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1981 Stratigraphy and sedimentology of the Sentinel Butte formation (Paleocene) near Lost Bridge, Dunn County, west-central North Dakota Bradley D. Nesemeier University of North Dakota
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Recommended Citation Nesemeier, Bradley D., "Stratigraphy and sedimentology of the Sentinel Butte formation (Paleocene) near Lost Bridge, Dunn County, west-central North Dakota" (1981). Theses and Dissertations. 209. https://commons.und.edu/theses/209
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STRATIGRAPHY AND SEDIMENTOLOGY OF THE SENTINEL B{JTTE
FORMATION (PALEOCENE) NEAR LOST- BRIDGE, DUNN·
COUNTY, WEST-CENTRAL NORTH DAKCY:rA
by Bradley D. Nesemeier
A Thesis
Submitted to the Graduate Faculty
of the
University of North Dakota
in partial fulfillment of the requirements
for the degree of
Master of Science
Grand Forks, North Dakota
May 1981
GEOLOGY LIBRARY Uilnrelty of Mort• D1bt, \
This thesis submitted by Bradley D. Nesemeier in partial fullfill ment of the requirements for the Degree of Master of Science from the University of North Dakota is hereby approved by the Faculty Advisory Committee under whom the work has been done.
This thesis meets the standards for appearance and conforms to the style and format requirements of the Graduate School of the University of North Dakota, and is hereby ap,iroved.
ii 53GZB7 l
! I Permission
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Formation (Pa,leocene) Near Lost Bridge, Dunn County,
West-Central North Dakota
Department __.:Gce.e=o"'l ="------Degree Master of Science
In presenting this thesis in partial fulfillment of the requirements for a graduate degree from the University of North Dakota, I agree that the Library of this University shall n\ake it freely available for inspection. I further agree that permis.sion for extensive copying for scholarly purposes may be granted by the professor who supervised my thesis work or, in his absence, by the Chairman of the Department or the Dean of the Graduate School. It is understood that any copying or publication or other use of this thesis or part therof for financial gain shall not be allowed without my written permission. It is also under stood that due recognition shall be given to me and to the University of North Dakota in any scholarly use which may be made of any material in my thesis.
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Date
iii TABLE OF CONTENTS
LIST OF ILLUSTRATIONS. V
LIST OF TABLES . • • vii
ACKNOWLEDGMENTS . . viii
ABSTRACT •••• ix
INTRODUCTION. 1
METHODS •••• 5
GENERAL STRATIGRAPHY. 8
DETAlLED STRATIGRAPHY AND SEDIMENTOLOGY • • 12
DEPOSITIONAL ENVIRONMENTS • 45
SUMMARY AND CONCLUSIONS • 55
APPENDIX •••• 58
APPENDIX I. PIPETTE AND SETTLING-TUBE TECHNIQUE OF GRAIN-SIZE ANALYSIS OF FINE SEDIMENTS • • 59
REFERENCES ••• 63
? r' I
'r I i iv LIST OF ILLUSTRATIONS
Plate I. Cross Section of Measured Sections I A-1 Through A-6 •••.••..•• back cover
I Figure .1. Location of Study Area and Measured I Sections A-1 Through A-6 •••• ...... "' . .. 3 2. Key Marker Beds and Study Interval in the I Sentinel Butte Format ion...... 10
I' 3. Silicified Stumps in Growth I'os ition in a Clayey Silt Bed Above the Upper "Yellow" Bed Near Measured Section A-3 (Plate I). 14 't i 4. Cyclic Sequences in the Study Area .••. 17
5. Cross-Stratification in Measured Section A-3 • 21
6. Large-Scale and Small-Scale Sedimentary I Structures in the Study Area • • • • • • • 23 I 7. Elongate Concretion Trends and Dip Direction of Fore set Beds of Cross-Strata in the Study Area • • ...... • .. .. • • .. .. • .. • ...... • ...... 25
8. Trace of Sand Bed B (Plate I) with Dip Direction of Fore set Beds of Large-Scale Cross-Strata, and Trends of Elongate Concretions in Bed B . 27
9. Plot of Graphic Means (Folk 1968) of 13 Samples from Sand Bed B (Plate I) • • • • • • • • • • 29
10. Plot of Graphic Mean (Folk 1968) of 8 Samples from Sand Bed E (Plate I) . . • . • . . ••• ...... 31
V 11. Plot of Graphic Means (F'olk 1968) of 9 Samples from Sand Bed F (Plate I) • • • • • • • • • 33
12 • Triangular Plot of Sand Size Components for Samples from Sand Beds A, B, C, E, and F (Plate I) • • • • • • • • • • • • • • • • • • ...... 36
13. A Set of 'i'ypical Diffractograms from a Clay Bed near the Base of Measured Section A-1 (Plate I) 42
14. Model for Ds,position of Tabular Sa,nd Beds by a Meandering River • • . • • . • • • • • . • • • . .. " . .
15. A .Depression in the Light Colored Lower "Yellow" Marker Bed Filled with Darker Colored Flood basin Silt's and Separated by a Thin Lignite· Bed· (Plate· I) -...... - ...... '°" •• 53
vi LIST or TABLES
Table. 1. Composition of the Sand Fraction ln
Beds A, B, C, E, and r • • . - • ...... ,.,, .. ~ ...... 38
I
vii ACKNOWLEDGMENTS
I would like to thank my committee members, Drs. Alan M.
C.vancara, Walter L. Moore, and Gerald H. Groenewold, for the.Ir help
and advice in preparing this paper. I would also like to thank Dr. Arthur
F. Jacob for·his advice and encouragement that led me to undertake this
study. I My appreciation ls extended to the Tribal Business Councll of the Fort Berthold Indian Reservation and to the Emerson Chase family, who ! granted me permission to work on the Reservation. i Richard N. Spaeth, a fellow graduate student, should also be I commended for assistance he rendered while in the field.
Special thanks go to my parents, Mr. and Mrs. Dale C. Nesemeier,
and the North Dakota State Geological Survey for financial support
without which this study would not have been possible.
viii ABSTRACT
The Sentinel Butte Formation (Paleocene) near Lost Bridge, Dunn I County, west-central North Dakota, is 190 meters thick, and is charac terized by four main lithologies: sand, silt, clay, and lignite. The
study interval is ISO meters thick, and lies between the basal sand of the I . . formation and the Bullion Butte lignite bed, neither of which are exposed
in the immediate study area. Sand, gray to yellow, makes up about 3S%
of the interval studied. It occurs in tabular beds 2-18 meters thick. It I is fine to very-fine, angular, and composed largely of quartz, feldspar, rock fragments, with minor amounts of biotite ,. chlorite, and organic
materials. Sand beds become finer grained from bottom to top, are poorly
to very poorly sorted, and have an erosional base. Large-scale cross
strata are visible in the lower and middle parts of the sand beds, and
small-scale cross-strata are usually abundant in upper parts of the beds.
Sand beds w_ere deposited by meandering rivers as indicated by their
tabular and U shapes, sedimentary structures, and textural analysis.
Paleocurrent data suggest a general southeasterly stream flow.
Silt, light yellow to grayish brown, makes up about 40% of the
formation and occurs l.n beds 1-15 meters thick. Small-scale cross-strata
ix and plant remains are common. Fossil gastropods and pelecypods indi cate a freshwater origin. Climbing ripple cross-strata, sand lenses, sillclfied stumps found in growth position, and iron-rich concretions with organic centers are evidence of a natural-levee environment for light-colored silt beds. A floodbasin environment is indicated for darker colored silt beds that are finer-grained, contain abundant plant debris, and are associated with clay and lignite beds.
Clay, gray to brown, makes up about 15% of the formation and occurs in beds up to 5 meters thick. Plant remains and carbonaceous materials are abundant. Montmorillonite, mica, kaolinite, and chlorite are the principal clay minerals. The dark color, organic matter, and association with ligntte beds indicate a lower floodbasin environment of deposition for the clay beds.
Lignite beds are black, hard, blocky, woody-textured, and are found associated with brown to black, soft, clayey, carbonaceous debris.
Most lignite beds are 1 meter or less thick, are excellent aquifers and enhance vegetation growth. Because lignite beds have a woody texture and are associated with floodbasln deposits and fluvial sands, they probably have resulted from peat accumulation in the lowest areas on the floodbasin between major streams.
X INTRODUCTION
The purpose of this study was to determine the depositional environments of the exposed portions of the Sentinel Butte Formation near
Lost Bridge in Dunn County, west-central North Dakota. This involved studying the. sedimentology and stratigraphy of the outcrops. This area was chosen because of excellent formation exposures and lack of previous deta !led study.
Early work on the Sentinel Butte Formation was a study of coal land by the. United States Geological Survey in the. early 1900s
(Campbell 1916). Since then, economic interest in the lignite-bearing strata has increased to a point where oil and coal companies are presently spending considerable effort exploring for lignite resources,
Environmental impact studies are now popular and private companies, state and federal agencies, and the public are involved with them. The most recent work on the Sentinel Butte Formation was done by Royse
(1967a, 1967b, 1970), Cherven (1973), Johnson (1973}, Hemish (1975},
Moran et al. (1978), Groenewold et al. (1979), and Brekke (1979).
The best exposures of the Sentinel Butte Formation are found in buttes along the Little Missouri River, along its tributary streams, and
1 2
along the bluffs of Lake Sakakawea from Riverdale north to Williston;
North Dakota.
The study area is in Dunn County, west-central North Dakota, about 33 kilometers north ·of the town· of Killdeer; along North Dakota
Highway 22 on the Fort Berthold Indian Reservation (Fig. 1). The area
is characterized by badlands-type topography along both sides of the
Little Missouri River, which flows approximately west to east in this area. The exposures in this type ·of topography are excellent on most
south-facing slopes where vegetation is sparse, and there are good opportunities for detailed study.
I constructed a cross section of well exposed strata in an area about 3. 6 kilometers long with about 100 meters of vertical relief.
Well exposed beds were traced in the field between six measured sections (Fig. 1). Included in the cross section are lithology and fossil occurrences, primary sedimentary structures, concretions, and areas containing carbonaceous materials and silicified wood (Plate I). 3
Fig. 1. Location of study area and measured sections A-1 through A-6. 4
NORTH DAKOTA
DUNN COUNTY
/:Jr, 22 f14 l I MJLE
• 3
b,2 26 I:;. LOCATION OF MEASURED SECTIONS A-I THROUGH A-6
1---....\--+-.L,:.<::====t---N.D. HIGHWAY 22
~----f----LOST BRIDGE
_.,-·-+--LITTLE MISSOURI RIVER METHODS
Field
Six stratigraphic sections were measured using a hand level and located on the 7 1/2 minute Lost Bridge quadrangle topographic map. Sea level was used as datum. Correlations between all measured sections were traced in the field.
Dip of cross-strata and trends of sand beds or elongate concretions were measured with a Brunton Compass. Cross-strata were classified
according to facob (1973).
Samples were taken to determine grain size, sand petrology, and
clay mineralogy. Sand beds less than 10 meters thick were sampled
vertically at half-meter intervals, and sand beds greater than 10 meters
thick were sampled vertically at I-meter intervals. Clay beds were
generally l meter or less in thickness and one sample was taken from
the middle of each bed. All samples, With the exception of some sand
samples, were taken at the location of measured sections.
Laboratory
Grain size analyses were performed on sand samples by a weight
accumulation settling tube similar to the one described by Felix (1969)
5 6 and by pipette analysis (Appendix I). The results of these analyses were combined into one cumulative frequency curve per sample. Data for computing the graphic mean {Folk 1968) and inclusive graphic standard deviation {Folk 1968) were obtained from the cumulative frequency curve.
A computer program was used to obta)n the graphic mean and inclusive graphic standard deviation of each sample.
Sand J:)etrology was studied by a grain-count method on prepared grain-mounts. Grain-mount preparation consisted of.heating a glass slide containing a few drops of caedex to 300°F and sprinkling the sand sample evenly over. the center of the slide. A cover glass was then placed on top, pressed lightly with a pencil eraser to remove air bubbles, and the slide was removed from the heat. Data from the point counts were used to classify the samples according to the sandstone classification of Folk, Andrews, and Lewis (1970) by means of a com puter program {Jacob 1974).
Clay mineral studies were done using oriented clay slide mounts and X-ray diffraction techniques. Slides were prepared by placing about
5 grams of sample in a 50 ml cylinder, which was then covered with a 4%
Calgon solution and filled with distilled water. Cylinders were left to stand for 48 hours and shaken vigorously. After 60 seconds, the sample was pipetted at a 5 cm depth onto a glass slide and allowed to dry.
X-raying was completed on glycolated and non-glycolated samples as well as on some samples heated to 6S0°C. All samples were X-rayed 7 using a Norelco high-angle diffractometer using copper K-alpha radiation produced at 37 kv and 18 ma. All samples were scanned from
2°20 to 32029 at a scan speed of 2°2e per minute, a chart speed of
60 inches per hour and a rate-meter setting of I X 10 3 . GENERAL STRATIGRAPHY
The Sentinel Butte Formation is in the upper part of the Paleocene
Fort Union Group. Included in this group, from youngest to oldest, are the Ludlow, Cannonball, Slope, Bullion Creek, and Sentinel Butte
Formations (Clayton et al. 1977). The Bullion Creek Formation is composed of nonmarine silt, sand, clay, lignite, and is yellowish.
The Sentinel Butte Formation is somber buff-gray containing silt, sand, clay, and lignite deposits.
The Paleocene-Eocene Golden Valley Formation overlies the Fort
Union Group and is composed of blue clay, siltstone, lignite, white and orange kaolinitic clay, fine-grained sandstone and shale with minor amounts of lignite.
All the above mentioned formations are present in the Williston
Basin which is centered south of Williston, North Dakota, and includes western North Dakota, eastern Montana, northwestern South Dakota, and southeastern Saskatchewan.
The Sentinel Butte Formation is widespread in western North Dakota
(Clayton et al. 1980). It is about 65 meters thick (Royse 1967a) on the flank of the basin near Richardton, eastern Stark County, North Dakota,
8 9 and approximately 19S meters thick (M7ldahl 19S6) closer to the center of the basin near Grassy Butte, south-central McKenzie County, North
Dakota.
There are six key marker beds .in the Sentinel Butte Formation
(Pig. 2). They are, from bottom to top, the basal sand, "blue" bed, lower "yellow" bed, upper "yellow" bed, Bullion Butte lignite, and the upper sand (Royse 1967a). Other marker beds include several major local lignite beds with varying names (Groenewold et al. 1979). 10
Fig. 2. Key marker beds and study interval in the Sentinel Butte Formation (modified from Royse 1967a) •
... 11
Golden Valley Fm. .. ·.. ~: . ·. ·.· _.. .. , . : .. Upper Sand
Bullion Bulle lignite
- .. - .. - • - • Upper " Yellow fl Bed • - .. - " - .. Cl) LI.I 0.. ~ - ::> u. 0::: 0 ..:.J w 0::: w en C) I- ~ I- 0::: .. w z ::> w co I- z 0 z w -z ...J u ::> w - 0 z >- 0 .. If 1t w I- I-- ::> - - • -.. •- - Lower Yellow Bed ...J 0::: z I- - • - " :•,,', ...... :, .. : .• ··. .. Basal Sand Bullion Creek Fm. DETAILED STRATIGRAPHY AND SEDIMENTOLOGY The Sentinel Butte Formation in the study area is about 190 meters thick. The maximum thickness of the study interval (Fig. 2) is approx!- mately 150 meters. The "blue," lower "yellow," and upper "yellow" marker beds. are present in the study area (Plate I). The lower "yellow" marker bed was easily identified but the "blue" and upper "yellow" marker beds did not possess the distinct colors that they have farther west, as in the North Unit of Theodore Roosevelt National Park, McKenzie County, North Dakota. The upper sand marker. bed was present in places on the uplands where badlands-type topography gives way to rolling hills and occasional buttes. It is not known whether the basal sand marker bed was present, as this portion of the formation was not exposed in the study area. The Sentinel Butte Formation ls composed of four main lithologles in the study area (in order of decreasing abundance): silt, sand, clay, and lignite. Silt Beds Silt beds are found throughout the section with the thicker beds present above the lower "yellow" marker bed (Plate I). The silt beds 12 13 are 1-15 meters thick. Beds are, for the most part, laterally continuous except in a few places where they grade into sand (Plate I). The silt in places is clayey, or sandy; its color varies from gray to a rust brown. Four types of concretions are present in the silt beds: (1) spherical, yellow, iron- and sulfur-rich concretions that are 1-25 cm in diameter; (2) tabular, rust colored, limonitic concretions that define bedding planes, and are 1-5 cm thick; (3) spherical, maroon, cherty, and fracture into rectangular blocks that accumulate into rockpiles about l meter in diameter; and (4) spherical or oblong, gray to buff, carbonate cemented, in places contain small-scale cross-strata, and up to 3 m long. Fossil pelecypods and gastropods are found in a clayey-silt bed that directly overlies the lower "yellow" marker bed (Plate I), The gastropods belong to the genus Lioplacodes (Yen 1948; Delimata 1969). This bed was the only one that contained fossils other than silicified wood or plant fragments. Silictfied stumps or wood fragments are found in some silt beds usually above or below a lignite bed (Fig. 3). Sedimentary structures in the silt beds are small-scale, grouped, planar, parallel, low-angle, straight cross-strata and small-scale, grouped, planar, parallel, gradational, high-angle cross-strata. These structures are best preserved in the sandy concretionary bodies within the silt beds. Sedimentary structures in beds other than the sandy 14 I I: Fig. 3. Silicified stumps i.n growth position in a clayey silt bec.l above the upper "yellow" bed near measured section A-3 (Plate I) • ... 16 concretions are commonly distorted, probably as a result of bioturbation, indicated by the presence of carbonaceous debris. Throughout the study area silt beds are overlain by a clay bed that is carbonaceous and grades upward into a lignite. The lignite, in turn, grades upward into a carbonaceous clay, which, in turn, grades upward into a pure clay, and, in turn, to another silt. This cyclic sequence occurs commonly throughout the section (Fig. 4). Sand Beds Sand beds are 2-18 m thick and are distributed throughout the section {Plate I). Below the lower "yellow" marker bed there are no sand beds thicker than 5 meters, but they are as thick as 18 meters above the lower "yellow" bed. Sand beds in some places are laterally continuous throughout the entire cross section, or, as tn bed B (Plate IL only 120 meters wide. Sand beds are (1) trough-shaped, and yellow (bed B, Plate I); (2) continuous, tabular, and gray to buff {beds A and E, Plate I); or (3) non-continuous, tabular, gray to buff (beds C and D, Plate I). Most sand beds directly overlie a lignite bed. The contact is usually erosional as indicated by the presence of lignite particles in the lower portions of the sand beds. There are two common stratigraphic sequences: one consists, from bottom to top, of sand, silt, clay, carbonaceou·s clay, and lignite; all contacts, except the basal sand 17 Fig. 4. Cyclic sequences in the study area. (4a) Common cyclic beds found near measured sections A-5 above lower "yellow" marker bed (Plate I). (4b) Cyclic beds in measured section A-.2 below lower "yellow" marker bed (Plate I). A = silt, B ~ clay and carbonaceous clay, C = lignite. 19 bed contact, ace gradational. The other sequence is a lignite bed directly overlying a sand bed (Plate I). Sand beds consist of fine-grained to very-flne-gra ined sand and, in most cases, contain high percentages of silt and clay. The sand beds are usually either gray or yellow although transitional colors are present apparently due to different degrees of oxidation or staining by iron oxide-rich concretions within the bed. Spherical or elongate, carbonate-cemented concretions are present in the sand beds and they normally exhibit preserved cross strata. Spherical, yellow, sulfur- and iron-rich concretions 1-10 cm . in diameter. that usually contain organic centers are present in. some beds. Sand bed B (Plate I) contains large, tabular, carbonate-cemented concretions O. S meters thick, which, in some places, exhibit small scale cross strata. Sedimentary structures present in the sand beds include large scale, grouped, curved, concave cross strata; large-scale, grouped, planar, parallel, high-angle, straight cross-strata; small-scale, grouped, planar, parallel, high-angle, straight cross-strata; and small-scale, grouped, planar, parallel, gradational, high-angle cross-strata. Bedding planes in some large-scale sedimentary struc tures contain thin layers of carbonaceous material. The small-scale cross-strata are best preserved in concretions found in the upper part of sand beds whereas the large-scale cross stratification is rarely 20 preserved in concretions and ls .found in the lower and middle parts of sand beds (Figs. S and 6). No fossils were present in the sand beds. Paleocurrent Data Elongate concretions containing sedimentary structures in the sand beds are apparently parallel to the trend of the bed and were used in some cases to determine current direction (Figs. 7 and 8). Other paleocurrent data were collected from measuring the dip direction of foreset beds of large-scale cross-strata. The yellow sand bed B (Plate I) has a paleocurrent direction of west-southwest. All other sand deposits that had obtainable paleocurrent information show that average current flow was predominately to the southeast (Fig. 7). Textural Analyses The graphic mean and inclusive graphic standard deviation (Folk 1968) were obtained from 32 samples in sand beds B, E, and F {Plate I). Results of the analysis are shown in Pigs. 9, 10, and 11. Sand bed B has a graphic mean of 3. 9-6. 3 phi (Fig. 9) with an average of 5. 0 phi. No overall fining- or coarsening-upward trend can be detected (l'ig. 9). Inclusive graphic standard deviation in the bed is 1. 6-3 .O phi and averages 2. 1, which is, according to terminology suggested by Folk (1968), very poorly sorted. The graphic means for samples from sand bed E are 4. 7-8 .4 phi ·and average 6. 6 phi (Fig. 10). An overall fining-upward trend is 21 Fig. S. Cross-stratification in measured section A-3. (Sa) Large scale, grouped, planar, parallel, high-angle, straight, discordant, heterogeneous cross-strata near base of sand bed C in measured section A-3. (Sb) Small-scale, grouped, planar, parallel, loo/-angle, straight, concordant, homogeneous cross-strata (upper part of concretion), and small-scale, grouped, planar, parallel, gradat!onal, high-angle, slgmoidal, discordant, homogeneous cross-strata (lower part of con cretion) in middle of measured section A-3. - a b 23 Fig. 6. Large-scale and small-scale sedimentary structures in the study area. (6a) Large-scale, grouped, curved, low-angle, concave, concordant, heterogeneous cross-strata found near the· base of sand bed B (Plate I). (6b) Asymmetrical ripple marks in a concretion in the sand bed below the lower "yellow" marker bed in measured section A-2. ' ' ... b 25 1lil, I i I. f Fig. 7. Elongate concretion trends and dip direction of foreset beds of cross-strata in the study area. (7a) Elongate concretion trends in sand bed A (Plate I). (7b) Dip direction of fore set beds of cross-strata in sand bed at bottom of measured section A-5. (7c) Elongate concretion trends in sand bed B. (7d) Dip directions of fore set beds of cross-strata in sand bed B. (7e). Dip direction of foreset beds of cross-strata in sand bed C. (7f) Elongate concretion trends in sand bed F. (7g) Dip direction of fore set beds of cross-strata ln sand bed F. 26 North a C d f g 27 1 ', ' Fig. 8. Trace of sand bed B (Plate I) with dip direction of foreset beds of large-scale cross-strata, and trends of elongate concretions in bed B • ... 28 Concretion Tnmd-Bed B Dip Of Cross strata -Bed B J_ -i------·---···-·--.;---- Covered/ 21 Covered 28 27 26 MiJes 0 1/4 l/2 I score ~------t--N.D. HIGHWAY 22 LOST 8RIDGE LITTLE MISSOURI RIVER T 148N 29 Fig. 9. Plot of graphic means (Folk 1968) of 13 samples from sand bed B (Plate· I). The meter scale indicates the distance of each sample above the base of the sand. ' .. 30 METERS 6 5 4 3 2 2 3 4 5 6 7 8 9 !1l (phi) 31 Fig. 10. Plot of graphic mean (Folk 1968) of 8 samples from sand bed E (Plate I). The meter scale indicates the distance of each sample above the base of the sand • .. 32 METERS 8 7 6 5 4 3 2 2 3 4 5 6 7 8 9 0 (phi) 33 I'•'.i?:tv jj I' . Fig. 11. Plot of graphic means (Folk 1968) of 9 samples from sand bed F (Plate I). The meter scale indicates the distance of each sample above the base of the sand. I· 'l I· .... 34 METERS II 10 9 6 7 6 4 3 2 2 3 4 5 6 7 6 9 (phi)" 35 present. Inclusive graphic standard deviations are 1. 7-2. 8 phi and average 2 .1 phi, which is, according to Folk (1968), very poorly sorted. The graphic means for sand bed F are 3. 1-5 .4 phi and average 4. 8 phi. There are no distinct overall fining- or coarsening-upward trends {Fig. 11). The inclusive graphic standard deviations are 1.3-2.4 phi and average 1.9 phi, which is, according to Folk (1968), poorly sorted. Generally sand beds B, E, and F are poorly to very poorly sorted with their graphic mean grain sizes falling, on the average, in the silt size range. Beds Band F display no overall fining- or coarsening upward trend but may show some fining and coarsening upward cycles (Figs. 9 and 11). There is an overall fining-upward trend in sand bed E (Fig. 10). A fining-upward trend in sand bed C (Plate I) was detected in the field. Sand Petrology Two grain mounts each were prepared from sand beds A, B, C, E, and F (Plate I) and 200 grains were counted on each mount. These data were used to classify the samples (Folk et al. 1970) by means of a computer program written by Jacob (1974). The results are shown in Fig. 12 and in Table 1. Quartz was the most abundant mineral in all samples and consisted of 68% to 89% common quartz; 5% to 28% 36 Iii, I i.! Fig. 12. Trlangular plot of sand size components for samples from sand beds A, B, C, E, and F (Plate I) • ... 37 QUARTZ I Roe\ Fraoment~ SEDIMEHTARY ROCK FRAGMENTS Volcanic: Met omorpldc Roell Frogm•rth: Roe.It Froamnn SAHDSTOM£ ANO SMALE ROCI< FRAGMENT$ Corbonote Rock FrO!JMH1:t TABLE 1 COMPOSITION OF THE SAND FRACTION IN BEDS A, B, C, E, AND F Rock Quartz Feldspar Fragment Cement Other Sand Bed Sample* Name (percent) (percent) (percent) (percent} (percent) A 1 plagiocla se subfeldsarenite 63 9 s 11 10 A 4 chert sublltharenite 52 7 8 27 5 w B 1 plagiocla se subfeldsarenite 74 4 4 14 2 0:, B 4 plagioclase subfeldsarenite 42 4 3 49 1. C 4 chert lithic feldsarenite 47 25 11 6 9 C 8 chert llthic feldsarenite 51 19 13 6 10 E s chert sublltharenlte 67 7 9 10 6 E 10 chert feldspath le litharenite 66 11 13 6 4 F 3 plagloclase subfeldsarenite 72 9 2 11 5 F 7 chert sublitharenite 71 2 9 11 5 *Sample numbers Indicate distance in meters from base of sand bed. Classified according to Folk et al. (1970). 39 polycrystalline quartz except chert, of which only a small fraction was metamorphic polycrystalline and the majority resembled coarse-grained chert; and 1% to 11 % monocrystalltne undulose quartz. Quartz grains were mostly angular. Subangular grains with an etched, pitted, or sutured surface were probably the result of dissolution. Plagioclase was by far the most abundant feldspar. K-feldspar was recorded in only two of the 10 grain mounts and made up 1% or less of the total composition. Feldspar grains were usually angular, and exhibited good cleavage and carlsbad twinning. Rounded to subrounded chert grains made up the majority of the rock fragments with minor amounts of volcanic, plutonic, and meta morphic rock fragments not exceeding 2%. The volcanic rock fragments were irregularly shaped gratns that consisted of an isotropic ground mass with crystal inclusions. The plutonic rock fragments were also irregularly shaped and contained two or more distinct minerals such as quartz and biotite. Metamorphic rock fragments were subangular to subrounded and foliated. Carbonate cement was present in all samples. Iron oxide cement or staining was most pronounced in sand beds B and E (Plate I). Carbonate grains present were almost always rhombohedral, exhibittng good crystal faces and cleavage. Because of their euhedral shape the grains are probably cement rather than elastic carbonate rock. 40 Clay Be~s Clay beds vary ln thickness from tenths of a meter to 5 meters. These beds consist of clay that is generally silty and gray to brown. Generally, the grayer clay beds are less silty and contain fewer plant remains than the brown clay beds. Concretions present in the clay are 1-10 cm in diameter, Irregularly shaped, yellow or rust colored, and sulfur-rich with carbonaceous centers. A white precipitate, possibly sodium sulfate, on the surface of the clay beds as well as selenite crystals, are common. Silicified wood and plant fragments are the only fossils found in the clay beds. Nearly all the clay beds contain carbonaceous material or plant fragments • Sedimentary structures are all small-scale cross-strata, but are usually distorted, probably as a result of bioturbation. Clay beds occur throughout the section In two main stratigraphic sequences. One typical sequence consists, from bottom to top, of lignite, carbonaceous clay, and lignite. The other common sequence consists, from bottom to top, of silt, clay, carbonaceous clay, lignite, carbonaceous clay, clay, and silt (Fig. 4) . Clay Mineralogy Analysis of 34 diffractograms from 15 clay samples obtained from measured sections A-1 and A-6 (Plate I) indicate the presence of four 41 main clay minerals; montmori llonite, mica, kaolinite, and chlorite, in order of decreasing abundance. Quartz is present in a significant amount and there are minor occurrences of feldspar, dolomite, and calcite. A typical set of diffractograms is shown on fig. 13. Chlorite peaks are present at 7.13 ~, 3.57 ~' and 4.72 .R (Fig. 13). Kaolinite also has 0 0 0 peaks at 7. 15 A and 3. 5 7 A but the 4. 72 A peak is an indicator of chlorite (Grim 1953). In order to check for the presence of kaolinite, some samples were heated to ,550°c at which temperature kaolinite becomes amorphous (Carroll 1970). Results obtained after heating show 0 the disappearance of the 3. 5 7 A peak and also disappearance of the 0 7 .13 A peak on some diffractograms (Fig. 13). This confirms the presence of kaolinite and lesser amounts of chlorite. Illite and mica both have a peak at 10 .R but the sharpness of the 0 peak indicates mica (Carroll 1970). The 5 A peak is a good indication of muscovite rather than biotite, but biotite is probably present in O O 0 smaller amounts as very small peaks at 1.54 A, 1. 52 A, and 1.47 A were present on a special check for biotite run from 59° 20 to 63° 29. Small amounts of illite may also be present but are masked by the mica peaks. The four main clay minerals and quartz were present in all diffractograms. There were minor changes in peak heights and in the presence of the minor non-clay minerals feldspar, calcite, and dolomite 42 I~ It, L,11. I, " ' Fig. 13. A set of typical diffractograms from a clay bed near the base of measured section A-1 {Plate I). Copper k-alpha radiation, a scan speed of 2° 28 per minute, a chart speed of 60 inches·per hour, and a rate meter setting of l X I o3. '.•J' ,'f< lQ.OOA• 7.13A• s;oeA 4,271 5.57A• 3.!41 3.04A• l7rlr4ri I I I 4.721 l I I 3,201 I 2.91A• I I l GLYCOLATED ,J:,. w HEATED TO 650°C NORMAL 44 both vertically up and down section and laterally. No apparent trends were noted in these fluctuations either vertically or laterally. Lignite Beds Lignite beds are black to brown and consist of lignite and carbonaceous material. The lignite is black, blocky, brittle, and has a woody structure. The carbonaceous material has a layered appearance, is brown to black, and usually contains clay or silt. Lignite beds are usually easily recognizable in the field by horizons of vegetation on relatively barren slopes. The lignite beds are excellent aquifers and enhance plant growth. Silicified wood is sometimes found on the upper or lower contact of lignite beds. Thicknesses of lignite beds are a few centimeters to 3 meters with most beds being O. 5-1. 0 meter thick. Lignite beds are usually under lain and overlain by carbonaceous clay but in some cases are overlain by a sand bed where an erosional boundary exists between the two beds. DEPOSITIONAL ENVIRONMENTS Sand Beds Sand beds are interpreted as having a fluvial origin. All sand beds except bed B (Plate I) were probably deposited by high-sinuosity streams similar to those described by Allen (1965b), Moody-Stuart (1966), and Fisher and McGowen (1969). The sand beds are lateral-accretion deposits that formed by sediment accumulation on the point bars as the steeper, concave banks of the streams were eroded, resulting in stream migration (Fig. 14). According to Leopold, Wolman, and Miller (1964) maximum flow intensity is found near the steep concave bank of the stream and the flow intensity decreases up the point bar. This decrease in stream energy results in deposition of finer-grained material near the top of the point bar and hence a fining-upward trend like that described by Allen (1965a) in alluvial sand bodies and as found in sand bed E (Fig. 10). Epsilon cross-strata (Fig. 14) were found in sand bed D (Plate I) and indicate point bar development (Allen 1965b), Other characteristics of meandering stream deposits (Allen 1965b; Mocdy Stuart 1966; Fisher and McGowen 1969) that can be found in sand beds A, C, D, and F (Plate I) include an overall tabular shape, a transition 45 46 II(. lt-J 11.1,!' ! Fig. 14. Model for deposition of tabular sand beds by a meandering river. Modifled from Moody-Stuart (1966). . ,, ,. I;' .. 47 :>, u0 "O C -0 (J) C ·a C n. 0 "O :>, -0 0 0 0 0 u ;;:: lJ.. "O "O C C <( "O <( C (J) "' 0 "' "'0 IJ') "'> C: ~ ...J"' u 0"' .0 C: 0' C: 0 "'C ~ "' "O C ::, C: 0 ·.; 0 0 0 .s;: 0 .s;: C. C: u z u lJ.. LL.I .!:! .; ~ 0 0 <( i 48 from large-scale cross-stratification at the base to small-soale cross stratification at the top, and an erosional base. The sorting of sand beds was poor to very poor in samples tested in the laboratory and all sand beds displayed a poorly sorted appearance in the field. The fine-grained and poorly sorted stream load could be expected in a meandering accretlng river (Allen 1965b). Sand beds C and D may represent coalescent streams on the same floodplain, or sand deposited by the same meandering river wlth flood plain deposits, that are described in the silt depositional section, in between {Moody-Stuart 1966). Sand bed B (Plate I) is interpreted as being a straight fluvial channel deposit. The U-shaped, elongate bed oontains large-scale cross-strata at the base and small-scale cross-strata at the top. Paleocurrent indicators show current flow was to the west-southwest, which is parallel to the trend of the bed (Fig. 8). The adjacent beds are truncated by bed Band scour is indicated at the base of bed B. Allen {1970c) has shown that deposits in a low-sinuosity fluvial environment are lateral accretion deposits because a stream's thalweg is sinuous even though the overall stream is straight. According to Allen {1966), large-scale cross-strata overlain by small-scale cross-strata may be due to lateral bar development on margins of low-sinuosity streams. 49 Silt Beds Silt beds were deposited in two environments, natural levees and floodbasins. Yellowish, brownish, or light colored silt beds that con tain lenses of very-fine sand, clay, and small-scale, grouped, planar, parallel, gradational, high-angle, slgmoidal, discordant, homogeneous, (climbing ripple) cross-strata along with plant debris, silicified wood, and iron-rich concretions are interpreted as natural levee deposits (Plate I). Climbing ripple cross-strata result from a high sedimenta tion rate from suspension (Allen 1970b). According to Allen (1965b) depositional rates ln the natural levee are the highest on the entire floodplain. This would account for the climbing rtpples in the light colored silt beds. Allen (1965b) and McKee (1966) agreed that climbing ripples and small-scale, grouped, planar, parallel, low-angle, straight (horizontal lamination) cross-strata are sedimentary structures typically found in natural levee deposits. j The presence of the sand lenses and clay in the silt beds are due to the periodical construction of the natural-levee during flooding (Allen 1965b). During floodstage more energy would be available to transport the sand to the natural-levee area and deposit it. The clay would thus I be deposited when the water motion decreased. Plant debris found ln the light colored and brownish silt beds are due to a vegetation ktll caused by high sedimentation rates on the natural-levee. Oxidation around organic nuclei in the natural-levee deposits would enhance iron 50 precipitation and concretion formation (Jacob 1972). This would explain the numerous secondary concretions and yellow and brown color of the silt beds. j' l Gray and brown silt beds that are clayey, contain plant remains, l iron-rich concretions, fossil mollusks, distorted small-scale cross- 1 strata, and are found in cyclic sequences along with lignite and clay beds are interpreted as floodbasin deposits (Plate I). ,, The grain size of the sediment, along with the small-scale cross- l j strata, indicate these beds were deposited in low-energy environments. I The good preservation of mollusks and plant fragments indicate little or l no transportation. The silt beds are associated·with fluvial sand beds 1 l and contain mollusks (e.g., Liopiacodes) described by Yen (1948) and Delima ta (1969) as freshwater organisms, which would indicate these beds were deposited on an alluvial plain in the floodbasin. Distorted sedimentary structures are attributed to bioturbation, indicated by plant remains, or to differential compaction, or both. Brown and gray colors reflect periodic change from conditions favorable for ferric iron precipi tation. This change could be caused by seasonal change, and/or water level fluctuation in the rivers. The organic nuclei of iron-rich concre l tions indicate iron precipitation around organic materials. I The cyclic pattern of the gray and brown silt beds (Fig. 4a) and l their association with clay and lignite beds are indicators of floodbasin l 1 deposits (Fisher 1964; Beerbower 1965). The absence of such cyclic l i 51 deposits may indicate a non-floodbasin environment (Beerbower 1965). Beerbower also indicated from his model studies that changes in stream dis charge, load, slope, unequal subsidence, differential compaction, depositional topography, arid substrate may all affect cyclic deposition. Clay and Lignite Beds Clay beds that are gray to brown, and contain plant remains, dis torted small-scale sedimentary structures, and typically become finer upward from underlying silt beds to carbonaceous clay and lignite beds are lnterpreted as lower floodbasin deposits. The abundant plant remains in the clay beds are due to clay deposition near .and adjacent to a well established swamp where there was abundant vegetation. The plant growth present in the lower floodbasin could have acted as a baffle preventing the elastic material from moving into the swamp and thus being deposited along with plant remains. The distorted sedimentary structures are probably due to bioturbation and/or compaction. The gray and brown colors of the clay beds are due to low Eh and ph conditions during depos itlon, or to the organic matter content of the sediment. Coleman and Gagliano (1965) showed that dark colors are typical of floodbasin I deposits and Beerbower (1965) described similar clay beds and suggested they were deposited in backswamps on the floodbasin. Lignite beds are black, blocky, brittle, and have a wood structure. The beds are overlain and underlain by carbonaceous clays previously 52 described and interpreted as lower floodbasin deposits. The lignite beds probably formed in the lowermost areas on the floodbasin which were forested peat swamps, indicated by the woody texture of the lignite and by their association with lower floodbasin carbonaceous clay beds. Fluvial lignite beds have a high percentage of woody material (Kaiser 1974) and are associated with the fine-grained overbank deposits of fluvial cycles (Fisher 1964). Sand beds A, C, D, E, and F directly overlie lignite beds {Plate I). I In this situation a migrating stream has deposited sand over the more resistant lignite beds after eroding the floodbasin silt and clay beds. I All lignite beds are gently dipping except the bed overlying the 1 lower "yellow" bed near sand bed B (Plate I). This exception is due to an existing depression in the lower "yellow" bed prior to lignite accumu lation. This depression, which was close to the water table, provided an excellent environment for plant growth and peat accumulation. The greatest peat accumulation occurred in the bottom of the depression as indicated by the thickening of the lignite bed. As shown in Fig. 15 the entire depression was later covered by floodbasin deposits (Plate I). 53 I l i 1 j J 1 i .l Fig. 15. A depression in the light colored lower "yellow" marker bed filled with darke"r colored floodbasin silts and separated by a thin j lignite bed (Plate I). l 54 ij .l ' SUMMARY AND CONCLUSIONS Silt, sand, clay, and lignite are the four main lithologies in the study area. Silt beds are most abundant and are characteristically clayey or sandy, light yellow to grayish-brown, and contain small-scale cross strata and carbonate-cemented and iron- and sulfur-rich concretions. Fossil pelecypods and gastropods indicate a freshwater origin. Silt. beds occur in cyclic sequences where they are overlain and underlain by clay beds, and are also found overlying or underlying sand beds (Plate I). Sand beds contain fine- and very-fine, angular and subangular grains of quartz and feldspar, rock fragments, carbonate cement and minor amounts of biotite, chlorite, and organic material. The sand is predomi nately gray but ls also buff and yellow. Tabular sand beds were most abundant and one U-shaped elongate sand bed was observed. Large scale, grouped, curved, .concave, and large-scale, grouped, planar, parallel, high-angle, straight cross-strata are present in some sand beds. Small-scale, grouped, planar, parallel. low-angle, straight and small-scale, grouped, planar, parallel, gradatlonal, high-angle cross strata were observed in the upper parts of sand beds in the abundant tabular and elongate, carbonate-cemented concretions. 55 56 Paleocurrent indicators for major sand beds show a general south easterly current direction. Sand beds overlie lignite beds or clayey-silt beds. Fining-upward trends were observed in the field and confirmed by particle settling velocity analysis. All sand beds are poorly sorted. Clay beds are gray to brown and usually contain abundant plant remains. X-ray diffraction data reveal that montmorillontte, mica, kaolinite, and chlorite are the principal clay minerals. Quartz and minor amounts of calcite, dolo1:1ite, and feldspar are also pre sent. Small-scale cross-strata in some clay beds are usually distorted. Clay beds are most commonly found overlying and underlying lignite beds or overlying a s llt or sand bed. Lignite beds, are black to brown, hard, blocky, have a woody texture, and in many places are found associated with carbonaceous material. Most lignite beds are l meter or less thick and are easily identifiable on relatively barren slopes by a vegetation band. The beds are overlain and underlain by clay beds except where there ls an erosional contact between a lignite bed and an overlying sand bed. Low-energy, high-sinuosity river environments described by Allen (1965b), Moody-Stuart (1966), and Fisher and McGowen (1969) were probably similar to environments of deposition in the study area. In these environments meandering rivers deposited tabular-shaped sand beds that typically become finer upward and were associated with silt, clay, and lignite beds in approximately a 35% sand:65% fines ratio. 1 i 57 ! J In the study area the sand fractipn of the stream load was pre dominately deposited in the main river channel wtth minor amounts included in natural-levee sediment. The silt fraction of the load was deposited on the natural-levee and in other areas on the floodplain near the main channel. Clay from the stream was carried farthest from the main channel and deposited in areas between peat swamps, which were the lowermost areas tn the floodbasin and the natural-levee. Lignite beds formed from peat accumulations in interstream swamps. The plagioclase, biotite, chlorite, and montmorillonite content of the stream load is an indicator of a volcanic source (Folk 1968). The high percentage of common quartz in the sand fraction Indicates a plutonic source (Folk 1968). The stream load was probably derived from Rocky Mountain plutonic and volcanic rocks in Montana or southern Canada along with some sedimentary rocks indicated by the chert content, possibly a replace ment product of carbonate rock fragments, Lateral and vertical composi tional changes are slight, which indicates little or no change in source area throughout the depositional period. The absence of any appareqt marine or shoreline deposits in the study interval, and the presence of an apparent fluvial system, indicates that all beds were deposited under continental conditions. 1l APPENDIX l j APPENDIX I PIPETTE AND SETTLING-TUBE TECHNIQUE OF GRAIN-SIZE ANALYSIS OF FINE SEDIMENTS 1 Introduction Sediment samples were texturally analyzed with as little pre treatment as possible. It was believed that the analysis should reflect depositional conditions so far as possible. Organic material was not eliminated because it was present at the time of deposition. Soluble salts were not removed because these are at least a partial remnant of the depositional environment. Procedure {adapted from Folk 1968) 1. Spllt the raw sample to obtain about 25 grams in a beaker. 2. Add exactly S .. 00 grams of Calgon to the sample. 3. Mix distilled water with the sample-Calgon mixture. This should be left to stand for about 24 hours and then mixed for S minutes in a blender. 4. Using the 4 phi wet sieve, ringstand, and large metal funnel, sieve the dispersed sample into a 100 ml cylinder. Wash the sample out of the blender container using distilled water. S. Wash any sediment remaining on the sieve into a beaker using. distilled water, then filter the beaker contents using filter paper and a glass funnel. Dry the sediment on the filter paper on a watch glass in the oven (about so 0 c). Re-sieve this sediment through a dry 4 phi sieve. Take the material passing through this sieve and add it to the sediment in the cylinder. This step is necessary because the effective diameter of the wet 4 phi sieve is less than the effective diameter of a dry 4 phi sieve, and I wanted to analyze all material finer than 4 phi (dry sieve) during the pipette analysis. 6. Place the dry sediment remaining on the sieve in a pre-weighed 50 ml beaker and weigh it. Record this on a data sheet. 60 l 61 7. Add enough distilled water to the cylinder to bring the water level to 100 ml. Stir vigorously and let the cylinder stand for a day. If no flocculation occurs, it is ready for analysis. If it starts to flocculate dispersion will have to be redone or the sample dis carded. 8. Stir the cylinder vigorously until all material is distributed uni formly throughout. As soon as the stirrer is removed, start the timer. Do not re stir after each pipette sample. 9. Take 20 ml samples at depths and times as given on the tabulation be low, and place in pre-weighed SO ml beakers. Phi Diameter Withdrawal Depth *Withdrawal Time at 20 C 4 20 cm 20 sec. 5 10 l min. 56 sec. 6 10 7 min. 44 sec. 7 10 31 min,. 8 10 2 hours 3 min. 9 5 4 hours 6 min. 10 5 16 hours 24 min. *If temperature is not 20° C, recalculate withdrawal time using Stokes' law with the other temperature .. 10. Evaporate all samples to dryness in an oven and record sample weights, correcting for Calgon and beaker weight. 11. With a sample splitter and the dried sand fraction of each sample obtain a sample weighing 1. 5-2. 0 grams. Using this sample and a settling tube like that described by Felix (1969) obtain a cumulative frequency curve for each sand sample. To combine the pipette and settling-tube analysis into one cumula tive curve, first obtain the sand weight for each desired phi value. The sand weight for each interval can be calculated by reading the percent value on the cumulative frequency curve for each corresponding desired phi interval and multiplying this percent times the total sand weight. In the case of Sentinel Butte Formation sand it was necessary to use quarter phi intervals in most samples in order to get enough points to draw a suitable curve. The total weight of the sample equals the weight l 62 of the sand fraction plus the weight of the 20-second pipetted sample times SO. This 20-second pipette sample includes all sediment finer than 4 phi (silt and clay). As the sample weight for each phi interval in the pipette analysis and the settling-tube analysis has been recorded, the cumulative weight and cumulative percent cannot be calculated far each desired phi interval in both the sand and fine fraction. A single cumulative curve can be constructed from the combined analysis, and graphic statistical parameters can be calculated. REFERENCES Allen, J. R. L. 1965a. Fining upward cycles in alluvial successions: Liverpool Manchester Geology Journal, v. 4, p. 229-246. 1965b. A review of the origin and characteristics of recent alluvial sediments: Sedimentology, v. 5, p. 89-191. 1966. On bed forms and paleocurrents: Sedimentology, V. 6, p. 153-190, J970a. A quantitative model of grain size and sedimentary structures in lateral deposits: Liverpool Manchester Geology Journal, v. 7, pt. I, p. 129-146. 1970b. A quantitative model of climbing ripples and the tr cross-laminated deposits: Sedimentology, v. 14, p. 5-26. 1970c. Studies in fluviatile sedimentation: A comparison of fining-upward cyclothems, with special reference to coarse member composition and interpretation: Journal of Sedimentary Petrology, v. 40, p, 298-323. Beerbower, J. R. 1965. Cyclothems and cyclic depositional mechanisms in alluvial plain sediments: Kansas State Geological Survey Bulletin 169, v. 1, p. 31-42. Brekke, D. W. 1979. Mineralogy and chemistry of clay-rich sediments in the contact zone of the Bullion Creek and Sentinel Butte Forma tions (Paleocene), Billings County, North Dakota: Unpublished master's thesis, University of North Dakota, Grand Forks, N.D. Campbell, M. R. 1916. Guidebook of the Western United States Part A. The Northern Pacific Route: United States Geological Survey Bulletin 611, 218 p. Carlson, C. G., and Anderson, S. B. 1966. Sedimentary and tectonic history of the North Dakota part of the Williston Basin: North Dakota Geological Survey Miscellaneous Serles 28, 13 p. 64 - 65 Carroll, Dorothy. 197 0. Clay minerals: A guide to their x-ray analysis: The Geological Society of America, Special Paper 126, 80 p. Cherven, Victor B. 1973. Hlgh- and low-sinuosity stream deposits in the Sentinel Butte Formation, McKenzie County, North Dakota: Unpublished master's thesis, University of North Dakota, Grand Forks, N.D. Clayton, L., Carlson, C. G., Moore, W. L., Groenewold, G. H., Holland, F. D., Jr., and Moran, S. R. 1977. The Slope (Paleocene) and Bullion Creek (Paleocene) Formations of North Dakota: North Dakota Geological Survey Report of Investiga tion 59, 14 p. Clayton, L., Moran, S. R., Bluemle, J.P., and Carlson, C. G. 1980. Geologic map of North Dakota: North Dakota Geological Survey, Grand Forks, N.D., scale 1:500,000. Coleman, J. M., and Gagliano, S. M. 1965. Cyclic sedimentation in the Mississippi River deltaic plain: Gulf Coast Association Geology Society Transcript, v. 14, p. 67-80. Delimata, John J. 1969. Fort Union (Paleocene) Mollusks from southern Golden Valley and southeastern Billings Counties, North Dakota; Unpublished master's thesis, University of North Dakota, Grand Forks, N.D. Felix, D. W. 1969. An inexpensive recording settling tube for analysis of sands: Journal of Sedimentary Petrology, v. 39, p. 777-780. Fisher, W. L. 1964. Sedimentary patterns in Eocene cyclic deposits Northern Gulf Coast region: Kansas Geological Survey Bulletin 169, v. 1, p. 151-170. Fisher, W. L., and McGowen, J. H. 1969. Depositional systems in the Silcox Group (Eocene) of Texas and their relation to occurrence of oil and gas: American Association of Petroleum Geologists Bulletin, v. 53, p. 30-54. Folk, R. L. 1968. Petrology of sedimentary rocks: Hemphill's: University of Texas, Austin, Texas, 170 p. 66 Folk, R. L., Andrews, P. E., and Lewis, D. W. 1970. Detrital sedimentary rock classification and nomenclature for use in New Zealand: New Zealand Journal of Geology and Geophysics, v. 13, p. 937-968. Grim, Ralph E. 1953. Clay mineralogy: McGraw-Hill Book Company, New York. Groenewold, G. H., Hemish, L.A., Chevvy, J. A., Rehm, B. W., Meyer, G. N., andWinczewski, L. M. 1979. Geology and geohydrology of the Knife River Basin and adjacent a_reas of West Central North Dakota: North Dakota Geological Survey Report of Investigation 64, 402 p. Hemish, L. A. 197 5. Stratigraphy of the upper part of the Fort Union group in southwestern McLean County, North Dakota: Unpublished master's thesis, University of North Dakota, Grand Forks, N.D. Jacob, A. F. 1972. Depositional environments of parts of the Tongue River Formation (Paleocene) of western North Dakota in, Depositional environments of the lignite-bearing strata in western North Dakota: North Dakota Geological Survey Miscellaneous Series 50, p. 43-62. _____ 1973. Descriptive classification of cross-stratification: Geology, v. 1, no. 11, p. 103-106. _____ 1974. Personal communication: Geology department, University of North Dakota, Grand Forks, N. D. Johnson, Robert P. 19 73. Depositional environments of the upper part of the Sentinel Butte Formation, southeastern McKenzie County, North Dakota: Unpublished master's thesis, University of North Dakota, Grand Forks, N.D. Kaiser, W.R. 1974. Texas lignite: Near-surface and deep basin resources: Bureau of Economic Geology Report of Investigations 79. Krumbein, W. C., and Pettijohn, F. J. 1938. Manual of sedimentary petrography: Appleton-Century-Crofts, New York, p. 162-172. Leopold, L.B., Wolman, M. G., and Miller, J.P. 1964. Fluvial processes in geomorphology: W. H. Freeman and Company, San Francisco, 522 p. 67 McGowan, J. H. 1969. Depositional systems in the Wilcox Group (Eocene) of Texas and their relat.ion to occurrence of oil and gas: American Association of Petroleum Geologists Bulletin, v. 53, p. 30-54. McKee, E. D. 1966. Significance of climbing-ripple structure: United States Geological Survey Professional Paper 550-D, p. 94:.103. Meldahl, E. G. 1956. The geology of the Grassy Butte area McKenzie County, North Dakota: North Dakota Geological Survey Report of Investigations 26. Moody-Stuart, M. 1966. High- and low-sinuosity stream deposits from the Devonian of Spitsbergen: Journal of Sedimentary Petrology, v. 36, p. 1102-1117. Moran, S. R. , Chevvy, J. A., Fritz, P. , Peterson, W. M. , Somerville, M. H., Stance!, S. A., and Ulmer, f. IL 1978. Geology, groundwater hydrology, and hydrogeochemistry of a proposed surface mine and lignite gasification plant site near Dunn Center, North Dakota: North Dakota Geological Survey Report of Investi gation 61, 263 p. Royse, C. F. 1967a. A stratigraphic and sedimentologic analysis of the Tongue River and Sentinel Butte Formations (Paleocene), western North Dakota: Unpublished Ph.D. dissertation, University of North Dakota, Grand Forks, N.D., 312 p. . 1967b. Tongue River-Sentinel Butte contact in western North Dakota: North Dakota Geological Survey Report of Investigation 45, 53 p. . 1970a. A sedimentologic analysis of the Tongue River --S-e-ntine l Butte Interval (Paleocene) of the Williston Basin, western North Dakota: Sedimentary Geology, v. 4, p. 19-80. ·---- 1970b. Sediment analysis: University of Arizona, Tempe, Az., p. 21-36. Yen, Teng-Chien. 1948. Paleocene fresh-water mollusks from southern Montana: United States Geological Survey Professional Paper 214-C, p. 35-44. A-6 PLATE I CROSS- SECTION OF A-4 MEASURED SECTIONS A-i through A-6 A-:...3 ''# 8. Nesemeler Mey 1981 ~ I# O' - - .. Sentinel Butte Fm. =5"5~)>6...... ,i, .. C:c, ,it, ... .. c-=:_-:, C2:, >f c::::, .. CH4NfvE:L ~ .. .. s,:wo .- .. $ .. .. - .. A-2 .. F" LoooaAs1N F ...... '# ...... N4TURAI ...... ~- "'"''" LE.:Vi:£ A.No .. r-· !i"q 0 .. .. N,AR CHANNEL FLoooeASiN .. " .. .. ' .. 0 0 ...... " " .. .. 4' 1 C ·.a,,=· ·=· ...... " .. ..= · fS " .. .. 0 ,, .. .. " " ...... " .. .. 0 .. .. 0 ...... Ill .. .. 0 ...... c.,..,4.rv,v;'- I'll ...... :...... 110 111 .. " .. .. ~4tv .. " ...... 11 0 " .. .. UPPER I I YELLOW BED---_ ...... _ =· c:::, -Ly . " .. FL000BAS1N .. .. -:7'- - LOW.ER ,, ,, .. ,-::::::.~- i'lf ... -1/f .. .. - " 0 " ,, " - .. .. ·.c:::;·sz· LOWER FLoooeASiN .. I c ..:c, . . <::::::, -£r -0- .. 55:i " -- ·,= • ,::=:, __g- - .. .. " ... . ,, . ------c:::,, .. Ill ilt " A-I .. .. 0 0 :'c::::; <::::::, " " " tit .. 111' ... ------~, .JS- " " 0 " ,:;, - " " @R, ~ " 0 " .. ·= .. " "~" " 55 4i .. .i, c.....~ _JJ- " ,,. " " .. - #ii - 0 JI ... """ " - ·= "'=' <.::::, " " e:P .. ' c.::::::, NATU RAL L EVEE ~ " - ~ a, AND C::,.7. ... -- ...... ______,4!r -....__ " c.:::::, "',, NATURAL LEVEE FLOOD BASIN ·= " .. - NEAR CHANl'I EL .. c::::, . " - 0 ,...___ " . Ill" -~~,,,..) - If' . # " " = " ~- . $ COVERED 0 " SAND D. . G CARBONACEOUS @] IRON OR SULFUR RICH SCALE o, II II II I GASTROPODS AND 05 \ CARBONATE l SILT CONCRETIONS 22 " PELECYPODS [g CEMENTED SAND 10 ~ 04 ------r M 5 SMALL-SCALE ,o B NORTH DAKOTA CLAY f{f5' ., LOCAT IONS OF MEASURED I I CHERTY 27 CROSS STRATA 26 SECTIONS A-I T HROUGH A-6 ~ ~ 02 I \ ~~ N, D HIGHWAY 22 0======!00 ===250======:::'Jo50C -- LOST BRIDGE LARGE-SCALE METERS ~ ~~ LITTLE MISSOURI RIVER L IGNITE CROSS STRATA SILICIFIED WOOD [] , 34 i', EJ DATUM !S S EA LEVEL c, m " Tl40N I m,l e