I 

Stratigraphy of Mid-Cretaceous 

Blackleaf and Lower Part of the 

Frontier Formations in Parts of 

Beaverhead and Madison 

Counties, Montana 

U.S. GEOLOGICAL SURVEY BULLETIN 1773 

Stratigraphy of Mid-Cretaceous 

Blackleaf and Lower Part of the 

Frontier Formations in Parts of 

Beaverhead and Madison Counties, 

Montana 

By THADDEUS S. DYMAN and DOUGLAS J. NICHOLS 

Description of Albian and Cenomanian to Turonian Strata in 

8/acktai/, Snowcrest, Tendoy, and Gravelly Ranges, and Pioneer 

and McCartney Mountains, Southwest Montana 

U.S. GEOLOGICAL SURVEY BULLETIN 1773 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U. S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Dyman, T. S. 

Stratigraphy of Mid-Cretaceous Blackleaf and Lower Part of the Frontier Formations in Parts of Beaverhead and Madison Counties, Montana 

(U.S. Geological Survey bulletin ; 1773) 

Bibliography: p. 

Supt. of Docs. no.: 119.3:1773 

1. Geology, Stratigraphic-Cretaceous. 2. Blackleaf Formation (Mont.) 3. Frontier 

Formation. 4. Geology-Montana-Beaverhead County. 5. Geology-MontanaMadison County. I. Nichols, Douglas j. II. Title. Ill. Series 

QE75.B9 no. 1773 557.3 s 87-600054 

[QE687] [551.7' 7' 0978669] 
CONTENTS 

Abstract 1 

Introduction 1 

Stratigraphy 2 

Nomenclature 3 

Blackleaf Formation 6 

Lower clastic lithofacies (unit 1) 7 

Lower mudstone-shale lithofacies (unit 2) 12 

Upper clastic lithofacies (unit 3) 17 

Volcaniclastic lithofacies (unit 4) 20 

Frontier Formation 22 

Lower part, lower clastic lithofacies (unit 5) 22 

Summary 25 

References cited 25 

Appendix 31 

FIGURES 

1. Mountain ranges in parts of Beaverhead, Madison, and Gallatin Counties, 

southwestern Montana 2 

2. Boreholes that penetrate Cretaceous strata in parts of Beaverhead and 

Madison Counties, Montana, and adjacent northeastern Idaho 3 

3. Map of southwestern Montana and adjacent areas showing outcrops and 

sample localities of the Blackleaf and Frontier Formations 5 

4. Stratigraphic description of upper part of the Kootenai Formation, 

Blackleaf Formation, and the lower part of the Frontier Formation, 

Beaverhead and Madison Counties, Montana 6 

5. Stratigraphic nomenclature for strata of mid-Cretaceous age in 

southwestern Montana, northeastern Idaho, and central Wyoming 7 

6. Map showing total Blackleaf Formation thickness in part of southwestern 

Montana 10 

7. Flat-bedded, iron-stained unit 1 sandstone, Blackleaf Formation, McCartney Mountain I section 10 

8. Nodular mudstone bed in lower part of unit 1, Blackleaf Formation, 

McCartney Mountain I section 11 

9. A limestone conglomerate, unit 1, Blackleaf Formation, Lima Peaks 

section 12 

10. Map showing thicknesses of unit 1, Blackleaf Formation in parts of 

southwestern Montana 12 

11. External mold of Inoceramus comancheanus Cragin, unit 2, Blackleaf Formation, Monument Hill section, Gravelly Range 17 

12. Outcrop of black shale in gully, lower part of unit 2, Blackleaf Formation, 

Monument Hill section, Gravelly Range 17 

13. Map showing thicknesses of unit 2, Blackleaf Formation in parts of 

southwestern Montana 18 

14. Sandstone and interbedded yellow-brown mudstone near middle of unit 3, 

Blackleaf Formation, Apex section, Pioneer Mountains 18 

15. Conglomeratic bed near top of unit 3, Blackleaf Formation, McCartney 

Mountain II section 20 

Contents Ill 
16. Map showing thicknesses of unit 3, Blackleaf Formation in parts of southwestern 

Montana 21 

17. Color-variant beds with "popcorn" texture, unit 4, Blackleaf Formation, Lima 

Peaks section 22 

18. Map showing thicknesses of unit 4, Blackleaf Formation in parts of southwestern 

Montana 23 

19. Basal conglomerate beds, unit 5, Frontier Formation, Frying Pan Gulch section, Pioneer Mountains 24 

TABLES 

1. Description of boreholes that penetrate mid-Cretaceous rocks in Beaverhead 

County, Montana and northern Clark County, Idaho 4 

2. Generalized stratigraphic sequence for southwestern Montana 5 

3. Historical review of stratigraphic nomenclature for Cretaceous strata in parts 

of Beaverhead and Madison Counties, Montana 8 

4. Descriptions of molluscan fossils and associated strata in the Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 13 

5. Descriptions of palynomorphs and associated strata in the Blackleaf and lower 

Frontier Formations, Beaverhead and Madison Counties, Montana 14 

6. Descriptions of paleobotanical megafossils, Blackleaf and lower Frontier Formations, Beaverhead and Madison Counties, Montana 19 

IV Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
Stratigraphy of Mid-Cretaceous Blackleaf and Lower 

Part of the Frontier Formations in Parts of 

Beaverhead and Madison Counties, Montana 

By Thaddeus S. Dyman and Douglas J. Nichols 

Abstract 

The Albian Blackleaf Formation and the Cenomanian to 

Turonian lower part of the Frontier Formation in Madison and 

Beaverhead Counties, Montana, were deposited within or east 

of the southwestern Montana fold-and-thrust belt prior to 

thrusting, near the western depositional edge of the foreland 

basin. 

The Blackleaf Formation ranges from 425 to 600 m in 

thickness and is subdivided into four mappable lithofacies units: 

lower clastic (unit 1 ), lower mudstone-shale (unit 2), upper 

clastic (unit 3), and volcaniclastic (unit 4). Unit 1 conformably 

overlies the upper carbonate member (gastropod limestone) 

of the Lower Cretaceous Kootenai Formation. This basal unit 

ranges from 13 to 87 min thickness and consists of mudstone, 

quartz- and chert-rich sandstone, and limestone. Unit 2 ranges 

from 17 to 73 m in thickness and consists predominantly of 

thin-bedded mudstone, shale, and siltstone. Unit 3 ranges from 

4 to 76 m in thickness and consists of thin- to thick-bedded 

quartz-rich sandstone and interbedded mudstone. Unit 4 ranges 

from 270 to 378 m in thickness and consists of porcelanitic 

mudstone, shale, and subordinate lithic sandstone. The Albian 

Age for the Blackleaf Formation was determined from fossil 

bivalves and palynomorphs. 

The Blackleaf Formation is overlain by the Cenomanian 

to Turonian lower part of the Frontier Formation. The lower 

part of the Frontier, which attains a thickness of at least 300 

m is composed of lithic sandstone, conglomerate, and subordinate mudstone and shale. 

INTRODUCTION 

The depositional history of the Cretaceous foreland 

basin in western Montana is represented by a westward 

thickening sedimentary sequence that attains a maximum 

cumulative thickness of nearly 7,000 m near Drummond 

(Gwinn, 1960; 1965). This sequence of interbedded 

marine and nonmarine clastic and carbonate rocks reflects 

both Sevier- and Laramide-style tectonism along the 

western margin of the Cretaceous seaway. Because this 

sequence exhibits extensive lateral and vertical facies 

variations, it poses complex sedimentologic and stratigraphic problems. Few detailed studies of this sequence 

have been undertaken; in some areas of southwest Montana it has not even been adequately described. Furthermore, stratigraphic nomenclature in the region is 

confusing, and several names have been applied to the 

same rocks even within the same area. 

The Lower and lower Upper Cretaceous sequence 

in the Lima Peaks region and in parts of the Tendoy, 

Gravelly, and Snow crest Ranges (Beaverhead and 

Madison Counties, Montana), and Pioneer Mountains 

is unique (fig. 1). The sequence lies within or near the 

easternmost frontal thrust sheets of the southwest Montana fold-and-thrust belt, along the western depositional 

edge of the foreland basin. 

The sequence has been a source of interest to 

petroleum exploration companies. Borehole data in 

Madison and Beaverhead Counties are limited. As of 

December 1986, seven dry holes have penetrated the 

Cretaceous in southern Beaverhead County, Montana, 

and northern Clark County, Idaho (fig. 2; table 1). 

Seismic exploration parties have been active within the 

area. 

Mid-Cretaceous formations in Madison and 

Beaverhead Counties include the Aptian to Albian 

Kootenai Formation, the Albian Blackleaf Formation, 

both of Early Cretaceous age, and the Cenomanian to 

Turonian or Late Cretaceous lower part of the Frontier 

Formation. This sequence is underlain by clastic and carbonate rocks of the Jurassic Morrison Formation and 

Ellis Group and is overlain by synorogenic conglomerate, 

limestone, and sandstone of the Upper Cretaceous 

Beaverhead Group (table 2). 

The purpose of this report is to describe the 

Blackleaf and lower part of the Frontier Formations in 

parts of Beaverhead and Madison Counties, Montana, 

to establish lithostratigraphic subdivisions of these formations, and to describe their paleontologic and biostratigraphic characteristics and age relationships. 

The study area (figs. 2 and 3) includes the (1) Lima 

Peaks region south of Lima, near Sawmill and Little 

Sheep Creeks; (2) Snowcrest and Gravelly Ranges in 

eastern Beaverhead and southern Madison Counties; (3) 

Introduction 
PIONEER 

MOUNTAINS --

~/I I I \ \ \\\ \ \" 

Gras h q,' o·Il s op <i:-."'\J 1 on 'Per Creek o 

0 

0 10 

MONTANA 

Study 

10 20 30 MILES 

20 30 KILOMETERS 

Figure 1. Mountain ranges in parts of Beaverhead, Madison, and Gallatin Counties, southwestern Montana. 

Centennial Mountains along the border of Idaho and 

Montana; (4) northern Blacktail and eastern Pioneer 

Mountains north and south of Dillon; and (5) McCartney Mountain area north of Dillon, in southern Madison 

County. A list of measured sections and sample localities 

described in this study is given at the end of the report 

in the Appendix. The list includes codes, locations, and 

sources of information. 

The Blackleaf-Frontier contact was established for 

this report at the base of the first significant sandstone 

or shale bed above mudrocks of the upper Blackleaf 

Formation. The Blackleaf-Kootenai contact was 

established as being at the last appearance of gastropodrich limestone at the top of the Kootenai Formation. 

The study was undertaken originally to include only 

the Blackleaf Formation. However, strata suggested to 

belong to the Frontier Formation are included in order 

to establish an upper Blackleaf contact, to define tectonic 

controls during the mid-Cretaceous, and to determine 

variations in provenance between the Blackleaf and Frontier Formations. 

STRATIGRAPHY 

The Blackleaf and lower part of the Frontier Formations outcrop in narrow belts along the margins of 

present-day ranges in southwestern Montana (fig. 3). Outcrop quality varies from excellent to poor. The best exposed sections are located in the Pioneer and McCartney 

Mountains area; composite sections were measured south 

of Lima and in the Snowcrest Range (Antone Peak and 

2 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
113° 

45°,_----------------~.---------------------,---------------------------.-------------~~ 

30' \, I ! I 

Hagenbarth '( / 11 r' 

May Petroleum 1 MONTANA 

Amer;c;~ ~ua~ 1?-- l \ 0 Ennis I \; 

No. 1 M. I I Study 

Hagenbarth j I •,.::.:ar.=ea'---___ j 

I I 

0 Dillon I 1 

I I 

AMOCO 

A._ No. 1 McKnight 

I Canyon 

Dell 0 

I ~ 

L_~ I 1 I I I 

L---. ~~~ I ZIZ 

I ~~~ 

u u 010 .... , 

i 61~ 

I ~~~ 

Cli...J L--l ~~(§ ---------, I 

1 r, 

L / \, _A_ ------::-r-- ~West y Shell BEAVERHEAD \ 1 Yellowstone 

34X-13 COUNTY I <. o 

CENEX _A_ ( ) 

Lima 9-31 ~ 1 Cities Service fAmerican Quasar " ( ~ Lima No. 1 Emerick 29-1 " \ 04-

.--

AMOCO ...... , .,..........-1 r----..-- / '«/ , J-k 1 _ 

~ Peet Creek Fed. ) ~ ~ 

No. 1_Snowline 1 ~, .... ........_ __ ~,........... --....,"' ,..-··-"' - ~)'b"'l'«/ I 

Grazmg Fed. 1 ~ ._I \, I 

\ EXXON -~ 

;,.....-"-----..........._____ / No.1 Myers 

("" '- Federal I 

~-...... ? (') 

10 

10 20 

I 

20 30 MILES 

30 KILOMETERS 

I 

I 

I 

! I 

Figure 2. Boreholes that penetrate Cretaceous strata in parts of Beaverhead and Madison Counties, Montana, and adjacent 

northeastern Idaho. See table 1 for borehole descriptions and geologic data. 

Lima Peaks sections, Appendix) where rocks are poorly 

exposed. 

The Blackleaf and lower part of the Frontier Formations in the study area are composed of a predominantly clastic sequence of sandstone, siltstone, mudstone, 

and shale with much lateral and vertical variation. The 

formations are herein subdivided into five informal 

lithofacies units from bottom to top: (1) Blackleaf lower 

clastic (unit 1), (2) Blackleaf mudstone-shale (unit 2), (3) 

Blackleaf upper clastic (unit 3), (4) Blackleaf volcaniclastic (unit 4), and (5) Frontier lower clastic (unit 5). 

These lithofacies units are readily identifiable on the basis 

of field observations and can be traced throughout the 

study area (fig. 4). The lithofacies units will be referred 

to by number in the following paragraphs. 

Dyman (1985a) has provided graphic lithology logs, 

sample numbers and lithofacies identification, grain size, 

porosity, and paleocurrent direction for sections 

measured in this study. Data presented in the following 

pages summarize and update the detailed descriptions of 

Dyman and others (1984), and Dyman (1985b). 

NOMENCLATURE 

Table 3 summarizes stratigraphic names used within 

or near the study area. Many different names have been 

used and no consistent pattern of nomenclature has been 

established, in part because of local lithologic and facies 

changes and the long distance from type localities. The 

Nomenclature 3 
Table 1. Description of boreholes that penetrate mid-Cretaceous rocks in Beaverhead 

County, Montana and northern Clark County, Idaho (see fig. 2). 

Well name/location 

May Petroleum Co. 

No. 1 Margaret 

Hagen barth, 

C NE 1

/4 NW lf4 sec. 12, 

T. 5 S. , R. 8 W. , 

Beaverhead Co. 

American Quasar Co. 

27-22 Hagenbarth, 

penetratioit 

SW 1/4 SW lf4 sec. 27, 

T. 5 S., R. 9 W., 

Beaverhead Co. 

Shell Oil Co. 

34X-13 Unit, 

sW lf4 SE lf4 sec. 13, 

T. 13 S., R. 5 W., 

Beaverhead Co. 

CENEX 9-31 Lima 

SW 1f4 NE 1j4 SE sec. 31, 

T. 14 S. , R. 7 W. , 

Beaverhead Co. 

Cities Service Co. 

No. 1 Emerick, 

W 1

/

2 NW 1

/4 NE lf4 sec. 33, 

T. 1 4 S. , R. 7 W. , 

Beaverhead Co. 

Amoco Oil Co. 

No. 1 Snowline 

Grazing Fed. , 

NE 1/

4 sE 1/

4 sec. 10, 

T. 15 S • , R. 7 W. , 

Be ave rhe ad Co. 

Exxon Co. 

No. 1 Myers Federal 

Unit, 

SW lf4 NE lf4 sec. 14, 

T. 14 N., R. 35 E., 

Clark Co., Idaho 

American Quasar Co. 

29-1 Peet Creek 

Federal Unit, 

SW lf4 NE lf4 sec. 29, 

T. 14 S • , R. 4 W. , 

Be ave rhe ad Co. 

Amoco Oil Co. 

No. 1 McKnight Canyon 

Unit, 

SE 1f4 NW 1

/4 sec. 21, 

T. 12 S., R. lOW., 

Beaverhead Co. 

Total depth in meters 

(feet) and formation 

at total depth 

1,230 (4,039) 

3,672 ( 12,048) 

Precambrian. 

3,122 (10,244) 

Lodgepole Limestone, 

cored Quadrant, 

1 drill-stem test, 

no shows. 

4,790 (15,715) 

Blackleaf Formation. 

4,240 (13,909) 

Cretaceous. 

4,392 (14,410) 

Cretaceous. 

5,650 (18,540) 

Flathead Sandstone, 

drill-stem test in 

Madison Limestone, 

gas show. 

3' 711 (12' 17 7) 

Precambrian, 7 drillstem tests, no shows. 

Unknown 

Comments 

Penetrated part of the 

Blackleaf Formation. 

Possibly penetrated the 

Blackleaf Formation. 

Penetrated the Backleaf 

Formation. Possible 

faulting. 

Penetrated the top of the 

Blackleaf Formation at 

8,400 feet (2,560 m). 

Stratigraphic sequence 

probably faulted. 

Redrilled as CENEX 2-33 

Lima 

Penetrated the Blackleaf 

Formation. Stratigraphic 

sequence probably faulted. 

Penetrated the Blackleaf 

Formation. Stratigraphic 

sequence probably faulted. 

Penetrated the Blackleaf 

Formation. 

4 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
Table 2. Generalized stratigraphic sequence for southwestern Montana. 

[Thicknesses are averages for the region] 

Stratigraphic 

unit 

Undifferentiated 

Beaverhead Gp. 

Frontier Fm. 

Blackleaf Fm. 

Kootenai Fm. 

Morrison Fm. 

Swift Fm. 

Rierdon Fm. 

Thaynes Fm. 

Woodside Fm. 

Di nwo ody Fm. 

Phosphoria Fm. 

Quadrant Ss. 

Amsden Fm. 

Big Snowy Gp. 

Mission Canyon Ls. 

Lodgepole Ls. 

Three Forks Fm. 

Jefferson Fm. 

Kinnikinic Qtzite. 

Pilgrim Ls. 

Park Sh. 

Meagher Ls. 

Wolsey Sh. 

Flathead Ss. 

Average 

thickness 

of chronologie 

Chronologie units meters 

units (feet) 

Cenozoic (5000) 

Upper 3962 

Cretaceous (13000) 

Lower 610 

Cretaceous (2000) 

Jurassic 133 

(400) 

Triassic 360 

( 1200) 

Permian (800) 

Pennsylvanian 884 

(2900) 

1007 

Mississippian (3500) 

Devonian 274 

(900) 

Ordovician 350 

350 

(1000) 

Cambrian 

decision to apply the names Blackleaf and Frontier to 

Cretaceous strata in Madison and Beaverhead Counties, 

Montana, was made after reviewing the literature (table 

3) and carefully examining the area near Blackleaf Creek, 

Montana, the type area of the Frontier at Cumberland 

Gap, Wyoming, and additional outcrops. 

The Blackleaf Formation in the study area is similar 

to the Blackleaf Formation on Blackleaf Creek (Cobban 

and others, 1976) northwest of Great Falls. The term 

"Colorado Group" is not used in this study because it 

includes both Lower and Upper Cretaceous rocks. The 

stratigraphy of the Upper Cretaceous Frontier Formation has not been worked out in southwestern Montana, 

and facies relationships between the Frontier Formation 

and the Colorado Group in northwestern Montana are 

unknown. The terms "Mowry" and "Thermopolis" 

Shales are not used because they represent more marine 

facies to the east. "Aspen" Formation is a useful term 

but is generally used in conjunction with the underlying 

Bear River Formation to the south in Idaho. Lithofacies 

described in this study resemble the Blackleaf Formation 

in northwest Montana more than they resemble the Bear 

River Formation of eastern Idaho. Figure 5 summarizes 

Blackleaf-Frontier equivalents in the region. 

For northwest Montana Cobban and others (1959) 

named four members of the Blackleaf Formation, from 

bottom to top: Flood, Taft Hill, Vaughn, and Bootlegger. Because these members cannot be readily mapped 

in Madison and Beaverhead Counties, the names were 

not used. In the course of developing Blackleaf stratigraphy in southwestern Montana, Dyman (1985a, b, d) 

and Dyman and others (1984) developed preliminary 

names for Blackleaf lithofacies (for example, the lower 

113° 

46°f--

o Butte 

_-4 

~3 -1 

2 / 0 Dillon 

-6 

\5 

112° 

I 

111° 

1 

S1 

Bozeman o I 

-

45°r- 7--...___ -8 

~54 

MONTANA 

I\WoMING--

11- I 

s-----10 '"'- 1 

~ 0 Lima / '~ If 12 /S3 ~ I 

') 13~-- ..,----... __,.---../ __ ,., 01 

<., (-.... .....-J..-1 :::1 '- S7 ~ \.1 o I 

0 

0 

-I 

iiS5, S6 (off map) I 

50 KilOMETERS 

EXPlANATION 

Outcrop area of 

mid-Cretaceous 

formations 

1 4 Location of outcrop 

section 

S2 Location of sample 

section 

50 MilES 

Figure 3. Map of southwestern Montana and adjacent areas 

showing outcrops of the Blackleaf and Frontier Formations and 

the location of outcrop sections and sample localities (see 

Appendix). 

Nomenclature 5 
z 

0 

~ ~ 

a: 

~ Lower clastic 

lithofacies a: 

w 

i= 

z 

0 

a: 

Ll.. 

(unit 5) 

Lower 

mudstone 

shale 

lithofacies 

(unit 2) 

____ __, 

---- - -~ ---- ----

-----

=-i.~=:=l 

::~=~, -----

. · .. ·.·.:..····J -=--z-~ 

==<==~\ =-=--=~ 

-~----- -------

f~~-=f=~~El --------

------ ---~--· ------- ------- ------ --------

~-----­ -------

------ -------

-----

Volcanic and nonvolcanic sandstone, siltstone, mudstone and 

shale. Fluvial environments. 

Basal unconformity in 

Snowcrest and Gravelly 

Ranges and Lima Peaks 

area. 

Volcanic sandstone, mudstone, 

bentonite, porcelanite, and 

siltstone. Floodplain environments. 270-380 m thick. 

Quartz- and chert-rich sandstone. 

Fluvial to shallow marine 

environments. 4-96 m thick. 

Mudstone, shale, and minor 

siltstone and sandstone. Marine 

(east) and nonmarine (west) 

environments 17-70 m thick. 

Lower 

clastic 

lithofacies 

(unit 1) 

Sandstone, siltstone, mudstone, 

shale, and limestone. Nodular. ::;.~:..:;:.~::~:·:.~ Fluvial and marine environ- ::·::-.:.:·::::::':. 'l • • •• .. '\ ments. 13-87 m thick. ·~;~;~:;~~ 

-=---~--:..1... 

lif~--<(~------~~·-i·:·~:.@·=-§::~~-a:~:~~:·~)~~r:}~----------------~ I • • • • • ••• -•• 

~ Upper -:' 

1 

• ~ ~ • • ~Micritic and bioclastic limestone, 

u.. carbonate 1 • • • .a. sandstone, mudstone, and 

~ member ..L .1 • • l -J shale. Abundant fossil gastrow ~---.-~!. pods in upper part. 

I- ;::.~ .... :. :·:-:-·:·.-~ 0 -~·::_. ............ ·.·:·1 

~ ~---=--=---~ 

Figure 4. Stratigraphic description of the upper part of the 

Kootenai Formation, the Blackleaf Formation, and lower part 

of the Frontier Formation, Beaverhead and Madison Counties, 

Montana. 

clastic lithofacies of this report was first called the lower 

transitional clastic lithofacies). Formal member names are 

not used with the Blackleaf Formation in this report 

because much work remains to be completed before 

lithofacies relationships can be fully worked out. Additional measured sections must be described and the prethrust-faulting spatial relationships of sections in different 

areas must be established. The Blackleaf Formation may 

be raised to group rank within the next few years as the 

stratigraphy of the Lima to Drummond area becomes 

better known, and some of the informal lithofacies names 

used here may become formations within the group. 

Other lithofacies may assume member names now used 

in the Drummond area. 

The part of the Frontier Formation described in this 

study area is similar to the sandstone-rich lower Frontier 

(Veatch, 1907) near Kemmerer, Wyoming; whereas, the 

lower part of the Marias River Formation (Cobban and 

others, 1959) in northwest Montana that overlies the 

Blackleaf there contains more shale. 

BLACKLEAF FORMATION 

The Kootenai-Blackleaf contact is conformable and 

is defined in this study as the top of the last gastropodrich limestone of the upper carbonate member of the 

Kootenai Formation (fig. 4). Although probably 

diachronous, the contact is well defined in the field. 

Discontinuous beds of micritic limestone and mudstone, 

rich in limestone nodules, occur above this contact, but 

these units contain no gastropods. 

The Blackleaf-Frontier contact is conformable in 

the Pioneer and McCartney Mountains area but may be 

unconformable in the Snowcrest and Gravelly Ranges and 

in the Lima Peaks area. The top of the Blackleaf Formation is defined in this study at the base of the first thick 

sandstone, conglomerate, or dark-gray shale bed above 

the volcaniclastic lithofacies unit. The contact is best exposed in the Lima Peaks area where it is recognized by 

a sharp color change and lithologic break and by an erosional surface and a lag conglomerate. This contact is 

probably diachronous, and correlation was best made 

where palynologic data were available. 

Thickness data for the total Blackleaf Formation 

are available from four surface sections and one exploratory well in the study area (fig. 6). The Blackleaf 

Formation varies in outcrop thickness from a minimum 

of 425 m south of Lima to a maximum of 600 m north 

of Dillon. Subsurface data within the Lima anticline are 

difficult to interpret because of possible structural complications (W. J. Perry, Jr., oral commun., 1984). Comparable apparent thickness values for the Blackleaf are 

available from wells (1) American Quasar 29-1 Peet 

Creek Federal (490 m); (2) Shell Oil Company 34X-13 

6 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
NORTHWESTERN SOUTHWESTERN EASTERN SOUTHWESTERN CENTRAL MONTANA MONTANA IDAHO MONTANA WYOMING (GREAT FALLS) (THIS STUDY) (BOZEMAN) 

en 0 ::J 1- 0 

UJ zz u <(<( 

~ UJ zz Marias River Frontier Formation Frontier Formation Frontier Formation Frontier Formation <(0 a: 

u :2:cr:: Shale (part, unit 5) (part) (part) (part) 

a: o=> UJ zl- CL. w CL. 

::J u 

~ ~Member 

Bootlegger 

tJ ~ 'U '<---' 

Volcaniclastic 

~ 

c Vaughn ·~ c lithofacies Aspen Formation Mowry Shale Mowry Shale 0 0 ·.;:::; Member ·.;:::; (unit 4) ro ro 

z E E 

<( 0 0 Upper clastic Ci5 u.. u.. 

"' ..... Taft Hill Member ..... lithofacies (unit 3) Upper sandstone Muddy Sandstone en _J ro ro ] ::J <( Q) Q) en 0 32 32 Lower mudstone shale .!:2 Thermopolis UJ (.) (.) 

u ro ro Bear River g_ Middle shale ~ iii iii lithofacies (unit 2) Formation § Shale UJ Flood Member a: 

u Lower clastic ~ Lower sandstone Fall River Sandstone a: ? lithofacies (unit 1) 

3: 

g ~ 

? ~~?~L'/ZZ2 Gastropod limestone Z/;7~~~ ....._. ~ Smoot Shale ~ ~?J.f~ 

c. 

::I Draney Limestone z e 

<( Kootenai Kootenai ~ Kootenai Cloverly ii: t:: Bechler Conglomerate Formation Formation Q) Formation Formation <( c 

c 

I 

ro Peterson limestone ~ 

Ephraim Conglomerate 

Figure 5. Stratigraphic nomenclature for strata of mid-Cretaceous age in western Montana, northeastern Idaho, and central Wyoming. Data from Gwinn (1960), Roberts (1972), McGookey and others (1972), Schwartz (1972), Cobban and others (1976), and 

Vuke (1984). 

(580 m); and (3) CENEX 9-31 Lima (594 m) (fig. 2; table 

1). Dipmeter data corrections (W. J. Perry, Jr., oral commun., 1985) suggest a true thickness of 465 m for the 

Blackleaf in the Peet Creek Federal well, a value comparable to the Lima Peaks surface section (425 m). 

Thickness variations from the Shell Oil Company 34X-13 

borehole and the CENEX 9-31 Lima borehole are affected by steep dips and faulting (Perry and others, 1983, 

p. 734). The two dry holes near Dillon (May Petroleum 

No. 1 Margaret Hagenbarth and American Quasar 27-22 

Hagenbarth boreholes) did not penetrate all of the Lower 

Cretaceous sequence. 

Published thickness variations for the Blackleaf 

Formation are in part related to placement of the 

Blackleaf upper contact. Schwartz's (1972, 1983) 

Blackleaf Formation north of Dillon in the Pioneer 

Mountains (Apex section in this report; see Dyman, 

1985a) was measured as more than 1,200 m (3,800 ft) 

thick. The upper part of the same section in this present 

report was considered part of the Frontier Formation. 

Because of poor exposures and structural complications, a complete Blackleaf section could not be measured 

in the northern Snowcrest and Gravelly Ranges. The 

Ruby River section is faulted and does not represent a 

true Blackleaf thickness (Dyman, 1985a). 

Lower Clastic Lithofacies (Unit 1) 

Lithology and Thickness 

Lower clastic lithologies include quartz- and chertrich sandstone (quartzarenite, sublitharenite, and 

litharenite of Folk, 1968), siltstone, mudstone, and subordinate limestone, shale, and conglomerate. The sandstone 

is (1) generally gray or brown, (2) fine to medium grained, 

(3) thin to thick bedded, ( 4) very calcareous and iron 

stained, (5) commonly bioturbated, (6) horizontally 

laminated (fig. 7) to trough cross stratified, and (7) commonly ripple-laminated with well-developed symmetric 

ripples. 

Siltstone is found above unit 1 sandstone in fining 

upward sequences that reach a maximum thickness of 7 

m. The siltstone is gray to brown, finely laminated or 

Blackleaf Formation 7 
Table 3. Historical review of stratigraphic nomenclature for Cretaceous strata in parts of Madison and Beaverhead Counties, 

Montana. 

Author -and 

date of 

publication 

Klepper 

(1950). 

Myers ( 1952). 

Zi eg le r ( 19 54 ) • 

Scholten 

and others 

(1955). 

Mann (1954, 

1960). 

Lowell ( 1965). 

Roberts (1965, 

19 6 7, 19 72) • 

Hadley (1969, 

1980). 

Moran ( 1971 ). 

Unit 

name 

Frontier Formation 

Aspen Formation 

Bear River Formation 

Kootenai Formation 

unnamed units 

Kootenai Formation 

Thermopolis Formation 

Kootenai Formation 

Aspen Formation 

Kootenai Formation 

Colorado Formation 

Kootenai Formation 

Color ado Shale 

Frontier Formation 

Mowry Shale 

Thermopolis Shale 

Kootenai Formation 

Frontier Formation 

Thermopolis Shale 

Kootenai Formation 

Thermopolis Shale 

Type and location 

of study 

Reconnaissance 

in the Snowcrest 

Range. 

Mapping in the 

Pioneer Mountains. 

Mapping in the 

Snowcrest 

Mountains. 

Mapping, and interpretations of the 

Lima Peaks area. 

Mapping, and interpretations of the 

Snowcrest Range. 

Mapping near 

Dillon, Montana. 

Stratigraphy 

near Livingston, 

Montana. 

Mapping and interpretations in the 

northern Snowcrest 

Range. 

Mapping in the 

Centennial Range. 

8 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 

Comments 

Recognized each 

formation but 

mapped only 

Kootenai and 

overlying 

undifferentiated 

Upper Cretaceous 

strata. 

Mapped 4 unnamed 

units, one 

equivalent to 

Aspen Formation. 

Mapped 

undifferentiated 

Upper Cretaceous 

strata. 

Recognized 6 

informal units 

above the Kootenai 

Formation. 
Table 3. Continued 

Author and 

date of 

publication 

James ( 1977) 

Wi t kind ( 19 7 7 ) , 

Wi tkind and 

PrOS t k a ( 19 8 0) • 

Pete r s ( 19 7 0) 

Sharp ( 19 7 0) 

Schwa r t z ( 19 7 2 , 

1983). 

Skipp and 

others (1979). 

Sadler ( 1980) 

A chuf f ( 19 8 3) 

Perry and 

others (1983). 

Unit 

name 

Blackleaf Formation 

Kootenai Formation 

Thermopolis Shale 

Kootenai Formation 

Colorado Group 

undifferentiated 

Colorado Group 

undifferentiated 

Blackleaf Formation 

Kootenai Formation 

sandstone-claystone 

unit Kootenai 

Formation 

Colorado Shale 

Kootenai Formation 

Colorado Group 

Kootenai Formation 

Frontier Formation 

Blackleaf Formation 

Type and location 

of study 

Sedimen tal ogy, 

stratigraphy, 

regional study in 

southwest Montana. 

Mapping in the 

Centennial Range. 

Mapping in the 

lioneer Mountains. 

Mapping in the 

Pioneer Mountains. 

Stratigraphy, 

sedimentology, 

and regional study 

in southwest 

Montana. 

Mapping in the 

Lima Peaks area. 

Mapping in the 

Lima Peaks area. 

Mapping and 

structure in the 

Blacktail Range. 

Structure in the 

southern Tendoy 

Mountains. 

Comments 

Described 

transitional 

beds be tween 

the formations. 

Recognized a 

lower sands tone 

member and an 

upper shale 

member. 

Subdivided the 

Blackleaf 

Formation into 

4 formal lithofacies intervals. 

Sandstone-claystone 

unit equvalent 

to Aspen Formation 

of Scholten and 

others (1955). 

Recognized members 

of Blackleaf 

of Cobban and 

others ( 19 7 6) • 

Blackleaf Formation 9 
46,, 13r=_' _________ :-; , ,-=- 2' _________ _: ,,:_,, 

45' 

AP 

600 MM1 MM2 

(1968) • • 

• 

FP • 521 ODillon 

(1701 ) 

AN 

457 

(1499) 

• 

eLM 

•WS 

•MH I 

e CC I 

Peet Creek f <I 

Lima Federal r \\ ~ 0 465 ) \ ~I -¢- (1525) l ~I (!) 

~ ,/~'-- -"---- .-- ~ \, ;[I oz:;: 

~- ~LP I' 

I 425 ~ 

.) (1394) 01 ~ :z:l 

50 MILES ~, 

0 50 KILOMETERS 

44 ~---------~----------u_~ 

• LP 

425 

(1394) 

-<:>- 465 

(1525) 

EXPlANATION 

Location of outcrop section-Letters 

designate section name, number 

represents thickness of unit in 

m eters , m designates minim um 

thickness. Thi ckn ess in feet in 

parentheses 

Borehole- Number designates thickness 

of formation in meters. Thi ckn ess in 

feet in parentheses 

Figure 6. M ap showing thickness of the total Blackleaf Formation in part of southwestern Montana. See Appendix for names 

and locations of outcrop sections. Missing data values due to 

incomplete sections. 

structureless, and commonly bioturbated with variably 

oriented burrows. It commonly contains carbonaceous 

matter and wood fragments and is variably calcareous. 

Calcareous beds laterally grade into silty limestone. 

Mudstone and shale are gray to red or green and 

often silty. They are variably calcareous, commonly 

nodular, and iron stained. Shale is relatively rare; 

however, interbedded fossiliferous mudstone and black 

shale are found at the base of unit 1 at the Ruby River 

section. Finely disseminated carbonaceous matter is present in some mudstone and most shale beds. 

Subordinate gray limestone is micritic with welldeveloped laminations and algal(?) coatings. The limestone is generally silty and unfossiliferous and contains 

variable amounts of finely disseminated carbonaceous 

matter. Limestone beds are commonly nodular with 

nodules as much as 10 em in diameter. Nodules are 

micritic and iron stained; they make up more than 50 percent of some beds (fig. 8). Limestone beds attain a maximum thickness of 1.8 m. 

Conglomerate beds within unit 1 are uncommon; 

where present, they include basal-lag rip-up zones, and 

limestone-channel deposits that reach a maximum 

thickness of 1.5 m. Basal-lag deposits contain angular to 

subrounded mudstone, siltstone, and limestone rip-up 

clasts up to 2.5 em (rare) in diameter, and occur at the 

bases of discontinuous sandstone beds. Rip-up zones are 

less than 5 em thick and discontinuous. Limestonechannel deposits include clasts up to 10 em in diameter 

that vary from 60 to 100 percent micritic limestone 

(fig. 9). Subordinate lithologies include mudstone, 

siltstone, and chert. 

Unit 1 thicknesses range from 87 mat the McCartney Mountain and Apex sections north of Dillon to 13 

m in the Gravelly Range east of Dillon (fig. 10). There 

is a marked eastward thinning of the unit. 

Figure 7. Flatbedded, iron-stained lithofacies unit 1 sandstone 

Blackleaf Formation, McCartney Mountain I section . Pen approximately 10 em long. 

10 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
Figure 8. Nodular mudstone bed in lower part of lithofacies unit 1, Blackleaf Formation, McCartney Mountain I section. Lens cap approximately 6 em in diameter. 

Stratigraphic Relations, Age, and Correlation 

The basal Blackleaf contact is conformable in the 

study area but is considered unconformable for equivalent 

rocks in parts of northwest Montana (Cobban and others, 

1976; Mudge, 1972) and west-central Montana (Roberts, 

1972). James (1977) considered the contact conformable 

in southwest Montana although he identified local fluvial 

channel scours at the contact. 

The upper contact of unit 1 is established at the base 

of the first thick gray shale bed above the upper carbonate 

lithofacies of the Kootenai Formation (fig. 4). This contact is difficult to define in parts of the study area because 

unit 2 gray shale varies significantly in thickness, and unit 

1 also contains such beds. The contact in this study is 

established arbitrarily but does define a major change in 

lithostratigraphic and sedimentologic character. Poor exposures at the Lima Peaks and Antone Peak sections 

prevented easy recognition of the upper contact. 

Table 4 illustrates sample identification and location, genera and species, lithofacies, age determinations, 

and environments of deposition for 14 bivalve specimens 

from Blackleaf and Frontier samples. Three Inoceramus 

comancheanus Cragin molds (fig. 11) were found in the 

upper part of unit 1 at the Monument Hill section in the 

Gravelly Range. A similar Albian fauna was described 

by Cobban (1951) from the Skull Creek Shale and Fall 

River Sandstone in the Black Hills, and by Mudge (1972) 

from the Blackleaf Formation in Sun River Canyon. Cobban and others (1976) in part based an Albian Age for 

the Blackleaf Formation in northwestern Montana on the 

presence of the late Albian Inoceramus comancheanus 

Cragin Faunal Zone in the Flood Member. 

Table 5 presents sample identification and location, 

genera and species, lithofacies, age determinations, and 

proposed environment of deposition for palynomorph 

assemblages in the study area. An assemblage near the 

base of unit 1 (Lima Peaks section, uppermost Kootenai 

Formation) exclusively provides a late Albian age (sample LP-7A-1). This uppermost Kootenai sample includes 

the species Appendicisporites jansonii, which ranges into the upper (but not uppermost) Albian (Nichols and 

others, 1982) and provides a maximum age for the overlying Blackleaf Formation. 

Unit 1 is in part lithostratigraphically correlative 

with the lower sandstone of the Thermopolis Shale near 

Bozeman, and the Flood Member of the Blackleaf Formation near Great Falls, which Roberts (1972) and Rice 

(1976) correlated with the Fall River Sandstone. 

Sedimentologically, unit 1 sandstone is predominantly fluvial and deltaic, especially to the west in the 

Pioneer Mountains. 

Blackleaf Formation 11 
Figure 9. A limestone conglomerate, lithofacies unit 1, Blackleaf 

Formation, Li ma Peaks section. Looking south w ith lower part 

of channel on left. Lens cap approximately 6 em in diameter. 

lower Mudstone-Shale Lithofacies (Unit 2) 

lithology and Thickness 

Lower mudstone-shale lithologies include 

mudstone, shale, siltstone, and subordinate chert- and 

quartz-rich sandstone (quartzarenite, sublitharenite, and 

litharenite of Folk, 1968). The shale is gray to black, is 

moderately to strongly fissile, and contains finely 

disseminated carbonaceous matter, wood fragments, 

coal, and rare bivalve fragments. Bioturbation is common and burrows and trails are well developed. 

Calcareous nodules up to 5 em in diameter are abundant 

but limited to discrete intervals. Shale is variably 

calcareous and may be stained by hematite or limonite; 

it is usually interbedded with gray mudstone that is less 

bioturbated and contains less carbonaceous matter. 

Sandstone is fine to very fine grained, brown to 

gray and light blue, variably calcareous, and parallel 

laminated. The sandstone contains generally straightcrested symmetric ripples, the tops of which may be 

strongly bioturbated. 

Sandstone and siltstone at McCartney Mountain 

and in the Pioneer Mountains (Apex section) form the 

thickest unit 2 beds in the study area and may be up to 

5 m thick. Black shale is the dominant lithology in the 

Gravelly Range, where interbedded siltstone and sandstone are rare (fig. 12). 

Unit 2 thicknesses increase to the east and north 

(fig. 13). The high values in the McCartney Mountain and 

Frying Pan Gulch sections may reflect the transitional 

nature of the upper contact. 

The lower mudstone-shale lithofacies in the Lima 

Peaks area and central Snowcrest Range is poorly 

4601 112° 111" 13;.::._0 ________ _:_;..::.._ ________ -..:.;..:., 

MM1 

AP 87 

87 (285) MM2 (285) • • • 

FP • 

80 00illon 

(262) RR 

•BT 16 

GH• 10m .(52) 

24m (3 3) 

45° (79) WS• 

eLM 

15 

(49) 

AN • eMH 

18 CC• 13 

(59) (43) 

Lima ,-r\ !I 

) \ """I l \!) ---/~'-- -~---- -~ \ ::;: 1 ~0 r-----.JLP 1 G 

I 67 I >- .; (220) 0 :;: J:l 

0 

0 50 MILES ~I 

50 KILOMETERS 

« o L_ ________________ _L ________________ _u~ 

• MM1 

87 

(285) 

EXPLANATION 

Location of outcrop section-Letters 

desi gnate section name. number 

represents thickness of unit in 

meters, m designates minimum 

thickness. Thickn ess in feet in 

parentheses 

Figure 10. Thicknesses of lithofacies unit 1, Blackleaf Formation in parts of southwestern Montana. Missing data values due 

to incomplete sections. See Appendix for detailed section 

locations. 

12 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
Table4. Descriptions of molluscan fossils and associated strata in the Blackleaf and Frontier 

Formations, Beaverhead and Madison Counties, Montana. 

[See Dyman (1985b) for additional stratigraphic information. Fossils identified by W. A. Cobban, U.S. 

Geological Survey. Leaders, no information] 

Sample 

number and Name or 

locality (see description Range span Stratigraphic Depositional 

Appendix 1) of fossils of fossil unit environment 

LP-A-1, Small, poorly Unit 1, 

LP-A-2, preserved Blackleaf 

Lima Peaks bivalves, Formation 

section. unidentifiable (near top of 

unit) 

AP-166, Apex Tellina(?) Unit 5, Shallow marine 

section. Frontier to brackish(?) 

Formation 

RR-50, Ruby Pleurocardia Cenomanian Unit 5, Shallow marine, 

River section pauperculum and Frontier nearshore, 

(Meek). Turonian Formation sandy or silty 

environments. 

AN-2, Antone Unidentified Unit 1, Brackish(?). 

Peak section. molds of Blackleaf 

bivalves and Formation 

gastropods. 

MH-4, (USGS Ostrea late Albian Unit 3, Marine. 

Mesozoic anomioides Blackleaf 

locality Meek and an Formation 

012625), unidentified 

Monument thick -shelled 

Hill section. bivalve. 

MH-6, Inoceramus late Albian Unit 2, Marine. 

Monument comanchean us Blackleaf 

Hill section. Cragin. Formation 

WS-7, Warm Ostrea late Albian Unit 3, Marine. 

Springs anomioides 

Creek Meek. 

section. 

exposed. Lithology and electric logs from the Exxon 

Company No. 1 Myers Federal well southeast of Lima 

(fig. 2) suggest the presence of approximately 14 m of 

mudstone and shale in this interval. 

Stratigraphic Relations, Age, and Correlation 

The lower contact of unit 2 is established at the base 

of the first thick gray shale bed above the sandstone of 

unit 1. This contact is gradational with unit 1 and is difficult to define, particularly in the Pioneer Mountains, 

where unit 2 is thin. The upper contact is established at 

the base of the first thick sandstone bed (minimum 

Blackleaf 

Formation 

thickness 5 m) of the upper clastic lithofacies. The upper 

boundary is also difficult to establish in the Pioneer 

Mountains because of interbedded sandstone and shale; 

however, the number and thickness of shale beds decrease 

significantly in this interval. 

The lower boundary of unit 2 is also difficult to 

establish at the Warm Springs Creek and Ruby River sections. Here, unit 1 sandstone is rare, and dark-gray shale 

is the dominant lithology above the Kootenai Formation. 

A single Inoceramus comancheanus Cragin mold 

(fig. 11) was found near the top of unit 2 at the Monument Hill section in the Gravelly Range supporting a late 

Albian age for the unit at this locality. Unit 2 palynomorph assemblages at both the McCartney Mountain 

Blackleaf Formation 13 
Table 5. Palynomorphs in the Blackleaf and lower Frontier Formations, Beaverhead and 

Madison Counties, southwest Montana 

[See Dyman 1985a for additional stratigraphic information] 

Sample 

number and 

locality (see Genera and Range span 

Appendix 1) species of fossils 

LP-7A-1, Appendicisporites late Albian 

Lima Peaks jansonii 

section Cicatricosisporites 

(USGS spp. 

paleobotany Concavissimisporites 

locality variverrucatus 

D6586-A) Cyathidites minor 

Pityosporites sp. 

LP-64-1, Cicatricosisporites sp. midLima Peaks Cyathidites minor Cretaceous 

section Gleicheniidites 

(USGS senonicus 

paleobotany Laevigatosporites sp. 

locality Taxodiaceaepollenites 

D6586-B) hiatus 

LP-102-1, A raucariacites midLima Peaks australis Cretaceous 

section Cicatricosisporites sp. 

(USGS Cyathidites minor 

paleobotany Gleicheniidites 

locality senonicus 

D6586-C) Laevigatosporites sp. 

Pityosporites spp. 

Taxodiaceaepol/enites 

hiatus 

Tricolpites sp. 

LP-131-1, Appendicisporites sp. Cenomanian 

Lima Peaks Cicatricosisporites 

section spp. 

(USGS Cupuliferoidaepaleobotany pollenites sp. 

locality Cupuliferoipol/enites 

D6586-D) sp. 

Cyathidites minor 

Densoisporites sp. 

Foveotriletes sp. 

Laevigatosporites sp. 

Microreticulatisporites sp. 

Podocarpidites sp. 

Pseudoschizaea sp. 

Rugubivesiculites sp. 

Taxodiaceapol/enites 

hiatus 

Tricolpites sp. 

Triporoletes 

reticulatus 

Vitreisporites pallidus 

isoetalean 

microspores. 

Stratigraphic 

unit 

Uppermost 

Kootenai 

Formation 

(near base 

of unit 1) 

Unit 4, 

Blackleaf 

Formation 

Unit 4, 

Blackleaf 

Formation 

Unit 5, 

Frontier 

Formation 

14 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 

Depositional 

environment 

Nonmarine. 

Nonmarine. 

Nonmarine. 

Nonmarine 

aquatic. 
Table 5. Continued 

Sample 

number and 

locality (see Genera and Range span Stratigraphic Depositional 

Appendix 1) species of fossils unit environment 

SRC-5-1, Araucariacites Albian to Unit 5, Nonmarine. 

Antone australis Turonian Frontier 

Peak section Callialasporites sp. Formation 

(USGS Cicatricosisporites sp. 

paleobotany Corollina sp. 

locality CostatoperforoD6735) sporites foveolatus 

Cupuliferoidaepollenites sp. 

Cyathidites minor 

Foveotriletes sp. 

Gleicheniidites 

senonicus 

Laevigatosporites sp. 

Pityosporites sp. 

Rugubivesiculites sp. 

Taxodiaceaepollenites 

hiatus 

Vitreisporites pallidus 

MM-33-1, Appendicisporites sp. mid- Unit 2, Nonmarine. 

McCartney Corollina sp. Cretaceous Blackleaf 

Mountain Cyathidites minor Formation 

section Gleicheniidites 

(USGS senonicus 

paleobotany Stereisporites sp. 

locality Vitreisporites pallidus 

D6737) 

MH-8-1, Appendicisporites sp. Albian and Unit 2, Marine. 

Monument Cicatricosisporites sp. Cenomanian Blackleaf 

Hill section Corollina sp. Formation 

(USGS Cupuliferoidaepolpaleobotany lenites sp. 

locality Gleicheniidites 

D6738) senonicus 

Taxodiaceaepollenites 

hiatus 

Pityosporites sp. 

Vitreisporites pallidus 

dinoflagellate cysts, 

unidentified. 

RR-17-1, Cicatricosisporites sp. Albian to Unit 2, Nonmarine. 

Ruby River Costatoperforo- Turonian Blackleaf 

section sporites foveolatus Formation 

(USGS Cupuliferoidaepaleobotany pollenites sp. 

locality Cyathidites minor 

06739-A) Gleicheniidites 

senonicus 

Laevigatosporites sp. 

Lycopodiumsporite$ 

sp. 

Pityosporites sp. 

Taxodiaceaepollenites 

hiatus 

Vitreisporites pallidus 

Blackleaf Formation 15 
Table 5. Continued 

Sample 

number and 

locality (see 

Appendix 1) 

RR-46-1, 

Ruby River 

section 

(USGS 

paleobotany 

locality 

D6739-B) 

p 3736-54, 

Lima Peaks 

section 

(collected by 

W. J. Perry, 

Jr.; identified by 

A.D. 

Williams, 

written commun., 1982; 

confirmed 

by D. J. 

Nichols). 

p 3736-83, 

near Lima 

Peaks 

section, 

collected by 

w. J. 

Perry, Jr., 

from beds 

south of 

Sawmill 

Creek on 

north flank 

of Shine 

Hill, sec. 

17, T. 15 

S., R. 7 W.; 

identified by 

A. D. 

Williams, 

written commun., 1982; 

confirmed 

by D. J. 

Nichols; see 

also Nichols 

and others, 

1985, locality D6600) 

Genera and Range span 

species of fossils 

Arecipites? sp. Cenomanian 

Cupuliferoidaepo/-

lenites sp. 

Cyathidites minor 

Eucommiidites minor 

Laevigatosporites sp. 

Nyssapollenites 

albertensis 

Pityosporites spp. 

Rugubivesiculites sp. 

Vitreisporites pallidus 

Cicatricosisporites sp. Probably 

Liliacidites cf. Cenomanian 

peroreticulatus to Turonian 

Foraminisporis 

wonthaggiensis 

Ephedripites sp. 

Quadripollis krempii 

tricolpate pollen 

Michrystridium sp. 

Veryhachium sp. 

Eucommiidites minor Albian to 

Krauselisporites cf. Turonian 

linearis 

Echinatisporis 

varispinosus 

Foveosporites 

sub triangularis 

Cicatricosisporites sp. 

Quadripollis krempii 

Triporoletes sp. 

Corollina sp. 

Cyathidites sp. 

Pityosporites sp. 

Taxodiaceaepollenites 

hiatus 

Stratigraphic 

unit 

Unit 5, 

Frontier 

Formation 

Unit 5, 

Frontier 

Formation 

Unit 5, 

Frontier 

Formation 

16 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 

Depositional 

environment 

Nonmarine. 

Nonmarine or 

brackish. 

Nonmarine. 
(sample MM- 33-1) and Monument Hill sections (sample MH-8-1) were not adequate to provide detailed 

ages. 

Table 6 illustrates sample identification and location, genera and species, lithofacies, age determinations, 

and proposed environment of deposition for megaflora! 

specimens in the study area . Two specimens of Anemia 

jremonti Knowlton (sample AP-X-1) were found in unit 

2 at the Apex section in the Pioneer Mountains. Brown 

(1933) recognized Anemia jremonti Knowlton as common to both the Aspen and Frontier Formations in 

southwest Wyoming. 

The lower mudstone-shale lithofacies is in part 

lithostratigraphically correlative with the middle shale 

member of the Thermopolis Shale near Bozeman, and 

the upper shale unit of the Flood Member of the Blackleaf 

Formation near Great Falls. 

Unit 2 sandstone and siltstone may be marine, 

lagoonal, or deltaic in origin. Paleontologic data suggest 

a nonmarine environment of deposition in the west and 

a marine environment of deposition in the east. 

Figure 11. External mold of Inoceramus comancheanus 

Cragin, lithofacies unit 2, Blackleaf Formation, Monument 

Hill section, Gravelly Range. Pencil approximately 10 em 

long. 

Figure 12. Outcrop of black shale in gully, lower part of 

lithofacies unit 2 Blackleaf Formation, Monument Hill section , 

Gravelly Range. View is north. Photo approximately 6 m across 

at base. 

Upper Clastic Lithofacies (Unit 3) 

Lithology and Thickness 

Upper clastic lithologies include quartz- and chertrich sandstone (sublitharenite and litharenite of Folk, 

1968) and subordinate mudstone, siltstone, shale, and 

conglomerate. Sandstone is gray to yellow brown, fine 

to coarse grained, variably calcareous, and medium to 

thick bedded (fig. 14). It contains abundant carbonaceous 

matter and wood fragments and is ripple laminated, 

trough cross-stratified, or horizontally laminated. In the 

east (Warm Springs Creek and Monument Hill sections), 

unit 3 sandstone is locally fossiliferous and contains rare 

glauconite grains. 

Subordinate mudstone and shale are olive gray to 

dark gray, variably fissile, usually silty, weakly to moderately calcareous, bioturbated, and limonite stained. Carbonaceous matter and root structures are present in 

places. Dark-gray shale is locally present at the base of 

the unit. Mudstone beds up to 7 m thick occur in the 

Pioneer Mountains (Dyman, 1985b). 

Subordinate siltstone is interbedded with unit 3 

mudstone and shale or lies above unit 3 sandstone in 

fining-upward sequences. Siltstone is gray to brown, 

limonite stained, moderately calcareous, and commonly 

burrowed and bioturbated. Abundant carbonaceous matter and wood fragments are present. Siltstone in the lower 

part of unit 3 is rippled and occurs as thin (less than 5 

em) discontinuous beds. Individual fining upward cycles 

may exceed 10 m in thickness. 

Blackleaf Formation 17 
46. 113r _• ____ _____ ,11_2• _______ ___ 1,1_1·, 

I I 

45' f--

AP 

27 

(89) 

FP • 

49 

(161) 

• 

MM1 

70 

(230) 

• • MM2 

ODillon 

AN • 

33 

(108) 

Lima 0 

RR WS • 73 

• (240) 

•MH 

42 

(138) 

eLM 

I 

I 

~\ ~I ) \ ;z:l l 01 \.? 

"'- /~'-- --'-.._,- ------.....J \~I ~o (-------JLP I " ~ I 17 >- \/ (56) 01 ~ :tl 

I 

0 

I 

50 MILES 

I 

50 KILOMETERS 

~I I 

I 

44•'--_____ ___~l _____ _ _ti.L__j I 

EXPLANATION 

• LP Location of outcrop section-Letters 

1 7 designate section name, number 

(56) represents thickness of unit in 

m eters, m designates minimum 

thickness. Thickness in feet in 

parentheses 

Figure 13, Thi cknesses of lithofacies unit 2, Blackleaf Formation , in parts of southwestern Montana. Missing data values 

due to incomplete sections. See Append ix for detailed section 

locations. 

Unit 3 conglomerate is locally abundant and occurs 

within sandstone beds as both intraformational rip-ups 

and exotic clasts. Intraformational deposits include 

angular-to-subangular mudstone, porcelanitic mudstone, 

and shale clasts (fig, 15). Exotic clasts include rounded 

to subrounded chert, quartzite, and argillite. Clasts rna:; 

exceed 5 em in diameter. 

Unit 3 thickness data are presented in figure 16. 

Thicknesses range from a maximum of 76 m in the 

Pioneer Mountains (Apex section) to a minimum of 4 m 

at the Ruby River section in the Gravelly Range. The unit 

appears to thin eastward. The 36 m thickness at Frying 

Pan Gulch may be in part due to the gradational nature 

of the lower contact at that location. 

Subsurface thicknesses for unit 3 range from a maximum of 135 m (Exxon Co. No. 1 Myers Federal Unit) 

to a minimum of 90 m (American Quasar Co. 29-1 Peet 

Creek Federal Unit) (figs. 2, 16). The Myers-Federal Unit 

section is structurally thickened (Perry and others, 1983). 

Stratigraphic Relations, Age, and Correlation 

The lower contact of unit 3 is at the base of the first 

thick sandstone bed (minimum thickness 5 m) above the 

shale and mudstone beds of unit 2 (fig. 4). The lower contact is locally unconformable because of the fluvial nature 

of unit 3 sandstone; it may be difficult to establish 

because of gradational change in lithologies from unit 1 

to unit 2. 

The upper contact is placed at the base of the first 

thick shale or mudstone bed above unit 3 sandstone. The 

character of this contact varies within the study area. In 

the Pioneer Mountains (Apex section), a thick sequence 

of unit 4 olive-green to brown mudstone lies above the 

Figure 14. Sandstone and interbedded yellow-brown mudstone 

near middle of lithofacies unit 3, Blackleaf Formation, Apex 

section, Pioneer Mountains. Upsection is to the right. Photo 

approximately 3 m across at base. 

18 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
Table 6. Descriptions of paleobotanical megafossils, Blackleaf and lower Frontier Formations, Beaverhead and Madison Counties, southwest Montana. 

[Samples identified by C. J. Smoleu and W. Rember, University of Idaho, Moscow. See Dyman 1985a 

for additional stratigraphic information] 

Sample 

number and 

locality (see Genera and Range span Stratigraphic Depositional 

Appendix 1) species of fossils unit environment 

AP-X-1, "Anemia jremonti" Identified in Unit 2, Nonmarine. 

Apex Knowlton Frontier Blackleaf 

section. Formation Formation 

in 

Wyoming. 

LP-138, Lima "Vitis(?)" Identified in Unit 5, Nonmarine. 

Peaks ''Populites '' Frontier Frontier 

section. "Aralia veatchi" Formation Formation 

Knowlton in 

Wyoming. 

SRC-8, Small, unidentified Unit 5, Nonmarine. 

Antone dicot leaf, wood Frontier 

Peak and bark. Formation 

section. 

AN-C, Four Vitis, unidentified Unit 5, Nonmarine. 

miles west dicot leaf base. Frontier 

of Antone Formation 

Peak 

section, on 

Clover 

Divide. 

AP-181, Apex Tempskya sp. Albian or Unit 5, Nonmarine. 

section. Cenomanian Frontier 

(?). Formation 

LP-X-1, Lima Unidentified log Unit 5, Nonmarine. 

Peaks Frontier 

section. Formation 

LP-114, Lima Bone fragments and Unit 4, 

Peaks fish scales. Blackleaf 

section. Formation 

Observation Tempskya sp. Albian or Unit 4, Nonmarine. 

only (no Cenomanian Blackleaf 

sample). (?). Formation 

contact. In the Lima Peaks, Gravelly Range, and McCartney Mountain sections, gray mudstone is interbedded 

with dark-gray shale and subordinate sandstone. With 

the exception of local channeling at the base of sand 

bodies, this contact is considered conformable. West of 

the Boulder batholith Schwartz (1972) placed the upper 

contact of his interval C at the base of the stratigraphically lowest ''volcaniclastic'' bed. The method was not used 

for this study because a significant stratigraphic variation exists in the first appearance of volcanic detritus in 

unit 4 sandstone, and the volcanic lithic content of sandstone is difficult to determine in the field. 

Ostrea anomioides Meek was identified from both 

the Warm Springs Creek and Monument Hill sections in 

a coquina bed at the base of unit 3 (table 4). Mann (1954) 

found similar specimens at Warm Springs Creek, and 

Cobban and others (1976) identified 0. anomioides in the 

Taft Hill Member of the Blackleaf Formation near Great 

Falls. Cobban (in Hadley, 1980) identified additional 

specimens in the Varney quadrangle in the northern 

Blackleaf Formation 19 
Figure 15. Conglomeratic bed near top of lithofacies unit 3, Blackleaf Formation, McCartney Mountain II section. Angular-tosubrounded mudstone clasts, imbricated. Pen approximately 10 em long. 

Gravelly Range. Ostrea anomioides is a marine bivalve 

of late Albian age (W. A. Cobban, oral commun., 1985). 

Neither palynomorphs or megaflora! specimens were 

found in unit 3. 

The upper clastic lithofacies is in part lithostratigraphically correlative with the upper sandstone member 

of the Thermopolis Shale near Bozeman, the upper sandstone unit of the Taft Hill Member of the Blackleaf Formation near Great Falls, and the Muddy Sandstone in 

Wyoming. 

Unit 3 sandstone is fluvial, especially to the west 

in the Pioneer Mountains. However, the presence of a 

brackish water to marine bivalve coquina bed and rare 

glauconite grains at the base of unit 3 in the Grave!Jy 

Range suggest some marine to shoreface influence 

(table 4). 

Volcaniclastic Lithofacies (Unit 4) 

lithology and Thickness 

Unit 4 is the thickest and most heterogeneous lithofacies unit in the study area; it marks the first significant 

influx of volcanic detritus during Blackleaf deposition. 

Unit 4 lithologies include mudstone, porcelanitic 

mudstone, siltstone, volcanic-rich sandstone (litharenite, 

lithic arkose, and feldspathic litharenite of Folk, 1968), 

tuff(?), limestone, and conglomerate (fig. 4). Mudstone 

is the dominant lithology. Lower unit 4 mudstone is 

generally olive green to gray, variably calcareous, weakly fissile, and structureless. Fossils are rare. 

Porcelanitic mudstone is abundant in the middle 

and upper parts of unit 4, but uncommon in the lower 

part. Porcelanitic mudstone is highly variable in color 

with shades of red, gray, and green being dominant; it 

is in part hard and dense, weakly to strongly calcareous, 

and locally bentonitic. Bentonitic beds exhibit welldeveloped "popcorn texture" on exposed slopes (fig. 17). 

Mudstone may contain intraformational mud rip-ups and 

contorted bedding. Strongly calcareous nonporcelanitic 

mudstone laterally grades into micritic limestone. Ovularshaped lithophysae (accretionary lapilli) up to 3 mm in 

diameter (Ross and Smith, 1961, p. 27) are abundant 

locally in tuffaceous(?) unit 4 mudstone beds in the 

Pioneer Mountains. Lithophysae were observed by 

Schwartz (1972) in equivalent beds, and by Wanless and 

others (1955) at the Willow Creek section near Alpine, 

Wyoming, in the upper part of the Aspen Formation. 

20 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
Locally, upper unit 4 porcelanitic mudstone is very finely laminated with individual laminations less than 1 mm 

thick. 

Unit 4 siltstone occurs as thin, discontinuous beds 

within unit 4 mudstone and above sandstone beds in 

discontinuous lenticular bodies. The siltsone is commonly 

tan or gray, rippled, micaceous, bioturbated, and variably 

calcareous. Pyrite crystals up to 1 em in diameter are 

locally present. 

Unit 4 sandstone is highly variable in color but is 

most commonly red or brown to gray. The sandstone is 

thin to medium bedded, generally fine grained, lithic-rich 

in the middle and upper part of the unit, variably 

calcareous, and hematite stained. Sandstone is subordinate to mudstone at all localities, especially in the 

Pioneer Mountains (Apex section), where the sand to 

shale ratio is 1 :6. Sandstone is most commonly ripple 

laminated or flat bedded. Unit 4 conglomerate occurs as 

quartzite- and chert-pebble channel fills and as rounded 

to angular mudstone, shale, siltstone, and chert-pebble 

lag deposits. 

Unit 4 thickness data are illustrated in figure 18. 

Data are sparse, and structural complications due to 

faulting exist at the Ruby River section. Thicknesses range 

from a maximum of 378 m in the Snowcrest Range 

(Antone Peak section) to a minimum of 271 m at the 

Lima Peaks section. Subsurface data near the Lima Peaks 

section vary in quality. Unit 4 is 270 m thick in the 

American Quasar 29-1 Peet Creek Federal well; however, 

a thickness of more than 600 mat the Exxon Co. No. 

1 Myers Federal Unit is considered suspect and may be 

due to faulting or folding. Total unit 4 thicknesses are 

not available for other sections in the study area due to 

surface cover or erosion. 

Stratigraphic Relations, Age, and Correlation 

The lower contact of unit 4 is established at the base 

of the first thick mudstone and shale bed (minimum 

thickness 10m) above unit 3 sandstone (fig. 4). The contact is considered conformable and is readily identifiable 

in the field. 

In the Pioneer Mountains the upper contact is 

established at the first thick sandstone or conglomerate 

bed of the lower clastic lithofacies of the Frontier Formation. In the Lima Peaks area, however, the upper contact may be unconformable because of a sharp color and 

lithologic change, the presence of lag gravels above the 

contact, and palynologic, petrographic, and vitrinite data 

(Dyman, 1985c). 

Sharp color and lithologic changes were also 

observed in the Snowcrest and Gravelly Ranges (Ruby 

River, Warm Springs Creek, and Antone Peak sections) 

within the same stratigraphic interval. The upper contact 

of unit 4 at Frying Pan Gulch is defined as at the base 

of a distinctive conglomerate bed 350 m above the base 

of the unit (fig. 19). This bed can be traced for more than 

a kilometer north of the measured section. Other conglomerate and sandstone beds occur within unit 4 at the 

Frying Pan Gulch, McCartney Mountain, and Apex sections, but they are laterally discontinuous (less than 50 

m in length) and are thin (less than 2 m thick). The upper unit 4 contact at the Apex section is less dramatic but 

occurs at the base of a similar conglomeratic sandstone 

bed. 

Two palynomorph assemblages from the Lima 

Peaks section (samples LP-64-1 and LP-102-1) indicate 

a mid-Cretaceous age for unit 4 at this locality (table 5). 

460 11~3_0 

_________ 1--,12_0 _________ 1,1-----,1° 

I I 

45° 1---

AP 

76 

(249) 

FP • 

• 

MM1 

11m 

(36) MM2 

• • 

36 ooillon 

(118) RR 

4 

• (13) 

eLM 

ws• 15 r--

(49) 

AN • •MH I 

28 12 I 

CC• (39) I 

Lima (

91

) t9

9

5) ,r\ ~ o ,.J \ zl 

-¢: l 01 '-' 

,....--< .... \ ---~....---..._) ' ~I z r---/J Peet Creek 'I :E ~ I LP Federal ~ 

\.~ 70 90 o I ~ 

(230)0 I(295) ~II 5

1

0 MILES 

lr--------,1--_j 

0 50 KILOMETERS 

I 

I 

44oL___ ______ ....J.._I ______ ___JIL..L..I___J 

EXPlANATION 

• LP Location of outcrop section-Letters 

70 designate section name, number 

(230) represents thickness of unit in 

meters, m designates minimum 

thickness. Thickness in feet in 

parentheses 

90 

(295) 

Borehole-Number designates thickness 

of formation in meters. Thickness in 

feet in parentheses 

Figure 16. Thicknesses of lithofacies unit 3, Blackleaf Formation in parts of southwestern Montana. Missing data values due 

to incomplete sections. See Appendix for detailed section locations. 

Blackleaf Formation 21 
Figure 17. Mudstone beds with " popcorn" texture (left), lithofacies unit 4, Blackleaf Formation, Lima Peaks section. Photo approximately 10 m across at base. 

An additional assemblage from the Ruby River section 

(sample RR-17-1) was limited in useful specimens and 

a more detailed age date is not available. A single 

specimen of Tempskya sp. was identified from unit 4 at 

the Lima Peaks section (table 6). Read and Ash (1961) 

recognized Tempskya only from the Albian of the 

Western United States, but C. 1. Smiley (oral commun., 

1985) indicated that it may in fact extend into the 

Cenomanian. 

The volcaniclastic lithofacies is in part lithostratigraphically correlative with the Mowry Shale in central 

Montana and Wyoming, the Vaughn Member of the 

Blackleaf Formation near Great Falls, and the Aspen 

Formation of western Wyoming and southeastern 

Idaho. 

Unit 4 was probably deposited on a broad floodplain. Fluvial channels are present but are relatively small. 

Periodic flooding resulted in the deposition of dark-gray 

mudstone. Finely laminated porcelanitic mudstone may 

have been deposited in low-energy lacustrine or lagoonal 

settings. Periodically, influx of volcanic detritus from 

nearby sources resulted in the deposition of bentonite and 

tuffaceous sediments. 

FRONTIER FORMATION 

lower Part, lower Clastic Lithofacies (Unit 5) 

Lithology and Thickness 

Unit 5 records the first significant influx of coarse 

clastic detritus following unit 3 deposition. Volcanism, 

initiated with deposition of unit 4, continued during initial deposition of the Frontier Formation in Cenomanian 

time. 

Unit 5 lithologies include sandstone (litharenite, 

lithic arkose, and feldspathic litharenite of Folk, 1968), 

conglomerate, shale, mudstone and porcelanitic mudstone, limestone, siltstone, and bentonite (fig. 4). Unit 

5 sandstone is heterogeneous, varying from quartz- and 

chert-rich to lithic-rich beds upward in each section. Sandstone is gray to brown, medium to coarse grained, 

medium to thick bedded, generally cross stratified, 

moderately calcareous, and iron stained. Unit 5 conglomerate contains (1) quartzite-, chert-, and porcelaniticrich, generally rounded to subrounded clasts in channels; 

or (2) angular to subangular rip-up clasts of porcelanitic 

22 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
mudstone at the base of small isolated channels. Clasts 

generally attain a maximum diameter of 0.3 m. Rare 

sandstone beds exceed 3m in thickness. Unit 5 mudstone 

and shale are olive green to dark gray but are locally 

highly variable in color. They are weakly to strongly 

calcareous and bentonitic. Mudstone is locally 

porcelanitic (Pioneer Mountains sections) and contains 

beds rich in ovular lithophysae similar to those encountered in unit 4. Dark-gray shale occurs at the base 

or within the lower Frontier Formation as thin, discontinuous beds. Dark-gray shale may contain root 

4601 ,13_0 _________ 11,-2_0 _________ 11,--1-,0 

I I 

AP 

342 MM1 MM2 

(1122) ••• 

FP • 

356 

(1168) 

OOillon 

RR 

81 m 

(266) 

• 

.ws 

110m 

(361) 

eLM 

AN • •MH I 

378 .cc I 

(1240) f <I 

Lima ( \ ~ o ) \ zl 

-Q l OJ " /~~--"----_...----0 \ 1:E z ~---~LP Peet Creek ' ~ """ 1 2 71 Federal 0 

\.1 (886) 270 01 ~ (886) :tl 

~ 91 5

1

0 MILES 

lr------,-1--_J 

I 

0 50 KILOMETERS I 

Mo~------------~~-------------~~~~ 

• AP 

342 

(1122) 

-¢- 270 

(886) 

EXPlANATION 

Location of outcrop section-Letters 

designate section name, number 

represents thickness of unit in 

meters, m designates minimum 

thickness. Thickness in feet in 

parentheses 

Borehole-Number designates thickness 

of formation in meters. Thickness in 

feet in parentheses 

Figure 18. Thicknesses of lithofacies unit 4, Blackleaf Formation in parts of southwestern Montana. Missing data values due 

to incomplete sections. See Appendix for detailed section locations. 

structures, leaf and wood impressions, bivalves, and 

isseminated coal. Concretions composed of micritic 

limestone as much as 0.4 m in diameter occur locally at 

the Apex section in the Pioneer Mountains. 

Subordinate siltstone is found interbedded with unit 

5 mudstone and shale or above unit 5 sandstone in fining 

upward sequences. Individual fining upward cycles may 

exceed 10m in thickness. Siltstone is olive brown to gray, 

moderately calcareous, commonly burrowed and bioturbated, and contains abundant carbonaceous matter and 

leaf and wood impressions. 

Unit 5 calcareous mudstone locally grades into 

micritic limestone in the Pioneer Mountains sections. 

Limestone is gray, thin-bedded, in part silty, and occurs 

as discontinuous beds. Unit 5 bentonite occurs as thin 

(less than 10 em thick) gray beds within unit 5 mudstone 

or shale. 

The basal sandstone of the Frontier Formation is 

easily identified in the subsurface near Lima (Exxon Co. 

No. 1 Myers Federal Unit and American Quasar Co. 29-1 

Peet Creek Federal), but a Frontier thickness value is impossible to determine objectively because of structural 

complications, poor outcrop condition, and uncertainties as to where to place the upper contact. 

Stratigraphic Relations, Age, and Correlation 

The lower contact of unit 5 is established at the base 

of the first thick conformable sandstone or conglomerate 

bed (minimum thickness 5 m) above the base of unit 4 

or at the suspected unconformity in the Snowcrest and 

Gravelly Ranges and in the Lima Peaks area. At both 

the Apex and Frying Pan Gulch sections, more than 300 

m of lithic-rich sandstone, mudstone, and siltstone are 

exposed above the base of the Frontier Formation. Sandstone and conglomerate are the dominant lithologies at 

or near the base of the unit at these sections, but they 

decrease in abundance upward in the section. 

In the Lima Peaks area, more than 150m of sandstone, shale, mudstone, and conglomerate are exposed 

in a series of discontinuous outcrops above unit 4. In the 

Lima Peaks area and in the Snowcrest and Gravelly 

Ranges, 10-20 m of olive-gray to dark-gray shale and 

subordinate siltstone and mudstone lie immediately above 

the suspected unconformity at the base of the Frontier 

Formation. Sandstone increases in abundance above these 

beds. R. G. Tysdal (oral commun., 1985) observed darkgray shale beds above the color-variant Blackleaf 

equivalents in the Madison Range to the east but considered them part of the Mowry Shale. These dark-gray 

shale beds are not correlative with the basal Frontier beds 

Frontier Formation 23 
Figure 19. Basal conglomerate beds, lithofacies unit 5, Frontier Formation, Frying Pan Gulch section, Pioneer Mountains. Upsection is to the right. Conglomerate bed approximately 6 m thick. Person at base of conglomerate bed approximately 2 m tall. 

in this study area (Tysdal and others, in press). More 

than 100 m of lower Frontier clastic rocks are exposed 

at the Ruby River section in the northern Snowcrest 

Range . 

A single specimen of P/eurocardia pauperculum 

(Meek) was identified from the lower Frontier Formation at the Ruby River section in the northern Snowcrest 

Range (table 4). The species is found in sandy and silty 

nearshore marine environments of either Cenomanian or 

Turonian age (W. A. Cobban, oral commun., 1985). 

Other specimens could not be conclusively identified. 

Palynomorph data also support a Cenomanian to 

Turonian Age for the lower part of the Frontier Formation (table 5). Sample LP-131-1 was collected 5 m above 

the upper Albian sample LP-102-1 at the base of the 

Frontier Formation. Sample LP-131-1 has a younger 

aspect than samples below in the Blackleaf Formation and 

resembles samples previously observed in the lower Frontier Formation in Wyoming. 

Ryder and Ames (1970) considered conglomerate 

in the Lima Peaks area (Shine Hill sample locality; 

Dyman, 1985b) to be part of their Upper Cretaceous to 

Paleocene synorogenic Beaverhead Formation (Upper 

Cretaceous Beaverhead Group of Nichols and others, 

1985), based in part on a palynomorph assemblage similar 

to sample P3736-83 (table 5). Sample P3736-83 was considered part of the Frontier Formation by Nichols and 

others (1985) based on a reinterpretation of the age 

significance of the assemblage and field observations 

from this study that suggest continuity with lower Frontier beds nearby. 

Palynologic samples from the McCartney Mountain area and Pioneer Mountains were not useful because 

of extensive destruction due to thermal alteration 

associated with batholith intrusion. An assemblage from 

both the Apex and Frying Pan Gulch localities would 

have been valuable in correlating these sections with those 

to the south and east. Without these data, the lithostratigraphic correlations used to determine the BlackleafFrontier boundary in this area are considered tentative. 

A single specimen of Tempskya sp. identified from 

the Frontier Formation at the Apex section (table 6) may 

24 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
represent an occurrence stratigraphically younger than 

previously recognized for the genus. 

SUMMARY 

The Blackleaf and lower Frontier Formations can 

be subdivided into five easily recognized lithofacies: 

(Blackleaf) lower clastic (unit 1), lower mudstone-shale 

(unit 2), upper clastic (unit 3), volcaniclastic (unit 4), and 

(lower Frontier) lower clastic (unit 5). The Blackleaf Formation reaches a maximum thickness of 600 m in the 

Pioneer Mountains. 

The lower clastic lithofacies (unit 1) is conformable 

with the underlying Kootenai Formation; varies from 87 

m (west) to 13 m (east) in thickness; includes quartzarenite, litharenite, mudstone, micritic limestone, siltstone, and limestone conglomerate; and was deposited 

in fluvial, deltaic, and lagoonal settings. 

The lower mudstone-shale lithofacies (unit 2) is conformable with unit 1; varies from 73 m (east) to 17 m 

(southwest) in thickness; includes mudstone, shale, siltstone, and subordinate sandstone; and was deposited in 

shallow marine (east) to lagoonal and floodplain (west) 

settings. 

The upper clastic lithofacies (unit 3) is conformable 

with unit 2; varies from 76 m (west) to 4 m (east) in 

thickness; includes litharenite, and subordinate siltstone 

and mudstone; and was deposited in fluvial and deltaic 

(west) to shallow marine (east) settings. 

The volcaniclastic lithofacies (unit 4) is conformable 

with unit 3; varies from 378 m to 270m in thickness; is 

lithologically heterogeneous and includes mudstone, 

shale, bentonite, porcelanite, lithic- and chert-rich sandstone, and conglomerate; and was deposited in a floodplain setting. 

The Frontier Formation, lower clastic lithofacies 

(unit 5) is in part unconformable with unit 4; includes 

chert- and lithic-rich sandstone, conglomerate, mudstone, 

and shale; and was deposited in fluvial to shallow 

marine(?) brackish water environments. 

The Blackleaf Formation is late Albian in age and 

the lower part of the Frontier Formation is Cenomanian 

to Turonian in age based on analysis of bivalve and 

palynomorph data. The Cenomanian or Turonian Shine 

Hill conglomerate unit in the Lima Peaks area is not 

equivalent to the Upper Cretaceous Beaverhead Group 

but is equivalent to or should be placed in the Frontier 

Formation on the basis of palynomorph data. 

REFERENCES CITED 

Achuff, J. M., 1983, Folding and faulting in the northern 

Blacktail Range, Beaverhead County, Montana: Unpublished M.S. Thesis, University of Montana, 64 p. 

Brown, R. W., 1933, Fossil plants from the Aspen Shale of 

southwestern Wyoming: Proceedings from the National 

Museum of the United States, v. 82, art. 12, p. 1-10. 

Cobban, W. A., 1951, Colorado Shale of central and northwestern Montana and equivalent rocks in the Black Hills: 

Bulletin of the American Association of Petroleum 

Geologists, v. 35, p. 2170-2198. 

Cobban, W. A., Erdmann, C. E., Lemke, R. W., and 

Maughan, E. K., 1959, Colorado Group on Sweetgrass 

arch, Montana: Billings Geological Society lOth Annual 

Field Conference Guidebook, p. 89-92. 

___ 1976, Type sections and members of the Blackleaf and 

Marias River Formations (Cretaceous) of the Sweetgrass 

arch, Montana: U.S. Geological Survey Professional Paper 

974, 66 p. 

Durkee, S. K., 1980, Depositional environment of the lower 

Cretaceous Smiths Formation within a portion of the 

Wyoming-Idaho thust belt: Wyoming Geological Association 31st Annual Field Conference Guidebook, p. 101-116. 

Dyman, T. S., 1985a, Preliminary Chart showing stratigraphic 

correlation and lithofacies description for the Lower 

Cretaceous Blackleaf Formation and lower Upper 

Cretaceous Frontier Formation (lower part) in Beaverhead 

and Madison Counties, Montana: U.S. Geological Survey 

Open-File Report 85-729, 9 p., 1 plate. 

___ l985b, Measured stratigraphic sections of Lower 

Cretaceous Blackleaf Formation and lower Upper 

Cretaceous Frontier Formation (lower part) in Beaverhead 

and Madison Counties, Montana: U.S. Geological Survey 

Open-File Report 85-431, 72 p. 

___ l985c, Petrographic data from the Lower Cretaceous 

Blackleaf Formation and the lower Upper Cretaceous Frontier Formation (lower part) in Beaverhead and Madison 

Counties, Montana: U.S. Geological Survey Open-File 

Report 85-592, 19 p. 

___ l985d, Stratigraphic and petrologic analysis of the Lower 

Cretaceous Blackleaf Formation and the Upper Cretaceous 

Frontier Formation (lower part), Beaverhead and Madison 

Counties, Montana: Washington State University, unpublished Ph.D. dissertation, 230 p. 

Dyman, T. S., Niblack, R., and Platt, J. E., 1984, Measured 

stratigraphic section of Lower Cretaceous Blackleaf Formation and lower Upper Cretaceous Frontier Formation 

(lower part) near Lima, in southwest Montana: U.S. 

Geological Survey Open-File Report 84-838, 25 p. 

Folk, R. L., 1968, Petrology of sedimentary rocks: Hemphills 

Inc., Austin, Texas, 170 p. 

Gwinn, V. E., 1960, Cretaceous and Tertiary stratigraphy and 

structural geology of the Drummond area, west-central 

Montana: Unpublished Ph. D. Dissertation, Princeton 

University, 165 p. 

___ 1965, Cretaceous rocks of the Clark Fork Valley, central western Montana: Billings Geological Society 16th Annual Field Conference Guidebook, p. 34-57. 

Hadley, J. B., 1969, Geologic Map of the Varney Quadrangle, 

Madison County, Montana: U.S. Geological Survey 

Quadrangle Map GQ-814, scale 1:62,500. 

___ 1980, Geology of the Varney and Cameron Quadrangles, 

Madison County, Montana: U.S. Geological Survey 

Bulletin 1459, 108 p. 

References Cited 25 
Hall, W. B., 1961, Geology of part of the Upper Gallatin Valley 

of southwestern Montana: Unpublished Ph. D. Dissertation, University of Wyoming, 238 p. 

James, W. C., 1977, Origin of marine-nonmarine transitional 

strata at the top of the Kootenai Formation, southwestern 

Montana: Unpublished Ph. D. Dissertation, Indiana 

University, 433 p. 

Klepper, M. R., 1950, A geologic reconnaissance of parts of 

Beaverhead and Madison Counties, Montana: U.S. 

Geological Survey Bulletin 969-C, 85 p. 

Lowell, W. R., 1965, Geologic map of the Bannack-Grayling 

area, Beaverhead County, Montana: U.S. Geological 

Survey Miscellaneous Investigations Map I-433, scale 

1:31,680. 

Mann, J. A., 1954, Geology of part of the Gravelly Range, 

Montana: The Yellowstone-Bighorn Research Project 

Contribution 190, 92 p. 

___ 1960, Geology of part of the Gravelly Range area, Montana: Billings Geological Society 11th Annual Field Conference Guidebook, p. 114-127. 

McGookey, D.P., Haun, J.D., Hale, L.A., Goodell, H. G., 

McCubbin, D. G., Weimer, R. J., and Wulf, G. R., 1972, 

Cretaceous System, in Mallory, W. W., ed., Geologic Atlas 

of the Rocky Mountains: Denver, Colorado, A. B. 

Hirschfeld Press, p. 190-228. 

Moran, J. L., 19il, Structure and stratigraphy of the Sheep 

Mountain area, Centennial Range, Montana-Idaho: Unpublished M.S. Thesis, Oregon State University, 175 p. 

Mudge, M. R., 1972, Pre-Quaternary rocks of the Sun River 

area, northwestern Montana: U.S. Geological Survey Professional Paper 663-A, 138 p. 

Myers, W. B., 1952, Geology and mineral deposits of the northwest quarter of the Willis Quadrangle and adjacent Browns 

Lake area, Beaverhead County, Montana: U.S. Geological 

Survey Open-File Report 52-105, 47 p. 

Nichols, D. J., Jacobson, S. R., and Tschudy, R. H., 1983, 

Cretaceous palynomorph biozones for the central and 

northern Rocky Mountain region of the United States, in 

Powers, R. B., ed., Geologic studies of the Cordilleran 

thrust belt: Rocky Mountain Association of Geologists, 

v. 2, p. 721-733, pl. 1. 

Nichols, D. J., Perry, W. J., Jr., and Haley, J. C., 1985, 

Reinterpretation of the palynology and age of Laramide 

syntectonic deposits, southwestern Montana: Geology, v. 

13, no. 2, p. 149-153. 

Perry, W. J., Jr., Wardlaw, B. R., Bostick, N., and Maughan, 

E. K., 1983, Structure, burial history, and petroleum potential of frontal thrust belt and adjcacent foreland, southwest 

Montana: Bulletin of the American Association of 

Petroleum Geologists, v. 67, no. 5, p. 725-743. 

Peters, J. F., 1970, Stratigraphy and structure ofthe Rock Creek 

area, Beaverhead County, Montana: Unpublished M.S. 

Thesis, Oregon State University, 112 p. 

Read, C. B., and Ash, S. R., 1961, Stratigraphic significance 

of the Cretaceous fern Tempskya in western conterminous 

United States: U.S. Geological Survey Professional Paper 

424-D, p. 250-254. 

Rice, D. D., 1976, Revision of Cretaceous nomenclature of the 

northern Great Plains in Montana, North Dakota, and 

South Dakota, in Cohee, G. V., and Wright, W. E., eds., 

Changes in stratigraphic nomenclature by the U.S. 

Geological Survey, 1975: U.S. Geological Survey Bulletin 

1422-A, p. 66-67. 

Roberts, A. E., 1965, Correlation of Cretaceous and lower Tertiary rocks near Livingston, Montana, with those in other 

areas of Montana and Wyoming: U.S. Geological Survey 

Professional Paper 525-B, p. B54-B63. 

___ 1967, Cretaceous and lower Tertiary rocks near Livingston, Montana: Billings Geological Society 16th Annual 

Field Conference Guidebook, p. 19-32. 

___ 1972, Cretaceous and early Tertiary depositional history 

of the Livingston area, southwestern Montana: U.S. 

Geological Survey Professional Paper 526-C, 120 p. 

Ross, C. S., and Smith, R. L., 1961, Ash-flow tuffs-their 

origin, geologic relations, and identification: U.S. 

Geological Survey Professional Paper 366, 81 p. 

Ryder, R. T., and Ames, H. T., 1970, Palynology and age of 

Beaverhead Formation and their paleotectonic implications 

in Lima region, Montana-Idaho: Bulletin of the American 

Association of Petroleum Geologists, v. 54, p. 1155-1171. 

Sadler, R. K., 1980, Structure and stratigraphy of the Little 

Sheep Creek area, Beaverhead County, Montana: Unpublished M.S. Thesis, Oregon State University, 289 p. 

Scholten, R., Keenmon, K. A., and Kupsch, W. 0., 1955, 

Geology of the Lima region, southwestern Montana and 

adjacent Idaho: Bulletin of the Geological Society of 

America, v. 66, p. 345-404. 

Schwartz, R. K., 1972, Stratigraphic and petrographic analysis 

of the Lower Cretaceous Blackleaf Formation, southwestern Montana: Unpublsihed Ph. D. Dissertation, Indiana University, 268 p. 

___ 1983, Broken Early Cretaceous foreland basin in 

southwestern Montana-sedimentation related to tectonism, in Powers, R. B., ed., Geologic Studies of the Cordilleran thrust belt, Volume 1: Rocky Mountain 

Association of Geologists Special Publication, p. 159-184. 

Sharp, G. C., 1970, Stratigraphy and structure of the 

Greenstone Mountain area, Beaverhead County, Montana: 

Unpublished M.S. Thesis, Oregon State University, 121 p. 

Skipp, B., and Prostka, H. J., and Schleicher, D. L., 1979, 

Preliminary geologic map of the Edie Ranch Quadrangle, 

Clark County, Idaho, and Beaverhead County, Montana: 

U.S. Geological Survey Open-File Report 79-845, scale 

1:62,500. 

Veatch, A. C., 1907, Geography and geology of a portion of 

southwestern Wyoming, with special reference to coal and 

oil: U.S. Geological Survey Professional Paper 56, p. 65. 

Vuke, S.M., 1982, Depositional environments of the Cretaceous 

Thermopolis, Muddy, and Mowry Formations, southern 

Madison and Gallatin Ranges, Montana: Unpublished 

M.S. Thesis, University of Montana, 141 p. 

___ 1984, Depositional environments of the Early Cretaceous 

western interior seaway in southwestern Montana and the 

northern United States, in Stott, D. F., and Glass, D. J., 

eds., The Mesozoic of North America: Canadian Society 

of Petroleum Geologists, p. 127-144. 

Wanless, H. R., Belknap, R. L., and Foster, H., 1955, Paleozoic 

and Mesozoic rocks of the Gros Ventre, Teton, Hoback, 

and Snake River Ranges, Wyoming: Geological Society of 

America Memoir 63, 68 p. 

26 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
Witkind, I. J., 1977, Structural pattern of the Centennial Mountains, Montana-Idaho: Wyoming Geological Association 

29th Annual Field Conference Guidebook, p. 531-536. 

Witkind, I. J., and Prostka, H. J., 1980, Geologic map of the 

southern part of the Lower Red Rock Lake Quadrangle, 

*U.S. GPO: 1988 '513-()!,7/'00}jj2 

Beaverhead and Madison Counties, Montana: U.S. 

Geological Survey Map 1-1216, scale 1:62,500. 

Ziegler, J. M., 1954, Geology of the Blacktail area, Beaverhead 

County, Montana: Unpublished Ph. D. Dissertation, Harvard University, 148 p. 

References Cited 27 

APPENDIX 
APPENDIX 

CODES, LOCATIONS AND SOURCE FOR SECTIONS AND SAMPLE 

LOCALITIES DESCRIBED IN THIS STUDY 

1. AP: 

2. FP: 

3. MM: 

4. MM2: 

5. GC: 

6. BT: 

7. RR: 

8. WS: 

9. CC: 

10. MH: 

11. AN and 

SRC: 

12. LP: 

Apex section. Lithofacies units 1-5 present. SE Y2 section 7, S Y2 

section 6, T. 5 S., R. 8 W., Twin Adams Mountain Quadrangle, 

Beaverhead County, Montana (Dyman, 1985b). 

Frying Pan Gulch section. Lithofacies units 1-5 present. Section 

30, T. 6 S., R. 9 W., Bond Quadrangle, Beaverhead County, 

Montana (Dyman, 1985b). 

McCartney Mountain I section. Lithofacies units 1-4 present. E Y2 

sections 21 and 28, SY2 section 16, T. 4 S., R. 8 W., Block Mountain Quadrangle, Madison County, Montana (Dyman, 1985b). 

McCartney Mountain II section. Lithofacies units 1-3 present. 

NEY4 section 35, T. 4 S., R. 8 W., Block Mountain Quadrangle, 

Madison County, Montana (Dyman, 1985b). 

Grasshopper Creek section. Lithofacies unit 1 present. SE Y4 section 26, T. 8 S., R. 10 W., Dalys Quadrangle, Beaverhead County, Montana (Dyman, 1985b). 

Blacktail Creek section. Lithofacies unit 1 present. NE Y4 section 

15, T. 9 S., R. 9 W., west of Crampton Ranch, Gallagher Mountain Quadrangle, Beaverhead County, Montana. (Dyman, 1985b). 

Ruby River section. Lithofacies units 1-5 present. SEY4 section 

18, T. 9 S., R. 3 W., Home Park Ranch Quadrangle, Madison 

County, Montana (Dyman, 1985b). 

Warm Springs Creek section. Lithofacies units 1-5 present. EY2 

section 15, and NEY4 section 22, T. 9 S., R. 3 W., Varney 

Quadrangle, Madison County, Montana (Dyman, 1985b). 

Cottonwood Iron Creek section. Lithofacies units 1-3 present. 

NY2 section 25, T. 10 S., R. 3 W., Monument Ridge Quadrangle, 

Madison County, Montana (Dyman, 1985b). 

Monument Hill section. Lithofacies units 1-5 present. Unsurveyed 

area about Y2 mile west of Gravelly Range Road along southwest 

flank of Monument Hill, Monument Ridge Quadrangle, Madison 

County, Montana (Dyman, 1985b). 

Antone Peak section. Lithofacies units 1-5 present. NWY4 section 22, SWY4 section 11, T. 12 S., R. 5 W., Antone Peak 

Quadrangle, Beaverhead County, Montana (Dyman, 1985b). 

Lima Peaks section. Lithofacies units 1-5 present. Sections 13, 

14, and 18, T. 15 S., R. 8 W., Lima Peaks Quadrangle, 

Beaverhead County, Montana (Dyman, Niblack, and Platt, 

1984). 

30 Blackleaf and Frontier Formations, Beaverhead and Madison Counties, Montana 
13. LS: 

S-1. RC: 

S-2. LM: 

S-3. CR: 

S-4. WS: 

S-5. SR: 

S-6. WC: 

S-7. SH: 

Little Sheep Creek sample locality. Lithofacies units 1-4 present. 

NYz section 26, T. 15 S., R. 9 W., Gallagher Gulch Quadrangle, 

Beaverhead County, Montana (Dyman, unpub. data, 1985). 

Rocky Creek Canyon sample locality. Lithofacies units 1-5 present. SW~ section 20, T. 2 S., R. 7 E., north side highway 1-90, 

Gallatin County, Montana (Roberts, 1972, p. C 61). 

Lincoln Mountain sample locality. Lithofacies units 1-5 present. 

Section 7, T. 9 S., R. 4 E., along south flank of Lincoln Mountain, Gallatin County, Montana (Hall, 1961). 

Centennial Range sample locality. Lithofacies unit 5 present. WYz 

section 30, T. 14 S., R. 37 E., west side Price-Peet road, Corral 

Creek Quadrangle, Beaverhead County, Montana (Dyman, unpub. data, 1985). 

Warm Springs Creek sample locality. Lithofacies unit 1 present. 

Section 21, T. 9 S., R. 3 W., junction Warm Springs road and 

Ruby River road, Varney Quadrangle, Madison County, Montana (Dyman, unpub. data, 1985). 

Snake River sample locality. Lithofacies units 1-3 present. Section 4, T. 37 N., R. 117 W., (unsurveyed) north side of highway 

89 east of Wolf Creek, Lincoln County, Wyoming (Durkee, 

1980). 

Willow Creek sample locality. Lithofacies units 1-5 present. Sections 6 and 7, T. 38 N., R. 116 W., West side of Willow Creek, 

Teton County, Wyoming (Wanless and others, 1955). 

Shine Hill sample locality. Lithofacies unit 5 present. EYz section 17, T. 15 S., R. 7 W., Snowline Quadrangle, Beaverhead 

County, Montana (Dyman, unpub. data, 1985). 

Appendix 31