Sedimentary Features of the 

Blackhawk Formation (Cretaceous) 

in the Sunnyside District, 

Carbon County, Utah

GEOLOGICAL SURVEY PROFESSIONAL PAPER 688

n 

--»
SEDIMENTARY FEATURES OF THE

BLACKHAWK FORMATION (CRETACEOUS)

IN THE SUNNYSIDE DISTRICT,

CARBON COUNTY, UTAH
The Blackhawk Formation and associated rocks at the mouth of Whitmore Canyon, Sunnyside, Utah. Rock units shown are: 

Kpr, Price River Formation; Kc, Castlegate Sandstone; Kb, Blackhawk Formation (Kbu, upper mudstone member; Kbs, Sunnyside Member; Kbl, lower mudstone member; Kbk, Kenilworth Member) ; Km, Mancos Shale. Scale is indicated by telephone 

poles at base of hill. View looking southeast from West Ridge, above town of Sunnyside.
Sedimentary Features of the 

Blackhawk Formation (Cretaceous) 

in the Sunnyside District, 

Carbon County, Utah

By JOHN O. MABERRY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 688

A discussion of the trace fossils, stratigraphy, 

depositional paleoenvironment, and engineering 

geology of coal-bearing rocks in a part of the 

Book Cliffs coal Jield of central Utah

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director

Library of Congress catalog-card No. 74-612071

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 65 cents (paper cover)
CONTENTS

Abstract_ _________________________________________

Introduction, ______________________________________

Location. ______________________________________

Previous work..________________________________

Acknowledgments_ ____________________________

Biogenic sedimentary structures ______________________

Uses of trace fossils,____________________________

Descriptive nomenclature-_______________________

Animal-sediment relationship.__________________

Subdivision of Blackhawk trace fossils__- __________

Ethological classes __________________________

Bathymetry of trace fossils._______________

Systematic description of Blackhawk trace fossils-__ 

Pascichnia_ ________________________________

Fodinichnia_ _______________________________

Domichnia__ _ ______________________________

Cubichnia. ________________________________

Page. 

1 

1 

4 

4 

6

6

7

7

7

7

10

10

10

10

11

15

17

Sedimentation and stratigraphy. _ _ 

Terminology. _______________

Mancos Shale.______________

Blackhawk Formation________

Aberdeen Member, ______

Kenilworth Member.____

Lower mudstone member _ 

Sunnyside Member______

Upper mudstone member. 

Castlegate Sandstone_______

Inorganic sedimentary structures __ 

Bedding structures._-_______.

Plane-bed forms____________-

Channel structures.__ _ _______

Load structures ___-_____-

Engineering and economic geology. 

References. ____-___---_---_--_--

Index. ________-_-_---_-._-------

Page 

17 

19

21

22

22

22

26

27

30

31

32

32

34

35

36

37

41

43

ILLUSTRATIONS

[Plates follow index] 

FEONTISPIECE. Photograph of the Blackhawk Formation and associated rocks in Whitmore Canyon, Sunnyside, Utah.

PLATE

FIGURE

1. Teichichnus.

2. Asterosoma and helicoid funnels.

3. Ophiomorpha. * Page

1 . Geologic map of the Blackhawk Formation and associated strata at Sunnyside _______________-__-------- 2

2. Photographs of subsidence cracks_.___-____________-_____-_-------__-------------------------------- ^

3. Index map of the Sunnyside district. _________________________-_---_-------------------------------- ^

4. Photograph of palm-leaf fossil- ____________________________________-----___--_--------------------- 7

5. Diagram showing types of preservation of trace fossils, _____._____________---_------------------------ 8

6. Diagram showing environmental grouping of trace fossils_-_--------___-------------------------------- ^

7-20. Photographs and sketches:

7. Chevron trails _____________________________________________-_----_------------------------ 1 1

8. Arthrophycus_._ ____ __________________________________________-___--_-----.---------------- 12

9. Smooth tubes __________________________________________--_--_----__-_--------------------- 12

10. Chondrites _________________________________________________--_---_-_---------------------- 13

11. Cylindrichnus reptilis Bandel__-____-__-_________-___-_-----_-------------------------------- ^

12. Labyrinth castings __ _______________________________________-_---_------------------------ ^

13. Gyrochorte __________-___________________________________-_-_-_---_------------------------ ^

14. Aulichnites _ _ ____________________________________-_______-------_------------------------ 1"

15. Arenicolites, __________________________________________--__-----_-------------------------- ^

16. Thalassinoides _ __ _ ___.____________________________________-_----------------------------- ^

17. Plural curving tubes. ______ ________________________-_-_-----_---_--------- ----------------- 17

18. Large horizontal burrows_____--________-__--_______---__-_-------------- ------------------- 18

19. Pelecypodichnus- _______________________________________--_------__----_------------------- 18

20. Ruhespuren ___________.__________________-_______________----_--_------------------------- 1^
VI CONTENTS

Page 

FIGURE 21. Columnar stratigraphic section of the Blackhawk Formation and adjacent strata at Sunnyside-_____________ 20

22. Graph of current velocities required for erosion, transportation, and deposition of sediments ________________ 21

23. Nomenclature for Upper Cretaceous rocks in Sunnyside area.___________________________________________ 23

24. Diagrammatic sketch of restored stratigraphic section of the Blackhawk Formation and associated rocks in

the Book Cliffs area of east-central Utah.________________________________________________________ 24

25-27. Photographs:

25. Bimodal tangential crossbedding in upper sandstone tongue of Kenilworth Member in Water Canyon. 26

26. Sandstone of Sunnyside Member in Slaughter Canyon_______________________________________ 28

27. Root marks in uppermost 1 foot of thick-bedded sandstone facies at top of Sunnyside Member. _______ 29

28. Fence diagram of Sunnyside coal bed and associated rocks___________________.________________________ 31

29. Diagrammatic sketches illustrating terminology of crossbedding _--_-_---_---_---___________________ 32

30-40. Photographs:

30. Tangential crossbedding in lower sandstone tongue of Kenilworth Member._____________________ 33

31. Ripple cross-lamination in middle thin-bedded sandstone facies of Sunnyside Member___________ 33

32. Bimodal crossbedding in upper thick-bedded sandstone facies of Sunnyside Member, Water Cany on __ 33

33. Planar upper surface of upper thick-bedded sandstone facies of Sunnyside Member,______________ 33

34. Oscillation ripple marks in upper thick-bedded sandstone facies of Sunnyside Member.__________ 34

35. Current ripple marks in upper thick-bedded sandstone facies of Sunnyside Member,______________ 34

36. Megaripples in middle tongue of Kenilworth Member, Slaughter Canyon._______________________ 34

37. Interference ripple marks in middle tongue of Kenilworth Member _____________________________ 35

38. Sandstone channel deposit in mudstone of upper unnamed shale member of Blackhawk Formation. __ 35

39. Small sandstone channel deposit in sandstone of upper tongue of Kenilworth Member_____________ 35

40. Sandstone channel deposit in sandstone of upper unnamed shale member of Blackhawk Formation. _ 36 

41. Diagram of fluvial-channel environment. _ _____-----__----_----_-_--__-_--__________________________ 36

42-44. Photographs:

42. Load cast in middle shale of Kenilworth Member in Slaughter Canyon _________________________ 37

43. Load casts in Sunnyside coal zone in No. 1 Fan Canyon___ ___________________________________ 37

44. Deformation of roof bolts by squeezing in Sunnyside No. 1 mine-______________________________ 37

45. Diagrammatic sections of deformation around mine workings in Sunnyside No. 1 mine___________________ 38

46. Photograph of aftermath of a coal-mine bump in Sunnyside No. 1 mine________________________________ 39

47. Photograph of large horizontal burrows in roof of Columbia coal mine__________________________________ 39

TABLE

Page 

TABLE 1. Universal ichnofacies_________________________-__________________-___-_---_---__-___--_--__------ 10
SEDIMENTARY FEATURES OF THE BLACKHAWK FORMATION 

(CRETACEOUS) IN THE SUNNYSIDE DISTRICT, CARBON

COUNTY, UTAH

By JOHN O. MABERRT

ABSTRACT

The Blackhawk Formation in the Sunnyside district, Utah, 

was deposited along the west margin of the Western Interior 

Cretaceous sea during southeastward withdrawal of the sea. 

Sand was the dominant type of terrigenous sediment deposited 

in the Sunnyside district during the regressive phases. Sand 

bodies prograded seaward in response to changing sediment supply from a source west of Sunnyside. Where conditions were 

favorable for the accumulation of vegetable material, peat 

deposits formed landward of the sand bodies and were later 

changed by diagenesis to bituminous coal. The coals formed from 

accumulation of small low-growing plants and plant debris that 

was transported into the area of accumulation. Remains of 

large plants in the coals are rare.

Trace fossils, which are tracks, trails, and burrows formed 

by organisms and preserved in the rock, are extremely abundant 

in the Blackhawk rocks. These biogenic sedimentary structures 

are common in Cretaceous deposits throughout the Western 

United States. Trace-fossil distribution in the rocks is controlled 

by the depositional environment preferred by the organisms 

that created the traces. A study of the trace fossils of a locality 

allows a more precise determination of the conditions that 

existed during deposition of the sediments. Water depth, bottom conditions, salinity, current velocity, and amount of suspended nutrients are some of the environmental factors that 

may be reconstructed by studying trace fossils.

The Blackhawk Formation in the Sunnyside district comprises the Aberdeen, Kenilworth, and Sunnyside Members. The 

Blackhawk Formation is underlain by and pinches out into the 

Mancos Shale and is unconformably overlain by the Castlegate 

Sandstone. Sandstone units of the members of the Blackhawk 

form the basal units of the Book Cliffs and thereby effect an 

abrupt transition from the low topography of Clark Valley to 

the sheer cliffs.

Coal mining is the principal industry of the Book Cliffs region. 

Mines of the Sunnyside district are loci for coal-mine bumps, 

which are sudden, catastrophic releases of stress in the coal. 

Bumps often cause loss of life, property damage, and loss of 

profit to mining companies. Bumps occur when shear stress built 

up in the coal exceeds the shear strength of the coal. Differential 

overburden pressure, faulting and other tectonic activity, and 

lithology and structure of the enclosing rocks are among the 

factors that influence bumps. Petroleum and natural gas 

(methane), which occur locally in pockets in the roof rocks above 

coal beds, may be diagenetic products of organic-rich sediments.

Investigation at Sunnyside has revealed that many factors 

influence coal-mine bumps. Among these factors are differential 

compression of the coal and ease with which the coal can move 

into mine openings in response to pressure. Whether the coial 

continually creeps into the entry and spalls off or whether it 

bursts under an excess of stored stress depends upon the 

lithology of the enclosing rocks and the geometry of the interfaces between coal and rock.

Where directional sedimentary structures are at large angles 

to entries, coal can slip relatively easily into the entries and 

continually relieve stress. Where friction builds between the 

roof or floor rock and the coal, stress may accumulate to the 

point of catastrophic failure of the coal. Such friction buildup 

may be due to structures oriented at small angles to the entries 

or to coarse-grained rocks enclosing the coal.

By studying inorganic and biogenic sedimentary structures 

and by mapping their trends, geologists may furnish a tool to 

help avoid mine bumps and rock bursts.

INTRODUCTION

This report stems from an investigation of geologic 

factors that may cause coal-mine bumps in the mines 

at Sunnyside, Utah. Future papers will discuss more 

comprehensively how these factors relate to mine 

bumps.

The coal mined at Sunnyside is in one of many thick 

coal beds that occur in the Blackhawk Formation. These 

beds are mined extensively in the Book Cliffs and 

Wasatch Plateau coal fields, and the coal industry is 

the basis for most of the economy of central Utah. 

Coal-mine bumps are sudden, catastrophic releases of 

stress in the rib, roof, or floor of a coal mine. These 

releases are of varying intensity, but all have the capacity to cause property damage (fig. 44) and work loss, 

as well as loss of life. Sunnyside mines long have been 

loci for violent bumps. Parallel goals of the present 

work were to ascertain the relationship of sedimentary 

structures to coal-mine bumps, to study and describe 

the trace fossils and inorganic sedimentary structures 

found in the rocks, and to ascertain the origin and mode 

of migration of petroleum and natural gas in the mines 

at Sunnyside.
2

110°24'

SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

23' 110° 22'

 -. - - -ii i , . * . ?'&**s-~

: /. ': : '-' r^j^-^^p.-;. J:

EvX-i/v. :-jf .\J5^J~'.". :\.'. '.-.'. j-.'.'X^^xvX-xv/

::::.f. . -JS. -JKrm .L-ir^, . - AA'-'.-Sv.-.v.v/f___,

Base modified from Osterwald 

Osterwald, Dunrud, and Mabei 

with additions by J. O. Maberry, 

Geology south of Number Two Canyon by 

J. O. Maberry, 1967; geology north of 

Number Two Canyon adapted from 

Osterwald (1962b)

CONTOUR INTERVAL 200 FEET 

DATUM IS MEAN SEA LEVEL
INTRODUCTION

EXPLANATION

Alluvium, colluvium, and gravel

Upper Cretaceous Price River

Upper mudstone member

Mudstone with sandstone and

siltstone lenses 

Contains Sunnyside coal bed

near base

Sunnyside Member

Lower mudstone member 

Mudstone with sandstone and

siltstone lenses 

Contains Rock Canyon coal bed

near base

Mancos Shale 

Overlies and underlies 

Aberdeen Member (Kba)

Contact

Dashed where approximately located 

U ______ 

D

Fault

Dashed where approximately located. 

U, upthrown s?'de; D, downthrown. side

6

Strike and dip of beds

74 §

Inclined Vertical 

Strike and dip of joints

Coal mine portal

FIGURE 1. Blackhawk Formation and associated strata at 

Sunnyside.

A major structural feature of east-central Utah is 

the San Rafael Swell, a northeast-trending asymmetrical anticline that plunges northeastward under the 

Book Cliffs (fig. 3). The swell probably is of preTriassic age and, therefore, probably caused localized 

depositional thinning of Blackhawk sediments at 

Sunnyside. The Blackhawk Formation crops out on the

south- and west-facing scarps of the Book Cliffs. The 

cliff front is a faceted surface that resulted from 

erosion of the Roan Plateau. South of Sunnyside, strata 

strike northward; as the structural strike approaches 

the northeast end of the San Rafael Swell, the beds 

gradually change strike toward the west as they are 

gently folded over the crest of the swell. North of 

Sunnyside, beds strike westward and dip northward. 

Dips of the beds are as much as 15° N. and E. at the 

cliff front and decrease downdip to about 7°. The 

steeper dip at the cliff front probably is due to the 

proximity of the front to the crest of the swell, where 

the structural inclination is greatest. Traced downdip, 

the strata pass into the Uinta Basin.

The regional joint pattern is characterized by two 

major sets of joints at nearly right angles to each other, 

striking N. 75°-85° W. and N. 12°-20° W. (Osterwald 

and Eggleton, 1958, p. 13; Maberry, 1968, p. 9). Joint 

orientations are relatively constant throughout the area. 

As might be expected, joints are best expressed and 

best preserved in sandstone units.

Known faults in the Sunnyside area are alined subparallel to the regional joint pattern, and many major 

faults strike N. 12°-20° W. (fig. 1). All faults in the 

area are normal faults; fault planes dip 75°-900 . No 

known faults in the Sunnyside area effect more than 

150 feet of stratigraphic separation at the surface. A 

buried northwest-trending fault south of the area, 

which was discovered by use of seismic methods 

(Tibbetts and others, 1966), may have as much as 2,000 

feet of stratigraphic separation; the fault is downthrown to the northeast. The principal fault system at 

Sunnyside is the Sunnyside fault zone (Osterwald and 

Dunrud, 1966), which trends northwest and is downthrown to the southwest. It is a series of long northwest-trending faults with many short curving spurs 

(fig. 1). The Sunnyside zone causes difficulties in mining because the faults offset the coal bed, affect 

stress distribution, and necessitate changes in mining 

procedure.

Coal extraction underground commonly produces 

subsidence cracks at the surface. Most subsidence cracks 

are formed on spurs or noses above mine workings and 

trend subparallel to joints. Joint orientation controls 

alinement of subsidence cracks because many en echelon 

subsidence cracks closely parallel nearby joint trends. 

Extraction of the coal removes support for overlying 

rocks. The rocks immediately above the coal fail, and 

the failure eventually continues upward to the surface. 

Mine air issues from some of the cracks, and some 

cracks are visible at the surface, as much as 1,200 feet 

above the mine workings. Subsidence cracks range in 

size from splits one-fourth inch wide and a few feet long 

to crevasses 4 feet wide and 50 feet long (fig. 2).

422-052 O - 71 - 2
SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

A B

FIGURE 2. Subsidence cracks. A, Small en echelon cracks trending northwest at surface about 800 feet above Sunnyside coal, at 

junction of Pasture Canyon and Whitmore Canyon. B, Large crack trending northwest about 900 feet above Sunnyside coal 

in west wall of Whitmore Canyon; mine air issues from crack. Photographs by F. W. Osterwald.

LOCATION

The Sunnyside coal-mining district is in the western 

Book Cliffs, 27 miles east of Price, Utah (fig. 3). As 

described herein, the Sunnyside district lies wholly 

within Carbon County. The district was named for 

Sunnyside, the first and largest incorporated town in 

the district, with a population of approximately 800. 

The district is accessible by State Highways 123 and 

124, which connect to the west and south, respectively, 

with U.S. Highway 6 and 50. The Denver and Rio 

Graiide Western Railroad and the Carbon County Railway furnish freight service to the area. The district is 

northeast of the San Rafael Swell and at the base of the 

Roan Plateau, a maturely dissected high plateau in the 

Colorado Plateaus physiographic province.

PREVIOUS WORK

The Book Cliffs coal field has been the subject of 

much investigation. The coal deposits are thick and well 

exposed and have low dips. In the Sunnyside district, 

the coal in the Blackhawk Formation is high-quality 

bituminous coking coal, which is particularly valuable 

to industry. The Sunnyside district is also the locus of 

spectacular mine bumps, which have been studied intensively because they are hazardous to life and property.

Most investigators have concentrated on the economic 

geology of the area. Weimer (1960, 1961) defined regional stratigraphic relationships and correlations and 

set the framework for concepts of Cretaceous history in 

the area of Colorado, Utah, and Wyoming. Fisher, Erdmann, and Reeside (1960) discussed regional stratigraphy in a comprehensive paper on the Book Cliffs of 

Utah and Colorado.

Spieker and Reeside (1925) named and defined many 

Cretaceous and Tertiary units in central Utah, where 

Spieker and Reeside (1926) also investigated paleoshoreline orientations. Young (1955, 1957) studied the 

facies interrelationships in the Upper Cretaceous rocks 

of the Book Cliffs and based his work largely on Pike's 

(1947, p. 13-25) work south of Sunnyside. Young 

named and defined some of the members of the Blackhawk Formation, but his work was on a regional scale, 

and his conclusions are subject to some controversy.

The most detailed work in the Sunnyside district was 

done by Osterwald (1961; 1962a, b); Osterwald and 

Eggleton (1958); Osterwald and Brodsky (1960); 

Osterwald and Dunrud (1964, 1966) ; Osterwald, Dunrud, and Maberry (1968), who mapped much of the 

area at a scale of 1:6,000; and Brodsky (1960), who 

studied the general stratigraphic relationships of the
INTRODUCTION

45' 30'

39°45' 

15' 

39°00' -

FIGURE 3. Index map of the Sunnysiide district. Axis of San Rafael Swell from Stam (1956). Topographic and structural form lines from Howard (1966a), Osterwald and Dunrud (1964), and Stam (1956).
SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

Mesaverde Group. Most of these works, however, are 

based primarily on lithologic variation, writh emphasis 

on the relationship of lithologies to the coal beds of the 

Blackhawk Formation.

Howard (1966a, b, c) studied trace fossils and sedimentary structures in Blackhawk strata in the Wasatch 

Plateau and western Book Cliffs, where the strata are 

stratigraphically lower than Blackhawk rocks at 

Sunnyside.

ACKNOWLEDGMENTS

I am indebted to W. A. Cobban and F. W. Osterwald, 

U.S. Geological Survey, for reviews of the manuscript. 

Osterwald's interest and direction during all phases of 

the work are particularly appreciated. James D. 

Howard, University of Georgia Marine Institute, instructed me in many aspects of trace fossils and sedimentary structures and furnished some illustrations. 

Discussions and field conferences with Dr. Howard were 

particularly valuable in understanding and interpreting 

the phenomena discussed herein. John Peperakis and 

Harry Elkin, Kaiser Steel Corp., allowed access to the 

study area and provided maps and other information 

regarding the coal beds. R. J. Weimer, John Hayes, and 

R. H. DeVoto, Colorado School of Mines, critically 

reviewed an earlier version of the report (Maberry, 

1968). E. E. McGregor, U.S. Geological Survey, 

analyzed selected lithologic samples with an X-ray 

diffractometer. Artist's sketches of trace fossils were 

made by Roger B. Williams, University of Kansas.

BIOGENIC SEDIMENTARY STRUCTURES

Biogenic sedimentary structures, commonly called 

trace fossils, are tracks, trails, burrows, or borings made 

by organisms and preserved in rock strata. In short, 

trace fossils indicate where organisms have been. The 

lack of body fossils, particularly in sandstones, has been 

partly responsible for a lack of detailed paleoecological 

stratigraphic work in much of the Western United 

States. These trace fossils, or lebensspuren, are valuable 

paleoecologic indicators. Where body fossils are present, 

traces may be used to reinforce interpretations; where 

body fossils are scarce or absent, trace fossils may be 

used effectively to interpret the paleoenvironment. Body 

fossils may be transported from the living site, or they 

may be destroyed by diagenesis. Trace fossils, on the 

other hand, are found almost unquestionably in place, 

although J. D. Howard (oral commun., 1967) indicated 

that some Ophionwrpha burrow casts may be reworked. 

Most trace fossils are emphasized by diagenesis.

Trace fossils have been investigated mostly by Europeans, particularly the German geologists Hantzschel 

(1962) and Seilacher (1964, 1967). In the present report, much of the material included in the term "trace

fossils" has heretofore been assigned to categories such 

as algae, fucoids, incertae cedis, problematica, inorganic 

structures, worms, or f eces. The accurate description and 

classification of trace fossils may help bring to American 

geologists a valuable tool to be used in reconstructing 

the geologic history.

Howard (1966a, c) described trace fossils in the 

Blackhawk Formation near Helper, Utah. No other 

trace fossils from central Utah have been described; 

therefore, this report contains a detailed and extensive 

discussion of trace fossils to provide references for 

stratigraphic interpretations based on traces.

Hantzschel (1962) and Seilacher (1964,1967) showed 

that trace fossils are grouped in sedimentary facies according to the environments preferred by their animal 

creators (fig. 6). Some traces definitely indicate shallow 

marine conditions; some indicate terrestrial deposition. 

The orientation of traces of the same type of organism 

indicates the relative rate of sedimentation. Seilacher 

(1967, p. 421) emphasized that vertical burrows in shallow-water deposits and the gradual tendency toward 

horizontal burrows in deeper water deposits correspond 

to a trend from suspension to sediment feeding. The 

type of feeding is a response to the amount of suspended 

nutrients at different levels in water and in sediment. In 

shallow zones, food for organisms is in suspension; at 

depth, in quiet water, nutrients settle out of suspension 

and become part of the sediment. Hence, in quiet waters 

the trend is toward horizontal intricately patterned 

burrows. By studying trace-fossil forms and associations on the outcrop, in mine workings, and in the 

laboratory, one can deduce the history and environment 

of deposition of strata. From these deductions, the positions of various strata in a depositional framework can 

be postulated with an increasing degree of accuracy.

The Upper Cretaceous strata of Wyoming, Colorado, 

and Utah have been the subject of intensive trace-fossil 

studies in recent years because of the paucity of body 

fossils and extreme wealth of trace fossils in these 

strata. Representative investigations are those by Toots 

(1961), who used trace fossils to delineate beach zones 

and strandlines in Wyoming, and by Masters (1966), 

who used trace fossils as environmental indicators in 

his study of the Mesaverde Group of northwestern 

Colorado. Howard (1966 a, b, c) exhaustively studied 

trace fossils in units slightly older than those discussed 

herein, and his work in the Wasatch Plateau west of 

Sunnyside dovetails with the studies described here.

The creators of all trace fossils described herein had 

an affinity for warm waters. Reeside (1957, p. 505) 

postulated a nearly tropical climate for the Western 

Interior for most of the Cretaceous Period, an interpretation based primarily on body fossils. Parker (1969)
BIOGENIC SEDIMENTARY STRUCTURES

collected fossil flora from the Blackhawk Formation 

near Salina, Utah, and concluded from his study that 

the regional climate was subtropical during Late 

Cretaceous time. My interpretation, which is based on 

the presence of thick coal beds and palm-leaf fossils in 

terrestrial deposits within the Blackhawk Formation 

(fig. 4), agrees with the conclusions of Reeside and 

Parker.

USES OF TRACE FOSSILS

Most sedimentary syngenetie economic minerals are 

controlled by physical and chemical conditions extant at 

the time and place of deposition. Oil and natural gas in 

stratigraphic traps associated with nearshore marine 

sediments are well known. Trace fossils may be used as 

environmental indicators to predict areas that are favorable for entrapment of such deposits, and, consequently, 

loci for exploration may be delineated. Localization of 

sedimentary mineral deposits of manganese, phosphate, 

barite, iron, and evaporites is controlled by factors such 

as depth of water, temperature, salinity, circulation barriers, and organisms that facilitate precipitation. In the 

Western United States, most coal deposits are associated 

with marine or transitional-marine sedimentary rocks. 

When trace fossils can be recognized in drill cores, depositi'onal conditions may be ascertained at some distance 

from the outcrop. Body fossils need not be present for 

one to interpret sedimentary environments. Geologists 

have become increasingly interested in trace fossils and 

their definition and uses (Howard, 1968). Some conditions of mining various commodities might also be predicted through knowledge of associated trace fossils.

DESCRIPTIVE NOMENCLATURE

Because it cannot be definitely known which genus 

and species of organisms made individual trace fossils,

FIGURE 4. Palm-leaf fossil found in upper part of the Sunnyside Member. On the basis of morphology, the fossil is inferred 

to be part of a leaf.

traces cannot be grouped into normal systematic taxonomic units. The trace-fossil nomenclature used in the 

present report was determined on the basis of the function, or ethology, of the fossil, according to the methods developed by Seilacher (1964). Traces are described 

partly on the basis of their relationship to the substrate 

on which they were formed.

ANIMAL-SEDIMENT RELATIONSHIP

Trace-fossil preservation is classed as epirelief, in 

which traces are present on the lower surfaces of beds 

(fig. 5) ; hyporelief, in which traces are present on the 

upper bedding surfaces; and full relief, in which traces 

are completely contained within the strata and are preserved as the original cavity or cavity filling. Originalcavity, full-relief trace fossils are very rare in the Book 

Cliffs. Epirelief and hyporelief trace fossils have convex 

and concave features. A convex feature is one that projects above the upper bedding surface or below the bottom of a bed. Conversely, a concave feature is one that 

is indented into the bedding surface.

Most trace fossils on bedding surfaces were formed 

either by locomotion of the animal, forming tracks and 

trails, or by excreta from the animal. Traces that are in 

upright positions were mostly living burrows, formed 

either by peristaltic contractions of the animal's body 

as it forced itself down into the substrate or by excavation accomplished by the animal's sediment intake. 

Walled or reinforced burrows were reinforced against 

a mobile substrate by excretions from the animal. Upright burrows that are interpreted as escape burrows 

(such as those that Asterosoma makes) were excavated 

by the animal and infilled with the sediment that passed 

through its system. Most horizontal trace fossils of infauna were formed by the animal by sediment intake and 

infilling with excretion, although some infaunal traces 

probably were informed by soft-sediment deformation.

SUBDIVISION OF BLACKHAWK TRACE FOSSILS

Every outcrop of Blackhawk rocks in the Sunnyside 

district exhibits some evidence of organism activity in 

the sediment at the time of deposition. The environment 

in which organisms responsible for trace fossils were 

most abundant and most varied is represented by interbedded siltstones and very fine to fine-grained sandstone. Some mudstones are also intensively burrowed, 

but preservation of trace fossils is poor in mudstone. 

The siltstone and fine-grained sandstone are rich in 

finely divided organic material and are very thinly and 

evenly bedded (fig. 6J.). This environment was inhabited dominantly by detritus feeders (also called filter feeders or sediment feeders), which were organisms 

that prowled the surface of deposition and (or) bur-
8 SEDIMENTARY FEATURES, BLACKKAWK FORMATION, CARBON COUNTY, UTAH

SEMIRELIEF PRESERVATION

CONVEX CONCAVE

EPIRELIEF 

(On lower surface of beds)

HYPORELIEF 

(On upper surface of beds)

CONCAVE CONVEX

PRIMARY CAST OF 

SURFACE TRAIL

PRIMARY CAST OF 

BURROW AT INTERFACE

Sedimentation fills groove Sediment fills burrow

Groove on mud Burrow along interface

SECONDARY CAST OF 

MUD BURROW

Sedimentation fills remnant

Erosion

Feces-stuffed burrow in mud

FULL-RELIEF PRESERVATION

ORIGINAL CAVITY CAVITY FILLING

Animal burrow 1. Active fill, stuffed by animal

2. Passive fill, filled by sedimentation

FIGURE 5. Types of preservation of trace fossils, showing means of creation (modified from Sellacher,

1964).

rowed below the surface in search of food. They derived 

nourishment from nutrients, either living microorganisms or dctrital organic material, that were part of the 

sediment. The actions of these detritus feeders in their 

search for food thoroughly altered the primary sedimentary structures and destroyed all but a few traces 

and suggestions of the morphology of the organisms 

themselves. Such alteration is called bioturbation. Evidence of primary lamination is scattered because the 

organisms churned the sediments before lithification.
BIOGENIC SEDIMENTARY STRUCTURES 9

The pattern of organic mottling suggests that the original sediments were thinly laminated and had little or 

no primary structural dip.

The smallest population of trace fossils is found in 

fine- to medium-grained moderately well sorted sandstone (fig. 6^). Sediments were often affected by currents that built ripple marks and cross-lamination and 

that shifted and reworked the sediments. The power of 

the transporting medium was sufficient to winnow out 

fine sediments and prevent deposition of organic detritus. Organisms in this environment were almost exclusively suspension feeders that built burrows which 

were strong enough or deep enough to exist in a mobile 

substrate. The organisms built their shelters upward 

to keep pace with sedimentation. Progressively fewer 

traces are found in rocks indicative of environments of 

increasingly stronger current velocity.

The environment in which organisms responsible for 

trace fossils lived in moderate abundance is represented 

by thin-bedded very fine to fine-grained sandstone that 

occurs above the interbedded siltstoiie and sandstone 

unit just described. The rocks of this sandstone unit

are cross stratified in long low-angle wedge-shaped sets. 

Both complete and truncated large ripple marks are 

common in this interval. The depositional environment 

supported both detritus-feeding and suspension-feeding 

organisms. Suspension feeders obtain nourishment from 

pelagic microorganisms. In beds where detritus feeders 

were dominant, the strata are very bioturbate. These 

beds are not quite as intensively disturbed as in the 

siltstone and sandstone zone below, however; mottling 

commonly occurs in patches or pockets within a bed. 

Laterally, in the same bed, the sediments may be relatively undisturbed. Such strata commonly are described 

by geologists as clean-to-mottled strata. Where suspension feeders were the dominant organisms, sediments 

are moderately well sorted and slightly carbonaceous 

(fig. 6Z>). The current velocity was sufficient to winnow 

out the fine sediment, including carbonaceous matter, 

but not great enough to permit constant reworking and 

mobilization of the substrate. Trace fossils of detritus 

feeders in rocks of this environment indicate an attempt by these organisms to escape to a more favorable 

habitat.

A B C

FIGURE 6. Environmental grouping of trace fossils. No scale. (Modified from Howard, 1966a.) A, Very calm 

water, shallow and deeper neritic and lagoon environments with much silt, clay, very fine sand, and 

carbonaceous debris. Sediments thoroughly reworkeld and mottled by organisms; primary structures and 

bedding destroyed. Poorly preserved trace foissilsi. B, Shallow neritic environment, characterized by 

medium kinetic energy. Very fine to fine sand, moderately well sorted, low cross-stratification. Many 

trace fossils, most of which are well preserved. C, Environment of high kinetic energy, typical of the 

littoral zone. Well-sorted fine- to medium-grained sediments. Much cross-stratification. Few trace f osisils; 

those present are mostly poorly preserved.
10 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

ETHOLOGICAL CLASSES

Seilacher (1964) established the following nomenclature for trace fossils on the basis of the function of 

the trace-fossil structure:

1. Repichnia: Trails or burrows left by vagile benthos 

forms during directed locomotion.

2. Pascichnia: Winding trails or burrows of vagile 

mud eaters, which reflect a grazing search for food 

by covering a given surface fairly efficiently and 

by avoiding double coverage.

3. Fodiniclmia: Burrows made by hemisessile deposit 

feeders. These burrows reflect the search for food 

and at the same time fit the requirements for 

shelter.

4. Domichnia: As the root suggests, permanent shelters 

dug by vagile or hemisessile animals that procurred food from outside the sediment as predators, scavengers, or suspension feeders.

5. Cubichnia: Shallow" tracks left by vagile animals 

that hid temporarily in the sediment, or lurked or 

rested on the sediment surface, that obtained their 

food as scavengers or suspension feeders.

BATHYMETRY OF TRACE FOSSILS

Seilacher (1964,1967) grouped trace fossils according 

to the bathymetric conditions preferred by the organisms that made the traces (table 1). The universal 

ichnofacies, or trace-fossil groupings based on a general, overall relationship between the ethological character of the trace fossils and the geological f acies indicated 

by lithology and inorganic sedimentary structures are:

1. Cruziana facies, in the littoral to sublittoral zone, 

above wave base. Dominant trace fossils are domichnia and cubichnia; fodinichnia of detritus 

feeders are found in deep water.

2. Zoophycos facies, in the sublittoral to bathyal zone, 

below wrave base and without turbidite sedimentation. Dominant trace fossils are fodinichnia of detritus feeders.

3. Nereites facies, defined by Seilacher (1964, p. 311) 

as "bathyal with turbidite sedimentation." Dominant trace fossils are repichnia and pascichnia.

Interpretations of the environmental significance of 

trace fossils are based largely on the work of Seilacher; 

my interpretations that differ from those of Seilacher 

are noted.

Illustrations of these trace fossils were prepared by 

Roger B. Williams, Paleontological Institute, University of Kansas, Lawrence, Kans., and many were first 

published by Howard (1966c). Mr. Williams' illustrations are used with the permission of Dr. Howard.

SYSTEMATIC DESCRIPTION OF BLACKHAWK TRACE 

FOSSILS

A structure commonly observed in trace fossils is 

spreite, defined by Hantzschel (1962, p. W178) as "a 

German noun literally translated as 'spread" and meaning something spread between twT o supports, as the web 

of a duck's foot." Spreite are common in fodinichnia 

structures.

PASCICHNIA

CHEVRON TRAILS

Figure 7

Chevron trails occur as convex epireliefs on bedding 

surfaces of very fine grained sandstone. Width of track 

ranges from 10 to 15 mm (millimeters) and averages 

12 mm. This trace fossil is commonly multitudinous. 

Trails are subparallel to parallel; many are aligned 

parallel to shoreline, as shown by measurement of associated ripple marks and sole markings and by alinement of detritus on bedding surfaces. Apparently, 

pascichnia formed by organisms grazing at the sediment-water interface. The fossil is a shallow^ neritic 

marine indicator (Howrard, 1966a).

TABLE 1. Universal ichnofacies 

[Modified from Seilacher (1964, p. 310, 311)]

Ichnofacies Dominant groups of trace 

fossils

Diagnostic inorganic 

sedimentary structures

Dominant lithology Probable depth

Cruziana facies.

Zoophycos facies, 

Nereites f acies _ _.

Cubichnia; domichnia 

of suspension feeders 

(shallow, turbulent 

zone); fodinichnia 

of detritus feeders 

(deeper zone).

Fodinichnia. __________

Pascichnia; repichnia_

Oscillation ripples, 

foreset bedding in 

shallow zone, welllaminated bedding 

in deep water.

Bedding and lamination poor.

Load casts, convolute 

lamination, other 

turbidite structures.

Well-sorted sandstone-- Littoral to sublittoral, 

above wave base.

Mottled siltsone and 

mudstone.

Mudstone and muddy 

and silty sandstone 

with high carbonaceous content.

Sublittoral to bathyal,

below wave base. 

Bathyal.
BIOGENIC SEDIMENTARY STRUCTURES 11

B

FIGURE 7. Chevron trails; movement indicated by arrows. A, 

Trails on bedding surface; from middle sandstone tongue 

of Kenilworth Member. B, CTose view of same specimen. C, 

Artist's illustration.

FODINICHNIA 

TEICHICHNUS A 

Plate 1, figures 1-3

Teichichnus A and B were differentiated by Howard 

(1966a, p. 145) on the basis of dissimilar morphological 

characteristics.

Teichichnus A is a burrow consisting of a series of 

spreite which form a vertical blade. When viewed from 

the side, the burrow resembles a narrow-angle "lazy" U. 

Inteiiayered with the spreite are carbonaceous silty laminae which have not been burrowed. The nonburrowed 

material is fine grained and not resistant and, hence, 

forms a constriction in the blade. The constrictions give 

Teichichnus A the gross appearance of a series of superposed round tubes, all emanating from a primary, or 

main, tube. The blades are 2-4 cm (centimeters) high 

and generally about 5 mm wide, blades more than 75 

cm long have been observed on outcrops. The blade itself is always normal to bedding, but spreite of the 

blade vary from horizontal to vertical and commonly 

form a sinuous pattern. Teichichnus A is found in 

closely packed sandy siltstone deposited in marine 

neritic environments (Seilacher, 1964, p. 310). It is a 

feeding burrow of a detritus feeder, possibly a polychaete worm.

TEICHICHNUS B

Plate 1, figures 4, 5

Teichichnus B was possibly formed by the same organisms that formed type A, but Teichichnus B is a 

much larger structure; all specimens are in the form of 

vertical blades cutting across bedding with spreite forming superposed tubes. The individual tubes are oval 

in cross section and are commonly as much as 1 cm high 

and 5 mm wide; in all observed specimens, the tubes 

are subparallel throughout their length. Most blades 

are about 5 cm high and 1-5 cm wide and vary in length 

owing to the random grazing habit of their creators. A 

fodinichnia-type burrow was found in very fine to 

fine grained sandstone. Because of the increased size of 

the organism and better sorting of sediments where 

Teichichnus B is found, this fossil is believed to represent deposition in water shallower than that in which 

type A was formed.

ARTHROPHYCUS

Figure 8

Arthrophycus is a conduitlike segmented trace commonly normal to bedding. Preservation varies from full 

relief to convex epirelief; cavities are commonly filled. 

Some branching forms have a slight bulge at the point 

of branching, but these forms are uncommon. The trace

422-052 O - 71 - 3
12 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

FIGURE 8. Arthrophycus. A, In nodular carbonaceous siltstone 

of Sunnyside Member. B, Sketch showing typical mode of 

occurrence and morphology similar to that of Ophiomorpha.

is round to flattened oval in cross section, 5-15 mm in 

diameter; its length is indeterminate where the trace 

passes into sandstone or turns away from the outcrop. 

Arthrophycus is often confused with Ophiomorpha because of its rough exterior and branching nature. It is

most common in siltstone and very fine to fine grained 

sandstone. Arthrophycus is a fodinichnia burrow, indicative of a relatively wide depth range (Seilacher, 

1964, p. 311).

SMOOTH TUBES

Figure 9

Some full-relief or convex-epirelief burrows are preserved as smooth curving uiiornamented tubes oriented 

at random throughout the rock .These smooth tubes may 

be Arthrophycus. Their cross section is round to oval 

and has a diameter of 8-15 mm; their length is indeterminate. Smooth tubes are found in finely mottled 

siltstone and clean-to-mottled fine-grained sandstone, 

and they are neritic marine indicators.

FIGURE 9. Smooth tubes. A, From siltstone 'above Sunnyside 

coal bed. (One tube shown by arrow.) B, Sketch.
BIOGENIC SEDIMENTARY STRUCTURES 13

CHONDRITES 

Figure 10

Chondrites is a concave-epirelief trace characterized 

by a plantlike appearance that results from the presence of numerous short branching segments. Horizontal 

branching trails reflect short excursions from a central 

vertical burrow. Diameter of the branches is 1 3 mm. 

Chondrites is found at Sunnyside in very fine grained 

sandstone, which is interpreted, on the basis of inorganic sedimentary structures associated with the trace 

fossil, to be very shallow neritic to littoral marine sandstone (Seilacher, 1964, p. 311).

ASTEROSOMA

Plate 2

A trace fossil previously named Cylindrichnus (Howard, 1966a, p. 73) was recently identified by Howard 

and H. W. Dresser (oral commuii., 1968-69) as a variant 

of Asterosoma (Hantzschel, 1962, p. W184). Asterosoma is a full-relief burrow found in orientations from 

horizontal to vertical. Horizontal burrows are found in 

very fine grained carbonaceous sediments. They reflect 

a random contented grazing search for food in a hospitable environment in which the animals roiled and 

mottled the sediments intensively. Steeply angled burrows are escapeways from hostile environments. The 

Asterosoma animal built steep burrows as the current 

velocity increased and food was winnowed from the 

sediment, or as the rate of sedimentation increased and 

there was less food for the animal as the finely divided

FIGURE 10. Horizontal branching trails of Chondritcs (circled), 

from middle sandstone facies of Sunnyside Member.

nutrients were winnowed out. High-angle and vertical 

burrows are common in clean well-sorted sandstone, 

where they are associated with Ophiomorpha. Highangle Asterosoma burrows culminate upward in what 

Howard (1966a, p. 70) called helicoid funnels (pi. 2, 

figs. 3, 4, and 6), full-relief vertically oriented funnelshaped structures which at the top range in diameter 

from 4 cm to as much as 25 cm. These funnels seem to 

indicate a change in the animal's burrowing habits, a 

fresh influx of carbonaceous material into the environment, and a lowering of current velocity.

CYLINDRICHNUS REPTILIS BANDEL 

Figure 11

Cylindrichnus reptilis was named by Bandel (1967, 

p. 6). This fossil is a vertical full-relief tube that is 1-3 

cm in diameter and usually 8-14 cm high; its cylindershaped burrows are found in coarsely mottled siltly 

sandstone. Cylindrichmbs reptilis Bandel is comparable 

in form to Cylindricum Linck (Hantzschel, 1962, p. 

W189), and it is common in thin-bedded sandstones in 

two members of the Blackhawk Formation. I believe this 

fossil to be an indicator of littoral to sublittoral marine 

zones.

LABYRINTH CASTINGS 

Figure 12

Local pockets of tightly interwound trails or castings 

are preserved as convex epireliefs on the bottom surfaces 

of fine- to medium-grained sandstone beds. These castings are similar morphologically to Phycodes (Hantzschel, 1962, p. W208). The small interstices between 

castings are filled with carbonaceous dust. The fossil is 

commonly associated with pieces of woody debris and 

is indicative of a littoral to flood-plain environment. 

The labyrinth trails possibly were made by polychaete 

worms, although W. A. Cobban (written commun., 

1969) suggested that they are ship worm borings.

GYROCHORTE

Figure 13

Gyrochorte is a simple bilobate trail preserved as convex hyporelief in well-sorted fine-grained sandstone. 

It is characteriezd by a median furrow and superficially 

resembles Avlichnites. Trails are 1 7 mm wide, of indeterminate length, and 1-3 mm high. Surfaces are generally smooth; crossing burrows pass over or under each 

other, never destroying another burrow. Traces indicate 

random, meandering locomotion; there is no branching. 

Gyrochorte was described by Seilacher (1964, p. 311) 

as nondiagnostic of depth, but because of the traces 

with which Gyrochorte is associated (fig. 38), I believe
14 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

B

FIGURE 11. CylindricJimis reptilis Bandel. A and B, At interface 

between carbonaceous sandstone and overlying mediumgrained well-sorted sandstone of the upper sandstone facies 

of Sunnyside Member.

that Gyrochorte indicates a sublittoral to littoral environment. This trace probably was made by gastropods 

(Hantzschel, 1962, p. W198).

AULICHNITES 

Figure 14

Aulichnites is a simple bilobate crawling trail preserved as convex-epirelief forms in very fine- to finegrained well-sorted sandstone. There is a median furrow 

in all trails. Meandering directions reflect a grazing 

search for food. Trails are 1-5 mm wide and 1-3 mm 

high, and they have smooth surfaces. Burrows were not 

reused and they do not branch. These trails probably 

were made by gastropods, perhaps the same genus as

B

c

FIGURE 12. Labyrinth castings in upright positions. A, Large 

castings; from upper part of Sunnyside Member. B, Smaller 

castings, similar morphologically to those shown in A; Castlegate Sandstone-Blackhawk Formation contact. (7, Sketch.

Gyrochorte but with different habits. Aulichnites indicates littoral deposits. (Description from Bandel, 196Y, 

p. 4.)
BIOGENIC SEDIMENTARY STRUCTURES 15

FIGURE 13. Gyrochorte; from lower sandstone facies of Sunnyside Member.

DOMICHNIA 

OPHIOMORPHA

Plate 3

Known for many years as Halymenites major 

Lesquereaux, a European algal form which it superficially resembles, OpMomorpha is one of the most widely 

distributed trace fossils in Mesozoic to Holocene sediments in the United States. The fossil is a full-relief 

burrow, many specimens of which are vertical, preFIGUEE 14. AulicJmites; from middle sandstone tongue of 

Kenilworth Member.

served as either cores or casts with characteristic bumpy 

surfaces. Casts of burrows found in deposits of shallowwater environments have a thick outer wall similar to 

that of burrows of the modern shrimp Callianassa major 

Say, which is considered the modern counterpart of the 

OpMomorpha organism (Weimer and Hoyt, 1964; Hoyt 

and Weimer, 1965). OpMomorpha burrows vary widely 

in size with variation in sedimentation. Well-sorted fineto medium-grained sediments contain the largest burrows ; burrows are smaller as the content of carbonaceous 

debris in the sediments increases. The animal that 

formed Opliiomorpha preferred environments with little suspended sediment for its role as a suspension 

feeder, because when there was an excess of suspended 

sediment the phytoplankton upon which the animal fed 

would not be present. OpMomorpha is found in many 

different types of sedimentary rocks at Suimyside, however. Several different species of Callianassa are found 

in modern estuaries, open lagoons, or tidal inlets, but 

burrows of species other than C. major Say cannot be 

confused with OpMomorpha. Burrows of other species 

of Callianassa resemble Arthrophycu^, smooth tubes, or 

large horizontal burrows (R. J. Weimer, written 

commun., 1968). Seilacher (1964, p. 313) pointed out 

the bathymetric inferences drawn from trace-fossil 

orientations.

ARENICOLITES 

Figure 15

Arenicolites is a full-relief vertically oriented 

U-shaped burrow with a diameter of 5-7 mm. Most burrows are oval in cross section, probably because of compression during lithification. The length of the burrow 

is controlled by the thickness of the enclosing bed. 

Arenicolites is preserved on bedding surfaces as pairs 

of depressions, usually 10-50 mm apart. This fossil is 

a domichnia- or f odinichnia-type burrow of a polychaete 

worm and is found in well-sorted fine- to mediumgrained sandstone; the burrow indicates littoral environments (Seilacher, 1964, p. 311).

THALASSINOIDES

Figure 16

Thalassinoides is a convex-epirelief burrow and is 

very common in sandstones throughout the area. Burrows are a series of Y-shaped branching tubes that are 

intimately interwoven. Tubes are circular to oval and 

have a diameter of 5-15 mm. Burrows are developed at 

a sand-to-sand, sand-to-muddy siltstone interface. They 

were considered by Hantzschel (1962, p. W218) to be 

burrows of a decapod crustacean. Burrows indicate 

shallow neritic conditions close to the littoral zone.
16 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

FIGURE 15. End view of Arenicolites (circled), expressed as 

pairs of indentations on top of lower sandstone tongue of Kenilworth Member; view normal to bedding.

PLURAL CURVING TUBES

Figure 17

Howard (1966a, p. 76) described groups of subparallel curving vertically oriented full-relief tubes that have 

definite wall structure. Tubes are very light gray to 

white and are very noticeable on outcrops. Tube diameter is constant at about 7 mm, and the tube wall is 1-2 

mm thick. Tubes are open at top and bottom. Grain size 

of the wall is the same as that of the enclosing rock, but 

organic matter and clay are absent. This fossil probably 

is the permanent burrow of a filter feeder in fine sands 

of the littoral zone (Seilacher, 1964, p. 311).

B

FIGURE 16. Thalassinoides. A, Underside of bedding, lower 

sandstone tongue of Kenilworth Member. B, Sketch.

LARGE HORIZONTAL BURROWS

Figure 18

Large branching burrows are preserved in full relief 

and in convex epirelief in carbonaceous silty, sandy 

mudstones. Described by many writers as fucoids, the 

trace is similar to Pfanolites montanus (Hantzsehel 

1962, p. W210). In the Sunnyside district, these traces 

are found only above coal beds or above medium-grained 

sandstones. Many burrows are alined subparallel to the 

strike of ripple-mark crests, where the crests are associated with them, but there is no indication of mechanical reworking of burrows. Burrows are oval in cross 

section and have a maximum diameter of 10-60 mm. 

Burrows are filled with very fine to fine sand and some 

carbonaceous material in a clay matrix. Burrows are distinctive on the outcrops. I believe, on the basis of stratigraphic position and lithologic association of the trace 

fossil, that these burrows were constructed by detritus 

feeders in terrestrial subaqueous areas of peat swamps.
17

A

CUBICHNIA

PELECYPODICHNUS

Figure 19

Pelecypodichmis is a pelletlike structure preserved 

as convex epirelief or convex hyporelief at sandstoneto-sandstone interfaces. It is ovoid and has a major axis 

of 5-10 mm and minor axis of about 5 mm. Locally abundant, these fossils exhibit no interior structure. They 

were formed as casts of pelecypod resting places just 

below the water-sediment interface, and all known structures are composed entirely of well-cemented sand 

grains. First described by Seilacher in 1953 (Hantzschel, 1962, p. W208), the trace is similar morphologically to ISagittichmis Seilacher, 1953 (Hantzschel, 1962, 

p. W208) and is easily confused with it. No shells or 

shell remains have been found associated with the trace, 

and it is inferred that the fossils were formed by infilling 

after the pelecypod had deserted the resting place. Environment of deposition was in shallow neriticto littoral 

waters, but Pelecypodichnus also has been found in paludal deposits.

RUHESPUREN

Figure 20

RuJiespuren are resting-place trace fossils preserved as 

concave hyporeliefs in fine- and medium- to fine-grained 

sandstones. Traces may form a circular pattern or an 

apparent trail, or they may occur singly. Howard 

(1966a, p. 78) suggested that they were made by "jellyfish or an animal with similar bottom configuration." 

Traces are oval and have a constant diameter of 10-15 

mm. In cross section, they exhibit a peripheral trough 

2-5 mm deep with transverse walls. The center of the 

trace is a raised boss slightly lower than the surrounding surfaces; the boss is 5-10 mm wide and is saucer 

shaped. The trace is uncommon, but its occurrence on 

outcrops probably is limited by the scarcity of horizontal bedding-surface exposures. The trace is indicative 

of a littoral to sublittoral environment (Seilacher, 1964, 

p. 311).

SEDIMENTATION AND STRATIGRAPHY

The Blackhawk Formation at Sunnyside is the lowest 

formation of the Mesaverde Group in the Book Cliffs. 

The unit was named by Spieker and Eeeside (1925, p.

FIGURE 17. Plural curving tubes. A, End view; from middle 

sandstone tongue of the Kenilworth Member. B, Longitudinal 

section; upper sandstone facies of the Sunnyside Member. C, 

Sketch showing typical mode of occurrence and morphology.
18 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

C

FIGURE 18. Large horizontal burrows. A, Filled with lightcolored sediment; in top of upper sandstone tongue of the 

Kenilworth Member. B, Light-colored fillings; from siltstone 

roof rock of the Sunnyside coal bed. C, Sketch. Burrow casts 

commonly are knobby on the surface.

443) for an exposure of Cretaceous coal-bearing rocks 

near the Blackhawk mine in the Wasatch Plateau. The

FIGURE 19. Pelecypodichnus. A, On top of middle sandstone 

fades of Sunnyside Member. B, Preserved as convex epireliefs 

on sandstone at base of Castlegate Sandstone; overhead view.

Blackhawk consists of arenaceous and argillaceous rocks 

and coal, deposited in a relatively complex sedimentational sequence (fig. 21). The term "Mesaverde Group" 

is subject to some controversy in Utah and Wyoming 

because there is some disparity in age between the 

section in those areas and the type Mesaverde at Mesa 

Verde National Park in Colorado (Young, 1955, p. 179). 

Abbott and Liscomb (1956, p. 120) and Brodsky (1960, 

p. IT) pointed out, however, that the term "group" has 

no time significance and that "Mesaverde Group" is 

the correct designation for the rocks under discussion. 

The term, therefore, is retained for use in this report.
SEDIMENTATION AND STRATIGRAPHY 19

B

C

FIGURE 20. Ruhespuren. A, Circular pattern (arrows). B, apparent trail of resting places preserved as concave hyporeliefs 

on top of lower tongue of Kenilworth Member. C, Sketch showing details of morphology.

TERMINOLOGY

The terminology used to describe sedimentation and 

stratigraphy in the present report follows:

Claystone, nonfissile indurated layers of argillaceous 

particles < 0.004 mm in diameter.

Mudstone, poorly indurated indistinctly bedded sediments composed of grains < 0.004 mm in diameter. 

Sandstone, indurated sediments composed of arenaceous particles 0.062-2 mm in diameter. 

Shale (capitalized), a group term indicating a collection of beds of dominantly argillaceous sediments. 

shale (lowercased), fissile mudstone, claystone, or siltstone.

Siltstone, indurated arenaceous and argillaceous sediments composed of particles 0.062-0.004 mm in 

diameter.

Grain-size designations are in accord with the Wentworth (1922) scale for clastic sediments. Figure 22 

shows current velocities necessary for erosion, transportation, and deposition of particles of these sizes and 

indicates the range of currents operating during the 

deposition of Blackhawk sediments.

Spatial relationships of the Blackhawk to strata of 

undoubted Late Cretaceous age define the age of the 

Blackhawk. Cobban and Reeside (1952) assigned the 

Blackhawk to the middle of the Campanian Stage 

(lower part of the Pierre Shale of the Western Interior) 

of the Late Cretaceous. Trace fossils that occur elsewhere in beds of undoubted marine origin occur also 

in the Blackha\vk, and fossils of organisms that are 

known to be marine are found in the underlying Mancos 

Shale (Fisher and others, 1960, p. 26-31). Spore and 

pollen analysis of Mancos rocks by Sarmiento (1957, p. 

1963) supports the conclusion that sedimentation of the 

Blackhawk Formation at Sunnyside wT as in the shallowT 

water of a retreating epicontineiital Late Cretaceous 

sea. The present report, therefore, attempts to determine how the sediments wT ere transported to the site of 

deposition and what the environment was during deposition of the Blackhawk Formation at Sunnyside.

Spieker (1949) and Young (1955, 195Y, 1966) interpreted the depositional environment of the Blackhawk 

as a series of sedimeiitational areas including eastwardprograding offshore-bar, shallow-marine, barrier, and 

beach-swamp-coastal-plain areas. A more detailed study 

of the sedimentary features leads to the conclusion that 

deposition was part of a deltaic sequence that included 

fluviatile, transitional, and marine environments. The 

delta during Blackhawk time probably covered an area 

much larger than the study area; field reconnaissance 

of Blackhawk rocks near Cisco, Utah, reveals a sedimeiitational sequence much like that in the Sunnyside 

area. The regional stratigraphic data necessary to reconstruct accurately the processes on and along the entire 

deltaic area are beyond the scope of this report. The 

paleoenvironmental interpretations presented herein are 

the simplest possible ones needed to explain the observed stratigraphic phenomena in the Sunnyside area.
20 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

0) V

Eg00 i!

, d> in

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\ ro ro 

1OW

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ro 

.c 

.*:

0

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ju

(0

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C/5

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0

o

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s

*

Mancos 

Shale

mudstone =r 

nember

Q. 

Q.

D

Sunnyside Member

c

IfE E,

»E

1

CD 

.O

E 

u>

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Kenilwc

." '-.' -"/ ." - / ."_ .' -1 Sandstone, medium-grained, with channel-fill structures throughout.

^ZIT '"\ Mudstone, gray, with sandstone and siltstone lenses and thin coal beds. 

__ Y Channel-fill sandstones common throughout. Forms covered slope. 

_ '_ .....~J Trace fossils in sandstones; a few shell fossils in scattered pockets in 

 - -7 mudstone.

sS|

^JU^JUUUU^^ Sunnyside coal bed and thin basal siltstone.

'". "''V i :^.';.:;j:^-iV '. . .;i!;^ Sandstone, thick-bedded, fine- to medium-grained; underlain by thin- 

 v ; .. \. .'.: ;. ' ;'.. :".-^ -^ bedded fine-grained sandstone and interbedded siltstone and fineL/^ ': '' '''- ''yij^r>' grained sandstone. Trace fossils, throughout.

 'Nv

....... - \ Mudstone, gray, with sandstone and siltstone lenses ana thin coal beds.

_ ;_'\. Channel-till sandstones common throughout. Weathers deeply; forms 

7T^__.. \ covered slope. Shell fossils scarce; trace fossils common in sand-

 - "-__.... X

 ... ......... ^^ WSA^^ Rork Canyon roal hed and thin basal siltstone

; , >"_. ^

 ~-^ ' - \. i - " ' _J Sandstone; three tongues in beds formed in three episodes of sedi-

 . ' - ' ;i : -- ' '> , . .-'. - -< siltstone, overlain by thin-bedded sandstone, overlain in turn by thick- 

^^?%*s>*££f*- '^.^y^ bedded sandstone. Trace fossils common throughout.

iSis^ f °

'^ VV---;' ;'-:?^"-'''";-L| ^ 100

 j&^sit^&iiiA _______________________________________

^j^_^_jr-_pt±-!'_ri^^j-.r^p^ Mudstone, gray, clayey, with scattered sandstone and siltstone lenses. 

~_rvr"_J~i^vr~_T"_rurL?^"'^ Carbonaceous detritus common; a few poorly preserved shell fossils

r- _^ - _~_r"I\

_____ ZJ Mudstone, gray; forms slopes and valleys.

*Aberdeen Member of Blackhawk Formation

FIGURE 21. Columnar stratigraphic section of the Blackhawk Formation and adjacent strata (Upper

Cretaceous) at Sunnyside.
SEDIMENTATION AND STRATIGRAPHY 21

10

0.5

Sedimentation

~ 0.1

5 0.05

Transportation

0.01

0.005

0.001 _LL

0.01 0.05 0.1 0.5 1 5 

VELOCITY, IN CENTIMETERS PER SECOND

10 50 100

FIGURE 22. Current velocities required for erosion, transportation, and deposition of sediments. Curves are based upon experiments with particles of specific gravity 2.60-2.65 (modified from Heezen and Hollister, 1964, p. 171).

Depositional environments that I recognized in the 

Blackhawk and associated rocks at Sunnyside include 

open-shelf, prodelta-slope, delta-platform, river-mouthbar, beach, swamp-marsh-lagoon, estuary, and floodplain environments. Each environment is discussed in 

the following pages in association with distinct units 

that are representative of those environments.

MANGOS SHALE

The upper part of the Mancos Shale Sunnyside is 

composed of massive and layered parts of dark-gray

silty very carbonaceous mudstone. The rocks of this 

interval are soft and easily eroded and form faceted 

slopes from the floor of Clark's Valley up to the base of 

the Book Cliffs (fig. 3). Thin tongues and stringers of 

carbonaceous very fine grained sandstone and siltstone 

occur throughout the upper part of the Mancos, but they 

are discontinuous and rapidly pinch out laterally. The 

formation is most fissile in the uppermost part, where 

layering is most pronounced. Many bedding surfaces in 

the mudstone exhibit tracks and trails of vagile 

benthonic marine organisms and much plant debris.
22 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

Shell fossils also are found in the upper part of the 

Mancos (Fisher and others, 1960, p. 27-30). Mancos 

lithology becomes mostly arenaceous upward as the 

lower boundaries of overlying sandstone zones are 

approached.

The Mancos Shale represents sediment deposited as 

mud on the sea floor during regression of the Late 

Cretaceous sea from the continental United States. The 

seaway was filled with very fine sediments supplied by 

a southeastward-prograding deltaic complex. As filling 

progressed, sedimentation took place in shallower water; 

current velocity was such that fine silt and mud were 

swept farther seaward, while coarse silt and very fine 

sand were being deposited in their place on the shallowing shelf. In the deltaic framework, the Mancos sediments represent the deep-water to open-shelf environments, and these sediments grade laterally and upward 

into sediments of the prodelta-slope environment.

BLACKHAWK FORMATION

As originally defined, the Blackhawk Formation is a 

unit of "buff sandstone, shale and coal of the kinds common to the Mesaverde group throughout the Southwest" 

(Spieker and Reeside, 1925, p. 440). In the type locality, 

the Blackhawk conformably overlies the Star Point 

Sandstone and is overlain unconformably by the Castlegate Sandstone. Clark (1928, p. 18) extended the use of 

the name "Blackhawk" to the Book Cliffs (fig. 23). The 

Blackhawk is the lowest unit of the Mesaverde Group, as 

the name is applied to eastern Utah. At Sunnyside, 

the Blackhawk conformably overlies the Mancos Shale 

and is unconformably overlain by the Castlegate Sandstone (fig. 24).

Clark (1928) included the Panther, Storrs, and 

Spring Canyon Tongues in the Star Point. All these 

units are present in the Wasatch Plateau and westernmost Book Cliffs, but all tongue out into the Mancos 

Shale west of the Sunnyside district.

Fisher (1936, p. 10) redefined the Blackhawk Formation in the Book Cliffs and included in it, in ascending 

order, the lower sandstone member, middle shale member, middle sandstone member, and upper member. In 

1955 Young (p. 183) redefined the Blackhawk, placing 

its base at the base of the Spring Canyon Tongue near 

the Wasatch Plateau and its top at the disconformable 

lower boundary of the Castlegate Member of the Price 

Kiver Formation.

Young (1955, p. 185) recognized six members (four 

of them new with his report) of the Blackhawk. Of 

these, only the Aberdeen, Kenilworth, and Sunnyside 

Members are present in the section at Sunnyside (figs. 

23, 24). Young's Spring Canyon Member tongues out 

northwest of Sunnyside, and his Grassy and Desert

Members begin south of the district, in the area south of 

Horse Canyon.

ABERDEEN MEMBER

The Aberdeen Member was named by Clark (1928, p. 

16) for a sandstone exposed near the Aberdeen mine 

near Kenilworth; the term Aberdeen was extended by 

Young (1955, p. 184) "to include the overlying coalbearing rocks and associated offshore bar deposits." The 

Aberdeen contains five bar sandstones, according to 

Young; the next to the lowest bar sandstone is the most 

persistent it disappears at Whitmore Canyon. At 

Sunnyside, the Aberdeen Member consists of a thin bed 

of very fine grained clayey organic-rich sandstone that 

is thinly laminated in ripple cross-stratification sets. 

The sandstone contains abundant trace fossils attributable to a neritic environment with a low sedimentation 

rate (Arthrophyciis, Teichichnus, other nereites-facies 

structures). The sandstone is calcareous and slightly 

gypsiferous and is composed of well-rounded grains of 

very fine quartz. The Aberdeen extends into the Sunnyside area as far as the east side of Whitmore Canyon, 

where it is covered by colluvium. The Aberdeen may 

extend into the area southwest of Horse Canyon (fig. 3) 

(F. W. Osterwa'ld, oral commun., 1968).

The southeastward extension of the Aberdeen probably is the transitional area between the open-shelf and 

prodelta-slope environments in the deltaic complex. In 

this transitional area, the distributary current was 

strong enough to lag fine quartz sediment, mixed with 

clay and mud, far out into the depositional basin to 

form a thin sheet of arenaceous sediment. The sandy 

environment was inhabited by burrowing and grazing 

organisms, and the sediment was shifted and slightly 

reworked by weak bottom currents. As the sediment 

supply dwindled, probably owing to a combination of 

environmental factors in the upland, sand sedimentation ceased and mud sedimentation of the lower 

prodelta slope resumed. At Sunnyside, the Aberdeen 

is unconformably overlain by 80-100 feet of mudstone 

of the Mancos Shale (fig. 24).

KENILWORTH MEMBER

The Kenilworth Member was named by Young (1955, 

p. 184) for an exposure near the coal-mining town of 

Kenilworth, Utah, the type locality, which is near the 

junction of the Book Cliffs and the Wasatch Plateau. 

According to Young, the unit consists of "a massive, 

cliff-forming, basal sandstone, an overlying series of 

coal-bearing rocks, and the offshore bar sandstones 

behind which they were deposited."

Young's definition of the unit derives from lithology, 

topographic expression, and inference of origin. Topographic expression of any unit is extremely variable
SEDIMENTATION AND STRATIGRAPHY 23

Clark 

(1928) 

Castlegate, Wellington, 

and Sunnyside quadrangles

Price River formation 

Castlegate sandstone 

member

Blackhawk formation

Star Point sandstone

Coal-bearing 

member

Aberdeen 

member

Spring Canyon 

tongue

Storrs 

tongue

Panther 

tongue

Mancos shale

Fisher 

(1936) 

Book Cliffs, south 

of Sunnyside

Price River formation 

Castlegate sandstone 

member

formation Blackhawk 

Upper member

Middle sandstone 

member

Middle shale 

member

Lower sandstone 

member

Not 

recognized

Mancos shale

Young 

(1955) 

Book Cliffs, Utah 

and Colorado

Price River formation 

Castlegate sandstone 

member

Blackhawk formation

Star Point 

sandstone

Desert member

Grassy member

Sunnyside 

member

Kenilworth 

member

Aberdeen 

member

Spring Canyon 

member

Storrs 

tongue

Panther 

tongue

Mancos shale

Fisher, Erdmann, 

and Reeside 

(1960) 

Central and eastern 

Book Cliffs

Price River Formation

Castlegate Sandstone

c 

o

Formati Blackhawk 

Upper member

Middle sandstone 

member

Middle shale 

member

Lower sandstone 

member

Mancos Shale

This report

Price River Formation

Castlegate Sandstone

Formation lackhawk 

m

Upper mudstone 

member

Sunnyside 

Member

Lower mudstone 

member

Kenilworth 

Member

^~~~~~"~2>- Mancos 

""^^Shale 

Aberdeen^~~~~~^- 

M ember ^~~~~ 

Mancos 

Shale

FIGURE 23. Nomenclature used by various writers for Upper Cretaceous rocks in the Sunnyside area.

owing to differential weathering, and inference of 

origin is subject to controversy owing to various interpretations by other investigators of the depositional 

environment. My detailed field investigations show that 

the basal sandstone of Young's Kenilworth actually is 

the upper sandstone bed of an orderly upward succession of interbedded sandstone and siltstone, thinbedded sandstone, and thick-bedded sandstone. All 

these rocks combine to make up a mappable unit of 

similar lithology. I here redefine Young's Kenilworth 

Member to include two underlying sandstone and siltstone sequences (fig. 21). The thin siltstone and coal 

are included in the overlying lower mudstone member.

Young (1955, p. 185) also stated that the Kenilworth 

"disappears into the Mancos shale near Sunnyside"; 

however, I traced the member as far south as the Beckwith Plateau (figs. 3,24) .

The Kenilworth Member, as here adopted for the 

Sunnyside district, is divided on the basis of the dominant morphology into three sandstone tongues, here 

informally designated the lower, middle, and upper 

sandstone tongues of the Kenilworth (fig. 24). The 

principal reference section here proposed for the 

Kenilworth Member in the Sunnyside district is on the 

north side of the mouth of Fan and Water Canyons, 

in the NW% sec. 8, T. 15 S., R. 14 E. (Salt Lake 

Meridian), in Carbon County (fig. 1). The basal part 

of each tongue consists of alternating layers of very 

thin bedded carbonaceous sandstone and sandy carbonaceous siltstone. The sandstone layers are evenly 

bedded and well sorted texturally and contain numerous 

trace fossils; most siltstone layers were thoroughly reworked by organisms and exhibit a bioturbate texture. 

Although the two lithologies are interbedded, boundaries between layers are sharp. The sandstone interbeds contain Ophiomorpha as the dominant trace fossil ; 

siltstone interbeds contain Asterosoma, Pelecypodichnus, and labyrinth castings of carbonaceous material.

422-052 O - 71 - 4
24 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

NORTHWEST 

Kenilworth Fish Creek 

I

0° 

0- (/)-/

ww

» , cv««"'."j «««7rv-r~^- ____ Pnce Rtver Formation

«"°c°«v^° o° o 'o °.^0' 0o'««''«°o'-"»«°'"o'-"'"*B-"^ o\V°VtV.o."c:V«!! = J°«o-"Sr°.*o*'.'-v-.«0!.c .vo'".«>..»:" ! ° ' c °> ° iV." V^??Fij' %*^«*;°'V.'^TTm ;, ' ;«. tr^n-rrr-r-

«V«*i>y. 0°'%"" ° °« '" ' »Ij °°°.° l>0 o°o°°c,°l°°\0°0 o-.° 0"°.°'>f'.i °^;° »!Castle_gate Sandstone jI 0°.° "oo»'.V'« °° «°.' <> .° 0 °.°o"; >l'°°*o o '%''-«: <''°«»t"> '*«'j'' °J "° oa «0 .'*v°°t»

Sunnyside area 

No. 1 Fan Canyon

I 

Price River Formation

Horse Canyon

SOUTHEAST 

Beckwith Plateau

Upper mudstone 

member

i Of Young (1955)

Sandstone

EXPLANATION

Coarse or conglomeratic 

sandstone

Scales are 

approximate

FIGURE 24. Restored stratigraphic section of the Blackhawk Formation and associated rocks in the Book Cliffs area of eastcentral Utah.

Labyrinth castings are most abundant at the interface 

of siltstone and overlying sandstone, a horizon that 

represents a surface of deposition. The sediment in 

these beds was so intensely deformed by the infauna, 

as exemplified in figures 6A and 6Z?, that few identifiable trace fossils are preserved.

Principal reference section, Kenilworth Member, Sunnyside 

district: North side of mouth of Fan and Water Canyons, 

Nwy* sec. 8, T. 15 8., R. Ut E., Salt Lake Meridian, Carbon 

County, Utah

Blackhawk Formation:

Lower mudstone member:

Mudstone, dark-gray, sandy, with siltstone and 

ferruginous claystone interbeds. Scattered 

lenses and pockets of impure coal near the 

base.

Kenilworth Member:

Sandstone (upper sandstone tongue), light-gray 

to grayish-orange-pink (WR 8/2) ; very fine to 

fine grained at base ; very calcareous ; wellsorted layers interbedded with dark-gray coaly 

siltstone, 8-12 ft thick. Overlain by 32-ftthick thin-bedded well-sorted calcareous finegrained slightly carbonaceous sandstone that 

is intensely mottled in thin zones (clean-tomottled texture). Contains Ophiomorpha,

Thickness 

(feet)

Principal reference section, Kenilworth Member, ISunnyside 

district: North side of mouth of Fan and Water Canyons, 

NW% sec. 8, T. 15 ft., R. 14 E., Salt Lake Meridian, Carbon 

County, Utah Continued

Blackhawk Formation Continued °^K 

Kenilworth Member Continued

Asterosoma, Arenicolites, -and plural curving 

tubes; few labyrinth castings. Upper part consists of fine- to medium-grained sandstone, 

which coarsens toward the middle of the unit, 

and then becomes more fine grained upward. 

The upper part has discontinuous streaks of 

white sandstone. Trace fossils uncommon in 

upper unit. Root marks in uppermost part 72

Interbedded dark-gray carbonaceous silty shale 

and moderate-reddish-brown (10R 4/6) claystone lenses ; unfossiliferous__________ 12

Sandstone (middle sandstone tongue) light-gray 

to very pale orange (10YR 8/2), very fine to 

fine grained, well sorted, calcareous. Upper 22 

ft is thick bedded and bjocky and contains 

channel structures. Resistant, forms overhanging ledge ; white zone 16 ft below top. Middle 

one-third composed of thinly bedded sandstone 

that is fine grained, crossbedded, and resistant, 

and has mottled zones. Contains abundant 

Ophiomorpha and Asterosoma and minor 

amounts of other trace fossils. Bedding
SEDIMENTATION AND STRATIGRAPHY 25

Principal reference section, Kenilworth Member, Sunnyside 

district: North side of mouth of Fan and Water Canyons, 

NWy^ sec. 8, T. 15 8., R. 14 E., Salt Lake Meridian, Carbon 

County, Utah Continued

Thickness 

(feet) Blackhawk Formation Continued 

Kenilworth Member Continued

thickens upward, transitional with uppermost 

sandstone unit. Basal one-third is thinly interbedded sandstone and medium-gray carbonaceous siltstone, intensely mottled; contains 

carbonaceous debris on bedding planes 60

Interbedded dark-gray carbonaceous silty and 

sandy mudstone and dark-reddish-brown 

(WR 3/4) ferruginous claystone lenses 22

Sandstone (lower sandstone tongue), grayishyellow (5Y 8/4) to light-yellowish-gray (5F 

8/2), fine grained, very calcareous, noncarbonaceous. Small channel bodies near base. Thin 

bedded, slabby; forms retreating ledge above 

lower interbedded part. Cross laminated in 

tangential foresets. Ophiomorpha, Gyrochorte, 

Aulichnites, Teichichnus A, and helicoid 

funnels are dominant trace fossils. Gradational with underlying sandstone____ 12

Sandstone, light-gray to grayish-orange-pink 

(10R 8/2), very fine grained, calcareous, carbonaceous ; contains Ophiomorpha, Asterosoma, 

Gyrochorte, Ruhespuren, and Teichichnus A 

and B. Thin bedded and slabby; mottled; interbedded with very dark gray carbonaceous siltstone. Sandstone forms slump or rounder 

structures in the siltstone 42

Total Kenilworth Member_________ 220 

Mancos Shale : Mudstone, dark-gray, silty, calcareous, shaly.

The next overlying part of the sequence in each 

tongue is mostly thin-bedded very fine grained sandstone 

with minor discontinuous lenses and pods of carbonaceous fossiliferous siltstone. The fine-grained sandstone 

commonly contains megaripples, current ripples, and 

oscillation ripples; most beds are crossbedded in tangential f oreset sets. These sandstone beds contain abundant 

trace fossils of the kind interpreted by Seilacher (1967) 

to be indicative of shallow-water deposition. (See p. 10 

of present report.) Thin-bedded sandstones are characterized by abundant trace fossils. Thalassionoides, 

Ophiomorpha, Asterosoma, Teichichnus, Gyrochorte, 

Aulichnites, and Arenicolites are some fossils that are 

preserved in the rocks of this type. One factor that 

governed the association of the animals that created 

the trace 'fossils was the amount of silt, mud, and 

organic debris in the depositional environment. Where 

much fine sediment and organic detritus were present 

during deposition, Ophiomorpha is small, most Asterosoma, are horizontally oriented, and well-developed 

helicoid funnels are associated with Asterosoma.

Teichichnus is common in rocks with a high content of 

carbonaceous detritus.

At Sunnyside, the three sandstone tongues of the 

Kenilworth Member are separated by variably thick 

deposits of dark-gray carbonaceous coaly, silty mudstone. The three sandstone tongues coalesce westward 

to form a single unit. The two sedimentational sequences 

just described the basal interbedded sandstone and 

siltstone and the overlying thin-bedded sandstone are 

in all three tongues. They form the entire arenaceous 

part of the lower sandstone tongue, the lower two-thirds 

of the middle tongue, and the lower half of the upper 

tongue.

The middle tongue of the Kenilworth Member at 

Sunnyside comprises the two sedimentational units just 

described and an upper sandstone bed which is moderately well sorted, thick bedded, and fine to medium 

grained and which commonly makes a massive cliff. 

The upper sandstone bed contains variable amounts of 

carbonaceous debris, and it commonly contains an 

abundant trace-fossil fauna. Channel-fill structures, 

which are common throughout the upper sandstone Ised, 

cut out bedding laterally and vertically and exhibit 

multilateral and multistory trough crossbedding. They 

are composed of coarser grained sediments than the enclosing sandstone and have roughly graded bedding.

The upper sandstone tongue of the Kenilworth Member at Sunnyside comprises the three sedimentational 

units that occur in the middle tongue plus an uppermost unit of very light gray sandstone that normally 

is well sorted, fine to medium grained, and, in many 

places, nonfossiliferous; its stratification is mostly in 

tangential foreset crossbeds. Streaks of very light yellowish gray to very light gray sandstone are common 

at various intervals throughout the upper part of the 

upper tongue. Young (1955, p. 184) called these streaks 

whitecaps and ascribed their formation to leaching 

and bleaching action of acid swamp waters in the paleoenvironment. Thick-bedded well-sorted sandstones of 

this unit locally contain abundant trace fossils that include large Ophiomorpha burrows ('3-5 cm diameter) , 

vertical Asterosoma burrows, burrows of Arenicolites, 

and tracks and trails of other animals on bedding 

surfaces.

Any parts of the depositional sequence may be missing or unrecoverable from the stratigraphic section at 

a given point, depending upon a variety of factors 

ranging from conditions at the time of deposition to 

colluvial cover of part or all of the unit. All three sandstone tongues of the Kenilworth Member at Sunnyside 

contain variable amounts of calcareous cement, which 

probably was derived from oxidation of methane gas 

derived from carbonaceous debris. Differential weather-
26 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

ing of the cement produces local pockmarked or honeycomb beds on the outcrop.

In the deltaic depositional framework that I propose 

for the Blackhawk Formation, the sandstone tongues 

of the Kenilworth were deposited in the delta-platform, 

river-mouth-bar, and beach-and-channel areas. Interbedded siltstones and very fine grained sandstones were 

deposited on the upper prodelta slope and lower delta 

platform under conditions of variable current velocity ; 

sedimentation was relatively slow, and sediment and 

waterlogged organic debris were intimately mixed during transport and deposition. The environment was 

physically quiet ; only small-scale ripple marks indicate 

any current. Bedding and lamination is thin and regular. Detritus-feeding organisms produced a severely 

mottled texture. Up the paleoslope, in the region of the 

delta platform, thin-bedded moderately well sorted 

sands were deposited in an environment in which the 

current velocity was sufficient to winnow out the fines 

and where sedimentation was usually moderately rapid. 

Currents worked the sediments into plane-bed forms 

such as megaripples and oscillation ripples. Organisms 

that built vertical burrows in pace with sedimentation 

left abundant trace fossils in the thin-bedded sandstones. Ophiomorpha, Arenicolites, Teichichnus, Cylindrichmis reptilis, Asterosoma, plural curving tubes, 

and smooth tubes are the most common trace fossils. 

Ripple-drift lamination is common on and within 

bedding.

The upper part of the thin-bedded sandstone sequence 

in each tongue locally contains channel-filled structures 

and is trough crossbedded. The channel-fill structures 

are small and pinch out laterally in a very short distance. These beds probably are representative of the 

river-mouth bar environment. Trace fossils are few, a 

condition common to areas of rapid sedimentation and 

energetic cutting and shifting of channels. That these 

areas are localized in the stratigraphic section further 

indicates that they formed under specialized environmental conditions, such as at the outlet of distributary 

streams at the lower part of the delta.

Thick-bedded medium-grained sandstone beds at the 

top of the middle and upper sandstone tongues are the 

result of beach deposits in interdeltaic areas. Depositional and postdepositional currents winnowed finer 

grains from the deposit and sent the fines farther seaward. Littoral currents produced low- to high-angle 

bimodal tangential crossbedding (fig. 25), and tidal 

creeks and inlets locally produced channel-fill structures in the top of a depositional set. Rill marks and 

swash marks occur on bedding planes. Trace fossils 

generally are confined to channel-fill structures in the 

thick-bedded well-sorted sandstones; Ophiomorpha is

FIGURE 25. Bimodal tangential crossbedding in upper sandstone tongue of Kenilworth Member in Water Canyon (fig. 

1), southeast of Sunnyside. Pen is 5 inches long.

the most common trace found in these deposits, and 

Aulichnites and Gyrochorte locally are found on parting lineation. The uppermost surface of the sandstone 

depositional sequence of the two upper tongues is 

planar, which indicates subaerial erosion prior to deposition of the overlying sediments. Root marks of plants 

commonly occur in the upper 1 foot of the sandstone 

beds ; many of these structures are preserved down to 

rootlets and root hairs.

The sandstone sedimentational unit (Kenilworth 

Member as redefined) ends at the top of the thickbedded well-sorted sandstone just described. The Kenilworth varies in thickness along the outcrop owing to 

environmental changes during deposition and to pinching out of the bed into the Mancos Shale down the paleoslope. At Kenilworth the sandstone is 190 feet thick; 

at Sunnyside it is 166 feet thick; at Horse Canyon, 

south of the district, it is 120 feet thick. Lapses in sand 

sedimentation during deposition of the Kenilworth are 

attributed by Young (1955, p. 177) to sharp pulses of 

subsidence of the depositional basin. I believe that these 

lapses were due to tectonic and climatic conditions in 

the upland source areas, which caused sediment starvation, landward invasion by the sea, and in turn the 

transport of mud and other fine sediments into the area.

LOWER MUDSTONE MEMBER

Overlying the Kenilworth Member is an upward sequence of very thin carbonaceous sandy siltstone, the 

Rock Canyon coal bed, a bed of siltstone or fine-grained 

sandstone, and dark inudstones that contain stringer 

beds of arenaceous rocks. This unit, here called the 

lower mudstone member of the Blackhawk Formation,
SEDIMENTATION AND STRATIGRAPHY 27

forms a slope above the sandstone bluffs of the Kenilworth Member.

The basal siltstone is irregular in shape and thickness, 

is structureless, and locally contains tracks and trails of 

organisms interpreted to be worms. The siltstone, where 

present, usually contains root marks and carbonized 

plant remains. The bed is in unconformable contact 

with the underlying sandstone and with the overlying 

coal and other sediments. The coal, locally called the 

Rock Oanyon coal bed, is discontinuous; and at 

Sunnyside it ranges in thickness from 0 to 4 feet and in 

many places is cut by channel-fill sandstone cutting 

down from above. The coal is hard, bright, slightly 

bony, and brittle, and it has cubic cleat. It is a detrital 

coal composed of small pieces of plant material derived 

from ferns, angiosperms, and conifers (Tidwell, 1966, 

p. 88). Where the coal is not present, the sediments of 

this interval are extremely carbonaceous owing to the 

presence of small pieces of carbonized reed and grass 

debris.

Overlying the coaly zone is a sequence of dark-gray 

to black mudstone of varying fissility, laced with thin 

discontinuous cross-stratified beds of claystone, siltstone, and very fine grained sandstone. These arenaceous beds occur at every level throughout the mudstone 

interval, but they are extremely lenticular and are not 

traceable from one side of a canyon to the other. Orientation of directional sedimentary structures within the 

stringer sands is dominantly east-southeast. Bedding is 

poorly preserved because of mottling by organisms. 

Large horizontal burrows are common in the inteirval 

immediately overlying the coal bed, and unidentifiable 

trace fossils of detritus-feeding organisms are very 

common throughout the interval.

The entire zone of argillaceous rocks overlying the 

sandstone sedimentational unit probably is the product of a swampy depositional environment. The environment was a large intertidal flat that sloped very 

gently seaward from the flood plain and in most places 

prograded seaward over older sediments. The flat was 

crossed and connected to the sea by an intricate network of small meandering streams and tidal channels 

that drained the delta area and resulted in the formation of small channel-fill sandstone bodies that are very 

lenticular and discontinuous. The water in the channels 

and streams was very brackish to saline, which allowed 

the landward migration of a few Ophimorpha and 

Asterosoma organisms, whose trace fossils occasionally 

are found in the resultant sandstones. Some areas of 

back swamp were bypassed by active sedimentation, and 

these were flooded at intervals by distributary streams. 

This flooding caused the formation of interbeds of 

black clayey siltstone and very fine grained sandstone

over a greater area! extent than that of the stream 

channel. Swamp areas were occupied by a lush growth 

of plants, whose decay and compaction resulted in 

peat beds that later became coals. Large plant pieces, 

such as stumps or logs, are rare in the carbonaceous 

sequence.

Marine fossils, although locally present in the lower 

part of the argillaceous unit, are nearly ubiquitous in 

the upper part of the unit. There is no apparent break 

between nonmarine sedimentation and marine sedimentation, although the upper mudstone beds are 

slightly sandier. Young (1955, p. 181) identified the 

whole argillaceous part as Mancos Shale that was deposited during sharp pulses of basinal subsidence. The 

mudstone is indeed a Mancos facies; the unit is traceable into the Mancos on the outcrop. I believe, however, 

that tectonic and climatic conditions in the upland 

source area combined with slow, normal subsidence of 

the basin margin owing to superloading to allow transgression of the sea. Normal transgressive sequences of 

the Mesaverde include a standstone bed deposited as 

the sea swept landward; no such bed separates nonmariiie from marine rocks at Sunnyside because there was 

not enough sand available for reworking and subsequent redepositioii by the transgressing waters. The 

invading waters reworked only the marine mud and 

silt.

SUNNYSIDE MEMBER

The Sunnyside Member was named and defined by 

Young (1955, p. 185) to comprise "a massive, basal 

sandstone tongue and the overlying coal-bearing rocks 

which are replaced eastward by offshore bar sandstone." Young's definition derives from bedding characteristics, lithology, and inference of origin. My field 

investigations show that the "massive, basal sandstone" 

is the top unit in an orderly stratigraphic succession 

from interbedded sandstone and siltstone at the base to 

thick-bedded medium-grained sandstone at the top. 

The member forms an easily recognizable, mappable 

part of the stratigraphic section at Sunnyside and 

throughout the Book Cliffs; I traced the sandstone 

cliff of the Sunnyside Member as far south as Green 

River, Utah. I here redefine the Sunnyside Member 

on the basis of lithologic continuity, mappability, and 

topographic expression and place the lower boundary 

of the member at the base of the continuous cliffforming sandstone above the Kenilworth Member. I 

place the upper boundary of the Sunnyside Member 

at the top of the same type of sandstone, just below the 

Sunnyside coal bed. The principal reference section I 

propose for the member is in the cliff just north of the 

town of Sunnyside in NEi/4 sec. 6, T. 15 S., R, 14 E.
28 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

Principal reference section of the Sunnyside Member of the 

Blackhawk Formation, in the Blackhawk Cliff above the 

town of Sunviyaidc, Utah, in NE~y± sec. 6, T. 15 S., R. 14 E., 

Salt Lake Meridian

Thickness 

(feet) Blackhawk Formation:

Upper mudstone member:

Interbedded dark-gray silty mudstone and darkred-brown (KXR3/4) ferruginous claysbone and 

siltstone, with thick coal bed 0-1 ft above base. 

Sunnyside Member:

Sandstone, light-gray to yellowish-brown (10Y.K 

5/6), very fine grained, thin-bedded, and shaly. 

Contains Ophiomorpha and labyrinth castings. 

RippTe cross laminated on bedding surfaces__ 23

Sandstone, light-gray, fine- to medium-grained, 

sugary-textured. Contains channel structures, 

carbonaceous debris; trace fossils dominantly 

are Ophiomorpha, Teichichnus, Asterosoma, 

labyrinth castings, and large horizontal burrows. Undulating bedding surfaces contain ripple marks. Some crossbedding in tangential 

sets __________________________ 36

Sandstone, light-grayish-yellow (5F 8/5), finegrained ; well sorted within beds, contains carbonaceous debris on bedding surfaces. Tangential crossbedding throughout, in thick sets that 

have even upper and lower surfaces. Contains 

few trace fossils. Calcareous and silty_____ 32

Sandstone, light-grayish-yellow to I ight-yel lowishgray (5Y 8/2), thin-bedded, and flaggy. Well 

sorted, with carbonaceous debris on bedding 

surfaces only; calcareous. Crossbedded in long 

sweeping tangential sets. Slump-and-founder 

structures on sandstone into underlying sandstone laminae, in ball-and-pillow forms. Honeycomb weathering___________________ 42

Sandstone, medium-yellow (5Y 7/4) to mediumgrayish-yellow (5Y 7/4), very fine grained, 

silty, carbonaceous; intensively burrowed and 

mottled; contains Ophiomorpha, Asterosoma, 

plural curving tubes, Arenicolites, Thalassinoides, and rare Ruhespuren. Interbedded 

with dark-gray coaly and carbonaceous shaly 

siltstone. Siltstone has been mottled intensively. Siltstone contains disks and small 

lenses of coal, probably derived from bark. 

Interbed contacts are sharp _ 57

Total Sunnyside Member____________ 190

Mancos Shale:

Mudstone, silty, carbonaceous, dark-gray; 

weathers light gray to medium gray. Contains 

abundant trace-fossil infauna.

The siltstone interbeds in the basal facies are medium 

to dark gray, sandy, clayey, and very carbonaceous. 

They are thin to very thin bedded and are crossbedded 

in trough-set beds. The siltstone beds have a highly 

mottled texture owing to action of burrowing organisms. Sandstone interbeds are very thin, very fine 

grained, clayey, calcareous, and very carbonaceous and

contain numerous trace fossils. The beds are crossbedded in trough-set beds, and crossbedding and interbedding occur in every scale from large to microscopic. 

Rocks of the basal facies probably reflect the offshore, 

delta-platform environment, a place of low kinetic energy that was below wave base, and that received periodic surges of active sedimentation that carried sandsized particles far seaward before depositing the load. 

The Sunnyside Member comprises three lithologic 

facies, and each facies represents a different set of environmental conditions at the time of deposition. The 

basal facies of the member of Sunnyside is interbedded 

siltstone and very fine grained sandstone (fig. 26). The

FIGURE 26. Sandstone of the Sunnyside Member at the mouth 

of Slaughter Canyon (fig. 1), showing root zone (R), whitecap unit (W), thick-bedded sandstone (tk), thin-bedded 

sandstone (tn), and interbedded sandstone and siltstone (I). 

Thick-bedded sandstone, whitecap unit, and root zone which 

are 45 feet thick in the area of the photograph make up 

the upper facies of the member. View southward.
SEDIMENTATION AND STRATIGRAPHY 29

siltstone is extremely carbonaceous and has been so intensively reworked by organisms that remains of original bedding are rare. The thin siltstone and coal are 

included in the overlying upper mudstone member. 

Trace-fossil preservation in siltstones is uncommon, because the thoroughness with which the substrate was 

reworked either destroyed or altered the biogenic sedimentary structures. Trace fossils are abundant in the 

sandstones; Ophiomorphia, Cylindriclinus, Asterosoma, 

Tewhichnus, Thalassinoides, and ArtTvrophycus are the 

most common types found in the thin-bedded 

sandstones.

The interbedded sequence of the basal facies is overlain by a thin-bedded cross-stratified sandstone facies 

that contains variable amounts of carbonaceous debris. 

Foreset and trough-set crossbedding are the most common types of cross-stratification. The rocks are light 

grayish yellow, fine to very fine grained, silty, clayey, 

and calcareous and contain abundant trace fossils. The 

individuals of the trace fauna vary with the amount 

of carbonaceous detritus in the sediment. The less carbonaceous beds contain Aulichnites, Gyrochorte, Ophiomorpha, vertical Cylindrichnus, plural curving tubes, 

and chevron trails. These trace fossils, with the exception of Cylindrichmis, were made by organisms that 

received their nourishment from sources other than carbonaceous detritus. Vertical CylindmcKnus burrows 

probably indicate an attempt by the animal to escape 

to a more favorable environment, Beds with a moderate 

to high carbonaceous debris content contain Teichichnus, Thalassinoides, Arenicolites, horizontal Cylindrichnus, and helicoid funnels. These traces reflect an 

intrasediment burrowing in search of the carbonaceous 

detritus for food.

The thin-bedded sandstone facies of the Sunnyside 

Member at Sunnyside reflects sedimentation in the 

upper delta platform, distributary-mouth-bar, and littoral subenvironments. Periods of low current velocity 

allowed deposition of carbonaceous detritus and fine 

sediment nearer to shore than periods of normally high 

transport velocity. During normal sedimentation, carbonaceous debris was winnowed out, and only clean fine 

sand was deposited in the area. The upper part of the 

facies is cross stratified in foreset crossbeds and appears 

to be the result of current action hi the littoral zone.

The uppermost facies of the Sunnyside Member comprises thick-bedded medium- to fine-grained sandstone, 

which is moderately carbonaceous, clayey and calcareous, dominantly light gray to light grayish yellow with 

local streaks of very light yellow to white sandstone at 

varying intervals. The unit locally is brick red owing 

to oxidation by burning of the overlying coal. Bed 

forms are trough-set crossbeds, which contain directional sedimentary structures that indicate that the 

dominant direction of transport was east-southeast. Bimodal foreset crossbedding occurs locally in the upper 

part of the unit. Trace fossils are less common in this 

unit than in others; the scarcity probably is due to 

rapid sedimentation at relatively high velocity. Scattered Ophiomorpha occur in the uppermost unit of the 

Sunnyside, and labyrinth castings are found associated 

with local small pockets of carbonaceous debris that 

occur near the edges of troughs. Gyrochorte are found 

on bedding surfaces in the uppermost part of the upper, 

sandstone unit. Other trace fossils are very rare. Root 

marks of plants that once grew on the sand commonly 

occur in the uppermost 2 feet (fig. 27). These root 

marks are preserved roots, rootlets, and occasional root 

hairs. Such features are carbonized limonite-stained 

branching tubes that terminate downward.

The uppermost unit of the Sunnyside Member represents channel-fill deposition in thick beds by distributaries in the upper delta area. As the transporting 

medium reached an open area at the end of its channel, 

current velocity decreased, which caused rapid sedimentation that constantly shifted direction as flow barriers were constructed and destroyed in the anastomosing channels. Local areas of beach sedimentation occurred, and these are indicated in the rocks by parts of 

the unit that are crossbedded in long sweeping foreset 

crossbeds that are tangential at their bases. These rocks 

exhibit no characteristics of channel-fill sedimentation. 

Rather, they contain trace fossils of the littoral zone 

such as Arenicolites, Aulichnites, Gyrocliorte, and plural curving tubes. Large pieces of carbonaceous woody 

debris are common to the beach rocks, and the pieces of 

debris are oriented with their long axes normal to the 

long axis of deposition, which possibly indicates their

FIGURE 27. Root marks in uppermost 1 foot of thick-bedded 

sandstone facies at top of Sunnyside Member; sit, siltstone 

which underlies Sunnyside coal bed.
30 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

deposition in tidal wash. Directional sedimentary structures in both the channel fill and the beach rocks indicate that the dominant direction of flow was eastward. 

The upper limit of the Sunnyside Member is placed 

at the top of the thick-bedded sandstone unit. The thickness of the sandstone, which ranges from 100 to 150 feet 

at Sunnyside, makes the unit easily distinguishable on 

the outcrop and mappable at scales as large as 

1:250,000.

UPPER MUDSTONE MEMBER

Overlying the Sunnyside Member is a basal thin 

discontinuous sandy siltstone, overlain by the thick 

Sunnyside coal bed and 250-300 feet of dark laminated 

shale and massive mudstone with lenticular bodies of 

sandstone and siltstone throughout. This unit is here 

informally called the upper mudstone member of the 

Blackhawk Formation. The mudstone is replaced southward by sandstone beds above the Sunnyside coal bed 

and is here delineated for continuity in mapping. I believe that the member is of continental origin at Sunnyside, although farther south it is of continental and 

marine origin.

The Sunnyside coal bed (Taff, 1906, p. 295) is a hard 

bright brittle coking coal of high-volatile A to B bituminous rank in the system of the American Society 

for Testing Materials. The coal has an irregular break, 

owing in part to the matting and interlayering of its 

plant parts. The Sunnyside coal is rich in spores and 

waxes. Fossil megaspores form resin blebs in the coal 

and are very common throughout the vertical and horizontl extent of the bed. The common spores and waxes, 

together with coal composed mostly of plant debris 

instead of woody material, indicate formation of detrital coal in shallow water (Tschudy, 1961, p. 57). The 

Sunnyside coal bed is split by siltstone and mudstone 

(fig. 28) which is a few inches to 75 feet thick in the 

deeper parts of the Sunnyside mines. In addition, many 

thin discontinuous coal beds occur in the coal-bearing 

interval. Because of the thickness of the split, miners 

and some earlier workers believed the coal to be two 

different beds. Detailed surface mapping and correlation of underground sections show that the upper seam 

and lower seam are splits of the same bed (Brodsky, 

1960, p. 36). The split is not everywhere present in the 

area; it thins to the north and east and thickens to the 

south and west. The lower surface of the coal is irregular, 

owing to the irregular and discontinuous siltstone below. The upper part of the coal commonly is intertongued with overlying sediments (fig. 28). Locally, 

channel-fill deposits cut downward into the coal and 

affect the thickness of the bed.

The coal beds and carbonaceous sandy siltstone overlying the Sunnyside Member represent deposition in

swamp and lagoonal areas peripheral to the coastline. 

Plants grew in shallow water and extended their root 

systems into the sandy soil below. Shifting distributaries brought additional carbonaceous detritus into the 

area; these channels also cut out the carbonaceous deposits and replaced them with channel-fill sands. Acidic 

waters that percolated downward from the swamp 

probably deposited sulfates in the sandy deposits, and 

the wT ater also probably aided in local bleaching of the 

sediments. Bleached zones also occur most commonly 

where the coal has been burned on the outcrop, and 

this suggests that oxidation by burning also influenced 

bleaching of the sediments.

Overlying the coal zone is a sequence of interbedded 

very carbonaceous shales, mudstones, siltstones, and 

lenticular sandstones and siltstones. The only trace fossils observed in rocks of this sequence are large horizontal burrows, labyrinth castings, and rare Ophiomorpha in the lenticular sandstones. Large horizontal 

burrowrs are nearly ubiquitous in the rocks overlying the 

upper split of the coal. Labyrinth castings are associated 

with carbonized pieces of material of varying size which 

are stratigraphically above or below the coal. A sparsely 

populated fauna of thin-shelled poorly preserved mollusks w^as found in sandy mudstones at various intervals 

throughout the carbonaceous argillaceous sequence. A 

collection of this fauna from an interval 40-60 feet 

above the upper coal (USGS Mesozoic loc. D6221) was 

identified by W. A. Cobban (written commun., 1968) 

of the U.S. Geological Survey as:

Ostrea sp.,

Corbula sp.,

Anomia micronema Meek,

BracMdontes sp., and

bits of gastropod molds.

Cobban commented that the fauna was a brackish-water 

assemblage. A collection of shelly fossils from a sandstone unit 130 feet above the coal, at a locality 10 miles 

south of Sunnyside (USGS Mesozoic loc. D6722), was 

identified by Cobban (written commun., 1968) as:

Crassostrea sp.,

Brachidontes sp.,

Corbula undifera Meek, and

membraniporoid bryozoan.

Cobban commented that the fossils were obviously 

transported, but that they probably had been deposited 

in a brackish-water environment.

The arenaceous rocks overlying the coal at Sunnyside 

represent deposition in a lowland environment a 

swampy, marshy area near sea level that occasionally 

was encroached upon by marine waters. Local estuaries 

and tidal channels allowed mixing of marine and nonmarine waters and allowed limited migration of marine
SEDIMENTATION AND STRATIGRAPHY 31

FIGURE 28. Fence diagram of the Sunnyside coal bed, illustrating stratigraphic relationships of coal and associated rocks. View 

is northwestward, up the paleoslope. Dark areas are coal; stippled areas, sandstone; unpatterned areas, siltstone and mudstone. Data from core holes drilled by Kaiser Steel Corp. Datum is base of Sunnyside coal bed. Numbers indicate township 

sections.

animals inland. As the coastline prograded eastward, 

the environment of deposition at Sunnyside became 

progressively more continental as the flood plain built 

eastward. Meandering distributaries cut channels across 

the swamp throughout the period of deposition, and 

these channels became larger and more numerous as 

continental sedimentation progress.

CASTLEGATE SANDSTONE

The Blackhawk Formation at Sunnyside is unconformably overlain by the Castlegate Sandstone, a sandstone as much as 300 feet thick that forms a prominent 

cliff and dip slope throughout the Book Cliffs. Named 

for an exposure at Castle Gate, Utah (Spieker, 1946, 

p. 131), the unit varies in composition from conglomerate west of the type locality to fine-grained silty 

sandstone in eastern Utah and shaly beds in western 

Colorado. At Sunnyside, the Castlegate is a mediumgrained light-grayish-yellow clayey sandstone that contains numerous clay galls and lenses of carbonaceous 

material. The formation is unconformable atop the carbonaceous rocks of the Blackhawk, and it fills local 

channels and interfingers into the top of the Blackhawk. 

The dominant sedimentary structures in the Castlegate 

are channel-fill sandstone bodies. Where the formation 

crops out in a direction normal to the direction of deposition, channel-fill structures occur throughout the 

unit.

The Castlegate in the Sunnyside area is the result of 

deposition of sand in a fluviatile and flood-plain en-
32 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

vironment. Where materials of more than one grain 

size occur, they are poorly graded. Local deposits of 

carbonaceous debris and large pieces of carbonized wood 

are the remains of detritus swept downstream and deposited on the flood plain and in eddies and backwaters. 

In summary, the depositional history of the Sunnyside area was: offshore sea-floor muds (Mancos Shale) ; 

progressively shallower marine deposition of Aberdeen, 

Kenilworth, and Sunnyside Members, with periods of 

marine transgression and deposition interspersed between progradational sequences; transitional marine 

and continental deposition in low-lying areas behind 

the coastline; and fluviatile and flood-plain deposition 

as the final eastward regression of the sea took place 

near the close of the Cretaceous Period. Latest Cretaceous and Tertiary rocks are the result of continental 

sedimentation in flood-plain and lacustrine environments.

INORGANIC SEDIMENTARY STRUCTURES

Observable inorganic sedimentary structures of the 

Blackhaw^k Formation may be grouped into four categories : bedding structures, which are wholly contained 

within the limits of bedding surfaces; plane-bed forms, 

which affect only bedding surfaces; channel structures, 

formed by erosion of preexisting sediments and redeposition in the erosion channels; and load structures, 

formed by foundering of a superincumbent mass of 

sediment into less competent strata.

BEDDING STRUCTURES

Sandstone beds of the Blackhawk Formation commonly are cross-stratified. The nature of the cross-stratification varies with the current velocity. Thickness and 

type of stratification also depend mostly upon the 

velocity of the transporting medium. In strata deposited 

in quiet water, laminar bedding is dominant, and depositional cross-stratification is uncommon; deposits in environments of higher kinetic energy are thin to thick 

bedded (2 in. to 5 ft), and most are found in wedgeshaped crossbedded sedimentational units (fig. 29) 6 

inches to 2 feet thick. Individual foreset beds within 

the sedimentational unit commonly are tangential to 

bedding planes at their bases and have planar tops (fig. 

30). Sole markings in beds of this type are parallel to 

the direction of crossbedding. This parallelism indicates 

that the beds were built up in the direction of sediment 

transport. Primary dip of crossbedding varies with the 

energy of the environment, but measured primary-dip 

angles greater than 20° are rare. The primary dip of 

most crossbedding in Blackhawk sandstones at Sunnyside is 2°-15° SE.; measurements of direction of transport indicate a dominant direction of S. 80° E. The

Thickness,

depth 

Transport direction

ss

r.p

Tabular 

crossbedding

FIGURE 29. Diagrammatic sketches illustrating terminology of 

crossbedding (modified from Potter and Petti John, 1963, p. 69). 

No scale.

directional features include crossbedding, flute casts and 

other sole markings, asymmetrical ripple marks, and 

orientation of plant debris on bedding surfaces. The
INORGANIC SEDIMENTARY STRUCTURES 33

FIGURE 30. Tangential crossbedding in lower sandstone tongue 

of Kenilworth Member.

nearly unidirectional sediment transport, which is discussed later in this report, is a major factor in the interpretation of depositional environment.

Many sandstone beds exhibit ripple cross-lamination 

(fig. 31), a bedding feature formed by low-velocity current drag penecontemporaneous with deposition (Potter 

and Pettijohn, 1963, p. 155). Laminae are built up by 

ripple marks migrating in one direction. Where this 

feature was found near Sunnyside, measurements of the 

direction of laminae buildup indicate ripple migration 

to the east-southeast.

Bimodal crossbedding, which indicates sediment 

transport in opposite directions in successively overlying 

sets of crossbeds (fig. 32), formed in local areas of deposition. This type of crossbedding is preserved in some 

outcrops of the Blackhawk Formation. In the upper 

sandstone of the Sunnyside in Water Canyon (fig. 32),

FIGURE 31. Ripple cross-lamination in middle thin-bedded sandstone facies of Sunnyside Member. Current from upper left to 

lower right.

FIGURE 32. Crossbedding in opposite directions in successively 

overlying sets of crossbeds in upper thick-bedded sandstone 

facies of Sunnyside Member, Water Canyon. View oblique to 

depositional strike.

particularly good outcrops of such beds display a vertical sequence of crossbedded units, each 6 inches to 1 foot 

thick, with f oreset beds that dip in opposite directions at 

low angles. Potter and Pettijohn (1963, p. 96) pointed 

out that most crossbedding points down the paleoslope. 

The bimodal crossbedding probably was deposited in 

a backshore environment, landward of the beach. 

Seaward-dipping foresets were deposited by tidal and 

other currents in the lagoonal area; landward-dipping 

foresets were deposited by currents operating in a landward direction.

The upper sandstone units of both the Sunnyside 

Member and the Kenilworth Member form a prominent 

cliff. The upper surface is planar at nearly every exposure (fig. 33). The planar surface may be an indication

FIGURE 33. Top of upper thick-bedded sandstone facies of 

Sunnyside Member, illustrating planar nature of bedding 

surface.
34 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

of subaerial erosion prior to deposition of the overlying 

sediments. Root marks occur in the upper foot of the 

uppermost sandstone bed in nearly all tongues of each 

member (fig. 27), which indicates that plants once grew 

at these horizons.

PLANE-BED FORMS

Ripple marks are the most common type of plane-bed 

form in the rocks at Sunnyside. Many are symmetrical 

(fig. 34) with relatively straight subparallel crests that 

are transverse to the oscillatory water movement that 

formed them (Potter and Petti John, 1963, p. 29). Current ripples (fig. 35), which are formed by directional 

movement or transport, are abundant in thin-bedded 

fine-grained sandstone in the Sunnyside area. Oscillation and current ripple marks vary widely in measured 

amplitude and wavelength. Megaripples with maximum 

amplitudes of 1.5 inches and wave^ngths of 6-8 feet 

occur in the middle tongue of the Kenilworth Member 

in Slaughter Canyon (fig. 36). Megaripples are best

FIGURE 34. Oscillation ripple marks in the upper thick-bedded 

sandstone facies of the Sunnyside Member.

FIGUKE 35. Current ripple marks in the upper thick-bedded 

sandstone facies of the Sunnyside Member. Overhead view.

B

FIGURE 36. Megaripples in the middle tongue of the Kenilworth 

Member, Slaughter Canyon. A, Sharp-peaked ripple marks (1) 

overlying and truncating low-ainplitude long-wavelength ripples (2). B, Same outcrop as A, showing megaripples with 

wavelengths of 6-8 feet and amplitudes of 1.5 inches (2).

preserved at this locality, although they are common 

elsewhere in the Sunnyside area. Gilbert (1899, p. 138) 

postulated that "ripplemarks are only half as broad as 

the wraves rolling above them are high." If this postulate 

is true, wraves that formed the megaripples described 

above were about 15 feet high. Heezen and Hollister 

(1964) have photographed current ripples on the sea 

floor at depths as great as 8,000 meters, however, thereby 

proving that fossil ripple marks have no bathymetric 

significance. Current ripples in the Blackhawk Formation are transverse to the direction of cross bedding; according to Potter and Petti John (1963, p. 94), these ripples aid in delineating the depositional strike. Interference ripple marks formed by currents operating at large 

angles to each other, and characterized by polygonal 

cusps, are found in some beds (fig. 37).
INORGANIC SEDIMENTARY STRUCTURES 35

FIGURE 37. Interference ripple marks on bottom of bed 

J

in middle tongue of Kenilworth Member, illustrating polygonal 

cusps.

CHANNEL STRUCTURES

Channel deposits occur in nearly all types of beds. 

They vary in width, depth, direction of transport, and 

orientation within beds. Few channel deposits can be 

traced for any appreciable distance laterally, however, 

because they commonly crop out high on inaccessible 

vertical cliffs and because they are covered by colluvium 

on north-facing slopes.

Channel deposits are found in two lithologic relationships: channels of sandstone that are scoured into 

mudstone beds and channels that are scoured into sandstone beds. Because these lithologic relationships may 

bear on interpretation of depositional environment, 

their data are presented separately.

Channel deposits of sandstone in mudstone (fig. 38) 

are commonly smaller than channel deposits of sandstone in sandstone. Most channel deposits in mudstone 

are bilaterally symmetrical about a thalweg at the center of the channel. Channel deposits of this type observed at Sunnyside are less than 50 feet wide and less 

than 20 feet deep. They are lenticular sandstone bodies, 

convex downward with nearly planar tops, and enclosed 

in and covered by the same general type of sediment 

into which the channels were cut. These channel deposits 

contain foreset crossbedding in trough-shaped sets that 

have their long axes parallel to the direction of dip of 

the foresets. The sets thicken in the direction of the 

foreset dip and truncate other sets throughout the depth 

and breadth of the deposit. Most trough sets display 

moderately graded bedding. No trace fossils were observed in units of this type.

Channels of sandstone in sandstone, which are larger 

than channels of sandstone in mudstone, are very common throughout the area. Nearly all sandstone 

sequences contain extensive channel deposits. The 

smallest observed channel of the sandstone-in-sandstone type (fig. 39) is at the mouth of Slaughter 

Canyon, in Whitmore Canyon (fig. 1). Although the 

northeast side of this channel deposit has been removed 

by erosion, the projected width of the deposit is 60 feet; 

it is 10 feet thick. The largest channel structure of this 

type observed in the area is in the south wall of Whitmore Canyon; it was measured by pacing and with steel 

tape and is 150 feet wide and 45 feet thick at the 

thickest point. These channels are asymmetrical in cross 

section, with the thalweg well to one side. Sediments in 

these channel fills are crossbedded in wedge-shaped 

sets that thicken laterally, normal to the long direction 

of the channel (fig. 40). Foreset bedding within sets 

dips in the direction of thickening of the sets. FormaFIGURE 38. Sandstone channel deposit in mudstone (arrows) in 

upper unnamed shale member of Blackhawk Formation. Channel deposit at its center is 12 feet thick.

FIGURE 39. Small sandstone-in-sandstone channel deposit in 

upper tongue of Kenilworth Member. Channel deposit is 10 feet 

thick at its thickest point and originally was about 60 feet 

wide. View northwest on west side of Whitmore Canyon, at 

mouth of Slaughter Canyon-
36 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

and very carbonaceous; some beds consist only of sandstone, and some are interbedded with siltstone. Trace 

fossils are sparse in channel-fill sandstone but abundant 

in many scoured beds. Most channel deposits of the type 

described here crop out high on the cliffs; hence, they 

are easier to trace laterally than are the smaller channels. Measurements of sediment-transport direction 

indicate that the principal direction was east-southeast.

LOAD STRUCTURES

Ball-and-pillow structures and load casts are the most 

common load structures in the rocks of the Sunnyside 

district. Both are caused by foundering and settling of a 

sediment into a less-dense sediment while both bodies 

are still hydroplastic (Potter and Petti John, 1963. p. 

145,148).

Ball-and-pillow structures are individual segments of 

a stratum which have settled into the underlying sediment. Ball-and-pillows at Sunnyside most commonly 

are segments of fine-grained sandstone which have 

foundered into mudstone, with stringers of mudstone 

squeezed up around the segments.

Load casts are formed by settling caused by differential loading of irregular sediment surfaces. Initial depressions on hydroplastic mud beds are filled with sediment which results in unequal loading (Middleton,

FIGURE 40. Sandstone-in-sandstone channel deposit in upper 

unnamed shale member of Blackhawk Formation. View northeast. Channel outlines shown by dashes. Scale indicated by 

long arrow, which represents 13 feet. Sets of crossbedding in 

lower part repeat laterally, normal to the direction of flow.

tion of channel-fill structures of this type is well illustrated in a model of fluvial channels (fig. 41) that form 

the sets. Sandstone that fills scours in sandstone is 

coarser grained and contains less carbonaceous debris 

than the beds into which the channels were cut. The 

scoured beds commonly are thinly and evenly bedded

Lower flow regime 

Very fine grained sediments

EXPLANATION

Upper flow regime

Fine- to medium-grained

sediments

Transitional-lower

flow regime 

Medium- to coarsegrained sediments

FIGURE 41. Diagram of fluvial-channel environment, illustrating vertical distribution of sedimentary structures and sediment 

grain sizes and lateral formation of channel-fill deposits and structures (modified from Visher, 1963, p. 132).
ENGINEERING AND ECONOMIC GEOLOGY 37

1965, p. 249). Load casts do not break away from the 

parent bed as do ball-and-pillow structures; load caste 

form pendants into the less dense sediment. Load casts 

are most common where sands are deposited on argillaceous sediments (figs. 42 and 43) and reflect penecoiitemporaneous soft-sediment deformation.

ENGINEERING AND ECONOMIC GEOLOGY

Nearly all engineering and economic aspects of mining in sedimentary formations are related ultimately to 

the sedimentology of the rocks. Depositional environment and sedimentation pattern control engineering factors such as strength and homogeneity of the rocks, degree of lithification, and geometry of interfaces between 

lithof acies. The amount and extent of material deposited

FIGURE 42. Load casts of very fine grained dense sandstone 

extending into underlying darbonaceous mudstone, middle 

shale of Kenilworth Member in Slaughter Canyon. Current 

 direction was from left to right.

FIGURE 43. Load casts of fine-grained carbonaceous calcareous 

sandstone extending into underlying mudstone; Sunnyside 

coal zone in No. 1 Fan Canyon. Current direction was from 

left to right.

depend upon physical environmental conditions during 

deposition. Uninterrupted accumulation of vegetal 

material over a long period of time may result in a thick 

peat deposit; accumulation interrupted by inorganic 

sedimentation over a similar period may result merely 

in a thick carbonaceous zone. Sedimentary structures 

affect mining on many scales; directional sedimentary 

structures and other sedimentary phenomena, observable on the outcrop and traceable underground, may be 

predicted and their influence on mining may be forecast 

if such factors are respected as mining engineering 

parameters.

Some areas in the Sunnyside mines are characterized 

by coal that continually squeezes into the entries and 

spalls off, thereby continually releasing stress (fig. 44). 

Other areas are marked by floor anticlines, roof synclines, and buckled ribs all conditions resulting from 

stress buildup in the coal (Osterwald, 1961, p. C349). 

The roof rock above squeezing areas commonly is a 

fine-grained siltstone or mudstone. The roof rock in 

other areas of coal deformation is a coarser grained 

siltstone or fine-grained sandstone. Osterwald (1962a, 

p. 65) showed that, other factors being equal, the difference in coefficient of friction with the coal between 

the finer grained and the coarser grained roof rocks 

determines the relative ease with which the coal can 

move laterally.

Where finer grained roof rocks allow the coal to 

move laterally with relative ease, the coal near the roof 

may spall off into the entry and effect the continual 

release of stress in the coal (fig. 45). Bumps that occur 

under these roof conditions are believed to be of lower

FIGURE 44. Deformed roof bolts in the roof of Sunnyside No. 1 

mine. Deformation resulted from the squeezing of the upper 

coal and intervening siltstone split into the entry owing to 

lateral pressure in the pillar at left. Photograph by J. C. Witt.
38 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

Bone coal, carbonaceous 

shale, or shaly siltstone

Coal Mine working

Loose coal

Loose coal -

Coal

Coarse-grained 

carbonaceous siltstone\

Medium- to finegrained siltstone.

Small shear fractures-''

Coal

Mine working Coal

Coarse-grained 

carbonaceous siltstone\

B

FIGURE 45. Deformation around mine workings in Sunnyside No. 1 mine. Diagonally lined areas are hollow. Arrows show relative 

direction of movement. (Modified from Osterwald, 1961, p. C352.) A, Roof syncline (s) and floor anticline (a), which develop 

where coal slips along argillaceous roof but adheres to coarser grained rocks in the floor. B, Bulged and buckled ribs of 

coal where coal adheres to roof and floor.

magnitude than bumps that occur in areas of coarser 

grained roof rocks. The coarser rocks, which have a 

higher coefficient of friction with the coal, contribute 

to a high buildup of stress in the coal and thereby to 

conditions favorable for large bumps.

Osterwald and Brodsky (1960, p. B146) concluded 

that when entries intersect fault zones at a small angle, 

slippage will occur in the rib before much stress can 

accumulate. If the long axis of the entry intersects a 

fault or fracture at a large angle, slippage will be less
ENGINEERING AND ECONOMIC GEOLOGY 39

likely to occur and a large stress concentration will be 

caused. If stress is allowed to continue to accumulate 

unabated, the plastic limit of strain will be exceeded, 

and a sudden, catastrophic release of stress will occur 

(fig. 46).

Coal-mine bumps partly are the result of vertical 

presssure on the coal from the overburden. The total 

stress 011 ,a point in space in a coal bed is a reflection of 

many factors. 'Surface topography «iiid the thickness of 

overburden cause differential loading of the point; 

hydrostatic conditions, loading history and current geological conditions, maiimade disturbances of the normal 

stress equilibrium, and other factors such as imposed 

heat gradients, vibrations, tidal forces, and the like all 

function together in varying degrees to form the sum of 

the stress (Corlett and Emery, 1959, p. 375). Spokes 

and Scott (1967, p. 46) showed that horizontal tensile 

stress is greatest near a caved area of a room-and-pillar 

mine. The magnitude of tensile stress is greatest near 

the surface, and it decreases to a neutral-stress axis 

somewhere near the middle point between the mined 

area and the surface. Downward from the neutral stress 

axis, horizontal compressional stress increases to a maximum in the area of mining. Stress tends to concentrate 

around the area of least support, which is the coal and 

rock surrounding the void created by mining. Much 

stress, therefore, concentrates around an entry, and the 

largest principal stress direction is at large angles to 

the axis of the entry.

Inorganic and biogeiiic sedimentary structures are 

three-dimensional. Both types of features commonly

FIGURE 46. Aftermath of a coal-mine bump in the Sunnyside 

No. 1 mine, December 1957. Rib (coal face) at right failed 

catastrophically from right to left, pulling a part of the roof 

with it. Mine entry was closed for more than 250 feet. Roof 

bolts are 1-inch-diameter steel. Photograph by J. C. Witt.

may have reliefs of as much as 18 inches in Blackhawk 

rocks, as do some load casts and ball-and-pillow structures, or they may be only films on the bedding surface, 

such as the trace fossil Chondrites. Locally, channel-fill 

sandstones completely cut out the coal. Most structures, 

however, are of sufficient relief to influence the friction 

at the interface of two rock bodies. A spatial and directional orientation of structures exists in the rocks at 

Sunnyside, but the continuity of orientation varies with 

the type of structure. The trace fossil Thdlassinoides 

exhibits no preferred orientation, whereas current ripple marks and large horizontal burrows (fig. 47) both 

have highly preferred orientations. Rocks containing 

large horizontal burrows, which are tubes of sandstone 

in a carbonaceous siltstone or mudstone matrix, have 

lower shear strength than rocks that are structurally 

more homogeneous. Youash (1965, p. 96-98) performed 

triaxial and unconfined uniaxial compression tests on 

roof rocks from the Sunnyside No. 1 mine. He found 

that the shear and cohesive strength of roof rock which 

contains burrows and other lithologic and structural

FIGURE 47. Zone of large horizontal burrows (arrows) in roof 

rock, oriented at a small angle to the long axis of entry; 

Columbia mine, Utah. Burrows are light-colored sandstone 

structures in dark-gray shaly isiltsitone. This mine is approximately 3 miles south of Sunnyside and is developed in the 

Sunnyside coal bed. Photograph taken after a bump-related 

roof failure at intersection of mine workings. Entry runs 

obliquely from left foreground to right background. Timbers 

at .lower right are 6 inches in diameter. Photograph by F. W. 

Osterwald.
40 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

discontinuities is less than that of rocks of similar 

lithology which do not contain structural inhomogeneities. Youash further found (1965, iii) that degree of 

failure of the rocks varies with the angular difference 

between the direction of principal stress and the direction of bedding surfaces in the rocks.

The relief and orientation of the sedimentary structures in the rocks of the roof and floor of a coal mine 

probably have a bearing upon the amount of stress that 

builds up in the coal seam. Where the preferred long 

direction of the sedimentary structures is parallel to 

or at a small angle to the long axis of the mine entry, 

these structures hinder movement of coal past rock at the 

interlithologic interface and cause the friction between 

the bodies to be greater. In areas where the dominant 

long direction of structures is normal to or at a large 

angle to the long axis of the entry, these structures form 

no barrier to movement and may actually aid movement 

by trapping and forming conduits for interformational 

and intraformational fluids that might be present in the 

rocks.

Sandstone-filled channels are sedimentary structures 

that affect mining on a larger scale than biogenic structures. Meandering channels are common to abundant in 

sediments above and below the Sunnyside coal. Regardless of their paleoenvironment, channel structures are 

composed of discontinuous layers of rock of irregular 

thickness. Individual layers in channels that are associated with the coal zone commonly are separated by thin 

films of coalified carbonaceous debris. Such films have 

nearly no structural strength and therefore cannot provide cohesion for the rock layers. When channel sandstones are encountered in the roof during mining, special 

roof-control measures should be taken to support the 

structures.

A channel sandstone represents a deviation from the 

usual lithologic pattern throughout the coal measures. 

Being a deviant, the channel body has a set of variables 

that influence the engineering characteristics of the body 

that are different from those of the surrounding rock. 

Among these variables are lithology, porosity, permeability, cement and degree of cementation, fluid content, strength, degree of homogeneity, and alinement of 

internal structures. Because of the physical and chemical 

differences between channel sandstones and their enclosing rocks, channel sandstones may be loci of mine bumps 

and other rock failures and should be regarded in mines 

with extreme caution.

A thick channel sandstone may completely cut out the 

coal locally and form a "want," or discontinuity in the 

coal. Such discontinuities are common in mines in the 

Wasatch Plateau coal field, in coal beds stratigraphically 

lower in the Blackhawk Formation than those at Sunnyside. The Wasatch Plateau coal field underlies most 

of the Wasatch Plateau from south of Huntington to 

near Helper. Also, coal near a channel may contain more 

impurities than coal elsewhere, owing to mixing of 

organic and inorganic sedimentation. Channel sandstone 

bodies commonly can be observed and mapped on the 

outcrop, and an indication of their general trend can be 

gained by measurement of internal structures. Then, on 

the basis of interpretation of the paleoenvironment, an 

area of mining where channels may be encountered can 

be forecast and precautions can be taken during development of a mine and extraction of coal.

Stratigraphic interrelationships are affected on a still 

larger scale by intertonguing f acies contacts. Resistance 

to pressure release by horizontal sliding is increased at 

intertonguing contacts because of the irregularity of the 

contact surface. Contacts, therefore, may be foci of increased stress.

Because of environmental differences during sedimentation, it may be impossible to preclude danger from all 

the features mentioned herein. If, however, all aspects of 

the rocks are noted at the outcrop and in other exposures 

such as exploration pits and core holes, a pattern commonly can be determined that will serve as a guide to 

forecast the most potentially dangerous conditions, and 

planning can be guided by this additional information.

In 1964, an oil seep, w^hich has long since dried up, 

was encountered during development wrork in the Sunnyside No. 3 mine. Earlier, 4 feet of saturated sandstone 

core was recovered from the coal interval in Pasture 

Canyon. Enough oil flowed from a channel-fill sandstone in the roof of the mine workings to cause a flurry 

of excitement among mine personnel. The oil at Sunnyside is believed to be a strictly local phenomenon. The 

oil probably was formed diagenetically either from 

organisms that inhabited the marsh or s\vamp areas or 

from the extremely carbonaceous sediments that surround the coal seam. The oil probably formed in discrete 

particles and then migrated into conduits formed by 

channels in the roof of the coal. When mining exposed 

the channels and disturbed the pressure equilibrium, the 

oil flowed into the opening. Asphaltic sandstones that 

may indicate proximity to petroliferous strata occur in 

association with coal beds in the Blackhawk Formation 

near Vernal, Utah, northeast of Sunnyside. Exploration for oil in the Blackha\vk Formation at Sunnyside 

should concentrate on the stratigraphic traps formed 

where the sandstone-filled channels pinch out into the 

less permeable mudstones. Most such channels trend 

east-southeast.

At approximately the same time the oil seepage wy as 

encountered in the mine, fresh outflows of natural gas 

(methane) from the roof rocks were noticed. Methane,
REFERENCES 41

mostly derived from coal beds, in coal mines is very 

common throughout the world, and the appearance of 

oil in coal mines in the Book Cliffs is not uncommon; 

miners in the Castlegate mine in the Wasatch Plateau 

once encountered an oil seep that leaked enough oil to 

wet the haulage track (F. W. Osterwald, oral commun., 

1968). I believe the methane is a product of decomposition of vegetable material during diagenesis and coal 

formation. Sedimentary structures such as channel-fill 

sandstones and trace-fossil horizons may have acted as 

a stratigraphic trap to concentrate the gas in the roof 

rocks. Other inflows of methane may be encountered 

when similar sandstone-filled channels are encountered. 

Results of this investigation indicate that mining 

areas should be studied in minute geologic detail before 

drift or entry headings are laid out. In addition to the 

usual geologic information gathered, these studies 

should focus upon types of biogenic and inorganic sedimentary structures, their magnitude, mode of occurrence, and spatial orientation. If such studies were incorporated into the framework of a mining operation, they 

could contribute materially to the safety and economy 

of the venture. Because continual creep and spalling of 

the coal aids mining efficiency as well as contributing to 

safety, a mine should be opened with the mining entries 

driven at large angles to the trend of directional sedimentary structures but at small angles to tectonic structures to take advantage of the natural creep and spalling 

during mining. Such studies should make mining safer 

and more economical.

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42 SEDIMENTARY FEATURES, BLACKHAWK FORMATION, CARBON COUNTY, UTAH

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INDEX

[Italic page numbers indicate major references]

A, B

Aberdeen Member.

Beekwith Plateau..__________________________ 23

Blaekhawk Cliff __________________________ 28

Book Cliffs....__.._____._______.___ 3,4,17,22,27,31

Bumps, coal-mine. See Coal-mine bumps.

Canyons, Fan.. _____.._._._...._________._._. 24

Horse....---.-----.-.-................... 26

Pasture __ ______________________________ 40

Slaughter.. _______________________________ 34

Water...... _._ ______________ _____________ 24

Wh.tmare.-. __ _- _-__ . -__ 22 

Castlegate Member, Price River Formation. _ _ 22 

Castlegate Sandstone.. ________ _______________ 22,5;

Channel-fill structures... .____. 25, 26, 30, 31, SB, 39, 40

dark's Valley.. ______________________________ 21

Coal..... .___.___ _________________________ 1,4,30,37

deformation in mines. See Coal-mine bumps. 

Coal beds, Rock Canyon...... _._____........ 26,27

Sunnyside.__ _____________________________ 30

Coalfields, Book Cliffs.- _. __________________ 1,4

Wasatch Plateau _______________________ 1,40

Coal-mine bumps... ________________________ 1,4,57

definition _ _ __________________________

relation to faults... ____________________

relation to roof-rock lithology. _________

relation to sedimentary structures. ____

relation to total stress __ _____________

Cobban, W. A., fossil identification________

_ 1

_ 38

_ 37

_ 39

_ 39

_ 30 

Crossbedding _ _________________ 25, 26, 28, 29, 3,-, 35

D, E

D efinitions, coal-mine bumps. 

rock types. _______________

spreite _ ________________

trace fossils. - ___-__ _____

__________ 1

__________ 19

_---_.-.__ 10

__________ 6

Deformation, coal in mines. See Coal-mine bumps,

faults ________________________________ 3,38

strike and dip of beds__________________ 3

Desert Member____________________________ 22

Economic geology..__________________________ 40

Engineering, mining._________________________ 37

Environment of deposition. See Sedimentation.

Fan Canyon _ _______________________________ 24

Faults.. _____________________________ _________ 3,38

Fossils, Anomia micronema. __ 

Brachidontes sp..._______

bryozoan. ________________

Corbula m.<-f/era___ ____

Corbula sp_________ _____ _

Crassostrca sp _ ________

gastropod molds__ _______

grass. ._ - _ -_-_ - 

lower mudstone member. 

MancosShale___________.

marine. _ ____________

Os.razsp._. _____________

palm leaf. _______________

__ 30

__ 30

__ 30

__ 30

__ 30

__ 30

__ 30

 27

__ 27

_ 21,22

__ 27

__ 30

__ 7

plant debriS--_____-._ _________________ 21,27,32

Fossils Continued

reeds...__.___..._._______

trace. See Trace fossils, 

upper mudstone member.

Page

27

30

G, H, J, K, L

Graded bedding ___________________________ 25,35

Grassy Member...._.____.._.________________ 22

Horse Canyon. 

Joints____._

Kenilworth Member...___________________ #..,33,34

principal reference section.._._____.-___-_ 24

sedimentary structures._______________ 23,25,26

sedimentation. ___________________________ 26

Location__ _ ____________

Lower mudstone member. 

Lower sandstone member.

M 

Mancos Shale.._________________________ 19,2/,22,27

Measured sections, Kenilworth Member..... _ 24

Sunnyside Member_____________________ 28

Mesaverde Group..-.________________.___. 17,18,22

Middle sandstone member..__________________ 22

Middle shale member_______________________ 22

Mines, Blackhawk____________________________ 18

Castlegate. --_-___________-___-_.__-______ 41

Sunnyside No. 1.___-_-_-___-_-__.___--_ 39 

Sunnyside No. 3_______-______--_____.-_ 40

Mining engineering-____-..___----.-___.-_--__ 37

N, O, P, R 

Natural gas.____ _ ____._._. _______ 7,40

Nomenclature, stratigraphic.___-_... -. 22

trace-fossil... _-_-___.______.______-.-----_ 7,10

Oil- 7,40

Panther Tongue, Star Point Sandstone.. _____

Pastur. Canyon..__________________--_.____--

Pierre Shale.._.__._-_____-____.__________-_--

Previous work______________________________

Price River Formation, Castlegate Member..

Ripple marks....._________________ 9,10,16,25,:

Roan Plateau...--_--_.______________-------- 3

San Rafael Swell...._.____.____________-.____ 3

Sedimentary structures, biogenic. See Trace fossils, 

directional features.________________ 27,32,39,40

inorganic.________________________________ S2

ball-and-pmow...---.-------_------- 36,39

bedding.. ___________________________ 3?

biogenic alteration__________________ 8,9

Castlegate Sandstone_-_-__--.____-_-_ 31

channel-fill............ 25,26,30,31, 36, 39,40

cross-lamination. _______-..---_-______ 9,33

crossbedding............. 25,26,28,29, SI, 35

graded bedding ____________________ 25,35

Sedimentary structures Continued 

inorganic Contin'ied

Kenilworth Member_......._....... 25,26

load.. __-__-_-_-___ - ___..-- 36 

load casts ------_--------__--_-_---_ 36,39

plane-bed forms-.- ..._-_._ 84

rill marks__........ ......_ 26

ripple marks_-. . . 9,10,16,25,26,34 

sole markings_- - .-.._._._.._. 10,32 

Sunnyside Member__..----.....-... 28,29

swash marks. _.-. ...... ..... 26

upper mudstone member............. 30

relation to coal-mine bumps.------------- 89

Sedimentation__ __..__..__..._..._. ...... 19

Aberdeen Member_..................... 22

Castlegate Sandstone.____________________ 31

Kenilworth Member____________________ 26

lower mudstone member.....____.______- 27

Mancos Shale_...._...__-_..-.-- -____- 22

relation to trace fossils. ...__-.__-... 6,7 

summary_ __________._-----__-_--_-___-- 32

Sunnyside Member...............-.-...-- 28,29

upper mudstone member.-.- ........... 30

Slaughter Canyon............-.-.-.--.-....-. 34

Spring Canyon Member. _.__ -_----- 22

Spring Canyon Tongue, Star Point Sandstone, 22 

Star Point Sandstone, tongues. _ - - 22 

Storrs Tongue, Star Point Sandstone. ____-_-. 22

Stratigraphy...____..__-___--______------ 17

Strike and dip of beds. - --- -- 3 

Structural geology..-------------------------- 8

Subsidence cracks---- -----------.---------- 3

Sunnyside fault zone.------------------------ 3

Sunnyside Member.....__ ... _. -- - 22,37,33

principal reference section.__.__ .-- 28 

sedimentary structures-.----------------- 28,29

sedimentation..-- --__----------------- 28,29

T

Terminology, sedimentation and stratigraphy. 19 

See also Definitions; Nomenclature.

Trace fossils.- -- --- ---------- #

Aberdeen Member..-._ ... .... -. 22

animal-sediment relationship - --------- 7

A renicolites------------------------- 16,25,26,29

Arthrophycug..... ------- ./, 12,15,22,29

Asterosoma ____________ 7, IS, 23,25,26,27,29; pi. 2

Aulichnttes.....-. - -- 13,/4,25,26,29

bathymetric facies__-___------------------ 1°

burrows, large horizontal-------- 15,16,27, 30,39

castings, labyrinth ------------- J3,24,29,30

chevron trails..- __ _ . - - ^0,29

Chondrites-------------------------------- 13,39

cubichnia __ - - -- 10, 17

Cylindrichnus --------------------------- 13,29

reptilis. ------------------------------ 13,26

Cylindricum. _ -- -- 13

definition __-.__---.-------------------- 6

domichnia -..---------------------- 1°. 1B

environment- ____ ---- -- -- 6,7

epir elief _ __...._____--_---------_-------- 7

fodinichnia-__-_-------------------------- 1°, M

f ucoids-.-___-_--------------------___---- 16

full-relief ------------------------- 7

Oyrochorte --------- 13, 14,25,26,29

Halymenites major. .-----------..--------- 15

43
44 INDEX

Trace fossils Continued Page 

helicoidfunnels___-____---______-_-- 13,29; pi. 2

hyporelief. _.______________-.___.___----_ 7

Kenilworth Member_ ________________ 23,25,26

labyrinth castings._________________ IS, 24,29,30

large horizontal burrows.________ 15, / 6, 27,30,39

lower mudstone member.________________ 27

Mancos Shale __-------_--_---_------- 21

modern relatives, Callianassa major.------ 15

nomenclature....___________......_----_. 7,10

Ophiomorpha.._ 12,13, 15, 23,25,26,27,29,30; pi. 3 

pascichnia..___-________--_ _______---_-_ 10

Pdecypodichnus. _________________________ 17, 23

Phycodes- ---..-----------_----.------- 13

Planolites montanus.... .--- _-__--_- _-_ 16

Trace fossils Continued Page 

plural curving tubes.--_______.__ ______ If;, 26,29

relation to sedimentation. ______ _ _________ 6, 7

repichnia. ________________________________ 10

root marks.-----.-----.-------- _-- 26,27,29,34

Ruhcspurcn.- -------------- ------------- 17

Sagittichn us ---------------------------- 17

smooth tubes--..----.--------------- fJ., 15,26

subdivision _ ____________________________ 7

Sunnyside Member. ______________________ 28, 29

Teichichn us.., --------------------- 22, 25, 26, 29

.4.-. --.....-.....-......------- 11; pi. i

Thalassinoides- ...__.___.__________- 15, 25, 29, 39

trails, chevron.. _._.--..-.._.__--_--___-_- ^0,29

Trace fossils Continued Pa&e 

tubes, plural curving. _._.._.....____ 16, 26,29

smooth_ ----.-.....-._......-.--... 1%, 15,26

universal ichnofacies_____..._____....__. 10

upper mudstone member, ___.__.______.._ 30

uses.. -.______--..-__._.-_.__,__.._.__--__ 6,7

See also Fossils.

U, W 

Uinta Basin.._-- ___.___..-_--_.___.....-._. 3

Upper member.----..-------.--..------------ 22

Upper mudstone member.___________________ SO

Wasatch Plateau-.._____..._______._._. 18,22,40,41

Water Canyon... ...__..__.._....._.-._-_-_. 24

Whitmore Canyon............-.-.-.....-.._ 22
PLATES 1-3
PLATE 1

FIGURE 1. Teichichnus A, indicated by arrows. Scale provided by encircled pencil.

2. Three-fourths view of Teichichnus A; arrow indicates up.

3. Sketch showing typical mode of occurrence and spreite construction of Teichichnus A.

4. Teichichnus B, from lower tongue.

5. Close view of same specimen of Teichichnus B, showing bladed structure.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 688 PLATE 1

TEICHICHNUS IN THE LOWER SANDSTONE TONGUE OF THE KENILWORTH MEMBER
	PLATE 2

FIGURE 1. Asterosoma burrow in fine-grained sandstone.

2. Asterosoma escape burrow in \vell-sorted sandstone.

3. Helicoid funnel at top of fine-grained sandstone bed; mouth of funnel is 20 cm across; specimen broken across trace fossil.

4. Helicoid funnels (arrows) at tops of Asterosoma burrows in sandstone.

5. Sketch of Asterosoma.

6. Sketch of helicoid funnel.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 688 PLATE 2

| 2 cm ,

5 6

ASTEROSOMA AND HELICOID FUNNELS FROM KENILWORTH MEMBER
PLATE 3

[Specimens 1,2,3,5, and 6 from upper sandstone fades of Sunnyside Member; 4 from upper tongue of Kenilwcrth Member]

FIGURE 1. External molds (center) and internal casts (upper right); view parallel to bedding surfaces.

2, 3. Longitudinal sections; view normal to bedding surfaces.

4. External mold.

5. External mold (scale in centimeters).

6. Filled burrow, illustrating branching nature; view parallel to bedding surfaces.

7. Sketch showing knobby external surface.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 688 PLATE 3

V

1 cm

U. S. GOVERNMENT PRtNTING OFFICE : 1971 O - 422-052