Quantitative Petrographic AnafySis of 

Mid-Cretaceous Sandstones, 

Southwestern ... Montana 

U.S. GEOLOGICAL SURVEY BULLETIN 1830 

Quantitative Petrographic Analysis of 

Mid-Cretaceous Sandstones, 

Southwestern Montana 

By T.S. DYMAN, K.B. KRYSTINIK, and K.l. TAKAHASHI 

U.S. GEOLOGICAL SURVEY BULLETIN 1830 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U. S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

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

endorsement by the U.S. Geological Survey. 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Dyman, T. S. 

Quantitative Petrographic Analysis of Mid-Cretaceous Sandstones, 

Southwestern Montana. 

(U.S. Geological Survey bulletin; 1830) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1830 

1. Sandstone-Montana. I. Krystinik, Katherine B. II. Takahashi, K. I. 

Ill. Title. IV. Series. 

QE75.B9 no. 1830 557.3 s [552.' 5] 87-600471 

[QE471.1 5.S25] 
CONTENTS 

Abstract 1 

Introduction 1 

Purpose 1 

Stratigraphy and sedimentology 1 

Study area 3 

Data 4 

Statistical analysis of framework data 4 

R-mode analysis 6 

Q-mode analysis 6 

Petrofacies I 6 

Petrofacies II 8 

Petrofacies III 8 

Petrofacies IV 9 

Petrofacies V 10 

Petrofacies VI 10 

Factor-score maps and petrofacies analysis 11 

Discussion 13 

QFL plots 13 

Paleocurrent data 15 

Lower part of Blackleaf Formation and tectonic quiescence 15 

Upper part of Blackleaf and lower part of Frontier Formations and midCretaceous tectonism 19 

Summary 19 

References cited 19 

Code, lithofacies, location, and source for sections and sample localities 21 

FIGURES 

1. Index map of study area in parts of Beaverhead, Madison, and Gallatin 

Counties, Montana 2 

2. Generalized geologic map, southwestern Montana 3 

3. Stratigraphic nomenclature chart for strata of mid-Cretaceous age in 

western Montana, northeastern Idaho, and central Wyoming 4 

4. Composite stratigraphic description of the upper part of the Kootenai 

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

Formation, Beaverhead and Madison Counties, Montana 5 

5. Weighted pair-group average Q-mode (sample) dendrogram of 

framework-grain constituents for Blackleaf Formation and lower Frontier Formation samples 8 

6-11. Photographs showing sandstone petrofacies: 

6. Petrofacies I sandstone 9 

7. Petrofacies II sandstone 9 

8. Petrofacies III sandstone 10 

9. Petrofacies IV sandstone 10 

10. Petrofacies V sandstone 11 

11. Petrofacies VI sandstone 11 

12. Correspondence-analysis factor-score map for factors 1 and 2 

(framework data) 12 

13. Correspondence-analysis factor-score map for factors 1 and 3 

(framework data) 13 

Contents Ill 
14. Correspondence-analysis factor-score map for factors 1 and 4 

(framework data) 14 

15. QFL plot of Blackleaf and lower Frontier sandstone samples 15 

16. QmFLt plot of Blackleaf and lower Frontier sandstone samples 16 

17. Paleocurrent data summary, Blackleaf and lower part of Frontier 

Formations, Beaverhead and Madison Counties, Montana 17 

18. Generalized paleogeographic map of Blackleaf and lower Frontier 

Formations in study area 18 

TABLES 

1. Absolute variable-factor contribution matrix (first 4 factors) and 

cumulative percent contribution for 13 original framework-grain 

variables 6 

2. Petrofacies summary, Blackleaf and lower Frontier Formations, 

Beaverhead and Madison Counties, Montana 7 

IV Contents 
Quantitative Petrographic Analysis of 

Mid-Cretaceous Sandstones, 

Southwestern Montana 

By T.S. Dyman, K.B. Krystinik, and K.l. Takahashi 

Abstract 

The Albian Blackleaf Formation and the Cenomanian to 

Turonian lower part of the Frontier Formation in southwestern 

Montana lie within or east of the fold-and-thrust belt in the 

Cretaceous foreland basin. Petrographic data from these strata 

record complex sedimentation patterns that reflect an interaction between source-area tectonism, basin subsidence, and a 

cyclic sequence of transgressions and regressions. Frameworkgrain summaries for 99 thin sections were subjected to multivariate statistical analyses to establish regional compositional 

trends for provenance analysis and to determine the usefulness 

of quantitative methods in petrographic studies. 

R-mode correspondence analysis was used to determine 

the importance (total variance) of key framework grains. Monocrystalline quartz, plagioclase, potassium feldspar, and sandstone, limestone, and volcanic lithic grains contribute most of 

the variation in the framework-grain population. Q-mode cluster 

and correspondence analyses were used to differentiate six 

petrofacies. Petrofacies I through Ill (lower part of the Blackleaf), 

which are distributed throughout the study area, contain monocrystalline quartz (55-90 percent) and sedimentary lithic grains 

(10-50 percent). Petrofacies I through Ill are differentiated by 

variable monocrystalline quartz and sedimentary lithic grain 

content. Petrofacies IV through VI (upper part of the Blackleaf 

and lower part of the Frontier) contain less monocrystalline 

quartz (20-50 percent), but more feldspar, and volcanic and 

sedimentary lithic grains. 

Information derived from quantitative analyses combined 

with quartz-feldspar-lithic ternary data indicate that Blackleaf 

and lower Frontier detritus was derived from varying source 

areas through time. Lower Blackleaf detritus was derived from 

Precambrian through Mesozoic sedimentary and metasedimentary terranes to the west, north, and east; whereas upper 

Blackleaf and lower Frontier detritus was derived from Precambrian through Mesozoic sedimentary, metasedimentary, and 

volcanic terranes to the south and west. 

INTRODUCTION 

Purpose 

A quantitative petrographic analysis of Blackleaf 

and Frontier Formation sandstone samples was conducted 

in order to (1) establish petrofacies units and compare 

them to lithofacies units for regional correlation in the 

northern Rocky Mountain region; (2) describe vertical and 

lateral variations in provenance in order to add to the 

sedimentary-tectonic framework for the mid-Cretaceous 

in the region; and (3) determine the usefulness of multivariate statistical analyses in petrographic studies. The 

petrographic data set was large, and because visual variations in the sample population were difficult to establish, 

a multivariate statistical approach was undertaken to aid 

the framework study. 

Stratigraphy and Sedimentology 

The depositional history of the Cretaceous foreland 

basin in southwestern Montana is represented by a sequence of interbedded marine and nonmarine clastic and 

carbonate rocks that reflect both Sevier- and Laramidestyle tectonism along the western margin of the Cretaceous 

seaway. The late Albian through Thronian sequence in the 

Lima Peaks region and in parts of the Tendoy Mountains 

and Gravelly and Snowcrest Ranges (Beaverhead and 

Madison Counties, Mont.) (fig. 1), lies within or near the 

easternmost frontal thrust sheets of the southwestern 

Montana fold-and-thrust belt and along the margins· of 

Late Cretaceous Laramide uplifts (fig. 2). 

This mid-Cretaceous sequence in Madison and 

Beaverhead Counties includes the late Albian Blackleaf 

Formation and the Cenomanian to Thronian lower part 

of the Frontier Formation (fig. 3) (Dyman and others, 

1985). This sequence is underlai~ by clastic and carbonate 

rocks of the Aptian to Albian(?) Kootenai Formation and 

the Jurassic Morrison Formation. The sequence is overlain 

by synorogenic conglomerate, limestone, and sandstone 

of the Upper Cretaceous Beaverhead Group (Nichols and 

others, 1985). 

Cretaceous rocks in the study area are very similar 

to those observed at Blackleaf Creek (Cobban and others, 

1976) and at the Frontier (Cobban and Reeside, 1952) type 

section. The Blackleaf and the lower part of the Frontier 

Introduction 
/ 

/ 

I 

>-1>- r-lr515 8t8 

~ 51~ / ~1::5 

/~ ~~~ I /1/j I~ 111 11111; 

- r 11 1 1 - }:- .;\.. "' 1 ~------::-r-- ~West I I I \ \" BEAVERHEAD ' l Yellowstone 

COUNTY I <. o River 

1W 

( -;~ Sawmill Creek I I 1 \ 1 1 /i 1 \... \~.t)t \ 1 1 \ \ I I I I I 1 \ I I I/___.-) /r. \ )'_ 

/""\,, \ I I II I I \ ,......,.....,...........-1"'-. _,------.-......_:::/ ~'1.ty,'.:!~ I 

/ .:::,.,.........._ __ r-..TENNIAL "' I MOUNTAINS " 0 I I 

' --- cEN - 1 ' '-... I \ /;l//!1\\illlll/1111111/11//lll/lil/111 -~ 

,_/ 

_ ....... 

0 10 20 30 MILES 

0 10 20 30 KILOMETERS 

Figure 1. Index map of study area in parts of Beaverhead, Madison, and Gallatin Counties, Montana. 

Formations are composed of a predominantly clastic sequence of sandstone, siltstone, mudstone, and shale with 

much lateral and vertical variation (fig. 4). The Blackleaf 

Formation varies from 425 to 600 m in thickness and is 

subdivided into four mappable lithofacies units, the lower 

three of which are equivalent to formations mapped east 

of the report area: lower clastic lithofacies (unit 1), lower 

mudstone-shale lithofacies (unit 2), upper clastic lithofacies (unit 3), and volcaniclastic lithofacies (unit 4). Formal member names are not used with the Blackleaf 

Formation in this report because additional work remains 

to be completed before lithofacies relationships with rocks 

beyond the report area can be fully worked out (Dyman 

and Nichols, in press). Formal member names that are 

used with the Blackleaf Formation in northwestern 

Montana cannot be fully mapped in Madison and Beaverhead Counties and are not used in this report (fig. 3). 

Lithofacies units will be referred to by number in this 

report (for example, unit 1 for lower clastic lithofacies). 

Unit 1 conformably overlies the upper carbonate 

member (gastropod limestone) of the Kootenai Formation. This basal Blackleaf unit varies from 13 m in thickness in the Gravelly Range to 87 m in thickness in the 

McCartney Mountain area and consists of mudstone, 

quartz- and chert-rich sandstone, and limestone deposited 

in fluvial, lacustrine, and shallow marine depositional environments. Lithofacies unit 1 is lithostratigraphically correlative with the Fall River Sandstone of south-central 

Montana (Rice, 1976). Unit 2 varies from 17m in thickness 

in the Lima Peaks area to 70 min thickness in the McCartney Mountain area and consists predominantly of mudstone, shale, and siltstone deposited in lagoonal to 

near-shore marine depositional environments. Lithofacies 

unit 2 is lithostratigraphically correlative with the Skull 

2 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 
( " '-J ('~A 1\ 

J "'\1 A 

( " " IB 

~~ ~~~ ~" \> 1"" " 1'7 

)" ,... ,... .... ,... r" ..,l ... I> I' I' '-J -..J4tt.J ,.._ 

\~~..,~~ 

J --r-- "" r ./ \> 

\, -"' ( 'J l 

t, ~ 

)~ 

EXPlANATION \, ~ 

~ l"t-

~ Mesozoic igneous '-y rocks ) 

r:::-:-:::1 

~ 

Precambrian meta- ( 

morphic rocks \ 

0 30 MILES I I I I 

0 30 KILOMETERS 

0 Drummond 

, • 

Figure 2. Generalized geologic map, southwestern Montana. 

BB = Boulder batholith; BT = Blacktail Range; FTB = leading edge, fold-and-thrust belt; IB = idaho batholith; PB = 

Pioneer batholith; RU = Ruby Range; TR = Tobacco Root 

batholith; unpatterned area represents Paleozoic, Cenozoic, 

Creek Shale of south-central Montana. Unit 3 varies from 

4 min thickness in the northern Snowcrest Range to 76 

m in thickness in the Pioneer Mountains and consists of 

quartz-rich sandstone bodies and interbedded mudstone 

deposited in fluvial, deltaic, and shallow marine depositional environments. Lithofacies unit 3 is lithostratigraphically correlative with the Muddy Sandstone of 

south-central Montana (Rice, 1976). Unit 4 varies from 

270 m in thickness in the Lima Peaks area to 360 m in 

thickness in the central Snowcrest Range and consists of 

porcellanitic mudstone, shale, and subordinate lithic sandstone deposited in fluvial, lacustrine, and shallow marine 

depositional environments. Lithofacies unit 4 is lithostratigraphically correlative with the Mowry Shale of south12 

\. S-3 _f 

,....,e-""'~ ' -"'s-7 IDAHO 

&-5 and &-6 are south of map area 

S-1 

Bozeman t/ 

0 -

... 

ONTANA 

fWvoMING 

I 

I 

non-Cretaceous Mesozoic, or upper Precambrian sedimentary 

rocks. Numbers represent measured section locations (Appendix). Numbers preceeded by letterS represent additional sample locations. Shaded areas represent Blackleaf-Frontier 

outcrop distribution. Modified from Schwartz (1972). 

central Montana. The overlying lower part of the Frontier Formation (lower clastic lithofacies, unit 5) reaches 

a maximum thickness of at least 420 m in the Pioneer 

Mountains and is composed of lithic sandstone, conglomerate, and subordinate mudstone and shale deposited in 

fluvial to shallow marine depositional environments. An 

upper Frontier contact could not be established because 

of poor exposures and structural complications. 

Study Area 

The study area (fig. 2) includes (1) sections in the 

Pioneer Mountains, northern Snowcrest Range, and 

McCartney Mountain area originally measured by 

Introduction 3 
NORTHWESTERN SOUTHWESTERN EASTERN SOUTHWESTERN CENTRAL MONTANA MONTANA IDAHO MONTANA WYOMING (GREAT FALLS) (THIS STUDY) (BOZEMAN) 

(I) 

c 

~ ~ w zz u :::!;:::!; .:: 

w zz Marias River Frontier Formation Frontier Formation Frontier Formation Frontier Formation 

<(0 a: Shale (part, unit 5) (part) (part) (part) u ~a: 

a: a:::> w zf- CL. w CL. 

~ u 

~ c: 

Bootlegger 

Member 

~~ 

Volcaniclastic 

~ 

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

z E E 

<( 0 0 Upper clastic a:i LL LL 

..... Taft Hill Member ..... ..!! Upper sandstone Muddy Sandstone lithofacies (unit 3) (I) ...J CIJ CIJ jg ~ <( Q) Q) Cl) 

0 32 32 Lower mudstone-shale .!!l w u u Bear River Thermopolis u CIJ 8. Middle shale CIJ Shale .:: co co lithofacies (unit 2) Formation Q 

E w Flood Member 

~ a: 

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

~ ~ ~ ~?L/2:/2Y2 .D~./.Z:~ ~? -:.t::£.z::z::a. g ? ......... "'- ~~ Gastropod limestone ........ - Smoot Shale ~ "-' 'L- '-

c. 

::I Draney Limestone z e 

<( Kootenai Kootenai (.!) 

Kootenai Cloverly t Formation Formation ~ Bechler Conglomerate Formation Formation 

<( c: 

c: 

CIJ Peterson Limestone (.!) 

Ephraim Conglomerate 

Figure 3. Stratigraphic nomenclature chart 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), Vuke (1982), and Cobban and others (1976). 

Schwartz (1972) (sections 1, 2, 3, 4, and 5); (2) sections 

in the central and northern Snowcrest and Gravelly 

Ranges (sections 7, 8, 9, and 10); and (3) sections near 

Lima and in the central Snowcrest and Blacktail Ranges 

(sections 6, 11, 12, and 13). The following additional 

reference sections were described and sampled in areas 

surrounding the study area: (1) Lincoln Mountain section, Madison Range (sample S-2; Vuke, 1982); (2) Rocky 

Creek section near Bozeman (sample S-1; Roberts, 1972); 

and (3) along the Snake River and near Alpine, in Teton 

County, Wyo. (samples S-5 and S-6; La Rocque and 

Edwards, 1954; Wanless and others, 1955; Durkee, 1980; 

Wallem and others, 1981). Two samples (samples S-3 and 

S-4) were collected in the Centennial Mountains and the 

northern Gravelly Range, respectively. The Appendix 

("Code, lithofacies, location, and source for sections and 

sample localities") contains detailed locations for outcrop sections and sample localities. 

The best exposed sections are those located in the 

Pioneer Mountains and McCartney Mountain area. Composite sections were measured where rocks are poorly exposed south of Lima and in the Snowcrest Range (Antone 

Peak section; Appendix). 

Lithofacies descriptions, thickness variations, contacts, and sedimentology and depositional environments 

for all measured sections are presented separately by 

lithofacies unit in Dyman (1985a, b), Dyman and others 

(1984), and Dyman and Nichols (in press). 

Data 

Ninety-nine sandstone samples were cut, thin sectioned, stained for potassium feldspar, and point counted 

using more than 300 point counts per slide. The table of 

framework-grain percents and a numbered key to framework grains counted are presented in Dyman (1985c). Data 

were aggregated according to Dickinson and Suczek (1979). 

STATISTICAL ANALYSIS OF 

FRAMEWORK DATA 

The following statistical procedure was used in this 

study: 

(1) R-mode correspondence analysis was used to 

determine the contributing effect (percentage 

4 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 
of total variance) of each framework-grain 

variable. Based on their contributing effect, 

variables were either discarded from further 

analysis or aggregated into groups. 

(2) Q-mode cluster and correspondence analyses 

were used to determine sample relationships. 

Samples were then aggregated into groups to 

study stratigraphic and geographic variation. 

Correspondence analysis is a form of factor analysis 

that combines the results of both R-and Q-mode studies 

and reduces variable scaling problems. Correspondence 

analysis reduces the problem of N-dimensional space 

(many variables) by projecting combinations of original 

variables on a new set of axes (eigenvectors) defining new 

hypothetical variables called factors (David and others, 

1977). Variable contribution on the new axes is based on 

variance. Output from correspondence analysis includes 

(1) relative and absolute factor-variable contribution 

matrices that define the relative or absolute contribution 

of each original variable (as a percent) to each new factor (which variables are important in distinguishing all 

samples together); (2) a factor-score data matrix that contains factor-score loadings (which variables are important in distinguishing each sample from other samples); 

and (3) factor-score maps (plots) created from the factorscore matrix that graphically display sample similarity in 

factor space. Lines are drawn on each map to illustrate 

how each numbered variable contributes to differences 

among samples. The lines pass through a portion of factor space defined by their R-mode loadings (table 1). The 

lines represent the magnitude and direction to which the 

variables affect the sample population (David and others, 

1977). The proximity of a group of sample points and 

variable points establishes the similarity of samples and 

the variable or variables that are responsible for the 

similarity. 

Cluster analysis is a multivariate classification 

method by which relatively homogeneous groups are 

defined (Davis, 1973). In hierarchical clustering, the most 

similar samples are first joined and then connected to the 

next most similar samples until all samples are connected 

together in a dendrogram. Raw-data framework-grain 

percents for both formations were first standardized using 

mean deviation (Davis, 1986, p. 30) to insure that each 

variable was weighted equally. 

The weighted pair-group Q-mode program of Davis 

(1973) was used in this study (Petroleum Information 

Corporation, 1984) with the r-correlation similarity coefficient. In the weighted pair-group cluster method, correlation matrices of samples are calculated and samples 

with high correlations are grouped. In subsequent steps, 

similarity matrices are recomputed treating clustered 

elements as a single element. Each new cluster member 

is given equal weight with the existing cluster. Thus, late 

z 

0 

~ ~ 

a: 

~ Lower clastic 

lithofacies a: 

LJ.J 

i= 

z 

0 

a: 

LL. 

z 

0 

i= 

<( 

~ 

a: 

0 

LL. 

(unit 5) 

Volcaniclastic 

lithofacies 

(unit 4) 

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. 27D-380 m thick. 

~~------~.~~~~~-----------------------, LJ.J 

....J 

~ 

u 

<( 

....J 

co 

Upper 

clastic 

lithofacies 

(unit 3) 

Lower 

mudstoneshale 

lithofacies 

(unit 2) 

Lower 

clastic 

lithofacies 

(unit 1) 

Upper 

carbonate 

~ member 

LJ.J 

1-

0 

0 

~ 

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. 

Sandstone, siltstone, mudstone, 

shale, and limestone. Nodular. 

Fluvial and marine environments. 13-87 m thick. 

Micritic and bioclastic limestone, 

l=:::i:;::E;:Jp~ sandstone, mudstone, and 

1:;._.1...-_... _ _..-......-.,.· shale. Abundant fossil gastropods in upper part. 

Figure 4. Composite stratigraphic description of the upper part 

of the Kootenai Formation, the Blackleaf Formation, and the 

lower part of the Frontier Formation, Beaverhead and Madison 

Counties, Montana. Maximum and minimum lithofacies 

thickness values in parentheses. 

Statistical Analysis of Framework Data 5 
Table 1. Absolute variable-factor contribution matrix (first 4 factors) and cumulative percent contribution for 13 

original framework-grain variables 

[Data in percent. See Dyman (1985c) for detailed variable description] 

VARIABLE 

1. Monocrystalline quartz ••••••••••• 

2. Polycrystalline quartz ••••••••••• 

3. Foliated polycrystalline quartz •• 

4. Chert •••••••••••••••••••••••••••• 

5. Plagioclase •••••••••••••••••••••• 

6. Potassium feldspar ••••••••••••••• 

7. Limestone •••••••••••••••••••••••• 

8. Mudstone ••••••••••••••••••••••••• 

9. Sandstone •••••••••••••••••••••••• 

10. Volcanics •••••••••••••••••••••••• 

11. Plutonics •••••••••••••••••••••••• 

12. Metamorphics ••••••••••••••••••••• 

13. Mica ••••••••••••••••••••••••••••• 

Cumulative percent contribution •• 

cluster arrivals carry more weight than do earlier arrivals. 

Other clustering procedures and similarity coefficients 

yielded similar groupings. 

R-Mode Analysis 

Table 1 represents the absolute factor-variable contribution matrix for the 13 framework-grain types. 

Together, the first four factors contribute 64 percent to 

the variation in the total sample of framework grains. 

The most important variables and the percentage of 

variability that they contribute are (1) for factor 1, 

plagioclase (55 percent) and volcanic fragments (19 percent); (2) for factor 2, monocrystalline quartz (19 percent) and sandstone fragments (55 percent); (3) for factor 

3, limestone fragments (63 percent); and (4) for factor 

4, potassium feldspar (60 percent). Polycrystalline quartz 

(foliated and nonfoliated), mudstone grains, mica, 

metamorphic and plutonic grains contribute less to the 

total variation in the sample. Chert exhibits intermediate 

discriminating ability. 

FACTOR 

1 2 3 4 

13.2 16.9 9.0 3.0 

0.4 1. 0 1. 5 0.1 

o. 1 0.4 o.o 0.5 

1. 0 11. 5 6.2 0.7 

54.9 0.5 3. 1 5.3 

6.7 1. 1 14.2 60.1 

2.0 1. 6 62.5 16.7 

0.1 0.2 1. 9 4.8 

0.4 55.4 o. 1 3.9 

18.5 1. 1 0.1 2.2 

o. 1 o.o 0.2 0.3 

0.1 0.1 0.9 0.6 

2.5 o. 1 0.1 0.7 

28 47 58 64 

Q-Mode Analysis 

Six well-defined petrofacies (with three additional 

subfacies) were identified using Q-mode cluster analysis. 

Petrofacies are here defined from petrographic data, 

whereas the Blackleaf-Frontier lithofacies are defined 

solely from outcrop studies. Figure 5 illustrates the 

weighted pair-group dendrogram and the identified 

petrofacies for 99 Blackleaf-Frontier sandstone samples 

using all 13 original variables. Table 2 summarizes the 

characteristics of each petrofacies. 

Petrofacies I 

Petrofacies I is divided into two petrofacies 

subgroups. Petrofacies 1-A is rich in quartz with abundant quartz overgrowths. Calcite cement and mudstone 

and chert grains are rare (fig. 6). Petrofacies 1-A is found 

predominantly in lithofacies unit 1 in the Gravelly and 

Snowcrest Ranges, in the Lima Peaks area, and at the 

Rocky Creek section near Bozeman. Petrofacies 1-B contains less quartz but more chert and mudstone grains 

6 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 
Table 2. Petrofacies summary, Blackleaf and lower part of Frontier Formations, Beaverhead and Madison Counties, Montana 

[Refer to Dyman (1985c) for locality identification] 

Petrofacies/ 

rock name 

I-A 

Quartzarenite. 

I-B 

Sedlitharenite. 

II-A 

Sedlitharenite. 

II-B 

Sedlitharenite. 

III 

Sedlitharenite. 

IV 

Sedlitharenite. 

V-A 

Sedlitharenite. 

V-B 

Sedlitharenite. 

VI 

Litharenite 

Mineralogy/cements/ 

comments 

Quartz: x=90%; quartz overgrowths abundant; lithic 

grains rare, but chert and 

mudstone grains most abundant. 

Quartz: x=63%; chert: x=10%; 

mostly mudstone lithic grains 

(x=12%), and rare sandstone, 

limestone, and volcanic grains; 

cement rare to abundant. 

Quartz: x=55%; chert: x=16%; 

mostly mudstone lithic grains 

(x=24%); volcanic grains 

rare or absent. 

Quartz: x=43%; chert: x=25%; 

mostly mudstone lithic grains 

(x=13%); limestone grains 

rare (x=5%); volcanic and 

sandstone grains less than 5%; 

calcite cement varies from 9 

to 45%; samples RR-38 and 

LM-5 (on edge of cluster) 

have no calcite. 

Quartz: x=47%; chert; x=17%; 

predominantly limestone lithic 

grains (x=19%); mudstone 

grains subordinate; volcanic 

grains rare; calcite cement. 

Quartz: x=38% (much variation); 

chert: less than 17%; 

sedimentary grains variable 

(less than 20%); volcanic grains 

subordinate; variable cement. 

Quartz: x=45%; abundant 

volcanic and sedimentary 

grains; plagioclase and 

potassium feldspar abundant; 

difficult to differentiate from 

petrofacies VI; variable cement. 

Quartz: x=50%; as much as 50% 

sandstone and siltstone lithic 

grains; volcanic lithic grains 

rare; arbitrarily placed with 

petrofacies V-A (only 3 samples); 

variable cement. 

Quartz: x=20%; abundant 

volcanic and sedimentary 

grains; abundant plagioclase 

and potassium feldspar; mica 

rare to abundant; variable 

cement. 

Lithofacies unit 

distribution 

All from unit 1, 

except one unit 3 

sample. 

Units 1, 2, and 3 

present; two unit 4 

samples (LP-56 and 

MH-2). Unit 4 samples 

from nonvolcanic 

lower part. 

Predominantly from 

units 1 and 3; Two 

unit 5 samples 

(AP-184 and RR-63) 

are more than 50 m 

above base of 

Frontier Formation. 

Predominantly from 

units 1 and 3 but 

some unit 4 and 5 

samples present. 

Units 1 and 3 

All lithofacies units 

represented. 

Units 4 and 5 

Units 4 and 5 

Units 4 and 5 

Aerial distribution/ 

measured sections 

Monument Hill, Warm Springs Creek, 

Rocky Creek, Cottonwood Iron Creek, 

Little Sheep Creek, Frying Pan 

Gulch (unit 3 sample), Antone Peak. 

Equally represented throughout 

study area. 

Snake River, Warm Springs Creek, 

Cottonwood Iron Creek, Lima Peaks, 

Antone Peak, Apex, Monument Hill. 

Equally represented throughout 

study area. 

Equally represented throughout 

study area. 

Predominantly in western part of 

study area. 

Western part of study area. 

Western part of study area. 

Represented throughout study area, 

but most abundant in western part. 

Statistical Analysis of Framework Data 7 
CORRELATION 

COEFFICIENT 

0.5 0.7 0.9 

(/) 

LU 

u - ~ 0 

a: 

1-

L.U 

Q.. 

Figure 5. Weighted pair-group 

average Q-mode (sample) dendrogram of framework-grain 

constituents for Blackleaf Formation and lower part of the Frontier Formation samples. See table 

2 for petrofacies description. 

and calcite cement than petrofacies I-A (fig. 6). 

Petrofacies I-B is found predominantly in lithofacies units 

1 and 3 throughout the study area. The increase in calcite 

cement may be in part due to alteration of limestone 

grains. 1\vo lithofacies unit 4 samples present within petrofacies I were collected from the nonvolcanic lower part 

of lithofacies unit 4 in the Gravelly Range and Lima Peaks 

area. 

Quartz in petrofacies I has straight to undulose extinction and straight to slightly curved grain contacts, and 

locally contains abundant dust vacuoles and overgrowths. 

Quartz may contain abundant rutile and zircon inclusions 

and may be stress fractured. Feldspar and volcanic grains 

are rare or absent in petrofacies I. Grains in petrofacies 

I are rounded to subangular and well sorted. 

Petrofacies II 

Petrofacies II is divided into two petrofacies subgroups. Petrofacies II-A contains abundant quartz with 

subordinate mudstone and chert grains. Other lithologic 

components and calcite cement are rare or absent. Reworked quartz overgrowths are present in some samples. 

Polycrystalline quartz (foliated and nonfoliated) is locally abundant (fig. 7). Petrofacies 11-B contains less quartz 

and more chert and calcite cement than petrofacies II -A. 

The relationship between petrofacies II-A and 11-B is 

transitional, and many intermediate forms exist. A few 

lower Frontier sandstone samples (for example, sample 

RR-38, Ruby River section) are similar to petrofacies III 

samples and contain as much as 10 percent volcanic 

grains. Petrofacies II sandstone is found in all lithofacies 

units (table 2), but is most abundant in units 1 and 2. 

Petrofacies II-A however contains only sandstone from 

lithofacies units 1 and 3. Some nonvolcanic sandstone incorporated in lithofacies units 4 and 5 commonly occurs 

in petrofacies II, but there appears to be no geographic 

control over petrofacies II distribution. 

Petrofacies II quartz has straight to slightly undulose extinction and as much as 20 percent strongly undulose extinction in some samples. Contacts between 

quartz grains are straight to slightly curved. Dust vacuoles, 

rutile, vermicular chlorite(?), zircon, and pyrite inclusions 

are common. Rare volcanic grains contain lathlike plagioclase or are microcrystalline and contain potassium 

feldspar. Mudstone grains are brown to black; they may 

be variably calcareous and grade compositionally into 

micritic limestone and chert. Chert grains locally contain 

inclusions. Some petrofacies II samples contain variably 

rounded grains and are poorly sorted, which suggests a 

mixed source. 

Petrofacies Ill 

Petrofacies III is characterized by abundant quartz 

and micritic limestone grains and subordinate sandstone 

and mudstone grains (table 2, fig. 8). Igneous and 

metamorphic grains are rare or absent. Only one sample 

8 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 
Figure 6. Petrofacies I sandstone. A, Lithofacies unit 1 (sample MH-13), Monument Hill section, Gravelly Range. Quartzarenite. (3 mm across.) 8, Lithofacies unit 1 (sample WS-7), 

Warm Springs Creek section, Gravelly Range. G = glauconite 

grain, M = metamorphic grain. (1 .5 mm across.) 

(sample MM2-3) from the McCartney Mountain II section contains more mudstone than limestone grains 

(Dyman, 1985c). The presence of this sample in petrofacies III may be a result of the clustering procedure. 

Micritic limestone transitionally grades into sparry calcite 

cement but, in all cases, it is more abundant than the cement. Petrofacies III is found throughout the study area 

but is only present in lithofacies units 1 and 3. This 

petrofacies is especially abundant at the Apex section in 

the Pioneer Mountains, where limestone is also abundant 

in the upper part of the Kootenai and lower part of the 

Blackleaf Formations. 

Mudstone grains are red brown to black and are 

variably calcareous. Sandstone grains are rounded to 

Figure 7. Petrofacies II sandstone, lithofacies unit 3. A, Warm 

Springs Creek section (sample WS-109), Gravelly Range. 

MD = mudstone. 8, McCartney Mountain I section (sample 

MM-36). C = limestone grain altering to calcite, M = metamorphic quartz grain. (Both 3.0 mm across.) 

subrounded and are commonly cemented with chert. 

Petrofacies III quartz grains are similar to those of petrofacies I and II, but more subangular grains are present. 

Hornblende and zircon are present in minor amounts in 

most petrofacies III samples. 

Petrofacies IV 

Petrofacies IV through VI are poorly defined and 

more heterogeneous than petrofacies I through III. 

Again, the presence of some samples in certain cluster 

groups may be due to the particular clustering method 

used (fig. 9). Petrofacies IV contains (1) variable quartz, 

chert, and sedimentary grains and (2) more mica and 

Statistical Analysis of Framework Data 9 
Figure 8. Petrofacies Ill sandstone, lithofacies unit 1. Apex 

section (sample AP-60), Pioneer Mountains. Quartz (Q) and 

limestone (L) rich. (2.0 mm across.) 

volcanic grains than petrofacies I through III. Petrofacies 

IV is distributed throughout all five lithofacies units, 

predominantly in the western part of the study area (table 

2). The sediments were probably derived from a heterogeneous source. Quartz occurs as rounded to subangular 

grains with straight or undulose extinction, or as foliated 

metamorphic(?), bipyramidal volcanic, and sedimentary 

quartz grains with abundant overgrowths. Petrofacies IV 

quartz grains may contain abundant dust vacuoles and 

a variety of inclusions including zircon, hornblende, 

rutile, and mica(?). Micritic limestone and sandstone 

grains and chert are typically more abundant than mudstone grains (fig. 9), but mudstone grains are locally abundant and include (1) dark-brown silty siliceous, (2) gray 

calcareous, and (3) red-brown opaque forms. 

Petrofacies V 

Petrofacies V is also heterogeneous but contains 

more volcanic, feldspar, and quartz grains (mean = 50 

Figure 9. Petrofacies IV sandstone. Frontier Formation, conglomerate (sample SH-1) from Shine Hill, approximately 1 km 

south of Lima Peaks section, south of Sawmill Creek. (4.0 mm 

across.) 

percent quartz) than petrofacies IV (table 2). Petrofacies 

V-A contains either (1) an anomalously high sandstonemudstone grain content (sample FP-19, Frying Pan 

Gulch section, fig. 10); or (2) high sandstone, mudstone, 

and feldspar grain content (sample LP-79, Lima Peaks 

section). More than 90 percent of petrofacies V samples 

are found in lithofacies units 4 and 5. Seventy-five percent of these samples are from the western side of the 

study area, but this may be in part due to sampling bias. 

Petrofacies V-B commonly contains abundant plagioclase or potassium feldspar. 

Petrofacies VI 

Petrofacies VI is the most heterogeneous group and 

occurs exclusively in lithofacies units 4 and 5, predominantly in the Lima Peaks area, and in the Snowcrest and 

Gravelly Ranges (table 2). Petrofacies VI sandstone contains abundant plagioclase and potassium feldspar and 

volcanic grains, and this sandstone is variably micaceous 

10 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 
Figure 10. Petrofacies V sandstone. A, Lithofacies unit 5 (sample FP-19), Frying Pan Gulch section, Pioneer Mountains. (3.0 

mm across.) 8, Lithofacies unit 4 (sample LP-79), Lima Peaks 

section. F = potassium feldspar grain, V = volcanic grain. (6.0 

mm across.) 

(fig. 11). Quartz and sedimentary grains are subordinate. 

Many petrofacies V and VI samples are difficult or impossible to differentiate visually. 

Factor-Score Maps and Petrofacies Analysis 

The relative importance of each grain type in differentiating between sandstone samples cannot be graphically presented using cluster dendrograms. Correspondence-analysis factor-score maps were therefore 

generated in order to (1) corroborate the petrofacies division identified by cluster analysis (can the 6 petrofacies 

defined using cluster analysis be recognized?), (2) observe 

sample distribution in factor space (how are the samples 

Figure 11. Petrofacies VI sandstone, Lima Peaks section. A, 

Lithofacies unit 5 (sample LP-133). 8, Lithofacies unit 4 

(sample LP-92), plagioclase and matrix rich. (Both 6.0 mm 

across.) 

compositionally related and what can be said about provenance?), and (3) identify variable influence for factorscore groupings (how does each variable affect each 

sample?). Figures 12-14 represent factor-score maps for 

the first four factors using only the six most important 

variables: monocrystalline quartz, plagioclase, potassium 

feldspar, and limestone, sandstone, and volcanic grains. 

Factor-score maps that included unimportant variables 

(polycrystalline quartz, mudstone, mica, and metamorphic and plutonic grains) provided similar results. 

Figure 12 is the factor-score map for factors 1 and 

2. Forty-seven percent of the sample population variance 

is represented by the first two factors (table 1). The cluster 

of points in the lower left represents petrofacies I through 

III, which are found predominantly in lithofacies units 1 

Statistical Analysis of Framework Data 11 
2.4 FP-20 

•FP-19 

5 

C\1 1.2 

a: ~C-4 •LP-79 0 

1- • (.) • • ct 0.6 •• LL • •/LP-1~5 • •• • 3 

• SRC-2 • 

0.0 • ~-\ • 

• -0.6 

FACTOR 1 

EXPlANATION 

1 Monocrystalline quartz 

2 Plagioclase 

3 Potassium feldspar 

4 Limestone 

5 Mudstone 

6 Volcanic 

Figure 12. Correspondence-analysis factor-score map for factors 1 and 2 (framework data). This map 

excludes redundant variables as determined from R-mode analysis. Refer to Dyman (1985c) and Appendix for sample identification and location data. Variable numbers represent variable contribution 

in factor space (lines on map). See also table 2. 

through 3. The scattered array of points to the right and 

top of the figure are from lithofacies units 4 and 5. 

Samples FP-19 and FP-20 at the top of the diagram 

represent anomalously high percents of sandstone grains 

in the lower Frontier at Frying Pan Gulch in the Pioneer 

Mountains (high factor 2 scores). Sample distribution in 

the scattered data set on the right is determined mostly 

by plagioclase, potassium feldspar, and volcanic grains. 

The occurrence of samples near the right center of the 

figure (for example, sample LP-79) is determined by the 

abundance of potassium feldspar (variable 3). Samples 

on the far right contain much plagioclase (variable 2) and 

volcanic grains (variable 6). The distribution of these 

points is gradational; no tight cluster groupings exist. 

Figure 13 is the factor-score map for factors 1 and 

3. An additional 11 percent of the sample population 

variance is represented by factor 3 (table 1). Samples on 

the left with negative factor 1 scores and highly variable 

factor 3 scores represent samples from lithofacies units 

1 and 3 with significant variations in limestone grain content. Sandstones range from those that contain less monocrystalline quartz and more limestone grains (samples 

AP-85 and FP-7 in the Pioneer Mountains) to petrofacies 

I-A samples that contain predominantly monocrystalline 

quartz (sample AN-2 in the Snowcrest Range). Again, 

many compositionally intermediate forms exist. The scattered array of samples to the right again represents 

petrofacies IV through VI from the upper volcanic-rich 

lithofacies. 

Figure 14 is the factor-score map for factors 1 and 

4. An additional 6 percent of the sample population 

variance is represented by factor 4 (table 1). Clearly 

12 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 
• 

0.9 

("I) 

0.6 • •LP-70 

a: 

0 • ~ • • (.) • 

<( 

LL 0.3 

• 

• 

• 0.0 

• • • • 

• • • • • -0.3 • • •• 

0.4 0.8 1.6 

FACTOR 1 

EXPlANATION 

1 Monocrystalline quartz 4 Limestone 

5 Mudstone 

6 Volcanic 

2 Plagioclase 

3 Potassium feldspar 

Figure 13. Correspondence-analysis factor-score map for factors l and 3 (framework data). 

This map excludes redundant variables as determined from R-mode analysis. Refer to Dyman 

(1985c) and Appendix for sample identification and location data. Variable numbers represent variable contribution in factor space (lines on map). See also table 2. 

defined groups include (1) Lima Peaks Frontier Formation potassium feldspar-rich (variable 3) outliers (samples 

LP-56, LP-59, and LP-70 in petrofacies V); (2) petrofacies I through III samples from the lower Blackleaf Formation; and (3) the scattered array of points on the right 

from the upper part of the Blackleaf and lower part of 

the Frontier Formations. Sample distribution patterns 

from additional combinations of factors 2, 3, and 4 

(not illustrated) show the same relationships presented 

here. 

The six petrofacies that were previously defined 

using cluster analysis can be recognized using the correspondence analysis method. The spatial distribution of 

sandstone samples based on the influence of each grain 

type is best illustrated using the correspondence-analysis 

factor-score maps. 

DISCUSSION 

QFL Plots 

QFL (quartz-feldspar-lithic) and QmFLt (monocrystalline quartz-feldspar-total lithic) plots (Dickinson 

and others, 1983) were prepared separately to verify and 

support the quantitative studies. These plots do not differentiate sandstones based on many variables but do support the results of the quantitative analyses. Results of 

these analyses are presented in figures 15 and 16. Sample numbers annotated on these figures are stratigraphically identified in Dyman (1985c). 

The QFL and QmFLt plots indicate that lower 

Blackleaf sandstones (petrofacies I through III) were derived from recycled-orogen (thrust belt) terranes, whereas 

Discussion 13 
~ 

a: 

0 

to 

<( 

LL 

1.8 

1.2 

0.6 

LP-56 

LOWER • 

BLACKLEAF I PETROFACIES t I AND:m 

... 

••• 

LP-59 

• 

• 

• 

•• 

UPPER 

BLACKLEAFLOWER 

FRONTIER 

iTROF.ACIES • 

• 

0.0 ~~::::;:::::::=-~----====~---~ • 

-0.6 • 

-0.4 0.0 

• • • • 

0.4 0.8 

• • 

1.2 1.6 

FACTOR 1 

EXPlANATION 

1 Monocrystalline quartz 4 Limestone 

5 Mudstone 

6 Volcanic 

2 Plagioclase 

3 Potassium feldspar 

Figure 14. Correspondence-analysis factor-score map for factors 1 and 4 (framework data). 

This map excludes redundant variables as determined from R-mode analysis. Refer to Dyman 

(1985c) and Appendix for sample identification and location data. Variable numbers represent variable contribution in factor space (lines on map). See also table 2. 

most upper Blackleaf and lower Frontier sandstones 

(petrofacies IV through VI) were derived in part from 

volcanic sources, which included dissected-arc and, to a 

lesser degree, transitional-arc terranes (fig. 15). The small 

population of very quartz rich lithofacies unit 1 samples 

(petrofacies 1-A), primarily from the eastern and southern part of the study area, were derived from the cratoninterior portion of the continental-block provenance 

(recycled cratonic detritus). Samples from Rocky Creek 

(Bozeman Pass; Dyman, 1985b) and Snake River (near 

Alpine, Wyo.) fall within this very quartz rich group. 

Lower unit 1 sandstones are locally more quartzose 

(petrofacies 1-A) than upper unit 1 or unit 3 sandstones 

(petrofacies 1-B, II, and III). In the eastern part of the 

study area, an upward trend exists from lower unit 1 

quartzose provenance to upper lithofacies unit 1 and units 

2 and 3 transitional- and lithic-recycled provenance. 

Lower Blackleaf sandstones in the western part of the 

study area are compositionally more heterogeneous than 

lower Blackleaf sandstones in the eastern part of the study 

area. Unit 3 sandstones were derived exclusively from 

recycled-orogen terranes. 

Upper Blackleaf and lower Frontier sandstones are 

very heterogenous, but samples from the southern and 

eastern parts of the study area were more consistently 

derived from volcanic arc terranes (for example, sample 

LP-121, fig. 15). Samples from the lower part of unit 

4, particularly from the Pioneer Mountains and McCartney Mountain area, contain little feldspar (note petrofacies subdivision in figure 5 and table 2). Lower 

sandstones of the Frontier Formation are very heterogeneous, with provenance varying from (1) more transitional and lithic recycled in the Pioneer Mountains to (2) 

more arc derived in the Lima Peaks area and Snowcrest 

14 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 
EXPlANATION 

e Lower Frontier Formation 

X Upper volcaniclastic lithofacies 

0 Upper clastic lithofacies 

S Lower mudstone-shale lithofacies 

• Lower clastic lithofacies 

X 

LPi21 

X IDA X X t X X 

e X~--· ----· -- --~!.- -- X TA 

LP-129 

L 

Figure 15. QFL (quartz-feldspar-lithic) plot of Blackleaf and lower Frontier sandstone samples based 

on Dickinson and others (1983) provenance boundaries. See Dyman (1985c) and Appendix for sample 

number identification. BU = basement uplift, Cl = continental interior, DA = dissected arc, F = 

total feldspar grains, L = total lithic grains, Q = total quartz grains, RO = recycled orogen, TA 

= transitional arc, TC = transitional continental, UA = undissected arc. 

Range. The two lithic-rich samples from the Frontier Formation at Frying Pan Gulch (samples FP-19 and FP-20) 

represent a more local influx of sandstone detritus 

(petrofacies V-A). Samples from the Frontier Formation 

in the Lima Peaks area (particularly sample SH-3) comprise components whose origin was close to the basementuplift portion (Archean terranes) of continental-block 

provenance (petrofacies V and VI). Samples become lithic 

and feldspar rich upward from the lower part of the 

Blackleaf Formation through the lower part of the Frontier Formation in the Lima Peaks area and the Snowcrest 

Range. 

Petrofacies-provenance relationships can best be 

analyzed by comparing the factor-score maps (figs. 12-14) 

with the QFL compositional plots (figs. 15, 16). The 

factor-score maps illustrate variable-sample relationships 

not readily seen on the compositional plots. For example, the direct relationship between monocrystalline 

quartz and limestone grains (fig. 12) in differentiating between quartzose and transitional recycled-orogen provenance, particularly in the western part of the study area 

(fig. 15), is best observed using both displays. 

Paleocurrent Data 

Vector means and composite rose diagrams for 

paleocurrent data from Blackleaf and Frontier lithofacies 

are presented in figure 17. More than 500 paleocurrent 

readings were collected from directional structures, which 

included trough cross-stratification, imbricated pebbles, 

parting lineations, and sole marks. Data from lower 

Blackleaf lithofacies units 1 and 3 are variable but suggest predominantly north-to-south, east-to-west, and 

southwest-to-northeast paleocurrent directions. Lower 

Frontier lithofacies unit 5 data suggest predominantly 

south-to-north paleocurrent directions. Blackleaf lithofacies units 2 and 4, however, contain few paleocurrent 

indicators, and the sparse data for these units were not 

aggregated for presentation here. 

Lower Part of Blackleaf Formation and 

Tectonic Quiescence 

Paleocurrent and compositional data suggest that 

Albian Age sandstones from lithofacies units 1 and 3 were 

Discussion 15 
Qm Lower Fall River lithofacies, 

~ Snowcrest and Gravelly Ranges 

EXPlANATION 

• Lower Frontier Formation 

X Upper volcaniclastic lithofacies 

0 Upper clastic lithofacies 

S Lower mudstone-shale lithofacies 

A Lower clastic lithofacies 

F Lt 

Figure 16. QmFLt (monocrystalline quartz-feldspar-total lithic) plot of Blackleaf and lower Frontier sandstone 

samples based on Dickinson and others (1983) provenance boundaries. See Dyman (1985c) and Appendix for 

sample number identification. BU = basement uplift, Cl = continental interior, DA = dissected arc, F = total 

feldspar grains, LR = lithic recycled orogen, Lt = total lithic grains, M = mixed, Qm = monocrystalline quartz 

grains, QR = quartz recycled orogen, TA = transitional arc, TC = transitional continental, TR = transitional 

recycled orogen, UA = undissected arc. 

derived predominantly from sedimentary and low-grade 

metamorphic source terranes to the north, west, and east 

(fig. 18). A westward increase in limestone detritus favors 

a western source for unit 1. By Albian time, the Cordilleran orogenic belt had migrated eastward into central 

Idaho, and southwestern Montana was a subsiding 

foreland basin (Kauffman, 1977; Schwartz, 1983). Sands 

in the uppermost Kootenai were derived from Paleozoic 

sources in central Idaho and lower Paleozoic sources in 

eastern Oregon and western Idaho (Suttner, 1969; James, 

1977). The absence of volcanic, plutonic, and high-grade 

metamorphic detritus in sandstone from lithofacies units 

1 and 3 in this study area suggests that batholith volcanism and unroofing had not yet begun. Schwartz (1972, 

1983) suggested an increase in provenance complexity 

beginning with Blackleaf sedimentation, but noted that 

unroofing of major batholiths (for example, Idaho 

batholith) did not take place during Albian time. 

Unit 1 sandstone is relatively homogeneous 

throughout the study area. This lower Blackleaf 

homogeneity reflects relative tectonic quiescence similar 

to conditions existing during deposition of the upper 

part of the Kootenai Formation. Unit 3 sandstone is 

rich in chert, which suggests that the detritus was derived from Mississippian through Permian sedimentary 

rock sources. The most obvious sources for sedimentary chert include equivalents of the Phosphoria, 

Madison, Wood River, and Quadrant Formations in 

the Paleozoic miogeoclinal belt to the west (Suttner, 

1969). Crinoid columnals were noted in unit 3 chert 

grains. An increase in sandstone and mudstone grains 

relative to limestone grains upward from lithofacies unit 

1 to lithofacies unit 3 reflects a source area change that 

may be related to sequential unroofing in the thrust belt 

of dominantly limestone terranes at first and of 

siliciclastic terranes later. 

16 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 
tfl 

\ 

\ t.tl \ 

t ' \ \ 1• .;/ Dillon 1 

\ \ 

' -~ ¥. I • • 

\ 

) ~ • • ~--- ' l., • 

• 

• ,-- ·~, t• . \ . (' ' 

N /<Z ,~, Lima •\ /'• 1:::?! ' 0 ~ 

t ($)~ ) ~ ~ • (o \ .s• -.._-_f'-y-... ""\.-t-1 I 

0 ,_..... ",_J >- ' r ... ~, ·"-'· ,3: , I 

"-J 

0 

I 

0 

30 MILES I I I Blackleaf Formation lower clastic lithofacies N=150 

30 KILOMETERS 

Blackleaf Formation upper clastic lithofacies N=120 

Figure 17. Paleocurrent data summary, Blackleaf and lower 

part of Frontier Formations, Beaverhead and Madison Counties, Montana. Circles show locations of sample sites. Singlebarbed arrows represent vector means for trough cross-bed and 

imbricated pebble axes. Double-barbed arrows represent vector 

means from parting lineations and sole structures. N = number 

of structures measured. Vector means calculated according to 

Potter and Pettijohn (1977). 

Discussion 17 
A 

B 

MM1 

AP e e e MM2 

• oDillon 

FORELAND (?) AND 

CRATONIC SOURCES 

CS,Ml 4 

PYROCLASTIC DETRITUS 

THROUGHOUT REGION 

MM1 MM2 

APe e e 

• 

GH • 

oDillon 

• BT 

AN 

• 

RR LM 

• • ::: ~-z 

Lima •cc /' 1~ 

0 J ~~~ I '-~ ....._, ~"""'- -"'.- .-/ 3: 

(v,s,M) JDAHO I 

Figure 18. Generalized paleogeographic map of study area. A, Lower part of Blackleaf Formation 

(lithofacies 1 through 3). 8, Upper part of Blackleaf and lower part of Frontier Formations (lithofacies 

4 and 5). M = metasedimentary rock sources, S = sedimentary rock sources, V = volcanic rock sources. 

Not palinspastically reconstructed. Probable source areas (arrows) determined by paleocurrent and compositional data. See Appendix for measured section identifications and locations. 

18 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 
Upper Part of Blackleaf and lower Part of 

Frontier Formations and Mid-Cretaceous 

Tectonism 

Late Albian volcanism in the area is represented by 

Blackleaf Formation lithofacies unit 4 mudstone and 

sandstone. Detritus was derived mainly from sedimentary, volcanic, and low-grade metamorphic source terranes. Pyroclastic detritus may have originated directly 

from volcanic centers such as those related to the Idaho 

batholith or from erosion of older pyroclastic deposits. 

Abundant plagioclase grains in sandstones with rare 

epiclastic volcanic grains may represent reworking of 

pyroclastic rocks. 

Frontier Formation unit 5 sandstones were derived 

predominantly from sedimentary, metasedimentary, and 

volcanic terranes to the south and west (fig. 18). Sandstones in the Pioneer Mountains contain less plagioclase 

and potassium feldspar and volcanic grains than do sandstones in the Lima Peaks area and Snowcrest Range 

(Dyman, 1985c). Frontier sandstones at the Apex and 

Frying Pan Gulch sections are rich in sedimentary lithic 

grains, which suggests that the sedimentary detritus was 

derived from sources in the thrust belt to the west and 

south. Abundant volcanic detritus in the Lima Peaks area 

and Snowcrest Range probably originated in volcanic 

centers associated with development of the Idaho 

batholith to the west. 

SUMMARY 

Quantitative techniques, such as correspondence 

and cluster analyses, are very useful in understanding 

variation and objectively establishing petrofacies in large, 

highly variable sample populations such as the one used 

in this study. 

Results from R-mode correspondence analysis indicate that the relative proportions of monocrystalline 

quartz, plagioclase, potassium feldspar, and volcanic, 

limestone, and sandstone grains best characterize the 

Blackleaf and Frontier Formations. 

Results from cluster analysis and Q-mode correspondence analysis indicate that lower Blackleaf (lithofacies units 1, 2, and 3) sandstones are relatively 

homogeneous and rich in monocrystalline quartz, chert, 

and sedimentary grains (petrofacies I through III). These 

sandstones exhibit some stratigraphic and geographic 

variation based primarily on the distribution of sedimentary grains. Lower Blackleaf sandstones can be subdivided into (1) an eastern quartzarenite province and (2) 

a northwestern litharenite province. Upper Blackleaf and 

lower Frontier sandstones (lithofacies units 4 and 5) are 

heterogeneous and variably rich in feldspar and volcanic 

and sedimentary grains (petrofacies IV through VI). 

Composition of upper Blackleaf and lower Frontier sandstones varies stratigraphically and geographically, but 

sandstones are most compositionally mature in the 

Pioneer Mountains and McCartney Mountain area. 

Blackleaf and Frontier lithic constituents are 

heterogeneous and represent the erosion of structurally 

complex sedimentary, volcanic, and metasedimentary 

source areas that lay predominantly to the north, west, 

and south. The upward increase in lithic complexity and 

volcanic content may be due partly to increased volcanism 

and partly to increased erosion of a complex Sevier-style 

orogen to the west of the study area. 

REFERENCES CITED 

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

E.K., 1976, 'JYpe 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. 

Cobban, W.A., and Reeside, J.B., 1952, Correlation of the 

Cretaceous formations of the western interior of the United 

States: Geological Society of America Bulletin, v. 63, 

p. 1011-1044. 

David, M., Dagbert, M., and Beauchemin, Y., 1977, Statistical 

analysis in geology-correspondence analysis method: 

Quarterly of the Colorado School of Mines, v. 72, no. 1, 

60 p. 

Davis, J.C., 1973, Statistics and data analysis in geology: New 

York, John Wiley, 550 p. 

__ 1986, Statistics and data analysis in geology, 2d ed.: New 

York, John Wiley, 646 p. 

Dickinson, W.R., 1970, Interpreting detrital modes of graywacke 

and arkose: Journal of Sedimentary Petrology, v. 40, 

p. 695-707. 

Dickinson, W.R., Beard, L.S., Brackenridge, G.B., Erjavec, J.L., 

Ferguson, R.C., Inman, K.F., Knepp, R.A., Lindberg, F.A., 

and Ryberg, P.T., 1983, Provenance of North American 

Phanerozoic sandstones in relation to tectonic setting: 

Geological Society of America Bulletin, v. 94, p. 222-235. 

Dickinson, W.R., and Suczek, C.A., 1979, Plate-tectonics and 

sandstone composition: American Association of Petroleum 

Geologists Bulletin, v. 63, p. 2164-2182. 

Durkee, S.K., 1980, Depositional environments of the Lower 

Cretaceous Smiths Formation within a portion of the IdahoWyoming thrust belt: Wyoming Geological Association 31st 

Annual Field Conference Guidebook, p. 101-116. 

Dyman, T.S., 1985a, Preliminary Chart showing stratigrahic correlation and lithofacies description for the Lower Cretaceous 

Blackleaf Formation and lower Upper Cretaceous Frontier 

Formation (lower part) in Madison and Beaverhead Counties, Montana: U.S. Geological Survey Open-File Report 

85-729, 9 p., 1 chart. 

__ l985b, Stratigraphic and petrologic analysis of the Lower 

Cretaceous Blackleaf Formation and the Upper Cretaceous 

Frontier Formation (lower part) Beaverhead and Madison 

Counties, Montana: Pullman, Wash., Washington State 

University, Ph. D. dissertation, 230 p. 

References Cited 19 
___ 1985c, Petrographic data from the Lower Cretaceous 

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Report 85-592, 19 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. 

Dyman, T.S., and Nichols, D.J., [in press], Stratigraphy of midCretaceous Blackleaf and lower part of the Frontier Formations in parts of Beaverhead and Madison Counties, 

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Dyman, T.S., Perry, W.J., Jr., and Nichols, D.J., 1985, A 

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

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Kauffman, E.G., 1977, Geological and biological overviewWestern Interior Cretaceous basin: Mountain Geologist, 

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Geologists, p. 190-228. 

Nichols, D.J., Perry, W.J., Jr., and Haley, J.C., 1985, Reinterpretation of the palynology and age of Laramide syntectonic 

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of the Lower Cretaceous Blackleaf Formation, southwestern 

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dissertation, 268 p. 

___ 1983, Broken Early Cretaceous foreland basin in 

southwestern Montana-sedimentation related to tectonism, 

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Geologists, p. 159-184. 

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Thermopolis, Muddy, and Mowry Formations, southern 

Madison and Gallatin Ranges, Montana: Missoula, Mont., 

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

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America Memoir 63, 68 p. 

20 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 
CODE, LITHOFACIES, LOCATION, AND SOURCE 

FOR SECTIONS AND SAMPLE LOCALITIES 
CODE, LITHOFACIES, LOCATION, AND SOURCE 

FOR SECTIONS AND SAMPLE LOCALITIES 

1. AP: Apex section. Lithofacies units 1-5 present. 

SE Y2 sec. 7 and S Y2 sec. 6, T. 5 S., R. 8 W., 

Twin Adams Mountain Quadrangle, Beaverhead 

County, Montana. 

Dyman (1985b). 

2. FP: Frying Pan Gulch section. Lithofacies units 1-5 

present. 

Sec. 30, T. 6 S., R. 9 W., 

Bond Quadrangle, Beaverhead County, Montana. 

Dyman (1985b). 

3. MM1: McCartney Mountain I section. Lithofacies units 

1-4 present. 

E Y2 sees. 21 and 28 and S Y2 sec. 16, T. 4 S., R. 

8W., 

Block Mountain Quadrangle, Madison County, 

Montana. 

Dyman ( 1985b). 

4. MM2: McCartney Mountain II section. Lithofacies units 

1-3 present. 

NE Y<l sec. 35, T. 4 S., R. 8 W., 

Block Mountain Quadrangle, Madison County, 

Montana. 

Dyman (1985b). 

5. GC: Grasshopper Creek section. Lithofacies unit 1 

present. 

SE Y<l sec. 26, T. 8 S., R. 10 W., 

Dalys Quadrangle, Beaverhead County, Montana. 

Dyman (1985b). 

6. BT: Blacktail Creek section. Lithofacies unit 1 present. 

NE Y<l sec. 15, T. 9 S., R. 9 W., west of Crampton Ranch, 

Gallagher Mountain Quadrangle, Beaverhead 

County, Montana. 

Dyman (1985b). 

7. RR: Ruby River section. Lithofacies units 1-5 present. 

SE Y<l sec. 18, T. 9 S., R. 3 W., 

Home Park Ranch Quadrangle, Madison County, Montana. 

Dyman (1985b). 

8. WS: Warm Springs Creek section. Lithofacies units 1-5 

present. 

E Y2 sec. 15 and NE Y<l sec. 22, T. 9 S., R. 3 W., 

Varney Quadrangle, Madison County, Montana. 

Dyman (1985b). 

9. CC: Cottonwood Iron Creek section. Lithofacies units 

1-3 present. 

N Y2 sec. 25, T. 10 S., R. 3 W., 

Monument Ridge Quadrangle, Madison County, 

Montana. 

Dyman (1985b). 

10. MH: Monument Hill section. Lithofacies units 1-5 

present. 

Unsurveyed area west of Gravelly Range Road 

along southwestern flank of Monument Hill, 

Monument Ridge Quadrangle, Madison County, 

Montana. 

Dyman (1985b). 

11. AN: 

and 

SRC: 

Antone Peak section. Lithofacies units 1-5 present. 

NW Y<l sec. 22 and SW Y<l sec. 11, T. 12 S., R. 5 W., 

Antone Peak Quadrangle, Beaverhead County, 

Montana. 

Dyman (1985b). 

12. LP: Lima Peaks section. Lithofacies units 1-5 present. 

Sees. 13, 14, and 18, T. 15 S., R. 8 W., 

Lima Peaks Quadrangle, Beaverhead County, 

Montana. 

Dyman and others (1984). 

13. LS: Little Sheep Creek sample locality. Lithofacies 

units 1-4 present. 

N Y2 sec. 26, T. 15 S., R. 9 W., 

Gallagher Gulch Quadrangle, Beaverhead County, 

Montana. 

T.S. Dyman (unpublished data, 1984). 

S-1 RC: Rocky Creek Canyon sample locality. Lithofacies 

units 1-5 present. 

SW Y<l sec. 20, T. 2 S., R. 7 E., northern side of 

Interstate 90, 

Gallatin County, Montana. 

Roberts (1972, p. C61). 

S-2 LM: Lincoln Mountain sample locality. Lithofacies 

units 1-5 present. 

Sec. 7, T. 9 S., R. 4 E., along southern flank of 

Lincoln Mountain, Gallatin County, Montana. 

Hall (1961). 

S-3 CR: Centennial Mountains sample locality. Lithofacies 

unit 5 present. 

W Y2 sec. 30, T. 14 S., R. 37 E., western side of 

Price-Peet road, 

Corral Creek Quadrangle, Beaverhead County, 

Montana. 

T.S. Dyman (unpublished data, 1985). 

S-4 WS: Warm Springs sample locality. Lithofacies 1-3 

present. 

SE Y<l sec. 21, T. 9 S., R. 3 W., near junction of 

Warm Springs road and Ruby road, 

Varney Quadrangle, Madison County, Montana. 

T.S. Dyman (unpublished data, 1984). 

S-5 SR: Snake River sample locality. Lithofacies units 1-3 

present. 

Sec. 4, T. 37 N., R. 117 W. (unsurveyed), northern 

side of U.S. Highway 89 east of Wolf Creek, 

Lincoln County, Wyoming. 

Durkee (1980). 

S-6 WC: Willow Creek sample locality. Lithofacies units 1-5 

present. 

Sees. 6 and 7, T. 38 N., R. 116 W., western side 

of Willow Creek, Teton County, Wyoming. 

Wanless and others (1955). 

S-7 SH: Shine Hill sample locality. Lithofacies 5 present. 

E Y2 sec. 17, T. 15 S., R. 7 W., 

Snowline Quadrangle, Beaverhead County, 

Montana. 

T.S. Dyman (unpublished data, 1984). 

22 Quantitative Petrographic Analysis, Mid-Cretaceous Sandstones, Southwestern Montana 

t.< U.S. GOVEEINMENT PRINTING OFFICE: 1988-575-047/66,046 REGION NO.8