distal sheetfloods on nearly level alluvial apron surfaces

bordering the Belt "sea". Smoot(1983) interpreted similar tabular sand

beds in the Eocene Green River Formation to have been deposited by

distal sheetfloods flowing over sandflats bordering Lake Gosiute.

Even Couplet Sediment Type

The even couplet sediment type contains graded layers 3 millimeters

to 3 centimeters thick of very fine grained sand and silt in the basal

portion that grades up to clay. Even couplets are wavy to parallel

laminated. The silty basal portion rests on locally scoured bases and

is flat-laminated or climbing-ripple cross laminated. In the Snowslip,

even couplets range in composition from entirely terrigenous to mixed

terrigenous and calcareous. Coarser grained terrigenous couplets are

mostly sand-to-mud and have thicker lower sand layers than capping clay

layers. They are mostly hematitic, intensely desiccation cracked, and

contain mudchips in the sand layers. Finer grained, terrigeneous

couplets have proportionately thinner lower sand and silt layers and

thicker capping clay layers. Mudcracks and mudchips are less abundant

and many intervals are chloritic. These green, muddier couplets

occasionally incorporate carbonate mud in the capping clay layer

forming the mixed terrigeneous and calcareous variety of even couplets.

Calcareous couplets weather yellowish green to light tan.

Even couplets form thick stratigraphie sequences in Snowslip

members 2 and k and in member 3 bas inward from the flat-laminated sand

and even couple sediment types. Sandy, mudcracked, couplets commonly

become interstratified basinward with the lenticular couplet sediment

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. type and with thin lenses of the coarse sand and intraclast sediment

type. Such a basinward progression occurs between member 3 at Hidden

Lake and rocks at approximately the same stratigraphie level at Red

Meadow Creek. Finer grained, mud-rich couplets, common in members 2 and

4, are interstratified with lenticular couplets. These finer grained,

even couplets also pass laterally to the microlamina or carbonate mud

sediment types such as in member 4 at Hidden Lake.

The coarser, generally hematitic, mudcracked variety of the even

couplet sediment type was deposited by sheetfloods flowing across

exposed mudflats. Flat-laminations in the lower portion of couplets

record shallow, upper regime flow of the flood waters. As the

sheetflood waned, flow velocity decreased and lower flow regime

conditions deposited climbing-ripple crossbeds. When flow ceased, clay

settled from the standing water, capping the couplets. This standing

water may represent broad, shallow ponds or rapid expansion of the Belt

"sea" in response to flooding. Water standing on the shallow mudflats

subsequently evaporated. The couplets then desiccated and cracked. The

resulting mud polygons were frequently broken up and incorporated as

mudchips in succeeding flood deposits.

Finer grained couplets with fewer mudcracks were probably deposited

when sheetfloods entered the shallow waters of the Belt "sea" and spread

in suspension out into the basin. These couplets generally remained

submerged for longer periods of time and consequently contain fewer

mudcracks and mudchips. They tended to be reduced and are commonly

chloritic. During times of carbonate precipitation, the couplets

incorporated carbonate mud in the upper muddy portion.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Lenticular Couplet Sediment Type

The lenticular couplet sediment type is composed of fine sand and

silt ripple lenses, sharply overlain by mud laminae, forming couplets 3

millimeters to 3 centimeters thick. Bedding surfaces are commonly

oscillation rippled. Clay layers draping the sand and silt ripples are

more uniform and continuous than the sand and silt below and are

COTinonly cut by desiccation cracks.

Two varieties of this sediment type are recognized: (1) the

terrigenous variety, which consists of terrigenous fine sand, silt and

clay and (2) the calcareous variety, in which terrigenous grains have

been mixed with carbonate mud. Within the terrigenous variety, fine

sand, silt and clay proportions vary widely. Two associations of grain

size, composition and sedimentary structures are recognized. In one

association, such as occurs in member 2 at Hidden Lake, lenticular

couplets are commonly 2 to 3 centimeters thick and many rest on scoured

bases. The silt portion forms well defined, discrete ripple lenses.

Rounded mudchips are abundant and are imbricated in a variety of

directions. Hudballs up to 4 centimeters in diameter composed of

accreted mudchips lie within some sandy layers. Desiccation cracks

commonly outline large polygons and are filled with silt and mudchips.

The coarse sand and intraclast sediment type containing ooliths and

coarse quartz grains is locally interstratified with this association of

the lenticular couplet sediment type. The second association, common at

Bluebird Creek, is characterized by 1 to 2 centimeter thick couplets in

which the clay layers are moderately cracked. The resulting angular

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. mudchips are incorporated in the fine sand and silt portions of the

couplets. The even couplet and microlamina sediment types are commonly

interstratified with these lenticular couplets.

Winston (1986 b) described a third association of terrigenous

lenticular couplets which is characterized by couplets up to 1

centimeter thick in which the silt layers thicken and thin only

slightly, and are sharply overlain by thicker clay layers. Mudcracks

and mudchips are fewer than in the other associations. Since the silt

portions of these couplets do not form well defined ripple lenses, I

have grouped them with even couplets. These "wavy couplets" are

abundant in Snowslip members 2 and 4 throughout the study area.

The calcareous variety of the lenticular couplet sediment type

contains both associations described from the terrigenous variety.

However, carbonate mud was incorporated along with clay in the upper

parts of the couplets. Calcareous lenticular couplets occur

occasionally in the central part of the study area at Granite Park,

Hidden Lake and Red Meadow Creek-

Abundant straight crested oscillation ripples record wave transport

and deposition of fine sand and silt. Clay settled out between periods

of wave reworking, completing the couplets. Grain size and composition

of lenticular couplets compare closely with those of even couplets.

This suggests that lenticular couplets formed in shallow standing water

by wave reworking of even couplets. Water periodically evaporated off

the mudflats and the sediments were desiccation cracked.

Lenticular couplets characterized by scoured surfaces, imbricated

and rounded mudchips and accreted mudballs reflect prolonged wave

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reworking near the zone of wave break. Interstratified lenses of the

coarse sand and intraclast sediment type, representing small shoals and

beaches, corroborate this interpretation. Medium to thick couplets

containing angular mudchips record less reworking. Wavy couplets were

deposited in quieter, more continuously submerged environments and

record only minor wave reworking. Thus, a continuum exists between even

couplets, wavy couplets and lenticular couplets, reflecting differing

amounts of wave reworking.

Tabular Silt Sediment Type

The tabular silt sediment type consists of beds, 1 to 40

centimeters thick, of flat-laminated and climbing-ripple cross laminated

silt and very fine grained sand. Tabular silt beds are not perceptibly

graded and are commonly interstratified with the lenticular couplet and

even couplet sediment types. Members 1, 2, 4 and 6 contain abundant

tabular silt beds.

A morphologic continuum exists in the tabular silt sediment type

from wavy beds as thin as 1 centimeter to beds up to 40 centimeters

thick with sharp bases and tops. The thick tabular beds described by

Winston (1986 b, d) represent one end member in this coninuum. These

beds have sharp bases, flat-laminations throughout most of the bed,

occasional climbing-ripple crossbeds in the upper portions and sharp,

flat tops. These thick tabular beds record major storms that swept

across the submerged mudflats. Sediment originally deposited as even

couplets was churned and resuspended by strong currents and waves

during the storms. Upper flow regime conditions concentrated the silt

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and very fine grained sand and redeposited it in flat-laminated layers.

Conditions shifted to the lower flow regime as the storms waned

depositing climbing-ripple crossbeds. Sharp tops to these beds indicate

the sporadic storms were short-lived events.

Thinner, wavy, "tabular silt" beds are as thin as 1 centimeter,

commonly lensoidal, have wavy bases and tops and exhibit climbing-ripple

crossbeds. These thinner silt beds record reworking of even and

lenticular couplets by storms much weaker than those described above.

Lower flow regime climbing-ripple crossbeds pass upward to straight

crested, oscillation ripples.

Thick, tabular beds of the tabular silt sediment type are

differentiated from flat-laminated sand beds by their finer grain size,

lack of accreted mudballs, relative lack of mudchips and their

interstratification with even and lenticular couplets. Flat-laminated

sand beds are generally intertratified with other flat-laminated sand

beds, crossbedded sand beds or even couples. Thin, wavy tabular silt

beds differ from even couples and couplets by being ungraded and lacking

the mud-rich upper layer of couples and couplets.

Microlamina Sediment Type

The microlamina sediment type is composed of millimeter scale

laminae of quartz or dolomitic silt sharply overlain by equally thin

clay laminae. Couplets of the micro lamina sediment type range from 1 to

3 millimeters thick. Small mudcracks cut some microlamina intervals.

Important in identifying this sediment type is the absence of

sedimentary structures common in other sediment types, such as

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. crossbeds* oscillation ripples and mudchips.

In the Snowslip Formation, two varieties of this sediment type can

be recognized; a terrigenous variety and a calcareous variety. In the

terrigenous variety, such as occurs in members 2 and 4 at Hidden Lake,

silt laminae are overlain by hematitic or chloritic clay laminae,

forming dark red or greenish gray microlamina. The calcareous variety

of microlamina, such as occurs at Bluebird Creek, contains terrigeneous

silt and occasional dolomite silt overlain by calcareous clay. Both

varieties of microlamina are interstatified with mudcracked, wavy

couplets and thin tabular silt beds.

The fine grain size and thin couplets of the microlamina sediment

type record the periodic influx and deposition of only limited amounts

of flood generated suspended sediments into the Belt "sea”. Absence of

crossbeds indicates transport and deposition fr«n suspension.

Microlamina has the appearance of a deep water deposit, but occasional

mudcracks indicate shallow water and perhaps periodic exposure.

In the Snowslip, terrigenous microlaminae were deposited basinward

from the even and lenticular couplet sediment types. Thus, the

micro lamina sediment type reflects quiet, protected environments with a

slow rate of sediment.accumulation. Calcareous microlamina formed where

carbonate mud was precipitated either by photosynthetic activity or

directly from supersaturated Belt "sea" water.

Coarse Sand and Intraclast Sediment Type

In the eastern sections, the most common constituent of the coarse

sand and intraclast sediment type is well sorted, medium to coarse

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. grained, well rounded and polished, slightly feldspathic quartz sand.

In the eastern part of the study area at Snowslip Mountain and Hidden

Lake, the coarse sand and intraclast sediment type forms continuous beds

up to 1 meter thick that are cross stratified at low angles. Ooliths,

mudchips and dolomite intraclasts are commonly mixed with the

terrigenous quartz grains, especially in member 1. Northwestward,

toward Red Meadow Creek, the coarse sand and intraclast sediment type

forms discontinuous lenses often less than 10 centimeters thick that are

crossbedded at high and low angles. Here the coarse sand and intraclast

sediment type is composed mostly medium grained, slightly feldspathic,

quartz sand with abundant calcareous intraclasts. Further to the

northwest at Bluebird Creek, the coarse sand and intraclast sediment

type is absent.

Although similar in grain size to the crossbedded sand sediment

type, the coarse sand and intraclast sediment type differs by commonly

having high angle crossbeds with a variety of dip directions

interstratified with low angle crossbeds with a preferred dip direction,

mudchips with opposing imbrication directions and accreted grains such

as ooliths. The coarse sand and intraclast sediment type is generally

interstratatified with wavy, desiccation cracked couplets.

The low, sweeping crossbeds of the coarse sand and intraclast

sediment type are interpreted as forebeach deposits of small beaches and

shoals. Thinner coarse sand and intraclast beds exhibiting low and

high angle crossbeds represent smaller beaches and shoals with steeper

forebeach and washover fans capable of imparting bipolar crossbed

directions. Smoot (1903) interpreted similar deposits from the Eocene

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Green River Formation as beach deposits and Schwartz (1982) described

high angle washover fans with opposing beach foresets from several

modem, small beaches.

The decreasing number of coarse sand and intraclast beds from Hidden

Lake and Snowslip Mountain westward to Red Meadow Creek and Bluebird

Creek indicates the relative abundance of small beaches and shoals along

the eastern part of the study area during deposition of Snowslip members

1, 2 and 4. Grain size of the well rounded, quartz sand within coarse

sand and intraclast beds decreases from coarse in the eastern part of

the study area to medium and occasionally fine in the western portions.

This indicates an eastern source for the quartz sand grains which

Winston (1986, b) interprets as a mature sand that blanketed the

crystalline basement east of the Belt basin. This sand is easily

differentiated mineralogically and texturally from northwestward-fining,

feldspathic sediments derived form the southwest side of the basin. The

distinctive coarse quartz sand population was probably transported from

the North American craton by ephemeral streams and was driven by

longshore drift westward along low shoals and beaches that extended into

the basin.

Beaches of the coarse sand and intraclast sediment type developed

where the shallow waters of the Belt "sea" met the adjacent sand and

mudflats. As the shoreline fluctuated, beaches were repeatedly

abandoned and reoccupied as recorded by interstratification of coarse

sand and intraclast beds with wavy couplets.

Discontinuous Layer Sediment Type

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The discontinuous layer sediment type is characterized by centimeter

scale, discontinuous beds composed of discontinuous lenses of climbing-

ripple cross laminated very fine sand and silt interlaminated with clay.

The absence of clearly defined, laterally continuous, fining-upward

layering differentiates this sediment type from even couples, even

couplets and lenticular couplets. Because individual couplets are not

recognizable in this sediment type, it is difficult to discern whether

specific beds were deposited by individual or multiple events. The

discontinuous very fine sand and silt ripple crossbeds and irregular

clay lenses that characterize this sediment type appear to have been

deposited from traction transport of very fine sand and silt,

alternating with settle out of suspended clay. Similar deposits occur

during falling flood stages in modem braided rivers and flood plains

(Anderson and Picard, 1974).

In Snowslip members 2 and 4 at Hidden Lake and member 4 at Granite

Park, occasional beds of the discontinuous layer sediment type are

interstratified with wavy couplets. In these intervals, the

discontinuous layer sediment type is chloritic and is only rarely

mudcracked. Here the discontinuous layer sediment type probably

represents single sheetfloods that deposited clay-rich sediment onto the

shallow, suknerged mudflats bordering the Belt "sea", Flow velocity of

the sheetflood decreased rapidly upon entering the standing water

allowing lower flow regime climbing-ripple crossbeds to form in silt

accumulations. However, the very limited supply of sand and silt

prevented the develoiwtent of continuous beds characteristic of even

couplets.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The discontinuous layer sediment type also forms the upper parts of

decimeter scale, fining-upward sheetflood sequences in members 3 and 5.

Sequences are composed of crossbedded sand at the base, grading up to

flat-laminated sand and the discontinuous layer sediment type at the

top. In this setting, beds of the discontinuous layer sediment type are

hematitic and intensely desiccation cracked. Here the discontinuous

layer sediment type represents the waning stages of individual

sheetfloods. Decreased water depth and velocity allowed ripples of very

fine sand and silt to form and migrate over small accumulations of clay.

Carbonate Mud Sediment Type

Rocks that contain more than 50 percent fine grained carbonate are

included in the carbonate mud sediment type. In its purest form, beds

composed entirely of carbonate mud are massive, homogeneous and weather

uniformly. Where fine grained terrigenous sediments are mixed with

carbonate mud, stratification becomes apparent and microlamina,

lenticular couplet and even couplet sediment types can be identified.

Thus a compositional continuum exists between the carbonate mud sediment

type and calcareous varieties of the microlamina, lenticular couplet and

even couplet sediment types.

Carbonate mud is very rare in the Snowslip Formation. It occurs only

at Red Meadow Creek, Bluebird Creek and in member 2 at Paola Crek and

member 4 at Hidden Lake. Carbonate mud is interstratified with

chloritic, wavy couplets.

This sediment type records the precipitation of carbonate mud from

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Belt "sea” water, probably in the original form of aragonite or high-

magnesinm calcite. Carbonate mud accumulated in protected environments

of low terrigenous sediment input.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ^Description of Type Section and Informal Members

Introduction

Two of the seven measured Snowslip sections are described in detail;

the Snowslip Mountain section described here, and the Bluebird Creek

section described in the following chapter. Snowslip Mountain is the

thickest complete section in the study area, it is the type Snowslip

section and it serves as the type locality for the informal members.

Snowslip Mountain is the most sourceward section in the study area and

contains abundant hematite and chlorite. Bluebird Creek in the northern

Whitefish Range is the most basinward section of the Snowslip Formation

and contains only chloritic sediments. Bluebird Creek is the thinnest

complete section and the informal members are not identifiable. Facies

changes occuring within the Snowslip Formation in the study area are

most pronounced when comparing the Snowslip Mountain and Bluebird Creek

sections.

Childers (1963) defined the Snowslip Formation in the extreme

southern portion of Glacier National Park (Figure 3). The section is

located along the north - south ridge joining Snowslip Mountain and

Mount Shields. The Snowslip Formation is conformably bound by the Helena

Formation below and the Shepard Formation above. Childers (1963)

described three main units in the Snowslip totalling 1606 feet. In

remeasuring the type section, I measured a total Snowslip thickness of

1672 feet thick, which is approximately 4 percent greater than Childers'

measurement.

Whipple and others (1984) divided the Snowslip Formation in Glacier

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. National Park into six informal members, numbered from bottom to top 1

through 6. Whipple and others (1984) defined the members partly on

distinctive lithologies and partly on color. Since color may be the

product of diagenetic alteration of the original mineralogy, I based the

members on distinctive suites of sediment types with no regard to color.

However, color changes closely follow changes in sediment type suites.

The six informal members are very convenient and useful for studying the

Snowslip Formation not only in Glacier National Park, but also the

Whitefish and Flathead ranges.

Member 1

The lowest member, 1, rests conformably above the Helena Formation

and is 330 feet thick at Snowslip Mountain. It is dominantly red and is

characterized by beds of the even couplet, tabular silt, and coarse

sand and intraclast sediment types. The dolomicrite and oolitic sand

beds of the uppermost Helena Formation pass stratigraphically upward to

red, calcareous even couplets, which mark the base of the Snowslip

Formation. In member 1, even couplets are mostly wavy and contain

abundant mudchips, desiccation and syneresis cracks and fluid escape

structures. Tabular silt beds occur in both red and green intervals and

reach a maximum thickness of approximately 30 centimeters. These silt

beds are ungraded, many exhibit flat-laminations and climbing-ripple

crossbeds and most are interstratified with even couplets. Beds of the

coarse sand and intraclast sediment type are common in member 1 at the

type section. Occasional beds are 1 meter thick but most are less than

30 centimeters. Both grayish green and light red beds occur in member

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1. The primary grains in these beds are coarse grained quartz, dolomite

intraclasts and ooliths. Beds are poorly sorted and cemented by calcite

and dolomite. Many of the ooliths are broken and deformed, some ooliths

form aggregate spherules, and some are hematitic, especially near the

base of the member (Whipple and Johnson, 1988). Coarse sand and

intraclast beds contain low angle crossbeds and are interstratified with

wavy couplets. Two hematitic strcwnatolite beds, Collenia undosa.

(Childers, 1963) are present in member 1. Both beds are discontinuous

and less than 30 centimeters thick. The last sediment type in member 1

is the micro lamina sediment type. One bed of hematitic microlamina

approximately 50 centimeters thick occurs near the base of member 1.

Member 2

Member 2 is 392 feet thick at the Snowslip Mountain and its lower

boundary is placed at the top of the uppermost, hematitic coarse sand

and intraclast beds of member 1. Member 2 is green and contains the

even couplet, tabular silt and coarse sand and intraclast sediment

types. Most abundant in member 2 are calcareous even couplets. They

are commonly wavy and contain abundant mudchips, desiccation and

syneresis cracks and range in color from grayish green to yellowish

gray. Tabular silt beds up to 30 centimeters thick are common in member

2. These beds of silt and very fine grained sand exhibit flat-

laminations and climbing-ripple crossbeds. Some beds show well the

transition from upper flow regime flat-laminations at the base of the

bed to lower flow regime climbing-ripple crossbeds near the top. The

coarse sand and intraclast sediment type is abundant near the base of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. member 2. Beds are generally white to light gray and are up to 30

centimeters thick. Mudchips and coarse grained, well rounded quêurtz

are the principal grains. Coarse sand and intraclast beds are

crossbedded at high and low angles and contain fewer ooliths than those

in member 1. Carbonate cement is abundant. Several pink stromatolite

beds up to 30 centimeters thick occur in the lower part of member 2.

Member 3

Member 3 is 146 feet thick at Snowslip Mountain and is dominantly

red. Its lower contact is placed where the wavy, chloritic couplets of

member 2 grade upward to hematitic, desiccation cracked, even couplets

and flat-laminated sand beds characteristic of member 3. Flat-

laminated sand beds are both flat-laminated and climbing-ripple cross

laminated. Mudchips and accreted mudballs are abundant. Beds range in

thickness from 10 to 30 centimeters and are inter stratified with even

couplets. Couplets are generally 1 to 3 centimeters thick, wavy,

desiccation cracked and contain abundant mudchips.

The upper portion of member 3 contains occasional fining-upward

sequences up to 50 centimeters thick that represent individual

sheetflood events. Ideal fining-upward sequences are few and contain

three recognizable units; crossbedded medium grained sand at the base,

grading up to fine grained flat-laminated sand up to desiccated mud of

the discontinous layer sediment type at the top (Figure 5). The medium

grained basal sand of the crossbedded sand sediment type is generally

white to very pale maroon, commonly lenticular and rests on an

erosional, scoured base. Mudchips and trough crossbeds with tangential

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31

Range in Thickness

Discontinuous layer sediment 5-20 centimeters type; dark maroon, occasional lenses of rippled silt, desiccation cracks

Flat-laminated sand sediment type; fine grained, pink, 10-50 centimeters subfeldspathic, flat- laminations near base, climbing-ripple cross laminations near top

Crossbedded sand sediment type; medium grained, white to light pink, 10-30 centimeters subfeldspathic, erosional base, trough crossbeds, dark maroon mudchips near base

Figure 5. Idealized fining-upward single sheetflood sequences from members 3 and 5 of the Snowslip Formation.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. toes are abundant. Quartz is the most abundant grain type followed by

K-feldspar and sedimentary rock fragments. Quartz grains are commonly

cemented by quartz overgrowths. Calcite and hematite are also present

as cements. This moderately well sorted quartz and subfeldspathic basal

sand is up to 20 centimeters thick. Above the crossbedded sand lies

flat-laminated, fine grained sand. It is subfeldspathic, light pink and

up to 30 centimeters thick. Flat-laminations near the base of the bed

grade upward to climbing-ripple crossbeds. Capping the ideal fining-

upward sheetflood sequence is the clay-rich, dark maroon, discontinuous

layer sediment type. Extensively desiccation cracked, the discontinuous

layer sediment type forms beds up to 10 centimeters thick. Fining-

upward sequences are interstratified with the abundant flat-laminated

sand and even couplet sediment types characteristic of member 3.

Member k

Member 4 is 269 feet thick and very similar to member 2. It is

dominantly green and its lower contact is placed where the hematitic

flat-laminated sand beds and even couplets of member 3 grade upward to

chloritic, wavy couplets. Member 4 is dominated by calcareous wavy

couplets and tabular silt beds that are identical to those in member 2.

Desiccation and syneresis cracks, fluid escape structures and mudchips

are abundant. Like member 2, several pink stromatolite beds up to 30

centimeters thick occur near the base of member 4. Rare beds up to 15

centimeters thick of the coarse sand and intraclast sediment type occur

low in member 4. Members 2 and 4 differ in three ways. Member 4 lacks

the abundance of coarse sand and intraclast beds common in the lower

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. portion of member 2. Secondly, the uppermost 35 feet of member 4 is red

where all of member 2 is green. And finally, the middle part of member

4 contains approximately 1 meter of even couples that differ from the

pervasive couplets only in thickness.

Member 5

Member 5 is 511 feet thick at the Snowslip Mountain and is entirely

red. It is the easiest member to recognize at Snowslip Mountain

because of its great thickness and resistance to weathering. The lower

contact of member 5 is placed where the wavy couplets of member 4 grade

upward to flat-laminated sand beds characteristic of member 5. Flat-

laminated sand beds are up to 50 centimeters thick and monocrystalline

quartz is the most abundant grain type followed by dolomite, sedimentary

rock fragments and K-feldspar. Mudchips and accreted mudballs are

abundant. Silica, hematite and calcite cements are common. Centimeter

scale, desiccation cracked even couplets are interstratified with the

flat-laminated sand beds. Oscillation ripples, raindrop impressions and

desiccation cracks indicating shallow water conditions and frequent

exposure are common throughout member 5.

Member 5 contains individual sheetflood, fining-upward sequences

that are slightly thicker than those in member 3. The basal crossbedded

sands are generally medium grained and reach a maximum thickness of 30

centimeters. Ranging up to 50 centimeters thick, the middle units of

flat-laminated sand are fine grained and contain abundant climbing-

ripple crossbeds in the upper portions. Beds of the desiccation

cracked, discontinuous layer sediment type up to 20 centimeters thick

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cap the fining “Upward sequences. Individual sequences are up to 1 meter

thick. Well defined, complete fining-upward sequences are rare.

Member 6

Member 6 is the final and thinnest member of the type Snowslip

Formation. Only 24 feet thick, member 6 contains dominantly green

rocks and is composed of the even couplet, tabular silt and coarse sand

and intraclast sediment types. The lower contact of member 6 is placed

where the flat-laminated sand beds of member 5 grade upward to the even

couplets and coarse sand and intraclast beds of member 6. Beds of the

coarse sand and intraclast sediment type range from 25 to 65 centimeters

in thickness and are crossbedded at low angles. Well rounded, medium to

coarse grained quartz is the principal grain type followed by mudchips

and minor K-feldspar. Tabular silt beds up to 15 centimeters thick

contain abundant ripple cross laminae, mudchips and oscillation rippled

upper surfaces. Thin, desiccation cracked mud drapes frequently cover

the tabular silt beds. Finally, chloritic, wavy couplets are common in

member 6. Mudchips, syneresis cracks and occasional fluid escape

structures characterize these couplets. The upper contact of member 6

is placed where the wavy couplets and coarse sand and intraclast beds

grade upward to carbonate mud and calcareous couplets of the Shepard

Formation.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Northern Whitefish Range Reference Section

In the northern Whitefish Range the Snowslip Formation differs

markedly from the Snowslip in Glacier National Park and the Flathead

Range, and the six informal members are not identifiable. The Bluebird

Creek section in the northern Whitefish Range is the furthest measured

section from Snowslip Mountain, 79.5 miles northwest, and serves as a

reference section for the area.

The Snowslip Formation at Bluebird Creek rests conformably above the

Helena Formation. The contact is placed where the tan weathering,

dolomitic microlamina and even couplets and black, carbonaceous

microlamina of the Helena grade upward to pale green, calcareous even

couplets of the Snowslip. The Snowslip Formation at Bluebird Creek is

575 feet thick and is pale yellowish green, grayish green and olive

green. No hematitic rocks are present but occasional carbonate-rich

beds weather tan. Diagenetic pyrite cubes up to 5 millimeters across

occur throughout the formation.

Calcareous, even couplets up to 1 centimeter thick dominate the

basal 12 feet of the Snowslip Formation. Grading upward from very fine

sand to clay, these couplets contain mudchips and silt filled syneresis

cracks. Tabular silt beds 3 to 10 centimeters thick and wavy couplets

up to 3 centimeters thick characterize the overlying 154 feet of the

Snowslip Formation. Flat-laminations and ripple cross laminations are

abundant in the tabular silt beds. Mudchips are cn in the lower

portion of some silt beds, and oscillation rippled upper surfaces are

abundant. Individual tabular silt beds are separated by very thin,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. micaceous, desiccation cracked mud drapes. Wavy couplets in this

interval are mostly silt with thin clay layers. Desiccation and

syneresis cracks are abundant as are mudchips along the base of some

couplets. For the next 360 feet, wavy and lenticular couplets, tabular

silt and microlamina are the principal sediment types. Wavy and

lenticular couplets range in thickness from 5 millimeters to 3

centimeters and commonly contain very fine grained sand in the silty

portion. The muddy portion is occasionally calcareous and weathers a

pale yellowish green. Many couplets contain mudchips along their bases.

Fluid escape structures, desiccation cracks and syneresis cracks are

common. Several beds of lenticular couplets contain large armored and

accreted mudballs up to 4 centimeters in diameter. Tabular silt is the

next most abundant sediment type in this interval. Beds are generally

less than 10 centimeters thick but range up to 20 centimeters. Most

beds are climbing-ripple cross laminated but flat-laminations are also

present. Thin desiccation cracked mud drapes and oscillation ripples

are prevalent. Some beds rest on scoured bases and have incorporated

mudchips from the underlying cracked mud drape. Occasional fine grained

sand lenses underlie some tabular silt beds. These sand lenses are

discontinuous, 2 to 5 centimeters thick and contain crossbeds. They

probably represent wave reworking of couplets which contained fine sand.

Microlamina beds are common in this interval and are locally

calcareous. Beds range frcm 5 to 70 centimeters thick and are

interstratified with wavy couplets. The uppermost Snowslip interval at

Bluebird Creek is 50 feet thick and is dominated by very thin tabular

silt beds. Beds range from 1 to 4 centimeters thick, are very wavy,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. contain climbing-ripple crossbeds and oscillation ripples, few

mudcracks, and are separated by paper thin, micaceous mud drapes. This

uppermost interval may be the bas inward extension of Snowslip member 5

seen elsewhere in the study area. It lacks the fining-upward sheetflood

sequences and hematitic, flat-laminated sand beds and even couplets

characteristic of member 5, but its coarser grain size and relative

stratigraphie position suggest this interval may correlate with member

5. The contact between the Snowslip Formation and the overlying Purcell

Lava is sharp and undulatory, but no evidence of a disconformity was

observed.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. stratigraphie Boundaries of the Snowslip Formation

Lower Boundary of the Snowslip Formation

The Snowslip Formation rests with apparent conformity on the

underlying Helena Formation. Whipple and Johnson (1988) however,

suggest the possibility of a disconformity below the Snowslip based on

pétrographie data. Beds of the coarse sand and intraclast sediment

type, common near the base of the Snowslip, contain abundant dolomicrite

intraclasts and ooliths along with quartz and feldspar grains. Many of

the ooliths are broken and deformed, and some are rimmed and partially

replaced by hematite. Whipple and Johnson (1988) believe the damaged

ooliths and dolomicrite intraclasts were derived from the Helena

Formation which is inferred to have been uplifted, exposed and

subsequently eroded at least in the eastern part of the basin. Ooliths

were broken and dolomicrite fragments were rounded during fluvial

transport from the uplifted region along the eastern margin of the Belt

"sea". The cause of the the inferred uplift which exposed the Helena

Formation in the eastern reaches of the basin is unknown. It is also

unclear whether Whipple and Johnson (1988) interpret the middle Belt

carbonate to have been exposed basinwide.

Broken, hematitic ooliths and rounded dolomicrite intraclasts do not

necessarily reflect uplift of the Helena Formation. A minor regression

of the Belt "sea" prior to Snowslip deposition would expose Helena

sediments in the eastern reaches of the basin. Fluvial reworking of the

uppermost Helena sediments could result in broken, hematitic ooliths and

rounded fragments of dolomicrite. These grains were then combined with

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. coarse quartz sand from the eastern basin margin to form small beaches

and shoals of the coarse sand and intraclast sediment type.

Although less plausible, in situ breaking of ooliths is possible.

Ooliths can be broken by the same wave oscillation responsible for their

accretion or by fluctuations in water salinity (Eby, 1977).

The contact between the Helena and Snowslip formations is sharp and

sedimentologic changes across the boundary are abrupt. Terrigenous

input greatly increased with the onset of Snowslip sedimentation and

carbonate production decreased. Minor carbonate production accompanied

Snowslip deposition as recorded by ooliths, calcareous couplets and rare

beds of carbonate mud. Megascopic evidence for a disconformity, such as

an irregular erosional surface, is lacking. I therefore interpret the

contact between the Helena Formation and the Snowslip Formation as

conformable in the study area.

In the eastern portion of the study area at Snowslip Mountain, Paola

Creek and Hidden Lake, the base of the Snowslip Formation is placed

where the tan weathering dolomitic and oolitic sediments of the

underlying Helena Formation pass upward to red, desiccation cracked

even couplets and oolitic coarse sand and intraclast beds of the

Snowslip. In the western portion of the study area at Red Meadow Creek

and Bluebird Creek, the contact between the two is placed where the tan

weathering dolomitic sediments of the Helena pass upward to green,

calcareous couplets of the Snowslip.

Upper Boundary of the Snowslip Formation

Determining the top of the Snowslip Formation has been a matter of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. great controversy and confusion. Three possibilities have been proposed

for the upper boundary of the Snowslip Formation; 1) at the top of

Snowslip member 5, 2) at the base of the Purcell Lava where present or

3) at the lowest tan weathering, dolomitic beds of the Shepard Formation

(Figure 6).

Childers (1960, p. 34) defined the contact between the Snowslip

Formation and the overlying Shepard Formation "where the dull red

medium-grained quartzites of the upper unit of the Snowslip (member 5)

grade into the calcareous shales and argillites of the Shepard". In the

southern portion of the Belt basin member 5 is the most evident and

easily recognized member of the Snowslip Formation. It is resistant to

weathering and forms prominent outcrops. For these reasons, the top of

member 5 has been mapped throughout the southern portion of the basin as

the Snowslip/Shepard contact by Mudge and others (1982), Wallace and

Lidke (1980), Wallace and others (1981) and Harrison and others (1981).

Member 5 thins rapidly to the northwest and is absent in the northern

Whitefish Range at Bluebird Creek (Figures 6 and 9). This prevents the

top of the Snowslip from being placed at the top of member 5 throughout

the study area.

In the northern portion of the Belt basin the Purcell Lava serves as

an important time plane in the Missoula Group. Like Snowslip member 5,

the Purcell Lava is resistant to weathering and forms bold outcrops. In

the northern Whitefish Range where member 5 is absent, the base of the

lava was chosen by Bames (1963) and Smith (1963) as the upper boundary

of the Snowslip Formation. The base of the Purcell Lava would be a

logical choice for the upper boundary of the Snowslip Formation

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ■DCD Q.O C Q.g Type Shepard Formation Shepard Formation of Willis (1902 Whipple and others (1984 ■D CD

C/) C/) dolomitic sediments

8 Member 6

Purcell Lava (O' dolomitic sediments

Member 6

3. Member 5 3 " CD H ■DCD RMC Member 4 Q.O C a o 3 Member 3 "O o CO Member 2 CD O.

Member 1 X \ i / \i/___ ■D CD c Smith (1963) Whipple and others (198k) Type Snowslip Formation Barnes ( 1963) Childers (1963) C/) Aclonan (this study) C/) Aclonan (this study)

It] c 41

1 Figure 5. Generalized stratigraphie section of the Snowslip Formation showing informal members and various interpretations of formation boundaries. Measured section abbreviations: BC = Bluebird Creek, RMC = Red Meadow Creek, GP = Granite Park. HL = Hidden Lake, PC = Paola Creek, SM = Snowslip Mountain, H2 = U.S. Highway 2 Roadcut. 41 everyiirtiere if it were present basinwide. However, the Purcell Lava

pinches out to the south.

Problems arise in the central part of the study area where Snowslip

member 5 and the Purcell Lava are both present. The top of Snowslip

member 5 and the base of the Purcell Lava are often separated by a

considerable thickness of rock, up to 65 feet at Granite Park. This

interval separating the top of member 5 and the base of the Purcell

clearly prevents the placement of the upper boundary of the Snowslip

Formation at the same stratigraphie level basinwide. This interval can

be interpreted as lacking a formation name because it rests above the

Snowslip Formation as defined by Childers (1963), but below the Purcell

Lava and Shepard Formation as defined by Willis (1902). On the other

hand, this interval could also be assigned to the Shepard Formation as

Winston (1984, 1986 a) discusses by projecting the Snowslip/Shepard

contact, as defined by Childers (1963), northward through Glacier

National Park and westward into the Whitefish Range. This

interpretation would lower the base of the Shepard Formation which

Willis (1902) defined as the top of the Purcell Lava. Thus, the Purcell

Lava would be enclosed by the Shepard Formation. I interpret the

interval above member 5 and below the Purcell Lava as Snowslip member 6.

Childers (1963) described the top of the Snowslip as the top of

m«nber 5 but in his measured section he placed the contact 24 feet above

m«nber 5 at the base of the lowest tan weathering, dolomicrite bed.

This 24 foot interval above member 5 and below the Shepard Formation is

Snowslip member 6 (Whipple and others, 1984). The dolomicrite bed which

marks the base of the Shepard Formation is 13 feet thick at Snowslip

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Mountain, contains molar tooth structures and a 30 centimeter thick bed

of hematitic, stromatolites. This dolomitic marker bed occurs at only

one other section in the study area, the U.S. Highway 2 roadcut. Here

it is approximately 15 feet thick and occurs 70 feet above member 5. I

believe Childers (1963) placed the contact at the base of the

dolomicrite bed simply to illustrate the sediroentologic changes that

occurred following the deposition of member 5. Childers clearly

intended the top of Snowslip member 5 to be the top of the Snowslip

Formation. It is unfortunate that Childers (1963) placed the top of the

Snowslip at different levels between his description and measured

section.

This discrepancy lead Whipple (1984), Whipple and others (1984) and

Whipple and Johnson (1988) to place the top of the Snowslip Formation

throughout the basin at the lowest tan weathering, dolomitic rocks of

the Shepard. Where the Purcell Lavas are present, the lowest tan

weathering rocks occur well above the uppermost flow. Thus, Whipple

(1984), Whipple and others (1984) and Whipple and Johnson (1988) enclose

the Purcell Lava within the Snowslip Formation. By elevating the top of

the Snowslip Formation well above the Purcell Lava, Whipple (1984),

Whipple and others (1984) and Whipple and Johnson (1988) clearly violate

the North American Stratigraphie Code (1983) by not adhering to the

definitions of both the Snowslip (Childers, 1963) and the Shepard

(Willis, 1902). Also, the stratigraphie level of the lowest tan

weathering beds of the Shepard Formation varies greatly throughout the

study area. At Snowslip Mountain the lowest dolomitic sediments, the

dolomicrite marker bed, occur just 24 feet above the top of Snowslip

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. member 5. At Paola Creek, 8.75 miles northwest of Snowslip Mountain,

the lowest dolomitic beds occur in the upper part of the Shepard

Formation and are 504 feet above member 5. Thus, if the top of the

Snowslip were placed at the lowest tan weathering dolomitic rocks of the

Shepard, the thickness of both the Snowslip and Shepard formations would

vary radically over short distances. I believe choosing such a highly

variable criterion for a formation boundary is unwise.

I place the upper boundary of the Snowslip Formation at the base of

the Purcell Lava where present, such as at Granite Park, Red Meadow

Creek and Bluebird Creek. This placement is in agreement with Bames

(1963) and Smith (1963) and preserves the original boundaries of the

Shepard as Willis (1902) defined them. To the south where the Purcell

Lava and dolomicrite marker bed are absent, such as at Paola Creek and

Hidden Lake, I place the top of the Snowslip Formation exactly where

Childers described it in 1963; at the top of Snowslip member 5. At

Snowslip Mountain and the U.S. Highway 2 roadcut I place the top of the

Snowslip Formation at the base of the lowest tan weathering, dolomitic

sediments of the Shepard Formation, This placement is also in accord

with Childers (1963).

Since the dolomicrite marker bed defining the top of the Snowslip

Formation, Childers (1963), occurs in only a small portion of the Belt

basin, the stratigraphie boundaries of the Snowslip should be redefined.

Where the Purcell Lava is absent, the top of Snowslip manber 5 as

defined by Whipple and others (1984) should represent the top of the

Snowslip Formation. This change would eliminate m«nber 6 as defined by

Whipple and others (1984) and would thin the overall Snowslip Formation

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. by a negligible amount. This change would also prevent Whipple (1984),

Whipple and others (1984) and Whipple and Johnson (1988) from placing

the top of the Snowslip at the lowest dolomitic sediments of the

Shepard. Where the Purcell Lava is present, the base of the lowermost

flow should mark the top of the Snowlsip. The interval separating

Snowslip member 5, if present, and the Purcell Lava would be Snowslip

member 6.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Generalised DspofitioMl

The following depositions! model, modified from Winston (1986 b,

d), serves well to interpret the depositional environment of the

Snowslip Formation. Alluvial aprons of tremendous areal extent flanked

the uplifted continent southwest of the Belt basin (Winston, 1986 b) and

sloped gently into the Belt "sea". A northwest trending depositional

axis during Missoula Group sedimentation resulted in pronounced

northwestward thinning and fining of the Snowslip Formation.

Figure 7 shows the generalized sediment type distribution in the

Missoula Group, but does not represent the distribution of sediment

types at any particular stratigraphie level. Sediment types

characteristically maintained regular positions relative to each other

throughout deposition of most of the Missoula Group (Winston, 1986 b).

Major transgressions and regressions of the Belt "sea" during Missoula

Group deposition resulted in four progradational sequences separated by

four transgressive sequences. The major progradational sequences

(Snowslip Formation, Mount Sheilds Formation member 2, Bonner Formation

and upper McNamara Formation) probably reflect periods of tectonic

uplift of the source area. More subtle oscillation of the sediment type

distribution basinward and sourceward throughout Snowslip deposition is

reflected in the members.

High on the alluvial aprons, the crossbedded sand sediment type was

deposited in braided flood channels. Channels exhibited low sinuosity,

were generally less than 1 meter deep and were floored by medium to

coarse grained bars and dunes. Trough and planar crossbeds in the bars

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. dftttsh Cotiimbia l4oho^ Montane

CHARACTERISTIC SEDIMENT TYPES làl'SJ Grovel. EZ) Crossbedded sand and discontinuous loyer. t £ l Corbonoceous voriety of the microlomina sediment type. i I Flot-lominoted sand and discontinuous loyer 1^1 Corbonote mud and calcareous E 3 Even couple. variety of the microlomina Coarse sand and introclost. sediment type.

I I Even couplet and lenliculor couplet

Figure 7. Hypothetical block diagram showing distribution of sediment types in the Missoula Group. From Winston 11986 b).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and dunes record lower flow regime deposition.

Further down the alluvial apron the broad flood channels responsible

for deposition of the crossbedded sand sediment type became unconfined,

shallow sheetfloods. These sheetfloods deposited the flat-laminated

sand sediment type. Shallow ponds commonly formed in broad depressions

over the flat-laminated sand. Wind generated waves produced abundant

oscillation ripples, and thin mud drapes settled from suspension. When

ponds evaporated, the mud drapes were intensely desiccation cracked and

the resulting mud polygons were commonly ripped up and incorporated as

mudchips in the next deposit.

Individual sheetfloods occasionally deposited a single fining-upward

sequence which has crossbedded sand at the base grading up to flat-

laminated sand and the discontinuous layer sediment type. Mud chips are

abundant along the base of fining-upward sequences and desiccation

cracks commonly cut the mud-rich upper portion.

Sheetfloods spread basinward beyond the toes of the alluvial apron,

where flat-laminated sand was deposited, and onto broad sandflats. Here

the thinner and finer grained flood deposits of the even couple sediment

type were deposited. Ponding was again common on these distal

sandflats and oscillation ripples are abundant. Desiccation cracks and

mudchips are ccximon.

The basinward progression from crossbedded channel sands to flat-

laminated sheetflood sands to distal sheetflood couples represents a

basinward fining and thinning sequence (Figure 8). The discontinuous

layer sediment type is locally interstratified with the flat-laminated

sand and even couple sediment types and it likely records waning

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 8. Diagramatic sediment type cross section of a single flood deposit from the proximal alluvial apron to the distal, submerged mudflats. From Winston (1986 b ) .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sheetflood conditions. Desiccation cracks and mudchips are common.

As the sheetfloods continued basinward from the sandflats, they

inundated the extensive, nearly level mudflats which bordered the Belt

"sea" and deposited the even couplet sediment type. As flood water

evaporated, the mud-rich portions of the couplets were desiccation

cracked. The resulting mudchips were then incorporated in the sandy

portion of the next flood deposit. The couplets deposited on these

exposed mudflats are commonly hematitic due to oxidation.

The sheetfloods that flowed beyond the exposed mudflats and into the

shallow water of the Belt "sea" also deposited even couplets. However,

these couplets were deposited by suspension settle out and contain more

clay than the couplets deposited on the exposed mudflats. Couplets

deposited here generally remained submerged. However, during periods of

extreme evaporation these distal mudflats became exposed. Desiccation

cracks are therefore sporadic but syneresis cracks are abundant locally.

Couplets deposited on these submerged mudflats are commonly chloritic.

It is here, on the submerged mudflats, that stromatolites were most

abundant.

Even couplets deposited on the submerged mudflats were commonly

reworked by wind generated waves producing wavy and lenticular couplets.

Even and lenticular couplets deposited under the shallow waters of the

Belt "sea" were occasionally reworked by storm generated waves and

currents. The silt and very fine grained sand was redeposited as the

tabular silt sediment type.

Small beaches of the coarse sand and intraclast sediment type formed

where the shallow water of the Belt "sea" met the adjacent mudflats.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Accreted grains such as ooliths and mudballs are ccmmon in these beach

deposits and were formed during repeated oscillation created by breaking

waves. The water level of the Belt "sea" was continuously fluctuating

and the beaches therefore migrated landward and basinward. For this

reason, the coarse sand and intraclast beach deposits are

interstratified with mudcracked even and lenticular couplets.

Further basinward from the mudflats, where even and lenticular

couplets were deposited, flood waters deposited only very small amounts

of silt and clay. Sediment settled from suspension to create the

microlamina sediment type.

Carbonate mud was occasionally incorporated into the clay-rich

portions of even and lenticular couplets and microlamina creating

calcareous varieties of those sediment types. However, homogenous

carbonate mud with no terrigeneous sediment incorporated, was deposited

in quiet, protected environments of the Belt "sea". These environments

do not necessarily reflect deeper water.

Based on the depositional model described above, each member of the

Snowslip Formation can be assigned to a specific depositional

environment. Snowslip members 1, 2, 4 and 6 throughout the study area

generally record deposition on distal sandflats, exposed mudflats and

submerged mudflats. Even couplets and lenticular couplets are the

dominant sediment types in these members. Frequent tabular silt beds

record storm reworking of the submerged mudflat sediments. Small

beaches and shoals, represented by the coarse sand and intraclast

sediment type, are common. Stromatolites were abundant on these

submerged mudflats. Occasional microlamina and rare beds of carbonate

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. mud indicate quieter water deposition basinward of the submerged

mudflats. Members 2, 4 and 6 contain abundant chlorite and syneresis

cracks and occasional desiccation cracks.

Snowslip members 3 and 5 represent the basinward progradation of the

alluvial aprons. Members 3 and 5 are characterized by the flat-

laminated sand, even couple and even couplet sediment types. Occasional

fining-upward sequences up to 1 meter thick in these members record

individual sheetfloods. Members 3 and 5 contain abundant hematite,

desiccation cracks and mudchips. The toes of these large alluvial

aprons grade basinward into the distal sandflat and mudflat environments

represented by members 1, 2 , 4 and 6. The entire Snowslip Formation at

Bluebird Creek in the northern Whitefish Range was deposited well

basinward of the alluvial aprons and records distal mudflat sedimentation.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Correlation of Informal Members

Introduction

The Snowslip Mountain section of the Snowslip Formation is divided

into six informal members defined by Whipple and others (1984). The

lower portion of the Granite Park section is covered leaving members 3

through 6 exposed. The Paola Creek and Hidden Lake sections contain

members 1 through 5. Limited exposure at the U.S. Highway 2 roadcut

reveals only the upper portion of member 5 and all of member 6. At Red

Meadow Chreek, only member 5 can be identified. None of the members are

identifiable at Bluebird Creek. The Purcell Lava is present at three of

the sections; Bluebird Creek, Red Meadow Creek and (Sranite Park.

North from the type section, the Snowslip Formation thins gradually

and all six members are present as far north as the International

Boundary at Hole-in-the-Wall (Whipple and Johnson, 1988). However,

northwest from the type section the Snowslip Formation thins more

rapidly and the ability to identify members is lost (Figure 9). Table 1

provides thicknesses of the Snowslip Formation throughout the study

area.

Tabic 1

Section location Thickness in feet

Snowslip Mountain 1672

Paola Creek Uncertain, base faulted

Hidden Lake 1495

Granite Park Uncertain, base not exposed

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54

Dominant Sediment Types

Flat-Laminated Sand

Coarse Sand and Intraclast

Tabular Silt

Even Couple, Even Couplet, Lenticular Couplet

Microlamina

Covered Section

Formation Boundaries

Correlation of Members

Figure 9. Key to stratigraphie correlation diagram.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. BLUEBIRD CREEK RED MEADOW CREEK GRANITE PARK HIDDEN LAKE U.S. HIGHWAY 2 PAOLA CREEK SNOWSLIP MOUNTAIN

Shepard Formation Shepard Formation Shepard Shepard Shepard Formation Purcell Lava Formation Formation

Covered

Helena Formation

Covered

Helena Formation

300

200 Helena ^ FEET Formation 100 Helena Formation

NORTHWEST

Fault Figure 9. Stratigraphie correlation of the Snowslip Formation 59 U.S. Highway 2 roadcut Uncertain, base not exposed

Hole-in-the-Wall 774 (Whipple and Johnson, 1988)

Red Meadow Creek 1210

Bluebird Creek 576

Members are identified and correlated on the basis of distinctive

suites of sediment types. Color is not used as a means of correlation

because color may be the result of diagenetic alteration of the original

mineralogy. However, color changes closely follow the changes in

sediment types.

Member 1

Member 1 thins northward from 330 feet at Snowslip Mountain to 210

feet at Hidden Lake and is 85 feet thick at Hole-in-the-Wall in the

extreme northern part of Glacier National Park (Whipple and Johnson,

1988). Member 1 thickness at Paola Creek is uncertain due to faulting.

Member 1 is not identifiable at Red Meadow Creek and Bluebird Creek and

is not exposed at Granite Park or the U.S. Highway 2 roadcut.

Beds of the coarse sand and intraclast sediment type, which

characterize member 1, are most abundant in the eastern part of the

study area at Snowslip Mountain and Hidden Lake. At Snowslip Mountain

occasional beds are up to 1 meter thick, such as at footages 204 and

310, but most are less than 30 centimeters thick. At Hidden Lake beds

range in thickness up to 60 centimeters, such as at footage 5. Coarse

sand and intraclast beds are more oolitic at these sections than

elsewhere in the study area. Coarse sand and intraclast beds become

thinner and fewer to the northwest. At Paola Creek beds reach a

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. maximum of 50 centimeters thick, such as at footage 556. At Red Meadow

Creek only a few discontinuous coarse sand and intraclast beds are

present at footages 82, 126 and 252, and none occur at Bluebird Creek.

The concentration of coarse sand and intraclast beds in the southeastern

part of the study area reflects abundant small beaches and shoals along

the eastern margin of Belt "sea”. Basinward, toward Red Meadow Creek

and Bluebird Creek, beach deposits quickly pass to chloritic, wavy

couplets and microlamina characteristic of submerged mudflat

environments. Hematitic couplets, common at Hidden Lake pass

northwestward to chloritic couplets and microlamina at Red Meadow Creek

and Bluebird Creek, also reflecting more basinward deposition. During

the deposition of member 1, the shoreline of the Belt "sea" is thus

interpreted to have trended approximately northeast and fluctuated at

least between Hidden Lake in the basinward direction and Snowslip

Mountain in the sourceward direction. Thin beds of flat-laminated sand

occur in member 1 at Paola Creek, footages 38 and 594, and record major

sheetfloods.

Member 2

Member 2, characterized by wavy couplets, thins northward but with

less regularity than other members. Thickest at Hidden Lake, 495 feet,

member 2 thins northward to 229 feet at Hole-in-the-Wall (Whipple and

Johnson, 1988). Member 2 at Snowslip Mountain is 392 feet thick and at

Paola Creek is 470 feet thick. Member 2 is not identifiable at Red

Meadow Creek and Bluebird Creek and is not exposed at (îranite Park or

the U.S. Highway 2 roadcut.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Even couples and occasional flat-laminated sand beds at Paola Creek,

footages 725, 752, 758, 878 and 930, thin northward to mostly centimeter

scale even couplets at Hidden Lake. Member 2 is not identifiable to the

northwest at Red Meadow Creek and Bluebird Creek, but some

sedimentologic trends are apparent. Centimeter scale even couplets

common at Paola Creek, Snowslip Mountain and Hidden Lake thin

northwestward to millimeter scale even couplets and microlamina at Red

Meadow Creek and Bluebird Creek. Tabular silt beds are common at all

locations but thin to the northwest. Coarse sand and intraclast beds

low in member 2 at Paola Creek, footages 668 and 686, are up to 40

centimeters thick and correlate with beds at Snowslip Mountain, footages

330 and 358 and Hidden Lake, footages 227 and 233. Beds of tabular silt

at Snowslip Mountain, footage 348, correlate to Paola Creek, footages

674 through 684. Stromatolite beds 30 to 40 centimeters thick can be

correlated between Snowslip Mountain, footages 488, 512, Paola Creek,

footages 859, 915 and Hidden Lake, footages 317, 345. One bed, 60

centimeters thick, of carbonate mud at Paola Creek, footage 915 records

a period of low terrigenous sediment input.

At the onset of member 2 deposition, the Belt "sea” is interpreted

to have transgressed over the distal mudflat and beach deposits of

member 1. The fluctuating shoreline of the Belt ”sea" again produced

abundant beach deposits in member 2. However, the abundance of

chloritic, wavy couplets, tabular silt beds and stromatolites in member

2 suggests the entire study remained submerged throughout much of member

2 deposition.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Manber 3

Member 3 thins northward from 328 feet at Paola Creek to 54 feet at

Hole-in-the-Wall (Whipple and Johnson, 1988). It is 146 feet thick at

Snowslip Mountain, 135 feet thick at Hidden Lake and thickens to 245

feet at Granite Park. Member 3 is not identifiable at Red Meadow Creek

or Bluebird Creek and is not exposed at the U.S. Highway 2 roadcut.

Member 3 is characterized by hematitic flat-laminated sand, even

couples and even couplets. In the southern portions of the study area

at Snowslip Mountain and Paola Creek, flat-laminated sand beds up to 30

centimeters thick dominate member 3. Flat-laminated sand beds record

sheetflood deposition on the distal portions of alluvial aprons. Beds

are generally medium grained and contain abundant mudchips and accreted

mudballs and are commonly overlain by a thin, desiccation cracked mud

drapes. Desiccation cracked even couples and couplets are

interstratified with the flat-laminated sands. Fining-upward sheetflood

sequences in the upper part of member 3 at Snowslip Mountain, footage

864, do not occur elsewhere in the study area. Flat-laminated sand beds

common in the southem sections pass northward, at Hidden Lake, Granite

Park and Hole-in-the-Wall (Whipple and Johnson, 1988), to even couples

and couplets interstratified with thin, flat-laminated sand beds

generally less than 20 centimeters thick. These sediment types

characterize exposed sandflat environments at the base of the alluvial

aprons. Flat-laminated sand beds are generally fine grained and contain

abundant mudchips and accreted mudballs. Even couples and couplets are

intensely desiccation cracked.

Following the Belt "sea" transgression recorded by member 2, large

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. alluvial aprons prograded basinward over the submerged mudflat sediments

of member 2 in response either to tectonic uplift in the source area or

major climatic changes.

Granite Park contains occasional beds of stromatolites up to 30

centimeters thick at footages 124, 142 and 215. Coarse sand and

intraclast beds occur at footages 46, 64, 96 and 142. Coarse sand and

intraclast beds are commonly oolitic and record the shoreline of the

Belt "sea” adjacent to the distal sandflats of the alluvial apron.

Thus, Granite Park marks the approximate northwestern limit of the

alluvial aprons responsible for the deposition of member 3. West and

northwest from Granite Park, the hematitic, flat-laminated sand, even

couple and even couplet sediment types that characterize m^nber 3 pass

into chloritic even and lenticular couplets at Red Meadow Creek and

Bluebird Creek. These sediments were deposited on submerged mudflats

basinward from the alluvial aprons. Oscillation ripples and occasional

desiccation cracks at approximately the same stratigraphie level as

member 3 at these sections record shallow water deposition and periodic

exposure.

Member 4

Member 4, where identifiable, varies relatively little in thickness.

It is approximately 260 feet thick at the northern and southern ends of

the study area at Snowslip Mountain, Paola Creek and Hole-in-the-Wall

(Whipple and Johnson, 1988). Member 4 thickens in central Glacier

National Park to 425 feet at Hidden Lake and 435 feet at Granite Park.

Member 4 is not identifiable at Red Meadow Creek or Bluebird Creek and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is not exposed at the U.S. Highway 2 roadcut.

Member 4 is characterized by beds of chloritic, wavy couplets,

tabular silt, coarse sand and intraclast and stromatolites. Couplets

are cut by syneresis and occasional desiccation cracks. Tabular silt

beds are abundant in member 4 and some beds can be correlated between

Snowslip Mountain, footages 930 and 938, and Paola Creek, footages 1508

to 1526. Coarse sand and intraclast beds can be correlated between

Snowslip Mountain, footage 872 and Granite Park, footage 270 and

between Snowslip Mountain, footage 942 and Paola Creek, footage 1528.

Stromatolites are common in member 4 except at Paola Creek, and can be

correlated from Snowslip Mountain, footage 900 to Hidden Lake, footage

887 to Granite Park, footage 274 and possibly to Red Meadow Creek,

footage 810. Member 4 becomes finer grained to the north, and beds of

centimeter scale, wavy couplets in the southern sections pass to

microlamina at Hidden Lake footages 915, 958, 1060, 1180, 1213, and

1259. Even and lenticular couplets at Hidden Lake and Granite Park are

occasionally interstratified with beds of the mud-rich discontinuous

layer sediment type. Two beds up to 1.5 meters thick of carbonate mud

with molar tooth structures occur near the middle of member 4 at Hidden

Lake.

Member 4 is not identifiable at Red Meadow Creek but the rocks

immediately below member 5 are dominantly millimeter scale, calcareous

even couplets and tabular silt beds up to 10 centimeters. At Bluebird

Creek, the rocks at approximately the same stratigraphie level as member

4 are dominantly calcareous, wavy couplets. Microlamina, footages 462

and 476, very thin tabular silt beds, and one bed of carbonate mud,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. footage 498, also occur at this level.

Honber 4 records the transgression of the Belt "sea" over the distal

alluvial apron sediments of member 3. Like member 2, the fluctuating

shoreline of the Belt "sea" produced abundant coarse sand and intraclast

beach deposits. The entire study area is interpreted to have been

inundated by the shallow Belt "sea" during most of member 4 deposition.

Member 5

Member 5 forms a northwestward tapering wedge (Figures 9 and 10).

Member 5 is thickest in the southern portion of the study area, 511 feet

thick at Snowslip Mountain and 444 feet thick at Paola Creek. Member 5

thins basinward to 230 feet at Hidden Lake, 180 feet at Granite Park and

132 feet at Red Meadow Creek. It is absent at Bluebird Creek and only

partially exposed at the U.S. Highway 2 roadcut.

Member 5 is characterized by hematitic flat-laminated sand, even

couples and even couplets. Member 5 is coarsest grained at Snowslip

Mountain and Paola Creek and is dominated by medium grained, flat-

laminated sand beds up to 50 centimeters thick. Monocrystilline quartz

is the most abundant grain type followed by K-feldspar and sedimentary

rock fragments. Oscillation ripples, mudchips, accreted mudballs and

cracked mud drapes are common. Desiccation cracked even couples and

couplets are interstratified with the flat-laminated sand beds. These

couples and couplets grade upward from fine sand to clay and contain

abundant mudchips. The flat-laminated sand beds thin and become finer

grained northward. At Hidden Lake, Granite Park, the U.S. Highway 2

roadcut and Red Meadow Creek, the flat-laminated sand beds are generally

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. r400

FEET -300

-200

-100 MILES

Bluebird Creek 131

Hole-in-the-Wal1

132 Red Meadow Creek Granite Park

lao

310

Huckleberry Ridge

4 4 4 511

Paola Creek

Snowslip Mountain

Figure 10. Fence diagram showing thickness of Snowslip member 5 throughout the study area. Hole-in-the-Wall and Huckleberry Ridge data from Whipple and Johnson (1988).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. fine grained, up to 30 centimeters thick and are commonly

interstratified with even couples and couplets. Oscillation ripples,

desiccation cracks, mudchips and accreted mudballs are common. Member 5

at Hole-in-the-Wall (Whipple and Johnson, 1988) is composed mostly of

flat-laminated sand beds up to 10 centimeters thick interstratified

with even couples and couplets. Fluid escape structures, raindrop

impressions and carbonate cement are abundant locally in m«nber 5

throughout the study area.

Member 5 also contains occasional fining-upward sheetflood

sequences. To the south, individual fining-upward sequences are up to 1

meter thick such as at Snowslip Mountain footage 1408, 1468 and 1620 and

at Paola Creek footages 2068 and 2110. At Red Meadow Creek, footages

1100, 1168 and 1182, Granite Park, footages 726 and 764, and the U.S.

Highway 2 roadcut, footages 92 and 146, fining-upward sequences are

considerably thinner, commonly incomplete and reach a maximum thickness

of approximately 50 centimeters. Those at Hidden Lake, footages 1284,

1450 and 1458 are up to 30 centimeters thick.

Member 5 is not identifiable at Bluebird Creek, but rocks

immediately below the Purcell Lava are at approximately the same

stratigraphie level. These rocks are entirely green and primarily very

thinly bedded tabular silts. Beds are up to 4 centimeters thick, wavy,

and are separated by micaceous parting planes. Pyrite is abundant

locally. Fining-upward sheetflood sequences are not present at

Bluebird Creek.

Like Member 3, member 5 records the progradation of alluvial aprons

basinward over the submerged mudflat sediments of member 4. Member 5

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. forms a well defined sand wedge similar to those of Mount Shields member

2 and the Bonner Formation. Unlike member 3 at Granite Park, member 5

lacks the coarse sand and intraclast beach deposits that developed where

the Belt "sea” met the distal sand and mudflats of the alluvial apron.

Beach deposits are probably present between the sandflat deposits of Red

Meadow Creek and the submerged mudflat deposits of Bluebird Creek.

Member 6

Member 6 is recognized at only three locations in the study area;

Snowslip Mountain, U.S. Highway 2 roadcut and Granite Park (Figures 6

and 9). However, the rocks immediately overlying member 5 at Paola

Creek and Hidden Lake are correlative with member 6 and are useful for

analyzing sedimentologic changes throughout the study area. Member 6 is

absent at Red Meadow Creek probably due to lack of deposition, and the

Purcell Lava directly overlies member 5. Member 6 cannot be identified

at Bluebird Creek because member 5 is not present.

Member 6 is 24 feet thick at Snowslip Mountain, 70 feet thick at the

U.S. Highway 2 roadcut, 65 feet thick at Granite Park and 14 feet thick

at Hole-in-the-Wall in northern Glacier National Park (Whipple and

Johnson, 1988). Differences in thickness reflect both sedimentologic

changes and the changing placement of the upper boundary of member 6.

Primarily green, member 6 is characterized by the even couplet, tabular

silt and coarse sand and intraclast sediment types. Even couplets are

commonly centimeter scale in the southern sections at Snowslip Mountain,

Paola Creek and the U.S. Highway 2 roadcut and thin to dominantly

millimeter scale couplets northward at Hidden Lake and Granite Park.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Couplets are commonly calcareous, wavy and contain abundant desiccation

and syneresis cracks and mudchips. Tabular silt beds rarely exceed 15

centimeters thick throughout the study area are frequently topped by

oscillation ripples. Beds of the coarse sand and intraclast sediment

type are abundant in member 6 and one bed can be correlated from

Snowslip Mountain, footage 1642, to the U.S. Highway 2 roadcut, footage

212, to Hidden Lake, footage 1500, to Granite Park, footages 902, and

possibly to Hole-in-the-Wall (Whipple and Johnson, 1988). Beds are

thickest at Snowslip Mountain and Granite Park, ranging up to 60

centimeters thick. Beds at other sections are less than 30 centimeters

thick. Coarse sand and intraclast beds are generally white to light

grayish green and grain size is medium to coarse. Mudchips are common

and quartz is the most abundant mineral followed by K-feldspar.

Carbonate cement is common at all sections. Pink, domal stromatolites

up to 30 centimeters thick can be correlated from the U.S. Highway 2

roadcut, footage 216, to Hidden Lake, footage 1511, to Granite Park,

footage 917 and possibly to Hole-in-the-Wall (Whipple and Johnson,

1988).

Member 6 records the third and final transgression of the Belt "sea"

during Snowslip sedimentation. The beach and submerged mudflat deposits

of member 6 migrated landward during the transgression over the

alluvial apron sediments of member 5. Member 5 sediments at Red Meadow

Creek probably represent a localized topographic high and remained

exposed during the early stages of this final transgression.

The pillowed basalts at the base of the Purcell Lava record its

emplacement into the shallow water of the Belt "sea". At Red Meadow

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Creek, the Purcell Lava directly overlies Snowslip member 5.

Transgression of the Belt "sea" continued through the deposition of the

Shepard Formation.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Sedimentologic Interpretations of the Snowslip Formation

Introduction

The Snowslip Formation is interpreted to have been deposited in a

broad, northwest trending basin (Winston, 1986 b), occupied during much

of its history by alluvial aprons that sloped basinward into the Belt

"sea". Within the confines of this study, it is not possible to

distinguish whether the Belt "sea" was part of an open Proterozoic ocean

or a landlocked, inland sea. The Snowslip Formation is a series of

alluvial apron deposits (members 3 and 5) separated by transgressive

sand and mudflat deposits (members 1, 2, 4 and 6).

Source Areas of the Snowslip Formation

During deposition of the Snowslip Formation, the Belt basin is

interpreted by Winston (1986 c) to have been bordered to the south by

the Archean Dillon block of the Wyoming Province (Figure 11). The

Dillon block was not a major sediment contributor to the Snowslip

Formation (Frost and Winston, 1987). A large upfilted terrane or

continent bearing Lower Proterozoic Sm/Nd age dates formed the western

border of the Belt basin (Frost and Winston, 1987). Prior to Snowslip

deposition, the northern portion of this inferred western continent had

subsided and was no longer a major sediment contributor (Winston, 1986

c; Frost and Winston, 1987). The southern portion of the western

continent however, experienced continued uplift and served as the

primary source terrane for the Snowslip Formation. Comparison of the

Snowslip Formation between Paola Creek and Snowslip Mountain suggests a

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. FfofAeod Lot!» 48»- CHARLO

block Greot font L u 8 OVANÛO Rogers Pass BLOCK M iS S O u iO L i r t l e 8 eM GARNET Moiiofams

H e le rw SAPPHIRE DEER 0 HELENA ( ALLOCHTMOH J Ï Tpen&end LODGE e m b a y m e n t block LINE D perr y T ViiRASSHOPPER PLATE DILLON BLOCK

D i i l o f t 100 rnttti

C H A ^ Q BLOCi OVANDO BLOCK :e r BLOCK

DILLON BLOCK

Figure 11. Diagram showing inferred Proterozoic structure of the Belt basin during Missoula Group deposition. From Winston (1986 c).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. subtle shift in dominant source areas during Snowslip deposition.

Members 1, 2 and 3 are thicker and slightly coarser grained at Paola

Creek, indicating a more southwesterly source terrane for these members.

Member k is virtually identical at both locations and records equal

sediment input from the south and southwest. Member 5 is thicker at

Snowslip Mountain and records the shift to a more southern source area.

The eastern margin of the Belt basin during Snowslip sedimentation was

tectonically stable and contributed the coarse, well rounded quartz

grains characteristic of the coarse sand and intraclast sediment type.

Coarse sand and intraclast beds are most abundant in the eastern portion

of the study area and decrease rapidly westward. These coarse quartz

grains were derived from the sedimentary veneer that is inferred to have

blanketed the craton east of the Belt basin (Winston, 1986 b).

Progradation of Members 3 and 5

Twice during Snowslip deposition large alluvial aprons prograded

northwestward far into the basin resulting in members 3 and 5. These

two episodes of dramatically increased grain size and sediment influx

may record rapid uplift in the southwestern source area or periods of

increased aridity. Slover and Winston (1986) attribute the large sand

wedge of Mount Shields member 2, similar to Snowslip member 5, to a

single major pulse of tectonic uplift in the source area. Similarly,

Whipple and Johnson (1988 p. 12) attribute Snowslip members 3 and 5 to a

period of "uplift in the source area, or increased basin subsidence, or

both."

Heward (1978) discusses the effects of climatic fluctuations on the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. progradation of alluvial fans. Periods of increased aridity would

result in the lowering of the Belt "sea” level and promote the hasinward

migration of the alluvial aprons. If the Belt "sea" were an

intracratonic lake as suggested by Winston (1986 b) and not open to the

Proterozoic ocean, periods of extreme evaporation would result in more

rapid and pronounced lowering of "sea" level. Within the scope of this

study, it is impossible to discern which factor, if not both, was

responsible for the progradation of the alluvial aprons which deposited

members 3 and 5. Snowslip members 1, 2, 4 and 6 record the relative

tectonic stability of the basin and the continental source terrane to

the southwest.

Marine Versus Lacustrine Controversy

Winston (1984, 1986 b) interprets the Belt "sea" as an intracratonic

lake. Whipple and Johnson (1988) interpret it as part of an open

Proterozoic ocean. Thorough treatments of this ongoing controversy are

given by Winston (1986 b, p. 114-119), Bames (1963, p. 52-55), Childers

(1960, p. 47-49), Smith (1963, p. 113-114) and Ross (1963 p. 98-99).

The following discussion focuses on several sedimentary structures

common to Snowslip sediments to exemplify the open marine versus

lacustrine controversy.

Desiccation cracked even couplets are abundant in the Snowslip

Formation. Their characteristic fining-upward layering is interpreted

by Whipple and Johnson (1988) as being tidal deposits. During periods

of low tide, the sediments were exposed and desiccated. Winston (1984,

1986 b) belives couplets represent distal sheetflood deposits and the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. mud layers settled from standing water as the Belt "sea" expanded in

response to flooding. This process is described by Hardie and others

(1978) from modern playa environments. According to Winston (1986 b),

when the shallow waters of the Belt "sea" receded by evaporation, the

mudflats were exposed and the couplets were cut by desiccation cracks.

Based on well documented basinward thinning and fining from flat-

laminated sand to even couples to even couplets, I agree with Winston

(1986 b) that even couplets represent distal sheetflood deposits.

However, it is not possible from this study to discern between mud

layers that settled from broad, shallow ponds and those that settled

from the Belt "sea" following rapid expansion.

Apparent bipolar crossbeds in the coarse sand and intraclast

sediment type is viewed by Whipple and Johnson (1988) as convincing

evidence of tidal deposition. Winston (1986 b) interprets these sand

beds as small beaches and shoals which formed along the eastern margin

of the Belt "sea". Tidal channel deposits are absent in the Snowslip

Formation and I therefore agree with Winston (1986 b) that the coarse

sand and intraclast sediment type represents small beaches and shoals

which were created by wind generated waves producing apparent bipolar

crossbeds.

In the northern Whitefish Range, the Snowslip Formation is composed

of chloritic even couplets, microlamina and thin tabular silt beds. The

hematitic, coarser grained sediments common elsewhere in the study area

are absent. Whipple and Johnson (1988 p. 19) feel the Snowslip in the

northern Whitefish Range "was deposited in deeper water than those

lithofacies of the Snowslip in Glacier National Park ... and these

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. faciès changes would also indicate that the paleoslope was down to the

northwest and west from the Park". I also believe that the basinward

direction was northwest from Glacier National Park. However, the

abundance of oscillation ripples, desiccation cracks and mudchips at

Bluebird Creek clearly record shallow water deposition and periodic

exposure. Therefore, I believe the Belt "sea" was very shallow,

probably no deeper than several meters, throughout the study area. This

very flat basin floor more closely resembles modem playa lakes than

open marine environments.

Although my interpretations of the Snowlsip Formation more closely

resemble the landlocked sea interpretation favored by Winston (1986 b),

this study does not conclusively resolve the marine versus lacustrine

controversy. It will in time be resolved through continued studies of

detailed, basinwide stratigraphy and increased knowledge of

sedimention.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Evaluation of Possible Thrusting Alone the Roosevelt and Nvack Faults

Introduction

Belt rocks in Glacier National Park form the upper

allochthonous plate of the Lewis thrust fault. The Lewis thrust fault

is a major, low angle, west dipping fault of Paleocene age that has

between 24 and 64 kilometers of northeast directed transport (Dahlstrom,

1970; Mudge, 1970, 1977; Price and Kluuver, 1974). The Whitefish and

Flathead ranges are structurally separated from Glacier National Park by

the northwest trending Flathead and Nyack fault systems (Figure 12).

Southward, the Flathead Fault splays into the Roosevelt and Blackball

faults. This series of listric normal faults cuts the upper plate of

the Lewis thrust fault, but exact geometries and amounts of displacement

are uncertain. Extensional forces responsible for normal faulting began

in the late Paleogene and have continued to the present (McMechan and

Price, 1980).

Whipple (personal communication, March 1987) believes the

extensional Flathead and Nyack fault systems may represent the Tertiary

reactivation of earlier Laramide thrust faults. This interpretation

could explain the anomalous sections of Rppekunny Formation in the

western portions of Glacier National Park. Only the uppermost member 5

of the Appekunny Formation is present in the western part of the Park.

The absence of members 1 through 4 may be explained by large scale

foreshortening by thrust faults, a major disconformity or a dramatic

facies change from east to west across Glacier National Park.

Possible foreshortening across the Roosevelt and Nyack faults was

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. BRITISH COLUMBIA ALBERTA INTERNATIONAL BOUNDARY

GLACIER NATIONAL PARK

Whitefish

Paola Creek .Snowslip Mountain

O Measured Sections

10 20 MILES

Figure 12. Generalized structure map.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. qualitatively evaluated by comparing two sections of the Snowslip

Formation located on opposite sides of the fault zone. The Snowslip

Mountain section in Glacier National Park lies east of the faults and

the Paola Creek section in the northern Flathead Range, 8.75 miles away,

lies west of the faults. If the Flathead and Nyack fault systems are

reactivated thrust faults, facies changes across the fault zone would be

compressed and accentuated. Thrusting between the two sections would be

expressed by major changes in sediment type distribution and in overall

formation thickness.

Comparison of Sections

Members 1 through 5 of the type Snowslip Formation are easily

correlated west across the faults to Paola Creek (Figure 9). The degree

of confidence of correlation between the two sections is very high as

individual beds, some less than 30 centimeters thick, are identifiable

at both locations, as discussed in chapter 7. Member 1 at Paola Creek

is cut by several faults of substantial displacement and must therefore

be ignored when comparing thickness. Member 6 is not recognized at

Paola Creek due to the lack of the dolomicrite marker bed defining the

top of member 6 at Snowslip Mountain (Figure 6). At Paola Creek the top

of the Snowslip Formation is placed at the top of member 5. Members 2

through 5 are 1318 feet thick at Snowslip Mountain and 1496 feet thick

at Paola Creek; a difference of 13.5 percent. However, the thickness

from the base of Snowslip member 2 to the base of the pervasive,

dolomitic sediments of the upper Shepard Formation is very similar at

both locations. This interval is 1932 feet thick at Snowslip Mountain

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and 2000 feet thick at Paola Creek; a difference of only 3.5 percent.

Member 1 at Paola Creek is at least 665 feet thick, more than double

the thickness of member 1 at Snowslip Mountain. Compared to Snowslip

Mountain, Paola Creek contains fewer coarse sand and intraclast beds,

fewer stromatolites and no microlamina. Even couples and thin beds of

flat-laminated sand occur at Paola Creek and not at Snowslip Mountain.

Even couplets at Paola Creek are generally slightly coarser grained,

containing more very fine sand. Based on increased thickness and these

sedimentologic changes, member 1 at Paola Creek appears to have been

deposited more sourceward than that of Snowslip Mountain.

M«nber 2 is 470 feet thick at Paola Creek and thins to 392 feet at

Snowslip Mountain. Individual beds of stromatolites, tabular silt and

coarse sand and intraclast are easily correlated between the two

sections. Unlike Snowslip Mountain, Paola Creek contains occasional

couples and beds of flat-laminated sand suggesting more sourceward

deposition.

Member 3 at Paola Creek is considerably thicker than at Snowslip

Mountain, 328 feet and 146 feet respectively. FI at-laminated sand beds,

characteristic of member 3, are slightly thicker at Paola Creek. The

most significant sedimentologic difference between the two sections is

the reduction of even couplets and increase in flat-laminated sand beds

at Paola Creek suggesting more sourceward deposition.

Member 4 differs in thickness by only 15 feet between the two

sections; 269 feet at Snowslip Mountain and 254 feet at Paola Creek. At

these two locations member 4 is virtually identical and beds of the

coarse sand and intraclast and tabular silt sediment types are easily

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. correlated. The only discernable difference is the occurance of

stromatolites and occasional even couples at Snowslip Mountain.

Member 5 thins from 511 feet at Snowslip Mountain to 444 feet at

Paola Creek. Beds of the flat-laminated sand sediment type, which

dominate member 5 at both locations, are slightly thicker at Snowslip

Mountain. Fining-upward sequences are also thicker at Snowslip

Mountain but connot be correlated to Paola Creek. Unlike Snowslip

Mountain, Paola Creek contins several stromatolite beds near the base of

the member. Member 5 at Paola Creek was deposited slightly basinward

from that of Snowslip Mountain based on overall thinning, thinning of

flat-laminated sand beds and thinning of fining-upward sequences.

Interpretations

Members 1, 2 and 3 at Paola Creek were deposited sourceward from

those of Snowslip Mountain. Member 4 is virtually identical at both

locations. Member 5 at Snowslip Mountain records more sourceward

deposition than that of Paola Creek. The thickness and sedimentologic

differences in the Snowslip members between Snowslip Mountain and Paola

Creek may represent the subtle shifting of dominant source areas

throughout Snowslip sedimentation. A southwestern source area appears

to have been dominant throughout the deposition of members 1, 2 and 3.

Member 4 records equal sediment input from both southwestern and

southern source areas. Member 5 records the shift to a dominantly

southern source area.

The facies changes exhibited between Snowslip Mountain and Paola

Creek are attributable to the spatial separation of the two sections

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (8.75 miles) and subtle shifting of the source area. It does not appear

that the two sections have been placed significantly closer together by

a thrust fault. Constenius (1981) interpreted the Flathead and NyacJc

fault systems to represent complex Tertiary listric normal faults

(Figure 13). According to Constenius (1981), these faults do not

represent reactivation of earlier thrust faults. They may however,

flatten with depth and merge with the Lewis thrust plane (Constenius,

1981; Dahlstrom, 1970). Constenius (1981) believes the Roosevelt and

Nyack faults which separate the Snowslip Mountain and Paola Creek

sections are responsible for as much as 5 kilometers of extension.

Another conclusion can be drawn from these data; the two measured

Snowslip sections may be located very near the end of the proposed

thrust fault where displacement approaches zero. The Snowslip Mountain

and Paola Creek sections are located near the southern limit of the

Flathead and Nyack fault system. Maximum slip along the fault is near

the center and approaches zero at the northern and southern ends

(Constenius, 1981). If the proposed thrust fault (Whipple, personal

communication, March 1987) occupied the same positions as the present

Flathead and Nyack faults, it is logical to assume that maximum thrust

displacement was also greatest in the center and approached zero near

the ends. Therefore, even if a thrust fault does separate Snowslip

Mountain and Paola Creek, displacement across the fault may be near

zero. In this situation, facies changes across the faults would be

subtle and not a good criterion for the recognition of tectonic

foreshortening. Measured sections near the center of the fault zone

(assumed maximum displacement along proposed thrust fault) would

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80

COMPRESSION COMPRESSION

lCWS TKHOST FAULT\ ) f g RAMP Of LEWIS Thrust' i 8ACKLMS Th r u s t FAULTS

INITIAL EXTENSION & ROTATION EXTENSION, ROTATION a SYNOROGENIC SEDIMENTATION FLATMEAO ROOSEVELT FAULT SYSTEM NYACK ___ \_ fault system

'REACTIVATED LEWIS THRUST SURFACE t

CONTINUED EXTENSION. ROTATION & SYNOROGENIC SEDIMENTATION

PRESENT EROSIONAL SURFACE

5 6

Figure 13. Schematic diagram showing tectonic history of Flathead and Nyack fault systems. From Constenius (1981)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. provide more definitive evidence.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Summary

The Snowslip Formation is the lowermost formation in the Missoula

Group of the Middle Proterozoic Belt Supergroup. It was deposited

roughly 1250 Ma and conformably overlies the Helena Formation in the

study area. Whipple and others (1984) divided the Snowslip Formation in

Glacier National Park into six informal members based on major

sedimentologic differences. The informal members are present in much of

the study area and are extremely useful in correlating and analyzing the

Snowslip Formation. The upper boundary of the Snowslip Formation is

placed at three positions throughout the study area; 1) the top of

member 5 (Childers, 1963), 2) the base of the Purcell Lava where present

(Bames, 1963; Smith, 1963) or 3) the lowest occurance of tan weathering

dolomitic rocks of the Shepard Formation (Childers, 1963; Whipple and

others, 1984). Where the Purcell Lavas are present in the northern

portions of the basin, I place the top of the Snowslip Formation at the

base of the lowermost flow. In the southern portions of the basin the

Purcell Lava is absent and the upper boundary of the Snowslip is placed

either at the top of member 5, or at the base of the dolomicrite marker

bed where present. The top of the Snowslip should be redefined and

placed at the base of the Purcell Lava where present or at the top of

m^nber 5 where the Purcell Lava is absent. Whipple and others (1984)

violate the North American Stratigraphie Code (1983) by inadequately

redefining the boundaries of the Snowslip Formation. They place the top

of the Snowslip Formation at the lowest tan weathering, dolomitic beds

of the Shepard and thus enclose the Purcell Lava within the Snowslip

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. F o m a t ion.

The Snowslip Formation was deposited into a broad, shallow,

northwest trending basin, occupied during much of its history by

alluvial aprons that sloped northward toward the Belt "sea". These

alluvial apron deposits are separated by transgressive sand and mudflat

deposits. The uplifted craton southwest of the Belt basin was the

primary source terrain for Snowslip sediments. 1672 feet thick at the

type locality on Snowslip Mountain, the Snowslip Formation thins

northwestward to 576 feet at Bluebird Creek.

Snowslip members 1, 2, 4 and 6 record deposition on distal sand and

mudflats bordering the Belt "sea". These members are dominated by the

even couplet sediment type. Even couplets that were deposited onto

submerged mudflats were commonly reworked into lenticular couplets and

tabular silt beds. Small beaches and shoals deposited the coarse sand

and intraclast sediment type.

Members 3 and 5 record the tectonically or climatically induced

progradation of large alluvial aprons far into the basin. Flat-

laminated sand beds and even couplets characterize members 3 and 5.

They also contain occasional fining-upward single sheetflood sequences

up to 1 meter thick. Crossbedded sand at the base of the sequence

grades upward to flat-laminated sand and the discontinuous layer

sediment type at the top. Snowslip member 5 exhibits more regular

basinward thinning and fining than member 3. Snowslip member 5 is

similar to the large sand wedges of the Mount Shields and Bonner

formations. Northwestward toward the basin center, the hematitic,

alluvial apron deposits of members 3 and 5 become thinner and finer

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. grained and grade into chloritic sand and mudflat deposits.

Glacier National Park is structurally separated from the northern

Flathead Range in part by the Roosevelt and Nyack faults. The

possibility of Laramide thrusting along these normal faults of Tertiary

age was qualitatively evaluated by comparing two sections of the

Snowslip Formation on opposite sides of the fault zone. The

sedimentologic differences across the fault zone are attributable to

minor shifts in the dominant source area and the spatial separation of

the two sections. The two sections do not appear to have been placed

closer together by a thrust fault.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. References

Anderson, D.W., and Picard, M.D., 1974, Evolution of synorogenic clastic deposits in the intermontane Uinta basin of Utah: Society of Economic Paleontologists and Mineralogists Special Publication 22, p. 167-189.

Bames, W.C., 1963, Geology of the northeast Whitefish Range, northwest Montana (Ph.D. dissertation): Princeton University, Princeton, New Jersey, 102 p.

Childers, M.O., 1960, Structure and stratigraphy of the southwest Marias Pass area, Flathead County, Montana: (Ph.D. dissertation): Princeton University, Princeton, New Jersey, 181 p.

Childers, M.O., 1963, Structure and stratigraphy of the southwest Marias Pass area, Flathead County, Montana: Geological Society of America Bulletin, v. 74, p. 141-164.

Constenius, K.S., 1981, Stratigraphy, sedimentation and tectonic history of the Kishenehn basin, northwestern Montana (M.S. thesis): University of Wyoming, Laramie, 116 p.

Dahlstrom, C.D.A., 1970, Structural geology in the eastern margin of the Canadian Rocky Mountains: Bulletin of Canadian Petroleum Geology, v. 18, p. 332-406.

Eby, D.E., 1977, Sedimentation and early diagenesis within eastern portions of the "Middle Belt Carbonate Interval" (Helena Formation), Belt Supergroup (Precambrian Y), western Montana (Ph.D. dissertation): State University of New York at Stony Brook, 712 p.

Eriksson, K.A., 1978, Alluvial and destructive beach facies from the Archean Moodies Group, Barberton Mountain Land, South Africa and Swaziland, in Fluvial Sedimentology, A.D. Miall, led.): Canadian Society of Petroleum Geologists Memoir 5, p. 287-311.

Frost, C.D. and Winston, D., 1987, Nd isotope systematics of coarse- and fine-grained sediments: examples frcan the Middle Proterozoic Belt - Purcell Supergroup: Journal of Geology, v. 95 p. 309-327.

Hardie, L.A., Smoot, J.P., and Eugster, H.P., 1978, Saline lakes and their deposits: A sedimentological approach, in Modern and Ancient Lake Sediments, A. Matter, and M. Tucker, (eds.): International Association of Sedimentologists, Special Publication 2, p. 7-41.

Harrison, J.E., 1984, Session on geochronology and geophysics, a summary, in The Belt; abstracts with summaries. Belt Symposium II, 1983 S.W. Hobbs, (ed.): Montana Bureau of Mines and Geology Special Publication 90, p. 98-100.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Harrison, J.E., and Jobin, D.A., 1963, Geology of the Clark Fork Quadrangle, Idaho-Montana: U.S. Geological Survey Bulletin 1141-K, 38 p.

Harrison, J.E., Griggs, A.B., and Wells, J.D., 1981, generalized geologic map of the Wallace 1* x 2® quadrangle, Montana and Idaho. U.S. Geological Survey Map MF-1354-A.

Heward, A.P., 1978, Alluvial fan sequences and megasequences: with examples frcan Westphalian D-Stephanian B coalfields, northern Spain, in Fluvial Sedimentology, A.D. Miall, (ed.); Canadian Society of Petroleum Geologists, Memoir 5, p. 669-702.

Lemoine, S.R., and Winston, D., 1986, Correlation of the Snowslip and Shepard Formations of the Cabinet Mountains with upper Wallace rocks of the Coeur d'Alene Mountains, western Montana, in Belt Supergroup - A guide to Proterozoic rocks of Western Montana and adjacent areas, and S. Roberts (ed.): Montana Bureau of Mines and (Seology Special Publications 94, p. 161-168.

Maxwell, D.T., 1973, Layer silicate mineralogy of the Precambrian Belt Series; Idaho Bureau of Mines and Geology, Belt Symposium, 1973, v. 2, p. 113-138.

McMechan, M.E., and Price, R.A., 1980, Reappraisal of a reported unconformity in the Paleogene (Oligocene) Kishenehn Formation: Implications for Cenozoic tectonics in the Flathead Valley graben, southeastern British Columbia: Bulletin of Canadian Petroleum Geology, v. 28, p. 37-45.

McMechan, M.E., Hoy, T., and Price, R.A., 1980, Van Creek and Nicol Creek Formations (new) - A revision of the stratigraphie nomenclature of the Middle Proterozoic Purcell Supergroup, southeastern British Columbia: Bulletin of Canadian Petroleum Geology, v. 28, p. 542-558.

Mudge, M.R., 1970, Origin of the disturbed belt in northwestern Montana: Geological Society of America Bulletin, v. 81, p. 377-392.

Mudge, M.R., 1977, General geology of Glacier National Park and adjacent areas, Montana: Bulletin of Canadian Petroleum Geology, v. 25, p. 739-751.

Mudge, M.R., Earhart, R.L., Whipple, J.W., and Harrison, J.E., 1982, Geologic and structure map of the Choteau 1® x 2® quadrangle, western Montana: U.S. Geological Survey Miscellaneous Investigations Map 1-1300.

North American Commission On Stratigraphie Nomenclature, 1983, North American Stratigraphie Code: American Association of Petroleum Geologists Bulletin, v. 67, p. 841-875.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Price, R.A., 1964, The Precambrian Purcell System in the Rocky Mountains and southern Alberta and British Columbia: Bulletin of Canadian Petroleum Geology, v. 12, p. 339-426.

Price, R.A., and Kluuver, H.M., 1974, Structure of the Rocky Mountains of the G1acier-Waterton Lakes National Park Area, from "Rock Mechanics: the American Northwest": International Society for Rock Mechanics, 3rd Congress Expedition Guide, Special Publication, College of Earth and Mineral Sciences. The Pennsylvania State University, University Park, PA. 16806.

Ross, C.P., 1963, The Belt Series in Montana: U. S. Geological Survey Professional Paper 346, I22p.

Rye, R.O., Whelan, J.F., Hayes, T.S., and Harrison, J.E., 1984, The origin of the copper-silver mineralization in the Ravalli Group as indicated by preliminary stable isotope studies (abs.), in The Belt; Abstracts with Summaries, Belt Symposium II, 1983, S.W. Hobbs, (ed.): Montana Bureau of Mines and Geology Special Publication 90, p. 104-107.

Schwartz, R.K., 1982, Bedform and stratification characteristics of some modern small-scale washover sand bodies: Sedimentology, v. 29, p. 835-849.

Slover, S.M. and Winston, D., 1986, Fining-upward sequences in Mount Shields members 1 and 2, central Belt basin, Montana, in Belt Supergroup: A guide to Proterozoic rocks of western Montana and adjacent areas, S. Roberts (ed.): Montana Bureau of Mines and Geology, Special Publication 94, p. 169-182.

Smith, A.G., 1963, Structure and stratigraphy of the northwest Whitefish Range, Lincoln County, Montana (Ph.D. dissertation): Princeton University, Princeton, New Jersey, 151 p.

Smith, N.D., 1970, The braided stream depositional environment: Comparison of the Platte River with some Silurian clastic rocks, north-central Appalachians: Geological Society of America Bulletin, V . 81, p. 2993-3014.

Smoot, J.P., 1983, Depositional subenvironments in an arid closed basin; the Wilkens Peak Member of the Green River Formation (Eocene), Wyoming, U.S.A.: Sedimentology, v. 30, p. 801-827.

Tunbridge, I.P., 1981, Sandy high-energy flood sedimentation - some criteria for recognition, with an example from the Devonian of S. W. England: Sedimentary Geology, v. 28, p. 79-95.

Wallace, C.A., and Lidke, D.J., 1980, Geologic map of the Rattlesnake Wilderness study area, Montana: U.S. Geological Survey Miscellaneous Field Studies Map MF-1235A. Scale 1:50,000.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Wallace, C.A., Schmidt, R.G., Waters, M.R., Lidke, D.J., and French, A.B., 1981, Preliminary geologic map of parts of the Butte 1 x 2 quadrangle, central Montana: U.S. Geological Survey Open-File Report 81-1013 Scale 1:250,000.

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 The Belt; Abstracts with summaries, Belt Symposium II, 1983 S.W. Hobbs (ed.): Montana Bureau of Mines and Geology Special Publications 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., Cdnnor, J.J., Raup, O.B., and McGrimsey, R.G., 1984, Preliminary report on the stratigraphy of the Belt Supergroup, Glacier National Park and adjacent Whitefish Range, Montana, in Northwest Montana and adjacent Canada, J.D. McBane and P.B. Garrison, (eds.): Montana Geological Society Guidebook, 1984 Field Conference and Symposium, p. 33-50.

Whipple, J.W. and Johnson, S.N., 1988, Stratigraphy and Lithocorrelation of the Snowslip Formation (Middle Proterozoic Belt Supergroup), Glacier National Park, Montana: U.S. Geological Survey Bulletin 1833, 30 p.

Willis, B., 1902, Stratigraphy and structure, Lewis and Livingston ranges, Montana: Geological Society of America Bulletin, v. 13, p. 305-352.

Winston, D. , 1973 a, The Bonner Formation (Precambrian Belt of Montana) as "a" braided stream sequence (abs.): American Association of Petroleum Geologists Bulletin, v. 57, no 4, p. 813.

Winston, D. , 1973 b. The Precambrian Missoula Group of Montana as a braided stream and sea-margin sequence, in Belt Symposium 1973: Department of Geology, University of Idaho and Idaho Bureau of Mines and Geology, v. 1, p. 208-220.

Winston, D., 1977, Alluvial fan, shallow water and sub-wave base deposits of the Belt Supergroup, Missoula, Montana, in Field Guide No, 5, 30th Annual Meeting, Rocky Mountain Section, Geological Society of America: Department of Geology, University of Montana, Missoula, p. 1-12.

Winston, D., 1978, Fluvial systems of the Precambrian Belt Supergroup, Montana and Idaho, U.S.A., in Fluvial Sedimentology, A.D. Miall, (ed.): Canadian Society of Petroleum Geologists Memoir 5, p. 343-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 359.

Winston, D., 1984, Sedimentology and stratigraphy of the Missoula Group (abs.), in The Belt: Abstracts with Summaries, Belt Symposium II, 1983, S.W. Hobbs, (ed.): Montana Bureau of Mines and Geology Special Publication 90, p. 30-32.

Winston, D., 1986 a, Stratigraphie correlation and nomenclature of the Middle Proterozoic Belt Supergroup, Montana, Idaho, and Washington, in Belt Supergroup: A guide to Proterozoic rocks of western Montana and adjacent areas, S. Roberts (ed.): Montana Bureau of Mines and Geology, Special Publication 94, p. 69-84.

Winston, D., 1986 b, Sedimentology of the Ravalli Group, middle Belt carbonate, and Missoula Group, Middle Proterozoic Belt Supergroup, Montana, Idaho and Washington, in Belt Supergroup: A guide to Proterozoic rocks of western Montana and adjacent areas, S. Roberts (ed.): Montana Bureau of Mines and Geology, Special Publication 94, p. 85-124.

Winston, D., 1986 c. Middle Proterozoic tectonics of the Belt basin, western Montana and northern Idaho, in Belt Supergroup: A guide to Proterozoic rocks of western Montana and adjacent areas, S. Roberts (ed.): Montana Bureau of Mines and Geology, Special Publication 94, p. 245-257.

Winston, D., 1986 d. Sedimentation and tectonics of the Middle Proterozoic Belt basin and their influence on Phanerozoic compression and extension in western Montana and northern Idaho, in Paleotectonics and Sedimentation in the Rocky Mountain Region, United States, J. Peterson (ed.): American Association of Petroleum Geologists Memoir 41, p. 87-118.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Appendix A

Measured Section Locations and Profiles

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Key to Measured Sections

SEDIMENT TYPES 70

Covered Section 60 Stromatolites

Carbonate Mud 50 -M Discontinuous Layer k Microlamina in (0 40 0) c: Coarse Sand and Intraclast "4 g Lenticular Couplet 30 Even Couplet, Even Couple (where noted)

Tabular Silt 20 Flat-Laminated Sand

Crossbedded Sand 10

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Snowslip Mountain Section

The Snowslip Mountain section is located in the extreme southern

portion of Glacier National Park. It is on the north-south ridge

joining Snowslip Mountain and Mount Shields. T. 29 N, R. 15 W,

southwest 1/4 of section 16 in the Essex, Montana 7.5' quadrangle.

Formation Thickness 1672'

Thickness of Member 6 = 24'

Member 5 511'

Member 4 269'

Member 3 146'

Member 2 392'

Member 1 330'

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Paola Creek Section

The Paola Creek section is in then northern Flathead Range. It is

on the northeast trending ridge (Tunnel Ridge) which lies to the

northwest of Paola Creek Road. The section lies in the central portion

of the Pinnacle, Montana 7.5’ quadrangle.

Formation Thickness = uncertain, base faulted

Member 6 is not recognized

Thickness of Member 5 - 444'

Member 4 = 254'

Member 3 = 328'

Member 2 = 392'

Member 1 = uncertain, base faulted

110

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~~153~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Granite Park Section~~

~~The Granite Park section is in the central part of Glacier National~~

~~Park. It is easily accessed by the Granite Park Trail which begins at~~

~~The Loop of the Going-to-the-Sun-Highway. The section is located north~~

~~of Granite Park on the Garden Wall. It is in the southeast portion of~~

~~the A h e m Pass, Montana 7.5' quadrangle.~~

~~Formation Thickness = uncertain, base not exposed~~

Thickness of Member 6 = 65*

Member 5 = 180*

Member 4 = 435*

Member 3 = 245*

~~Members 1 and 2 are not exposed~~

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~~The Red Meadow Creek section is in the east-central part of the~~

~~Whitefish Range. It lies 0.5 miles north of Red Meadow Creek road~~

~~approximately 9.5 miles west of the North Fork Road. The section is in~~

~~the central portion of the Red Meadow Lake, Montana 7.5' quadrangle.~~

~~Formation Thickness = 1210'~~

~~Member 6 is absent~~

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~~Members 1 through k are not identifiable~~

~~165~~

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~~177~~

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~~171~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bluebird Creek Section~~

~~The Bluebird Creek section is located in the northern Whitefish~~

~~Range in the Ten Lakes Scenic Area. It is easily accessed by Trail 83~~

~~which begins at the end of Road 319 (Grave Creek Road). The section is~~

~~on the east-west ridge which forms the northern edge of Bluebird Basin.~~

~~It is in the central portion of the Ksanka Peak, Montana 7.5'~~

~~quadrangle.~~

~~Formation Thickness * 576'~~

~~Members are not identifiable~~

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