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1973 Depositional environments of the upper part of the Sentinel Butte Formation, southeastern McKenzie County, North Dakota Robert Post Johnson University of North Dakota
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Recommended Citation Johnson, Robert Post, "Depositional environments of the upper part of the Sentinel Butte Formation, southeastern McKenzie County, North Dakota" (1973). Theses and Dissertations. 150. https://commons.und.edu/theses/150
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SENTINEL BUTTE F0R1'1ATI0N, SOUTHEASTERN
MCKENZIE COUNTY, NORTH DAKOTA
by
lobert Post Johnson Bachelor of Philosophy, University of North Dakota, 1970
A Thes.is
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 1973 This thesis submitted by Robert Post Johnson in partial ful fillment of the requi=a~ents 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.
ii Permission
DEPOSITIONAL ENVIR0~11ENTS OF THE UPPER PART OF THE SENTINEL Title BUTTE FORMATION, SOUTHEASTER...~ MCKENZIE COUNTY, NORtH DAKOTA
Degree~~~~-M_a_s_t_e_r__ o_f ___ S_c_i_e_n~c_e __ ~--~------~--~--~~------~
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 make it freely available for inspection. I further agree that permission 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 under stood that any copying or publication or other use of this thesis or part thereof 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.
iii ACKNO'WLEDGMENTS
I am deeply indebted to several people on the faculty of the
University of North Dakota Geology Department for their advice and assistance in the preparation of this paper. These people include
Dr. Art Jacob, Dr. Alan Cvancara, and Dr. Walter Moore. I am par ticularly indebted to Dr. Jacob for his interest, enthusiasm, and advice. Dr. Francis Ting and Dr. Lee Clayton are to be thanked for their interest and suggestions.
I am also indebted to the National Forest Service and
National Park Service for their permission in gaining access to
National Grassland areas and the North Unit of Theodore Roosevelt
National Memorial Park. Several farmers and ranchers are to be thanked for allowing me access to their property.
Many hours of conversation with Victor B. Cherven, a fel low graduate student doing a similar study of another part of the
Sentinel Butte Formation, led to a considerable exchange of valu able ideas and opinions used in formulating this paper. Other graduate students who contributed in various ways are Eill Hickey and Ron Richardson.
My wife Linda, and my parents deserve special acknowledg ment for their moral support and financial assistance which made this study possible.
iv TABLE OF CONTENTS
Page
ACKNOWLEDGMEtrr s iv LIST OF FIGURES vi ABSTRACT ...... viii
INTRODUCTION 1
GENERAL STRATIGRAPHY ...... " . . . 5
LITHOSTRATIGRAPHY • • • 9
Yellow or Gray Sand Beds Yellow- to Red-Brown Sand, Silt, and Clay Beds Gray and Brown Silt and Clay Beds Lignite Beds
CYCLIC UNITS 54
SUMMARY • • • 58
REFERENCES CITED 61
y LIST OF FIGURES
Figure Page
1. Location of Study Area. 2
2. Key Beds of the Sentinel Butte Formation and Location of the Study Interval 8
3. Map of Sand Bed I 10
4. Stratigraphic Cross-Section A 13
5. Vertical Distribution of Silt-Clay in Six Measured Sections of Sand Bed I •••• 16
6. Vertical Distribution of the Median Fall Diameter of the Sand Fraction in Four Measured Sections of Sand Bed I • • . . . . • . . . • . • . • . . 18
7. Tabular Sets of Large-Scale Planar Cross Stratification in an Elongate Concretion in Sand.Bed I •••••• 20
8. Model for the Origin of Sand Bed I 23
9. Channel Plug Deposit in Sand Bed I 26
10. Map of Sand ned II. 29
11. Stratigraphic Cross-Section B 31
12. Vertical Distribution of the percent silt-clay and Median Fall Diameter of the Sand Fraction •. • 34
13. Development of Lateral Bars in a Low-Sinuosity Stream 36
14. Large-Scale Planar Cross-Stratification Overlain by Small-Scale Ripple Cross-Stratification and Plane Bed ••.•••.•.• 38
15. Stratigraphic Cross-Section C 41
16. (A) Sand Bed III Outlined by Dark Solid Lines (B) The South Edge of the Sand Bed Truncating Adjacent Sand, Silt, and Clay Beds ..•.•. 43 17. (A) Elongate Vertical Concretion in Alternating Beds of Sand, Silt, and Clay Adjacent to Sand Bed II (B) Climbing Ripples in the Alternating Beds of Sand, Silt, and Clay Adjacent to Sand Bed II 46
18. (A) Exposure of Weathered Gray and Brown Silt and Clay (B) Fresh Exposure of Highly Disturbed Gray and Brown S.il t and Clay • • • • . 51
19. Cyclic Units in the Sentinel Butte Formation in the Study Area ...... 56
vii ABS TR.A.CT
The depositional environments of a 40 meter thick interval in
the upper part of the Sentinel Butte Formation in southeastern McKenzie
County, North Dakota have been determined from the sedimentary struc
tures, geometry, distribution of grain· sizes, and stratigraphic rela
tions of cyclic lithostratigraphic units. The top of the study inter
val is the top of the upper yellow marker bed.
An elongate, tabular sand bed was studied in detail. It is 12
meters thick and 3 kilometers wide and it is interpreted to have been
deposited by lateral accretion in a high-sinuosity stream. Paleo
current indicators are parallel to the long axis of the sand bed.
In this bed are bodies of interbedded silt and clay that are inter
preted as channel plug deposits. Epsilon cross-strata are comm.on.
Cross-stratification grades from large-scale at the base to small
scale at the top of the bed and grain size decreases upward.
An elongate, trough-shaped sand bed 15 meters thick and 400 meters wide and an elongated trough-shaped sand bed 10 meters thick
and 200 meters wide are interpreted as deposits of low-sinuosity
streams. Paleocurrent indicators trend parallel to the trends of
the sand beds. These beds lack the silt and clay bodies and epsi
lon cross-strata of the elongate, tabular sand bed, but they ha~e
similar vertical distributions of cross-stratification and grain
size.
viii Yellow- to red-brown sand, silt, and clay beds occur above and adjacent to the three sand beds. The sand, silt, and clay beds become
thinner and finer away from the sand beds. These characteristics, plus little organic matter, abundant iron-stained concretions, and climbing ripple cross-stratification,indicate that these beds are natural-levee and crevasse-splay deposits.
Laterally extensive, gray and brown silt and clay beds grade laterally and vertically from the natural-levee deposits. These highly bioturbated beds contain abundant plant fragments and are generally overlain by lignite beds. The gray and brown silt and clay beds and the lignite beds are interpreted to be floodbasin deposits.
ix INTRODUCTION
The Paleocene Sentinel Butte Formation of McKenzie County,
North Dakota has previously been studied by Clark (1966), Fisher
(1953, 1954), Laird ·(1956), Meldahl (1956), and Royse (1967a, 1967b,
1970). All of this work, w:.l,th the exception of that of Royse, is primarily descriptive with little emphasis on the interpretation of environments. Royse (1967a) interpreted the formation as being fluvial. His study is based largely on textural analysis from which he recognized a fluvial environment grading from stream channels to floodbasin swamps.
The current study is a detailed field study of the geometry, sedimentary structures, textures, lithologies and stratigraphic rela tionships of the beds in the upper part of the Sentinel Butte Forma- tion to determine the depositional environments.
The study area (Figure 1) is in McKenzie County in the vicin ity of the North Unit of Theodore Roosevelt National Memorial Park.
The area is highly dissected by the Little Missouri River and its tributaries, and contains exposures of several hundred feet 'of the
Sentinel Butte Formation. The semi-arid climate caused the slopes to remain relatively free of vegetation.
The ;l;iel.d wo:rk was concentrated in a;x:eas with excellent exposures. Stratigraphic sections were measured in these areas, .., not more than 0.3 km. apart, and an altimeter or transit was used to establish a datum. Detailed stratigraphic cross-sections were
1 2
Fig. 1.--Study area in southeastern McKenzie County, North Dakota showing locations of measured sections for Figures 4, 11 and 15. 3
NORTH DAKOT A 4 then constructed (Figures 4, 11, 15). Shown on the finished diagrams are detailed lateral and vertical relationships of lithologies, pri mary and secondary sedimentary structures, grain size, and fossils.
Sand beds were mapped in the field on aerial photographs
(scale, 1:20,000). Paleocurrent indicators and orientations of large elongate concretions in the sand beds were measured and com pared with the maps. Petrographic and grain size analyses were performed in the laboratory .. Grain-size analyses were performed by a weight-accumulation settling tube of the type described by
Felix (1969). GENERAL STRATIGRAPHY
The Ludlow Formation (laterally equivalent to the Cannonball
Formation), Tongue River Formation and Sentinel Butte Formation, in ascending order, comprise the Paleocene Fort Union Group. The Fort
Union is underlain by the Cretaceous Hell Creek Formation and is overlain by the faleocene-Eocene Golden Valley Formation. These units occur within the boundaries of the Williston Basin.
The Williston Ba.sin generally includes western North Dakota, eastern Montana, southeastern Saskatchewan, and northwestern l\fo~th
Dakota. The basin contains sedimentary roe.ks of every geologic period from the-Cambrian through the Tertiary. The basin was partic ularly active in controlling sedimentation from the Middle-Ordovician through the end of the Permian, but had little effect on sedimenta tion from the Triassic through Cretaceous Periods (Carlson and
Anderson, 1966).
The Tertiary :Period is represented by a wedge of predominantly nonmarine beds which thicken westward. through the Rocky Mountains.
Tectonic control of sedimentation of these strata is indicated by the thickening of these deposits in the center of the Williston Basin
(Royse, 1967a),
The Sentinel Eutte Formation is widespread in the western half of North Dakota (Carlson, 1969). The thickness of this unit ranges from apJ?ro:ximately 65 meters along the northeast flank of the Cedar Creek Anticline to approximately 190 meters in the cen ter of the Williston Basin (Royse, 1967a). The best exposures of 6 the formation occur in the badlands of the Little Missouri River.
Other exposures are found along the shores of Lake Sakakawea and in other scattered areas throughout the western part of the state.
The Sentinel Butte Fonnation in the study area is approxi mately 190 meters thick (Royse, 1967a). Several key beds have been noticed in the area by several workers. These include the basal sand bed, the blue bed, and the upper and lower yellow marker beds
(Laird, 1956; Fisher, 1953; Meldahl, 1956; and Royse, 1967a). The location of these beds and the stratigraphic interval studied are shown in Figure 2. 7
Fig. 2.--Approximate location of key beds in the Sentinel Butte Formation and the location of the study interval. 8
VJ C 0 LI.I ·-... ::, a -et: E 0 ... upper yellow marker bed 0 LIJ '- I.I- VJ (!) ..• I.LI C :, lower yellow marker bed z 0 m la.I, ·- u C - blue bed 0 => -u L&.I C -1 ·-...... C The Sentinel Butte Formation, in the study area, consists of the following basic lithostratigraphic units: (1) yellow or gray sand beds, (2) yellow- to red-brown sand, silt, and clay beds, (3) gray and brown silt and clay beds, and (4) lignite beds. The beds are poorly indurated, although locally they may be cemented by cal cite or iron oxide. Limonitic, hematitic, marcasitic-pyritic, and calcareous concretions may be locally abundant. Yellow or Gray Sand Beds Sand bed I Stratigraphy and Sed~mentology.--Sand bed I is mapped on Figure 3. This bed is 8 to 13 meters thick ~igure 4). It is an elongate-tabular bed that may exceed 3 kilometers in width (Figure 3). Its base is in sharp contact with the underlying lignite and clay beds. Its top grades to finer silt and clay beds, which in turn, grade up into a thin lignite bed. The edges of the bed shQw both gradationa1 and scoured contacts with adjacent silt and clay beds. There is little lateral variability in this sand bed except for bodies of thin interbedded silt and clay. These bodies of silt and clay have concave-up bases, do not exceed more than 200 meters across, and extend from the base to the top of the sand bed (Figure 4, sections 3 and 4). 9 10 Fig. 3,--Map of sand bed I. Solid lines indicate areas of exposure of sand bed I (Figure 4). Dotted line indicates edge of the sand bed. Circular diagram 1 indicates directions of dip of foresets of cross-strata. Circular diagram 2 shows orientation of elongate concretions in the sand bed. (Aerial photographs AXD-4V- 72-75). 11 12 Fig. 4.--Stratigraphic cross-section A.,. Location of measured . sections are shown on,,zigure 1. A-6 A-lS A-4 A-:S A-2 A-1 _.,,_..,,, __ _.,,,_. __ ~-·..-r-·111&'711ii•-'"T.:.--.-.--;:;;;;.;-- .. --·-•V'l"9~•-•W,."WT"\R·-·~----- .. _._...._.. __ .. ·.~·Na1ur';i'·,.;.·.1·.~.. 1ioi;ii .. -·-·:::.:.::: ·-·-· Datum ·-·-·-· -uPPER - 1 ::-Y~:LLfW ":;--··MARKER BED ~ . Aft~~:~~ ~ =:::;:-.:· _ -~ _:; --.:- -~ Q -- Nallrol L~.vaa-==....- "'-- ... --~ --- -· "' .... ---._-..~·~~L·~.., -- -:-:-- .-~ - -- f-'· .- ". - - w ~~., SCALE ~qf:'~~$ - ·1-).i UND ~ CLAY ~ TR~~::!s~i~~: CROSS"' PLANE BED eJ EPSILON CROSS-STRATA (3 fERRUG!NOUS CONCRETIONS STRATA ~ LAROE-SCALE i::;;:) SMALL-ICAI.E SILT 111111 LIGNITE PLANAR CROSS-STRATA - RIPPLE CllllU-STRATA ~ SANOSTONE CONCRETIONS G1;J SIL!Clf'IED STUIIP 14 Petrographic analysis reveals that the sand grains are pri marily sedimentary rock fragments. Angular grains of quartz and plagioclase feldspar are present. The grain size of the sand ranges from medium to very fine and the sand contains an average of 20 to 30 percent silt-clay. A few of the measured sections show consider able increases in silt-clay at the top of the sand bed (Figure 5). The sand fraction becomes finer upward in two vertical sections within the bed (Figure 6). Figure 6 also suggests more than one fining-upward cycle in the measured sections. The cross-strata in this sand bed were classified according to McKee and Weir (1953). Large-scale trough cross-strata are found ~hroughout the middle and lower parts of the bed. Tabular sets of planar cross-strata are also quite common (Figure 7). The height of these cross-strata never exceeded 0.7 meters although they may be several meters in width. The size of these cross-strata generally decreased upward in the bed. Plane bed may be found close to the base but it is more connnon in the middle and upper parts of the bed. Small-scale ripple cross-strata are only in the upper parts of the bed. Epsilon cross-strata (Allen, 1963) are also quite common. The cross-strata are bounded by a thin (0.1 m) reddish-brown bed of alternating layers of silt and clay. The cross-strata have a dip of less than 10 degrees and may have associated tabular, calcite-cemented sandstone concretions. Dip directions of foresets of large-scale cross-strata are unimodal and parallel the elongate trend of the sand bed (Figure 3). 15 Fig. 5.--Vertical distribution af sflt-clay in six measured sections of sand bed I. I A- --- A-2 A-3 F-1 F-2 F-3 I I 1-1 M I M M Mi M .1 .- V"" ~ 12 ~ -1 ~J 2 .... - I 2 • 2 ,,:_ .,,. I \ ... I ,• J i V • .... • i ' 4-.. I I'. i -, I ,.. r i I 10 I ' -1 IO -.... I 0 • 10 . • • • :::::.u •' I \ L.--' I I• \ \ , .-. ..-- • \ I I ~ ,• . L J •, • , 11 , ' 8 - B 8 .. 8 8 . r • \ J \ r • \ l •\ i I ; • V• l'r ,_j i \ ' .,. I--' J 6 - 6 I 6 6 6 'it -'. '·/ I °' • ' •, r". i lat ./ \ i 1 • \ I I /' I • Li 4 i \ • • J 4 4 4 I 4 ! J-, ' I'• ! t, t, I I ,•• • •I I'-. I • ,_ 1l /' I • 2 ' 2 • 2 2 i l - ' v, 2 ,• I ' •• I •I ' .. \ • I ! ' 1 I iL__ / - t / i ·, 1- 0 50 100 0 50 100 0 50 1000 50 100 0 50 100 0 50 100 o/o SILT CLAY 17 Fig. 6.--Vertical distribution of the median fall diameter of the sand fraction in four measured sections of sand bed I. MEDIAN FALL DIAMETER A-I A-2 F-1 F 2 - • I t I 112 12 I I I a tl2 12 • I • , _.. « 1 1 •I 0 : IO I I Jlha rlQ IQ \ • I I :J,< I 18 ./ 8 I II I 18 8 • \ I I I• • \ I-' ..', • (1.) 1 , , 1 •6 M ' \ '• 6M I t \\ I 16 M 6M I 0 1' 4 I I f I 14 4 •I L \ 2 2 I ,to«: I 12 2 "· I • •I , I / I• • ~ -- ~5 2.0 2.5 3.0 3.5 2.0 2.5 3.0 3.5 2.0 2.5-3.0 3.5 2.0 2.5 3.0 3. g -···--··-··- -·· ,,ff ______···--·-·------. ~----- ··-- ...... Jlf 19 Fig. 7.--Tabular sets of large-scale planar cross-stratification in an elongate concretion in sand bed I. (SE% sec. 9, R. 99 W., T. 147.) 20 scale 21 Numerous calcite-cemented concretions that may be several meters long and a few meters across are present in this sand bed. The orienta tions of these elongate concretions also are parallel to the elongate trend of the sand bed and are useful in predicting the trend of the bed (Figure 3). No invertebrate or vertebrate fossils were found in this sand bed. However, small plant fragments of lignite are found near the base of the bed and may have resulted from erosion of underlying lignite beds. Depositional Environment.--Sand bed I was probably deposited by a high~sinuosity stream. The elongate-tabular shape of the bed (Figure 4) is attributed to lateral migration of a stream channel (Figure 8) causing the lateral accretion of the sand over a wide area. Paleocurrent orientations indicate a southeasterly flow parallel to the elongate trend of the sand bed (Figure 3), The sharp contact between the base of the sand bed and the underlying clay or lignite beds is probably the result of scour at the bottom of the channel as it migrated laterally. The fining upward grain size and the upward sequence of sedimentary structures from large-scale trough and planar cross stratification at the base of the sand bed to plane bed and small scale cross-strata near the top can be explained using Allen's (1970a) quantitative model of grain size and sedimentary struc tures in lateral deposits. In the channel bend of a stream, the velocity, shear stress, and stream power generally decrease up the point bar from the deepest part of the channel to the inner bank. Because these parameters decrease, the particle size of 22 Fig. 8.--Model for the origin of sand bed I. Lateral accretion in a high-sinuosity stream results in the vertical distribution of sedimentary structures and relative grain size shown. Modified after Visher> 1965) N w Lateral 411 • Migration . . . .··~· ...... f ~~ " ] Fine Grain Size ~ Medium Grain Size ~ Coarse Grain Size .. ~·: "':.' Ripple Cross .. s trota ~ Plane Bed ..:; Trouoh Cross-strata 24 the bed-load material also decreases up the profile of the point-bar resulting in a fining upward sequence in the deposit. The sequence of sedimentary structures compares favorably with Allen's scheme for a highly sinuous stream, that is, a stream with a low ratio of radius of curvature to width and a concave-do·wn point-bar profile. Such a stream would have predominantly dune and ripp~e cross-stratification and less abundant upper-phase plane bed. Abundant trough and planar cross-stratification occur near the base of the sand bed and probably formed under moderately high shear stress. Increased shear stress up the point-bar may have formed plane bed. The abundance of ripples near the top of the sand bed lndicates low shear stress (Allen, 1970a). The epsilon cross-strata may be traces of channel cross sections resulti-ng from deposition on a point-bar surface following a period of nondeposition or erosion. Epsilon cross-strata have been described in ancient sand deposits by Allen (1965a) and Moody Stuart (1966). No known descriptions of this type of cross stratification in recent fluvial deposits is known by the writer. The inset bodies of thin interbeds of silt and clay with concave-up bases (Figure 4, section 4) are interpreted as being channel plug deposits. They probably resulted from the filling of an oxbow lake with silt and clay (Bernard and Major, 1963; Fisk, 1947). These bodies have the shape of the original channel unless scoured by further migration of the channel (Figure 9 and Figure 4, section 4). A beach origin for this sand is ~ot likely. The paleocur rent indicators are generally unimodal and parallel to the elongate 25 Fig. 9.--(A) Channel plug deposit (outlined in solid line) scoured by channel sand (outlined by dashed line) in sand bed I. (B) Close-up of A showing silt-clay of channel plug above dashed line (sloping surface of point-bar) with sand below. (S~~ sec. 10, R. 99 W., T. 147 N.) 2.6 A scale 5 M f Lz.o, B scale 2 M [ 27 trend of the sand bed. Unimodal paleocurrent distributions are par allel to the elongate trends of sand bodies for fluvial deposits. Paleocurrent distributions are generally bimodal and perpendicular to the elongate trend of shoreline sand bodies (Klein, 1967; Selley, 1970). The vertical profiles of grain size fining upward and an upward sequence from large-scale cross-strata to small-scale cross strata could indicate a transgressive beach deposit. However, the overlying beds do not consi~t of offshore silt and clay. Rather, they consist of highly bioturbated organic silt and clay that grade up into a thin lignite bed. So they are probably swamp deposits. The large-scale trough and planar cross-strata could indi cate eolian deposition. This is unlikely because of high percent ages of silt-clay, small-scale ripple cross-stratification, abundant plant remains, associated lignite, and the presence of aquatic inver tebrate fossils. The height of the cross-strata does not approach the height of those usually contained in eolian deposits. Saud bed II Stratigraphy and sedimentology.--The sand bed mapped on Fig ure 10 and associated with the upper yellow marker bed is an elon gate bed about 400 meters wide and up to 15 meters thick (Figure 11). It has an erosional concave-up base. The body appears to fill a large depression in the underlying beds of silt and clay. The edges of the bed are not distinct, but appear to intertongue and grade laterally to beds of yellow silt and clay. Petrographic analysis of the sand grains reveals primarily limonite-stained, subangular quartz grains and a few sedimentary 28 Fig. 10.--Map of sand bed II (Figure 11). Exposures are indi cated by solid lines. Approximate edges of the bed are indicated by dashed lines. Circular diagram shows the directions of dip of fore sets of cross-strata. (Aerial photographs AXD-4V-93, 94, and 75) 29 30 Fig. 11.--Stratigraphic cross-section :B. Location of measured sections is sho"¥m on Figure 1. B-7 8;6 B-5 804 8,3 S,2 a., 1- L,. •• I( Natural Levee ~'L""-='"..... ~·~.£ :::._--::;::::=::;::;:=::::tj::cc-=.,=---'!!..__ - ...__.. .• " n ""o - ~- 8 -~#~. : ~~·.I~. ;//(_:~·A:~o.-~E·oi~- ..~~ . ~ - . ">,&·· ': ___0 .. 1 ------1-- ,. ~ ,___,.,...,u-...... _..:.. ~//// .. ~"= ~--- .• a ..... - .. ··~= N~ ~- - -- f'.. 1'1ocdDOIIII '":~~ ._..-----·· .....-.~-. . ,...J,QJl\1!1),-- ---1---- ·-· I\ fi!I04)Qtift .• ··- ~E~ ~ .. ---c?' -I--- w --- • I-' '~~~-> SCALE 4mL !IOm [IZJ ~ LARGE SCALE SAND CLAY l.!U£.J PLANAR CROSS STRATA E::l PLANE BED ~ l'ERRUGINOIJS CONCRETIONS SMALL SCA LE SILT • LIGNITE -~ RIPPLE CROSS STRATA rn VERTICAL CONCRETIONS a FOSSIL INVERTEBRATES 32 rock fragments. The yellow color of this sand bed contrasts with the gray color of sand bed I. This contrast is attributed to a difference in mineral composition between the two beds. Sand bed II becomes finer upward (Figure 12) from fine sand at the bottom to yellow silt and clay at the top, which, in turn, grades up to the overlying beds of highly organic, brown clay and lignite. The top is flat but a lens-shaped body of clay is located at the top (Figure.:, 11, section 4). Larg~-scale, tabular sets of planar cross-strata, small~scale ~ipple cross-strata, and plane bed are present. Planar cross-strata overlain by plane bed and small-scale ripple cross-strata is a common sequence in this sand bed. Dip directions of foresets of large-scale cx:oss-stra.ta. show a unimodal distribution parallel to the elongate trend of the sanct bed (Figure 10). Depositional environment.--Sand bed II is interpreted as being fluvial. The fining-upward sequence of grain size and the vertical sequence of sedimentary structure from large-scale planar cross stratification to plane bed and small-scale ripple cross-stratification is similar to sand bed I. Moody-Stuart (1966) discusses lenticular sand bodies deposited by low-sinuosity streams that exhibit fining upward sequences of grain size and sedimentary structures indicative of an upward decrease in flow regime. He attributes the upward decrease in flow regime to widening and shoaling of a stream dur- ing aggradation. Allen (1970c) disproves vertical accumulation through aggrada tion in stream channels. Allen showed that deposits of low-sinuosity streams are deposited by lateral accretion, because all streams 33 Fig. 12.--Vertical distribution of the percent silt-clay and median fall diameter of the sand fraction in sand bed II at measured section E-4, Ftgure 11. Vertical scale is distance above the base of the body. B-4 B-4 18 .-...... - .....~!,; 18 , ' 16 ' 1t I 14 ...... --- ...... ,4 I • ' 12 12 i '~ I I m.. m.1I t I I I ...... 10 10 I ~ ·< ~ r--,...... 4 /, a -- 8 , ~ I L,.," • • / .v • 0\ 6 6 I • \ ' ._...... __..._ .. 4 0 25 50 75 106 25 . 3.0 3.5 4.0 o/oSIL T-CLAY ,8' MEDIAN FALL DIAMETER 35 possess a sinuous thalweg even though the stream may be relatively straight. Repeated lateral deposition of these deposits in the same location may produce a multi-story sand body giving the appearance of vertical accumulation. The sequence of planar cross-stratification overlain by plane bed and ripples may be due to the development of lateral bars on the margins of a low-sinuosity stream (Allen, 1966) (Figure 13). The planar cross-stratification results from the preservation of the avalanche slopes of lateral bars migrating downstream. Plane bed and small-scale ripple cross-stratification developed and were pre served on the gentle slope on the backside of the bar as it migrated downstream. This sequence of sedimentary structures is shown in Figure 14. The stream that deposited sand bed II occupied a depression in a floodbasin. The depression was the result of erosion as evi denced by the truncation of bed G (Figure 11). After the depression was fanned, highly organic clay and lignite were deposited in the low area. Once the stream was diverted into the depression it began to deposit laterally and a multi-story sand bed resulted due to repeated lateral deposition. The exact mechanism that caused the multi-story deposit is not understood but may be related to subsi dence and tectonics. The cohesiveness of the adjacent silt and clay beds may have caused the stream to be confined to the depres sion and wide lateral migration was kept to. a minimum. On the basis of geometry, morphology, arid associated litho logies, this sand bed is similar to the deposits of low-sinuosity distributary channels in deltaic complexes as described by 36 ---'lll>Thalweg Fig. 13.--Development of lateral bars in a low~sinuosity stream (Allen, 1966). 37 Fig. 14.--(A) Large-scale planar cross-stratification overlain by small scale ripple cross-stratification and plane bed in sand bed II. (B) Close-up of plane bed and ripple cross-stratification. (NE~ sec. 10, R. 99 W., T. 147 N~, nea.r section B-4, Figure 11). 38 39 Donaldson (1969), Fisk (1960), Fisk and others (1954), Fisher and HcGowen (1969), Jacob (1972), and Kolb and Van Lopik (1966). These sand bodies are generally described as elongate bodies, with concave up bases, fining upward sequences of grain size, sedimentary struc tures that range from large-scale at the base to small-scale at the top, and associated lithologies of sand, silt, clay and lignite. Sand bed III Stratigraphy and sedimentology.--This light gray sand bed is 200 meters wide and up to 10 meters thick (Figure 15). The bed has a flat top and an erosional, concave-up base (Figure 16[A]). Adja cent thin beds of sandt siltt and clay are sharply truncated by the bed (Figure 16[B]). Samples for determining grain size variations and mineral composition were not obtained from this bed. Field observations indicate that the bed becomes finer upward from medium sand at the base to very fine sand and silt at the top. A highly organic clay is present across the top of the bed. Sedimentary structures are similar to those of sand bed II. Large-scale cross-strata are common in the lower part of the bed and small-scale ripple cross-strata and plane bed are common in the upper part of the bed. Paleocurrent-orientation data were not taken from this bed nor was the bed w~pped. Depositional environment.--This sand bed is similar to sand bed II and probably had a similar origin. It has a trough-shaped cross-section and is assumed to be elongate like sand bed II. The sequence of sedimentary structures from planar cross-strata near 40 Fig. 15.--Stratigraphic cross-section C. Location ot measured sections is shown on Figure 1. C-1 C':'2 R ------..~--,;;- -~, ,,,...... --.., - - - - ... :~- .····~- · SAND sEo ·1i :-:_:_ ·.. ~· ~ ~ ~ .. _ • • ,.. • • • //,t// • • • ! - - - ••- ,- • .;rq/ • • • s . . ~ •• II#. ~. • . . . . . • . . -~ -- -- -==o -.-. Floodbasin - .• -- --.. • __ ...!..,~ .. = COVERED .. K _;J"::"''F~:db~-==- --.. ::. Floodbasin H"" G Floodbasin .. --- -- .. .i:: E Floodbasin -~ ___ _ t-' ..-=-- .. - . .::;;:r-:D...... •• .. • ...... •• • • .. ·~ •• - ·~~,.6~0~~~~~~·~~~:;·:~--~·~k. .. ~A~·o ~e;o.nt·~:2· ··_: •· Noturol Levee -- .• ·· .. ~. · ...... ,;_ _._. P . . ~cc-;, ... ··• ·.: ,/p. •. SCALE 4M~ . 50M LARG E•SCA LE D . SANO lb?R1 PLANAR Cnoss~srRATA SMALL SCALE SILT j:·,..:·J EJ RIPl-'LE CROSS STRATA 1-:H CLAY ICJ SANDSTONE CONCRETION LIGMTE ~ FERRUGINOUS CONCRETIONS 42 Fig. 16.--(A) Sand bed III outlined by dark solid lines. (B) The south edge of the sand bed truncating adjacent sand, silt, and clay beds. (S~ sec. 12, R. 99 W., T. 14 7 N., near sections c-1 and C-1). 43 scale lOM Lr~~~--- 20M B scale lM [ 44 the base to plane bed and ripples near the top could indicate the pre- sence of lateral bars in a low-sinuosity stream as in sand bed II. Repeated lateral deposition of a low-sinuosity stream after initial scouring, and possible subsidence allowed the vertical accumulation of sand bed III. Yellow- to Red-Brown Sand, Silt, and Clay Beds Stratigraphy and sedimentology.--Beds consisting of thin inter beds of yellow- to red-brown sand, silt, and clay are a few tenths of a meter to approximately 10 meters thick. They are found above sand bed I (Figure 4) and sand bed II (Figure 11) and above a few of the gray and brown silt and clay beds and lignite beds (Figure 11). Sand bed I truncates these deposits (Figure 4) or grades laterally into them (Figure 11). Sand bed II grades laterally into beds of sand, silt, and clay (Figure 11), but sand bed III truncates similar beds (Figure 15). Small, spherical, iron-stained concretions are commonly con centrated in various horizons within these units. Larger, iron stained, upright-cylindrical concretions (Figure 17[A]) reaching almost a met.er in length and up to three-tenths of a meter across, occur in the yellow- to red-bro·wn sand, silt, and clay beds adj a cent to sand bed II. The center of these concretions are lignitic. Small-scale ripple cross-stratification, climbing-ripple cross-stratification (Figure 17[B]) and plane bed are characteris tic of thes.e beds although they are poorly preserved except in the yellow- to red-brown sand, silt, and clay beds adjacent to sand bed II. 45 Fig. 17.--(A) Elongate vertical concretion in alternating beds of sand, silt .. and clay adjacent to sand bed II (SE\, Sec. 10, R. 99 W., T. 147 N. near measured section B--5). (B) Climbing ripples in the alternating beds of sand, s:Ut, and clay adja.cent to sand bed II (SE!t; sec1 10, R. 99 W., T. 147 N., near section E-6). 46 47 Depositional environment.--The vertical interbedding of the sand, silt, and clay beds is probably the result of repeated submergence and the intermittent construction of natural levees during flooding (Allen, 1965b; Fisk, 1947). The high relief of these deposits allowed repeated exposure and oxidation of these sediments after flooding, causing the development of the yellm,1- to red-brown colors.· The yellow- to red brown sand, silt, and clay beds overlying sand bed I may be poorly developed natural-levee sediments deposited on the upper surface of point-bars during flooding. Sedimentary structures are poorly pre served because of bioturbation by plants. The highest rates of sadimentation probably occurred near the channel where these bed$ are the thickest and g·rain size :i.s coarsest. Tbe rates of sedimentation and grain size of modern natural-levee deposits decreases away from the channel (Allen, 1965b). The high rates of sedimentation from suspension on the natural levee during flooding could have caused the formation of climbing-ripple cross stratification close to the channel. According to Allen (1970b), a high rate of sedimentation from suspension results in the formation of climbing ripples. McKee (1966) and Singh (1972) observed that climbing ripples are very common in natural-levee deposits. High sedimentation rates on the natural levee may also have caused the rapid burial of tree trunks in growth position. After decaying, the organic matter served as nuclei for the precipita tion of iron compounds causing the iron-stained, vertical concre tions present in the natural-level deposits adjacent to sand bed II (Figure 17(AJ). Smaller, spherical concretions may be of similar 48 origin. The occurrence of these concretions at given horizons may result from rootlet zones in ancient soils. Some of the thin sand beds found in these units may be crevasse-splay deposits. One such sand bed is shown on Figure 15 adjacent to sand bed III. It is much coarser than the adjacent silt and clay beds. This sand bed has a sharp base and beCOI:leS thinner away from sand bed III into silt and clay beds. The bed is characterized by plane bed with small-scale ripple cross-strata and small channels near the top. The occurrence of this bed in a se~uence of silt and clay beds, the thinning away from a channel sand deposit, the sequence of sedimentary structures from plane bed at the base to small-scale ripples at the top, and the presence of small channels at the top of the bed may indicate a crevasse-splay deposit (Allen, ·1965b). Gray and Bro'Wn Silt and Clay Beds Stratigraphy and sedimentology.--Beds of gray and brown silt and clay grade laterally from the beds of yellow- to red-brown sand, silt, and clay (Figure 11, between sections land 2, bed~). The gray and brown silt and clay beds are of great lateral extent and can be traced ~ith little variability. They overlie beds of yellow to red-bro~vn sand, silt, and clay and lignite beds. The gray and brown silt and clay beds become finer upward and grade from silt to hig~ly organic clay to lignite (Figure 11, bed~). The bases of these deposits are generally horizontal but the tops may be undulatory. The horizontal stratification of these deposits is accentuated by thin alternating beds of gray and brown silt or clay and thin beds 49 of red-orange clay 1 or 2 centimeters thick. The stratification is largely disturbed throughout these beds (Figure 18). Finely lami nated beds of silt and clay and invertebrate fossils are present but quite rare. Well preserved plant fossils such as leaves, twigs, and rootlets are common. Many of the plant fragments are lignitized and are associated with limonitic and marcasitic-pyritic concretions. Depositional envirorunent.--These beds are interpreted to have formed in a floodbasin and w~re probably deposited from suspension in the lowest areas of the floodbasin. The predominantly gray and brown colors of the silt and clay beds indicate either low iron content due to low Eh and pH conditions unfavorable for the formation of iron com pounds duri~g deposition, or high organic matter masks the iron con tent, or both. Coleman and Gagliano (1965) and Fisk (1947) indicated that dark colors·are. typical of floodbasin deposits. The thin, red orange beds may be the result of a periodic lowering of the water table with subsequent oxidation shortly after deposition. The disturbed horizontal stratification is attributed to bio turbation by plants (Coleman and Gagliano, 1965). Compaction and repeated wetting and dessication may contribute to this distortion. Small channels that drained the floodbasin after ~eriods of flooding may explain the undulations in the upper parts of these beds (Figure 11, sections 1 a.nd 2, bed B). The lignite beds above the gray and brQvm silt and clay beds tend to conform to the shape of these undulations. The gray and brown silt and clay beds are not to be confused with prodelt:a silt and clay beds. Colenian and Gagliano (1964) pointed out that prodelta silt and clay beds are usually finely 50 Fig. 18.--{A) Exposure of weathered gray and brown silt and clay. (B) F~esh exposure of highly disturbed gray and brown silt and clay. (NE!z; sec. 10, R, 99 W., T. 147 N., near section B-3, bed B). 51 52 laminated and generally coarsen upward from fine clay and silt and are overlain by distributary-mouth-bar sand or delta-front sand. The gray and brown silt and clay beds of the study area are poorly laminated and become finer upward from silt to clay to lignite. Lignite Beds Stratigraphy and Sedimentology.--Lignite beds in the study area are co-17ered in most places except on fresh road cuts . and slump surfaces. A lignite bed is usually indicated by the occurrence of a band of vegetation because these units are excellent aquifers and make moisture available to stimulate plant growth. The lignite beds grade up from highly organic clay of the gray and brown silt and clay units. Their thicknesses range from less than one-tenth of a meter to about two meters. They may be traced laterally for several kilometers even though _the thickness of an individual lignite bed may be only one-tenth of a meter. The lignite beds vary considerably in elevation over short distances, and they may split from one thick bed into two thinner beds, separated by a gray and brown silt and clay bed. These properties make the correlation of the lignite beds.over a large. area difficult. The lignite beds are generally blocky, have a woody structure and contain little elastic material. The extremely thin lignite beds may have silicified wood fragments and occasional silicified stumps. Burned out lignite beds and resulting "scoria11 (baked clay), which are so common in the Badlands, are rare in the study area. 53 Depositional Environment.--The lignite beds of the study area are associated with deposits that have been interpreted as being formed in rivers, on natural levees, and in floodbasins. So the lignite beds probably represent peat accumulations in alluvial backswamps. The lignite beds tend to reflect the topography of the floodbasin at the time of deposition. This accounts for the difficulties in using lig nite beds for correlation. The lateral persistence of the lignite beds and the absence of shoreline sands discounts a lago6nal origin for these beds. These lignite beds may have originated on a deltaic plain. The woody struc ture of the thin lignite beds may suggest deposition in the upper sub aerial part of a delta where forested swamps occurred. Lignite beds that formed on the lower subaerial part of a delta should be thicker than those of the study area and should be associated with prodelta silt and clay beds and delta front sand beds (fisher and McGowen. 1969). Prodelta silt and clay beds and delta-front sand beds are not recognized in the study area. CYCLIC UNITS Cyclic units were observed in the study area and were also appar 'ent in much of the Sentinel Butte Formation elsewhere. The most common and simplest cyclic unit (Figure 19[A]) consists of a bed that fines upward from silt at the base to highly organic clay at the top. This silt and clay bed may range from a few tenths of a meter thick to eight meters thick. It is overlain by a lignite bed from one-tenth of a meter to two meters thick. Examples of the simple cyclic unit are beds Band C or D and E (Figure 4) and E and F (Figure 11). This simple cyclic unit is interpreted to have formed by the filling of a suqsiding floodbasin. When the floodbasin fills to groundwater level and the rate of elastic influx is not too great, swamps may form. Once formed, the swamps will exist until subsi dence exceeds the accumulation of peat and the swamp drowx1s, or until enough elastic sediments are introduced to suffocate the swamps. Peat accUlllulation should equal the rate of subsidence in order to produce thick lignite beds. Rapid subsidence res.ults in a higher water table which destroys the swamp and may result i~ a thick accumulation of elastic sediment. Slow subsidence results in the filling of the floodbasin restricting the thickness of the peat or preventing the accumulation of any peat at all. The thick nesses of the cyclic unit and the indivtdual beds in the unit depend upon the interrelatiQn between the rate of supply Qf 54 55 Fig. 19.--Cyclic units in the Sentinel Butte Formation in the study area. A C NatLl'al Levee Creva111-8pay ,,,. " ' . ' \ .,' Floodbasln ' Floocbnln ..---- ...... - .. - ...... ----...... Floodbatin ,...... •• •• •• •• h I• • • • I • a ...... KEY lJl f °' .:·:: =: ·: Yellow or Gray Sand 8 D ~ Yellow-to Red-Brown .. Natural Levee~ Sand, SUt, and Clay .:aE?"r • t • ,. • r t::::::-,.. CrncH1a Channel Sand Gray and Brown Sit and Clay •• .. •• Splay ,,...... , Floodbasln ...... Ltonft• 57 elastic sediment, the rate of subsidence~ the rate of production of organic matter, the rate of decomposition, and the location of the water table. Other cyclic units may be formed by the invasion of a stream into the floodbasin, resulting in the scouring of some floodbasin sediments and the deposition of a fluvial sand body (Figure 19[B]). After abandonment of the stream course, subsidence may allow the re-establishment of the simple floodbasin cycle. An example of this cyclic unit is shown in Figure 4 by beds A-D. The encroachment of a stream near a floodbasin with a peat accumulating swamp, will introduce natural-levee and crevasse-splay sand, silt, and clay and destroy the swamp; the cyclic unit is shown in Figure 19(C) will result. An example of this cyclic unit is repre sented in Figure 4 by beds F and G. If conditions are not favorable for the accUntUlation of peat, natural-levee and crevasse-splay sand, silt, and clay may be deposited directly on the gray and brcrwn silt and clay beds of the floodbasin (Figure 19[D]). An·example of this cyclic unit is shown on the stratigraphic cross-section (figure 4) by beds I and J. A stream deposit that scours through the cyclic unit (Figure 19fE]) is represented on Figure 15 by sand bed III and beds C and D. SUM1'IARY Four types of basic lithostratigraphic units are present in the Sentinel Butte Formation in the study area. These are (1) yellow and gray sand beds, (2) yellow- to red-brown sand, silt, and clay beds, (3) gray and brown silt and .clay beds, and (4) lignite beds. Three sand beds were studied. Sand bed I is an elongate tabular bed. It has an erosional base, inset bodies of silt and clay interpreted as being channel plug deposits, epsilon cross-strata, and fining-upward grain size. It also shows large-scale cross-strata at the bottom and small-scale cross-strata at the top, abundant organic debris, and paleocurrent indicators that are parallel to the elongate trend of the sand bed. It is interpreted as a high-sinuosity stream deposit. Sand beds II and III lack epsilon cross-strata and the inset bodies of interhedded silt and clay that are present in deposits of high-sinuosity streams. They are elongate, and haye concave-up bases and fining-upw~rd grain size. They have a vertical sequence of sedimentary structures from pla,,,.ar cross-stratification near the base to plane bed and ripples near the top, and the paleocurrent indicators parallel the elongate trends of the sand beds. These two·sand beds are interpreted to be deposits of low-sinuosity streams. 58 59 The yellow- to red-brown sand, silt, and clay beds are inter preted as being natural-levee deposits. The interbedding of sand, silt, and clay, the light colors, abundance of ferruginous concre tions, and climbing-ripple cross-stratification characterize these beds. The thinning of beds and fining of grain size away from the channel, little organic matter and associated channel sands and floodbasin deposits are further evidence that these beds are natural-levee deposits. The gray and brown silt and clay beds show.i dark colors, highly disturbed horizontal stratification, abundant organic debris and a$sociated channel and natural-levee deposits that characterize floodbasin deposits. The lignite beds, on the basis of ass.ociation with fluvial deposits, probably accumulated in alluvial backswamps. Cyclic units are present. The most common and simplest cyclic unit consists of a silt and clay bed overlain by a lignite bed and was formed by the filling of a floodbasin. Other cyclic units may have formed by the introduction of natural-levee and stream-channel deposits. Deposits of high-sinuosity streams have been reported in the alluvial plain facies or the upper-deltaic plain facies, and low sinuosity-stream deposits of deltaic distributaries have been reported in the lower sub-aerial delta facies by Donaldson (1969) and Fisher and McGowen (1969). The high- and low-sinuosity-stream deposits of the study area may have originated in an environment transitional between the alluvial plain facies and lower-subaeria.1 deltaic facies, where the site of deposition fluctuated between these two environments. 60 Jacob (1972) interpreted the Tongue River Formation as repre senting the lower subaerial facies of a high-constructive delta. The Sentinel Eutte Formation may represent the upper-subaerial deltaic or lower-alluvial plain facies of this same delta complex. Perhaps the delta-front facies of the complex is the Cannonball Formation. REFERENCES CITED Allen, J. R. L. 1963, The classification of cross-stratified units, with notes on their origins: Sedimentology, v. 2, p. 98-114. 1965a, Fining upward cycles in alluvial successions: Liverpool Manchester Geol. Jour., 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-i90. !970a, A quantitative model of grain size and sedimentary structures in lateral deposits: Geol. Jour., v. 7, pt. I, p .• 129-146. 197Gb, A quantitative model of climbing ripples and their cross-laminated deposits: Sedimentology, v. 14, p. 5-26. 197oc·. Studies in fluviatile sedimentation: A comparison of fining-upward cyclothems, with special reference to coarse member composition and interpretation: Jour. Sed. Petrology, v. 40, p. 298-323. Bernard, H. A, and Major, C. F. 1963, Recent meander belt deposits of the Brazos River: An alluvial "sand11 model (abstract): A.m. Assoc. Petroleum Geologists Bull.,. v. L~7, p. 350. Carlson, Clarence G. 1969, Bedrock geologic map of North Dakota: North Dakota Geological Survey Misc. Map no. 10. Carlson, C. G. and Anderson, s. B. 1966, Sedimentary and tectonic history ·of the North Dakota part of the Williston Basin: North Dakota G~ological Survey, Misc. Series no. 28, 13 p. Clark, M. B. 1966, The stratigraphy of the Sperati Point Quadrangle, McKenzie County, North Dakota: unpublished Univ. of North Dakota Master's thesis, 108 p. Coleman, J.M. and Gagliano, S. M. 1964, Cyclic sedimentation in the Mississippi River deltaic plain: Gulf Coast Assoc. Geol. So.cs. Trans., v. 14, p. 67-80. 61 62 Coleman, J.M. and Gagliano, S. M. 1965, Sedimentary structures: Mississippi River deltaic plain in, Primary sedimentary structures and their hydrodynamic interpretation: Soc. Econ. Paleontologists and Mineralogists, Spec. Pub. 12, p. 133-148. Donaldson, A. C. 1969, Ancient deltaic sedimentation (Pennsylvanian) and its control on the distribution, thickness, and quality of coals in, Some Appalachian coals and carbonates: models of ancien~shallow-water deposition: Donaldson, A. C. (editor), West Virginia Geological and Economic Survey, p. 93-121. Felix, D. w. 1969, An inexpensive recording settling tube for analy sis of sands: Jour •. Sed. Petrology, v. 39, p. 777-780. Fisher, S. P. 1953, Geology of west-central McKenzie County, North Dakota: North Dakota Geological Survey, Rept. Inv. 11, plate IV. 1954, Structural geology of .the Skaar-Trotter area, McKenzie and Golden Valley Counties, North Dakota: North Dakota Geological Survey Rept. Inv. 15. Fisher, W. L. and McGowan, J. H. 1969, Depositional systems in the Wilcox Group (Eocene) of Texas and their relation to occur rence of oil and gas: Am. Assoc. Petroleum Geologists Bull.~ v. 53, p. 30-54. Fisk, H. N. 1947, Fine-grained alluvial deposits and their effects on Mississippi River Activity: Mississippi River Commission, 82 p. 1960, ~ecent Mississippi River sedimentation and peat accu mulation in, 4th Cong. Advancement Etudes Stratigraphic et Geologic Carbonifere (Heerlen, 1958), Comte Rendu, v. 1, p. 187-199. Fisk, H. N., McFarlan, D., Kolb, C.R., and Wilbert, L. J. Jr. 1954, Sedimentary framework of the modern Mississippi delta: Jour. Sed. Petrology, v. 24, p. 76-99. Jacob, A. F. 1972, Depositional environments of parts of the Tongue River Formation (Paleocene) of western North Dakota in, Depositional enviromnents of the lignite-bearing strata in western North Dakota: North Dakota Geological Survey Misc. Series no. 50, p. 43-62. Klein, G. deV. 1967, Paleocurrent analysis in relation to modern marine sediment dispersal patterns: Am. Assoc. Petroleum Geologists Bull., v. 50, p, 366-382. 63 Kolb, C.R. and Van Lopik, J. R. 1966, Depositional environments of the Mississippi River deltaic plain-southeastern Louisiana in, Deltas in their geologic Framework: Houston Geol. Soc., p. 17-61. Laird, W. M. 1956, Geology of the North Unit of Theodore Roosevelt National Memorial Park: North Dakota Geological Survey Bull. 32, 27 p. ~ McKee, E. D. 1966, Significance of climbing-ripple structure: U.S. Geological Survey Prof. Paper 550-D p. 94-103. McKee, E. D. and Weir, G. W. 1953, Terminology for stratification and cross-stratification in sedimentary rocks: Geol. Soc. America Bull, v. 64, p. 381-390. Meldahl, E.G. 1956, The geology of the Grassy Butte area McKenzie County, North Dakota: North Dakota Geological Survey Rept. Inv. 26. Moody-Stuart, M. 1966, High- and low-sinuosity stream deposits frot:1 the Devonian of Spitsbergen: Jour. Sed. Petrology, v. 36, p. 1102-1117. Royse, C. F. 1967a, A stratigraphic and sedimentologic analysis of the Tongue River and Sentinel Butte formations (Paleocene), western·North Dakota: unpublished Univ. of North Dakota Ph.D. dissertation, 312 p. 1967b, Tongue River-Sentinel Butte contact in western North Dakota: North Dakota Geological Survey Rept. of Inv. 45, 53 p. 1970, A sedimentologic analysis of the Tongue River Sentinel Butte Interval (:Paleocene) of the Williston Basin, Western North Dakota: Sed. Geol., v. 4, p. 19-80. Selley, J.C. 1970, Ancient sedimentary enviroTu~ents, a brief sur vey: Cornell University Press, 237 p. Visher, G. S. 1965, Use of vertical profile in enyi~onmental recon struction: Am. Assoc. Petroleum Geologists Bull., v. 49, p. 41-46.