Geologic History of Salt Beds and Related Strata in tJie 

Upper Part of the Madison Group (Mississippian), 

Williston Basin, Montana and North Dakota 

U.S. GEOLOGICAL SURVEY BULLETIN 2112 
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Geologic History of Salt Beds and Related Strata in the 

Upper Part of the Madison Group (Mississippian), 

Williston Basin, Montana and North Dakota 

By William J. Sando 

U.S. GEOLOGICAL SURVEY BULLETIN 2112 

Paleogeographic evolution of an ancient salt lake based on 

biostratigraphic analysis of Mississippian rocks in 

Montana and North Dakota 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director 

For sale by U.S. Geological Survey, Information Services 

Box 25286, Federal Center 

Denver, CO 80225 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government 

Library of Congress Cataloging-in-Publication Data 

Sando, William Jasper. 

Geologic history of salt beds and related strata in the upper part of the Madison Group 

(Mississippian), Williston Basin, Montana and North Dakota I by William J. Sando. 

p. cm.-(U.S. Geological Survey bulletin ; 2112) 

Includes bibliographical references. 

Supt. of Docs. no. : I 19.3:2112 

1. Geology, Stratigraphic-Mississippian. 2. Salt deposits-Montana. 3. Salt 

deposits-North Dakota. 4. Geology-Montana. 5. Geology-North Dakota. 

6. Madison Group. I. Title. II. Series. 

QE75.B9 no. 2112 

[QE672] 

557.3 s-dc20 

[551.7'51] 94-23450 

CIP 
CONTENTS 

Abstract. ......................................................................................................................... . 

Introduction .. . . . . . . . . . . . . . . .. . . . . . . . . . . . ................ .. . . .. . . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . .. . . . . . .. . 1 

Development of Current Concepts······································································~·········· 2 

Lithostratigraphic Classification............................................................................. 2 

Early History in Outcrop Area........................................................................ 2 

Subsurface History ... ............ ....... .. ........ .. . ........... .. ... ....... ........... ........ ...... ...... 4 

Chronostratigraphy................................................................................................. 11 

Mission Canyon Limestone............................................................................ 11 

Kibbey Formation........................................................................................... 13 

Charles Formation . ... . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . .. . . . . . . . . 15 

Lithic Marker Horizons Versus Biozone Boundaries as Time Planes .... ....... 17 

Madison-Kibbey Contact........................................................................................ 18 

Outcrop Area . . . . . . . . . . .. . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . .. . . . . . .. . 18 

Subsurface ........... .............. ..... ......... .. ... . . . ... .............. ... . . . ........ .. . . ........ ...... ...... 20 

Salt Beds in the Madison Group............................................................................. 20 

Stratigraphic and Geographic Distribution..................................................... 21 

Origin.............................................................................................................. 21 

Interpretive Summary of Previous Work................................................................ 22 

New Interpretation of Critical Evidence......................................................................... 24 

Contact Between Madison Salt and Kibbey Formation . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . ... . .. 24 

Truncation of Beds in the Salt Sequence Below the Top Madison Salt......... 24 

Biostratigraphic Evidence............................................................................... 24 

Relation of Top Madison Salt to Beds Above and Below.............................. 29 

Origin of Madison Salt Sequence................................................................... 29 

Biozone B<;mndaries Versus Lithic Marker Horizons in Regional 

Chronostratigraphy......................................................................................... 29 

Evaluation of Chronostratigraphic Methods........................................................... 39 

Summary of Regional Depositional History . ..... .. . ......... .. .. . . .. ... .. ......... .. ......... ............... 39 

Regional Chronostratigraphic Lithofacies Profile.................................................. 39 

Regional Paleogeographic Maps .. . . . . . . . . . . . .. . . . .......... .. ... ... .. . .......... ... ......... ............... 42 

Shorelines .. . .. .. .............. ................... .. . .. .......... .. ... ................. .. ......... ............... 42 

Time Slice A (CZ 10, Middle Osagean)......................................................... 42 

Time Slice B (CZ 11, Late Osagean) ............................................................. 42 

Time Slice C (CZ 12, Earliest Meramecian).................................................. 42 

Time SliceD (CZ 13, Early Meramecian)..................................................... 42 

Time Slice E (CZ 14, Late Early Meramecian).............................................. 42 

Time Slice F (CZ 16, Middle Meramecian)................................................... 43 

Time Slice G (CZ 19, Late Meramecian)....................................................... 43 

Time Slice H (CZ 20, Earliest Chesterian)..................................................... 43 

General Conclusions About Geologic Mechanisms............................................... 45 

Eustacy............................................................................................................ 45 

Tectonism . . . ....... ..... ..... ......... ... ...... .. ...... .. .. . . . . . ..... ... .. ............ ......... ....... ....... ... 45 

Climate ........................................................................................................... 46 

References Cited............................................................................................................. 46 

III 
IV CONTENTS 

FIGURES 

1. Map showing location of Williston Basin and other structural and geographic features in Montana 

and adjacent States................................................................................................................................................. 2 

2. Chart showing evolution of lithostratigraphic classification and chronostratigraphy of Carboniferous rocks 

in central and southwestern Montana outcrop area................................................................................................ 3 

3-7. Charts showing evolution of lithostratigraphic classification and chronostratigraphy of Osagean through 

Chesterian rocks and overlying formations in subsurface of: 

3. Montana........................................................................................................................................................... 4 

4. North Dakota................................................................................................................................................... 6 

5. South Dakota................................................................................................................................................... 10 

6. Saskatchewan.................................................................................................................................................. 12 

7. Manitoba.......................................................................................................................................................... 14 

8. Chart showing radiometrically calibrated Western Interior Mississippian biozonations ....................................... 15 

9. Map showing locations in central and southwestern Montana at which a disconformity was reported at the 

Madison-Kibbey contact ... ... ............... .......... ....... ....... ... . . . . .... ...... ... ......... ........... ............ ........... ........... ................. 19 

10. Paleotectonic map of part of western North America showing isolation of Madison salt area from 

marine areas during post-early Meramecian, pre-Chesterian time ........................................................................ 23 

11. Lithostratigraphic profiles across margin of top Madison salt basin showing erosional truncation of beds 

at top of Madison Group beneath Kibbey Formation in western North Dakota.................................................... 25 

12. Map showing locations of well sections of Charles Formation and Mission Canyon Limestone in 

Montana and North Dakota from which corals, foraminifers, and algae were collected ....................................... 28 

13, 14. Lithostratigraphic profiles of Charles Formation and uppermost Mission Canyon Limestone 

across Madison salt basin in Montana and North Dakota: 

13. Approximately south to north ....................................................................................................................... 30 

14. Approximately east to west........................................................................................................................... 32 

15. Generalized paleogeographic map of Williston Basin and adjacent areas during latest Osagean and 

earliest Meramecian (CZ 11 to CZ 12) time .......................................................................................................... 36 

16, 17. Stratigraphic profiles: 

16. From Madison outcrop area into Williston Basin ......................................................................................... 37 

17. From margins to center of Williston Basin .. . ......... ........ ... .................... ........ .. . ..... ... . .. .. . ......... .............. ........ 38 

18. Chronostratigraphic lithofacies profile of Madison and Big Snowy Groups from central Montana to 

eastern North Dakota .............................................................................................................................................. 40 

19. Sequential time-slice paleogeographic maps of the Mission Canyon Limestone and Charles Formation 

in Montana, North Dakota, and adjacent States ..................................................................................................... 44 

TABLES 

1. Conodont faunules from approximate type section of Otter Formation at Belt Creek, 

Little Belt Mountains, Cascade County, central Montana...................................................................................... 16 

2. Locations and sources of data for well sections shown in figure 12 ...................................................................... 34 

3. Locations and sources of data for stratigraphic sections shown in figure 18 ......................................................... 43 
Geologic History of Salt Beds and Related Strata in the 

Upper Part of the Madison Group (Mississippian), 

Williston Basin, Montana and North Dakota 

By William J. San do 

ABSTRACT 

During the latter part of Mississippian time, the Williston Basin of eastern Montana and North Dakota was part of 

an almost circular area of more rapidly subsiding crust on a 

broad, relatively stable cratonic platform. The Mississippian 

stratigraphic record on the platform consists of two continuous depositional sequences separated by a major hiatus, 

except in the center of the Williston Basin, where a thick 

deposit of halite at the top of the lower depositional sequence 

(Madison Group) is overlain conformably by basal, transgressive, terrigenous sediments of the upper depositional 

sequence (Big Snowy Group). 

The upper part of the lower depositional sequence, represented by the Mission Canyon Limestone and Charles Formation, consists mainly of shallowing-upward, regressive 

shelf-carbonate and evaporite sediments deposited during 

the middle and late Osagean and early Meramecian. Intermittent deposition of marine anhydrite was common on most 

of the shelf during this time, but intermittent deposition of 

marine halite was confined to the central part of the Williston 

Basin later in the early Meramecian. The sea began a westward retreat from the Cordilleran platform in the late Osagean and left most of the platform exposed to subaerial 

erosion during the middle Meramecian, except for a vestigial 

landlocked salt lake at the center of the basin. A marine 

transgression, which originated in the Antler foreland basin 

west of the platform, swept eastward across the platform in 

middle Meramecian to Chesterian time, depositing mainly 

terrigenous sediments on the eroded surface of the Madison 

Group. The landlocked salt lake at the center of the basin was 

covered and extinguished by the basal deposits (Kibbey Formation) of this transgression. 

A thorough review of previous research on Mississippian depositional sequences of the Williston Basin evaluates and reconciles seemingly contradictory evidence 

pertaining to the origin of the salt deposits and to the age 

relationships of associated strata. Lithic marker horizons, 

used widely as synchronous planes in chronostratigraphy in 

the subsurface, are shown to be regionally diachronous 

with respect to biozone boundaries, but they are considered 

suitable for most exploration work within the basin. 

Changes in relative sea level in the study area are probably 

the result of an interplay of eustacy and tectonism. Regionally variable changes in climate had an important effect on 

shaping the character of the sediments. 

INTRODUCTION 

The Mission Canyon Limestone and equivalent formations of the Madison Group comprise a thick, regressive 

sequence of shallow-water shelf carbonate and evaporitic 

rocks of Mississippian (middle Osagean-early Meramecian) 

age that occupies a large area of the northern Rocky Mountains and Great Plains (Sando, 1976). The Mission Canyon 

sequence is overlain in most places by the Big Snowy Group 

or Amsden Formation, which includes transgressive, mostly 

terrigenous rocks that range from Late Mississippian (middle Meramecian) to Middle Pennsylvanian in age (Sando and 

others, 1975). 

During the latter part of Mississippian time, the Williston Basin of eastern Montana and North Dakota was part of 

an almost circular area of more rapidly subsiding crust (interior sag basin of Kingston and others, 1983, p. 2177-2178) 

on a broad, relatively stable cratonic platform (Cordilleran 

platform). In the subsurface of the Williston Basin (fig. 1), 

most geologists recognize a sequence of dolomite and 

evaporite beds called the Charles Formation at the top of the 

Madison Group and regard the contact between the Madison 

and the overlying Big Snowy as conformable and transitional, even though this contact represents a karst event of 

considerable duration in surface exposures of the Madison in 

the areas surrounding the Williston Basin to the south and 

west (Sando, 1988). The absence of karst features in the subsurface and the presence of a thick, unleached halite 

sequence at the top of the Madison in the center of the Williston Basin seems to support a transition between the two 

stratigraphic groups. 

Discovery of fossils no younger than early Meramecian 

near the top of the Madison Group in cores from wells near 

the center of the Williston Basin (Sando, 1978; Sando and 
2 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

OVERTHRUST 

BELT 

Little Rocky 

Mountains 

Judith BLOOD CREEK 

Little Belt Mountains SYNCLINE 

Mountains 

CRAZY 

MOUNTAINS 

BASIN 

&& 

tl?o G>"<'o Pryor v/J Ot; POWDER ---"'G>. %> Mountains MONTANA RIVER ''l.s _____ _ 

--vwoM~-8A:SJN ____ _ 

0 100 

1' " " " 1'

1 I I I I 

0 50 

I 

200 KILOMETERS 

I 

100 MILES 

0 Pierre 

Figure 1. Location of Williston Basin (shaded) and other structural and geographic features in Montana and adjacent States. Hachured 

lines outline area of figure 12. Modified from Peterson (1984, fig. 3 ). 

Mamet, 1981) is seemingly incompatible with the traditional 

subsurface interpretation of the age and geologic history of 

the top of the Madison. This paleontologic evidence suggests 

that a hiatus representing middle to late Meramecian time is 

present between the top of the Madison and the overlying 

Kibbey Formation, which is-generally thought to be of Chesterian age in the Williston Basin (Sando, 1978). This interpretation does not explain, however, how marine salt deposits 

could be preserved beneath the top of the Madison if the central Williston Basin area had been exposed to subaerial erosion similar to the surrounding areas of Madison rocks. 

This report presents a new interpretation of the depositional history of the upper part of the Madison Group, and of 

the origin of the Madison salt, that reconciles apparently contradictory evidence concerning the nature of the top of the 

Madison in the Williston Basin. The new interpretation was 

incorporated in paleogeographic maps by Sando ( 1989a, b, 

1992) without discussion. The present report also examines 

some basic questions regarding ihe recognition of disconformities and time planes in the Williston Basin subsurface. 

Acknowledgments.-! am indebted to S.B. Anderson 

(North Dakota Geological Survey, retired) for lithostratigraphic data on some North Dakota wells. I am also grateful 

to my U.S. Geological Survey colleagues J.T. Dutro, Jr., 

T.W. Henry, J.A. Peterson, and B.R. Wardlaw for their helpful reviews of the manuscript. 

DEVELOPMENT OF CURRENT 

CONCEPTS 

A review of the evolution of stratigraphic concepts is 

useful for understanding current interpretations of the top of 

the Madison Group and of the origin of the Madison salt 

deposits. After a brief synopsis of the early history of Madison and Big Snowy nomenclature, the following discussion 

is focused on the classification, age, and geologic history of 

the upper part of the Madison and of the lower part of the Big 

Snowy in the Williston Basin subsurface. Although the 

present study deals mainly with data from Montana and 

North Dakota, studies in South Dakota, Saskatchewan, and 

Manitoba are included in the historical summary because 

they affected development of the stratigraphic classification 

in Montana and North Dakota. 

LITHOSTRATIGRAPHIC CLASSIFICATION 

EARLY HISTORY IN OUTCROP AREA 

Current stratigraphic concepts and nomenclature originated in studies of Carboniferous rocks in the mountains of 

southwest and central Montana made at the end of the 19th 

century and in the early years of the 20th century (fig. 2). Subdivisions of Peale's (1893) Madison Formation by Weed 
*Peale 

(1893) 

Three Forks area, 

southwest 

Montana 

Cherty 

limestones 

Red 

limestones 

Jaspery 

limestones 

Massive 

limestones 

Laminated 

limestones 

*Weed 

(1899a, b, 1900) 

Little Belt 

Mountains, 

central Montana 

erosion 

Otter 

Shale 

Kibbey 

Sandstone 

Castle 

Limestone 

Woodhurst 

Limestone 

Paine 

Shale 

Collier and 

Cathcart (1922) 

Little Rocky 

Mountains, 

central Montana 

Mission Canyon 

Limestone 

Lodgepole 

Limestone 

Freeman 

(1922) 

Big Snowy 

Mountains, 

central Montana 

Madison 

Limestone 

*Hammer and 

Lloyd (1926) 

Big Snowy 

Mountains, 

central Montana 

hugwater Formation 

(Triassic) 

*Reeves 

(1931) 

Big Snowy 

Mountains, 

central Montana 

*Scott 

(1935) 

Big Snowy 

Mountains, 

central Montana 

*Sloss and 

Hamblin (1942) 

Little Belt, Little 

Rocky, and Big 

Snowy Mountains, 

central Montana 

Not 

discussed 

Perry 

(1945) 

Big Snowy and 

Little Rocky 

Mountains, 

central Montana 

Mission 

Canyon 

Limestone 

Lodgepole 

Limestone 

Figure 2. Evolution of lithostratigraphic classification and chronostratigraphy of Carboniferous rocks in central and southwestern Montana outcrop area prior to intensive deep drilling 

in Williston Basin. Chronostratigraphic units are shaded; vertical line pattern denotes hiatus; horizontal lines denote formation contacts (straight where conformable; wavy where disconformable or unconformable). Stratigraphic units are arranged in each column according to chronostratigraphy assigned by author(s) cited. Asterisk(*) marks reference in which fossils 

are described or discussed. 

0 

tTl 

< tTl 

r 

0 

'ij 

~ 

tTl 

~ 0 

'Tl 

n 

c 

:::0 

:::0 

tTl 

z 

>-3 

n 

0 

z 

n 

s 

CZl 

w 
4 

1 (C and SE) 

*DeWolfe and 

West (1934a), 

Jones (1940) 

UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

2 (E) 

Seager (1942), 

Seager and 

others (1942), 

*Perry and 

Sloss (1943) 

3 (C) 

*Weller and 

others (1948) 

4 (C and E) 

Leatherock 

(1950) 

5 (C and E) 

Sloss (1952), 

Barnes (1952), 

Nordquist (1953), 

Mickelson (1956), 

*Sando (1960a), 

Billings Geological 

Society ( 1964) 

6 (C and E) 

McCabe (1954), 

Davis and Hunt 

(1956) 

7 (SE) 

Andrichuk 

(1955) 

Amsden 

8 (C) 

*Mundt (1956) 

Alaska Bench Minnelusa Upper Amsden Upper Amsden Amsden Upper Amsden Amsden 

Formation Formation Formation Formation Formation Formation Formation 

(PENNSYVLANIAN) (PENNSYLVANIAN) (PENNSYLVANIAN) Formation (PENNSYLVANIAN) (PENNSYLVANIAN) (MISSISSIPPIAN (MISSISSIPPIAN 

,,,, ~ l I I . . AND • • AND 

ll 'iii~ti Lower (MISSISSIPPIAN iiH:' Lower Amsden J J I PENNSYLVANIAN) PENNSYLVANIAN) 

,l Amsden Lower Amsden AND ,, ~-----,_F_o_rm_a_ti_on_---+--Y--v--~'-""'L~~Uri----.----------'-i Tyler Formation 

,. ,, , Formation F~~~t?~n Formation PENNSYLVANIAN) a. Heath a. Heath a. Heath l 1 1.1 W.r-JJjJ 

~ H:a-th _____, ____ §;>- -~ ... ' ~ Formation ~I----Fo_~-~-t:-t;o_n_ ~f---Fo_~_m_tta_etr_io_n-1j Heath:t:~:ation .c Formation a. .,·.'. 0 Otter ~ ~ Q ~a. Heat~ Heath r--------1 :l u c Formation g f--Fo_r_m_a_tio_n_____, g, __ Fo_r_m_a_t_io_n---1 ~'----Fo_r_m_a_f_lo_n---1 o :l Formation Formation 0 Cfl (f) (f) .-- g .-- t5 e r--------1 a. Otter t5 Otter Cl Kibbey Cl Kibbey Cl Kibbey Cfl 

.~c..9 Otter ~ Otter :l > Formation iii Formation iii Formation iii Formation Cl 

~c:q . 0 e Formation ~ iii 

ii,i,' Format1on t5 Formation c..9 g I I 1 I ] il,ll'' ~r--K-ib_b_e_y _ _, ~r------1~r-------1 ;:,,'' J g 

' ~ g iii :> c Formation (f) Kibbey Kibbey . 1 

1 

-~ 

~ Upper ~ ~ Formation Sandstone -~ § 

Upper 

unit 

i ...... E Charles u.. Mississippian CJ _ ?---+--'----------1 ~ Formation IJ) r------1 

, (undifferentiated) Charles ' t Charles t ~ 

Formation Charles :;as ~ Formation co co 

-a. t .3-6 'II• Formation co a. ,,,, :l a. :l 

0 0 

~---~~-+-+--~~--+--+-~~?~ .Charles • • ~ t5 1--~---1 §-f-+---~~_,t5 ri

,j"' jil, +: +: Formation c e c c: .... .... and o o o 

-~ ~ Madison :6 c..9 .!:!? ~ 

Middle 

unit 

Madison 

Limestone 

(part) 

- a. Mission Limestone co 6 -g E 

§- Mission :l Li~~it~~e undifferentiated c ~ Mission :6 Mission ~ ,f r------1 

~ Li~~it~~e ~ (part) ·i Li~~it~~e ~ Li~~it~~e ~ ~ ~ ~ ~ :0 :o-?- 0 

co ~ Woodhurst ,

1 -~ 

~ Limestone " ' ~ (part) 

Lower 

unit 

(part) 

Kibbey 

Formation 

Charles 

Formation 

Mission 

Canyon 

Limestone 

Figure 3 (above and facing page). Evolution of lithostratigraphic classification and chronostratigraphy of Osagean through Chesterian 

rocks and overlying formations in subsurface of Montana. Chronostratigraphic correlations in each column are those of the author(s) of that 

column or were determined by lithostratigraphic correlations to other columns. Mississippian provincial series are shaded. Base of diagram 

marks base of Osagean; other provincial series boundaries are marked by dots. Vertical line pattern denotes hiatus. Solid lines denote formation contacts (straight where conformable; wavy where disconformable or unconformable). Dashed lines denote boundaries of marker 

beds or marker-bed intervals. Asterisk (*) marks reference in which fossils are described or discussed. 

(1899a, b, 1900) and Collier and Cathcart (1922) led ultimately to the classification of Sloss and Hamblin (1942), 

which served as a basis for all subsequent work on the Madison in Montana and North Dakota. The original Early Carboniferous assignment of the Madison was changed to Early 

Mississippian, and Kinderhookian and Osagean age equivalents were later recognized in it. The overlying Big Snowy 

Group (Scott, 1935) and its component formations evolved 

from subdivisions of Peale's (1893) Quadrant Formation by 

Weed (1899a, b, 1900), Hammer and Lloyd (1926), and 

Reeves (1931 ). The lower part of the Quadrant, originally 

thought to be of Late Carboniferous (Pennsylvanian) age, was 

reclassified as Late Mississippian. A regional disconformity 

was recognized at the top of the Madison, which was previously thought to be conformable with the overlying beds. 

SUBSURFACE HISTORY 

When petroleum companies first drilled deep test wells 

in 1935-1940 in the Williston Basin of eastern Montana, 

western North Dakota, and northeastern South Dakota, they 

encountered severe difficulties in correlating the subsurface 

Mississippian sequence with stratigraphic sequences 

exposed in the mountains of central Montana and western 

South Dakota, the closest areas of Mississippian outcrop 

(figs. 3-5). The first deep wells were drilled in the Porcupine 

dome and Cedar Creek anticline of southeastern Montana 

(fig. 1), where a thick, predominantly terrigenous sequence 

bearing Upper Mississippian fossils was found overlying 

Lower Mississippian carbonate rocks (fig. 3, col. 1 ). The subsurface Upper Mississippian rocks could not be correlated 
9 (C and E) 

*Willis (1959), 

Sandberg (1962), 

Clement (1986) 

10 (NE) 

Fish and 

Kinard 

(1959) 

DEVELOPMENT OF CURRENT CONCEPTS 

11 (C and E) 12 (C and E) 13 (C and E) 14 (C and E) 

Peterson (1978a, b, 

*Sando (1976, 1978), 1981,1984, 1987), Maughan and Craig (1972,1979), *Smith and Brown and 

Roberts *Sheldon and Gi lmour (1979), others ( 1984), (1967) Carter (1979) *Sando and Peterson and 

Mamet (1981) McCary (1987) 

15 (E) 16 (C and E) 

Bluemle and 

others (1981), 

Montana Gerhard (1982, 

Geological Gerhard and 

Society (1978) Anderson 1988), 

Ballard and 

others (1983) 

Tyler Amsden Tyler Tyler Tyler Tyler Tyler Tyler 

Formation Formation Formation Formation Formation Formation Formation Formation 

(PENNSYLVANIAN) (PENNSYLVAN IAN) (PENNSYLVANIAN) (PENNSYLVANIAN) (MISSISSIPPIAN (PENNSYLVANIAN) (PENNSYLVANIAN) (PENNSYLVANIAN) 

:-;,;,h~ 11' I 

11 II I §t I §t I'l l! ~ P~Nff~ .. I'~J~ 11 i ~ l l'l :1 1

1

1

1

1 h ";:::::1 

e Otter I ~ Otter ~ Otte~ '\ : og- ~~~~ation og- FoHrmeaatt~IOn .I ~(!) Kibbey Fm.< ~ Formation > Formation > Formation .... ~Otter .... g. Heath ( 3: > (!) • (!) Otter o .< o E; ~ Form~ ~ ~ Formation \' cJ5 cJ5 ~ g ~bey' g Formation ~ Otter , 

> 

3: ci. Otter 0 (!) 

c > Formation (f) ~ r-----___,.2! Kibbey ) 0) Kibbey ~ ~ formation en Kibbey ~ Formation ( 

r---;-A-zo_n_e___," Formation m~ I : o :t l i" I ~~ :;T ~1 :t I· Fo rmail onl :t t~~;t", \I . C~ar~es. ~ 0) Kibbey g Kibbey iii Formation en 

0> Formation i:D 

Charles 

Formation 

~ ~ ~ ! l ~ F~r~;~~~; ~~ ..• ; F~r~~t~~n ! 1 ( ! ef-+-~ __ ..........,e ~ .... ; e~~~ . ~ rr=-z:12- ~ . u~ ~ ~ ~ c::: D zone c Mission ) ~ Mission ;.·1 o. .3- E ~ 

~ ~ -~ ~ Canyon ) § Canyon ~ MISSIOn ~ :=; t---M

8 5

_ § Mission ) 

'6 -o E '6 Limestone :6 Limestone e Canyon e 5 . :6 Canyon '-

co ~ ~ co co ~ Limestone ~ ~ co ~ Mission c::: ~ ~ § § ~ ~ Formation 

Canyon ~ Q) Q) :6 :6 ~r--M7-

F . 'V 0 c Ctl Ctl ~ 

ormat1on ~ o..8 Woodhurst ~ ~ ~ 

.o~- I ~ ~ Limestone f.=..L-------1 

Lodgepole -g.§ Member tj( Lodgepole Lodgepole 

~ Limestone .....J .....J +• Limestone Limestone 

(part) :iii (part) (part) 

Mission 

Canyon 

Formation 

5 

into the Black Hills section in northeastern Wyoming and 

northwestern South Dakota, where the Pahasapa Limestone 

(Lower Mississippian, Madison equivalent) was overlain disconformably by the Minnelusa Formation (Pennsylvanian). 

Hence, the subsurface section was compared to sections in 

central Montana, where Scott (1935) (fig. 2, col. 7) had 

recently established the Upper Mississippian Big Snowy 

Group, which included the Kibbey, Otter, and Heath Formations, resting disconformably on the Lower Mississippian 

Madison Limestone. Scott also recognized the Amsden Formation (Upper Mississippian), whose type section was in the 

Bighorn Mountains of northern Wyoming, resting conformably and disconformably on the Big Snowy Group. 

(1942) named it the Charles Formation, included in the Big 

Snowy Group. Stratigraphic limits of the Charles in its type 

well were defined by Perry and Sloss (1943, p. 1301, fig. 3) 

and redefined by Nordquist (1953, p. 79). Because the Charles 

Formation was not recognized in the outcrop area of Mississippian rocks in Montana, Wyoming, and South Dakota, it 

was thought to fill the erosional gap between the Madison and 

Big Snowy of outcrop. Hence, the Williston Basin sequence, 

unlike that of the outcrop area, was thought to represent continuous sedimentation through the Mississippian. These early 

lithostratigraphic concepts formed the basis for most later 

work on the Mississippian sequence, parts of which became 

major producers of petroleum, in the Williston Basin. 

Another correlation problem arose when a deep test well 

drilled in 1937-1938 on the Nesson anticline in northwestern 

North Dakota revealed a thick sequence of limestone, dolomite, anhydrite, and halite between the Big Snowy Group and 

typical Madison Limestone (Kline, 1942, see also fig. 4, cols. 

1, 2 of current report). This evaporitic sequence was also 

encountered in wells drilled in southeastern Montana (Mosby 

dome, Cedar Creek anticline) (fig. 3, col. 2), where Seager 

Perry and Sloss (1943) (fig. 3, col. 2; fig. 4, col. 2) presented a synthesis of the Mississippian stratigraphy of Montana and North Dakota and established lithologic criteria for 

recognizing the contact between the Madison and the Charles, 

which was causing some difficulty in the subsurface because 

of a gradation from normal marine limestone (Madison) into 

a carbonate and evaporite sequence (Charles). Lithogenetic 

similarity of the Charles Formation to the underlying Mission 
6 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

1 (NW) 

Jones 

(1940) 

2(W) 

Seager and 

others (1942), 

*Perry and 

Sloss (1943), 

Laird (1951) 

3(NW) 

Sloss and 

Moritz (1951) 

Minnelusa Upper Amsden Upper Amsden 

Formation Formation Formation 

(PENNSYLVANIAN) (PENNSYLVANIAN) (PENNSYLVANIAN) 

4(W) 

Barnes (1952), 

Laird and 

Folsom (1956) 

Amsden 

Formation 

(PENNSYLVANIAN 

AND 

MISSISSIPPIAN) 

5(W) 

McCabe 

(1954) 

Minnelusa 

Formation 

(PENNSYLVANIAN) 

6 (NC) 

Folsom and 

Anderson (1955), 

Anderson and 

Nelson ( 1956) 

Spearfish 

Formation 

(TRIASSIC) 

7(NW) 

Middleton and 

Kennedy (1956) 

Amsden ~ Formation < 

(PENN.) < 

• • • • • ~,..,.----,T--,-,.rr-r..,-T"T"""irT"T"T"T~""TT''rT"lr""7"T...,..-;-t-.-,.....- r---J 

1-----r--------!11,1 lJ 1 II J J I I I I I 

,, 

Amsden 

Formation 

Heath 

§- Formation §-

Heath 

Formation 

.• <3 9 c: 2 1-------1 ,,!E (.9 1-------1 

> Otter 2 > Otter 

Lower 

Amsden 

Formation 

Lower 

Amsden 

Formation 

(J §- ~ Formation ~ ~ Formation 

o Heath Heath Heath b3 u b3 r-------t 

' ',:!!,, 1-- o_r_m_a io_n---1 Formation §- Formation c:n c:n ':11: ;:- 1------ - -1 ~~ r----- ----1 ii:i Kibbey 1:''1 :: ii:i o '-' Formation I'", 

.2..-- b3 Otter o.. Otter ~ 

c:n Formation :::J Formation ° 

Otter 

Formation ii:i 2 c: f-----'--------1 (.9 f--- ------1 CJ) f---------1 

.Q'l 

u 

Q.) 

> 

~ 0 

c: 

CJ) 

Kibbey 

Formation 

c:o Kibbey 

Formation 

E Upper c:n r-------+---t--------1 

~ Mississippian ii:i 

::lE (undifferentiated) 

" 

Charles 

Formation 

c: 

co 

·u 

Q.) 

E 

co 

(U 

Kibbey 

Formation 

I 1 

Charles 

Formation 

Heath ~ o.. Formation ( 

:::J 2 1---- --------,/ 

(.9 

> Otter ) 

~ Formation ~ CJ) f--- ----{Jj 

Kibbey 

Formation 

Charles 

Formation 

I Til::,',:,:: 

Charles 

Formation 

Charles 

Formation 

t ~ Charles t t 

~ 1.:: Formation ~ ~ 

t §- ! :· t §- §-

r---..,- '11 +- -~~---t~+--------...........j ~ 2 ~f-o----~~ 2 2 0.. f-+---~- ---1 (.9 f-----+----- ---+--1 (.9 ~--....... -----1 (.9 ~~-- --1 

I 

'(]) 

0) 

co 

(/) 

0 

Madison 

Limestone 

(part) 

t 

co 

0.. 

0.. 

:::J 

2 

(.9 

c: 

0 

.~ 

"'0 

co 

~ 

Mission 

Canyon 

Limestone 

:::J c: 0.. c: c: c: 

2 -~ e ~ 'E Upper -~ ~ ~ 1,, ~ ro E Mission -g 0 ~ 0 ~ 0 Canyon ~ 

-~ Mission c: (/) u._ -o Mission co -o Mission 1---------1 

co Canyon ·en co g Middle ~ Limestone Canyon ~ ~ Canyon ~ anhydrite Formation 0 Limestone ~ (part) , ' u 

c: 

0 

'iii 

-~ 

~ 

Lower 

Mission 

Canyon 

Mission 

Canyon 

Formation 

Figure 4. Evolution of lithostratigraphic classification and chronostratigraphy of Osagean through Chesterian rocks and overlying formations in subsurface of North Dakota. Chronostratigraphic correlations in each column are those of the author(s) of that column or were determined by lithostratigraphic correlations to other columns. Mississippian provincial series are shaded. Base of diagram marks base of 

Osagean; other provincial series boundaries are marked by dots. Solid lines denote formation contacts (straight where conformable; wavy 

where disconformable or unconformable). Dashed lines denote boundaries of marker beds or marker-bed intervals. Asterisk(*) marks reference in which fossils were described or discussed. 
DEVELOPMENT OF CURRENT CONCEPTS 7 

8 (NC) 9 (NW and NC) 10 (W) 11 (N) 12 (N) 13 (Nand W) 

North Dakota Smith (1960), 

Ha rrison and Anderson *Willis Fish and Geological Anderson and 

Flood (1956) (1958) (1959) Kinard (1959) Society others (1960), 

(1959) Carlson and 

Anderson (1965) 

Amsden and Tyler PENNSYLVANIAN Tyler and 

Minnelusa Formation OR Minnelusa-Amsden 

Formations 

Not (PENNSYLVANIAN) TRIASSIC Formations 

(PENNSYLVANIAN) Not (PENNSYLVANIAN) 

1

1

11: I! 11

1

1 

I 

II I I I 

Heath Heath 0. Formation 

I 

Formation ::::l J ~ 0. 

discussed 2 ::::l 

(.9 2 

Big > 0. (.9 

Snowy ~ Otter ::::l Otter ( > Otter 0 2 ~ Group c Formation (.9 Formation ~ discussed 0 Formation (/) c > (f) O'l ~ as 0 c: ) O'l 

Kibbey c >-0 as 

Kibbey (/) Q) ·.;::::; 

_oco Kibbey Limestone member ( Formation Formation O'l ,eE Formation as ~._ 

0 

u.. 

C-8 Cl) ( V) 

------ Cll Q.) 

u ·u c C-7 "' f------- 0 ~ "' f---A zone __ ·.;::; ------ c: Poplar c V) Poplar Poplar ro Cl Q.) 

§ C-6 ~ Beds 0 ~ 

------ ·.;::; ---------1 Member Member co 

C-5 Cl) ro B zone ..c: 0 Cll § u LJ... ------

~ 

--------' 

(/) C-4 Charles 0 r--

~iffeMb; Q) ------ u ------ Formation LJ... ---------1 -----·-

Q.l- ~ C-3 -

~ffeBed~ (/) __ J2.3one_~ ~co 

ro ------ Q) =2: ..c 

u C-2 Midale ~ r------_j -~--- .g ~- Mid ale- ------ t t ro t ~id~ngu~ t beds ..c Midale zone _:=.·~~ub1nte v~L C-1 ro ro u ro ro - ------ (/) ---- 0. E- r--~~ E- 0. ro rBI.\@isubmterv.i!L 

MC-5 Q) Hastings ·u 0. 0. 0. 0. > ------ ~ robisher ::::l ::::l ::::l ::::l 03 c MC-4 Beds 2 2 Bottineau Evaporate 2 2 c 0 ro (.9 .. c 

~-3 (.9 (.9 (.9 ·.;::; ro ro O'l 

ro c c c Upper c Frobisher- c ~ § ~ 0 0 0 0 0 

MC-3 -~ -~ ·.;::; Mission -~ Alida (/) 

0 c "0 "0 ro ~ Canyon "0 "0 LJ... 0 

---~ ro ro § ro 

-Me~~ ro 03 c > ~ ~ porosity ~ ~ ..c 0 c Mission 0 "0 (/) 

> ro LJ... Q) :a c ------u Canyon c "0 

____ __, 0 ro MC-2 c MC-2 0 :~ Middle u U:: 0 Limestone > anhydrite c "0 c ------ "Cii ------ ro c -------' --'----- 0 (/) u :::> "Cii ~ Lower (/) c Tilston Tilston ~ MC-1 0 Mission 

MC-1 "Cii 

I I 

Member interval -~ Canyon 

~ Porosity 
8 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

14 (E) 15 (W) 16 (NC) 17 (W) 18 (C and W) 

Eastwood Craig 

(1961 ), Sandberg Harris and Carlson (1972, 1979), 

Ballard (1962) others ( 1966) (1967) *Sheldon and 

(1963) Carter (1979) 

Amsden 

Formation Tyler 

(PENNSYLVANIAN) Formation 

~-r-r--,,.--,----,--,---,-,-----,-,.--,-___,. (PENNSYLVANIAN) [f 1]1 ~ u J J 1 

Tyler Formation 

(MISSISSIPPIAN 

and 

PENNSYLVANIAN) 

PENNSYLVANIAN 

and 

JURASSIC 

Not 

l 

Heath 

g. Formation l e 

~ j Otte> '~ ~ o > Formation ~ ~f------- ~ 

Heat~ c. Formation 

e ' i ~ Otter I I ~ \ 0 Formation 1 c: 

(/) 1---------l... 

Cl Cl 0 

iii Otter ~ 

Formation Cl 

Kibbey 

Formation 

c.. 

:::::1 

~ Otte~ ~ Formatio~ 

iii Kibbey 

Formation I 

iii 

Kibbey Formation 

~ 

Charles 

Formation 

discussed 0 

f----r-~-------'-1 

~ Kibbey 

iii Formation 

c: Poplar 

o interval ·.;::::; 

co 

E-----

o 

LJ.... 

~ - Midale- h ~c ~ ~ ~ ~ ~ ~ Ratcliffe ~ , a: subinterval_ "S ~ .~ Midale Limestone -;:; -;:: t --;- "' ..,-- ~ ~----- !;::; co interval t? co co Rival subintery& c. - ·~ R 1 L ·~ 

? -

1· 

Charles 

Formation 

( 

( 

( 

c. 2:: ~ § ,_ __Jy~meston~_ c. 6 ~ 

c. ~ g. f- ~~~~~ g. ----- ~--~ :::::l .!: e c Sherwood beds o :::::l 

~ ~ ~ v· . -~ ~ f--.! M~ha;~ds !_ ~-; .Fr~bi~he;- ~ Mis~io~ g ~ -~ ~ ~ ,_Gienbu;-bed~ ~ -~ . Alida g Canyon 

~ -t5 --g ~ c --b -d -- :0 E Interval ~ LI-mestone ::;:: :.0 0::::: c.. ~ ayne e s ro ..... ro '" o ..:::: C..c f------ ~ 0 

~ Lot ::::~ ~ Landa beds u.... ~ f--'------ f----.=-~----- c: 

Tilston 

interval 

Mission c -~ MC-2 Evaporite ~ Canyon .2 ~ ro ~E U Limestone ~ 0 c: 

LL 0 

Cll c ·u; 

s ~ -~ 0 c __Jco 

u 

Tilston 

interval 

Lodgepole 

Limestone 

19 (NC and SW) 

Anderson 

(1974) 

Tyler Formation 

(PENNSYLVANIAN) 

and Spearfish 

Formation 

(TRIASSIC) 

c.. " e Otter Fm. (!) 

0 

~ 

c 

(/) 

Cl 

iii 

l 

Kibbey l 

Formation ( 

Poplar 

interval 

(.)Cl) ----

1~-~ ---- roE Midale 

t ~-- subintervqL co 

c. 

c. 

:::::l 

e 

(.!) 

c: 

0 

-~ -c 

ro 

~ 

FrobisherAlida 

interval 

f------

Tilston 

interval 
DEVELOPMENT OF CURRENT CONCEPTS 

20(W) 

*Sando 

(1976, 1978), 

Smith and 

Gilmour (1979), 

*Sando and 

Mamet (1981) 

Tyler Formation 

(MISSISSIPPIAN 

and 

PENNSYLVANIAN) 

r----

~ ECharles ~ 

" Formation ° ~t ~ 

~-=f---------1 ~ 

21 (W) 

Cook (1976), 

Gerhard and 

others (1978) 

Not 

discussed 

Poplar 

interval 

I" ~ :;? 

e ·~ ~ r <.5 Mission ' ~ 

FrobisherAlida 

interval 

~ t; Canyon ~ ? ~ Limestone 

} _§ 

~f-----------1 

Lodgepole 

Limestone 

(part) 

t-----

Tilston 

interval 

22 (W) 

Montana 

Geological 

Society 

(1978) 

23 j_Wl 

Peterson (1978, 

1981, 1984, 1987), 

Brown and 

others (1984) 

24 (Wand q 

Bluemle and others 

(1980, 1981,1987), Gerhard (1982), 

Gerhard and others 

(1982, 1990), Ballard 

and others (1983), 

Lefever and Anderson 

(1986), Carlson and 

Lefever (1987), Lindsay (1988), Kerr (1988), 

Gerhard and Anderson 

(1988), Bory ~~~ and 

others ('1990) 

Tyler Tyler Tyler 

Formation Formation Formation 

(PENNSYLVANIAN) PENNSYLVANIAN, (PENNSYLVANIAN 

I I I 

l J 11 e. Otter \ 

Formation~ 

~ 

~ Kibbey 

~ Heath 

~ Formation I Fo~~(;on .~ Kibbey 

Formation 

I. l

1

.1111 I 

~'-" ~ Otter \ 

Formation 

Kibbey { 

_Ee_ Formation 

t; ) 

1 c/.i Formation 

~ ( 

~ ~ 

F I 

t;: Poplar 

Poplar 

unit 

Ratcliffe 

unit 

I 

( 

( 

~~ 

$ interval 

;~ _9-6 

~ 

~ 1--------+--=---~ 

_ L -~ Rai&liffe 1--V'-~~,--._C,....ha'--""r....._le"s-.Y'-JI ~ Q intervalz; 

1--------:;~-------', l F r ~ ffi ---~ 

I /Frobisher- :0;,orma IOn d!! L .... ~ 

5 I""> Alida '= ~ 1<.5 :§ <._·uni.t •' ~ M12- t; •.• . 

~ 1? > '! .~ --z= ~ Frobisher- : 

~ ~ < 1~ ~r--M8.5- J Alida , 

:=- f > 9- ~ c interval 

10 < IO -~ ·~ 

I~ 

> t;] ~ < ~ ·~ r-- ,_ 

'"- § ~ I~ 2 

Tilston 

unit ( 

( 

l~r---'--------

Lodgepole 

Limestone 

(part) 

r--~Tilston ·nterval 

Lodgepol 

Formation : 

25 (Wand C) 

*Waters (1984), 

*Waters and 

Sando 

(1987a, b, c) 

Not 

discussed 

f 

I~ ~----------~ ~~- Kibbey 

Formation 

I• ,. 1.1,. 

~ g Frobisher 

It? ~ Alida 

:;> F interval ~ ~ g :..:J 

•~ ~ •~ ~ 

_Q 

·~ Tilston 

~ interval 

9 
Jones 

(1940) 

Minnelusa 

Formation 

(PENNSYLVANIAN) 

Pahasapa 

Limestone 

(part) 

Perry and Sloss 

(1943) Leatherock 

Perry (1950) 

(1945) 

Mmnelusa Formation . 

1 

Minnelusa 

Formation (PENNSYLVANIAN) 

(PENNSYLVANIAN) 1 1\mrrlnn t:nrm~•;nn 

Charles 

Formaton 

Pahasapa 

Limestone 

(part) 

Pahasapa 

Limestone 

(part) 

Sloss (1952), McCabe 

Barnes (1952) (1954) 

Minnelusa Minnelusa 

Formation Formation 

(PENNSYLVANIAN) (PENNSYLVANIAN) 

Andrichuk Craig Peterson (1978b, Bluemle and 

(1955), Sandberg (1972, 1979), 1981,1984, 1987), others (1981), 

Gries and Gerhard (1982) (1962) Sheldon and Brown and Michelson Carter (1979) others ( 1984) Ballard and 

(1964) others (1983) 

Minnelusa Minnelusa Minnelusa Minnelusa Fairbank 

Formation Formation Formation Formation Formation 

(PENNSYLVANIAN) (PENNSYLVANIAN) (PENNSYLVANIAN) (PENNSYLVANIAN) (PENNSYLVANIAN) 

Figure 5. Evolution of lithostratigraphic classification and chronostratigraphy of Osagean through Chesterian rocks and overlying formations in subsurface of South Dakota. Chronostratigraphic correlations in each column are those of the author(s) of that column or were determined by lithostratigraphic correlations to other columns. Mississippian provincial series 

are shaded. Base of diagram marks base of Osagean; other provincial series boundaries are marked by dots. Vertical line pattern denotes hiatus. Solid lines denote formation contacts 

(straight where conformable; wavy where disconformable or unconformable). Dashed lines denote boundaries of marker beds or marker-bed intervals. Asterisk(*) marks reference in 

which fossils are described or discussed. 

0 

c 

'i:l 

'i:l 

tTl 

:::0 

'i:l 

)> 

:::0 

...., 

0 

.'Tl 

~ )> 

u 

(;) 

0 

z 

a 

:::0 

0 

c 

'i:l 

~ (;) 

C/:l 

(;) 

C/:l 

::a 

'i:l 

> 9 

~ 

0 

z 

...., 

)> 

z 

)> 

)> 

z 

u 

z 

0 

:::0 

...., 

::r: 

u 

)> 

~ 

0 

...., 

)> 
DEVELOPMENT OF CURRENT CONCEPTS 11 

Canyon Formation led to the removal of the Charles from the 

Big Snowy Group and its recognition as the uppermost formation of the Madison Group in the subsurface (see fig. 3, cols. 

4, 5; fig. 4, col. 4; fig. 5, col. 4). The classification of Perry 

and Sloss was used in Montana and North Dakota well into 

the 1950's (see fig. 3, cols. 3-9; fig. 4, cols. 3-7). 

As more successful Madison wells were drilled in 

northeast Montana and northwest North Dakota and across 

the international boundary in adjacent Saskatchewan (fig. 6) 

and Manitoba (fig. 7), the need for a finer stratigraphic classification increased, particularly in the Mission Canyon and 

Charles Formations where most of the producing zones were 

found. Generally, the base of the Charles was placed at the 

base of the lowest evaporite encountered in the sequence, but 

geologists working in oil fields began to use local lithic 

marker horizons based on prominent, stratigraphically consistent deflections on mechanical, gamma ray-neutron, and 

gamma ray-sonic logs caused by thin layers of clay, silt, and 

sand (Cumming and others, 1959) to correlate adjacent well 

sections (fig. 3, col. 1 0; fig. 4, col. 8; fig. 6, col. 4; fig. 7, col. 

1 ). As correlations became more dependent on lithic marker 

beds, the stratigraphic inconsistency of the Mission Canyon-Charles boundary became more apparent, and these traditional rock units were regarded as time-transgressive 

facies (Porter, 1955) (fig. 3, col. 1 0; fig. 4, col. 9; fig. 6, col. 

5; fig. 7, col. 2). A system of named, but informal, lithicmarker-defined intervals was established by the 

Saskatchewan Geological Society (1956) (fig. 6, col. 6) and 

the North Dakota Geological Society (1959) (fig. 6, col. 7; 

fig. 4, col. 12) for correlations across the international 

boundary during the late 1950's, and this system was 

adopted by the North Dakota Geological Survey in the early 

1960's (fig. 4, col. 13). Geologists working in Montana continued using the traditional Mission , Canyon and Charles 

concepts but recognized the boundary between them as timetransgressive, until late in the 1970's, when the Montana 

Geological Society ( 1978) adopted the Saskatchewan and 

North Dakota system of named lithic-marker-defined units 

(fig. 3, col. 15; fig. 4, col. 22). 

The system of named lithic-marker-defined intervals, 

with various minor modifications, prevailed into the 1960's 

and 1990's in Saskatchewan (fig. 6, col. 13), Manitoba (fig. 

7, col. 4), and North Dakota (fig. 4, col. 24), whereas the 

marker-bed classification was not used generally in Montana 

(fig. 3, col. 16) and South Dakota (fig. 5, col. 10). J.A. Peterson (U.S. Geological Survey) presented a synthesis of subsurface Madison lithostratigraphy based on marker horizons 

without named intervals in Montana (fig. 4, col. 23), South 

Dakota (fig. 5, col. 9), and North Dakota (fig. 4, col. 23) in 

the 1980's. 

The current lithostratigraphic classification and correlation of rock units between wells by means of physical log 

deflections has served the petroleum industry extremely well 

in the Williston Basin of the United States and Canada. By 

1990, Saskatchewan had produced 1 billion barrels of oil 

(BBO), followed by North Dakota (840 million barrels of oil 

(MBO)), Montana (622 MBO), Manitoba (166 MBO), and 

South Dakota (16.5 MBO), for a grand total of more than 2.5 

BBO mainly from Mississippian reservoirs (Gerhard and 

others, 1990, p. 507). Despite this excellent record of success 

in oil-finding, currently popular interpretations of the temporal relationships of the upper part of the Madison Group to 

coeval sedimentary rocks outside . the Williston Basin are 

controversial, and this controversy about temporal relationships has a major effect on interpretations of the regional 

depositional history of the Mississippian System in the 

Western Interior region. 

CHRONOSTRATIGRAPHY 

Parts of the Mission Canyon Limestone and of the Big 

Snowy Group contain moderately rich marine invertebrate 

faunas in the mountains of central and southwest Montana, 

where the subsurface lithostratigraphic classification originated (fig. 2). Hence, much of the rock sequence included in 

these original lithostratigraphic units is well suited for determination of geologic age and correlation by traditional paleontologic methods. The Charles Formation, known certainly 

only in the subsurface, is less fossiliferous because it represents a restricted sedimentary facies characterized mostly by 

dolomite, anhydrite, and salt. 

In recent years, the distribution of corals, foraminifers, 

and conodonts has been used extensively to zone and correlate Mississippian rocks in the Western Interior region 

(Sando, 1985) (fig. 8). In the following discussion, MFZ 

refers to foraminiferal zones of B.L. Mamet (in Mamet and 

Skipp, 1970a, b) and CZ refers to composite biozones of 

Sando ( 1985). 

The precise position of the Osagean-Meramecian 

boundary in the Western Interior region is controversial, 

owing to differences of opinion regarding the ranges of foraminifers and conodonts in the type area of the Mississippian 

System (compare Mamet and Skipp, 1970a, b, with Brenckle 

and others, 1974, 1982). In this report, the Osagean-Meramecian boundary is placed between MFZ 9=CZ 11 and MFZ 

10=CZ 12, a horizon that is well established on corals and 

foraminifers throughout the Western Interior region of the 

United States and Canada (Sando and Bamber, 1985). 

MISSION CANYON LIMESTONE 

Early studies of fossils from the Madison Limestone by 

C.D. Walcott (in Peale, 1893, p. 34-39), Charles Schuchert 

(in Weed, 1900, p. 293), and G.H. Girty (in Reeves (1931, p. 

144) resulted in an age assignment of Early Carboniferous or 

Mississippian for the formation or group in southwest and 

central Montana. Sloss and Hamblin (1942, p. 311, 313) discussed the meager faunal studies available for dating the 
12 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

1 (SE) 

Barnes 

(1952) 

TRIASSIC AND 

JURASSIC 

2 (SE) 

McCabe 

(1954) 

JURASSIC 

3 (S) 4 (SE) 

*McDonald Thomas (1954), Vogt 

(1956) (1956), Edie (1958), 

(age correlation (age correlation 

based on fo from McCabe, 1959) 

TRIASSIC AND Watrous Formation 

JURASSIC (JURASSIC) 

5 (SC and SE) 

Fuller (1956a, b), 

Edie (1958), 

Fish and Kinard (1959) 

TRIASSIC AND JURASSIC 

6 (SE) 

Saskatchewan 

Geological Society 

(1956), 

Edie (1958) 

Watrous Formation 

(JURASSIC) 

7 (NC and SE) 

North Dakota 

Geological Society 

(1959) 

Not discussed 

Poplar 

member 

Tilston 

member 

Figure 6 (above and facing page). Evolution of lithostratigraphic classification and chronostratigraphy of Osagean through Chesterian 

rocks and overlying formations in subsurface of Saskatchewan. Chronostratigraphic correlations in each column are those of the author(s) 

of that column or were determined by lithostratigraphic correlations to other columns. Mississippian provincial series are shaded. Base of 

diagram marks base of Osagean; other provincial series boundaries are marked by dots. Vertical line pattern denotes hiatus. Solid lines denote formtion contacts (straight where conformable; wavy where disconformable or unconformable). Dashed lines denote boundaries of 

marker beds or marker-bed intervals. Asterisk (*) marks reference in which fossils are described or discussed. 

Madison and concluded that the group included both 

"Kinderhook" and "Osage" equivalents, but they did not date 

the Mission Canyon Limestone specifically, and they left 

open the possibility that beds of Late Mississippian age might 

be present in its upper part. Perry ( 1945, correlation chart) 

showed the age of the Mission Canyon Limestone as 

"Osage," overlying beds of "Kinderhook" age in the Lodgepole Limestone in central Montana, but he did not discuss the 

basis for these age assignments. James Steele Williams (in 

Weller and others, 1948, chart 5, cols. 39, 40, p. 139) showed 

the Mission Canyon Limestone as Osagean and the underlying Lodgepole Limestone as Kinderhookian and Osagean, 

but he did not discuss the faunal evidence for these age 

assignments. Williams (in Weller and others, 1948, p. 

138-139) noted that, although many paleontologists had 

studied collections of fossils from the Madison, no consensus 

had been reached on detailed correlations with the Mississippi Valley section. Fossils from the Madison in two well 

cores in eastern Montana were not diagnostic for detailed correlation (A.H. Sutton in DeWolfe and West, 1939a, p. 472, 

473). Peter Harker (in MacDonald, 1956, p. 27) studied 

marine invertebrates from well cores in the Mission Canyon 

of Saskatchewan and suggested that the fauna had "a Kinderhook and Osage aspect," but he was unable to make positive 

specific identifications of the fossils. These tentative age 

assignments based on limited faunal data formed the basis for 

the Osagean age assigned to the Mission Canyon Limestone 

in the subsurface of the Williston Basin by most geologists 

into the early 1950's (figs. 3-7). 

Detailed biostratigraphic studies of corals, brachiopods, 

foraminifers, and conodonts from the Madison Group in 

central and southwest Montana beginning in the 1960's 

(Sando, 1960a, 1976; Sando and Dutro, 1960, 1974; Sando 

and others, 1969; Gutschick and others, 1980; Sando and 

Bamber, 1984, 1985) provide a sound basis for determining 

an Osagean (MFZ 8-9=CZ 10-11) and early Meramecian age 
DEVELOPMENT OF CURRENT CONCEPTS 13 

8 (SE) 

*Brindle (1960) 

(age correlation Fusezy (1960, 1973), 

based on fossils) Kent (1984, 1987) 

Watrous Formation 

Not discussed (TRIASSIC AND JURASSIC) 

(MFZ 10-11=CZ 12-13) for the Mission Canyon Limestone 

of outcrop area. Studies of corals, brachiopods, and foraminifers from well cores in eastern Montana (Sando, 1960b, 

1978; Sando and Mamet, 1981), southern Saskatchewan 

(MacDonald, 1956; Brindle, 1960; Kent, 1974), and western 

and central North Dakota (Sando, 1978; Sando and Mamet, 

1981; Waters, 1984; Waters and Sando, 1987a-c) indicate 

that the subsurface Mission Canyon has approximately the 

same age range as it does in the outcrop area (fig. 3, cols. 5, 

13; fig. 6, cols. 3, 8; fig. 4, col. 20). These paleontologic constraints on the age of the Mission Canyon Limestone were 

accepted in recent subsurface studies by members ofthe U.S. 

Geological Survey in Montana (fig. 3. col. 14) and North 

Dakota (fig. 4, col. 23) but were ignored by other geologists 

in Montana (fig. 3, cols. 15, 16), North Dakota (fig. 4, cols. 

21, 22, 24), and Saskatchewan (fig. 6, cols. 12, 13), who 

extended the age of the Mission Canyon into younger 

Meramecian without explanation of the basis for their age 

determinations. 

KIBBEY FORMATION 

The Kibbey Formation is mainly red-weathering quartz 

sandstone, siltstone, and shale that disconformably overlie 

the Mission Canyon Limestone and form the basal unit of the 

10(SW) 

Hutt 

(1974) 

Watrous and 

Gravel bourg 

Formations 

(JURASSIC) 

11 (SW) 

*Kent 

(1974) 

Watrous and 

Gravelbourg 

Formations 

(JURASSIC) 

Strathallen 

beds 

(part) 

12 

Montana 

Geological 

Society 

(1978) 

Lower Watrous 

Formation 

(PERMIAN AND 

TRIASSIC) 

Tilston 

member 

13 (S) 

Bluemle 

and others 

(1959) 

Lower Watrous 

Formation 

(TRIASSIC) 

Midale/ 

.. 

Frobisher 

Alida 

Tilston 

Big Snowy Group in the mountains of southwest and central 

Montana (fig. 2). The Kibbey was traced into the subsurface 

of eastern Montana (fig. 3), western North Dakota (fig. 4), 

and western South Dakota (fig. 5), where most geologists 

believe that it rests conformably on the Charles Formation 

and where it includes a medial limestone and anhydrite unit 

(Ray Member of Rawson, 1968, 1969). 

Fossils are very rare in the Kibbey Formation. Easton 

(1962, p. 11) reported fragmentary, unidentifiable brachiopods and ostracodes in strata questionably referred to the 

formation at Durfee Creek in central Montana, and Rawson 

(1968, p. 45; 1969, p. 167) recorded unidentified fragments 

of brachiopods, crinoids, and ostracodes from the Ray 

Member in the subsurface. Maughan (1984, p. 183) noted 

that B. Skipp identified "late Meramecian fossils in southwest Montana" from the Kibbey, but he gave no details of 

the occurrence. B.R. Wardlaw (in Sando and others, 1985, 

p. 7) reported middle or upper Meramecian (CZ 15-19) conodonts in the lower part of the formation at Bell Canyon in 

the Tendoy Mountains, extreme southwestern Montana, 

where the Kibbey rests conformably Ofl the McKenzie Canyon Formation (lower Meramecian, MFZ 12=CZ 14). These 

conodonts, which consist ofa few specimens of Hindeodus 

penescitulus in sample W82-135, 41 ft (12.5 m) above the 
14 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

1 (SW) 2(SW) 

Thomas 

(1954) McCabe 

(age correlation (1959) 

from McCabe, (1959) 

Watrous Formation Amaranth Formation 

(JURASSIC) (JURASSIC) 

MC1 member 

3(SW) 

McCabe (1963), 

Kent (1984, 1987) 

(age correlation 

from McCabe, 1959) 

Amaranth Formation 

(Watrous Formation) 

(JURASSIC) 

4 (S) 

Bluemle and 

others (1981), 

Gerhard and 

others (1982) 

Lower 

Amaranth Formation 

(TRIASSIC) 

Mission Canyon 

Formation 

Figure 7. Evolution of lithostratigraphic classification and chronostratigraphy of Osagean through Chesterian rocks and overlying formations in subsurface of Manitoba. Chronostratigraphic correlations in each column are those of the author(s) of that column or were determined by lithostratigraphic correlations to other 

columns. Mississippian provincial series are shaded. Base of diagram marks base of Osagean; other provincial 

series boundaries are marked by dots. Vertical line pattern denotes hiatus. Solid lines denote formation contacts (straight where conformable; wavy where disconformable or unconformable). Dashed lines denote 

boundaries of marker beds or marker-bed intervals. Asterisk (*) marks reference in which fossils were described or discussed. 

base of the Kibbey (B.R. Wardlaw, oral commun., 1993), 

were incorporated in Wardlaw's (1985) transgressive models for the Upper Mississippian and Lower Pennsylvanian 

rocks of Montana and Wyoming. 

Most geologists dated the Kibbey in the subsurface as 

late Meramecian or early Chesterian by bracketing the formation between the presumed Meramecian or Chesterian 

Otter Formation overlying the Kibbey and the presumed 

Meramecian Charles Formation beneath it (figs. 3-5). This 

dating depended on variable interpretations of the age of the 

fossils in the Otter Formation and variable interpretations of 

the age of the Charles Formation made without paleontologic evidence. Some of this dating involved circular 

reasoning because the age of the Kibbey was also used as a 

constraint on the age of the Charles Formation. Interpretations of the Kibbey as early Chesterian by members of the 

U.S. Geological Survey (fig. 3, col. 14; fig. 4, col. 23) and by 

other geologists as middle or late Chesterian (fig. 3, col. 16; 

fig. 4, col. 24; fig. 5, col. 1 0) are the latest published opinions 

on the age of the formation in the Williston Basin subsurface. 

Ostracodes from the uppermost beds of the Otter Formation were regarded by Scott (1942, p. 153) as "most similar to middle and upper Chester faunas." Conodonts from 

the type Otter Formation at Belt Creek (Gilmour, 1989, p. 

32) indicate that the Meramecian-Chesterian (CZ 19/20) 

boundary is in the lower half of the Otter and that the Kibbey 
DEVELOPMENT OF CURRENT CONCEPTS 15 

(/) z (/) 

~ w <( z ZCJ) w ~ (/) z w w <( <(~ w 1-CJ) i=~ a... u uc: c: z 0 

CJ)w U ro ~(/) -(/) -w WCJ) 0 N 

>-- -~ ffi~ C:C/) !:!::w 0 C/)c: c:~ :JW w....J zz CONODONT N w iii 1-w wt9 ~w ~<( -o 0 ZCJ) W....J z<C <Ct; <Co ~N BIOZONES iii w <Co ~<( I- 0:1- I>- Iz <Co _J 

wz ou WC/) U5 f-C/) I-- C:- <( :5<( iS(/) I- c: c:> QCl c: 0 

c: <( (/) 0 oo u.. 0 a... 

:::> c: w z zc: u ~ 

s a... w 0 

u 

z z ::;!; <( z Other zones omitted si= "0 "0 i= <X:i= 20 <ll <ll 

Cl~~ oc: c c c: 320- c:<( 0 0 <( >-a... c:a... (part) Declinognathodus N N 

~ ~- c c 

i= 0~ :::> :::> (/) z ~ noduliferus :::> c: L.U 

* <( a... 0 \ c: 

w z 

~ Rachistognathus primus ~ u.. 

z 325- <( 19 Adetognathus 

0 0: VI 25 

Cl :::> unicornis c: ~ <( * ~ <( z -

u <( 24 c: 0: 18 w w Cavusgnathus altus- 23 a... 330- I- a... (/) f---- Gnathodus girtyi ~ 

:::> w B I 17 22 u 

- * -'---- f v_ -

A 21 

Cavusgnathus altus- - 335- z Hindeodus cristulus 20 

<( \l 15 19 - Cavusgnathus altus- IV -

- 14 Hindeodus 18 

340- z a... - penescitulus D 17 

<( z --,-s w <( 13 (/) a... u c 15 (/) > w f---- 1---f---- :::> - ~ 0 <( 12 B 14 c: c: w (/) w Taphrognathus III u.. 345- ~ f---- I--1---

z (/) 11 varians 13 0 

Cl 

c: - 1--- A f---- <( LY u (/) 10 12 c: 

w 350*-1--- s (/) z 9 Scaliognathus anchoralis- 11 0 <( Doliognathus latus B _J 

- w 

~ - (.9 

<( 8 Gnathodus II 10 ~ (/) 

f---- typic us z 0 '----a;-

355- U5 

<( I--~ 

~ 7 A Siphonodella isosticha- 7 <( z f----

z <( ...... UpperS. crenulata c 6 c: :;2 dJ 'B :::> --g- 0 0 ~ L. Siphonodella crenulata 0 C/) 

I- <ll 

i-=-~ 

I -ro Siphonodella sandbergi I 3 360- c: 

w ii5 0 Siphonodella duplicataf-3- Aiti "0 z ~ I!ZI :;2 ·c: Siphonodella sulcata 1 

:::!; * z :::> z z z a- <( <( c Siphonodella praesulcata "0 "0 >I- zi= <(~ zi= "0 <ll <ll L.LJO: 365- -I- c c o<t zc: Zc: zc: <ll 2 0 a:!::. w<C 0<( w<C c Other zones omitted N 

L.U ~~ >a... ~~ 0 c c a.. w~ N :::> :::> a.. <( <( c ::::l u.. 0 u.. :::> 

Figure 8. Radiometrically calibrated Western Interior Mississippian biozonations. Modified from Sando (1985, fig. 3). Asterisks in 

radiometric scale mark radiometric check points from Harland and 

others (1990). Vertical lines in series column denote hiatus. See 

Sando ( 1985) for sources of biozonations. 

Formation is no younger than late Meramecian (CZ 19) in 

central Montana (table 1). The youngest paleontologically 

dated strata in the underlying Mission Canyon Limestone in 

central Montana are of early Meramecian age (MFZ 10=CZ 

12, Monarch-U.S. 60 section, Sando and Dutro, 1974, pl. 1, 

col. 2). Hence, the possible age range of the Kibbey in its 

type area in central Montana, based solely on paleontologic 

constraints, is early Meramecian (MFZ 10=CZ 12) to latest 

Meramecian (MFZ 15=CZ 19). 

Determination of the precise age of the Kibbey in central Montana requires accounting for the amount of time represented by the hiatus between the Kibbey and the underlying 

Mission Canyon Limestone. Data on the karst event that produced the hiatus in Wyoming and Montana indicate that deposition of the Madison Limestone or Group continued into 

latest early Meramecian time (MFZ 12=CZ 14) and was followed by retreat of the sea from the Cordilleran shelf to the 

Antler foreland basin to the west (Sando, 1988). 

A Late Mississippian transgressive model based on bioand lithostratigraphy (Sando and others, 1975, p. A54-A66) 

depicts the Kibbey Formation as the basal phase of a transgressive lobe that moved eastward across the Cordilleran 

platform in Montana slightly earlier than another transgressive lobe represented by the Amsden Formation in Wyoming. In Wyoming the transgression continued into the 

Pennsylvanian, whereas in Montana the transgression was 

more rapid and was terminated by uplift and erosion during 

latest Chesterian (MFZ 19=CZ 25-26) time. Recent conodont dating of the Kibbey Formation in southwestern Montana and of the lower part of the Otter Formation in central 

Montana (Wardlaw, 1985, in Gilmour, 1989) suggests that 

transgression of the Kibbey across Montana was even more 

rapid than postulated by Sando and others (1975). Eastward 

projection of the base of the Kibbey based on the new evidence suggests that the formation is probably of early 

Chesterian (CZ 20-21) age at its eastern limit in the 

subsurface of North Dakota . 

CHARLES FORMATION 

No fossils were reported from the Charles Formation 

when it was first described from a well core in southeastern 

Montana (Seager, 1942), although some of the fossils listed 

earlier by Sutton (in DeWolfe and West, 1939a, p. 472-475) 

from cores in the Baker-Glendive anticline near the eastern 

boundary of the State probably were from the sequence later 

referred to the formation. MacDonald ( 1956, p. 30) was 

unable to identify fossils found in cores of the Charles Formation in Saskatchewan. Fossils, mostly brachiopods, from 

cores of the Charles Formation in Montana were considered 

by J. Steele Williams, J.E. Smedley, and Mackenzie Gordon, 
16 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

Table 1. Conodont faunules (in ascending order) from approximate type section of the Otter Formation at Belt Creek in 

sec. 11, T. 17 N., R. 6 E., Little Belt Mountains, Cascade County, central Montana. 

[Identified by B. R. Wardlaw (written commun., 1993) in collections made by Gilmour (1989). See also Easton (1962, p. 114, pl. 14) for 

measured section. Conodont and composite zones are shown in figure 8. USGS numbers (-PC) refer to the Late Paleozoic Locality file of 

U.S. Geological Survey at National Center, Reston, Va.] 

USGS Feet (meters) Feet (meters) 

collection above base of above base of Composite 

number Gilmour Otter Conodont assemblage Conodont zone zone 

(-PC) section Formation 

30003 14.4 (4.4) 56.4(17.1) Hindeodus spiculus? Cavusgnathus altus-Hindeodus penescitulus 19 

30004 19.5 (5.9) 61.5 (18.6) Cavusgnathus altus, Hindeodus scitulus, Cavusgnathus altus-Hindeodus cristulus 20 

H. spiculus 

30005 24.3 (7.4) 66.3 (20.1) Cavusgnathus altus, Hindeodus cristulus Cavusgnathus altus-Hindeodus cristulus 20 

30006 25.5 (7.7) 67.5 (20.5) Cavusgnathus altus, Hindeodus sp. Cavusgnathus altus Hindeodus cristulus 20 

30007 34.0 (10.3) 76.0 (23.0) Cavusgnathus altus, Hindeodus cristulus, Cavusgnathus altus-Hindeodus cristulus 20 

H. spiculus 

Jr., as very similar to or identical with fossils in the Mission 

Canyon Limestone (Lower Mississippian) of outcrop (Gardner, 1959, p. 332). 

Early dating of the Charles as encompassing all of 

Meramecian time (fig. 3, cols. 2-11; fig. 4, cols. 2-4, 6-17; 

fig. 5, cols. 2, 4, 5, 7) was based on the premise that the formation represents continuous sedimentation from the top of 

the Mission Canyon Limestone (Osagean) to the base of the 

Kibbey Formation (Chesterian), thus filling the time gap 

postulated between these formations in the outcrop area. 

Restriction of the Charles to the subsurface Williston Basin 

was thought to indicate that this basin was a depositional 

feature in which sedimentation was continuous through 

Mississippian time, in contrast to the surrounding outcrop 

area in which uplift and erosion of the basin margin had 

interrupted deposition between Mission Canyon and 

Kibbey times. These paleotectonic and depositional concepts were maintained into recent years by many Williston 

Basin geologists (fig. 3, cols. 15, 16; fig. 4, cols. 21, 22, 24; 

fig. 5, col. 10; fig. 6, cols. 12, 13). Early dissent from the 

prevailing view was registered by W.S. McCabe (1954) and 

Davis and Hunt (1956) (fig. 3, col. 6; fig. 4; col. 5; fig. 5, 

col. 5), who postulated an unconformity between the 

Charles and the Kibbey in the subsurface. Geologists working in Saskatchewan and Manitoba were mostly relieved of 

the problem of the Charles-Kibbey boundary because preMesozoic erosion removed the critical part of the Mississippian sequence except for a narrow area adjacent to the 

international boundary (figs. 6, 7). 

Brindle (1960) listed and illustrated a large marine 

invertebrate fauna consisting mostly of brachiopods and corals from cores of the Frobisher-Alida, Midale, Ratcliffe, and 

Poplar beds, which constituted the "Charles facies" and part 

of the "Mission Canyon facies" in southeastern 

Saskatchewan. He concluded that the three older lithicmarker-bed units are of Osagean age and that the Poplar beds 

are of early Meramecian age. Brindle's (1960, p. 12) work 

demonstrates the partial time-equivalence of the Mission 

Canyon and Charles "facies." Although his collections of 

lower Meramecian fossils from the Poplar came from only 

two wells and did not extend to the top of the unit, they cast 

some doubt on the conventional interpretation of the Charles 

Formation as spanning the Meramecian in the area south of 

the international boundary. 

Sando (1960b) described and illustrated a moderately 

large coral fauna from three well cores of the Madison Group 

in northeastern Montana, including one core in which the 

corals were in limestone beds interbedded with anhydrite 

and anhydritic carbonate at several levels in the Charles Formation, the highest of which was only about 50 ft (15 m) 

below the top of the formation. No specific statement on the 

age of the Charles was made in this paper because Sando's 

studies of Western Interior corals had just begun, and he did 

not collect data that led to his coral zonation until after the 

paper was submitted for publication. 

In a later paper on seven well cores of the Madison 

Group in northeastern Montana and northwestern North 

Dakota, including the three cores previously studied, Sando 

(1978) found lower Meramecian (CZ 12-13) corals ranging 

from about 300 ft (92 m) below the top of the Mission Canyon Limestone to about 50ft (15 m) below the top of the 

Charles Formation. Sando (1978, p. 236, 237) concluded that 

the top of the Charles in the subsurface can be no younger 

than early Meramecian and that its contact with the overlying Kibbey Formation must be a disconformity, just as it is 

in the outcrop area. Stratigraphic variation of the base of the 

Charles with respect to a coral zone boundary confirmed the 

diachronous nature of that lithologic boundary based on the 

first appearance of evaporite in the sequence. 
DEVELOPMENT OF CURRENT CONCEPTS 17 

Study of foraminifers and algae by Mamet (in Sando 

and Mamet, 1981) in coral samples from four of the well 

cores discussed by Sando ( 1978) confirmed the conclusions 

of the earlier study. Impoverishment of the foraminifer faunas and increased abundance and diversity of the algae were 

interpreted as results of the restricted depositional environments of the Mission Canyon and Charles Formation near 

the center of the Williston Basin. Samples from the Charles 

Formation indicated a possible biozone range of MFZ 

10=CZ 12 to MFZ 12=CZ 14, which confirmed the early 

Meramecian age previously based on corals. 

Waters (1984) and Waters and Sando (1987a-c) recognized four coral zonules ranging from Osagean to early Meramecian in age on the basis of a large coral fauna recovered 

from 29 well cores of the Mission Canyon Limestone (Tilston and Frobisher-Alida intervals) and Charles Formation 

(lower half of Ratcliffe interval) in western North Dakota. 

Although no corals were recovered from the Poplar interval, 

the Charles Formation was regarded as probably entirely of 

early Meramecian age, and a disconformity was thought to 

mark the top of the Charles. 

LITHIC MARKER HORIZONS VERSUS 

BIOZONE BOUNDARIES AS TIME PLANES 

Widespread thin beds of siltstone, sandstone, shale, 

anhydrite, and dolomite that cause sharp deflections on 

gamma-ray logs have been used as datum planes for stratigraphic correlations of well sections of the Madison Group 

since the early days of petroleum exploration in the Williston 

Basin, particularly the northern part (figs. 4, 6, 7). On the basis 

of radioactivity log studies, Thomas (1954, p. 70) used "persistent silt zones terminating limestone depositional cycles" 

to divide the Mission Canyon Limestone of Saskatchewan 

into five "members." Terrigenous beds were used most commonly in subsequent work on the lithic markers. 

The premise that terrigenous marker horizons are 

approximately synchronous time planes was suggested by 

Porter (1955, p. 127, 128), who used the markers to demonstrate the diachroneity of the conventional boundary 

between the Mission Canyon Limestone (shelf carbonate 

sequence) and the Charles Formation (evaporitic sequence) 

in Manitoba and Saskatchewan. Porter (1955, p. 128) 

thought that the markers represent "times of epeirogenic 

fluctuations" within the cyclic carbonate and evaporite 

sequence. A similar interpretation was advanced by Harrison 

and Flood (1956), who modified Thomas' (1954) markerbed system and extended it into North Dakota. Harrison and 

Flood (1956, p. 39) regarded the markers as breaks in sedimentation that resulted from minor tectonic movements, but 

they noted that the markers are not uniformly developed 

across the entire basin owing to the "steepness of the depth 

profile." Fuller (1956a, b) showed that some terrigenous 

marker beds mark the tops of transgressive-regressive 

carbonate-evaporite cycles, and he illustrated plant remains 

from a marker bed in the Mission Canyon Limestone of 

Saskatchewan. Although Fuller (1956a, p. 27) noted that the 

validity of lithic marker horizons as time planes "can be 

proved only by paleontology," he thought that the great areal 

extent of the marker beds was evidence of synchroneity. 

Cumming and others ( 1959) summarized the theoretical 

basis for regarding the terrigenous marker horizons as 

approximately synchronous surfaces, based mostly on previous work, and introduced the term "non-sequential beds" for 

the terrigenous layers. They regarded the carbonate and 

evaporite intervals bounded by the terrigenous marker layers 

as informal para-time-rock units called "beds" and suggested 

that the marker beds represent introductions of terrigenous 

sediment resulting from rhythmic diastrophic pulses that terminated periods of widespread stillstand of normal shelf-carbonate sedimentation. The terrigenous materials in the 

marker beds were regarded as "accumulated sweepings of an 

exposed strand" or "no more than fossilized collections of 

beach combings" (Cumming and others, 1959, p. 730). 

Hence, although the marker beds are not synchronous 

because of their inherently transgressive character, their 

bounding surfaces were thought to be time-parallel and to be 

useful for chronostratigraphy. The conclusions of Cumming 

and others ( 1959) were accepted in most later lithostratigraphic studies of the Madison Group in the northern part of 

the Williston Basin. 

Relatively few paleontologic tests of the validity of the 

marker horizons for chronostratigraphy have been published, and the published tests are seemingly contradictory. 

Brindle (1960, p. 12) found that species of brachiopods and 

corals "showed little or no tendency to "follow" the westwardly rising [carbonate and evaporite] facies" and that different faunal assemblages are generally restricted to 

intervals bounded by the marker beds in the Mission Canyon Limestone of Saskatchewan. He concluded that the 

paleontologic evidence did not contradict the validity of 

units bounded by lithic marker beds as para-time-rock 

units. On the other hand, Sando (1978, p. 234) and Sheldon 

and Carter (1979, p. 252, fig. 54) noted a significant angular difference between paleontologically determined Mississippian series boundaries and lithic marker horizons in a 

stratigraphic profile of the Madison Group from central 

Montana to southeastern Saskatchewan. 

Waters (1984, p. 75, 105-108; Waters and Sando, 

1987a, p. 198) observed that, although coral abundance and 

diversity are affected by water depth and salinity, coral 

zonules can be traced through several different depositional 

environments in the Mission Canyon Limestone of western 

North Dakota. Waters noted close parallelism between coral 

zonule boundaries and lithic marker horizons in three stratigraphic profiles from the margins to the center of the Williston Basin. He also pointed out that coral zonule boundaries 

can be traced into the center of the basin where the Bottineau, 

Tilston, and Frobisher-Alida interval boundaries are difficult 

to determine using lithic marker beds. Waters concluded that 

the marker-bed horizons are essentially time parallel. 
18 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

Peterson (1978a, b, 1984, 1987) recognized four lithic 

marker horizons within the Madison Group of Montana, 

North Dakota, South Dakota, and Wyoming, two of which 

were correlated with standard lithic marker horizons recognized by other geologists in the Mission Canyon Limestone 

of North Dakota. Peterson (1987, p. 177) suggested eolian 

derivation, distribution during low sea level, and reworking 

by subsequent marine transgression during rising sea level 

for the origin of the terrigenous marker beds. He plotted 

coral zone boundaries from Sando (1978) on two well sections from northeastern Montana in a stratigraphic profile 

that shows the marker horizons (Peterson, 1987, fig. 7). 

Using these data and other information provided him by 

Sando, Peterson ( 1987, p. 178) concluded that two of his 

marker horizons were close to Mississippian series boundaries established on coral zones by Sando (1978). This exercise, although based on limited data, provided a tentative 

linkage between chronostratigraphy based on paleontology 

and the lithic marker bed system over a wide area of the 

Williston Basin subsurface. 

MADISON-KIBBEY CONTACT 

The contact between the Kibbey Formation and the 

underlying Mission Canyon Limestone (outcrop) or the 

Charles Formation (subsurface) has been interpreted, on the 

basis of physical relationships of the strata immediately 

below and above the contact, as disconformable or unconformable by some geologists and as conformable and transitional by others. Detailed observations of the relationships of 

these strata are made difficult by generally poor exposures in 

the outcrop area and by the lack of continuous cores through 

the contact in the subsurface. Most geologists working in the 

outcrop area favored a disconformity or unconformity, 

whereas majority opinion favored a conformable contact in 

the subsurface. These contradictory opinions have been 

influenced by different concepts of the regional geologic history of the upper part of the Mississippian sequence based on 

other evidence. 

OUTCROP AREA 

Most early investigators of the Madison and overlying 

rocks in central and southwestern Montana concluded that 

these sequences are conformable and that sedimentation was 

continuous across the boundary between them (Peale, 1893; 

Weed, 1899a, b; Freeman, 1922; Reeves, 1931), but they did 

not describe the contact or give reasons for their conclusions. 

Their ideas were probably biased by the opinions of paleontologists, who regarded the fossils from these rocks as representing a continuous biostratigraphic succession. 

Scott ( 1935) concluded that the contact is a disconformable erosion surface, based on his observations of silicification and glazing of the top of the Madison, contact relief of 

4-6 ft ( 1.2-1.8 m), and the presence of solution cavities, 

filled by sediments of the Kibbey, below the top of the Madison at many localities in southwestern and central Montana. 

Sloss and Hamblin (1942) used similar criteria to assert that 

the top of the Madison was an erosion surface throughout the 

area of its outcrop. Perry and Sloss ( 1942), Gardner and others (1946), and Walton (1946) described channels and filled 

solution cavities in the Madison in central Montana. Sando 

and Dutro (1960) measured relief of 30 ft (9 m) and 200 ft 

(60 m) in sinkholes in the top of the Madison beneath the 

Kibbey in southwestern Montana. 

Similar observations of post-Madison, pre-Kibbey 

karst features in the outcrop area were recorded by Sloss 

(1950, 1952), Norton (1956), Miller (1959), Robinson 

(1963), and Sando and Dutro (1974). The Madison-Kibbey 

contact was also regarded as a disconformity or unconformity in the outcrop area, without detailed description, by 

Gardner and others (1945), Perry (1945), Leatherock (1950), 

Sloss and Moritz (1951), Gardner (1959), Easton (1962), 

Craig (1972), Sando and others (1975), Sando (1976, 1988, 

1989a, b, 1992), Smith and Gilmour (1979), Wardlaw 

(1985), and Gilmour (1989). The distribution of specific 

locations at which physical evidence of disconformity has 

been reported is shown in figure 9. The only exception to the 

rule known to me is in the Tendoy Mountains in extreme 

southwestern Montana (fig. 9), where the Kibbey conformably overlies a Mississippian sabkha deposit represented by 

the McKenzie Canyon Fomiation of the Tendoy Group 

(Sando and others, 1985). 

Maughan and Roberts ( 1967, p. B5) and Roberts ( 1979, 

p. 238) acknowledged published records of an unconformity 

in central and southwestern Montana, but they regarded the 

unconformity as of merely local significance. Their statement (Maughan and Roberts, 1967, p. B5) that the unconformity is confined to the "margin of deposition" is not verified 

by the distribution of locations at which this feature has been 

reported (fig. 9), which suggests instead that post-Madison, 

pre-Kibbey erosion characterized all the area of Kibbey deposition in central and southwestern Montana. Maughan 

(1984, p. 183) also minimized the significance of the hiatus 

between the Madison and the Kibbey by asserting that "karst 

development and some of the solution features are related to 

postdepositional collapse and flowage of the unconsolidated 

Big Snowy sediments into solution caverns in the Madison." 

These attempts to minimize or discredit evidence of a 

regional intra-Mississippian erosional event in the outcrop 

area are related to a pervasive belief by Maughan that the 

Mississippian-Pennsylvanian boundary is marked by an 

unconformity everywhere in North America and that the erosional event that produced this feature is the only significant 

erosional event recorded in the Carboniferous of North 

America. This concept, which stems from Chamberlin and 

Salisbury (1906)(see Maughan and Roberts, 1967, p. B20), 

has not been confirmed by modem biostratigraphic studies in 

the northern Cordilleran region (Dutro and others, 1984 ). 
113° 

49° 

48° 

4T 

46° 

45° 

DEVELOPMENT OF CURRENT CONCEPTS 

112° 11r 110° 109° 

UNITED STATES 

0 Great Falls .------- , 

SOUTH MOCCASIN 

MOUNTAINS 

/./ 6. 7 '\ (-- \ 

5• • •9 ' 115 IL a• I '- ~ 6 _e~istown 

•1o I --- --- 1 / ', 

108° 

\ • // 14. 16. 17 \ Helena , 11 / 1 13 20 • \ BIG SNOWY 

0 '---1------- \~ 12 ••••18 -::-MOUNTAINS 

10T 

Fort Peck 0 

106° 105° 

Glendive 0 

LITTLEBELT '- 19 / MOUNTAINS -. _____ .- 0

Miles City 

/;4'\ THREE FORKS-

/ \ /TOWNSEND 

1 3• / AREA 

I 2• I \ I 

9___T_!:Iree Forks 

LOCATION INFORMATION 

1. Baldy Mountain, sees. 26 and 27, T. 7 S., R. 3 W., Madison County (Sando and Dutro, 1960) 

2. Eustis, sees. 7 and 8, T. 2 N., R. 2 E., Broadwater County (Gardner and others, 1946) 

3. Lombard, sec. 7, T. 4 N., R. 3 E., Broadwater County (Sando and Dutro, 1960) 

4. Townsend, sec. 7, T. 6 N., R. 1 E., Broadwater County (Scott, 1935) 

5. Monarch-US 89, sec. 22, T. 16 N., R. 7 E., Cascade County (Perry and Sloss, 1942; Sando and Dutro, 1974) 

6. Riceville-Belt Creek, sees. 24-26, T. 16 N., R. 6 E., Cascade County (Walton, 1946; Norton, 1956) 

7. Kibbey School, sec. 8, T. 16 N., R. 8 E., Judith Basin County (Norton, 1956) 

8. Peterson Gulch-Lone Tree Gulch, sec. 35, T. 16 N., R. 9 E., Judith Basin County (Norton, 1956) 

9. Lone Tree Dome, sec. 20, T. 16 N., R. 10 E., Judith Basin County (Norton, 1956) 

10. Running Wolf Creek, sec. 31, T. 15 N., R. 11 E., Judith Basin County (Norton, 1956) 

11. Judith River, sec. 25, T., 13 N., R. 11 E., Judith Basin County (Norton, 1956) 

12. Oka Creek, sec. 21, T. 11 N., R. 15 E., Judith Basin County (Norton, 1956) 

13. Big Careless Creek, sec. 12, T. 11 N., R. 18 E., Fergus County (Norton, 1956) 

14. Potter Creek Dome, sec. 8, T. 13 N., R. 21 E., Fergus County (Norton, 1956) 

15. South Moccasin Mountains, sec. 11, T. 16 N., R. 17 E., Fergus County (Miller, 1959) 

16. Beacon Hill, sec. 6, T. 12 N., R. 20 E., Fergus County (Gardner, 1959) 

17. Durfee Creek Dome, sec. 13. T. 12 N., R. 22 E., Fergus County (Gardner and others, 1946; Gardner, 1959) 

18. Stonehouse Ranch, sec. 32, T. 11 N., R. 21 E., Golden Valley County (Gardner, 1959) 

19. State Road 25, sec. 25, T. 11 N., R. 20 E., Golden Valley County (Gardner, 1959) 

20. Swimming Woman Canyon, sec. 16, T. 11 N., R. 19 E., Golden Valley County (Sloss and Hamblin, 1942) 

19 

104° 

Figure 9. Locations in central and southwestern Montana at which a disconformity was reported at the Madison-Kibbey contact. Hachured 

line marks erosional zero edge of Kibbey Formation; hachures are on side where Kibbey is present. Modified from Maughan and Roberts 

(1967, pl. 3). 
20 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

SUBSURFACE 

Most reports on the Charles or Kibbey Formations in 

the subsurface portrayed the boundary between the formations as conformable on graphic stratigraphic sections or 

made statements implying conformity, but they did not 

describe detailed physical relations at the contact (Dewolfe 

and West, 1939b; Jones, 1940; Seager and others, 1942; 

Sloss and Hamblin, 1942; Hadley and others, 1945; Perry, 

1945; Walton, 1946; Sloss, 1952; Barnes, 1952; Folsom and 

Anderson, 1955; Fish and Kinard, 1959; Willis, 1959; 

Sando, 1960b; Easton, 1962; Sandberg, 1962; Carlson and 

Anderson, 1965; Carlson, 1967; Rawson, 1968; Craig, 1972; 

Cook, 1976; Bluemle and others, 1980, 1981, 1987; Gerhard, 1982; Gerhard and others, 1982, 1990; Ballard and others, 1983; Gerhard and Anderson, 1988; Kerr, 1988). In 

other reports, the terms "transitional" or "gradational" have 

been used to characterize contact relations, without detailed 

description (Perry and Sloss, 1943; Gardner and others, 

1945; Hadley, 1950; Leatherock, 1950; Nordquist, 1953; 

Gardner, 1959). Maughan and Roberts (1967, p. B5, pl. 2, 

profile D-D') described the Charles-Kibbey contact as conformable throughout the subsurface of Montana and interpreted lithic changes at the contact in several wells in 

northeastern Montana as evidence of local intertonguing of 

the two formations. 

The early literature on the Williston Basin includes a 

few reports that presented evidence for an unconformity at 

the Charles-Kibbey contact. Allen (1939, p. 1247) regarded 

variations in "thickness, lateral extent, and composition" of 

dolomite beds beneath the Kibbey Formation in eastern 

Montana as evidence of unconformity at the contact with the 

underlying "Madison." McCabe (1954) recognized an 

unconformity between the Charles and the Kibbey throughout the Williston Basin; he believed that axes of thinning 

shown by an isopachous map of the Madison Group were the 

results of erosion associated with pre-Kibbey folding. 

Although Middleton and Kennedy (1956, p. 56-57) believed 

that the Kibbey rests conformably on the Charles Formation 

over most of the Nesson anticline in northwestern North 

Dakota, they noted that absence of the uppermost salt 

beneath the Kibbey at the margins of the Williston Basin 

suggested "an unconformable relationship." Davis and Hunt 

(1956, fig. 2) showed the Charles-Kibbey contact as unconformable in a preliminary correlation chart for the northern 

part of the Cedar Creek anticline in eastern Montana but did 

not discuss the nature of the boundary. Mickelson (1956, p. 

70, 71) recognized an unconformity between the Charles and 

the Kibbey in the subsurface of central Montana but gave no 

evidence for his conclusion. The North Dakota Geological 

Society (1959, p. 2) stated that the top of the "Charles facies" 

is "generally unconformable with overlying beds" in the 

Williston Basin. Ballard ( 1963, p. 26) stated that the Poplar 

interval (uppermost part of Madison Group) "is unconformably overlain by the Kibbey and Otter Formations" in eastern 

North Dakota, and he noted a breccia between the Poplar and 

the Kibbey in one well. Like McCabe (1954 ), Ballard attributed some thinning of the Poplar to pre-Kibbey erosion. 

Arguments by Sando (Sando and others, 1975; 1976; 

1978; Sando and Mamet, 1981) favoring a disconformity 

between the Charles and Kibbey Formations in the Williston 

Basin subsurface were based mainly on age relations established by biostratigraphy and lacked presentation of physical 

evidence at the contact. Sando ( 1978, p. 236) pointed out, 

however, that the presence of lower Meramecian corals only 

50 ft (15 m) below the top of the Charles Formation in the 

Shell Pine well in northeast Montana contradicts Maughan 

and Roberts' (1967, pl. 2, profile D-D', well 50) postulated 

intertonguing of the Charles and Kibbey in that section. 

Sando's interpretation of the contact as a regional disconformity was followed by Peterson ( 1978a, b, 1984, 1987, 1988), 

Sheldon and Carter (1979), Smith and Gilmour (1979), 

Waters (1984 ), Brown and others (1984 ), Waters and Sando 

(1987a-c), and Peterson and McCary (1987) without significant discussion of physical relations of beds at the contact. 

SALT BEDS IN THE MADISON GROUP 

Bedded salt deposits were first recorded in the Madison 

Group by Kline (1942, p. 373, 374) in a part of the sequence 

referred to the Charles Formation by Seager and others 

(1942, p. 1420) in the Kamp 1 well on the Nesson anticline 

in northwestern North Dakota. Individual salt beds or the 

collective salt interval (commonly referred to as "Madison 

salt" or "Charles salt") have been noted, described, or discussed in many subsequent reports on the central area of the 

Williston Basin in northeastern Montana and western North 

Dakota (Perry and Sloss, 1943; Nordquist, 1953; McCabe, 

1954; Folsom and Anderson, 1955; Beekly, 1956; Harrison 

and Flood, 1956; Laird and Folsom, 1956; Middleton and 

Kennedy, 1956; Anderson and Nelson, 1956; Anderson and 

Hansen, 1957; Kohanowski, 1957; Anderson, 1958, 1964; 

Fish and Kinard, 1959; Great Northern Railway Company, 

1959; Sando, 1960b, 1976; Sandberg, 1962, 1973; Billings 

Geological Society, 1964; Carlson and Anderson, 1965; 

Carlson, 1967; Maughan and Roberts, 1967; Cook, 1976; 

Peterson, 1978b, 1984; Sheldon and Carter, 1979; Smith and 

Gilmour, 1979; Bluemle and others, 1980; Orchard, 1987), 

in southern Saskatchewan (Thomas, 1954; Fuller, 1956a, b; 

Brindle, 1960; Fuzesy, 1960), and in general summaries of 

Williston Basin Madison stratigraphy (Barnes, 1952; Sloss, 

1952, 1953, 1956; North Dakota Geological Society, 1959; 

Pierce and Rich, 1962; Sando, 1976, 1989a, b, 1992; Gerhard, 1982; Gerhard and others, 1982, 1990; Brown and others, 1984; Peterson, 1987, 1988; Peterson and McCary, 

1987; Gerhard and Anderson, 1988; Kerr, 1988; Borchert 

and others, 1990). 

In this report, the informal term "Madison salt" is used 

for the entire salt-bearing sequence in the Madison Group. 

The informal term "top Madison salt" is used for the uppermost salt bed in the salt-bearing sequence. 
DEVELOPMENT OF CURRENT CONCEPTS 21 

STRATIGRAPHIC AND 

GEOGRAPHIC DISTRIBUTION 

Early paleogeographic maps of the Charles Formation 

in Montana, North Dakota, South Dakota, and southern 

Canada by Perry and Sloss (1943, fig. 7B) and Sloss (1953, 

fig. 4) do not distinguish distribution of halite from that of 

anhydrite. Nordquist (1953, p. 79) noted that "a massive salt 

bed is present at the top of the Charles over an extensive 

area" in northeastern Montana and that the top of the salt 

made a good marker for separating the Charles and Kibbey 

Formations (see also North Dakota Geological Society, 

1959, p. 2). He distinguished as many as eight salt beds in 

the Charles on his stratigraphic profile for northeastern 

Montana (Nordquist, 1953, fig. 5). 

Nordquist (1953, p. 80) suggested that thinning of the 

Charles Formation on the East Poplar anticline may be due 

to subaerial erosion on islands in the Charles sea, but he also 

observed that the absence of the salt in the Poplar area may 

have resulted from leaching rather than nondeposition. 

Beekly (1956, fig. 4) presented a map showing thickness variation of the "Charles salt" (Madison salt of this report) in the 

Poplar area, but he did not explain the reason for the variation. 

Brown and others (1984, p. B 17) noted that the thickness of 

the Charles Formation in the area of salt deposition may have 

been affected by postdepositional dissolution of halite. 

Orchard ( 1987) presented evidence that the absence of salt 

beds on the Poplar dome was the result of Tertiary dissolution. 

Fuller (1956a, p. 36, fig. 2) described two "salt beds" in 

the "Charles evaporites" between the top of the Ratcliffe 

beds and the pre-Mesozoic unconformity in south-central 

Saskatchewan, but he pointed out that these "salt beds" are 

mostly anhydrite and mudstone containing molds of halite 

crystals. These "upper and lower" salt beds in the Poplar 

interval of Saskatchewan were also noted by Brindle (1960, 

p. 13, fig. 2) and by Fuzesy (1960, p. 39). 

Anderson and Hansen ( 1957) distinguished six separate 

salt beds, labeled A to F in descending order, interbedded 

with anhydrite, limestone, and dolomite in the Charles Formation of North Dakota and a seventh salt bed (bed X) near 

. the base of the Charles in a small area east of the main body 

of Mississippian salt deposits. They indicated that beds A to 

F are also present in northeastern Montana and that beds D 

and F extend into Canada. Isopach maps showing the distribution of each salt bed in North Dakota were presented. Beds 

A-X comprise the "Madison salt," and bed A is the "top 

Madison salt" of this report. 

Six salt beds were reported in the Charles Formation or 

Poplar interval in the northern part of the Williston Basin in 

Montana and North Dakota by Anderson (1958, fig. 2), Fish 

and Kinard (1959, pl. IV), Sandberg (1962, p. 60-62), Pierce 

and Rich (1962, p. 57), and Cook (1976), but as many as 

seven or nine salt beds were reported by Kohanowski ( 1957, 

p. 77) and Great Northern Railway Company (1959, appendix 1), respectively. Sandberg (1962) and Pierce and Rich 

(1962) followed the classification of Anderson and Hansen 

(1957), but they placed the X salt in the upper part of the 

Mission Canyon Limestone. 

Most of the information on the distribution of salt beds 

in the Madison Group is based on radioactivity log studies 

because of the great expense of coring the salt and the difficulties encountered in recovering good cuttings and cores of 

such soluble material. Kohanowski's (1957, p. 74) study of 

the petrography and chemistry of core samples of the Charles 

salt in northwestern North Dakota led him to conclude that 

"electric logs portray an idea of continuous salt horizons, 

while in reality there are numerous disconnected but overlapping lenses." He also found evidence of much paragenetic 

alteration of original halite, and he noted that alteration 

becomes more advanced as thickness of salt lenses increases. 

Study of cores from three wells on the Nesson anticline in 

northwestern North Dakota by Great Northern Railway 

Company (1959, appendixes F-H) revealed many beds of 

ankerite, anhydrite, and green shale 1-4 in. (2.5-1 0 em) thick 

within the salt deposits. 

Total isopach maps of the Madison salt were presented 

by Great Northern Railway Company (1959, appendix A), 

Pierce and Rich (1962, fig. 21), Sandberg (1962, fig. 16; 

1973, fig. 26), Cook, 1976, pl. 3), and Sheldon and Carter 

(1979, fig. 66). The area of Madison salt distribution was 

also shown by Peterson (1984, fig. 11, pl. 3; 1987, fig. 20; 

1988, figs. 8, 9), Peterson and McCary (1987, figs. 15, 24), 

and Kerr (1988, fig. 21). Isopach maps of the top Madison 

salt (A salt of Anderson and Hansen, 1957) were presented 

by Anderson and Hansen (1957, fig. 4), Great Northern Railway Company (1959, appendix B), and Anderson (1964, fig. 

4). These distribution data for the salt deposits of the Charles 

Formation indicate that a depocenter was located in 

northwestern North Dakota, that the salt beds thin toward the 

margin of the area of salt deposition, and that the area of salt 

deposition expanded, then contracted during Charles time. 

ORIGIN 

Early explanations of the origin ofthe Charles evaporite 

sequence, including the salt, postulated an increase in salinity owing to restriction of the last phases of the Madison sea 

in the central and deeper part of a depositional basin in Montana and North Dakota (Sloss and Hamblin, 1942, p. 325; 

Perry and Sloss, 1943, p. 1301; Hadley, 1950, p. 46; Nordquist, 1953; Sloss, 1953, 1956; Thomas, 1954). Perry and 

Sloss's (1943, fig. 7B) paleogeographic map of the Charles 

Formation shows the formation separated from coeval rocks 

in the geosyncline to the west by an intervening area exposed 

to subaerial erosion, although they postulated intermittent 

marine connections to account for the alternation of anhydrite and limestone in the Williston Basin. Most theories on 

the origin of the salt deposits postulate a marine environment 

for all the salt beds. 

In his general theory of the origin of ancient evaporite 

deposits, Sloss (1953, p. 151-153, 156-158, table 1) classified the Charles Formation as a tectonically silled 

intrabasinal evaporite sequence and showed marine 
22 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

connections between the western geosyncline and the Williston Basin on his paleogeographic map of Charles time 

(Sloss, 1953, fig. 4). This apparent westward extension of 

the Charles sea, seemingly inconsistent with evidence of erosion in the area between the Williston Basin and the western 

geosyncline during pre-Kibbey time, may have been influenced by Nordquist's (1953, fig. 8) recognition of the 

Charles Formation in the subsurface across northern Montana. Sloss's (1953, p. 156-158; 1958, p. 11) intrabasin 

model for the Charles evaporites postulates separation of a 

rapidly subsiding basin of deposition from a surrounding 

open-circulation shelf by a tectonically stable submarine sill, 

increased salinity in the restricted area caused by excess 

evaporation of surface waters in an arid climate, and gravity 

flow of the denser, highly saline brines into the deeper central part of the basin. Sloss's ( 1953) theory of evaporite deposition was followed by most later writers on the origin of 

Mississippian salt in the Williston Basin (Thomas, 1954, p. 

72;Landes, 1960,p.56;Sandberg, 1962,p.63,64; 1973,p. 

149; Billings Geological Society, 1964, p. 107). 

Sandberg (1962, p. 63, 64; 1973, p. 149) suggested that 

the ancestral Cedar Creek anticline may have been a restricting shoal area during deposition of the Charles salt beds 

(beds A-F of Anderson and Hansen, 1957). He postulated a 

sabkha or salt-marsh origin for the salt at the top of the Mission Canyon Limestone (bed X of Anderson and Hansen, 

1957) because of its location near the eastern shoreline of the 

Mississippian sediments. Smith and Gilmour (1979, p. X19) 

attributed the origin of evaporite beds in the Charles Formation of northeastern Montana to sabkhas and salt pans developed during Late Mississippian regression. 

Sando (1976, fig. 6) noted that the area oflate Osagean 

and early Meramecian evaporite deposition was much larger 

than indicated by previous writers because of the presence of 

evaporite-solution breccias in western Montana and parts of 

Wyoming. He invoked the evaporite model of Adams and 

Rhodes ( 1960), originally proposed for the Permian of the 

southwestern United States, to explain the distribution of 

anhydrite, salt, and dolomite in the Mississippian of the 

northern Rocky Mountain region (Sando, 1976, p. 333-335). 

In this model, an evaporite lagoon formed on a broad shelf 

when restriction of circulation on the shelf by sediment 

buildup at the shelf margin caused a salinity increase within 

the lagoon. Shoreward increase in salinity resulted in a 

shoreward progression of less soluble to more soluble 

evaporite deposits. Application of the model to the Mississippian of the Williston Basin places emphasis on this basin 

as a part of the huge Cordilleran shelf and not as a separate 

depositional system, as has been implied in most subsurface 

studies. Sando ( 1988, 1989a, b, 1992) modified this model to 

include a continental salt lake as the final phase of the shallowing-upward sedimentary progression represented by the 

Madison Group in the Williston Basin. 

INTERPRETIVE SUMMARY 

OF PREVIOUS WORK 

Despite a distinguished record of research into the history of Mississippian sedimentation in the Williston Basin 

and successful exploitation of its petroleum resources, some 

troublesome inconsistencies in interpretation of the geologic 

history remain to be resolved. Review of previous work 

evokes the following observations. 

1. Many subsurface stratigraphers, particularly those 

working in the heart of the basin in North Dakota, have paid 

little or no attention to biostratigraphic evidence, from the 

outcrop area to the west and even from the subsurface of the 

basin itself, that contradicts ages and regional chronostratigraphic correlations assigned by them to Mississippian 

rocks. Although biostratigraphy seems to confirm the validity of lithic marker beds as approximate time planes within 

the basin, apparent divergence of some biostratigraphic and 

lithic marker horizons between stratigraphic sections in the 

basin and those in outcrop areas to the west presents a problem for regional interpretation of geologic history. Timetested traditional biostratigraphic methods are still the most 

reliable means for regional chronostratigraphy. Recent work 

by Peterson (1987, p. 187) suggests that some lithic marker 

horizons are close to biostratigraphic horizons traced into the 

subsurface from outcrop sections where fossils are obtained 

and studied relatively easily. Some coral zonules have been 

shown to extend into the heart of the Williston Basin, where 

lithic marker horizons are absent or poorly developed 

(Waters and Sando, 1987a, p. 199). Regional stratigraphic 

syntheses and future development of petroleum resources 

within the Williston Basin would benefit by consideration of 

all available evidence by geologists working in the basin. 

2. Biostratigraphic studies (Brindle, 1960; Sando, 

1960a, 1978; Sando and Mamet, 1981; Waters, 1984; Waters 

and Sando, 1987 a-c) show that strata in the upper part of the 

subsurface Madison Group outside of the area of salt 

deposition and beneath the Madison salt at the center of the 

Williston Basin are the same age (early Meramecian, 

MFZ 11-12=CZ 13-14) as strata at the top of the Madison 

in the outcrop area of central Montana, where a disconformable relationship with the overlying Kibbey Formation (early 

Chesterian) is well established on physical evidence. The age 

of the Madison salt remains to be determined unequivocably 

because the salt has not yielded fossils; however, the only 

biostratigraphic evidence of post-early Meramecian, preearly Chesterian strata known from the Cordilleran platform 

west of the Williston Basin is in the Mississippian sequence 

at the western edge of the platform in the Tendoy Mountains 

of extreme southwestern Montana (Sando and others, 1985) 

(fig. 10), where a shoreline is defined by a sabkha facies in 

the McKenzie Canyon Formation. Although shelf-carbonate 

strata of the Madison Group and equivalent formations 
130° 

50° 

40° 

DEVELOPMENT OF CURRENT CONCEPTS 23 

120° 

D 

~ 

~ 

D 

110° 100° 

1 1 111~ 1 I, 1 1 111~ 1 ' 111~11 

".. I ......_ / - ......._ I / ' I ....._ ../ - ........_ I / """- II ........_ ,.......- - ......._- I -

I I , / ;- - \ - I I \ , / ;- 1- \ - I , / "-

\ 1\......, /_I , \ \ I ' ,..._J / - / \ ./ I / 

500 KILOMETERS 

100 MILES 

EXPLANATION 

Madison salt (central Williston Basin)-Area of top Madison 

salt bounded by dashed line 

Mississippian rocks (Antler foreland basin and Prophet 

trough) 

Area where paleontologically dated post-early Meramecian, 

pre-Chesterian rocks are absent (Cordilleran platform) 

Pre-Mississippian Paleozoic rocks (Transcontinental arch 

and border of Canadian shield) 

Pre-Mississippian rocks (Antler orogen) 

Precambrian rocks (Canadian shield) 

,-,1'-_,...., 

'./ - / ' I / I _' !__ / '/' I I _' !__ 

\~- ~ '_ _: ~. CANADIAN/ 

\ I I ; SHIELD ; 

\ ~ I I : I ~ I I I /' I I 

\_ I - / "', II -..... / / ......._- I -

',1 \ - \I \ , "- I 

\t- - I ...... _ ' I ./ I / 

\ ./ ' ./ ...... - '/ 

I / / ' / I _' !__ 

/ I,/ \- - \ ./' 

/ ' ; \ / ,'-/ \-, ,~~\.,._ , ,--. I \ 

~~~~~~- / ......... / - ......... 1 

11\,/--: 

I ...... ,....._, / 

' I 

Figure 10. Paleotectonic map of part of western North America showing isolation of Madison salt area from marine areas during postearly Meramecian, pre-Chesterian time. Modified from Sando and others ( 1990, fig. 1 ). 
24 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

extend northward from Montana and North Dakota into Canada and southward into Wyoming and South Dakota, no evidence exists for marine connections between the Williston 

Basin and the Antler foreland basin to the west through these 

areas during middle and late Meramecian time. After initial 

flooding of the Cordilleran platform during Kinderhookian 

time, major transgressions and regressions of the Madison 

sea proceeded across the platform in an essentially east-west 

direction perpendicular to shorelines that trended northeastsouthwest (Sando, 1976). Hence, no marine source was 

accessible to the center of the Williston Basin between early 

middle Meramecian (MFZ 13=CZ 15) evacuation of the shelf 

and Chesterian transgression (fig. 10). 

3. Although a few writers noted physical evidence of 

disconformity or unconformity near the center of the Williston Basin, most writers described the contact between the 

Madison Group and the overlying Kibbey Formation as gradational and transitional in that area. Moreover, the top Madison salt is apparently continuous over most of the central 

part of the basin and shows little or no evidence of preKibbey dissolution (with the possible exception of the Poplar 

dome area). Thus, these two lines of physical evidence 

remain as apparent contradictions to the geologic history 

derived from biostratigraphy. 

NEW INTERPRETATION 

OF CRITICAL EVIDENCE 

The preceding historical summary suggests that the controversy about the age and stratigraphic relations ofthe upper 

part of the Madison Group in the Williston Basin is not the 

result of a lack of information but rather is a conflict in interpretations of existing lithic and paleontologic data. Resolution 

of this conflict requires explanation of all available evidence. 

CONTACT BETWEEN MADISON SALT 

AND KIBBEY FORMATION 

TRUNCATION OF BEDS IN THE SALT SEQUENCE 

BELOW THE TOP MADISON SALT 

Careful examination of some published stratigraphic 

profiles across the margins of the Madison salt basin reveals 

geometric evidence of erosional truncation of carbonate and 

evaporite beds in the upper part of the Charles Formation 

beneath the Kibbey Formation outside the area of the top 

Madison salt. Such truncation is particularly evident in the 

detailed profiles of Cook (1976, pis. 5-9) in western North 

Dakota, which are reinterpreted in figure 11. Carbonate and 

evaporite beds beneath the top Madison salt were shown by 

Cook as pinching out before reaching the top of the Charles 

Formation between control points, requiring convergence to 

explain angular differences in attitudes of these beds from 

attitudes of beds beneath them. A simpler explanation, consonant with prevailing dips, extends these beds to the 

truncated top of the Charles Formation (figs. liB, C, E, F). 

Truncation of beds at the top of the Charles is also clearly 

shown, without revision, by Anderson's (1958, fig. liB) 

profile in western North Dakota (fig. 11 C). 

Other evidence of truncation of individual beds in the 

upper part of the Charles can be seen in Leatherock' s ( 1950) 

profile A-A' (sections 1-1 0) in southeastern Montana and in 

her profile B-B' (sections 11-16) in northwestern South 

Dakota. Peterson (1984, pl. 5) showed variations in thickness of his M-12 to Me interval that are suggestive of truncation in his profile B-B' (sections M-Y -5 to M-GF-5) in 

southeastern Montana and in his ( 1984, pl. 4) profile A-A' 

(sections M-Y -5 to ND-ML-2) in northeastern Montana 

and northwestern North Dakota. 

BIOSTRATIGRAPHIC EVIDENCE 

Corals and foraminifers representative of lower Meramecian CZ 12, CZ 13, and probably CZ 14 were recovered 

from the upper part of the Charles Formation beneath the 

Kibbey Formation in two wells just outside the area of the 

Madison salt in Montana (well numbers 1 and 3 in figs. 

12-14, table 2). Within the salt basin, the youngest corals 

recovered represent lower Meramecian CZ 12, and these 

fossils are restricted to the lower part of the Charles Formation beneath the oldest salt bed (figs. 13, 14, table 2); this is 

due to adverse environmental conditions within the salt 

basin. The CZ 12/CZ 13 boundary was projected through the 

unfossiliferous sequence by assuming approximate parallelism with lithic marker horizons within the salt basin. 

Thes.e biostratigraphic data, together with the evidence for truncation at the top of the Charles, indicate that 

the salt sequence below the top Madison salt is a lateral 

equivalent of the surrounding marine shelf carbonate and 

evaporite sequence and that it is no younger than early 

Meramecian (CZ 14). 

Figure 11 (adjacent and following pages). Lithostratigraphic 

profiles across margin of top Madison salt basin showing 

erosional truncation of beds at top of Madison Group beneath 

Kibbey Formation in North Dakota. See Cook (1976) and Anderson (1958) for detailed locations of well sections. Index map modified from Cook (1976, pl. 9). A, Profile modified from Cook 

(1976, pl. 5): 1, NDGS 4193; 2, NDGS 3441; 3, NDGS 2721; 4, 

NDGS 984. B, Profile modified from Cook (1976, pl. 6): 5, 

NDGS 2892; 6, NDGS 3596; 7, NDGS 3979; 8, NDGS 3363; 9, 

NDGS 3406; 10, NDGS 3235. C, Profile modified from Anderson 

(1958, fig. 2}: 11, S.G. Harrison, J.H. Anderson et all; 12, Hunt 

Oil Co., L.C. Anderson 1; 13, Hunt Oil Co., Home 1; 14, Amerada Petroleum Co., H.O. Bakken 1. D, Profile modified from Cook 

(1976, pl. 8): 15, NDGS 2929; 16, NDGS 2930; 17, NDGS 4153; 

18, NDGS 2051; 19, NDGS 2779; 20, NDGS 4386. E, Profile 

modified from Cook (1976, pl. 9): 21, NDGS 4198; 22, NDGS 

1536; 23, NDGS 2117; 24, NDGS 4833; 25, NDGS 4455. 
49° 

48° 

4T 

104° 103° 

8300 

8400 

8500 

8600 

8700 

8800 

CANADA 

--UNiTED! STATES--

0 40 KILOMETERS 

0 

~ 20 MILES 

B' 

10 

B 

MAP EXPLANATION 

Well section in which top 

Madison salt underlies 

Kibbey Formation 

Well section in which beds 

below top Madison salt 

underlie Kibbey Formation 

~·Lithostratigraphic profile shown 

inA-E 

I I Erosional zero edge of Kibbey 

Formation; hachures on side 

on which Kibbey is present 

Area in which top Madison salt 

underlies Kibbey Formation 

A 

6100 

6200 

6300 

6400 

"'p.:tcurrt. '~'£"'\} t>-L 

RATCLIFFE INTERVAL 

B 

6600 

6700 

6800 

200 FEET 

50 METERS 

100 

5 KILOMETERS 

2 MILES 

7300 

7400 

7500 

7600 

7700 

z 

m 

:E 

z ...., 

m 

:;o 

'"tj 

:;o 

m 

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Ut 
26 

~ 

z 

0 

f= 

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0 

LL 

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CXl 

CXl 

Q 

s:? 

0 

0 

LD 

rUPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

~ 

~ 

;:: 

~ 

z 

0 

f= 

<t 

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0 

LL 

>- w 

CXl 

CXl 

Q 

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1-

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8700 

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25 

E 

24 KIBBEY 23 22 

E 

21 

~~~~::::;;;:;;;;;;;;;;~-~-~ 8100 

?>'-J p..\.. ,~,f'\€ 

?>p..iC\..\rr~ SECTION EXPLANATION 

D Limestone and dolomite 

Anhydrite 

D Halite 

A1,A2 Key beds of Cook (1976) 

~~~~~ Postulated angular unconformity 

~ 8200 Feet below top of Poplar interval

- Datum 

is top of Poplar interval 

8200 

50 METERS 

2 MILES 

z 

tTl 

~ 

z ....., 

tTl 

10 

'1::) 

10 

tTl 

....., 

> ....., 

a 

z 

0 

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6 

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4T 

---

----

UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONT ANA AND NORTH DAKOTA 

----1600--

MONTANA 

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

.... , 

• @ 

102" 

CANADA 

50 1 DO KILOMETERS 

EXPLANATION 

Well section from which corals were collected 

Well section from which corals, foraminifers, and 

algae were collected 

--1600-- Total Madison Group isopach line-Contour interval 

200 feet 

Erosional zero edge of Kibbey Formation- Hachures 

on side on which Kibbey is present 

Area in which salt beds are present in Charles 

Formation and Mission Canyon Limestone-Limits 

approximate 

; ; 

10r 

/ 

/ 

I 

~ 9.:,\S 

I 

I 

I 

/ 

/ 

/ 

; 

; 

; ; ; 

--~-------

,; 

,; 

,; 

/ ; 

Figure 12. Locations of well sections of Charles Formation and Mission Canyon Limestone in Montana and North Dakota from which 

corals, foraminifers, and algae were collected. Area of Madison salt and total Madison Group isopachs from Sandberg (1962, fig. 15). Erosional zero edge of Kibbey Formation from Maughan and Roberts (1967, pl. 3), Rawson (1968, fig. 4), and Anderson (1974). See figure 1 

for location of map area with respect to limits of Williston Basin. See figures 13 and 14 for stratigraphic profiles A-A' and B-B' across area 

of Madison salt and table 2 for locations and sources of data for well sections. 
NEW INTERPRETATION OF CRITICAL EVIDENCE 29 

RELATION OF TOP MADISON SALT 

TOBEDSABOVEANDBELOW 

The top Madison salt is readily distinguished from other 

salt beds in the Madison salt sequence by its stratigraphic 

position at the top of the sequence and its greater thickness 

(almost a third of the total thickness of the Madison 

salt)(figs. 13, 14 ). It has a slightly smaller areal extent than 

several older salt beds that define the maximum limits of the 

salt basin. A bed of limestone or anhydrite separates it 

locally from the overlying Kibbey Formation. No fossils 

have been recovered from the top Madison salt or from the 

overlying limestone. Although most geologists described the 

contact between the salt and the overlying Kibbey Formation 

as conformable and transitional (seep. 20), contact relations 

are difficult to determine because of dissolution and caving 

of the salt and the paucity of cores at the contact. 

ORIGIN OF MADISON SALT SEQUENCE 

Continuity of marine carbonate strata no younger than 

CZ 14 that are complexly interbedded with continuous and 

discontinuous anhydrite and salt beds suggests that the 

evaporite sequence in the Charles Formation beneath the top 

Madison salt represents restricted, mostly marine sedimentation in the Madison salt basin during early Meramecian time. 

The intrabasinal model of Sloss (1953) (seep. 21 of current 

report) is a reasonable explanation for this part of the Charles 

Formation. The discontinuous nature of many of the salt and 

anhydrite beds in the marine evaporite sequence (figs. 13, 

14) suggests a complex of smaller, deeper areas of high 

salinity that shifted geographically within the basin during 

much of the time represented by the sequence. 

The stratigraphic position of the top Madison salt above 

beds dated paleontologically as no younger than early Meramecian (CZ 14) and beneath beds probably no younger than 

early Chesterian (CZ 21) (see p. 13-17) suggests an age 

range of middle Meramecian possibly into early Chesterian 

for this highest salt. Assuming that published interpretations 

of the contact between this salt and the Kibbey Formation are 

valid, the top Madison salt represents a central area of continuous sedimentation from early Meramecian into early 

Chesterian time within the area of the older marine salt basin. 

In view of the evidence for truncation of older marine salt 

beds at the basin margins and the absence of evidence of 

marine connections of the salt basin during middle Meramecian to early Chesterian time, the top Madison salt probably 

represents a landlocked remnant of the epeiric sea that was 

becoming shallower throughout Madison time. This ancient 

salt lake was gradually overrun by the transgressing Kibbey 

sea during Chesterian time. The prevalence of an arid climate may explain the absence of solution features in the carbonate bedrock beneath the karst plain in the central part of 

the Williston Basin. 

BIOZONE BOUNDARIES VERSUS 

LITHIC MARKER HORIZONS IN 

REGIONAL CHRONOSTRATIGRAPHY 

A critical analysis of the depositional history represented by the upper part of the Madison Group in the Williston Basin must first consider the accuracy of methods used 

for establishing a chronostratigraphic framework for this 

lithostratigraphic sequence. Basic questions are: 

1. How reliable are the lithic marker horizons that 

have been used extensively as planes of synchroneity in 

Williston Basin Madison stratigraphy? 

2. Are biozone boundaries more reliable planes of 

synchroneity than lithic marker horizons? 

3. Are the lithic time planes parallel to the paleontologic time planes? 

Previous work provides seemingly contradictory 

answers to these basic questions (see p. 17-18). Brindle 

(1960) and Waters (1984; Waters and Sando, 1987a) concluded that the lithic marker horizons parallel faunal zone 

boundaries and that the lithic markers are reliable time 

planes, whereas Sando (1978) and Sando and Dutro (in Sheldon and Carter, 1979) noted a significant angular difference 

between the two measures of synchroneity. 

Stratigraphic profiles replotted from Sheldon and 

Carter (1979) and Waters and Sando (1987a) reveal remarkably consistent angular differences of 3°-4° between lithic 

marker horizons and paleontologic boundaries in directions 

approximately parallel with inferred sedimentary progradation directions (perpendicular to paleoshorelines) across the 

Cordilleran shelf in Montana and North Dakota (figs. 

15-17). These profiles show that the top of the Tilston interval and the top of the Frobisher-Alida interval climb stratigraphically with respect to the Osagean-Meramecian 

paleontologic boundary westward and southwestward (that 

is, in directions seaward from the Mississippian shoreline). 

The only exception is in profile C-C (figs. 15, 17), probably 

due to poor selection of the lithic marker horizon in well 1 

near the center of the salt basin, where Waters (Waters and 

Sando, 1987a, p. 198, 199) noted that the boundaries of lithic 

marker intervals are difficult to identify. 

The angular differences between lithic markers and 

paleontologic markers in the directions of progradation can 

cause significant differences in the stratigraphic positions of 

time planes based on the markers. Over short distances 

within North Dakota (fig. 17, profiles A-C and B-B'), the 

angular differences result in stratigraphic discrepancies of 

approximately 75-80 ft (23-24 m), whereas, from central 

Montana to southeastern Saskatchewan (fig. 16, profile 

A-E), the stratigraphic discrepancy is approximately 300 ft 

(92 m). In a profile perpendicular to progradation (fig. 15, 

profile A-B), the angular difference is zero and there is no 

stratigraphic discrepancy. 
z 

0 

f= 

<( 

~ 

a: 

0 

LL 

(/) 

UJ 

_J 

a: 

<( 

I 

u 

i= 

a: 

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0 

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(/) 

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u 

UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

A 

EXPLANATION 

D Mostly limestone and dolomite 

Mostly anhydrite 

D Mostly halite 

• Collection of corals-May represent 

more than one collection 

o Collection of foraminifers and 

algae-Includes MFZ number 

_...._______..._____,L_ Lithic marker-bed interval boundary 

JE JE JE Faunal zone boundary-Inferred from 

other data in beds lacking paleontologic 

control 

---- Conformable lithic boundary 

~ Disconformable lithic boundary 

---- Lithofacies boundary 

9000 --1 Feet below surface 

50 METERS 

10 20 MILES 

Figure 13 (above and facing page). Approximately south to north lithostratigraphic profile of Charles Formation and uppermost Mission Canyon Limestone across Madison salt basin in Montana and North Dakota. Datum is top of Charles Formation. See figure 12 and table 2 for data on 

well sections. 
NEW INTERPRETATION OF CRITICAL EVIDENCE 

19 KIBBEY FORMATION 21 22 22A 

TOP OF POPLAR INTERVAL 

MERAMECIAN/OSAGEAN BOUNDARY 

9100 

A' 

24 

31 
32 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

B 

EXPLANATION 

CJ Mostly limestone and dolomite 

Mostly anhydrite 

Q Mostly halite 

• Collection of corals-May represent 

more than one collection 

o Collection of foraminifers and 

algae-Includes MFZ number 

__...___.._......._ Lithic marker-bed interval boundary 

l< l< l< Faunal zone boundary-Inferred from 

other data in beds lacking paleontologic 

control 

----Conformable lithic boundary 

~ Disconformable lithic boundary 

- - - - Lithofacies boundary 

9000 -j Feet below surface 

50 METERS 

10 20 MILES 

Figure 14 (above and facing page). Approximately east to west lithostratigraphic profile of Charles Formation and uppermost Mission 

Canyon Limestone across Madison salt basin in Montana and North Dakota. Datum is top of Charles Formation. See figure 12 and table 2 for 

data on well sections. 
NEW INTERPRETATION OF CRITICAL EVIDENCE 

19 KIBBEY FORMATION 20 

33 

B' 

34 
34 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

Table 2. Locations and sources of data for well sections shown in figure 12. 

[Asterisk(*) denotes well section in stratigraphic profiles in figures 13 and 14. NDGS numbers refer to Wilson M. Laird Core and Sample Library of 

the North Dakota Geological Survey, Grand Forks, N.Dak. Amstrat refers to well logs of American Stratigraphic Company, Denver, Colo.] 

Well Sources of data 

No. Well name Location Litholog~ Paleontolog~ 

MONTANA 

1* Shell Oil Co., Pine Unit 1 SW1

4SW14NEI;{j sec. 30, Amstrat log M-705 Sando (1960b, pl. 13; 1978, 

T. 12 N., R. 57 E., Wibaux Co. pl. I), Sando and Mamet 

(1981, fig. 2). 

2* Shell Oil Co., Richey area SW1

4NWJANW14 sec. 19, Amstrat log M-2425 Sando (1960b, pl. 13; 1978, 

Northern Pacific Railroad I T. 23 N., R. 50 E., Dawson Co. pl. 1), Sando and Mamet 

(1981, fig. 2). 

3* Hodge, Smith, and Hodge Co., Center SWJASEJA sec. 3, Amstrat log B-220 Sando (1978, pl. 1), Sando and 

Eggebrecht 1 T. 23 N., R. 49 E., McCone Co. Mamet (1981, fig. 2). 

4 C. H. Murphy Co., Center SW1

/.!NEY2 sec. 2, Amstrat log B-29 Sando(l960b,pl. 13; 1978, 

East Poplar Unit 1 T. 28 N., R. 51 E., pl. 1 ), Sando and Mamet 

Roosevelt Co. (1981, fig. 2). 

5 California Co., Grimm 1 Center NE1

4SEJA sec. 13, Amstrat log B-260 Sando (1978, pl. 1 ), Sando and 

T. 32 N., R. 49 E., Mamet (1981, fig. 2). 

Roosevelt Co. 

6 Socony Vacuum Oil Co. NWJASEJA sec. 23, T. 29 N., Amstrat log B-430R Sando (1978, pl. 1 ), Sando and 

(Mobil Producing Co.), R. 54 E., Roosevelt Co. Mamet (1981, fig . 2). 

Damm F-33-23- P 

7 Texas Co., Donahue 1 Center SW1

4NE14 sec. 23, Amstrat log M-760 Sando (1978, pl. 1 ), Sando and 

T. 154 N., R. 100 W., Williams Mamet (1981, fig. 2). 

Co. 

NORTH DAKOTA 

8 Sun Oil Co., State Lease 1 NW1

4NW14 sec. 16, T. 156 N., Waters (1984, pl. 2), Waters and Waters (1984, pl. 2), Waters 

(NDGS 3235) R. 101 W., Williams Co. Sando (1987a, fig. 8), Cook (1976, and Sando (1987a, fig. 8). 

pl. 6) 

9* Shell Oil Co., SE1

4NEJA sec. 28, T. 148 N., Waters (1984, pl. 1), Waters and Waters (1984, pl. 1), Waters 

Shell USA 42-28-43 R. 104 W., McKenzie Co. Sando (1987a, fig. 7), S.B and Sando (l987a, fig. 7). 

(NDGS 7207) Anderson (written commun., 1993) 

10* Texaco Oil Co., SW1

4NW14 sec. 14, T. 146 N., Waters (1984, pl. 1), Waters and Waters (1984, pl. 1), Waters 

Govt. Mary Pace 1 R. 101 W., McKenzie Co. Sando (1987a, fig . 7), Cook (1976, and Sando (1987a, fig. 7). 

(NDGS 2667) pl. 9) 

11 Tiger Oil Co., Roughrider SWJANE1

4 sec. 32, T. 145 N., Waters (1984, pl. 1), Waters and Waters (1984, pl. 1), Waters 

Federal 3-32 (NDGS 5258) R. 101 W., McKenzie Co. Sando (1987a, fig. 7) and Sando (l987a, fig. 7). 

12 Shell Oil Co., SEJASEJA sec. 14, T. 144 N., Waters (1984, pl. 1), Waters and Waters (1984, pl. 1), Waters 

Northern Pacific Railway Co., R. 102 W., Billings Co. Sando ( 1987 a, fig. 7) and Sando (1987a, fig. 7). 

Govt. 44-14 (NDGS 441 9) 

13* Shell Oil Co., NE1

4NE14 sec. 18, T. 143 N., Waters (1984, pl. 1), Waters and Waters (1984, pl. 1), Waters 

Govt. 41 x-18 R. 101 W., Billings Co. Sando ( 1987a, fig. 7), Cook (1976, and Sando (1987a, fig. 7). 

(NDGS 4455) pl. 9) 

14 W. H. Hunt Trust Estate, SE14SW1

4 sec. 3, T. 142 N., Waters (1984, pl. 1), Waters and Waters (1984, pl. 1), Waters 

Rodakowski l (NDGS 71 04) R. I 00 W., Billings Co. Sando (1987a, fig. 7) and Sando (1987a, fig. 7). 

15 Tenneco Oil Co., SE1

4NE14 sec. 35, T. 142 N., Waters (1984, pl. 1), Waters and Waters (1984, pl. 1 ), Waters 

David USA 1-35 (NDGS 7446) R. 101 W., Billings Co. Sando (1987a, fig. 7) and Sando (1987a, fig. 7). 

16 Socony Vacuum Oil Co., SW1

4SW14 sec. 24, T. 134 N., Waters (1984, pl. 1), Waters and Waters (1984, pl. 1), Waters 

Jacobs 1-F-14-24-P R. 96 W., Hettinger Co. Sando (1987a, fig. 7), Cook (1976, and Sando (1987a, fig. 7). 

(NDGS 511) pl. 9) 

17 Socony Vacuum Oil Co., SE1

4NE14 sec. 6, T. 141 N., Waters (1984, pl. 1), Waters and Waters (1984, pl. 1), Waters 

Dvorak F-32-6-P R. 94 W., Dunn Co. Sando (1987a, fig. 7), Cook (1976, and Sando (1987a, fig. 7). 

(NDGS 505) pl. 9) 
NEW INTERPRETATION OF CRITICAL EVIDENCE 35 

Table 2. Locations and sources of data for well sections shown in figure 12. 

[Asterisk(*) denotes well section in stratigraphic profiles in figures 13 and 14. NDGS numbers refer to Wilson M. Laird Core and Sample Library of 

the North Dakota Geological Survey, Grand Forks, N.Dak. Amstrat refers to well logs of American Stratigraphic Company, Denver, Colo.] 

Well Sources of data 

No. Well name Location Lithology Paleontology 

NORTH DAKOTA-Continued 

18 Gulf Energy and Minerals Co., SW1

4NE4 sec. 13, T. 145 N., Waters (1984, pl. 1 ), Waters and Waters (1984, pl. 1), Waters 

Lind 2-13-2-D R. 98 W., McKenzie Co. Sando (1987a, fig. 7), Cook (1976, and Sando (1987a, fig. 7). 

(NDGS 6230) pl. 9) 

19* California Oil Co., NW1

4NE14 sec. 13, T. 148 N., Waters (1984, pl. 2), Waters and Waters (1984, pl. 2), Waters 

Rough Creek Unit 1 R. 98 W., McKenzie Co. Sando (1987a, fig. 8), S.B. and Sando (1987a, fig . 8). 

(NDGS 527) Anderson (written commun., 1993) 

20* Mobil Oil Co., SW1

4NE14 sec. 24, T. 149 N., Waters (1984, pl. 2), Waters and Waters (1984, pl. 2), Waters 

Kennedy F- 32-24--P R. 93 W., Dunn Co. Sando (1987a, fig. 8), S.B. and Sando (1987a, fig. 8). 

(NDGS 607) Anderson (written commun., 1993) 

21 * Amerada Petroleum Corp., NE1

4NE14 sec. 1, T. 152 N., Waters (1984, pl. 2), Waters and Waters (1984, pl. 2), Waters 

Brenna-Lacey Unit 1 ( 1 Antelope R. 95 W., McKenzie Co. Sando (1987a, fig. 8) and Sando (1987a, fig. 8). 

Unit A) (NDGS 1350) 

22*, Amerada Petroleum Corp., Jens NE'4SW1

4 sec. 29 and Waters (1984, pl. 2), Waters and Waters (1984, pl. 2), Waters 

22*A Kvam 4 (NDGS 480), and SE1

4SW14 sec. 16, T. 156 N., Sando (1987a, fig. 8), Carlson and Sando (1987a, fig. 8). 

Amerada Petroleum Corp., R. 95 W., Williams Co. (1967, pl. 5) 

9 Unit A 

23 Pan American Petroleum Corp., SWIANWIA sec. 12, T. 161 N., Waters (1984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

Calma Dove 1 (NDGS 3510) R. 94 W., Burke Co. Sando (1987a, fig.9) and Sando (1987a, fig. 9). 

24* Phillips Petroleum Co., NE'4NW'4 sec. 29, T. 162 N., Waters (1984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

Braathen 1 R. 95 W., Divide Co. Sando ( 1987a, fig. 9), Anderson and Sando (1987a, fig. 9). 

(NDGS 1024) (1958, fig. 3) 

25 Cardinal Petroleum Co., SW1

4SE14 sec. 17, T. 163 N., Waters (1984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

Orrin Lien 1-3417 (NDGS 4692) R. 95 W., Divide Co. Sando (1987a, fig . 9) and Sando (1987a, fig. 9). 

26 Sun Oil Co., NEIAS£14 sec. 3, T. 162 N., Waters (1984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

A. Bloom 3 (NDGS 2630) R. 92 W., Burke Co. Sando (1987a, fig. 9) and Sando (1987a, fig. 9). 

27 U.S. Smelting, Refining, & SW'4NW1

4 sec. 29, T. 163 N., Waters (1984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

Mining Co., Radenz "A" 1 R. 89 W., Burke Co. Sando (1987a, fig. 9) and Sando (1987a, fig. 9). 

(NDGS 3932) 

28 Kissinger Petroleum Corp., SE'4SW1

4 sec. 1, T. 163 N., Waters (1984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

Knutson 14-l (NDGS 5551) R. 87 W., Renville Co. Sando (1987a, fig. 9) and Sando (1987a, fig. 9). 

29 Chandler and Associates, Inc., SWIASEIA sec. 25, T. 162 N., Waters (1984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

Crooks 15-25 (NDGS 5247) R. 84 W., Renville Co. Sando (1987a, fig. 9) and Sando (1987a, fig. 9). 

30 Chandler and Associates, Inc., NE1

4SW14 sec. 21, T. 163 N., Waters (l984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

Hall off 1 (NDGS 3944) R. 82 W., Bottineau Co. Sando (1987a, fig. 9) and Sando (1987a, fig. 9). 

31 Lion Oil Co., SE1

4NW14 sec. 27, T. 163 N., Waters (1984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

Einar Madsen 1 (NDGS 939) R. 77 W., Bottineau Co. Sando (1987a, fig . 9) and Sando (1987a, fig. 9). 

32 California Oil Co., SW1

4SE14 sec. 31, T. 160 N., Waters (1984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

Blanche Thompson 1 (NDGS 38) R. 81 W., Bottineau Co. Sando(1987~fig. 9) and Sando (1987a, fig. 9). 

33 Phillips Petroleum Co., NW'4SE1

4 sec. 19, T. 158 N., Waters (1984, pl. 3), Waters and Waters (1984, pl. 3), Waters 

Olivia Saude 1 (NDGS 274) R. 74 W., Pierce Co. Sando (1987a, fig. 9) and Sando (1987a, fig. 9). 

34* Herman Hansen Oil Syndicate, SE1

4SW'4 sec. 32, T. 146 N., Waters (1984, pl. 2), Waters and Waters (1984, pl. 2), Waters 

Samuelson 1 (NDGS 1516) R. 82 W., McLean County Sando (1987a, fig. 8), S.B. and Sando (1987a, fig. 8). 

Anderson (written commun., 1993) 

35 Tom F. Marsh Co., NW1

4SW14 sec. 10, T. 140 N., Waters (1984, pl. 2), Waters and Waters (1984, pl. 2), Waters 

Clark 1 R. 76 W., Burleigh Co. Sando (1987a, fig. 8), S.B. and Sando (1987a, fig. 8). 

(NDGS 6254) Anderson (written commun., 1993) 
36 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

ALBERTA I 

,, I 

100 

I II II I 

I 

200 

I 

300 

I 

I 

400 KILOMETERS 

I 

[I] 

[]] 

100 200 MILES 

EXPLANATION 

Land (Antler orogen, Transcontinental arch, 

Canadian shield) 

Deep-water terrigenous and carbonate sediments 

(Antler foreland basin and Prophet trough) 

Shallow-water shelf carbonate and evaporite 

sediments (Cordilleran shelf)-Stippled pattern 

marks area of Williston Basin. Dashed line within 

Williston Basin delineates area of Madison salt in 

central region of basin 

-------Approximate position of shoreline of Cordilleran 

shelf 

~Stratigraphic profile showing angular difference 

between lithic marker horizon and OsageanMeramecian boundary based on paleontology 

o41111111-·· Generalized inferred regional progradation 

direction on Cordilleran shelf 

Figure 15. Generalized paleogeographic map of Williston Basin and adjacent areas during latest Osagean and earliest Meramecian (CZ 11-12) time showing component progradation directions and magnitudes as measured by angular differences between 

key lithic marker horizons and paleontologically determined Osagean-Meramecian boundary in profiles shown in figures 13, 14, 

and 16. Outline of Williston Basin modified from Peterson ( 1984, fig. 3) and Kent (1984, fig. 2). 
Eastern limit of 

Williston Basin"'- c E A 8 

Madison salt area ~I 

,-,-------- --- --- - ·- ----- - -

"' . ~ '" " ~ ~ • r-----

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1 

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l5. 

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~ U . . ? N ~ ~~ u 0 

50" 

110" 105" 100" 

ALBERTA I 

I 1?7 D 

CANADA ~ __ -1- --,::-:.§9, ----- 195 UNITED STATES I / 

\ /61 Madison 

318 

& 

330 

303 

326 

A3o2 

\ 44 ~ 54 I salt area 

30 \ 39 46 ''--,,, I 32 ',, 

/ C '\~ l', / A 25 

26 

27 tz;;-~<>,.. I 'NORTH D~- MONTANA ~"'to~~~- ~UTHDAKOTA "O>~"'o S 

45" I===- - - =-- I 

""'1)'\ ---tJ I \I 

0 1 DO 200 KILOMETERS 

l"'""ld 1111 1 I 

0 50 1 DO MILES 

EXPLANATION 

"Charles facies" 

0 "Mission Canyon facies" 

200 METERS 

"Lodgepole facies" 

-----@-- Marker beds 

® Ratcliffe-Poplar marker bed 

@ Shale kicks-Xis a submember bed 

® Richey shale 

® Kisbey sandstone 

0 Tilston-Alida marker bed-At places obscure 

• • • - ~ ~x x Osagean-Meramecian boundary based on 

paleontological evidence-Dots mark boundary 

position in areas of good control. Dashes mark 

boundary position inferred between areas of good 

control. X's mark position in Saskatchewan based 

on Brindle (1960) 

100 

1 ODD FEET 

500 

50 100 150 200 KILOMETERS 

50 100MILES 

Figure 16. Stratigraphic profile from Madison outcrop area into Williston Basin showing relation between lithic marker beds and Osagean-Meramecian boundary as determined 

biostratigraphically. Datum is Tilston-Alida marker bed. Replotted from Sheldon and Carter (1979, fig. 54). See Sheldon and Carter (1979, table 4) for locations of control sections. 

z 

tTl 

:E 

...., 

z 

tTl 

:;o 

'"0 

:;o 

tTl 

...., 

...., 

~ 

5 

z 

0 

'Tl 

n 

:;o 

:::3 

n 

~ 

t""' 

tTl 

< 8 

tTl 

z 

n 

tTl 

VJ 

-.,.J 
38 

6200 

6300 

6400 

6500 

6600 

6700 

8900 

9000 

9100 

9200 

9300 

9400 

9300 

9400 

9500 

9600 

9700 

9800 

A 

B 

11 

c 

UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

TOP OF STELECHOPHYLLUM 

BANFFENSE ZONULE ........................... TOP OF MICHELINIACYATHAXONIA ZONULE • • • • • • • • • • • • • • • • • • • • • • • 9400· 

B 

11 

TOP OF FROBISHER-ALIDA 

INTERVAL 

.... ····· .... ······ .... ... . ... .... .... 

TOP OF TILSTON INTERVAL 

c 

100 METERS 

50 

EXPLANATION 

= Limestone and dolomite 

Anhydrite 

I .... · .. :ii i No lithic data 

9900 -1 Feet below surface 

• • • • • ·····Top of coral zonule 

A 

500 FEET 

0 50 100 KILOMETERS 400 f+rl-rJ 

0 50 100 MILES 

300 

200 

100 

50 1 DO KILOMETERS 

10 20 30 40 50 MILES 

Figure 17. Stratigraphic profiles-in western North Dakota showing relations between lithic marker beds, lithofacies, and coral zonule tops 

from margins to center of Williston Basin. Datum is top of Frobisher-Alida intervaL Replotted from Waters and Sando (1987a, figs_ 7-9). 

See Waters and Sando (1987a, table 1) for locations of control sections_ 
SUMMARY OF REGIONAL DEPOSITIONAL HISTORY 39 

EVALUATION OF 

CHRONOSTRATIGRAPHIC METHODS 

The lithic marker beds of the Madison Group have been 

interpreted as terrigenous interruptions that terminate periods of widespread stillstand in a cyclic carbonate-evaporite 

sequence (seep. 17). Although neither the stillstands nor the 

pulses of terrigenous sediment that follow them are 

theoretically instantaneous over the broad expanse of the 

Cordilleran shelf, the lithic marker horizons are clearly more 

reliable measures of synchroneity than conventional lithic 

datum planes used to define formations. The widespread 

distribution of the lithic markers and their ease of recognition on radioactivity logs (except for the central area of the 

Madison salt basin) have made these markers excellent practical tools for approximate chronostratigraphy in the subsurface of the Williston Basin. 

Biozone boundaries recognized in the Madison Group 

are based on abrupt evolutionary changes in assemblages of 

benthic marine organisms. Similar to the lithic marker horizons, these interruptions in the marine evolutionary continuum were not theoretically instantaneous over the entire shelf 

because the organisms were restricted to the bottom environment of a shallow sea that shifted seaward and shoreward 

many times during Madison time. Net seaward progradation 

of the shallow-water carbonate sediment forced benthic 

organisms to migrate seaward along with the sediment; hence 

the seaward occurrences of these organisms are inevitably 

progressively younger than their occurrences closer to shore. 

The fact that the lithic marker horizons climb stratigraphically with respect to faunal zone boundaries in directions perpendicular to the shoreline suggests that the 

terrigenous pulses represented by the lithic marker beds prograded seaward at a slower rate than that of migrations of the 

organisms. Stillstands, some marked by surfaces of subaerial 

exposure, could not have affected the entire expanse of the 

huge Cordilleran shelf instantaneously because the 

assemblages of benthic organisms immediately above the 

stillstands are indistinguishable from the assemblages below 

them, indicating that the organisms did not migrate to some 

distant area off the shelf. If such migrations had occurred, the 

character of succeeding organic assemblages would have 

changed dramatically because none of the shallow-water 

genera are known in coeval deep-water areas west of the Cordilleran shelf. 

I conclude that the biozone boundaries are closer 

approximations to absolute synchroneity than are the lithic 

marker horizons. The time differences between the two 

time measures are not greatly significant for exploration 

stratigraphy within the subsurface of the Williston Basin, 

but the differences can be quite significant in regional chronostratigraphic correlations between the outcrop area and 

the subsurface of the Williston Basin. 

SUMMARY OF REGIONAL 

DEPOSITIONAL HISTORY 

REGIONAL CHRONOSTRATIGRAPHIC 

LITHOFACIES PROFILE 

A chronostratigraphic lithofacies profile of the Madison 

and Big Snowy Groups from central Montana to eastern 

North Dakota (fig. 18, table 3) places the Madison salt in a 

regional framework of Mississippian depositional history 

and forms the principal basis for analyzing the history of the 

salt. This profile shows two depositional sequences separated by a major hiatus, except in the center of the Williston 

Basin, where the top Madison salt is present. 

The upper part of the lower depositional sequence consists mainly of shallowing-upward, regressive, shelf carbonate and evaporite sediments of the Mission Canyon 

Limestone and Charles Formation deposited during the 

Osagean and !vleramecian (CZ 10 to CZ 14). Intermittent 

marine anhydrilte sedimentation was common on most of 

the shelf during the middle and late Osagean and early Meramecian (CZ 10 to CZ 14), but intermittent marine halite 

deposition was confined to the central area of the basin during later early Meramecian time (CZ 13 to CZ 14). 

Although marine sedimentation on the shelf surrounding the 

Williston Basin continued into CZ 14, as it did in the basin, 

preservation of younger (CZ 13 and CZ 14) strata in the 

basin indicates that these strata were protected from the erosion that removed more of the stratigraphic record during 

middle and late Meramecian (CZ 15 through CZ 19) from 

areas surrounding the basin. Sinking of the crust beneath the 

Williston Basin evidently was the principal factor in preserving the stratigraphic record, but an arid climate that curtailed solution during emergence probably also contributed 

to the preservation of carbonate and evaporite strata. The 

top Madison salt, deposited in a landlocked lake, represents 

the final phase in the drying up of the Madison sea. 

Diachroneity of boundaries between lithofacies in the 

lower depositional sequence is evident from the margins of 

the Williston Basin toward its center owing to slow progradation of carbonate sediments. West of the basin, the lithofacies boundariles appear to be synchronous because progradation was too rapid to be detected by the biozonation. 

The upper depositional sequence consists mainly of 

deepening-upward, transgressive, terrigenous sediments of 

the Big Snowy Group deposited on the eroded surface of 

the Madison Group during late Meramecian (CZ 17 

through CZ 19) and Chesterian (CZ 20 through CZ 26) 

time. Sediments of the Kibbey Formation, basal phase of 

the transgression, swept eastward across the Madison karst 

plain, invaded the salt lake, and gradually extinguished 

halite deposition in the early Chesterian (CZ 20). 
40 

325 - ~ ~ e::. a: - (/) <( 

- :J e::. a:o <( - wa: 

a..w z - O..u... <( :::>- a: 330 - z 

0 :J 

- OJ ~ a: <( - <( z u 

-

335 -

-

-

-

-

340 - z - <( 

~ w - a: (/) 

- <( > e::. - (/) 

345 - :J 

0 - a: 

w - ~ 

z - 0 

OJ - a: 350 - <( - u - a: - w 

5 ~ 

- 0 a: _J <( 

- e::. 

355 - z 

<( 

- U5 

- ~ 

z - a: 

:J - 0 

360 - 1-

-

UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

Z(f) ::t:<CZ ~EB (f)z 1-~0 

a: a:- Oo Ow~ a..N z~:=:: ~0 

~ a: 

<( 

e::. 

z 

<( 

a: 

a.. 

U5 

(/) 

U5 

(/) 

~ 

<(0 ouOJ 

\ll 25 

~ r--- a: 24 <( 

e::. r---n z 1--

<( 22 a: 

w 

(/) 

1- 1--

w 21 J: r--- u 20 

\U 19 

~ 

'17 z r---;-s <( r--- u 15 w 1--

~ 

~ 14 

:rg r------

13 

r---

? I 12 

_j ~E-----------iE11 

MONTANA 

0 50 100 200 300 

I I I I I 

6 ~0 1b0 2b0 I 300 460 56o 

2 0 ® ® 

o T1y.llerFolU• '~~:~~~lip:;~ IJ:JWL~--~--::-~~~~~~~~~~~~~~~ .~ -

1 ~t ~:r---Heathf:armatioil!Part1_~---------------~.~~- _ _ 

~ Lombard ~~J- -~ ~ - - J-- - - -

T Limestone v 

!• I I J?- - - - - - -r- OtterFormation - - - - - 11.?----t----------t-------

• I ~ =:lf=o==r= I .r -f1.;;; 

Kibbey Formation 

IIIII 

-

J--

.~· 

'· · .. 

-

.:. 

Approximate limit of deposition of lower depositional sequence(= shoreline) 

e ///////////// II/III/////// ~ IIIII/ Ill~ 

Ill////////// II 5 II 1JJJ///////// ///IIIII///// 1//1/111111 I !!li/lfflf>Y'l~l...'-. 

11,11riii!IL. 

++~ ./ 'bJ'//,_,Jf;;j/ ~l~/-....,7/,.,.,.,.,{ff-t;,//'//// 

>Q) 

• ///////////// ///IIIII/// a 5 ////// IIIII /////l/l/1111 ///////////II ~l!l~lljlj(l_ X _IJ.l!l~l!llj(_ X M~f/j_l!l~/- X -Jji~I!IIJ._f!llll_ X_ 11/~/~lljll/ X 

* !/~/IIIII * II c: m II ~ 1111!111&! *11111111* llfkll/11 I* IIIII* Ill/ * ///////*// *111/1///-J *////////* Ill. ~ e /////11////// Ill/////// ·~ ~ /IIIII ~~II !l/1///111111 !l/////////11 ~17lftJ7Jlfl! X - >flfliftJlJ/fr X - .M~~:.f:?!l!X - -X - X - - X - X - pc -

~: ~. i ~i pc- X- X- X- X- X- X- X- M-7- X- X- X- X- X- X- X- X- X X 

l:l I I I I I r~ I I I ~-.,.-)1. )l.-r--)I.I-)I.-IJI.-M-3-IJI._1_1JI. )1.-f-JI.rX-p<-X X I 

1:1 I I I I I 1:1 Lodgepole Limestone,--LI-,+__L_,--L-I--,--'----r 1-'---.--L..,- 1 -'-,--L 1--.--__L_,--JL 1--,--'----r 1 --'---.-L..,- 1 -'--n--c1- • I I I I I • I I 

• I I I I I • I I 

EXPLANATION 

= LITHOFACIES Shallow-water shelf carbonate 

HIATUS 

Sedimentary record removed by post-Carboniferous erosion 

~ Shallow- to deep-water carbonate 

Shelf carbonate and anhydrite-Represented by solution 

breccia in sections 1-4 

Shelf carbonate, anhydrite, and halite 

U Lacustrine halite 

D Peritidal quartz sandstone and siltstone 

U Black shale 

II -;J Green shale and carbonate 

Sedimentary record removed by intra-Carboniferous 

erosion-Restored limit of deposition shown by dashed line 

SEDIMENTARY BOUNDARIES 

Unconformity 

Beginning of deposition on unconformable surface-Dashed 

where inferred in areas in which sedimentary record was 

removed by erosion 

Transitional or interfingering lithofacies boundary-Dashed 

where inferred in areas in which sedimentary record was 

removed by erosion 

LITHOCHRONOLOGIC CONTROL 

- x M-7 x - Time plane based on marker bed of Peterson (1984) 

Figure 18. Chronostratigraphic lithofacies profile of Madison and Big Snowy Groups from central Montana to eastern North Dakota. See table 3 

for locations and references for control sections. Time-slice positions A-H at right margin of diagram refer to paleogeographic maps in figure 19. 

Vertical lines in column for North American divisions denote hiatus. 
SUMMARY OF REGIONAL DEPOSITIONAL HISTORY 

NORTH DAKOTA ----------------4-DD----~L_ ________________ 5_0_0 ________________________ 6_00 _______________________ 70~0~M~IL~E~S ~~ 

~6 --------~6D_O ____________ L_70~0 ______________ 8_DD ______________ 9_00 ______________ 1_00_0 __________ 1_1D_D_K_ILO_M_E_T_ER_S~~~ goo 

BIOCHRONOLOGIC CONTROL 

• Collections of fossils critical for composite zone 

determination 

o Collections of other fossils used for biostratigraphic 

correlation * * Osagean-Meramecian boundary based on fossils and 

used as datum for profile 

STRATIGRAPHIC SECTIONS 

(see table 3 for locations and references) 

Outcrop section 

Subsurface section 

Composite of outcrop and subsurface sections 

INDEX MAP 

1 DO 200 KILOMETERS 

1""'"1" 1111 1 I 

50 100 MILES 

41 

H 

G 

F 

E 

D 

c 

B 

A 
42 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

REGIONAL PALEOGEOGRAPHIC MAPS 

Regional paleogeographic maps (fig. 19) for selected 

sequential time slices through the chronostratigraphic lithofacies profile (pl. 4) are also useful for visualizing Mississippian depositional history in the study area. These maps were 

prepared by using the profile as the main determinant and 

augmenting data in the profile with data from other control 

points in Montana, North Dakota, South Dakota, and Wyoming from Sando and Bamber (1985) and Peterson (1984 ). 

Maps published by Sando and others (1975) and Sando 

( 1988, 1989a) served as general guides. 

SHORELINES 

Movements of the shoreline during deposition of the 

Mission Canyon Limestone and Charles Formation shown on 

the maps are an improvement over the static shorelines 

shown on previous maps. These movements were revealed 

by projection of the maximum limit of deposition of the lower 

depositional sequence on the profile to the erosional zero 

edge of the Madison Group in North Dakota. This projection 

is based on the time constraints imposed by biostratigraphic 

dating of the youngest Madison strata and earliest Big Snowy 

strata and chronostratigraphic projection of these constraints 

eastward through the Williston Basin to a line slightly east of 

the erosional zero edge of the Madison. The time plane of 

maximum deposition inclines downward toward the erosional zero edge because withdrawal of the Madison sea was 

more rapid in the area adjacent to the shoreline than at the 

center of the Williston Basin, where subsidence of the sea 

floor proceeded at a faster rate. Successive shoreline positions shown on the maps are locations where the time-slice 

planes intersect the time plane of maximum deposition. 

TIME SLICE A (CZ 10, MIDDLE OSAGEAN) 

Middle Osagean time (CZ 10) was characterized by 

deposition of carbonate sediments in shallow marine water 

(depths probably 50 m or less) over most of the Cordilleran 

shelf except in a linear belt several hundred kilometers west 

of the shoreline, where anhydrite was deposited intermittently in many small, very shallow areas of restricted circulation within the complex of shelf carbonate environments. 

The evaporite belt may have originated on a slightly higher 

area of the sea floor. The climate was arid. 

TIME SLICE B (CZ 11, LATE OSAGEAN) 

By late Osagean time (CZ 11), the shoreline had 

moved westward more than 100 km as the sea retreated. 

The area of intermittent anhydrite deposition within the carbonate complex had expanded to cover most of the Cordilleran shelf except for areas of freer circulation in slightly 

deeper water in a belt adjacent to the shoreline and in the 

center of the Williston Basin. 

TIME SLICE C (CZ 12, EARLIEST MERAMECIAN) 

Earliest Meramecian time (CZ 12) was characterized by 

continued westward movement of the shoreline and expansion of the area of restricted circulation that resulted in anhydrite deposition within the shelf carbonate complex. The 

entire Cordilleran shelf in the study area was characterized 

by a complex of very shallow, restricted environments. 

TIME SLICED (CZ 13, EARLY MERAMECIAN) 

Slightly later in early Meramecian time (CZ 13), marine 

halite was deposited intermittently in the center and slightly 

southwest of the center of the Williston Basin. The two discrete areas of halite deposition shown on the paleogeographic 

map may have been connected, and the absence of salt in the 

intervening Poplar dome area may be due to removal of salt 

by later solution in that area. The shoreline had moved 

slightly west of its position in time slice C, and the eastern 

edge of the area of halite deposition was less than 100 km 

from the shore. Intermittent halite deposition took place in 

more restricted marine areas, probably in somewhat deeper 

water, according to the model of Sloss (1953)(see p. 21). 

The area of the X salt of Anderson and Hansen ( 1957) 

and Anderson ( 1964) is not shown on the map for this time 

because this salt is not intersected by the time slice, and the 

salt is not shown on Peterson's (1984, pl. 4, ND-W-1 and 

ND-ML-2) graphic sections used to construct the chronostratigraphic lithofacies profile (fig. 18). The X salt was 

thought to be "near the base of the Charles Formation" by 

Anderson and Hansen ( 1957) or in the upper part of the Mission Canyon Limestone by Sandberg (1962, p. 60, fig. 5). 

This salt was originally shown by Anderson and Hansen 

( 1957, fig. 1 0) as occupying a small area in Bottineau, Renville, Ward, and McHenry Counties, North Dakota, but it 

was extended southward into McLean, Mercer, and Oliver 

Counties by Anderson ( 1964, fig. 1 0). The X salt is probably 

a nearshore eastward extension of the marine carbonate, 

anhydrite, and halite lithofacies shown in figure 18. 

TIME SLICE E (CZ 14, LATE EARLY MERAMECIAN) 

During late early Meramecian time (CZ 14), the sea 

continued to retreat westward across the Cordilleran platform, and the shoreline moved westward into central 

Montana, leaving most of the platform exposed to subaerial 

erosion. Continued subsidence of the crust in the center of 

the Williston Basin produced a landlocked salt lake that contained the last vestige of the restricted shelf sea that had previously covered the platform. 
SUMMARY OF REGIONAL DEPOSITIONAL HISTORY 43 

Table 3. Locations and sources of data for stratigraphic sections shown in figure 18. 

Section 

No. Name 

Logan-Lombard composite 

2 Dry Fork-Monarch composite 

3 Stonehouse CanyonShell 21-19 NP well composite 

4 Ralph Lowe Sandquist 1 well 

5 Pan American NPRR well 

6 Shell Richey NPRR 1 wellHodge, Smith, and Hodge 

Eggebrecht 1 well composite 

7 Shell USA 42-28--43 wellJ.H. Moore et all Olson well 

composite 

8 California Rough Creek Unit 1 

well-Texas 1 Hovde well 

composite 

9 Mobil Kennedy F-32-24P wellHunt W. and D. Dunham well 

composite 

10 Herman Hansen Samuelson 1 wellStanolind 1 McLean Co. well 

composite 

11 Calvert 1 Zwinger well 

12 Wetch et al I C. E. Blaskey well 

Location 

Logan: sec. 25, T. 2 N., R. 2 E., Gallatin Co., 

Montana. Lombard: SW% sec. 7, T. 4 N., R. 3 E., 

Broadwater Co., Mont. 

Dry Fork: sees. 35 and 36. Monarch: sees. 22 and 

27. Both in T. 16 N., R. 7 E., Cascade Co., Mont. 

Stonehouse Canyon: sec. 25, T. II N., R. 20 E., 

and sec. 29, T. 31 N., R. 21 E. Shell well: sec. 19, 

T. 9 N., R. 21 E. Both in Golden Valley Co., Mont. 

Sec. 28, T. 16 N., R. 36 E., Garfield Co., Mont. 

Sec. 33, T. 17 N., R. 45 E., McCone Co., Mont. 

See entries 2 and 3 in table 2 for locations and data 

sources. 

Shell well: see entry 9 in table 2 for location and 

data source. Moore well: sec. 18, T. 151 N., 

R. 103 W., McKenzie Co., N.Dak. 

California well: see entry 19 in table 2 for location 

and data source. Texas well: sec. 15, T. 154 N., 

R. 98 W., Williams Co., N.Dak. 

Mobil well: see entry 20 in table 2 for location 

and data source. Hunt well: sec. 24, T. 155 N., 

R. 90 W., Mountrail Co .. N.Dak. 

Hansen well: see entry 34 in table 2 for location 

and data source. Stanolind well: sec. 28, T. 150 N., 

R. 80 W., McLean Co., N.Dak. 

Sec. 8, T. 146 N., R. 68 W., Wells Co., N.Dak. 

Sec. 9, T. 148 N., R. 62 W., Eddy Co., N.Dak. 

Source 

Logan: Sando and Dutro (1974, p. 4-8). 

Lombard: Wardlaw and Pecora (1985, p. B4-6), 

Sando (unpub. field notes). 

Dry Fork: Sando and Dutro (1974, p. 12-16). 

Monarch: Sando and Dutro (1974, p. 8-12). 

Stonehouse Canyon: Easton(1962, p. 121-124), 

Sando and others (1975, pl. 10). 

Shell well: Peterson (1984, pl. 8, M-GV-1). 

Peterson (1984, pl. 5, M-GF-5). 

Peterson (1984, pl. 4, M-MC-9). 

Moore well: Peterson (1984, pl. 4, ND-MK-18). 

Texas well: Peterson (1984, pl. 4, ND-WI-23). 

Hunt well: Peterson (1984, pl. 4, ND-M0-7). 

Stanolind well: Peterson (1984, pl. 4, ND-ML2). 

Peterson (1984, pl. 4, ND-WL-2). 

Peterson (1984, pl. 4, ND-ED-1). 

TIME SLICE F (CZ 16, MIDDLE MERAMECIAN) The initial phase of the transgression in the study area consisted of deposition of peritidal terrigenous sediments of the 

Kibbey Formation, which invaded and partly covered the 

eastern half of the salt lake at the center of the Williston 

Basin. A lobate area of lagoonal terrigenous and carbonate 

sediments of the Otter Formation that followed Kibbey deposition was present in central Montana. 

The entire Cordilleran platform in the study area was 

subaerially exposed during middle Meramecian time 

(CZ 16), forming a karst plain subjected to deep solution by 

groundwaters in areas outside the Williston Basin (Sando, 

1988). The shoreline had retreated to extreme southwestern 

Montana, where the earliest phase of the Big 

Snowy--Amsden transgression had already begun (Sando, 

1988, fig. 12.3.D). Deposition of halite continued in the 

landlocked lake at the center of the Williston Basin. 

TIME SLICE G (CZ 19, LATE MERAMECIAN) 

Late Meramecian time (CZ 19) was characterized by 

eastward transgression of the Big Snowy-Amsden sea across 

much of Montana and Wyoming (Sando, 1988, fig. 12.3.D). 

TIME SLICE H (CZ 20, EARLIEST CHESTERIAN) 

Earliest Chesterian time (CZ 20) is close to the culmination of the Big Snowy-Amsden transgression. The frontal 

lobe of the transgression, represented by the Kibbey 

Formation, completely covered the salt lake at the center of 

the Williston Basin. The lagoonal phase (Otter Formation) 

that followed Kibbey deposition occupied most of central 

and eastern Montana. 
44 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONTANA AND NORTH DAKOTA 

A E 

110' 100' 

46' 

B F 

110' 100' 110' 100' 

46' 

c G 

110' 100' 110' 100' 

46' 

D H 

Figure 19. Sequential time-slice paleogeographic maps of the Mission Canyon Limestone and Charles Formation in Montana, North Dakota, and adjacent States. See figure 18 for chronostratigraphic positions of maps A-H. On index map x's mark locations of surface control 

sections and dots mark locations of subsurface control sections. 
SUMMARY OF REGIONAL DEPOSITIONAL HISTORY 45 

EXPLANATION 

Approximate shoreline inferred from stratigraphic geometry 

Approximate boundary between lithofacies 

Land 

Shelf carbonate 

Shelf carbonate and anhydrite 

Shelf carbonate, anhydrite, and halite 

~ Basinal carbonate 

Q Lacustrine halite 

J.• • j Peritidal terrigenous silt and sand 

r---_] Lagoonal terrigenous mud and carbonate 

GENERAL CONCLUSIONS ABOUT 

GEOLOGIC MECHANISMS 

The sequence of events inferred from lithic and biotic 

data in this report strongly suggests marked changes in relative sea level produced by more than one geologic mechanism. Moreover, other factors in addition to sea level were 

important in shaping the character of the sediments. 

EUSTACY 

Movements of the sea across the Cordilleran platform in 

the study area follow the general pattern of the eustacy curve 

·described by Ross and Ross (1987, fig. 2) for the Osagean to 

Chesterian interval as defined in this report. Regression on 

the Cordilleran platform coincides with the Keokuk-Warsaw 

regression of Ross and Ross, the post-Madison, pre-Kibbey 

evacuation of the platform coincides with their post-Warsaw, 

pre-Salem lowstand, and the Big Snowy-Amsden transgression coincides with their Salem-Chester highstand. Ross and 

Ross (1987, fig. 2) also identified an exposed lowstand surface in their coastal onlap curve that coincides approximately 

with the post-Madison, pre-Kibbey hiatus. Biostratigraphic 

correlations between the study area and the type Mississippian, based mainly on foraminifers identified by B.L. Mamet, 

provide a general confirmation of the Ross and Ross sealevel 

46° 

40° 

INDEX MAP OF CONTROL POINTS 

120° 

I 

I 

I 

?, ~\ i 

110' 100° 

\ 8 > l ,Ill~ Wllllill"""Wllllillill~~U.J .. ll;)' 

)Ql....... \ ~ 

~"~~~;,/ : !j '&' ~~ r--~ i 0: A...!j~ ,' ~ . 

: '5:-tp~"\1 8. 

'<'-'~<1:: \ v.,O <Q~/ :1~(:--' /'_ 

INDEX MAP 

curves; however, the eustacy curve and coastal onlap curves 

of Ross and Ross show several eustatic events not detected 

on the Cordilleran platform. 

The stratigraphic sequence of the Cordilleran platform 

is a record of local events, some of which may have had 

global causes. Although the general pattern of eustacy 

appears to be confirmed, I cannot agree that all the events 

ascribed to eustacy by Ross and Ross are truly global. 

TECTONISM 

Evidence of vertical crustal movements is manifested 

by pulses of terrigenous sediment derived from the adjacent 

Transcontinental arch and by concentric sinking of the sea 

floor about the center of the Williston Basin. 

The greatest influx of terrigenous sediment occurred 

during the Big Snowy-Amsden transgression, which suggests that sources of this sediment on the Transcontinental 

arch were subjected to uplift in that area at the same time 

that the Cordilleran platform was experiencing a highstand 

of the sea. A humid climate in the terrigenous source area 

may also have been a factor. Submergence of the southern 

part of the platform at the same time that the northern part 

was subaerially exposed (Sando, 1989a, fig. 3E-G) substantiates, however, the role of tectonism as a factor in 
46 UPPER PART OF MADISON GROUP (MISSISSIPPIAN), MONT ANA AND NORTH DAKOTA 

controlling movements of the sea as well as shaping the 

character of the sediments. 

Differential sinking of the sea floor in the Williston 

Basin was an important factor in the origin of the landlocked 

salt at the center of the basin. Sinking of the sea floor produced a topographic depression that, coupled with an arid 

climate, created conditions necessary for halite accumulation. The probable cause of sea-floor sinking was downward 

movement of the underlying crust. 

CLIMATE 

An arid climate was necessary for production of marine 

evaporite sediments that characterize parts of the Mission 

Canyon Limestone and most of the Charles Formation on 

most of the Cordilleran platform. However, the existence of 

an extensive river system and deep solution effects in the 

carbonate bedrock of the karst plain in the area surrounding 

the Williston Basin (Sando, 1988) are evidence of a humid 

climate in that part of the platform and on the Transcontinental arch. Moreover, the presence of a salt lake on the emergent platform in the Williston Basin, indicating aridity in that 

area, shows that the two contrasting climate regimes were 

operating in different parts of the platform at the same time. 

These coeval climatic indications suggest a complex 

regional climatic picture. 

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U.S. Geological Survey Bulletin 1895-B, 29 p. 

Sando, W.J., and Dutro, J.T., Jr., 1960, Stratigraphy and coral zonation of the Madison Group and Brazer Dolomite in northeastem Utah, western Wyoming, and southwestern Montana: 

Wyoming Geological Association Annual Field Conference, 

15th, Guidebook, p. 117-126. 

---1974, Type sections of the Madison Group (Mississippian) 

and its subdivisions in Montana: U.S. Geological Survey Professional Paper 842, 22 p. 

Sando, W.J., Gordon, M., Jr., and Dutro, J.T., Jr., 1975, Stratigraphy and geologic history of the Amsden Formation (Mississippian and Pennsylvanian) of Wyoming: U.S. Geological Survey 

Professional Paper 848-A, 78 p. 

Sando, W.J., and Mamet, B.L., 1981, Distribution and stratigraphic 

significance of Foraminifera and algae in well cores from Madison Group (Mississippian), Williston Basin, Montana: U.S. 

Geological Survey Bulletin 1529-F, 12 p. 

Sando, W.J., Mamet, B.L., and Dutro, J.T., Jr., 1969, Carboniferous 

megafauna} and microfau~al zonation in the northern Cordillera of the United States: U.S. Geological Survey Professional 

Paper 613-E, 29 p. 

Sando, W.J., Sandberg, C.A., and Perry, W.J., Jr., 1985, Revision 

of Mississippian stratigraphy, Tendoy Mountains, southwest 

Montana: U.S. Geological Survey Bulletin 1656-A, 10 p. 

Saskatchewan Geological Society, 1956, Report ofthe Mississippian Names and Correlation Committee: Regina, Saskatchewan 

Geological Society, 4 p. 

Scott, H.W., 1935, Some Carboniferous stratigraphy in Montana 

and northwestern Wyoming: Journal of Geology, v. 43, no. 8, 

pt. 2, p. 1011-1032. 

---1942, Ostracodes from the Upper Mississippian of Montana: Journal of Paleontology, v. 16, no. 2, p. 152-163. 

Seager, O.A., 1942, Test on Ced~ Creek anticline, southeastern 

Montana: American Association of Petroleum Geologists Bulletin, v. 26, no. 5, p. 861-864. 

Seager, O.A., Blackstone, D.L., Jr., Cobban, W.A., Downs, G.R., 

Laird, W.M., and Sloss, L.L., 1942, Stratigraphy of North 

Dakota: American Association of Petroleum Geologists Bulletin, v. 26, no. 8, p. 1414-1423. 

Sheldon, R.P., and Carter, M.D., 1979, The Williston Basin region, 

in Paleotectonic investigations of the Mississippian System in 

the United States: U.S. Geological Survey Professional Paper 

1010-0, p. 249-271. 

Sloss, L.L., 1950, Paleozoic sedimentation in Montana area: American Association of Petroleum Geologists Bulletin, v. 34, no. 3, 

p. 423-451. 

---1952, Introduction to the Mississippian of the Williston 

Basin: Billings Geological Society Annual Field Conference, 

3rd, Guidebook, p. 65-69. 

---1953, The significance of evaporites: Journal of Sedimentary Petrology, v. 23, p. 143-161. 

---1956, Geologic comparison of Williston and other productive basins: North Dakota and Saskatchewan Geological Societies Williston Basin Symposium, p. 6-13. 

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1110-X, 32 p. 

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REFERENCES CITED 51 

Weed, W.H., 1899a, Description of the Fort Benton quadrangle 

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Geological Survey Twentieth Annual Report, pt. 3, p. 257-461. 

Published in the Central Region, Denver, Colorado 

Manuscript approved for publication August 5, 1994 

Edited by Judith Stoeser 

Photocomposition by Carol Quesenberry 

Graphics by Carol Quesenberry and Dennis L. Welp 

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stratigraphy of central Montana and Williston Basin: American 

Association of Petroleum Geologists Bulletin, v. 43, no. 8, p. 

1940-1966. 

tr U.S. GOVENMENT PRINTING OFFICE: 1995 - 673-046 / 20001 REGION NO. 8 

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