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Graduate Student Theses, Dissertations, & Professional Papers Graduate School
2000
Sedimentary record of Upper Cretaceous through Tertiary tectonism northeastern Crazy Mountains Basin central Montana
Joshua K. Borrell The University of Montana
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Recommended Citation Borrell, Joshua K., "Sedimentary record of Upper Cretaceous through Tertiary tectonism northeastern Crazy Mountains Basin central Montana" (2000). Graduate Student Theses, Dissertations, & Professional Papers. 7188. https://scholarworks.umt.edu/etd/7188
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SEDIMENTARY RECORD OF UPPER CRETACEOUS THROUGH TERTIARY
TECTONISM, NORTHEASTERN CRAZY MOUNTAINS BASIN, CENTRAL
MONTANA
by
Joshua K. Borrell
B S , University of Minnesota Duluth, 1998
Presented in partial fulfillment of the requirements
for the degree of
Master of Science
The University of Montana
2000
Approved by; .
aimerson
Dean, Graduate School
______(p - ( " ZfftTD Date
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Borrell, Joshua K , M.S., May 2000 Geology
SEDIMENTARY RECORD OF UPPER CRETACEOUS-TERTIARY TECTONISM, NORTHEASTERN CRAZY MOUNTAINS BASIN, CENTRAL MONTANA (95 pgs) Director: Marc S. Hendrix /v\iU ABSTRACT During Cretaceous and Tertiary time, western and central Montana underwent a fundamental tectonic transition from ‘thin-skinned’ to ‘thick-skinned’ basement-involved deformation. Although the foreland basin of central Montana preserves a well-recognized series of Upper Cretaceous-Tertiary strata, the sedimentary record of the transition from thin-skinned’ to thick- skinned’ basement-involved deformation has not been thoroughly studied in this area. The purpose of this investigation is to document the sedimentology, sandstone compositions, and orientation of paleocurrent indicators in Santonian through Thanetian strata in the Crazy Mountains Basin, south-central Montana and use this information to interpret the tectonic history of the northeastern Crazy Mountains Basin. Three stratigraphie sections were measured near Harlowton, MT Each section includes the Upper Cretaceous Montana Group (Eagle, Claggett, Judith River, Bearpaw, and Lennep Formations) and Hell Creek Formation, and the Pal eocene Bear, Lebo, and Melville Formations. The Montana Group records sea-level changes of the Cretaceous Interior Seaway in the foreland basin. Inferred depositional environments range from open marine to fluvial. The Hell Creek and Bear, Lebo, and Melville Formations are inferred to be fluvial deposits. Marine sandstones of the Eagle through Lennep Formations are quartzose. These formations contain southeast-directed marine paleocurrent indicators that likely reflect transport by longshore drift. Fluvial sandstones of the middle Judith River Formation through the Lennep Sandstone are lithic-volcanic-rich; east-directed paleocurrent indicators likely reflect transport away from the Elkhom Mountains Volcanics. Sandstones of the Hell Creek Formation through the Bear Formation are quartz- and lithic-rich; south-directed paleocurrent indicators may reflect partitioning of the foreland basin in this region and initial development of the Crazy Mountains Basin. Volcanic-rich sandstone compositions associated with south and southeast- directed paleocurrents of the lower Lebo Formation may be linked to erosion of rocks associated with the Central Montana Alkalic Province to the north of the study area. Quartzolithic sandstone compositions and north-directed paleocurrent indicators in the Melville Formation probably record uplift of the Beartooth Mountains to the south. Post-Eocene terrace gravels, derived directly from the mountain ranges they flank, unconformably overlie Cretaceous-Paleocene strata. Gravels from the Little Belt Mountains are composed primarily of Paleozoic limestone clasts; gravels from the Crazy Mountains are primarily composed of Eocene volcanic clasts.
II
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS
My first round of thanks must go to my thesis advisor, Marc Hendrix. His help, doled out
whenever he could be found, has been more valuable than he probably knows. This project
surely would never have gotten started or finished without his help To my other thesis
committee members, Jim Sears and Jim Jacobs, your time and feedback was much appreciated. I
would also like to offer sincere thanks to the other faculty members at the University of Montana
who have shared their knowledge with me, especially Don Winston.
Special thanks must go out to Jared Wells, “the field assistant”. I would still be out there
measurin’ paleocurrents and stretchin’ tape if it wasn’t for you.
I would like to thank the McDonough Research Grant for providing funding for this project.
Financial assistance was much needed and much appreciated.
Of those not directly related to my project, I have to thank my parents and sisters first and foremost. My appreciation for your encouragement through fhistrations, accidents, and accomplishments can not be put into words, but I hope you know how much it means to me To all of the other geo grads that have shared a beer, a laugh, or a meaningful discussion with me, you are a big part of this end result (on your left, baby). Special thanks go to my officemates of Y2K, Molly and Steve. You’ve made wasting an hour for lunch everyday something to look forward to. I would also like to thank other family, friends, and acquaintances not already mentioned for their fnendship and support. You know who you are.
Ill
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS Abstract ii Acknowledgments iii Table of Contents _ iv List of Tables vü List of Figures viii
Introduction 1 Geologic Setting 3 Methods of Study Stratigraphie Studies 5 Provenance Studies 6 Terrace Gravel Studies 7 Stratigraphie and Sedimentologic Results and Interpretations Eagle Formation Previous Work 8 WPA Section Stratigraphic/Sedimentologic Observations 8 SA Section Stratigraphic/Sedimentologic Observations 9 Eagle Formation Paleocurrent Indicators 10 Eagle Formation Stratigraphic/Sedimentologic Interpretations 11 Claggett Formation Previous Work 11 WPA Section Stratigraphic/Sedimentologic Observations 12 SA Section Stratigraphic/Sedimentologic Observations 12 Claggett Formation Paleocurrent Indicators 13 Claggett Formation Strat./Sed. Interpretations 13 Judith River Formation Previous Work 14 WPA Section Stratigraphic/Sedimentologic Observations 15 SA Section Stratigraphic/Sedimentologic Observations 16 Judith River Formation Paleocurrent Indicators 17 Judith River Formation Strat./Sed. Interpretations 18
IV
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bearpaw Shale Previous Work 19 WPA Section Stratigraphic/Sedimentologic Observations 19 SA Section Stratigraphic/Sedimentologic Observations 19 Bearpaw Shale Paleocurrent Indicators 20 Bearpaw Shale Stratigraphic/Sedimentologic Interpretations 20 Letmep Sandstone Previous Work 20 WPA Section Stratigraphic/Sedimentologic Observations 21 SA Section Stratigraphic/Sedimentologic Observations 21 Letmep Sandstone Paleocurrent Indicators 21 Letmep Sandstone Strat./Sed. Interpretations 22 Hell Creek Formation Previous Work 22 WPA Section Stratigraphic/Sedimentologic Observations 23 SA Section Stratigraphic/Sedimentologic Observations 23 Hell Creek Formation Paleocurrent Indicators 23 Hell Creek Formation Strat /Sed. Interpretations 24 Bear Formation Previous Work 24 SA Section Stratigraphic/Sedimentologic Observations 25 191 Section Stratigraphic/Sedimentologic Observations 25 Bear Formation Paleocurrent Indicators 25 Bear Formation Stratigraphic/Sedimentologic Interpretations 26 Lebo Formation Previous Work 26 SA Section Stratigraphic/Sedimentologic Observations 26 191 Section Stratigraphic/Sedimentologic Observations 27 Lebo Formation Paleocurrent Indicators 28 Lebo Formation Stratigraphic/Sedimentologic Interpretations 28
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Melville Formation Previous Work 28 SA Section Stratigraphic/Sedimentologic Observations 29 191 Section Stratigraphic/Sedimentologic Observations 29 Melville Formation Paleocurrent Indicators 29 Melville Formation Strat /Sed Interpretations 30 Sandstone Provenance Observations Eagle Formation 31 Claggett Formation 32 Judith River Formation 32 Bearpaw Shale 33 Lennep Sandstone 33 Hell Creek Formation 34 Bear Formation 34 Lebo Formation 35 Melville Formation 35 Provenance Interpretations 36 Terrace Gravel Studies Terrace Gravel Compositions and Paleocurrent Data 39 Terrace Gravel Interpretations 40 Conclusions Marine Deposits of the Montana Group 41 Fluvial Deposits of the Montana Group 42 Hell Creek Formation 43 Bear Formation 44
Lebo Formation 4 5
Melville Formation 4 5 Terrace Gravels 46
References 4 7
VI
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES
Table 1. Trigonometry and thickness of the Woman’s Pocket Anticline section 52
Table 2. Trigonometry and thickness of the Shawmut Anticline section 53
Table 3. Trigonometry and thickness of the Highway 191 section 54
Table 4. Summary of compositional data for sandstone thin-sections 55
Table 5. Counted and recalculated grain parameters used for this study 56
Table 6. Recalculated grain framework data 57
Table 7. Paleocurrent trends, and inferred environments of deposition
for formations of this study 58
Table 8 Key for measured stratigraphie sections (Figs. 4-17) 59
YU
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES Figure 1. Simplified diagram of major foreland uplifts of the western U.S. 60 Figure 2 Location of study area and major features 61 Figure 3. General stratigraphie column of study units 62 Figure 4. Eagle Formation measured section, WPA section 63 Figure 5 Eagle Formation measured section, SA section 64 Figure 6. Claggett Formation measured section, SA section 65 Figure 7. Judith River Formation measured section, WPA section 66 Figure 8. Judith River Formation measured section, SA section 67 Figure 9. Paleocurrent indicators from the Bearpaw Shale, SA section 68 Figure 10. Bearpaw, Lennep, and Hell Creek Formations, WPA section 69 Figure 11. Lennep Sandstone measured section, SA section 70 Figure 12. Hell Creek Formation measured section, SA section 71 Figure 13. Bear Formation measured section, SA section 72 Figure 14. Bear Formation measured section, 191 section 73 Figure 15. Lebo Formation measured section, SA section 74 Figure 16. Lebo Formation measured section, 191 section 75 Figure 17. Melville Formation measured sections, SA and 191 sections 76 Figure 18. Correlated stratigraphie sections 77 Figure 19a. Eagle and Claggett Formations, QtFL diagram 78 Figure 19b. Eagle and Claggett Formations, QmFLt diagram 78 Figure 19c. Eagle and Claggett Formations, QmPK diagram 78 Figure 19d. Eagle and Claggett Formations, QpLvLsm diagram 78 Figure 20a. Judith River Formation, QtFL diagram 79 Figure 20b. Judith River Formation, QmFLt diagram 79 Figure 20c. Judith River Formation, QmPK diagram 79 Figure 20d. Judith River Formation QpLvLsm diagram 79 Figure 21a. Bearpaw Shale and Letmep Sandstone, QtFL diagram 80 Figure 21b. Bearpaw Shale and Lamep Sandstone, QmFLt diagram 80 Figure 21c. Bearpaw Shale and Lennep Sandstone, QmPK diagram 80 Figure 2 Id. Bearpaw Shale and Lennep Sandstone, QpLvLsm diagram 80
V lll
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 22a. Hell Creek Formation, QtFL diagram 81 Figure 22b. Hell Creek Formation, QmFLt diagram 81 Figure 22c. Hell Creek Formation, QmPK diagram 81 Figure 22d. Hell Creek Formation QpLvLsm diagram 81 Figure 23a. Bear Formation, QtFL diagram 82 Figure 23b. Bear Formation, QmFLt diagram 82 Figure 23c, Bear Formation, QmPK diagram 82 Figure 23d. Bear Formation QpLvLsm diagram 82 Figure 24a. Lebo Formation, QtFL diagram 83 Figure 24b. Lebo Formation, QmFLt diagram 83 Figure 24c. Lebo Formation, QmPK diagram 83 Figure 24d Lebo Formation QpLvLsm diagram 83 Figure 25a. Melville Formation, QtFL diagram 84 Figure 25b. Melville Formation, QmFLt diagram 84 Figure 25c. Melville Formation, QmPK diagram 84 Figure 25d Melville Formation QpLvLsm diagram 84 Figure 26. LvLsLm diagram of all sandstone samples 85 Figure 27. Marine sandstones of the Montana Group, QtFL diagram 86 Figure 28. Paleogeographic model, terrace gravel deposition 87 Figure 29. Terrace gravel clast count composition data 88 Figure 30. Pebble imbrications in terrace gravels 89 Figure 31. Cretaceous Interior Seaway, North America 90 Figure 32. Simple paleogeogrtqahic model, sea-level highstand 91 Figure 33. Fluvial sandstones of the Montana Group, QtFL diagram 92 Figure 34. Paleogeographic model, sea-level lowstand 93 Figure 35. Paleogeographic model. Hell Creek-Lebo deposition 94 Figure 36. Paleogeographic model, lower Melville deposition 95
IX
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 INTRODUCTION
The foreland basin of western North America has long been an area of geologic interest because
of its extensive petroleum and coal reserves and because of its well preserved record of the
Cretaceous Interior Seaway (e.g. Weed, 1899; Stone, 1909; Bowen, 1918; Gill and Cobban, 1973;
Rice, 1980). Much of the recent geologic research in the foreland basin has been directed
towards understanding the timing and nature of the transition from thin-skinned (fold-thrust) to
thick-skinned (basement-involved) deformation and the sedimentary response to this transition
(e.g. Suttner et a!., 1981; Dickinson et al., 1986; Schwartz and DeCelles, 1988; and Whipkey et
a l, 1991).
The northeastern Crazy Mountains Basin of south-central Montana was selected as the location
for this thesis because it represents the northernmost extent of partitioning in western North
America’s foreland basin (Jackson, 1989) (Fig. 1) and because the units of interest are moderately
well-exposed in several small domes. The units of interest include the Upper Cretaceous
Montana Group and Hell Creek Formation, the Paleocene Bear, Lebo, and Melville Formations,
and the post-Eocene Terrace Gravels.
The main hypothesis this study seeks to test is that the sedimentary record in and around the
northeastern Crazy Mountains Basin should record the transition from thin-skinned to thick-
skinned deformation. If this hypothesis was true, the following scenarios would be expected:
1) Strata deposited in the ‘unbroken’ foreland basin should record depositional environments
controlled mainly by the sea level of the Cretaceous Interior Seaway. ‘Partitioned’ foreland basin
strata should reflect depositional environments controlled by tectonic events in the foreland basin
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 2) ‘Unbroken’ foreland basin fluvial strata should record paleocurrents directed away from the
fold-thrust belt and toward the Cretaceous Interior Seaway. ‘Partitioned’ foreland basin fluvial
strata should record paleocurrents directed away from individual uplifts within the foreland
3) Sandstone compositions of unbroken’ foreland basin strata should be uniform, reflecting
mixing of recycled sedimentary and volcanic rocks distal to the fold-thrust belt. Sandstone
compositions of partitioned’ foreland basin strata should reflect provenance from individual
uplifts within the foreland.
My objectives for this study were three-fold;
1) To constrain the timing of the transition from thin-skinned to thick-skinned deformation in
the northeastern Crazy Mountains Basin by using sandstone compositions to infer
provenance, paleocurrent indicator orientations to infer transport directions, and facies
relationships to infer environments of deposition.
2) To improve the stratigraphie detail of Upper Cretaceous through Tertiary strata in the Crazy
Mountains Basin area
3) To form paleogeographic models of central Montana through time by correlating my data
with that of previous work
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. GEOLOGIC SETTING
The Crazy Mountains Basin is bounded on the north by the Little Belt and Big Snowy Mountains
and to the south by the Beartooth Mountains. TTie Bridger Mountains form the western edge of
the Crazy Mountains Basin This area represents the northernmost extent of foreland basin
partitioning (Fig. 1).
The Little Belt and Big Snowy Mountains are WNW-ESE striking basement-involved uplifts.
Weed ( 1899) was the first to map the area in and around the Little Belt Mountains. The Big
Snowy Mountains were mapped by Reeves (1930). Rock types at the surface primarily consist of
Paleozoic rocks, dominantly the Mississippian Madison Group Limestone. Minor exposures of
the Proterozoic Belt Supergroup are found in the core of both ranges. The Archean basement
crops out in two places in the center of the Little Belt Mountains dome. Mesozoic rocks flank
both mountain ranges. The Little Belt Mountains have small Eocene intrusions exposed at
several places. Witkind et al. (1970) used geologic and geophysical evidence to show that these
intrusions might be related to a much larger laccolith that caused the doming of the Little Belt
Mountains. Figure 2 generalizes the major structures in the study area.
The Beartooth Mountains comprise a WNW-ESE striking, Archean basement-cored uplift.
Paleozoic and Mesozoic strata flank the basement. The northern and eastern edges of the
Beartooth Mountains are thrust &ults. The Cretaceous ‘igneous member of the Livingston
Formation’ crops out on the north flanks of the range (Parsons and Stow, 1942). Stow (1939)
also described this unit as the Deer Creek volcanic rocks. This unit consists of andesitic breccia
and flows that are syndepositional with Upper Cretaceous sedimentary rocks.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 The Crazy Mountains postdate formation of the Crazy Mountains Basin The Crazy Mountains
are composed of a N-S striking series of Eocene igneous plutons. A series of dikes are spatially
related to these intrusions. These dikes occur throughout the Crazy Mountains Basin.
The eastern limit of the fold-thrust belt is approximately 80 km west of Harlowton, Montana.
The Big Belt Mountains represent the easternmost extent of the fold-thrust belt in central
Montana. The Bridger Mountains are an Archean basement-involved uplift just south of the Big
Belt Mountains that form the western edge of the Crazy Mountains Basin The Belt Supergroup
also crops out and is flanked by Paleozoic and Mesozoic strata.
Figure 3 is a general stratigraphie column of the units in this study. Several early workers
recorded the stratigraphy o f upper Cretaceous strata in central Montana (e.g. Stone, 1909; Bowen,
1915; Roberts, 1972; Gill and Cobban, 1973). The Cretaceous Interior Seaway twice inundated
this area during Late Cretaceous time The Claggett Formation and Bearpaw Shale record the T8
and T9 transgressions, respectively, of Kaufman (1977). The Eagle and Judith River Formations
and Lennep Sandstone record the R7, R8, and R9 regressions, respectively, of the Cretaceous
Interior Seaway. Rice (1980) and Rogers (1993) studied the Eagle and Judith River Formations,
respectively, in north-central Montana. The Hell Creek, Bear, Lebo, and Melville Formations and
Terrace gravels are all continental deposits within the foreland basin. Very little sedimentologic
work has been conducted on these continental strata in the vicinity of my study area
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. METHODS OF STUDY
Stratigraphie Studies
Three sections were measured within and around the northeastern Crazy Mountains Basin in the
vicinity of Harlowton, Montana (Fig. 2). From east to west the sections are; Woman’s Pocket
Anticline (WPA section), Shawmut Anticline (SA section), and Highway 191 (191 section). The
Montana Group and Hell Creek Formation were measured in the WPA section. The Montana
Group through Melville Formation was measured in the SA section. The Bear through Melville
Formations were measured in the 191 section. These sections were chosen based on the
continuous, quality exposure of the selected formations. Stratigraphie sections were measured at
a meter- to submeter-scale with a 25 m tape in order to document the style of sedimentation. Rock
types, grain size, sedimentary structures, and bedding relationships were recorded. Since bedding
was not horizontal, trigonometry was used to calculate true vertical thickness from measured
oblique thickness through the use of an Excel spreadsheet (Tables 1, 2, and 3). The thickness of
strata underpinning broad covered valleys (e.g., Bearpaw Shale) was estimated using a Magellan
Global Positioning System, Brunton compass, topographic map; the same trigonometry as above
was then used to estimate the thickness of the covered units.
A Brunton compass was used to measure both unidirectional and bidirectional paleocurrent
indicators. A stereonet program (Richard Allmendinger’s Stereonet v. 4.5, 1988) was used to
restore beds to horizontal and create rose diagrams. Trough cross-beds were the predominant
paleocurrent indicator. Poor exposures dictated measuring available limbs, rather than trough
axes (DeCelles et al., 1983). In this thesis, I report trough cross-bed measurements on rose
diagrams by showing all of the restored slip-face dip directions (rose “petals”) as well as the
vector average of all restored measurements, shown by a single vector. This vector average is
interpreted to represent the mean paleoflow direction (e.g. Fig 6).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Provenance Studies
Rock samples were collected from sandstone beds within each section to determine framework
grain compositions. Collected samples were the coarsest available and appeared in the field to be
the least altered. Thin sections were prepared from the sandstone samples. One half of each thin
section was stained with sodium cobaltinitrate to aid in the identification of potassium feldspar
and Alazirin red to aid in the identification of calcite and plagioclase feldpar One half of each
thin section was left unstained. Five hundred grain counts were made across the stained half of
the sample. Thin sections were counted on an automatic stage with a Leitz pétrographie
microscope. Grains were placed into one of the following groups; Monocrystalline quartz (Qm),
polycrystalline quartz (Qp), chert (Cht), potassium feldspar (K), plagioclase feldspar (P), lithic
sedimentary and lithic metasedimentary (Ls), lithic volcanic and metavolcanic (Lv), lithic
metamorphic (Lm), lithic carbonate (xb CO 3), unidentified lithic (unid L), unidentified nonlithic
(unid nonL), biotite (bt), muscovite (ms), chlorite (chi), dense minerals (heav), cement (Cmt),
matrix (Matr), and porosity (Por). Crystals or grains larger than the sand-silt cutoff (0.0625 mm)
within lithic grains were counted as monocrystalline grains, consistent with the Gazzi (1966)-
Dickinson (1970) method as tested by Ingersoll et al (1984).
Specific criteria were used to identify lithic grains in tins study: 1) Grains were identified as Cht
when a clast contained either uniform microcrystalline or macrocrystalline quartz or a
combination of both (+/- the presence of sponge spicules and/or radiolarians), usually with a
characteristic brown color. Chalcedony was tabulated as Cht; 2) Chains were classified as Lm
only when a schistose texture was present or foliated quartz was present and the grains contained
at least one other crystal of a mineral other than quartz (e.g. muscovite); 3) Grains were identified
as Ls when silt grains were well-outlined within the lithic fragment, or if no silt grains were
present, the grain consisted of a matrix of aligned clay grains; and 4) a grain was identified as Lv
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 if definite phenocrysts were present or if grain boundaries were obviously interlocking or ill-
defined. Table 4 is a summary of the raw grain count data collected for this study.
Sandstone compositional data were normalized on five ternary diagrams according to the
recalculated parameters listed in Table 5:1) QtFL [percentages of total quartz (including chert),
total feldspar (plagioclase and potassium feldspars), and total lithic grains (lithic metamorphic +
lithic sedimentary (including XBCO 3) + lithic volcanic + lithic unknown)]; 2) QmFLt
[percentages of monocrystalline quartz, total feldspar, and total lithic grains (including chert)]; 3)
QpLvLsm [percentages of polycrystalline quartz (including chert), lithic volcanic, and lithic
sedimentary + lithic metamorphic grains]; 4) QmPK [percentages of monocrystalline quartz,
plagioclase, and K-feldspar grains]; and 5) LvLsLm [percentages of lithic volcanic, lithic
metamorphic, and lithic sedimentary grains (including chert)]. These values were plotted on the
appropriate ternary diagram of Dickinson and Suczek (1979) or Dickinson et al. (1983). The data
were also analyzed for other compositional changes that do not show up on ternary diagrams,
such as dense mineral and mica concentrations and cementation. Table 6 is a summary of the
normalized framework grain data used to plot the ternary diagrams in this study.
Terrace Gravel Studies
Tertiary terrace gravels were included in order to study the late Tertiary events in and around the
northeastern Crazy Mountains Basin. Sections were measured where available, noting
depositional style and sedimentology. Pebble imbrications were measured on the outcrop with a
Brunton compass. Outcrops were horizontal, so no restoration was necessary. Clast samples
were collected from the outcrop on a 3x3 m grid used to eliminate unintentional bias toward clast
collection. Samples were collected roughly 10 cm apart, yielding about 100 clasts per sample
location. Clast lithologies were then identified and counted.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. STRATIGRAPHIC and SEDIMENTOLOGIC RESULTS and INTERPRETATIONS
Eagle Formation
Previous Work
The Eagle Formation was originally described by Weed (1899) for outcrops near Eagle Creek
along the Missouri River, east of Great Falls. Bowen (1915) subsequently named the Virgelle
Saiidstone Member from exposures near Virgelle, Montana to describe the lower “white rocks” of
the Eagle Formation. Several studies in central Montana during the early 1900’s noted the
presence of coal in the Eagle Formation and the Eagle Formation’s general lithology (e.g. Stone,
1909). Bowen (1918) measured sections and listed stratigraphie and sedimentologic observations
related to potential petroleum reservoirs in the Musselshell Valley. Rice (1980) provided a
detailed stratigraphie and sedimentologic report of the Eagle Formation on the southern flanks of
the Bearpaw Mountains north of this study area.
Woman’s Pocket Anticline Section Stratigraphic/Sedimentologic Observations
The Eagle Formation is represented by two prominent sandstone ridges separated by a covered
interval in the Woman’s Pocket Anticline (WPA) section (Fig, 4). Total thickness of the
formation is roughly 45 m. The Virgelle Sandstone Member is approximately 11m thick in the
WPA section. The lower 4 m (0-4 m. Fig. 4) are interbedded fine to medium-grained sandstone
(-5 cm thick) and siltstone (~1 cm thick). Bioturbation has obscured sedimentary structures in
the sandstone beds although symmetrical ripple marks are present on some bedding surfaces. The
interval from 4-8 m (Fig 4) consists of medium-grained sandstone with planar bedding and
hummocky cross-stratification. The interval from 8-11 m (Fig. 4) is predominantly planar
bedded, medium-grained sandstone with local tabular crossbeds. Bioturbation becomes less
common upwards from the base (8 m) but is present at the top (11 m). A 24 m thick covered
interval separates this lower sandstone from the upper sandstone. The upper sandstone is about
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 10 m thick (35-45 m. Fig. 4) and fine-grained throughout. The lowest interval (35-37 m. Fig. 4)
is 2 m thick, has dm-scale hummocky cross-stratification with mud drapes on the bedding
surfaces and rare Thallasanoides burrows as recognized in Frey (1975). The interval from 37-39
m (Fig 4) contains wavy to planar bedding, rare burrows, and local climbing ripples, with
preserved oscillation ripples on bedding surfaces. The upper 6 m of the Eagle Formation (39-45
m. Fig 4) contain 5 cm thick fine- to medium-grained sandstones. Climbing ripples are the only
observed sedimentary structure. Burrows are more abundant and 3-D flow ripples are present on
some bedding surfaces. The Claggett Formation overlies this upper sandstone.
Shawmut Anticline Section Stratigraphic/Sedimentologic Observations
The Eagle Formation is approximately 62 m thick in the SA section (Fig. 5). It consists of 3
fairly prominent ridges, separated by 2 covered intervals. The Virgelle Sandstone Member is -21
m thick in the SA section. The lower 2 m (0-2 m. Fig. 5) are fine-grained and have hummocky
cross-stratification. The interval from 2-4 m (Fig. 5) consists of medium-grained massive
sandstone (-20 cm thick) interbedded with fine-grained sandstone (-10 cm thick). The medium-
grained massive beds are heavily bioturbated and contain vertical burrows. The thinner fine
grained sandstone beds contain small cross-beds. A 6 m thick, well-sorted, white sandstone
occupies the interval from 4-10 m (Fig 5). Bedding is essentially planar and lacks burrows. The
upper 12 m of the Virgelle Sandstone Member (10-22 m. Fig. 5) consist of high-angle tabular
cross-bedded and trough cross-bedded white sandstone. The uppermost 0 .5 m of the Virgelle
Sandstone Member lacks the characteristic cross-beds and contains abundant large wood
fragments. Overlying the Virgelle Sandstone is a transition from dark brown siltstone with thin
coal seams to black shale, which leads into a 23 m thick covered interval (22-45 m. Fig. 5). The
middle sandstone of the Eagle Formation is 5 m thick, fine-grained, planar bedded, and tabular
cross-bedded (45-50 m. Fig. 5). The upper 1 m contains rare bioturbation. This interval is
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10 overlain by 6 m of covered slope (50-56 m. Fig. 5), exhibiting a transition from brown to black
shale. The uppermost sandstone layer is 6 m thick (56-62 m. Fig. 5). The lower 4 m of this
interval (56-60 m. Fig. 5) are tabular cross-bedded and contain hummocky cross-stratification.
The upper 2 m of this interval (60-62 m. Fig 5) contain high-angle planar cross-beds and
preserved oscillation ripple marks on the uppermost surface. The Claggett Formation overlies
this sandstone.
Eagle Formation Paleocurrent Indicators
Trough cross-bed dip directions were measured and restored from the upper sandstone of the
Eagle Formation in the WPA (n=17) (Fig. 4). The trend of paleocurrent flow is either bi
directional or directed to the southwest. High angle trough cross-bed dip directions were
measured and restored from the inferred upper shoreface deposits of the Virgelle Sandstone
Member in the SA section (n=94) (Fig. 5). The random pattern of foreset dip directions is
characteristic of upper shoreface deposits (Clifton et al ., 1971). A southeast trend is apparent
from foreset dip directions in trough cross-beds measured from the 45-50 m interval in the SA
section (n=23) (Fig. 5). This trend is inferred to reflect the fluvial transport direction. A
southwest trend predominates in restored planar cross-bed slip-face dip directions measured in the
uppermost Eagle sandstone in the SA (n=17) (Fig. 5).
E ^le Formation Stratigraphic/Sedimentologic Interpretations
I interpret the Virgelle Sandstone Member of the Eagle Formation in both the WPA and SA
sections to have been deposited in a coastal environment, similar to the regressive barrier island
model of Reinson (1979), Three-dimensional facies studies to determine whether the
environment was a barrier island or an interdeltaic coastline were beyond the scope of this
project. I interpret lower shoreface deposits that grade upward to middle shoreface and upper
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 shoreface deposits (Fig, 5), similar to the Galveston barrier island model of Davies et al. (1971).
This model also grades upward from bioturbated silt and hummocky cross-strati6ed sand (lower
shoreface) to low-angle cross-bedded sandstone (upper shoreface) to trough cross-bedded
sandstone (eolian). The top of the upper shoreface in the SA section may represent backshore
deposition. This backshore is not observed in the WPA, but may be covered. The Virgelle
Sandstone represents a relative sea-level regression, the R-7 regression of Kaufinan (1977). I
interpret the siltstone with coal seams and shale in the SA and the covered interval in the WPA
that overlie the Virgelle Sandstone Member as coastal plain deposits. Marine shales may occur in
the upper portion of this covered interval in the SA section and possibly in the covered interval of
the WPA section. The middle sandstone of the Shawmut Anticline (45-50 m. Fig 5) is
interpreted as a fluvial channel on the coastal plain based on the facies relationships (Collinson,
1978). I interpret the uppermost sandstone of the WPA and SA to record another sea-level
regression based on the fecies relationships that signify a lower-middle shoreface to upper
shoreface sequence, similar to tiie Galveston barrier island presented by Davies et al. (1971) A
lag deposit may be located at its contact with the underlying covered interval although I did not
observe this feature in either section. The transgressive Claggett Formation overlies the
regressive upper sandstone of the Eagle Formation in both sections. Ryer (1977) noted that
transgressions are rm’ely preserved in the sedimentary record as meirine processes generally
eradicate them.
Claggett Formation
Previous Work
Stanton and Hatcher (1905) originally described the Claggett Formation from exposures along the
Missouri River near Fort Claggett. TTie Claggett Formation of central Montana has not been
thoroughly studied in previous work. This is probably due to the predominance of shale and its
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 2 typically poor exposure. Bowen (1918) noted an increasing amount of sandstone to the west
within the Claggett Formation of the Musselshell Valley.
Woman’s Pocket Anticline Section Stratigraphic/Sedimentologic Observations
Thickness of the Claggett Formation in the WPA is about 145 m The entire interval is present as
a grass-covered valley. However, Bowen (1918) recorded a measured section of Claggett
Formation near the WPA section that is 96% shale or covered. A Baculites (sp?) was found by
the author near the 100 m level in the covered interval (G. Stanley, 1999 pers. comm.). The
inference is that the vast majority of the Claggett Formation in the WTA section is erodable,
marine shale.
Shawmut Anticline Section Stratigraphic/Sedimentologic Observations
The Claggett Formation is approximately 220 m thick in the Shawmut Anticline. For this study,
the top of the Claggett Formation was placed at 281 m This may conflict with previous studies
(e.g. Stanton and Hatcher, 1905). The Claggett Formation in the SA is predominantly covered,
but better exposed than the WPA section. Several thin sandstone bodies crop out throughout the
section. A 21 m thick, partially exposed outcrop occurs at the base of the Claggett Formation
(67-88 m. Fig 6). A 1.5 m thick, planar bedded, fine-medium-grained sandstone is found at the
base of this interval (67-68.5 m. Fig. 6). Thallasinoides burrows are found in the upper .5 m of
this sandstone. This is overlain by 19 .5 m of shale and siltstone interbedded with thin sandstone
(Fig 6). The sandstone is heavily bioturbated and contains abundant wood fragments and fossil
vegetation, seen as cm-scale black or rusty flecks within bedding. A 72 m covered interval (88-
160 m. Fig 6) is followed by -13 m of siltstone interbedded with several thin sandstone lenses
(160-173 m. Fig. 6). The sandstone lenses are -0.5 m thick and are hummocky cross-stratified.
Some beds contain fossil vegetation and bioturbation as well. This is overlain by a 48 m thick
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 3 covered interval (173-221 m. Fig. 6). A 13 m thick exposure shows a similar pattern of siltstone
and shale inteihedded with sandstone (221-234 m. Fig. 6). Sandstone beds are generally upward-
thickening. The lower beds have planar bedding at the base, grading up to either climbing ripples
or decimeter-scale trough cross-beds, usually with symmetrical ripples on the surface. The
surface is usually bioturbated and a thin siltstone veneer covers each bed. The upper sandstone is
upward-fming and -thinning with trough cross-bedding. Mud intraclasts are found at the base
with bioturbation at the top A 36 m covered interval overlies this sandstone (234-270, Fig. 6).
Several -0.5 m thick sandstone beds crop out from 270-272 m (Fig 6). These sandstones
generally consist of hummocky cross-stratification grading up to ripple cross-stratification,
capped by bioturbation and a thin, silty veneer. The beds are upward-thickening and -coarsening.
The uppermost bed has hummocky cross-stratification below a soft-sediment-deformed layer that
contains mud intraclasts. A 9 m thick interval of organic-rich shale overlies the sandstone layer
(272-281 m. Fig 6). Above this is the interpreted contact with the Judith River Formation.
Claggett Formation Paleocurrent Indicators
Trough crossbed attitudes were measured from five different sandstone beds throughout tiie
Claggett Formation (n=285). A strong southeast trend is evident in all beds (Fig. 6). This trend is
inferred to be the direction of longshore drift along the western margin of the Cretaceous Interior
Seaway.
Claggett Formation Stratigraphic/Sedimentologic Interpretations
The Claggett Formation was deposited during a transgression [Kaufman’s (1977) T8
transgression] of the Cretaceous Interior Seaway (Gill and Cobban, 1973). Rice (1980) noted the
presence of a chert pebble lag deposit at the base of the Claggett Formation. However, I did not
observe such a lag in the sections of this study. In the WPA section, the Claggett Formation is
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14 entirely covered. The predominance of organic-rich black shale and the presence of a Bacuiites
(sp?) fossil (G. Stanley, 1999 pers, comm.) indicate that Claggett Formation shale was deposited
in an offshore marine environment. Lithologies are better exposed within the SA section. The
lowest interval of the Claggett Formation in the SA section was likely deposited in a lower
shoreface environment (Fig. 6). The hummocky cross-stratified sandstone beds are interpreted as
storm deposits in areas that were below fairweather wave base and above storm wave base, i.e.,
shallow marine (Harms, et al., 1975). These shallow marine deposits grade upward into offshore
marine deposits, represented by the covered intervals (probably organic-rich shale). Regression
occurred during deposition of the upper Claggett Formation This regression began at around 79
Ma, during deposition of the middle Claggett (Gill and Cobban, 1973). Hummocky cross
stratified sandstones appearing in the upper Claggett Formation suggest shallowing of the
Cretaceous Interior Seaway (160-270 m. Fig 6). The upper Claggett is upward-thickening and
coarsening. Sandstone beds generally contain hummocky cross-stratification, burrows, climbing
ripples, intraclasts, and trough cross-beds. These facies relationships are similar to those
exhibited by the Upper Jurassic Femie-Kootenay Formations of Canada’s foreland basin
(Hamblin, 1978). That is, an overall upward-coarsening, with hummocky cross-stratified
sandstones that grade upward to typical shoreface deposits. As such, I interpret these units to
have been deposited in a lower shoreface marine environment although a deltaic environment of
deposition cannot be ruled out.
Judith River Formation
Previous Work
The Judith River Formation is perhaps the best known formation in this study. Meek and Hayden
(1856) named the Judith River Formation for exposures near the confluence of the Judith River
with the Missouri River. Early workers focused on the age and correlation of the formation, but
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15 Stanton and Hatcher (1905) completed a detailed study of the geology and paleontology in the
type area. Bowen (1918) reported on the stratigraphy of the Judith River Formation in the
Musselshell Valley. Fiorillo (1991) documented the Judith River Formation-hosted Careless
Creek Quarry in Wheatland County near the WPA section. Rogers (1993) described a lower and
upper marine facies within the Judith River Formation in its type section. The lower marine
facies is termed the Parkman Sandstone Member, named by Knetchel and Patterson (1956) for
exposures in the Hardin, Montana area.
Woman s Pocket Anticline Section Stratigraphic/Sedimentologic Observations
The Judith River Formation is characterized by thick sandstone beds at the base, grading upward
to shale, coal, siltstone, and local sandstone beds. It is approximately 105 m thick in the WPA
(Fig. 7). The lowest 1 m (188-189 m. Fig, 7) is a fine-grained, hummocky cross-stratified
sandstone. The next 2 m (189-191 m, Fig 7) are fine-grained, planar bedded sandstone.
Symmetrical ripple marks are found at the base of this sandstone. The interval from 191-208 m is
composed of fine-grained sandstone (Fig 7). Trough and tabular cross-beds are common;
burrows are rare. The upper 3 m (208-211 m. Fig. 7) are fine-grained, planar bedded sandstone.
A 5.5 m covered interval, which is probably gray siltstone and interbedded sandstone, overlies
this sandstone (211-216.5 m. Fig 7). Lenticular fine-grained sandstone (216.5-224.5 m. Fig. 7)
overlies the covered interval. Bedding is poorly preserved but appears to contain tabular cross
bedding throughout. Another sandstone lens that was just off the measured section line has
burrows, trough cross-beds, and local soft-sediment deformation. A 28 m thick covered interval
overlies the sandstone (224.5-252.5 m. Fig 7). A 0.3 m thick oyster bed is found at -250 m
(Fig 7). This is poorly exposed, but abundant oyster shells are found in float. The shells appear
to be disarticulated and abraded. Thus they are probably a death assemblage and not a life
assemblage. A im thick interval of fine-grained sandstone (253-254 m, Fig 7) overlies the
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 6 covered interval. This sandstone contains mud intraclasts and seems to consist entirely of soft-
sediment deformation. A covered interval (254-265 m, Fig. 7) overlies this sandstone. Thin
sandstone with ripple cross-stratification overlies the covered interval (265-267 m. Fig. 7).
Bedding is poorly preserved in the upper 1 m and fossil wood fragments are locally common.
Gray shale interbedded with rust-colored concretionary siltstone overlies this sandstone (267-
273.5 m. Fig 7). The upper 20 m of the WPA section Judith River Formation are composed of 3
upward-fining sequences (273.5-293.5 m. Fig 7). They grade from sandstone to siltstone to coal.
The sandstones contain ripple cross-stratification, local trough cross-bedding, concretions, and
root casts. The Bearpaw Shale overlies the uppermost coal unit (293.5 m. Fig. 7).
Shawm ut Anticline Section Stratigraphic/Sedimentologic Observations
The Judith River Formation is approximately 101 m thick in the SA section (Fig. 8 ). It lies
conformably on the Claggett Formation. The Judith River Formation is upward-coarsening and
thickening firom the base, then is upward-thinning and fining at the top. The base of the Judith
River Formation was placed at 281 m (Fig 8 ). A 5 m thick interval of -0.5 m thick very fine- to
medium-grained sandstone beds makes up the basal Judith River Formation in the SA (281-286
m. Fig. 8 ). Individual beds contain hummocky cross-stratification and rare Thallasanoides
burrows at the base, and are bioturbated at the top with a thin, silty veneer. Local symmetrical
ripple marks may be preserved on some surfaces. A 3 m thick covered interval separates this
sandstone from the above sandstone (287-290 m. Fig. 8 ). The next sandstone (290-300 m. Fig. 8 )
is medium-grained with abundant Thallasanoides burrows and seems to have meter-scale trough
cross-beds although bedding is commonly difficult to see due to weathering. Local 3-D flow and
asymmetric ripple marks are preserved on bedding surfaces. The upper 1 m (299-300 m. Fig. 8 )
contains some coarse-grained sandstone beds and mud intraclasts. This sandstone is overlain by
23 m of covered interval (300-323 m. Fig. 8 ). Above the covered interval is a 2.5 m thick fine
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 7
grained sandstone with ripple cross-stratification (323-325.5 m. Fig. 8 ). There is another covered
interval above this sandstone, from 325.5-330 m. Fig. 8 ). A 1.5 m thick, fine-grained, ripple
cross-stratified sandstone (Plate 3) overlies the covered interval (330-331.5 m. Fig 8 ). A covered
interval of 1 m (331.5-332.5 m. Fig 8 ) separates the sandstone below from the sandstone above,
which is 1 m thick, upward-fining, from coarse-grained at the base to medium-grained at the top
(332.5-333.5 m. Fig. 8 ). Mud intraclasts are present at the base, and trough cross-beds are
common. Olive-green silty shale makes up the next 4 m (333-337 m. Fig. 8 ). Another 1.5 m
thick, upward fining, trough cross-bedded smidstone is above this shale (337-338.5 m. Fig. 8 ).
This sandstone is overlain by 3 .5 m of cover (338.5-342 m. Fig. 8 ), which is in turn overlain by 1
m of medium-grained, trough cross-bedded sandstone (342-343 m. Fig 8 ). A 25 m covered
interval is separated by a .5 m thick medium-grained sandstone that is trough cross-bedded with
mud intraclasts on the foresets (343-368 m. Fig. 8 ). The next 13 m (368-381 m. Fig. 8 ) are a
series of fine to medium-grained sandstones interbedded with sandstone and shale. The lower
sandstone beds are trough cross-bedded and the upper beds contain climbing ripples. Some beds
have large wood debris (up to 30 cm long), intraclasts, and/or root casts. Fossil plant material is
common. The Bearpaw Shale overlies the uppermost sandstone (381 m. Fig 8 ).
Judith River Formation Paleocurrent Indicators
Trough cross-bed slip-face dip directions were measured and restored ft^om the two lower
sandstone beds of the Judith River Formation in the WPA. Restored cross-bed slip-face dip
directions in the lower sandstone (n=67) show a dominant southeast trend, which I attribute to
longshore drift (191-208 m. Fig 7). The next sandstone, interpreted as fluvial (212-224 m. Fig
7), contains trough cross-beds with restored dip directions trending to the east (n=15) (Fig 7). 1
interpret this strong unidirectional trend to reflect fluvial transport away from the fold-thrust belt.
Paleocurrent indicators were measured from six sandstone beds (n=283 total) in the Shawmut
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 Anticline. Restored trough and planar cross-bed slip-face dip directions from the two lower
sandstone beds exhibit a southeast trend (Fig. 8 ), again attributed to longshore drift. Restored
trough cross-bed slip-face dip directions from the four upper beds cluster around the eastern pole
(Fig. 8 ). I interpret these strongly unidirectional trends to reflect transport directions of the
fluvial channels.
Judith River Formation Stratigraphic/Sedimentologic Interpretations
The lower sandy units of the WPA and 191 sections are correlative with the Parkman Sandstone
Member that Rogers (1993) describes as being deposited on an eastward advancing beachfront
due to a regression of the Cretaceous Interior Seaway. I interpret the lower sandy units of the
Judith River Formation in the WPA and SA sections to be shoreline deposits, similar to the
Virgelle Sandstone Member of the Eagle Formation. Hummocky cross-stratification passes
upward to planar bedding (lower-middle shoreface), then trough and tabular cross-beds (upper
shoreface), which are overlain by more planar beds (foreshore). These facies relationships are
similar to the classic regressive barrier island/coastline model of Reinson (1979). Based on
comparisons with facies models of Collinson (1978), I interpret that the upper Judith River
Formation in both sections was deposited in a coastal plain. Persistent upward-fining sequences,
coal seams, root casts, abundant wood and organics, and green shale are indicative of a low-lying,
swampy plain (Collinson, 1978). I interpret the cross-bedded sandstone overlying the basal
sandstone in the WPA section to be a distributary channel within the coastal plain based on its
lenticular appearance and tabular cross-bedding. I interpret the Judith River Formation to change
upwards from a regressive, interdeltaic coastline to a coastal plain with brackish water,
distributary channels, and abundant swamps.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 9 Bearpaw Shale
Previous Work
Stanton and Hatcher (1905) named the Bearpaw Shale for exposures near the Bearpaw Mountains
in north-central Montana. WulfF (1964) described “shoestring sandstones” which he interpreted
as deltaic distributary channels in the Bearpaw Shale in the Lake Basin area (-60 km southeast of
Harlowton), Braun (1982) commented on the nature of the Judith River-Bearpaw Shale transition
in north-central Montana. Previous workers noted that the Bearpaw Shale was deposited by a
transgression [T9 transgression of Kaufman (1977)] of the Cretaceous Interior Seaway (Gill and
Cobban, 1973, Rogers, 1993).
Woman’s Pocket Anticline Section Stratigraphic/Sedimentologic Observations
The Bearpaw Shale is approximately 260 m thick in the WPA section. It forms a large covered
valley with virtually no exposure. Based on exposures of the Bearpaw Shale elsewhere, I infer
that this covered interval is probably black shale.
Shawmut Anticline Section Stratigraphic/Sedimentologic Observations
The Bearpaw Shale is present in a large grassy valley in the SA section It is approximately 350
m thick in the Shawmut Anticline (381-728m), though this thickness may be inaccurate due to
lack of outcrop over a large area It is possible that the shale was structurally thickened and my
estimate of stratigraphie thickness is too high. Only one sandy interval is exposed in the lower
Bearpaw Shale (479-48 Im). This interval consists of fine-grained, poorly exposed sandstone and
medium-grained, poorly exposed sandstone beds that are separated by 1 m of cover. The rest of
the Bearpaw Shale is covered until the base of the overlying Leimep Sandstone. I infer that the
covered interval is predominantly organic-rich shale.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 0 Bearpaw Shale Paleocurrent Indicators
I measured the attitude of trough cross-bed foresets in the sandstone units from the lower
Bearpaw Shale in the SA section (n=17. Fig. 9). The trend of restored dip directions is to the
southeast. I interpret friis trend to reflect the longshore drift direction.
Bearpaw Shale Stratigraphic/Sedimentologic Interpretations
The Bearpaw Shale forms a basinwide westward-thinning wedge within the Cretaceous Interior
Seaway (Braun, 1982). My interpretation is that the dark, frssile shale of the Bearpaw Shale was
deposited in an offshore marine environment in both the WPA and SA sections. Hummocky
cross-stratified sandstone beds were probably deposited by storm events. Rogers (1993) noted
lag deposits at the base of the Bearpaw Shale in the type area of the Judith River Formation.
These lags were not observed in my field area, but a lag deposit is necessary to explain the
seemingly conformable relationship of marine shale over a coastal plain deposit. Battacharya and
Walker (1992) described an example o f‘subtle transgression’ from the Upper Cretaceous
Dunvagen Formation in Alberta and explained how this type of transition could easily be missed
in the stratigraphie record, particularly in regions of poor exposure such as my field area.
Lennep Sandstone
Previous Work
Stone and Calvert (1910) named the Lennep Sandstone for exposures near Lennep Station in the
Crazy Mountains Basin. They correctly correlated the Lennep Sandstone to the Fox Hills
Sandstone of eastern Montana and Wyoming, Gill and Cobban (1973) documented the regression
of the Cretaceous Interior Seaway during deposition of the Leimep-Fox Hills Sandstones. This
regression was termed the R9 regression by Kaufman (1977). Lepp and Flores (1980)
documented deltaic sedimentation in the Fox Hills Sandstone and Wheeler (1983) documented
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 1 barrier island sedimentation in the Fox Hills Sandstone of nordieastem Montana. Minimal work
has been conducted on the Lennep Sandstone in the Crazy Mountains Basin.
Woman s Pocket Anticline Section Stratigraphic/Sedimentologic Observations
The Lennep Sandstone is only 11m thick in the WPA section (553-564 m. Fig. 1 0 ). It is a fine- to
medium-grained, upward-coarsening sandstone. Rare bioturbation and hummocky cross
stratification are found at the base. Near the top are planar beds and local trough cross-beds.
Shawmut Anticline Section Stratigraphic/Sedimentologic Observations
TTie Lennep Sandstone is approximately 100 m thick in the SA section (728-831 m. Fig. 11). The
majority of the interval is poorly exposed black shale with abundant organic material. Several
fine to medium-grained, coarsening-upward sandstones are interbedded with the shale The
sandstone beds contain hummocky cross-stratification, most are bioturbated, and they are
generally full of organic material. A 0.5 m thick, medium-grained, trough cross-bedded
sandstone outcrops at 796.5 m (Fig. 11). Overlying this sandstone are 35 .5 m of bentonitic
variegated mudstone interbedded with lenticular sandstone (796.5-831, Fig. 11).
Lennep Sandstone Paleocurrent Indicators
Trough cross-bed foreset dip attitudes were measured from the SA section Lennep Sandstone
(n=l 14). Upon restoration, foreset dip directions cluster in the southeast. I attribute this mean
dip direction to reflect longshore drift (Fig 11). Trough cross-bed foreset dip attitudes firom the
upper Lennep Sandstone coastal plain deposits are included in the summed rose diagram. Their
dip directions trend eastward, probably as a result of fluvial transport directed away from the
fold-thrust belt
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 2 Lennep Sandstone Stratigraphic/Sedimentologic Interpretations
The Lennep Sandstone in the WPA section is thin, but shows a typical sequence of a regressive
beach (Reinson, 1977). Lower shoreface deposits are overlain by upper shoreface deposits,
which are overlain by a covered interval that I interpret to represent coastal plain deposition. I
interpret most of the Lennep Sandstone in the SA section to have been deposited in the lower
shoreface. Again, the regressive barrier island model of Reinson (1977) matches the observed
facies relationships from the Lennep Sandstone. The Galveston barrier island is an example of a
regressive barrier island (Davies et al 1971). The trough cross-bedded sandstone at 796 m is
interpreted to represent the shoreface based on the continental mudstone and coal above it and the
marine sandstones below, although it is much thinner than a shoreface sandstone should be
(Reinson, 1977). Above this is a poorly exposed interval of mudstone, siltstone, and coal that I
interpret to represent coastal plain deposits. Gill and Cobban (1973) documented the “Fox Hills
regression” as being the final regression of the Cretaceous Interior Seaway from Montana.
Hell Creek Formation
Previous Work
Brown (1907) named the Hell Creek Formation for exposures along Hell Creek in Garfield
County, Montana. The Hell Creek Formation is well studied in eastern Montana, but little work
has been done in the Crazy Mountains Basin. A majority of the literature available on the Hell
Creek Formation focuses on the location of the Cretaceous-Tertiary boundary or the paleontology
of the formation (e.g. Hurlbert and Archibald, 1995; Thompson and Arens, 1998; and White et
al., 1998). Few sedimentologic studies have been done (e.g. Connor, 1992). The Hell Creek
Formation is also known as the Lance Formation in earlier Crazy Mountains Basin work (Bowen,
1918 and Reeves, 1930).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 3 Woman’s Pocket Anticline Section Stratigraphic/Sedimentologic Observations
Only the lowermost 31 m of the Hell Creek Formation were measured in the WPA section due to
poor exposures above (564-595 m. Fig. 10). The Hell Creek Formation is the uppermost unit
preserved in the WPA section. The base of the formation is placed at the sandstone that overlies
the covered interval above the Lennep Sandstone (564 m. Fig. 10). The Hell Creek Formation
consists of several lenticular sandstone units interbedded with coal, mudstone, and siltstone. The
sandstones are upward-fining with trough cross-bedding at the base and ripple cross-stratification
at the top. A covered interval of 7.5 m overlies the uppermost sandstone (587.5-595 m, Fig 10)
and marks the top of the WPA section.
Shawmut Anticline Section Stratigraphic/Sedimentologic Observations
The Hell Creek Formation is approximately 400 m thick in the SA section (831-1230 m. Fig. 12).
It is predominantly covered, but there are two good exposures in the lower 100 m (831-840 m,
and 910-920 m. Fig 12). The lower exposure consists of variegated mudstone interbedded with
lenticular sandstone bodies. The mudstones have a “popcorn” texture and gypsum occurs in float.
The sandstone is upward-fining, with large trough cross-beds and convoluted bedding. It also
contains 0.5 cm diameter iron concretions. The exposure fi"om 910-920 m (Fig. 12) is similar to
below Sandstone is interbedded with mudstone. Hie upper sandstone is lenticular and upward-
fining. At its base is a mudstone intraclast “conglomerate”. Trough <^oss-bedding and
convoluted bedding are the predominant sedimentary structures in these sandstones.
Hell Creek Formation Paleocurrent Indicators
Restored foreset attitudes firom trough cross-bedded fluvial sandstones in the WPA section are
less obvious, but suggest transport to the southwest (n=39) (Fig. 10). Restored attitudes of trough
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 4 cross-bed foresets from fluvial sandstones in the SA section Hell Creek Formation show an
obvious southward trend (n=77) (Fig. 12). 1 infer that this trend reflects fluvial transport to the
south from a northern uplift.
Hell Creek Formation Stratigraphic/Sedimentologic Interpretations
I interpret the lower Hell Creek Formation to have been deposited within a coastal plain.
Sandstones of the lower Hell Creek are interpreted as fluvial channels based on the facies
relationships. An ancient analog of the Hell Creek Formation is the Devonian Battery Point
Sandstone in Quebec (Cant and Walker, 1976). These sandstones are upward-fining with trough
cross-beds representing the channel floor, tabular cross-beds representing point-bar accretion, and
ripple cross-stratification representing in-channel deposition. Overbank deposits with roots
overlie the sandstones. In the Hell Creek Formation, overbank deposits of siltstone and mudstone
are also present, with thin coal beds representing coal swamps on the coastal plain. The covered
upper interval of the SA section and unmeasured upper interval of the WPA section are presumed
to be similar fluvial channels, overbank deposits, and coal beds.
Bear Formation
Previous W ork
The Bear Formation was named by Simpson (1937) for exposures east of Bear Butte, in the
northeastern Crazy Mountains Basin. It is correlative to the Tullock Member of the Fort Union
Formation of eastern Montana and Wyoming. Most of the work done on the Bear Formation has
been paleontological, focusing on the mammalian and molluscan feunas found in it (Hartman and
Krause, 1993). The Tullock Formation has been extensively studied in eastern Montana and
Wyoming due to its coal content, namely in the Tongue River, Powder River, and Williston
Basins (Sholes, 1992 and references therein).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 5 Shawmut Anticline Section Stratigraphic/Sedimentologic Observations
The Bear Formation is 251 m thick in the SA section (1231-1482 m, Fig. 13). Only the
lowermost 140 m are well-exposed. The upper 110 m are poorly exposed. In the exposed lower
portion, poorly exposed siltstone is predominant and interbedded with mudstone and thin
sandstone beds. The sandstones contain trough cross-stratification, tabular cross-stratification,
ripple cross-stratification, or are massively bedded (Fig 13). Some sandstone beds are also soft-
sediment deformed. Sandstone beds generally fine upward, but some beds appear to coarsen
upward. Organic material and root casts are common in the upper part of the exposed section.
Highway 191 Section Stratigraphic/Sedimentologic Observations
The Bear Formation is approximately 190 m thick in the Highway 191 section (Fig. 14). Terrace
gravels truncate an unknown thickness of the basal Bear Formation, so this measured thickness is
a minimum. A roadcut along Highway 191 offers 90 m of excellent exposure. The Bear
Formation consists of fine- to medium-grained sandstone interbedded with siltstone, shale, and
thin coal beds in the Highway 191 section. Some sandstones have trough cross-stratification,
tabular cross-stratification, soft-sediment-deformation, and root casts. Leaf imprints and large
fossil wood fiagtnents are very common. An approximately 96 m thick covered interval makes
up the upper part of the Bear Formation in the Hwy 191 section (88-184 m. Fig. 14). A 4 m thick
sandstone crops out from 129.5-133.5 m (Fig 14). This sandstone is medium-grained and has
low-angle cross-bedding.
Bear Formation Paleocurrent Indicators
Restored trough cross-bed dip directions in the SA section Bear Formation indicate a strong trend
to the south (n=122. Fig. 13), as in the Hell Creek Formation. Restored trough cross-bed dip
directions from the 191 section Bear Formation indicate a strong trend to the southeast (n=144.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 6 Fig. 14). I interpret these restored trough cross-beds to indicate the downstream direction of
fluvial transport.
Bear Formation Stratigraphic/Sedimentologic Interpretations
I interpret the Bear Formation to have been deposited within a fluvial plain. The SA and 191
sections both contain what I interpret to be sandy meandering channel deposits as well as
overbank deposits and crevasse-splay deposits. These interpretations are based on comparison to
an ancient analog, the Old Red Sandstone which also contains crevasse-splay deposits, which are
generally less than 1 m thick and commonly upward-fining (Allen, 1964). Crevasse-splay
deposits represent breeching of levees. Coal deposits in the well-exposed roadcut of the Hwy 191
section suggest development of swamps on the fluvial plain. Detrital organic material attests to
the abundant vegetation this fluvial plain must have had.
Lebo Formation
Previous Work
Stone and Calvert (1910) named the Lebo Formation for exposures near Lebo, MT in the Crazy
Mountains Basin. The Lebo Formation of the Crazy Mountains Basin is correlative to the Lebo
Member of the Fort Union Formation of eastern Montana and Wyoming. Very little
sedimentological work has been done on the Lebo Formation in the Crazy Mountains Basin,
although it has been fairly well studied in Eastern Montana and Wyoming (Sholes, 1992 and
references therein).
Shawmut Anticline Section Stratigraphic/Sedimentologic Observations
The Lebo Formation in the Shawmut Anticline is about 607 m thick (1482-2089 m. Fig. 15). It is
poorly exposed except at the base. Exposure from 1482-1550 m shows two thick sandstone units
separated by a covered interval (Fig. 15) The basal sandstone is 15 m thick (1482-1513 m. Fig.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 7 15). It contains abundant high-angle, meter-scale trough cross-beds as well as soft-sediment
deformation. A 50 m thick poorly exposed brown siltstone to greenish-brown mudstone interval
overlies this sandstone (1498-1548 m. Fig. 15). This is overlain by a 9 m thick, coarse-grained
sandstone (1548-1557 m. Fig 15) This sandstone has high-angle trough cross-stratification and
soft-sediment-deformation. Mud intraclasts and fossil wood fragments are very common This
upper sandstone is overlain by a 532 m thick covered interval (1557-2089 m. Fig 15). Very poor
exposures of the upper Lebo Formation indicate that variegated mudstones and siltstones are the
predominant rock type.
Highway 191 Section Stratigraphic/Sedimentologic Observations
The Lebo Formation is approximately 706 m thick in the Hwy 191 section (184-890 m. Fig. 16).
The base of the Lebo Formation in the Hwy 191 section contains several lenticular sandstone
bodies (Fig 50). A fine- to medium-grained, trough cross-stratified and tabular cross-stratified
sandstone with abundant large ( ~ 2 0 cm long) fossil wood fragments and smaller organic material
forms the base of the Lebo Formation (184 5-188 5 m. Fig. 16) Wood fragments decrease
upward in this smidstone. A covered interval overlies this sandstone from 188.5-281 m (Fig. 16).
Upward-fining sandstone beds, thin sandstone beds, mudstone, and siltstone all occur above this
covered interval (281-385 m. Fig. 16). A roadcut from approximately 520-565 m offers excellent
exposure of a portion of the upper Lebo Formation. From the roadcut to the covered interval,
fine- to medium-grained upward-fining sandstones with trough cross-stratification, tabular cross-
stratification, ripple cross-stratification, root casts, oscillation ripple marks, and organic detritus
are interbedded with gray siltstone and mudstone. The upper 125 m of the Lebo Formation are
poorly exposed (765-890 m. Fig. 16) until the base of the Melville Formation (890 m. Fig 16).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 8 Lebo Formation Paleocurrent Indicators
The restored attitudes of trough cross-bed foresets firom the Lebo Formation in the SA section
appear to be mostly random, with a cluster of restored dip directions plotting to the southeast
(n=l 14, Fig 15). Restored dip directions from trough cross-beds from the 191 section Lebo
Formation cluster to the southeast also (n=100. Fig 16). This southeast trend from restored dip
directions is interpreted to be the direction of channel transport. The cause of this southeast trend
may have been uplift to the north and subsidence of the Crazy Mountains Basin.
Lebo Formation Stratigraphic/Sedimentologic Interpretations
I interpret the Lebo Formation to be deposited on a fluvial plain, much like the Bear Formation.
Individual facies suggest predominantly crevasse-splay deposits as described by Collinson
(1978). The interpreted crevasse-splay deposits exhibit features indicative of rapid
sedimentation, such as ripple cross-stratification and graded bedding. The abundant fossil
vegetation and coal beds indicate the vegetated nature of this fluvial plain. The Old Red
Sandstone as described and interpreted by Allen (1964) is a suitable ancient analog for the
sedimentology of the Lebo Formation.
Melville Formation
Previous Work
Simpson (1937) named the Melville Formation for exposures near Melville, Montana in the
Crazy Mountains Basin. It is correlative with the Tongue River member of the Fort Union
Formation. This unit is actively studied in the Crazy Mountains Basin due to the mammalian
fauna that it contains (Hartman and Krause, 1993). Little sedimentologic work has been done on
this formation. The Tongue River Formation has been studied in eastern Montana (e.g. Whipkey
et al., 1991; and Sholes, 1992 and references therein).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 9 Shawmut Anticline Section Stratigraphic/Sedimentologic Observations
Only the lowermost 8 m of the Melville Formation were measured in the SA section due to poor
exposures above the base (2084-2092 m. Fig. 17). The thickness of the Melville Formation in the
Crazy Mountains Basin area is estimated at 1500 m thick (Hartman and Krause, 1993). Most of
the upper part of the formation has been eroded in the northeastern Crazy Mountains Basin. The
SA section Melville Formation consists of two lenticular sandstone beds interbedded with coal
and gray shale. The lowermost sandstone (2084-2085 m) has ripple cross-stratification and the
upper sandstone (2089-2090 m) is upward-fining and has tabular cross-stratification and trough
cross-stratification with some soft-sediment deformation (Fig 17). Root casts are common, as is
fossil vegetation. Several large wood fragments are found at the top of the upper sandstone bed.
Highway 191 Section Stratigraphic/Sedimentologic Observations
The Melville Formation in the Highway 191 section is similar to the SA section. Only the basal
10 m were measured due to poor exposure in the upper part of the formation (889-899 m. Fig
17). A laterally extensive, 7 m thick sandstone outcrops at the base. This sandstone has trough
cross-stratification, tabular cross-stratification, planar bedding, and soft-sediment deformation.
This sandstone is overlain by 3 m of thin sandstone interbedded with light gray mudstone. Fossil
plant material and wood fragments are common throughout the measured interval.
Melville Formation Paleocurrent Indicators
Restored dip directions in trough cross-beds from the 191 section Melville Formation trend to the
northeast (Fig 17). Restored dip directions in trough cross-beds from the SA section trend to the
north. Wood fragments on bedding planes from the SA section Melville Formation are also
aligned north-south. I interpret these restored trough limb dip directions to reflect northward flow
from the uplifting Beartooth Mountains into the Crazy Mountains Basin.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 0 Melville Formation Stratigraphic/Sedimentologic Interpretations
I interpret the Melville Formation to be a fluvial plain deposit. The basal sandstones are
interpreted as sandy meandering stream channels. Again, the Old Red Sandstone of the Anglo-
Welsh Basin is a good ancient analog to the Melville Formation, where I interpret the upper
sandstone and mudstone to be overbank deposits within the floodplain.
Table 7 is a summary of the inferred depositional environments, paleocurrents, and tectonic
interpretations for each formation. Figure 18 is a schematic diagram of the measured sections and
their inferred environments of deposition.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 1 SANDSTONE PROVENANCE OBSERVATIONS
Table 4 is a collection of the complete point-count data set. Table 5 is a collection of the
normalized and recalculated data used in the ternary diagrams. Each formation has a QtFL,
QmFLt, QmPK, and QpLvLsm diagram. It is important to note that by plotting sandstone
samples on the ternary diagrams of Dickinson and Suczek (1979) and Dickinson et al (1983), I
am not implying a particular tectonic setting for the sandstone samples, but rather I am simply
using the ternary diagrams as a way to compare sandstone compositions to each other.
Eagle Formation Provenance Observations
Nine sandstone thin-sections from the Eagle Formation were point-counted, three from the WPA
section and six from the SA section. Sandstone of the Eagle Formation is dominated by stable
grains. Monocrystalline quartz is the most common constituent, having a ()mFLt%Qm from 49-
90%. All samples have QtFL%F of 25.3% or less (Table 4). All samples contain <20% cement +
matrix relative to the total grain population (500 counts). The sandstones of the Eagle formation
show compositional variations by stratigraphie position and very little compositional variation
between the sections. The sandstone samples from the basal Virgelle Swdstone Member (1-Eag-
1 and 3-Eag-l) and sandstones from the uppermost sandstone of the Eagle Formation (1-Eag-lO
and 3-Eag-2) plot similarly. Both groups occupy the recycled orogen field or the adjacent
transitional continental field of Dickinson et al .’s (1983) (JtFL diagram and the ‘mixed’ field of
the QmFLt diagram (Figs. 19a and 19b). Sandstones from the middle-upper Virgelle Sandstone
Member (l-Eag-2, 4, and 5 and 3-Eag-3) plot in the craton interior field or adjacent to it in the
recycled orogen field of the QtFL diagram (Fig. 19a) and the quartzose recycled field of the
QmFLt diagram (Fig. 19b, Dickinson et al., 1988). Sample l-Eag- 8 , from the middle sandstone
of the Eagle Fm in the SA section plots between these 2 groups of sandstones (Figs. 19a and 19b)
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 2 Claggett Formation Provenance Observations
Five sandstone thin sections were collected but only one sample (1-Eag-l 1) from the lower
Claggett Formation of the SA section was point-counted (Table 4). The other samples are
increasingly fine-grained (silty), quartz-rich, and carbonate cemented and replaced These
samples likely would not have yielded accurate results of the true sandstone composition. 1 -Eag-
11 is compositionally very similar to the Eagle Formation sandstones. It is predominantly Qm
and chert (QtFL%Qt 85%). ()tFL%F is less than 10% and QtFL%L is less than 6 %. It has <4%
matrix relative to the total grain population and no observed cement. 1-Eag-l 1 plots in the
recycled orogen field of Dickinson et al.’s (1983) QtFL diagram (Fig 19a) and the quartzose
recycled field on the QmFLt diagram (Fig 19b). 1-Eag-l 1 plots in the increasingly mature field
of the QmPK diagram (Fig. 19c).
Judith River Formation Provenance Observations
Eight sandstone thin-sections from the Judith River Formation were point-counted, one from the
WPA section and seven from the SA section. These samples will be described as being either
from the lower Judith River Formation (1-Jr-l and 2) or the upper Judith River Formation (l-JR-5
through 11 and 3-JR-l) (Table 4). Samples from the lower Judith River Formation have a
QmFLt%Qm of between 43-46%. They are similar to samples of the Eagle and Claggett, but
have a higher QtFL%L (Table 5). Samples from the lower Judith River Formation contain <10%
cement + matrix relative to the total grain population The lower Judith River samples plot in the
recycled orogen field of Dickinson et al. ’s (1983) QtFL diagram (Fig. 20a) and in the ‘mixed’ or
transitional recycled field of the QmFLt diagrmn (Fig. 20b). They plot toward increasing stability
on the QmPK diagram (Fig. 20c). Samples from the upper Judith River Formation are
compositionally different from the lower Judith River Formation samples (Table 5). Feldspars
are predominantly euhedral plagioclase grains and lithics are predominantly andesitic rock
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 3 fragments. The upper Judith River samples plot in the undissected and transitional volcanic arc
fields of both the QtFL and QmFLt diagrams and in arc related fields of both the QmPK and
QpLvLsm diagrams (Figs. 20a, b, c, and d). Sample 3-JR-l is anomalous to other upper Judith
River Sandstones (Figs. 20a, b, c, and d).
Bearpaw Shale Provenance Observations
One sample was point-counted from the SA section Bearpaw Shale (Table 4). Sample l-BP-2
has a QtFL%Qt of 59%. Calcite cement + matrix make up 16% of the sample relative to the total
grain population. This sample plots in the recycled orogen field of the C^FL diagram and in the
mixed field next to the recycled orogen field of the QmFLt diagram (Figs. 2 la and b).
Lennep Sandstone Provenance Observations
Four sandstone thin-sections were point-counted from the Lennep Sandstone of the SA section.
Sample 1-Len-l is compositionally different from l-Len-2, 3, and 4 (Table 5), 1-Len-l has
roughly equal percentages of QmFLt%Qm, QmFLt%F, and QmFLt%Lt (Table 5). It has 20%
cmt + matrix relative to the total grain population. 1-Len-l plots in the dissected arc field of both
the QtFL and QmFLt diagrams of Dickinson et al. (1983, Figs. 2 la and b). Lithic volcanic grains
and Plagioclase dominate samples from the upper Lennep Sandstone (l-Len-2, 3, and 4).
QmFLt%Qm is never higher than 8 %. Cement + matrix varies from 17-23% of the total grain
population. Sample l-Len-2 plots in the undissected arc field of the QtFL diagram (Fig. 21a).
The other upper Lennep Sandstone samples plot in the transitional arc field of the QtFL diagram
(Fig. 21a). All upper Lennep Sandstones plot in the transitional arc field of the QmFLt diagram
(Fig. 21b) and in the arc orogen field o f the QpLvLsm diagram (Fig. 21c).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 4 Hell Creek Formation Provenance Observations
Five sandstone thin-sections were point-counted from the Hell Creek Formation, two from the
WPA section and three from the SA section. No samples were collected from the upper several
hundred meters of the formation due to poor exposure. QtFL%Qt ranges from 42-49% in these
samples. This is the first appearance of significant quantities of XBCO3 across the field area and
throughout the formation (Table 4). The Hell Creek Formation samples have 22% or less ant +
matrix relative to the total grain population (Table 4). These samples plot closely on all ternary
diagrams except for the ()pLvLsm diagram. The samples plot in the recycled orogen field of the
QtFL diagrams (Fig. 22a). In the QmFLt diagram, all samples plot in the dissected arc field or
the mixed field (Fig 22b).
Bear Formation Provenance Observations
Five sandstone thin-sections were point-counted from the Bear Formation, three from the 191
section, and two from the SA section. Sample 2-JR-5 from the 191 section was reported to be a
quartz syenite sill by Hartman and Krause (1993). In hand sample, it does appear to be an
igneous rock. However this bed exhibits cross-bedding in outcrop and contains Lv fragments in
thin section. Nonetheless, this sample is anomalous. All samples except 2-JR-5 have QtFL%Qt
ranging from 54-59%. matrix is <21% relative to the total grain population in all samples. The samples from the Bear Formation plot in the recycled orogenic field of Dickinson et al.’s (1983) QtFL diagram (Fig. 23a). Samples from the SA section (1-Tul-l and 3) plot in the transitional recycled orogen field of the QmFLt diagram while samples from the 191 section (2-JR-l and 3) plot in the mixed field (Fig 23b). All samples except l-Tul-3 plot in the arc orogen field of the QpLvLsm diagram (Fig 23d). Its QpLvLsm%Lsm of 87% places it in the collision orogen field Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 5 Lebo Formation Provenance Observations Eight sandstone thin-sections were point-counted from the Lebo Formation, Two samples are from the lower Lebo Formation in the SA section and six are from the entire 191 section The lower Lebo Formation samples (l-Leb-3 and 1 and 2-Len-l) are very similar. QmFLt%Qm is about 9%, QmFLt%F ranges from 30-33%, and QmFLt%Lt is about 58%. The lower Lebo samples have <7% cement + matrix. These 3 samples plot in the transitional arc field of both the QtFL and QmFLt diagrams of Dickinson et ai. (1983, Figs. 24a and b). They plot in the arc orogen of both the QpLvLsm and QmPK diagrams (Figs. 24c and d). The upper Lebo sandstones have increasingly higher QmPK%Q and QpLvLsm%Lsm moving upsection. QmPK%P and QmPK%K decrease upsection. XBCO 3 forms between 1 and 7% of the total grain population (Table 4). Cement + matrix is 26% or less in the upper Lebo sandstone samples. All samples plot in the recycled orogenic field of the QtFL diagram (Fig. 24a). All samples but 2-HC-3 plot in the transitional recycled orogen of the QmFLt diagram (Fig 24b). 2-HC-3 plots in the dissected arc field. The samples do not plot tightly on the QmPK or QpLvLsm diagrams, reflecting an increase in Qm and Lsm content upsection (Figs. 24c and d) Melville Formation Provenance Observations Three sandstone thin-sections were point-counted from the lower Melville Formation, one from the SA section, and two from the 191 section. All samples have a QtFL%Qt of between 41-60% and ()tFL%L from 41-60%. Cement + matrix is <23% of the total grain population in all samples. The lower Melville sandstones plot in the recycled orogen field of the Dickinson et al. (1983) QtFL diagram and in the transitional recycled orogen field of the QmFLt diagram (Figs. 25a and b). Samples plot toward the increasingly stable of the QmPK diagram and in or near the collision orogen field of the QpLvLsm diagram (Figs. 25c and d). Figure 26 shows the high Lm proportions in the Melville samples relative to the other formations in a LvLsLm ternary diagram Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 6 PROVENANCE INTERPRETATIONS Several provenance interpretations can be made based on the sandstone compositions of each formation. The Eagle Formation has a high QtFL%Qt (including Qm, Cht, and Qp) and rare lithic and feldspar grains reflecting the compositional maturity of the formation. I interpret that the Eagle Sandstones were derived from recycled sedimentary sources, prior to the initiation of major volcanism in the Elkhom Mountains Volcanics. Stone and Calvert (1910) noted the presence of andesite-clast bearing sandstone lenses in the Eagle Formation to the west and northwest of the Crazy Mountains Basin. Stratigraphie variations of sandstone compositions in the Eagle Formation are apparent. The Virgelle Sandstone Member samples are more quartzose than the other samples. One reason for this may be that only stable quartz grains were able to withstand significant reworking associated with the high-energy upper shoreface environment. The point-counted sample of the Claggett Formation is very similar to the Eagle Formation in composition (Figs. 19a-d); thus my interpretation of a recycled sedimentary source is also the same. Initiation of the Elkhom Mountains Volcanics was established by this time, resulting in bentonite deposition in the marine shales (i.e., the Ardmore Bentonite in the lower Claggett Formation of eastern Montana, Wyoming, and the Dakotas) and volcanic tuffs in their nonmarine equivalents (Gill and Cobban, 1973). However, the interpreted offshore marine sandstones of the Claggett Formation are quartzose, indicating that coarse volcanic detritus was limited to continental and nearshore marine environments. The nearshore marine lower Judith River Formation sandstones have higher lithic mid felsic proportions than similar nearshore marine sandstones of the Eagle and Claggett Formations. I interpret the provenance of the lower Judith River sandstones to be recycled sedimentary rocks carried southward by longshore drift. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 7 A volcanic component (probably from the Elkhom Mountains Volcanics and the ‘igneous member of the Livingston Group’) is also present, resulting in higher lithic and felsic percents at the expense of Qm (Table 5). The upper Judith River Formation sandstones are compositionally very different from the lower sandstones. They are dominated by euhedral plagioclase grains and lithic volcanic (andésite) grains. I interpret the upper Judith River Formation sandstones to be derived from the Elkhom Mountains Volcanics (via the Livingston Group) and also derived from the igneous member of the Livingston Formation’ of Parsons and Stow (1942). The Livingston Group is a well-documented fluvial/deltaic complex in the western end of the Crazy Mountains Basin. Sims (1969) documented northeast-trending paleocurrent indicators in the Livingston Group (see also; Skipp and McGrew, 1972; Roberts, 1972). The Livingston Group supplied volcanic detritus to the Cretaceous Interior Seaway and associated Montana Group strata (McMannis, 1955) but perhaps the area near the WPA section had a different sediment source. The one sample counted from the Bearpaw Shale Formation plots similarly to the Eagle and Claggett marine sandstones (Fig. 27). I interpret its provenance to be a mixture of volcanic and recycled sedimentary sources due to longshore drift along the Cretaceous Interior Seaway. The sample counted from the lower Lennep Sandstone (1-Len-l) is also interpreted as having a mixed volcanic/recycled sedimentary provenance due to longshore drift. The upper Lennep Sandstone samples are dominated by lithic volcanic (andésite) and euhedral plagioclase grains that were probably carried eastward from the Elkhom Mountains Volcanics by fluvial channels to the coast of the Cretaceous Interior Seaway. Lower Hell Creek Formation sandstones plot tightly, except for their Lsm and Lv proportions (Figs. 22a-d). Cannibalized sedimentary sources to the north are the inferred provenance for the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 8 Hell Creek Formation. Volcanic debris would be included in these recycled sedimentary rocks. This may explain why the contents of Ls and Lv differ so drastically from sample to sample, yet the total lithic component is quite similar. Another explanation might be due to volcanic activity in the Central Montana Alkalic Province, which is north of the Crazy Mountains Basin This volcanic activity and associated uplift would have supplied both sedimentary and volcanic sources to the Hell Creek Formation. The samples fr^om the Bear Formation are compositionally similar to the Hell Creek samples They are also interpreted as being derived from recycled sedimentary rocks with some influence from a volcanic source. The volcanic clasts may be recycled or may be derived from the Central Montana Alkalic Province to the north. The samples from the lower Lebo Formation contain high proportions of volcanic (andesitic) and felsic (plagioclase and K-spar) clasts. I interpret these to be derived from a volcanic source to the north or northwest, possibly within the Central Montana Alkalic Province. Samples from the upper Lebo Formation in the 191 section become increasingly quartz- and lithic sedimentary-rich upsection. I infer this to represent a relative decrease in volcanic debris supplied to the Lebo Formation and a relative increase in sedimentary material supplied to the Lebo Formation. The lower Melville Formation sandstones are predominantly lithic sedimentary and lithic metamorphic-rich. The abundance of Lm clasts relative to the other formations is significant (Fig. 26). The abundance of biotite is also significant (Table 4). Biotite is an Fe-bearing, dense mineral Its presence indicates proximity to a biotite-bearing source (D. Winston, 2000 pers. comm ). The event that supplied this material is interpreted to be the uplift of the Beartooth Mountains and exposure of the Precambrian basement core. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 9 TERRACE GRAVEL STUDIES Gravels overlie Cretaceous through early Tertiary strata within and around the northeastern Crazy Mountains basin. The contact is marked by a sharp angular unconformity. These gravels were incorporated into early studies of the area (Bowen, 1918 and Reeves, 1930) and were identified as “terrace gravels”. They will be referred to as such in this paper. They are inferred to be post- Eocene, possibly Oligocene or Miocene in age based on the presence of Eocene volcanic clasts in the gravels and the level of the gravels above their source rocks (Reynolds, M , 2000 pers. comm ): The terrace gravels are found adjacent to the local mountain ranges, including the Little Belt, Big Snowy, Crazy, and Beartooth Mountains (Fig. 28). They generally slope toward the plains at 1-2 degrees. They thicken from a meter or less out on the plains to about 25 m proximal to the mountains. Terrace gravels were studied in seven locations throughout the area in order to study the provenance of the gravels (Fig. 28). Terrace Gravel Compositions and Paleocurrent Data The terrace gravels were classified into three groups based on their location; Gravel proximal to the Crazy Mountains (Sample Gr-5), gravels proximal to the Little Belt Mountains (Gr-1 and Gr- 2), and gravels along the Musselshell River (Gr-3, Gr-4, and Gr-7). These 3 groups have distinct compositions that can be related to their inferred provenance. Gr-5 was collected from the Patricia Douglas homestead, proximal to the Crazy Mountains (n=107. Fig. 28). It has a strong volcanic influence (Fig. 29) It contains 70% volcanic clasts, almost all of which are andésite porphyry. 29% of the clasts are sandstone, including daric gray, fine-grained sandstone and rusty medium-grained sandstone. The remaining 1% are white quartzite clasts. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 0 Gr-1 (n=168) and Gr-2 (n=133) were collected proximal to the Little Belt Mountains from exposures along county roads northwest of Harlowton (Fig. 28). Plotting these samples on a pie diagram shows the predominance of limestone clasts, fonning 93% of the combined total (Fig 29). Sandstone (probably derived from Jurassic or Early Cretaceous sedimentary rocks) makes up 5.5% of the combined total, while chert (probably derived from Paleozoic limestone) and quartzite compose the remaining 1.5% of the total clasts. Gr-3 (n=123), Gr-4 (n=132), and Gr-7 (n=63) were collected from 3 locations near the Musselshell River, intermediate between the Little Belt Mountains and Crazy Mountains (Fig. 28). The combined compositional plot of these intermediate gravels is shown in Figure 29. Limestone clasts dominate the samples, making up about 80% of the total. Volcanic clasts make up 10% of the total, with tiie remaining 10% being divided between sandstone, quartzite, chert, rhyolite, and vein quartz. Pebble imbrications were measured from Gr-4 and Gr-7 (Fig 30). Gr-4 shows a south and southeast trend, while Gr-7 shows a more random trend, presumably to the southwest. Imbrications were not measured from other locations but field notes indicate that transport was to the south from Gr-1 and Gr-2. Terrace Gravel Interpretations Gravel compositions and pebble imbrication data clearly indicate that gravels proximal to the Little Belts are composed of Paleozoic and Early Mesozoic strata; gravels proximal to the Crazy Mountains are composed of igneous clasts; and mixing of these sources occurred along the ancestral Musselshell River. This data indicate that the Little Belt, Big Snowy, and Crazy Mountains were certainly uplifted after post-middle Eocene time, possibly by Oligocene time Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 1 CONCLUSIONS Marine Deposits of the Montana Group The Eagle, Claggett, Judith River, Bearpaw, and Lennep Formations all contain strata interpreted to be from a marine environment. Gill and Cobban (1973) thoroughly document the presence of marine fossils in these units and their correlative formations throughout the Cretaceous Interior Seaway. 1 interpreted marine environments ranging from upper shoreface to offshore marine. The marine strata record marine transgressions and subsequent regressions of the Cretaceous Interior Seaway. T8 (Claggett) and T9 (Bearpaw) (Kaufrnan, 1977) are the major transgressions recognized in the field area (Fig 18), Paleocurrent directions are predominantly directed to the southeast in the interpreted marine strata. This probably reflects the major longshore drift direction. Southeast-directed longshore drift matches the position of the Cretaceous Interior Seaway shoreline during the Upper Cretaceous in the field area (McGookey et al., 1972). Modeling of circulation patterns in the Cretaceous Interior Seaway (Kump and Slingerland, 1999) and sedimentary investigations of marine strata in the Cretaceous Interior Seaway (e.g. Brain, 1993) record south-directed longshore drift directions (Fig 31). Modeling infers that cold water from the ancestral Arctic Ocean flowed southward along the western side of the Cretaceous Interior Seaway and warm water from the Tethys Sea flowed northward along the eastern side of the Cretaceous Interior Seaway, producing a counter-clockwise rotation. Apparently, the Cretaceous Interior Seaway was too narrow and shallow to have a circulation pattern dominated by the Coriolis effect, which would have produced a clockwise rotation (Kump and Slingerland, 1999). The inferred marine sandstones of the Montana Group have similar compositions (Fig. 27). These sandstones plot in the recycled orogen or mixed provenance fields in Dickinson et al.’s (1983) QtFL diagram. My interpretation is that recycled sediment from the fold-thrust belt to the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 2 west was initially carried eastward by fluvial channels on the coastal plain to the shore of the Cretaceous Interior Seaway. Longshore drift then carried this sediment toward the southeast. Volcanic detritus was not being shed into the central Montana foreland basin in significant quantities during deposition of the Eagle Formation (Latest Santonian-Campanian time). As a result. Eagle sandstones are more quartzose than other marine sandstones of the Montana Group. By 80 Ma, the Elkhom Mountains Volcanics were providing volcmic detritus to the foreland. This volcanic detritus traveled northeastward, via fluvial and deltaic channels into the Cretaceous Interior Seaway (Sims, 1969). Nearshore marine sandstones deposited after 80 Ma (the Judith River, Bearpaw, and Lennep Formations) have mixed sources from recycled sedimentary rocks (longshore drift) and volcanic rocks (deltaic). As such, they plot closer toward the lithic and feldspathic poles of the QtFL and QmFLt diagrams than sandstones deposited prior to 80 Ma (Fig. 27). Offshore sandstones of the Claggett and Bearpaw Formations are more quartzose than their fluvial equivalents because water-transported coarse-grained volcanic detritus failed to be transported into the offshore marine environment. Fig. 32 is a simple paleogeographic model of central Montana during Late Cretaceous sea-level highstands as inferred from the results of this study and previous worit in central Montana. Fluvial Deposits of the Montana Group The Eagle, Judith River, and Lennep Formations contain inferred fluvial sandstones that were deposited on the coastal plain during sea-level regressions of the Cretaceous Interior Seaway. No evidence for a ‘partitioned’ foreland basin during deposition of the Montmia Group appears to exist in my field area. Rather, the deposits seem to have been a continuous, eastward thinning wedge (Fig. 18). This model is different from Early Cretaceous foreland basin deposits (Kootenai-Blackleaf Formations) in southwestern Montana that suggest sedimentation within a partitioned foreland basin (Schwartz, 1981; DeCelles, 1986; Schwartz and DeCelles, 1988). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 3 Fluvial paleocurrent indicators in both the Judith River and Lennep formations are directed to the east, away from the fold-thrust belt. Fiorillo (1991) also documented east-trending paleocurrent indicator dip directions from the Judith River Formation in northeastern Wheatland County. These fluvial sandstones are lithic volcanic (andésite) and plagioclase-rich with very little quartz (Fig 33). This volcanic sediment is likely derived from the Elkhom Mountain Volcanics and the “igneous member of the Livingston formation” (McMannis, 1955). The WPA section Judith River Formation may have been sourced from recycled sedimentary rocks to the west rather than through the Livingston Group, as it does not contain Lv in the abundance of SA section samples. Fig 34 is a simple paleogeographic model of central Montana during a sea-level lowstand of the Cretaceous Interior Seaway. Hell Creek Formation Facies relationships within the Hell Creek Formation suggest that this unit was deposited on a coastal plain during the final regression of the Cretaceous Interior Seaway (R9 of Kaufman, 1977). Paleocurrent indicators are directed to the south. The cause of this shift in inferred paleocurrent flow directions from southeast and/or east to the south is well supported by the present data set. The following scenarios might account for these south-directed paleocurrent indicators; 1) Local uplift the north (ancestral Little Belt-Big Snowy Mountains) shed recycled sediment into the initially subsiding Crazy Mountains Basin, or; 2) The south-directed paleocurrent indicators reflect longitudinal drainage parallel to the fold-thrust belt, or; 3) Uplift to the north, possibly due to igneous activity in the Judith, Little Rocky, and Moccasin Mountains (Central Montana Alkalic Province), which were all active in late Maastrichtian time (Hearn et al., 1989). These southward trends contrast with northeast-directed paleocurrents measured by Dripps (1992) within the Hoppers Formation of the Livingston Group (Hell Creek correlative) in the western Crazy Mountains Basin and southeast-directed paleocurrent indicators in a ‘major Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 4 trunk drainage’ in northeastern Montana (Belt et al., 1997). They also contrast with paleocurrent indicators of underlying strata. If scenario 1 or 3 is true, an unconformity or disconformity might be expected at the base of the Hell Creek Formation. One was not observed in the field, but a more detailed study in areas of better exposure might reveal such an unconformity. Sandstone compositions for the Hell Creek Formation plot in the recycled orogen field of the QtFL diagram (Fig. 22a). My interpretation is that one o f the above scenarios is true, resulting in erosion and recycling of sedimentary rocks and/or volcanic rocks southward into the subsiding Crazy Mountains Basin. A dense minerals study in the Beartooth Mountains region by Stow (1946) indicated that the Crazy Mountains Basin might have been subsiding as early as the Late Maastrichtian. A more detailed study of the Hell Creek Formation where it is better exposed is needed to determine if foreland partitioning indeed began in central Montana by Late Maastrichtian time. Fig. 35 is a simple paleogeographic model of central Montana during deposition of the Hell Creek through Lebo Formations as inferred from the present study and previous work Bear Formation The Bear Formation is interpreted to represent fluvial plain deposition based on facies relationships. Restored paleocurrent indicators suggest south-directed transport, like the Hell Creek Formation. Sandstone compositions plot in the recycled orogen field of the QtFL diagram, indicating a source of recycled sedimentary rocks (Fig. 23a). The source of these Bear Formation sediments is unknown, but may be the same source area that supplied sediment to the Hell Creek Formation. Figure 34 is a simple paleogeographic model of south-central Montana during deposition of the Bear Formation as inferred from the results of this study. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 5 Lebo Formation Facies relationships within the Lebo Formation also suggest deposition on a fluvial plain. Paleocurrent indicators in the Lebo Formation are also generally directed southward. The basal sandstone is lithic volcanic-plagioclase-rich, with overlying sandstones becoming increasingly Qm and Ls-rich (Figs. 24c and d). The volcaniclastic basal sandstone is likely derived from the Central Montana Alkalic Province, as several igneous intrusions were active during deposition of the Lebo Formation (Heam et al., 1989). These intrusions are found in the Little Rocky, Moccasin, and Judith Mountains, to the north of this field area. TTie mature sandstones of the upper Lebo in the Highway 191 section may reflect derivation from uplifted recycled sedimentary rocks as volcanism ceased in the Central Montana Alkalic Province or possibly derivation from recycled sedimentary rocks to the northwest. Again, note Figure 34. Melville Formation Like the other Paleocene formations, facies relationships suggest the Melville Formation was deposited on a fluvial plain However, a paleocurrent shift and changing sandstone composition indicate a tectonic reorganization after deposition of the Hell Creek-Lebo Formations. Paleocurrent indicators in the Melville are directed northward. The sandstones plot in the lithic recycled orogen field of the QtFL diagram (Fig. 25a). They are compositionally different fix»m the Hell Creek-Lebo Formations in that metamorphic grains form a significant percentage (12- 50%, Table 5) of the lithic grain finmework (Fig. 26). Qm, Biot, and Ls grains are also common in the lower Melville Formation. I interpret the north-directed paleocurrents and compositional change to be due to the Beartooth Mountains uplift. The Archean basement was apparently exposed by this time Interestingly, no unconformity was observed at the base of the Melville Formation. More detailed field studies might identify this unconformity. Studying the Hell Creek through Melville formations on the south side of the Crazy Mountains Basin might yield Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 6 more insight into the unroofing of the Beartooth Mountains and subsidence of the Crazy Mountains Basin in Late Maastrichtian through Late Paleocene time. Figure 36 is a simple paleogeographic model during deposition of the lower Melville Formation as inferred from the interpretations of the present study and previous woric. Terrace Gravels I interpret the terrace gravels to be deposited as a result of a period of Eocene through post- Eocene uplift in central Montana. This interpretation is based on several lines of evidence; 1) the terrace gravels rest on underlying strata with an a i^ la r unconformity; 2) the compositions of the gravels match the bedrock of the mountains they flank; 3) Pebble imbrications in the gravels indicate transport away from the mountains they flank, and; 4) Reynolds (1980) reported on the age of the terrace gravels to the northeast of the Little Belt Mountains. He found Eocene volcanic clasts in the gravels, indicating the gravels are younger than the Eocene. The apparent lack of Montana Group sandstones in terrace gravels adjacent to the Little Belt Mountains is a possible indication that these sandstones were eroded off of the Little Belt Mountains prior to this Eocene- post-Eocene uplift, for example, during deposition of the Hell Creek-Lebo Formations. Figure 28 is a simple paleogeographic model of south-central Montana during deposition of the terrace gravels as inferred from the results of this study study. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 7 REFERENCES Allen, J.R.L., Studies in fluviatile sedimentation; Six cyclothems from the Lower Old Red Sandstone, Anglo-Welsh Basin: Sedimentology, v. 3, p. 163-198. Battacharya, J.P., and Walker, R G , 1992, Deltas, in: (Walker, R.G., and James, N P , eds.) Facies Models: response to sea-level change, p, 157-178. Belt, E S , Hicks, J F , and Murphy, D A , 1997, A pre-Lancian regional unconformity and its relationship to Hell Creek paleogeography in southeastern Montana, in. Contributions to Geology, v. 31, n. 2, University of Wyoming. Bowen, C F., 1915, The Stratigraphy of the Montana Group, with special reference to the position and age of the Judith River Formation in north central Montana: U.S.G.S. Professional Paper 90-1, p. 95-153. Bowen, C F ., 1918, Anticlines in a part of the Musselshell Valley, Musselshell, Meagher, and Sweetgrass Counties, Montana: U.S.G.S. Bulletin 691-F, p. 185-209. Brain, T H , 1993, Facies analysis and depositional environments of the Late Cretaceous (Campanian) Hatfield Sandstone Member of the Haystack Mountains Formation, Rawlins, WY [Master’s Thesis]: Laramie, WY, University of Wyoming, p. 1-115. Braun, R E , 1982, Stratigraphy and sedimentology of the transition between the Judith River and Bearpaw Formations (Cretaceous), north-central Montana: Geol. Soc. of America Abstracts w/ Programs, v. 14, n. 6, p. 304. Brown, B B , 1907, The Hell Creek beds of the upper Cretaceous of Montana; their relation to contiguous deposits, with faunal and floral lists, and a discussion of their correlation: Bulletin of the Amer. Museum of Nat. Hist V 23, p. 823-845. Cant, D J , and Walker, R G , 1976, Fluvial processes and facies sequences in the sandy braided South Saskatchewan River, Canada: Sedimentology, v. 25, p. 625-648. Clifton, H E , Hunter, R E , and Phillips, R L , 1971, Depositional structures and processes in the non-barred high-energy nearshore: Journal of Sedimentary Petrology, v. 41, p 651-670. Collinson, J D , 1978, Alluvial Sediments, in: (Reading, H G , ed.) Sedimentary environments and facies, Oxford: Blackwell Scientific Publications, p. 20-62. Connor, C W , 1992, The Lance Formation: petrography and stratigraphy. Powder River basin and nearby basins, Wyoming and Montana: U.S.G.S. Bulletin 1917-1, p. 11-117. Davies, D.K., Ethridge, F G , and Berg, R R , 1971, Recognition of barrier environments: A A P G Bulletin, v. 55, p. 550-565. DeCelles, P G , Langford, R P , and Schwartz, R.K., 1983, 2 new methods for paleocurrent determination from trough cross-stratification: Journal of Sed. P et, v. 53, n. 2, p. 629- 642 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 8 Decelles, P.G., 1986, Sedimentation in a tectonically partitioned, nonmarine foreland basin; The Lower Cretaceous Kootenai Formation, southwestern Montana: G S A Bulletin, v. 97, p. 911-931. Dickinson, W.R., 1970, Interpreting detrital modes ofgraywacke and arkose: Journal of Sed. Pet, V. 40, n 2, p . 695-707. Dickinson, W.R., and Suczek, C A , 1979, Plate tectonics and sandstone compositions: A A P G Bulletin, v. 63, n. 12, p 2164-2182 Dickinson, W.R., Beard, L.S., Brakenridge, G R , Eijavec, J L , Ferguson, R C , Inman, K F , Knepp, R A , Lindberg, F A , and Ryberg, P T , 1983, Provenance of North American Phanerozoic sandstones in relation to tectonic setting: G S A Bulletin, v. 94, n, 2, p. 222- 235. Dickinson, W R , Lawton, T F , and Inman, K F , 1986, Sandstone detrital modes, central Utah foreland region: Stratigraphie record of Cretaceous-Paleogene tectonic evolution: Journal of Sed. P et, v. 56, n 2, p. 276-293. Dripps, W.R., 1992, Sedimentological revision of the Hoppers and lower Fort Union Formations near Livingston, Montana [B A thesis]: Amherst, MA, Amherst College, p. 1-176. Fiorillo, A R , 1991, Taphonomy and depositional setting of Careless Creek Quarry (Judith River Formation), Wheatland County, Montana, U.S.A.: Palaeogeography, Palaeoclimatology, and Palaeoecology, v. 81, n 3-4, p. 281-311. Frey, R.W. (ed), 1975, The study of trace fossils: a synthesis of principles, problems, and procedures in ichnology: New York: Springer-Verlag, p. 1-562. Gazzi, P., 1966, Le arenie del flysch sopracretaceo dell’ Appennino modense: correlazini con il flysch di monghidoro: Mineralogica e Petrografica Acta, v. 12, p. 67-69. Gill, JR., and Cobban, W.A., 1973, Stratigraphy and geologic history of the Montana Group and equivalent rocks, Montana, Wyoming, and North and South Dakota: U.S.G.S. Prof. Paper 776, p . 1-37. Hamblin, A P , 1978, Sedimentology of a prograding shallow marine slope and shelf sequence. Upper Jurassic Femie-Kootenay transition, southern Front Ranges, [M.S. thesis] : McMaster University, p. 1-196. Harms, J C , Southard, J B , Spearing, D R., and Walker, R G , 1975, Depositional environments as interpreted from primary sedimentary strucutres and stratification sequences: S E P M , Tulsa, Short Course 2, p. 1-161. Hartman, J H , and Krause, D W , 1993, Cretaceous and Paleocene stratigraphy and paleontology of the Shawmut Anticline and the Crazy Mountains Basin, Montana: Road log and overview of recent investigations, in: (Hunter, V., ed.) 1993 Field Conference Guidebook, Old timers ’ rendezvous edition; Energy and mineral resources of central Montana, Montana Geological Society, p. 71-84. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 9 Heams, C.B. et al., (eds.) 1989, Montana High-Potassium Igneous Province Field Trip Guidebook: T346, 28**' International Geologic Congress, American Geophysical Union: Washington D C , p. 1-86. Hurlbert, S.H., and Archibald, J .D., 1995, No statistical support for sudden (or gradual) extinction of dinosaurs; Geology, v. 23, n. 10, p. 881-884 Ingersoll, R.V., Bullard, T F , Ford, R.L., Grimm, J.P., Pickle, J.D., and Sares, S.W., 1984, The effect of grain size on detrital modes: A test of the Gazzi-Dickinson point-counting method: Journal of Sed. P et, v. 54, p. 103-116. Jackson, J L , 1989, Evidence for the interaction of foreland uplift and thrust belt structures in the Little Belt and Castle Mountains, west-central Montana: G S A Abstracts w/ Programs, V. 21, n. 6, p. 137. Kaufinan, E.G., 1977, Geological and biological overview: Western Interior Cretaceous Basin: The Mountain Geologist, v. 14, n. 3-4, p. 75-99. Knetchel, M M , and Patterson, S H , 1956, Bentonite deposits in marine Cretaceous formations of the Hardin District, Montana and Wyoming: U.S.G.S. Bulletin v. 1023, p. 1-116. Kump, L.R. and Slingerland, R L , 1999, Circulation and stratification o f the early Turonian Western Interior Seaway and sensitivity to a variety of forcings, in: (Barrera, E. and Johnson, C C , eds.) Evolution of the Cretaceous Ocean-Climate System: G S A Special Paper 332, p. 181-190. Lepp, C L , and Flores, R M , 1980, Environmental-stratigraphic relationships of the Upper Cretaceous Fox Hills and Hell Creek Formations and Paleocene Fort Union Formation in northeastern Montana: G S A Abstracts with Programs, v. 12, n. 6, p. 278. McGookey, D P , Haun, J D , Hale, L A , Goodell, H G , McGubbin, D G , Weimer, R J , and Wulf, G R , 1972, Cretaceous System, in: (Mallory, W W , ed.) Geologic Atlas o f the Rocky Mountain Region, U Hirschfeld:S A, Denver, p. 190-228 McMannis, W J , 1955, Geology of the Bridget Range, Montana: G S A Bulletin v. 66, p. 1407- 1413. Meek, F.B, and Hayden, F V , 1856, Description of a new species of Acephala and Gastropoda from the Tertiary formations of Nebraska Territory, with some general remarks on the geology of the country about the sources of the Missouri River: Proc. of the Acad, for Natural Science, Philadelphia, v. 8, p. 111-126, Parsons, W.H. and Stow, M H , 1942, Origin and structural relationships of the igneous member of the Livingston Formation, Montana: Am. Geophys. Union Transactions, p. 344-345. Perry, W J , Nichols, D J , Dyman, T S , and Haley, C J , 1991, Sequential Laramide deformation of the Rocky Mountain Foreland of southwestern Montana, Wyoming, and north-central Colorado, in: (Thurman, CH., oà.) Application o f structural geology to mineral and energy resources o f the central and western United States, p. C1-C14. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 0 Reeves, F , 1930, Geology of the Big Snowy Mountains, Montana: U S .O S. Prof. Paper 165, P. 135-149. Reinson, G.E., 1979, Barrier Island Systems, in: (Walker, R G , ed.) Facies Models, p. 57-74. Reynolds, M. W , 1980, Tertiary gravels. Little Belt Mountains, Montana: U.S.G.S. Prof. Paper 1175, p. 78. Rice, D D , 1980, Coastal and deltaic sedimentation of Upper Cretaceous Eagle Sandstone: relation to shallow gas accumulations, north-central Montana: A A P G Bulletin, v 64, ■ n.3, p. 316-338. Roberts, A E , 1972, Cretaceous and Tertiary deposits and tectonic history, Livingston, southwestern Montana: U.S.G.S. Prof Paper 526-C. Rogers, R R , 1993, Marine facies in the Judith River Formation (Campanian) in the type area, north-central Montana, in: (Hunter, V., ed.) 1993 Field Conference Guidebook, Old timers ' rendezvous edition; Energy and mineral resources o f central Montana, Montana Geological Society, p. 255-268. Ryer, T A , 1977, Patterns of Cretaceous shallow-marine sedimentation, Coalville and Rockport areas, Utah; G S A Bulletin, v. 88, n 2, p. 177-188. Schwartz, R K , 1982, Broken Early Cretaceous foreland basin in southwestern Montana: Sedimentation related to tectonism, in: Powers, R.B. (ed). Geologic Studies of the Cordilleran Thrust Belt, V. I, Rocky Mountain Assoc, of Geologists, Denver, CO, p. 159-183. Schwartz, R.K., and DeCelles, P G , 1988, Cordilleran Foreland Basin evolution in response to interactive Cretaceous thrusting and foreland partitioning, southwestern Montana, in: G S A Memoir 171, p. 489-513. Sholes, M.A., (ed ), 1992, Coal Geolc^y of Montana, M B M G Spec. Publication 102: Butte, MT, p. 1-157 Simpson, G.G., 1937, The Fort Union Formation of the Crazy Mountain Field, Montana, and its mammalian founa. U.S. National Museum Bulletin 169, p. 1-287. Sims, J D , 1969, Stratigraphy and paleocurrents of the Livingston Group, northern Crazy Mountains, Montana: O.S.A. Special Paper, n. 121, p. 636. Skipp, B. and McGrew, L.W., 1972, The Upper Cretaceous Livingston Group of the western Crazy Mountains Basin, Montana, in: Crazy Mountains Basin, 21"^ Annual Field Conference, Montana Geol. Soc., p. 99-106. Stanton, T W , and Hatcher, JB , 1905, Geology and paleontology of the Judith River beds: U.S.G.S. Bulletin, v. 257, p. 1-128. Stone, R W , 1909, Coal near the Crazy Mountains, Montana: U S G S Bulletin 341, p. 78-91. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51 Stone, R.W., and Calvert, W R , 1910, Stratigraphie relations of the Livingston Formation of Montana; Econ. G eol, v. 5, p. 741-764. Stow, M H , 1939, Structure and origin of the Deer Creek volcanic rocks, Montana: O S . A. Bulletin, v. 50, pt. 2, p. 1927. Stow, M H , 1946, Dating sedimentation, vulcanism, and orogeny in the Beartooth Mountain region, Montana: G S A Bulletin, v. 57, n. 7, p. 675-685. Thompson, Anna, and Arens, N.C., 1998, Late Cretaceous flora changes; evidence for pre-impact terrestrial instability?: A A P G Bulletin, v. 82, n. 11, p. 2169. Weed, W.H., 1899, U.S.G.S. Geologic Atlas, Little Belt Mountains Folio (n. 56). Wheeler, K.L., 1983, Latest Cretaceous (Maastrichtian) barrier island sedimentation, northeastern Montana: G S A Abstracts with Programs, v. 15, n. 4, p. 226 Whipkey, C E , Cavaroc, V.V., and Flores, R M , 1991, Uplift of the Bighorn Mountains, Wyoming and Montana - A sandstone provenance study; U.S.G.S. Bulletin 1917-D, p. D1-D20 White, P D , Fastovsky, D E and Sheehan, P.M., 1998, Taphonomy and suggested structure of the dinosaurian assemblage of the Hell Creek Formation (Maastrichtian), eastern Montana and western Nortit Dakota; Palaios, v. 13; n. 1, p. 41-51 Witkind, I., Kleinkopf, M D , and Keefer, W R , 1970, Geologic and gravity evidence for a buried pluton. Little Belt Mountains, central Montana: U.S.G.S. Prof. Paper 700-B, p. B63-B65 Wulff, G R , 1964, Shoestring sandstone in Cretaceous Bearpaw Shale in central Montana: A.A.P.G. Bulletin, v. 48, n. 7, p 1196-1198. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 ch O ^ 5 2 i rsj ro kn «OA#^M»/* 3 0| 5*^eO"— Tt'tücor^r^eoff>u?r‘J^Jk/>kA»o€0 w> O O eo > f\j #— f ^ m- *— #w f #»» ^ - T— ^ ^ to f\J *— « »| INI li- « 0 r>. N . fio cr> CO CM o o 15 2 ru rg fSIs c o t) % S(\j(M<^mrofor^r»ievjoococoooeocoookO»-nmL/^<\i^*— *— •— {intoOOOOOOOh-r^r^f^r*r^-r>-rororor^cor^rof'Ofo r^(OtocO(oScooocotnw>m«Atninu)cocou)u>ioi0fsir\jfMr^«O(o to to to tototo to toto to to to to to I N CM CM o to TT fO tO A t 3 !t/|i/)Q0 «0 fi0 C0 C0 CDe0 OOOOOOOcAc/)i/)ii/lc/>«/)t/)k/>t/) c am 5 •E 5 V ^ to O kO f— to I c o D) E CM h-4/>tr»toiotr>wiikOioi/imAOr*«»N^i^f^ooi/>c*«-Ako fj l(MCMfM 5l M" re S. ( to «0 CM to m tn to to o to to to t o O o o to to CM i fsi » - rvj Û. Û. CL CL CL CL CL Cl Û . o . 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ID NW 65 20 sc 90 1.57 0.17 0.35 234 205M 24.5 152 6 SC 62 S€ 90 1.57 0-10 0.24 237 21SH 25 151 8 St 62 sc 89 1.55 0.14 0.24 240 22SH 25 152 3 NW 62 St 90 1.57 0.05 0.24 247 23SW 25 152 6 NW 62 St 90 1.57 0.10 0.24 255 24SH 25 152 15 NW 62 SE 90 1.57 0.26 0.24 268 25SM 8 5 147 23 62 SC 85 1.48 0.24 273 26SH 14 158 20 68 23 St 90 1.57 0.35 0.40 282 27SH 5 162 42 72 19 St 90 1.57 0.73 0.31 287 28SH 12 164 6 74 sc 90 1.57 0.10 0,24 291 295H 17 164 21 74 sc 90 1.57 0.37 0.24 300 30SH 25 172 2 SC 82 17 sc 90 1.57 0.03 0.30 307 3ISH 24 171 5 82 17 SC 99 1.55 0.09 0.30 9 316 32SH 22.5 172 9 MW 82 17 SC 90 1.57 0.16 0.30 10 10 326 33SH 25 172 10 SC 82 17 SC 90 1.57 0.17 0.30 3 329 34SH 25 171 1) St 72 IS sc 99 1.73 0.1» 0.26 2 330 35SH 25 163 n St 72 15 sc 91 1.59 0.19 0.26 332 36SM 16 164 10 sc 72 15 St 92 1.61 0.17 0.26 334 37SM 9 163 19 NW 72 15 St 91 1.59 0.33 0.26 339 38SH 25 163 12 SC 72 15 St 91 1.59 0.21 0.26 340 39SM 25 167 22 sc 90 1.57 0.19 0.38 354 405H 167 0 77 16 St 90 1.57 0.00 0.28 355 41SH 25 167 10 St 77 16 sc 90 1.57 0.17 0.28 357 4294 25 168 7 St 82 15 SC 86 1.50 0 ) 2 0.26 361 43SH 25 172 4 NW 82 15 sc 90 1 57 007 0.26 369 445H 25 172 6 St 82 15 SE 90 1 57 0.10 0.26 373 45SH 25 172 1 NW 62 18 St 90 1 57 0.02 0.3 T 381 46SM 25 173 IS St 62 18 sc 91 1 59 0.26 0.31 382 47SH 25 173 13 sc 82 18 sc 91 1.59 0.23 0.31 384 48SH 25 174 6 sc 82 18 sc 92 1.61 0.10 0.31 390 49SM 25 172 2 NW 82 18 sc 90 1.57 0.03 0.31 398 50SH 25 174 5 SE 82 18 St 92 1.61 0.09 0.31 404 51SH 25 174 9 SE 82 sc 92 1.61 0.16 0.31 408 S2SM 25 173 8 SE 82 sc 91 1.59 0 14 0.31 412 53SH 25 173 6 SE 82 St 91 1.59 0,10 031 417 S45M 25 172 6 SC 82 18 sc 90 1.57 0.10 0.31 422 55SK 25 173 5 SE 82 18 St 91 1.59 0.09 0-3) 428 565M 25 173 NW 82 St 91 1.59 0.07 0.31 437 57SH 25 173 3 82 St 91 1.59 0.05 0.31 446 58SH 25 173 6 SE 82 St 9) 1.59 0 10 0,3) 4SI S9SH 25 173 0 82 St 91 1.59 0,00 0.31 459 605M 25 173 4 SE 82 St 91 1.59 0.07 0.3) 465 61SH 25 173 r 80 16 sc 93 1.62 0.02 0,28 472 62SM 25 174 6 80 16 St 94 1 64 0 10 0.28 482 63SWC4iC 792 173 2 80 16 sc 93 1 62 0.03 0.28 244 244 726 64SH 25 169 12 82 26 St 87 1.52 0.21 0.45 15 15 742 655W 15 172 25 82 26 St 90 1.57 0.44 0.45 12 12 753 66SM 25 172 7 NW 82 26 sc 90 1.57 0.12 0.45 767 67SM 16 172 10 SE 82 26 sc 90 1.57 0.1 7 0 4 5 771 68SH 25 172 8 NW 82 26 sc 90 1.57 0.14 0.45 785 69SH 17 176 5 NW 86 26 St 90 1 57 0.09 0.45 794 705H 25 174 17 sc 75 23 St 99 1.73 0.30 0.40 3 797 71SH 25 175 6 SE 75 23 sc 100 1 75 0.10 0.40 7 72SH 25 176 8 NW 75 23 St 101 1.76 0.14 0.40 13 13 816 73SH 6 164 26 NW 75 23 St 89 1-55 0.45 0.40 5 5 821 74SH 20 164 17 SE 75 23 St 89 1 55 0.30 0.40 2 823 75SM 25 164 16 NW 75 23 sc 89 1.55 0.28 0.40 839 I09SH 240 204 0 75 23 St 129 2.25 0.00 0.40 912 76SH 21 5 163 1 NW 74 26 sc 89 1.55 0.02 0.45 921 loesH 948 131 0 90 30 S 0.72 0.00 0.52 311 1232 77SH 25 184 13 NE 94 sw 90 1.57 0.23 0,77 21 1253 78SH 25 184 11 NE 94 sw 90 1.57 0.19 0.77 20 1274 79SH 22 185 11 t€ 95 sw 90 1.57 0.19 0.77 1292 80SH 25 186 7 SW 95 37 sw 91 1.59 0.12 0.65 12 1304 81SH 25 185 10 sw 95 37 sw 90 1.57 0.17 0.65 11 1316 825H 25 186 5 sw 93 31 sw 93 1.62 0.09 0.54 11 1326 83SH 25 186 5 sw 93 31 sw 93 1.62 0 0 9 0.54 1337 84SH 25 185 10 sw 93 31 sw 92 1.61 0.17 0.54 9 1346 85SH 25 184 8 sw 95 27 sw 89 1.55 0.14 0.47 8 1354 86SH 25 182 8 sw 95 27 sw 87 t.52 0.14 0.47 8 1362 87SH 25 186 10 sw 95 27 sw 91 1.59 0.17 0.47 7 1370 0.47 88SM 25 187 4 sw 95 27 sw 92 1.61 0.07 10 1380 89SH 25 185 5 sw 95 27 sw 90 1.57 0.09 0.47 9 1389 90SH 25 187 5 sw 97 28 sw 90 1.57 0.09 0.49 10 1399 91SH 25 187 5 sw 97 28 sw 90 1.57 0.09 0.49 10 1409 1418 92SH 25 187 6 sw 97 28 sw 90 1.57 0.10 0.49 9 93SM 25 186 6 rc 97 28 sw 89 1.55 0.10 0-49 1432 1450 94SH 25 186 17 K 97 28 sw 89 1.55 0.30 0.49 18 20 1470 9SSM 25 185 27 97 28 sw 88 1.54 0.47 0.49 20 11 37 NE 95 26 sw 91 1 59 0.65 0.45 10 10 1480 965M 186 1491 97SM 31 248 11 NE 95 26 sw 153 2.67 0.19 0.45 11 11 1496 98SH 25 225 9 SW 95 26 sw 130 2.27 0.16 0.45 5 4 1500 25 227 10 SW 95 26 sw 132 2.30 0.17 0.45 99SH 3 150% 1005H 11 SW 95 26 sw 139 Z 41 0.19 0.45 25 233 6 1509 lOISH 25 230 sw 95 26 sw 135 2.36 0.09 0.45 5 17 1526 I02SM 25 205 20 NE 95 26 sw 110 1.92 0 3 5 0.45 0.42 0.44 17 1544 1035H 25 215 24 NE 93 25 sw 122 Z)3 0 14 0.44 7 155) 104SM 25 184 8 SW 93 25 sw 91 1.59 0.16 0.44 1558 105SH 25 184 9 SW 93 25 sw 91 1.59 0.00 0.1? 526 2084 107SW 3060 190 0 92 10 sw 98 1.71 0.70 2088 106SH 7 127 40 0 127 2.22 5 Table 2; Trigonometric variables and thickness calculations, Shawmut Anticline (SA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 4 Tap# # TapeLemglh Slope Slope Bod Bod (Azi-Sirfc) (A^Strk) Two TMdcnoos SpoeHk Thidutoos totd (moteet) B M M M M i m m m HI 2S 175 4 SE 60 50 SE 115 2.007 0.070 0.873 16 16 16 H2 2S 177 2 SE 60 50 SE 117 2.042 0.035 0.873 16 17 33 H9 2$ I7S 1 SE 60 50 SE 118 2.059 0.017 0.873 17 17 49 H4 * 2S ISO 2 S 60 50 SE 120 2.094 0.035 0.873 16 16 65 HS 2S ISO 2 S 60 50 SE 120 2.094 0.035 0.873 16 16 81 H6 10 175 4 SE 60 50 SE 115 2.007 0.070 0.873 6 7 86 H? 2S 149 S SE 59 47 SE 90 1,571 0.140 0.820 16 16 104 HS 25 149 9 SE 59 47 SE 90 1.571 0.157 0.820 15 15 119 H9 25 20S 7 SW 59 47 SE 149 2.600 0.122 0.820 7 7 126 m p 12 206 15 NE 59 47 SE 147 2.565 0.262 0.820 7 7 133 H11 25 152 2 NW 62 43 SE 90 1-571 0.035 0.750 18 18 151 HI 2 25 100 1 NW 62 43 SE 38 0.663 0.017 0.750 11 11 161 HI 3 25 101 2 NW 62 43 SE 39 0.681 0.035 0.750 11 11 173 HI 4 22 120 4 NW 59 40 SE 61 1.064 0.070 0.698 14 14 186 HIS 5 147 IS SE 59 40 SE 88 1.536 0.262 0.698 2 2 188 HI 6 25 172 9 SE 59 40 SE 113 1.972 0.157 0.698 12 12 200 HI7 25 1S2 9 SE 59 40 SE 123 2.146 0.157 0.698 10 10 210 HIS 25 140 18 SE 65 37 SE 75 1.309 0.314 0.646 8 8 218 H19 25 176 6 SE 65 37 se 111 1.937 0.105 0.646 12 12 230 H20 25 192 6 SW 65 37 SE 127 2.216 0.105 0.646 10 10 240 H21 25 193 4 SW 56 57 SE 137 2.391 0,070 0.995 13 13 253 M22 25 197 5 sw 56 57 SE 141 2.460 0.087 0.995 12 12 265 H23 25 1SS 2 s w 56 57 SE 132 2.303 0.035 0.995 15 15 280 H24 4.5 174 S SE 56 57 SE 118 2.059 0.140 0.995 3 3 283 H2S 25 1S6 9 SW 56 57 SE 130 2.269 0.157 0.995 14 14 297 H26 24.5 186 3 sw 56 57 SE 130 2.269 0.052 0.995 15 15 312 H27 25 187 2 NE 56 57 SE 131 2.286 0.035 0.995 16 16 328 H2S 25 183 6 SW 56 57 SE 127 2.216 0.105 0.995 15 15 343 H29 25 177 3 SE s e 57 SE 121 2.111 0.052 0.995 17 17 361 H30 25 188 5 NE 56 57 SE 132 2.303 0.087 0.995 17 17 377 H31 25 208 2 SW 56 57 SE 152 2.652 0 0 3 5 0.995 9 9 387 H3Z 25 163 9 SW 56 57 SE 127 2.216 0.157 0.995 14 14 401 H33 25 177 2 NW 56 57 SE 121 2.111 0 0 3 5 0l99S 18 18 419 H34 25 174 ? NW 56 57 s e 118 2.059 0.122 0,995 20 20 439 H3S 10 175 5 NW 56 57 SE 119 2.077 0.087 0.995 6 8 447 H36 25 196 11 SW 60 54 se 136 2.373 0.192 0.942 11 11 458 H37 12 195 14 sw 60 54 SE 135 2.356 0.244 0.942 5 5 463 H3S 25 192 3 sw 60 54 SE 132 2 303 0.052 0.942 14 14 477 K39 25 184 7 sw 60 54 SE 124 2.164 0.122 0.942 15 15 492 H40 25 176 2 NW 60 54 SE 116 2.024 0.035 0.942 19 19 511 H41 IS 187 7 fC 65 37 SE 122 2.129 0.122 0.646 9 9 520 H42 4 117 34 NW 65 37 SE 72 1.256 0.593 0,646 4 4 524 H43 16 186 2 65 37 se 123 2.146 0.035 0.646 9 9 532 H44 25 187 5 SW 59 57 SE 128 2.234 0.087 0.995 15 15 548 H4S 25 186 4 sw 58 28 SE 130 2.269 0.070 0.489 7 7 555 H46 25 187 3 SW 58 28 SE 129 2.251 0.052 0.489 8 8 563 H47 25 197 S sw 58 28 SE 139 2.426 0.140 0.489 S 5 568 H4S 25 160 7 SE 58 28 SE 102 1.780 0.122 0.489 9 9 576 H4» 25 166 8 SE 58 28 SE 108 1.885 0.140 0.489 8 8 584 HSO 25 135 2 SE 52 37 SE 83 1.448 0.035 0.646 14 14 599 H51 25 157 5 SE 52 37 SE 105 1.832 0.087 0.646 13 13 611 HS2 25 145 4 SE 52 37 SE 93 1.623 0.070 0.646 14 14 625 HS3 25 149 9 SE 52 37 SE 97 1.693 0.157 0.646 12 12 636 HS4 25 135 3 SE 52 37 SE 83 1.448 0.052 0.646 14 14 650 H&S 25 145 3 SE 53 35 SE 92 1.605 0.052 0.611 13 13 664 HS6 25 149 2 NW 53 35 SE 96 1.675 0.035 0.611 15 15 679 H57 25 125 1 NW 53 35 SE 72 1.256 0.017 0.611 14 14 693 HSS 25 149 11 se S3 35 SE 96 1.675 0.192 0.611 10 10 703 HS9 25 115 2 NW 53 35 SE 62 1.082 0.035 0.611 13 13 716 H60 12 133 7 NW 53 35 SE 80 1.396 0.122 0.611 8 8 724 H61 25 135 9 SE S3 35 SE 82 1.431 0.157 0.611 11 11 735 HQ2 25 133 3 SE 53 35 SE 80 1.396 0.052 0.611 13 13 748 H63 25 133 3 SE 53 35 SE 80 1.396 0.052 0.611 13 13 761 764 H64 25 60 S SW 53 35 SE 27 0.471 0.140 0.611 4 4 H6S 25 140 5 SE 53 35 SE 87 1.518 0.087 0.611 12 13 777 H66 25 141 4 SE S3 35 SE 88 1.536 0,070 0 6 1 1 13 13 790 H67 25 142 2 SE 53 35 SE 89 1.553 0.035 0.611 14 14 803 816 H6S 25 139 5 SE 53 35 SE 86 1.501 0.087 0.611 12 13 828 MS9 25 166 3 SE 53 35 SE 113 1.972 0.052 0.611 12 12 834 H70 IS 162 7 SW 53 35 SE 129 2.251 0.122 0.611 6 6 5 5 839 H7Î 20 191 S hE 75 8 SE 116 2.024 0.140 0.140 50 889 H73 40S 194 0 75 8 SE 119 2,07? 0.000 0.140 50 8 897 H72 15 233 30 NE 0 0 233 4.066 0.524 0.000 7 Table 3: Trigonometric variables and thickness calculations. Highway 191 (191 section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 5 Oi/^u^L/iiy->LnLntO'»j-*rm*»-t/iinin'if'«-Lr)'ti-iA«i-ir>'q-iALnuOLnu%rt-^tO'>l-rr)rriTi-i/>irtir)LriT)-tt-' V CQ LO LO CO CO to N. m fOiALOwfj^^Noj^^wm&Oh^ lo _ CO o ^ to VOfl0^^fsjf\jC00> gt—OfMOOmojincocNjcMOj' irocMO'crcMCM^cno.-CMOOcocoooomrocMCMiom^.— . - o o o I 'gOOOO^OOOOOOOO OOOOOOOOOOOOOOOOOOOOr^'TOOO'-OOOOO I £0000r00.- — 00.-00 OOOOCMOCMOOOco»-CMO.— .— OCM.— OOOOOO.— OCMM-CMrO I ^CMf— OOOOCMi— M" O '— — f— .—r-owcor^^CM'f'4-cMNCMM-coinin — LnLnf-^oO'4-mr-.-coiMCM%P*co I cMTt-ootOr-mi^omtocMO I00'*-0ff)000'i'tocrif—cM^poom.— coocsjcotM.tnco't-CM^^-'j-rs. § I E OOOOOOOOOOOOOOOOO.— OOOCMOOOO co M-Om'.i-OCMr-.— O CO O CM CM CO % CO o U00000000100000 ooooco^oooioi^ooioocoj^^enr^oooo^^j^io^coo^ 0> 5 V* O CsS . ^lOiOOJ.AiO^OO •— CvJCMf— ^ t o I (/> 6 fs.CO^UO#-^^CO s°:2 c ^ < < < CO< ^ < w < E c c e t BC |||îï?jSSill llllliilllllll Si ÿ > •wCfffiifp WC 'w' SmC SwC 'W —( * s s s I liiiiiiiiiiiii H t fc ^-ii|ili|ipi|||§i|||llii|i o ° = = 2 §§§II- ■8 E9 -g>vv g> tv g> tvg> tv^ Ô. g> ® » Vf44 . . . . , r— ^ ^ ^ ^ CO CO rO Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 6 Grain Categories Recalculated Parameters Qm - Monocrystalline Quartz Qt - Qm + Qp + Cht Qp - Polycrystalline Quartz (not inc. Cht) F -K + P Cht - Chert L - Lv + Ls + Lju + X K - Potassium Feldspar QP — Qp + Cht P - Plagioclase Feldspar Lsm — Ls + Lm Lv - Volcanic rock fragments Cmt + Mat = cement + matrix Ls - Sed. and metased. rock fragments QFL%Q = 100Qt/(Q+F+L) XBC03 - extra-basinal carbonate QFL%F = 1(X)F/(Q+F+L) Unid L - unidentified rock fragments QFL%L = 1(X)L/(Q+F+L) Bt - Biotite LmLvLs%Lm = 100Lm/(L) Ms — Muscovite LmLvLs%Lv = 100Lv/(L) Chi - Chlorite LmLvLs%Ls = 100Ls/(L) Heav. - Dense Minerals QPLvLsm%QP= 100Qp/(L + QP) Cmt - Cement QPLvLsm%Lv = 100Lv/(L + QP) Matr - Matrix (<.03mm) QPLvLsm%Lsm = 100Lsm/(L + QP) Por — Porosity QmFLt%Qm = 100Qm/(Qm + F + Lt) QmFLt%F = 100F/(Qm + F + Lt) QmFLt%Lt = 100Lt/(Qm + F + Lt) QmPK%Qm = 100Qm/(Qm + P + K) QmPK%P = 100P/(Qm + P + K) QmPK%K = l(X)K/(Qm + P + K) Table 5: Grain categories and recalculated grain parameters used for this study (after Ingersoll et al., 1984) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 7 Sample# Formation (section) QM F LT QT FL QP LV LSM QM P K Lv Ls Lm 1 -£ag-1 EAGLE(SA) 49.0 23.3 27.7 71.8 23.3 4.8 83.9 7.6 8.5 67.7 20.4 11.8 7.6 92.4 0.0 l-Eag-2 EAGLE(SA) 66.4 7.2 26.3 86.5 7.2 6.3 78.9 10.1 11.0 90.2 0.0 9.8 10.1 89.9 0.0 l-Eag-4 EAGLE(SA) 81.7 5.0 T3.4 93.1 5.0 2.0 85.2 3.7 1 1.1 94.3 3.7 2.0 3.7 96.3 0.0 l-Eag-S EAGLE (SA) 89.4 0.7 9.9 98.3 0.7 1.0 90.0 2.5 7.5 99.2 0.5 0.3 2.5 97.5 0.0 1 -Eag-6 EAGLE(SA) 61.4 11.6 27.0 75.6 11.6 12.9 55.6 30.3 14.1 84.2 13.0 2.8 30.3 69.7 0.0 l-Eaq-10 EAGLE(SA) 52.5 20.4 27.1 67.4 20.4 12.2 55.5 23.5 21.0 72.0 22.7 5.3 23.5 76.5 0.0 3-£aq-1 EAGLE (WPA) 62.4 18.8 18.8 70.9 18.8 10.3 48.2 21.7 30.1 76.8 16.1 7.1 21.7 78.3 0 .0 3-Cag-2 EAGLE (WPA) 49.1 25.3 25.6 59.9 25.3 14.8 44.9 35.5 19.6 66.0 22.6 11.4 35.5 64.5 0.0 3-£ag-3 EAGLE (WPA) 75.6 10.3 14.0 85.6 10.3 4.1 70.8 20.0 9.2 88.0 5.3 6.8 20.0 80.0 0.0 1-Eag-11 CLAGGETT (SA) 57.7 9.3 33.1 85.1 9.3 5.7 85.5 4.6 9.9 86.2 10.7 3.1 4.6 95.4 0.0 1 -JR-2 JUDITH RI'ÆR (SA) 43.1 18.7 38.3 54.9 18.7 26.4 32.1 40.7 27.2 69.7 12.5 17.7 40.7 59.3 0.0 1 -JR-1 JUDITH RrVER (SA) 45.6 9.7 44.7 63.2 9.7 27.1 39.8 30.6 29.6 82.4 9.4 8.2 30.6 69.4 0.0 1-JR-S JUDITH RIVER (SA) 1.6 56.5 41,8 1.6 56.5 41.8 0.0 98.9 1.1 2.8 94.8 2.4 98.9 1.1 0.0 1-JR-7 JUDITH RIVER (SA) 2.5 45.6 51.8 3.5 45.6 50.9 1.8 95.4 2.7 5.3 90.0 4.8 95.4 4.6 0.0 1-JR-9 JUDITH RIVER (SA) 0.8 40.3 59.0 1.0 40.3 58.8 0.4 98.3 1.3 1.8 97.0 1.2 98.3 1.7 0.0 l-JR-10 JUDITH RIVER (SA) 1.4 34.6 64.0 1.7 34.6 63.7 0.5 99.5 0.0 3.9 94.5 1.6 99.5 0.5 0.0 1-JR-H JUDITH RIVER (SA) 0.8 51.8 47.4 0.8 51.8 47.4 0.0 100.0 0.0 1.6 97.4 1.0 100.0 0.0 0.0 3-JR-l JUDITH RIVER (WPA) 35.1 34.8 30.1 39.3 34.8 25.9 15.0 71.7 13.3 50.2 28.3 21.6 71.7 27.4 0.9 1-BP-2 BEARPAW (SA) 45.5 29.0 25.5 59.3 29.0 11.6 54.5 16.8 28.7 61.0 29.2 9.8 16.8 83.2 0.0 1-Len-t LENNEP (SA) 38.0 35.0 27.0 39.8 3 5 0 25.2 6.7 92.4 1.0 52.1 38.7 9.2 92.4 7.6 0.0 1 -Len-2 LENNEP (SA) 3.9 37.2 58.9 4.7 37.2 58.1 1.4 98.6 0.0 9.5 83.8 6.8 98.6 1.4 0.0 1-Len-3 LENNEP (SA) 7.7 30.1 62.3 11.5 30.1 58.5 6.3 90.2 3.6 20.3 69.6 10.1 90.2 8.9 0.9 H .en-4 LENNEP (SA) 7.9 31.8 60.3 11.8 31.8 56.4 6.7 89.5 3.8 19.9 73.9 6.2 89.5 10.5 0.0 l-HC-1 HELL CREEK (SA) 39.4 24.9 35.7 45.4 24.9 29.7 17.3 21.1 61.7 61.2 29.4 9.4 21.1 78.9 0.0 1 -HC-2a HELL CREEK (SA) 36.6 25.5 37.9 41.9 25.5 32.6 14.1 41.6 44.3 58.9 28.5 12.6 41.6 58.4 0.0 l-HC-3 HELL CREEK (SA) 39.1 29.0 31.8 42.4 29.0 28.5 10.5 48.4 41.1 57.4 31.9 10.7 48.4 51.6 0.0 1-La-l HELL CREEK (WPA) 44.0 24.7 31.3 49.1 24.7 26.2 18.2 67.4 14.4 64.1 27.2 8.8 67.4 30.3 2.3 l-La-3 HELL CREEK (WPA) 37.7 29.3 33.1 43.8 29.3 27.0 18.9 55.1 26.0 56.3 33.8 9.9 55.1 44.1 0.8 1-Tul-l BEAR (SA) 46.5 14 4 39.0 54.3 14.4 31.3 19.9 49.3 30.8 76.3 22.4 1.3 49.3 47.9 2.7 1 -Tul-3 BEAR (SA) 50.4 4.8 44.8 54.1 4.8 41.1 8.5 4.9 86.6 91.3 4.3 4.3 4.9 95.1 0.0 2-JR-l BEAR(191) 51.9 21.1 27.0 56.9 21.1 22.0 18.7 39.6 41.8 71.1 12.0 16.9 39.6 54.9 5.5 2-JR-3 BEAR(191) 49.3 20.4 30.4 58.9 20.4 20.7 32.9 39.0 28.0 70.8 9.7 19.5 39.0 56.1 4.9 2-JR-5 BEAR(191) 4.0 85.4 10.7 4.0 85.4 10.7 0.0 100.0 0.0 4.4 86.7 8.9 100.0 0.0 0.0 l-Let>-3 LEBO (SA) 8.3 33.3 58.4 12.4 33.3 54.4 7.0 89.9 3.1 20.0 73.0 7.0 89.9 9.3 0.8 1-Leb-1 LEBO (SA) 10.4 30.1 59.5 16.8 30.1 53.1 10.9 85.9 3.3 25.8 64.2 10.0 85.9 13.8 0.4 2-Een-l LEBO (WPA) 9.0 33.2 57.8 15.2 33.2 51.6 10.9 82.0 7.0 21.4 68.8 9.9 82.0 17.6 0.4 2-HC-3 LEBO (WPA) 27.0 38.2 34.8 35.1 38.2 26.7 24.4 66.4 9.2 41.4 33.6 25.0 66.4 33.6 0.0 2-HC-4 LEBO (WPA) 42.1 20.9 37.0 47.1 20.9 32.0 13.9 59.9 26.3 66.8 21.8 11.3 59.9 39.4 0.7 2-Leb-I LEBO (WPA) 36.2 10.1 53.8 41.7 10.1 48.2 10.5 30.5 59.0 78.3 11.4 10.3 30.5 68.1 1.4 2-Leb-4 LEBO (WPA) 30.7 12.4 56.9 37.6 12.4 50.0 12.2 52.7 35.0 71.3 14.9 13.8 52.7 44.3 3.0 2-Leb-2 LEBO (WPA) 32.0 6.1 61.9 40.0 6.1 53.9 13.1 40.5 46.3 84.0 9.3 6.8 40.5 58.3 1.2 1-TR-l MELVILLE (iSA) 47.6 11.0 41,4 53.2 11.0 35.8 13.7 8.2 78.1 81.3 13.9 4.8 8.2 41.8 50.0 2-TR-1 MELVILLE (WPA) 49.2 8.5 42.3 60.7 8.5 30.8 28.0 13.3 58.7 85.2 14.8 0.0 13.3 73.3 13.3 2-TR-2 MELVILLE (WPA) 30.8 9.4 59.8 41.3 9.4 4 9.2 18.1 19.7 62.2 76.5 7.3 16.2 19.7 68.0 12.4 Table 6: Recalculated arain framework data Table 6; Recalculated and normalized grain framework data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 8 Formation Environment of Paleocurrent Interpretation Deposition Trends M elville Fluvial plain To the N Transport away from uplifting Beartooth Mtns to the S Lebo Fluvial plain To the SE Transport away from northern uplift with volcanic influence? Bear Fluvial plain To the SE and S Transport away from northern uplift? Hell Creek Coastal plain To the S Transport away from northern uplift? Lennep Nearshore marine - Fluvial- to the E Fluvial- Transport away from coastal plain Marine- to the SE Fold-Thrust Belt Marine- Longshore drift Bearpaw Offshore marine ? ? Judith Nearshore marine - Fluvial- to the E Fluvial- Transport away from River coastal plain Marine- to the SE Fold-Thrust Belt Marine- Longshore drift Claggett Nearshore marine- To the SE Longshore drift Offshore marine Eagle Coastal marine - Random High-energy coastal plain upper shoreface Table 7; Inferred environments of deposition, paleocurrent trends, and inferred interpretations of Upper Cretaceous-Tertiary strata in and around the northeastern Crazy Mountains Basin. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 9 Sandstone Tabular Cross-stratification Siltstone Hummocky Cross-stratification : Mudstone/Shale Ripple Cross-stratifrcation Root Casts ■ I Organic detritus (vegetation) (T) Iron concretion Trough Cross-stratification \ f Bioturbation Soft-sediment Deformation —Z=-^ Planar bedding Mud Intraclast Fossil wood fragments .Ripple marks ☆ 1-JR-2 Sandstone sample location and sample number ^ Unknown or inferred trough limbs N = 122 Paleocurrent indicator measurement type, number measured, and result with inferred paleocurrent flow direction direction (arrow) Table 8: Key for measured stratigraphie sections (Figures 4-17) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 0 400 km Fold-Thrust Belt ^ Principal uplifts in the foreland basin ^ Basins or lowlands Eastern extent of Folt-Thrust Belt BTM- Beartooth Mountains, CMB- Crazy Mountains Basin Figure 1 : Simplified diagram of major foreland uplifts of the western U.S. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 Central Montana Alkalic Province tM e Big Snowy Mountains .1 cc sz"Ô =3 Harlowton Billings ^ Thrust fault Anticline axis and limbs Syncline and limbs Uplifts Figure 2: Location of study area showing Crazy Mountains Basin and surrounding mountain ranges. Measured stratigraphie sections are shown by black dots (WPA-Woman’s Pocket Anticline section; SA-Shawmut Anticline section; and 191-Highway 191 section). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 2 0 O) Terrace Gravels O) Melville Formation g>1 Lebo Formation œ Bear Formation 66.4 Ma Hell Creek (8 Formation tO CL Lennep 3 Sandstone 74.5 Ma 2 (3 c CO Bearpaw CL ID B co S ^ a ié 3 S o > 2 C c CD £5 ■ > as c Judith River i co c OC CL co o E Formation c CO o o Claggett Formation Eagle Formation 84 Ma Sant. Virgelle Sandstone Member Figure 3; General stratigraphie column of study units Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 3 S. 0) N = 17 ü A i 5 2 W 3-Eag-2 o co trough limbs Marine? o* c 0_ 15 (/) co o ü (D E sh sit f m c gr Figure 4: Eagle Formation measured section. Woman’s Pocket Anticline (WPA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 4 l-PC'Eag-3 i5 trough limbs 40m o_ I CO Ü 30m thin coal beds Q) 2 0 m C l-Eag-5 o 1-PC'Eag-l z>I *co N = 9 4 l-Eag-4 A (D *D VEag-2 c £ CO 1 0 m « ^ 0) (D V 5 trough limbs 1-Eag-l I I f V V V > 2 Om sh sit f me gr Figure 5: Eagle Formation measured section, Shawmut Anticline (SA Section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 5 N = 285 270m 250m Total Claggett trough limbs 2 3 0 m Storm deposits 21 Om 1 9 0 m 1 YOm V Storm deposits 150m 130m 1 1 Om 90m 70m Lag -E a g -1 2 —I Figure 6: Claggett Fonnation measured section, Shawmut Anticline (SA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 6 300m 290m — 280m 270m __ 260m 250m — oyster bed 240m 230m N = 15 220m 210m trough limbs N = 67 200m i CD 190m — trough limbs 180m sh sit f m e gr Figure 7: Judith River Formation measured section. Woman’s Pocket Anticline (WPA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 7 N = 144 3 8 0 m 1-JR-10 trough limbs 3 6 0 m 3 5 0 m 1 -JR-9 c 3 4 0 m 'CX 1-JR-7 Û- B 1-ÜR-5 i/> 3 3 0 m CO O O 3 2 0 m 31 D m N = 139 3 0 0 m 1-JR-1 N 1-JR -2 2QOm trough limbs 2 8 0 m sh sit f m c gr Figure 8: Judith River Formation measured section, Shawmut Anticline (SA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68 N= 17 trough limbs Figure 9: Rose diagram of trough cross-bed limbs measured from the Bearpaw Shale, Shawmut Anticline (SA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. m 6 9 600 Hell Creek Fm. N = 3 9 ^ 3 fluvial channel KJ luV 3 -U -3 c jO trough limbs CL 1 5 03 co 575 oo _ /K I7 N . Q) (/) I (/) => CL W 3-La-1 C I c o Q) -C 550 — ^ ~ ^ 7 — I c o CD (0 œ 2 o SI I <Ù t d> o CÛ 550 I I I I ~ i stt f gr Figure 10: Bearpaw, Lennep, and Hell Creek Formations, Woman’s Pocket Anticline (WPA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70 142 830m "Ct 1 -Len-4 trough limbs 81 Om 800m upper s ho reface? 'Cr 1 -Len-2 *►- L. 4-» sh sit f m c gr Figure 11 : Lennep Sandstone measured section, Shawmut Anticline (SA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71 1230m trough limbs N = 62 1-HC-3 ☆ 920m V O / àiocmd& ûêOL 1-HC-2a Ù 840m trough limbs o N = 15 -HC-1 830m — sh sH f m c gr Figure 12; Hell Creek Formation measured section, Shawmut Anticline (SA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 2 1370m Total Bear Fm trough limbs 1 3 e O m N = 122 1350m — 1340m 1330m 1320m 1310m 1300m — 'Cr 1 Tu-2 1290m — 1280m — 1270m — 1260m — 1250m — 1240m — 1 -Tu-"I sh sit f m c gr Figure 13: Bear Formation measured section, Shawmut Anticline (SA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 80m —I 7 7 3 Total Bear Formation trough limbs 150m — 1 N= 144 lOOm -^3- 2-ÜR-5 thin coal beds thin coal beds thin coal beds 2-Ü R -3 2-JR-1 10m thin coal beds s h s i t f m c gr Figure 14; Bear Fonnation measured section. Highway 191 (191 section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 4 m 2 0 8 9 Total Lebo Fm trough limbs N = 114 covered interval 1 5 7 0 1 5 6 0 1 5 5 0 'Cx 1-Leb-l fluvial channel 1 5 4 0 1 5 3 0 u> 0 1 5 2 0 Q- - s C CO 1 5 1 0 ■e 1 1 5 0 0 CD 1*Leb*3 C c CO 1 4 9 0 JZ o > 1 4 8 0 sh stt f m c Figure 15; Lebo Formation measured section, Shawmut Anticline (SA section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 5 Total Lebo Fm trough limt)s m X 8 0 0 X Q ± D ^ 2-L eb -2 N = 100 2-Leb -4 ^ coal beds ^ ^ 3 7 0 0 J 2-Leb-1 6 0 0 coal t>eds 2 -H C -4 C 5 0 0 ]co CL " g > 3 4 0 0 H C -3 3 0 0 (E Ü 3 )O I 200 CT^TD 2 Len-1 n - 'l I [ = ] sh sit t m c gr Figure 16; Lebo Formation measured section. Highway 191 (191 section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 6 Melville Fm trough limbs SA section m N = 53 2090 — 1-TR-1 N = 4 2085 — Aligned sh sIt f m e gr Fossil Wood m 8 9 5 2-TR -2 58 Melville Fm trough limbs 2-TR-1 191 Section 8 9 0 — sh sit f m Figure 17; Melville Formation measured sections, (top) Shawmut Anticline (SA section) and (bottom) Highway 191 (191 section) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ■o I I West East '7 % Melville C/) CO 3o' CD 1 Paleocene continental 8 Lebo Lebo c5' ■ Cretaceous continental ■ Marine shale 3 CD □ Shoreface deposits C p. ■oCD Ic a o Hell Creek 3 ■o o & 3O " a % T9 CO CO o' 3 18 WPA Fig. 18; Correlated generalized stratigraphie sections, showing inferred erwironmenls of deposition and sea-level transgressions and regressions 78 era ton is Virgelle Sandstone Member in tenor transilionai lower and upper 0 Eagle Formation continental Eagle Formation S am ples 0 Claggett Formation ecyci S am p le Qm undi c raton interior 1 Virgelle Sandstone 'Member Fig. 19a: E agle Formation QtFL t * transitional r# Ilk cuartzose continental •ecvcled lower and upper Eagle Formation Qm ition lower and upper F undissected arc Lt Eagle Formation Fig. 19b: Eagle Formation QmFLt Fig. 19c: Eagle Formation QmPK Lv Lsm Fig. 19d: Eagle Formation QpLvLsm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 9 c r a t o n in terio r re c y c le d o ro g e n transitional continental- lower Judith River Formation Qm c r a t o n in te rio r q u a rtz o s e re c y c le d transition lower Judith River sitsona c o n tin t Formation F I L upper Judith River Formation Fig. 20a; Judith River Formation QtFL it f o n Qm undissected arc Lt upper Judith River Formation Fig. 20b: Judith River Formation QmFLt upper Judith Formation P K Fig. 20c: Judith River Formation QmPK upper Judith River Formation Lv Lsm Fig. 20d: Judith River Formation QpLvLsm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80 cralo!-! interior Q Bearpaw Shale Sam ple transitional H Lennep Sandstone continental Samples Qm c r a to n interio ortel transi! ;o n iir ii Fig. 21a: Bearpaw Shale and Lennep Sandstone QtFL Qm s itio t upper ______yanastone undlssecteci arc Fig. 21 b: Bearpaw Shale and Lennep Sandstone QmFLt -Len-1 ' Qp upper Lennep Fig. 21c: Bearpaw Shale and Lennep Sandstone QmPK total Lennep Sandstones rirc orocierr Lsm Fig. 21 d: Bearpaw Shale and Lennep Sandstone QpLvLsm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SI Qt c r a t o n in t e r io r transftionaf continental r e c y c le d e r o q e n Qm c r a t o n in t e r io r <9 transitional transitional continental a rc u n d is c e c t e a r c N. Fig. 22a: Hell Creek Formation QtFL Om ransitionol arc: undissected arc |_| Fig. 22b: Hell Creek Formation QmFLt Qp Fig. 22c: Hell Creek Formation QmPK a r c o r o g s n Lsm Fig. 22d: Hell Creek Formation QpLvLsm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 2 Qt c r a t o n interior transitional continental Qm c r a t o n i n t e r i o r transitiortaf transi tionai continental a r c ^ Ondissecteo^ a rc Fig. 23a: Bear Formation QtFL \V ciissecte arc_ _ - transitional arc Om % Li n cli s s e c t e ci a re Fig. 23b: Bear Formation QmFLt Qp Fig. 23c: Bear Formation QPK a r c o r o g e n Lsm Fig. 23d: Bear Formation QpLvLsm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 3 c ra to n i n t e r i o r transitional continental Qm o a e n lower Lebo Formation e r a to. t r a n s i l i o r c o n t i n e î^nsjtion3 Fig. 24a: Lebo Formation QtFL transition Qm lower Formation undissected arc Fig. 24b: Lebo Formation QmFLt lower Formation Fig. 24c: Lebo Formation QmPK lower Lebo Formation Lv Lsm Fig. 24c: Lebo Formation QpLvLsm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 4 Qt craton interior transitional continental Om oratory interior a r c % transitional a r c Fig. 25a: Melville Formation QtFL % Qm transitional arc undissected arc Fig. 25b: Melville Formation QmFLt Qp Fig. 25c: Melville Formation QmPK a r c o r o g e n Lv Lsm Fig. 25d: Melville Formation QpLvLsm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 5 A Melville Formation ♦ Lebo Formation Lv o Bear Formation Hell Creek Formation Lennep Sandstone Bearpaw Shale Judith River Formation Claggett Formation Eagle Formation Lm Figure 26: LvLsLm ternary diagram plotting all sandstone samples Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 86 ■ Lennep Sandstone □ Bearpaw Shale crato n + Judith River Formation interior • Claggett Formation 0 Eagle Formation transitional continental □ 0 recy cled o ro q e n d is s e c te d arc transitional a rc undissected a rc Figure 27; QtFL ternary diagram plotting inferred marine sandstones of the Montana Group Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 87 112W now 108W 4 8 N Reynolds, 1980 47 N ig Snowy Mountains • 'w PA 4 6 N Crazy Mountains 0 65km L J I ^ Terrace Gravel transport Terrace Gravels Major uplifts ^ Unknown or Inferred Thrust faults *1 Terrace Gravel Sample Location Figure 28: Paleogeographic model of south-central Montana during deposition of the terrace gravels as described in this study. H- Harlowton, B- Billings, Bz- Bozeman Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 Gravels proximal to Crazy Mtns (Sample Gr-5) c h e r t é Gravels proximal to Little Belt Mountains (Samples Gr-1 and Gr-2) quartzite sandstone chert Gravels along the Musselshell River (Samples Gr 3, Gr-4, and Gr-7) Figure 29: Terrace gravel composition diagrams Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 9 Gr-4, pebble imbrications Gr-7, pebble imbrications N = 27 N = 27 Figure 30: Rose diagram of pebble imbrications measured from terrace gravels Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 0 Arctic Ocean -o USA Gulf of Mexico 800km V Direction of seawater circulation In KIS Exposed land surface 9 Inferred land extent (2 2 ) Ocean water Figure 31: Diagram of Cretaceous Interior Seaway of North America (modified from Gill and Cobban, 1973) superimposed on modem Gulf of Mexico and Arctic, Atlantic, and Pacific Oceans. Note dashed line representing the U.S.A. border. Arrows show simplified circulation of ocean water in the Cretaceous Interior Seaway (Kump and Sunderland, 1999). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 1 112W 110W 108W 48 N s»' ï ^ 5> V. ^ k«.S^MW ■.V.W.W&S « ", MPÿWÏ-iSSW^'.iliSftïè^ Cï" 47 N -t-j,**,.-® ,, Z< 'SSK C o a sta l P lain / v - > . ;r-.'T£ -.-: : F rT ' f 4» ^ ''■' ' j * / s i' 46 N / »s_ •BZ C o a sta l Sim s, P lain *7 1 9 6 9 WY T I r T r Fluvial transport (recycled sed.) Marine transport (recycled sed.) Fluvial transport (volcanic sed.) Marine transport (mixed sed.) Sedimentary source Volcanic source X River and delta (inferred) ? Unknown or inferred \ Eastern limit of FTB Figure 32: Simple paleogeographic model of south-central Montana during sea-level highstands (T8 and T9). H- Harlowton, B- Billings, Bz- Bozeman. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 2 craîon ■ Lennep Sandstone interior o Bearpaw Shale + Judith River Formation # Claggett Formation transitional continental 0 Eagle Formation recycled orogen dissected arc transitional arc undissected arc Figure 33; QtPL ternary diagram plotting inferred fluvial sandstones of the Montana Group Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 3 112W 110 W 108W % 47 N Coastal Plain f A A AV<, < « . *W*ÿkK)%vi« A %m4K* M^mfWAMW «Wk % 1' i \Cm A> ^ 191 -X Sims, *SA<>AV «fc*. » w^M«l ■ , ^.- Fluvial transport (recycled sed.) Marine transport (recycled sed.) c=:=C> Fluvial transport (volcanic sed.) Marine transport (mixed sed.) Sedimentary source / \ Volcanic source X River and delta (inferred) Eastern limit of FTB J \ 0 65km ? Unknown or Inferred 1 I I Figure 34; Simple paleogeographic model of south-central Montana during sea-level lowstands (R7, R8, and R9) H- Harlowton, B- Billings, Bz- Bozeman. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 4 110W 108W 48 N- 1 1 Belt, et aL^ Central Montana 1997 Alkallc Province 47 N _ Local Uplift? A A H i . A y .: ? / Wf% m a m m : i « = > , 191 ' SA 46 N— A A • B - ! 'BZ 65 km ❖ ? A ? j I WY / \ Volcanic Source Fluvial transport (volcanic sed.) Bear Fluvial transport (recycled sed.) JIIIIi^ Sedimentary Source Bear Formation A Local source of Fluvial transport (recycled sed.) recycled sediment? Hell Creek River (inferred) Volcanic sediment transport, Hell Creek equivalent ^ Unknown or inferred Eastern limit of FTB \ Figure 35: Simple paleogeographic model of south-central Montana during deposition of the Hell Creek through Lebo Formations, H- Harlowton, B- Billings, Bz- Bozeman. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 5 112W now 108 w 48 N — Central Montana Alkalic Province 47 N 4 6 N Decetles, 991 7 Fluvial transport (Ls, Lm, and Blotite -rich sed.) Local uplift Alluvial fan River and delta (inferred) 7 Unknown or inferred Eastern limit of FTB 0 65km \ J I Figure 36; Simple paleogeographic model of south-central Montana during deposition of the lower Melville Formation. H- Harlowton, B- Billings, Bz- Bozeman. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.