Late Precambrian Sixtymile Formation and 

Orogeny at Top of the 

Grand Canyon Supergroup^ 

Northern Arizona
Late Precambrian Sixtymile Formation and 

Orogeny at Top of the 

Grand Canyon Supergroup, 

Northern Arizona

By DONALD P. ELSTON

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1092

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1979
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress Cataloging in Publication Data

Elston, Donald Parker, 1926-

Late Precambrian Sixtymile Formation and orogeny at top of the Grand Canyon Supergroup, northern

Arizona.

(Geological Survey Professional Paper 1092) 

Bibliography: p. 16-17. 

1. Geology, Stratigraphic-Pre-Cambrian. 2. Geology-Arizona. I. Title. II. Series: United States.

Geological Survey. Professional Paper 1092. 

QE653.E47 551.7'15 78-21287

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

Washington, D.C. 20402

Stock Number 024-001-03139-6
CONTENTS

Abstract

Introduction _______

Acknowledgments 

Geologic setting _

Page

____________________________ 1

____________________________ 1

.___________________________ 1

____________________________ 1

Previous work ________________________ 2

Structure ______________________________ 4

Stratigraphy ___________________________ 4

Pre-Sixtymile strata _____________________ 6

Kwagunt Formation _________________ 6

Development of contact relations __________ 6

Page

Stratigraphy —Continued

Sixtymile Formation ________________— — ___ 10

Lower member _________________— —— __ 10

Middle member _______________________ 11

Upper member _____________________ 12

Tapeats Sandstone ______________________——_ 12

History and age ____________________——___ 14

Correlation ______________________________ 16

References cited ___________________________ 16

ILLUSTRATIONS

FIGURE

Page

Geologic map of Sixtymile Formation in Chuar syncline __________________———__ ———— ___ — --————— 1

Type section of Sixtymile Formation and units described at end of report ________ ————— ___ —— ————— ——— 5

Photograph showing Sixtymile Formation and Chuar syncline in north fork of Sixtymile Canyon ___ ————————— __ 7

Stratigraphic relations in Chuar syncline, north fork of Sixtymile Canyon ____________—————————- — - 8

Details of stratigraphic relations in central part of Chuar syncline ________________ — _____——————— 9

TABLES

Page

TABLE 1. Late Precambrian and Cambrian strata exposed in eastern and central Grand Canyon, Arizona ———__———————— 3

2. Walcott's stratigraphic section of upper division of his Chuar terrane measured on Nankoweap Butte with stratigraphic

nomenclature of Ford and Breed _________________________________________________ 3

3. Outline of depositional and structural events of the Grand Canyon orogeny, Sixtymile Canyon, eastern Grand Canyon,

Arizona ____________________________________________________________ 13

4. Description of strata at type section of Sixtymile Formation _______________________ — _ ————— — ___— 18

ill

LATE PRECAMBRIAN SIXTYMILE FORMATION AND OROGENY AT 

TOP OF THE GRAND CANYON SUPERGROUP, NORTHERN ARIZONA

By DONALD P. ELSTON

ABSTRACT

The Sixtymile Formation, a 60-m-thick red-bed unit at the top of 

the late Precambrian Chuar Group, crops out at three places in the 

Chuar syncline in the eastern Grand Canyon. Its base is marked by 

a transition from gray marine shale to red sandstone. The Sixtymile 

was deposited in the deepening trough of the north-trending Chuar 

syncline during and as a consequence of regional uplift, tilting, and 

large-scale block faulting. Folding to form the Chuar syncline occurred in response to faulting on the parallel-trending Butte fault, 

about 1 km to the east. About 3.2 km of structural relief was developed across the Butte fault, principally during deposition of the 

lower member of the Sixtymile Formation. Landslide debris shed 

from the upthrown block on the east constitutes a major part of the 

material in the lower member. Conglomeratic strata of the upper 

member of the Sixtymile were deposited after the last increment of 

subsidence on the Chuar syncline, indicating that deposition of the 

Sixtymile Formation spanned the time of the structural disturbance. The folding and faulting are part of a regional structural 

episode that here is called the Grand Canyon orogeny, an event that 

signaled the end of deposition of strata of the Grand Canyon Supergroup and the beginning of a long interval of erosion.

The age of the Grand Canyon orogeny is estimated at about 830 

m.y., inferred from an evaluation of maximum and minimum reset 

K-Ar ages reported for the l,100-m.y.-old Cardenas Lavas of the 

Unkar Group. In age and structural style, the Grand Canyon 

orogeny appears generally correlative with the East Kootenay 

orogeny of British Columbia, which separates the Purcell (Belt) and 

Windermere Supergroups. By analogy, strata of the Chuar Group 

below the Sixtymile Formation are correlated with strata of the 

upper part of the Belt Supergroup, and conglomeratic strata of the 

Sixtymile deposited after the structural episode are correlated with 

conglomeratic strata of the Windermere that unconformably overlie 

the Belt.

INTRODUCTION

The upper two formations of the Chuar Group of the 

Grand Canyon Supergroup contain evidence of structural events that resulted in the end of deposition of 

the late Precambrian strata of the Grand Canyon. Details of folding, faulting, and landsliding reported here 

are part of a regional episode of block faulting and 

tilting of strata, an episode called the Grand Canyon 

revolution by Maxson (1961) and here called the 

Grand Canyon orogeny. The faulting gave rise to 

fault-block mountains with relief measured in 

kilometers. This report is concerned with the geologic 

history deduced from exposures preserved in Sixtymile Canyon near the Colorado River (fig. 1).

Fieldwork leading to this report was carried out October 14-17, 1973. The north fork of Sixtymile Canyon was reached by helicopter; a suitable landing site

was found on the west side of the Chuar syncline, on 

a point and small flat that is developed on the upper 

bed of a pair of ledge-forming carbonate beds in the 

Walcott Member of the Kwagunt Formation. This site 

allows ready access to the type section of the Sixtymile Formation exposed in the trough of the syncline. 

Reference hand samples and drill-core samples collected on close stratigraphic spacings are avail-able 

for inspection. They currently are stored in the U.S. 

Geological Survey's Paleomagnetics Laboratory in 

Flagstaff, Ariz.

ACKNOWLEDGMENTS

Permission given by the National Park Service to 

work and sample in the Grand Canyon National Park 

is gratefully acknowledged, as is the kind cooperation 

of David C. Ochsner and Robert Yearout of the Park 

Service. The successful and safe completion of the 

fieldwork was due in a large measure to the efforts of 

Alien L. Wilson, who ably assisted in the collection of 

samples for paleomagnetic analysis on one-thirdmeter stratigraphic intervals across a section of the 

Sixtymile Formation that required some effort to 

traverse. Samples for the stratigraphically controlled 

K-Ar ages of the Cardenas Lavas determined by E. H. 

McKee were collected during joint field studies with 

McKee.

GEOLOGIC SETTING

The Chuar Group (Chuar Group of Walcott, 1883; 

Ford and Breed, 1972a, 1973) is the upper of three divisions of the Grand Canyon Supergroup (Elston and 

Scott, 1976; table 1). The Chuar Group is subdivided 

by Ford and Breed (1972a, 1973) into three formations, the Galeros and Kwagunt Formations, which 

total 1.9 km in thickness, and the overlying Sixty 

Mile Formation, 1 which is 60 m thick. The Galeros 

and Kwagunt Formations are dark-gray marine shale 

with subordinate locally stromatolite-bearing carbonate rocks and a few red beds. This study is concerned 

with gray shale and dolomite in the Walcott Member 

of the Kwagunt Formation and with overlying red 

sandstone and landslide breccia of the Sixtymile For1 Ford and Breed's (1972a. p. 5, 8) name Sixty Mile Formation is here revised to Sixtymile Formation to agree with the spelling of the canyon as it appears on the topographic 

map of the Vishnu Temple quadrangle.
PRECAMBRIAN SIXTYMILE FORMATION AND OROGENY, ARIZONA

mis EXPLANATION

Paleozoic strata, undivided

CAMBRIAN

Tapeats Sandstone—As mapped, locally 

includes Bright Angel Shale

PRECAMBRIAN

GRAND CANYON SUPERGROUP 

CHUAR GROUP

Sixtymile Formation

Walcott Member of Kwagunt Formation 

(fine dotted line traces pair of marker 

carbonate beds)

Lower strata of Chuar Group, undivided

Nankoweap Formation and Cardenas 

Lavas-Exposed at north end of Butte 

fault

Lower part of Dox Sandstone—Exposed 

in upthrown fault block on Colorado 

River

————— Contacl

——j-I— Fault, high angle-Bar and ball on downthrown side; circle indicates Precambrian 

displacement; dot indicates postPaleozoic displacement

+ — --••- Axial trace of Chuar syncline—Longdashed where approximately located; 

short-dashed where indefinite; dotted 

where concealed

y'

/ Strike and dip of beds

-C^j: Mesa

FIGURE 1.—Geologic map of Precambrian Sixtymile Formation in Chuar syncline, eastern Grand Canyon, Ariz. Modified from Ford and

Breed (1973, fig. 1). LS, landing site; TS, type section.

mation (table 1). The Sixtymile was examined at its 

type locality at the head of the north fork of Sixtymile 

Canyon (fig. 1), where the most complete section 

exists and where evidence is preserved of its history of 

deposition and origin.

PREVIOUS WORK

Materials of the Sixtymile Formation were first recognized and described by Walcott (1894, p. 508, unit 

1; table 2) from exposures at the top of Nankoweap 

Butte (fig. 1). He assigned the reddish-brown sandstone, which he noted passes into sandy and argillaceous shale at the base, to the upper part of the upper

division of his Chuar terrane, which he had earlier 

called the Chuar Group, attributing the name to J. W. 

Powell (Walcott, 1883, p. 440). The thickness Walcott 

reported is 61 m, almost identical to the thickness 

reported here for its type section in Sixtymile Canyon. Walcott indicated that reddish-brown sandstone 

containing fragments (breccias and conglomerates 

of the Sixtymile Canyon section) is 38 m thick and 

that this unit overlies 23 m of reddish sandy shale. 

Walcott's twofold subdivision parallels relations described for the lower part of the Sixtymile Formation 

at Sixtymile Canyon. 

The Sixtymile Formation was named and described
INTRODUCTION

TABLE 1.—Late Precambrian and Cambrian strata exposed in 

eastern and central Grand Canyon, Arizona1

Thickness (meters I

Units Cumulative

Cambrian:

Tonto Group ____________ 180-395 

Muav Limestone ________ 180

Bright Angel Shale __________ 0-105

Tapeats Sandstone _______ 0-110 

Unconformity 

Precambrian: 

Grand Canyon Supergroup _____ 3,689-4,503

Chuar Group ___________ 1,956 

Sixtymile Formation ______ 60( + )

Kwagunt Formation __________ 594

Walcott Member ______ 2 174 

Awatubi Member ________ 344

Carbon Butte Member ___ 76 

Galeros Formation ________ 1,302

Duppa Member ______ 174

Carbon Canyon Member __ 471 

Jupiter Member _______ 462 

Tanner Member ________ 195

Unconformity

Nankoweap Formation ______ 113-150(7) 

Upper member ________ 100( + )

Unconformity

Ferruginous member ___ 13(+)

Unconformity

Unkar Group __________ 1,620-2,197 

Cardenas Lavas _______ 3244-450 (300) 

Box Sandstone _______ 884-915 (900) 

Shinumo Quartzite _____ 324-475 (400)

Unconformity

Hakatai Shale _______ 131-253 (200) 

Bass Limestone _______ 37-104 (75)

395

215

110

60

234

578

654

828

1,299

1,761

1,956

2,056

2,069

2,369

3,269

3,669

3,869

3,944

irTonto Group from McKee and Resser (1945); Chuar Group from Ford and Breed 

(1972a, 1973); Nankoweap Formation and Unkar Group from Elston and Scott (1976); 

with modifications from unpublished data.

2Thickness reported by Walcott (1894, p. 508, units 2-9) from south side of Nankoweap 

Butte.

3Nominal thicknesses for strata of the Unkar Group are shown in parentheses and are 

used in the listing of cumulative thickness.

by Ford and Breed (1972a, p. 8; 1973, p. 1252-1255) 

and Breed and Ford (1973, p. 12-18). They reported a 

thickness of 36 m for the Sixtymile, which they measured on Nankoweap Butte. Because Ford and Breed 

reported breccia at the base of the Sixtymile and because the thickness they reported is close to the 

thickness of the upper fragmental unit of Walcott, it 

appears that more than 20 m of red sandy shale underlying the breccia has been excluded from the redbed unit in Ford and Breed's study. Although Ford 

and Breed (1973) designated exposures in the north 

fork of Sixtymile Canyon as the type locality, most of 

their description of the Sixtymile Formation has come 

from the sections at Nankoweap Butte and Awatubi 

Canyon (fig. 1).

Ford and Breed (1973) reported an unconformity at 

the base of the Sixtymile Formation marked by breccia and by deep bleaching and silicification of the underlying Kwagunt Formation. They also recognized 

that beds of the Sixtymile are slumped toward the 

axis of the Chuar syncline and that angular breccia 

fragments were derived from the Kwagunt Formation. 

Breed (1975) since proposed that the Sixtymile Formation is a slide breccia. Breed and Ford (1973, p. 14)

reported three units in the Sixtymile, which in ascending stratigraphic order are "(a) massive yellow to 

purple breccia with clasts of silicified shale. 15-30 ft. 

(4.5-9 m); (b) massive red-brown sandstone with frequent slump structures and irregular masses of breccia. 100-130 ft. (30-33 m [sic]); (c) massive unbedded 

breccia with clasts of silicified shale up to 2 ft. [0.6 m] 

diameter. 21 ft. (6 m)." The total thickness of these 

units is appreciably greater than the nominal 36-m 

thickness they reported for the Sixtymile and approaches the 60-m thickness given in this report. 

There are, moreover, differences between the stratigraphy reported by Breed and Ford (1973) and the 

stratigraphy that can be seen in Sixtymile Canyon.

Because Ford and Breed considered the contact between the Kwagunt and Sixtymile Formations to be 

an unconformity, they assumed that an unknown 

thickness of beds of the Kwagunt has been eroded 

(Ford and Breed, 1973, fig. 2) and that warping of the 

Chuar syncline and deposition of the Sixtymile occurred in some undefined interval of late Precambrian 

time between deposition of the Kwagunt Formation 

and the Cambrian Tapeats Sandstone. This concept

TABLE 2.—Walcott's (1894, p. 508) stratigraphic section of upper 

division of his Chuar terrane measured on Nunkoweap butte 

(= Nankoweap Butte) with stratigraphic nomenclature of Ford 

and Breed (1973) shown on right

Thickness

Meters

Chuar terrane

Upper division

1. a. Massive reddish-brown sandstone, with irregular layers of 

similar color and containing 

numerous fragments of 

sandstone-shale of lighter

color _______________ 38 (125) 

b. The sandstones of 1 become shaly 

near their base and pass into a 

reddish, sandy, and then argillaceous shale, with a few thin 

compact layers of sandstone in 

the shale ______________ 23 ( 75)

2. Black fissile argillaceous shale that 

crumbles on exposure to the 

weather _____________________ 69 (225)

3. Compact gray limestone in massive 

layers; buff on weathered surface ____________________ 16 ( 50)

4. Shale similar to 2 ____________ 19 ( 60)

5. Gray limestone similar to 3 ______ 16 ( 50)

6. Black argillaceous shale similar to

2 and 4 ________________ 43 (140)

7. Hard buff limestone with irregular 

oolitic, cherty bands that at times 

constitute most of the stratum ______ 1 ( 4)

8. a. Black argillaceous shale with

compact layers two or three

inches thick _______ 9.1 (30)

b. Dark earthy limestone __ .3 ( 1) 10 ( 33) 

c. Black shale __________ .6 ( 2)

9. Gray Stromatopora1 !?) limestone ______________________ 2 ( 8)

10. Black argillaceous shale with variegated shales below, containing more 

or less arenaceous matter in the 

form of arenaceo-argillaceous shale 

and thin layers of sandstone. On the 

slopes light-drab, pea-green, vermilion, chocolate, maroon, and buffcolored shales of various shades 

alternate ____________________ 245 (740)

11. Massive stratum of concretionary

limestone ______________________ 3-8 (10-251

Chuar Group.

Sixtymile Formation.

Not reported.

Kwagunt Formation. 

Walcott Member.

(Doublet 

carbonate 

marker 

beds of 

this 

report.)

Pisolitic 

chert.

Flaky dolomite.

Awatubi Member.

1 Probably a species of Cryptozoon. (Walcott's note.)
PRECAMBRIAN SIXTYMILE FORMATION AND OROGENY, ARIZONA

has affected the timing of geologic events they have 

deduced from the stratigraphy (Breed and Ford, 1973, 

p. 17).

The following sections document that the Sixtymile 

is the uppermost formation of the Chuar Group and 

that no significant hiatus occurred between deposition 

of the Kwagunt and Sixtymile Formations. The Sixtymile thus should be considered as the uppermost 

"few pages of Chapter two" (late Precambrian) in the 

history of the Grand Canyon, and not as a separate 

"Chapter two-and-a-half" (Breed and Ford, 1973). 

STRUCTURE

Walcott (1890) recognized that the Chuar strata are 

preserved in a syncline bounded on the east by the 

north-trending Butte fault and truncated beneath 

Paleozoic strata on the west. The Chuar syncline has 

been described by Ford and Breed (1973, p. 1255). Its 

axial trace north of Sixtymile Canyon (fig. 1) has been 

drawn from Ford and Breed's description and from the 

distribution of outcrops shown on their map. The axis 

of the Chuar syncline closely parallels the trace of the 

Butte fault. Strata in the comparatively narrow east 

limb tend to have steeper dips than strata in the west 

limb and locally near the Butte fault dip very steeply. 

At the head of the north fork of Sixtymile Canyon, the 

strike of the axis of the Chuar syncline shifts abruptly 

to the northwest, paralleling a shift in the trace of the 

Butte fault.

West of the axis of the syncline, strata of the Chuar 

Group dip rather uniformly to the east. Southwest of 

the area of figure 1, underlying strata of the Grand 

Canyon Supergroup also dip about 10° eastward (see 

Maxson, 1967; Huntoon and others, 1976). These relations reflect a regional eastward tilting of the Precambrian strata during an episode of block faulting, 

the youngest decipherable Precambrian structural 

event in the Grand Canyon (see Maxson, 1961; Huntoon and Sears, 1975). The regional and local settings 

thus indicate that the Chuar syncline is a local feature related to high-angle faulting on the Butte fault.

The Butte fault was named by Walcott (1890, p. 50) 

for the line of six spectacular buttes that lie east of 

the fault and that in part owe their origin to the fault 

(fig. 1). The Butte fault is exposed where Paleozoic 

strata have been eroded from the East Kaibab monocline, an east-facing structure of post-Paleozoic age. 

The East Kaibab monocline extends northward about 

200 km, well into Utah. Exposures in the Grand Canyon indicate that this very long Phanerozoic structure 

is underlain by a Precambrian fault.

As is the case with a number of other faults in the 

Grand Canyon, the Butte fault has undergone repeated movements. In general, the northwest- and 

north-trending faults in the Grand Canyon show 

down-on-the-west senses of displacements in Precambrian rocks and down-on-the-east displacements 

in overlying Paleozoic rocks. The decipherable record 

of faulting begins during deposition of the Shinumo 

Quartzite of the Unkar Group (table 1), with highangle reverse faulting, east side up, on the northeasttrending Bright Angel fault (Sears, 1973; Huntoon 

and Sears, 1975). The Bright Angel fault is about 20 

km southwest of Sixtymile Canyon. Because strata as 

old as the Shinumo Quartzite and Hakatai Shale are 

not exposed along the Butte fault, evidence for such 

early movement is concealed. However, 10-13 km 

south of Sixtymile Canyon, complex relations exist 

that reveal faulting on the Butte fault and on associated faults after deposition of the Cardenas Lavas 

and before and during deposition of the Nankoweap 

Formation (Elston and Scott, 1976). Thus, the Butte 

fault was in existence before deposition of sediments 

of the Chuar Group.

Two episodes of movement are recognized on the 

Butte fault since deposition of the Nankoweap Formation. The older is a Precambrian episode that marked 

the end of deposition of Precambrian strata, and 

which this report describes. The younger is a postPaleozoic episode that was assigned to the Tertiary by 

Walcott (1890, p. 57) from studies of C. E. Dutton 

(1882) and that probably is of "Laramide" (Late Cretaceous or early Tertiary) age (Huntoon, 1971, 1974). 

The post-Paleozoic displacement is about 810 m, down 

on the east, measured on the base of the Cambrian 

Tapeats Sandstone (Ford and Breed, 1973, p. 1255). 

The pre-Paleozoic displacement was about 3.2 km, 

down on the west. This estimate is derived from the 

thickness of Precambrian strata removed from the 

eastern, upthrown side of the Butte fault before deposition of the Tapeats. The Tapeats rests on the Sixtymile Formation west of the Butte fault but east of 

the fault directly overlies beds in the lower part of the 

Dox Sandstone (fig. 1; table 1; Elston and Scott, 1976, 

p. 1768), at least 3,200 m stratigraphically beneath 

the Sixtymile Formation. Strata of the entire Chuar 

Group, Nankoweap Formation, Cardenas Lavas, and 

most of the Dox Sandstone were eroded from the upthrown block before deposition of the Tapeats. 

STRATIGRAPHY

Ford and Breed (1973, p. 1244, 1252-1253) designated the type section of the Sixtymile Formation as 

outcrops of breccia and sandstone on cliffs on the 

north side of the upper part of Sixtymile Canyon and 

indicated its location by the letter H on their figure 2.
STRATIGRAPHY

Landslide block derived 

from unit 1 of Walcott 

Member and detached 

from scarp of Butte 

fault

EXPLANATION

Sandstone,

conglomeratic

Breccia- and

chert-bearing

Landslide 

Monomict (o)

and 

polymict (°)

METERS 

r 15

FIGURE 2.—Type section of Sixtymile Formation and units described at end of report. Wavy lines indicate an erosion surface.
PRECAMBRIAN SIXTYMILE FORMATION AND OROGENY, ARIZONA

A description of the type section, including immediately underlying and overlying strata, is given at 

the end of this text (table 4) and is shown diagrammatically on figure 2. These excellent exposures 

have enabled the stratigraphy and facies relations of 

the Sixtymile to be understood, in turn providing new 

insight on the formation of the Chuar syncline and 

faulting on the Butte fault.

PRE-SIXTYMILE STRATA

Strata of the Chuar Group beneath the Sixtymile 

Formation are mainly drab, monotonous sequences of 

gray to blue-black shale and subordinate interbedded 

limestone and dolomite. Three horizons of algal 

stromatolitic limestone, in part biohermal, and the 

primitive organism Chuaria are found within sequences of shale of the Chuar Group (Ford and Breed, 

1972b, 1973). Additionally, microflora consisting of 

spheroids and filaments have been discovered by 

Schopf, Ford, and Breed (1973) in a thin cherty pisolite bed 20 m above the basal dolomite bed of the Walcott Member of the Kwagunt Formation (tables 1 and 

2). On morphologic and geologic grounds, Schopf, 

Ford, and Breed believe that the siliceous pisoliths are 

of biologic origin, formed in a shallow, gently agitated 

marine setting. The gray shale and carbonate beds are 

very similar in aspect to gray marine shale and limestone of Paleozoic and Mesozoic age. The lithologic 

similarity and the presence of probable marine plant 

fossils suggest that much of the Chuar was deposited 

in a marine to possible intertidal environment. Sandy, 

silty, and shaly red beds occur at two horizons within 

the dominantly gray shale section of the Chuar Group 

and presumably reflect fairly brief intervals of 

emergence from beneath sea level and deposition near 

sea level.

KWAGUNT FORMATION

The Kwagunt Formation, nearly 600 m thick, was 

named by Ford and Breed (1972a, p. 7-8; 1973, p. 

1242-1255), who subdivided it into three members 

(table 1). This report is concerned only with the upper 

or Walcott Member, which is about 175 m thick. The 

Walcott is dominantly gray to black shale. The strata 

at the type section of the Walcott Member on the 

south side of Nankoweap Butte (Ford and Breed, 

1973, fig. 1) were measured and described by Walcott 

(1894, p. 508, units 2-9; table 2). It seems appropriate, 

in the absence of a detailed stratigraphic description, 

to designate Walcott's description as the description of 

the type section for the Walcott Member.

Three buff- or brown-weathering dolomitic limestone beds serve as marker beds in the Walcott. One 

is at the base of the member (unit 9 of Walcott), and 

a pair (or "doublet") occurs in the interval 90-105 m 

above the base (unit 3 of Walcott). The pisolitic chert

bed that contains the microflora is unit 7 of Walcott's 

section. Except for one other interval of limestone 

(unit 5 of Walcott), the intervening materials are dark 

shale.

The basal bed, 2.5 m thick, is informally called the 

Flaky Dolomite by Ford and Breed (1973, p. 1252), 

who noted that it contains "wildly oriented" silicified 

flakes of what probably are relict algal laminations, 

which Walcott called "Stromatopora(?)." Ford and 

Breed suggested that the source rock was a disrupted 

stromatolitic limestone and that the cause of the disruption may have been contemporary seafloor slumping.

Two layers of buff-weathering dolomitic limestone 

form a distinctive ledge-forming doublet in the Walcott (figs. 3 and 4). In Nankoweap Butte, the interval 

is reported by Walcott (1894, p. 508, unit 3) to be 15 m 

thick and its top to lie 68.6 m below red strata of unit 

1 (Sixtymile Formation). Characteristic thicknesses for 

the carbonate layers reported by Ford and Breed 

(1973, p. 1252) are about 7.5 m for the lower bed and 

about 12 m for the upper bed, separated by about 12 m 

of shale. Time was not available for the measurement 

and description of these beds in the trough of the 

Chuar syncline in Sixtymile Canyon during this 

study. However, the pair of beds are persistent in the 

trough and west limb of the syncline (fig. 1), and they 

thin and in part pinch out toward the Butte fault in 

the east limb of the syncline (figs. 3 and 4). The 

stratigraphic interval between the top of the doublet 

beds and the Sixtymile Formation on the axis of the 

syncline is estimated to be about 70 m. The upper bed 

of the doublet, observed at the helicopter landing site 

on the west limb of the syncline, is a limestone, in 

part fragmented, in which the fragments have been 

dolomitized and silicified. In this respect, it is similar 

to the flaky dolomite at the base of the Walcott.

DEVELOPMENT OF CONTACT RELATIONS

The contact of the Walcott Member with the overlying Sixtymile Formation has been described as an unconformity, beneath which shale of the uppermost 15 

m of the Walcott is silicified (Ford and Breed, 1973, p. 

1253). This observation applies to the east limb of the 

Chuar syncline in the Sixtymile Canyon area, where 

landslide material of the Sixtymile Formation rests on 

altered shale of the Walcott. However, landslide is not 

the stratigraphically lowest material of the Sixtymile; 

it overlies basal red laminated sandstone (unit 1) and 

siltstone of the Sixtymile that is preserved locally on 

the west limb and in the trough of the syncline (figs. 

3, 4, and 5). In the trough of the syncline the uppermost Walcott is unaltered, and it contains beds in a 

1.5-m interval that are transitional between underlying black shale typical of the Walcott and overlying
STRATIGRAPHY

100 200

APPROXIMATE SCALE

300 METERS

__I

p€kw

FIGURE 3.—Sixtymile Formation and Chuar syncline in north fork of Sixtymile Canyon. View is to north-northwest. p-Ckw, 

Walcott Member of Kwagunt Formation; pCs (lower), pCs (middle), and pCs (upper), respectively, of Sixtymile Formation; 

Ct (red) and Ct (brown), red beds and brown beds, respectively, of Tapeats Sandstone; Cba, Bright Angel Shale.

red sandstone of the basal unit of the Sixtymile Formation. Although the contact of unit 1 of the Sixtymile with the Walcott is concealed by colluvium on 

the west limb of the syncline for an interval of one to 

a few meters, no alteration of underlying beds of the 

Walcott was observed, and the character of the contact 

is presumed to be transitional, as it is in the exposure 

in the trough of the syncline. The transition beds and 

the basal laminated red sandstone of the Sixtymile do 

not contain fragmental or exotic materials, unlike 

succeeding strata. Field relations thus indicate that 

deposition was continuous across the KwaguntSixtymile boundary.

The thin interval of red siltstone preserved in the 

syncline normally would be included with the Sixtymile. However, for convenience of portrayal of 

stratigraphic relations in the figures of this report, the 

transition beds in the syncline are considered to be at 

the very top of the Walcott Member, and the boundary 

between the formations is arbitrarily drawn between 

laminated red sandy siltstone below (in the trough of 

the syncline) and laminated very fine grained red 

sandstone above (on the west limb of the syncline).

Red laminated sandstone of the lowermost Sixtymile (unit 1) is preserved only locally on the west 

limb of the syncline. Equivalent beds almost certainly 

once rested on red laminated siltstone in the trough of 

the syncline but were removed by landsliding. Contorted, sheared green and red siltstone, 3-5 cm thick, 

presently separates unaltered and undisturbed red
00

\__— (Pennsylvanian and Permian) ———s———————^__

—-—. 

Bright Angel Shale

Supai

Redwa" Group 

Limestone ' Tapeats Sandstone

____(Cambrianti__< 

Brown beds of

' \ Bright Angel Shale ' ——————— ^— t ^

Bright Angel Shale — Brown beds of 

Tapeats Sandstone

Sixtymile Formation" 

(Precambrian)

EXPLANATION

_ _ _ Contact-Dashed where inferred—— Fault- Strike and dip of beds

DO 

» O

FIGURE 4.-Stratigraphic relations in Chuar syncline, north fork of Sixtymile Canyon. View is to northwest. In Walcott Member, note section, containing pair of

ledge-forming carbonate beds thins eastward toward Butte fault and upper carbonate bed pinches out.
STRATIGRAPHY

Maroon beds 

Middle member

Transition

beds y Doublet carbonate

beds? 

,<^

Doublet carbonate 

beds

EXPLANATION

_ _ _ Contact —Dashed where inferred 

•—— Line of measured section

Strike and dip of beds

FIGURE 5.—Details of stratigraphic relations in central part of Chuar syncline showing lines of section used for 

measurement of type section of Sixtymile Formation. Numbers refer to table 3.

siltstone below from overlying landslide material of 

unit 3 of the lower member of the Sixtymile (figs. 2, 4, 

and 5; see table 4). The contact on and east of the axis 

of the syncline is an unconformity separating landslide material from unaltered and altered beds of the 

Walcott Member. The landslide material of units 3 

and 5 contains an increasing proportion of clasts of 

red sandstone of the Sixtymile as it is traced westward from the axis of the syncline. Near slumped beds 

of red, laminated Sixtymile sandstone in the west 

limb of the syncline, the landslide becomes a 

monomict breccia consisting entirely of angular fragments of Sixtymile sandstone. Thus laminated 

sandstone once present in the trough of the syncline 

was disrupted and incorporated in the landslide. Evidence for an east-to-west movement of polymict landslide materials is summarized in the description of the 

Sixtymile Formation. The monomict and polymict 

landslide materials overlie and clearly are younger 

than the laminated red sandstone at the base of the 

Sixtymile Formation.

To summarize the above: beds of the uppermost 

Walcott are preserved in the trough of the syncline. 

They are transitional in color and lithology between 

lower Walcott rocks and laminated red sandstone of 

the Sixtymile Formation that is preserved locally on 

the southwest flank of the syncline. The transition 

beds are unaltered in the axis of the syncline, and no 

evidence for alteration was found beneath the laminated red sandstone of the Sixtymile on the west limb 

of the syncline. These facts indicate that a transition 

in depositional conditions occurred between deposition 

of the Walcott and Sixtymile and that deposition was 

continuous across the formational boundary.

The stratigraphic relations are interpreted to record 

the following events in the development of the contact 

relations between the Walcott Member and the Sixtymile Formation: (1) emergence from euxinic marine 

conditions to an aerated tidal-flat or littoral marine 

environment, which resulted in deposition of laminated red sandstone at the base of the Sixtymile (unit 

1); (2) subsidence on the Chuar syncline, presumably
10 PRECAMBRIAN SIXTYMILE FORMATION AND OROGENY, ARIZONA

reflecting an increment of movement on the Butte 

fault, caused slumping of the basal (unit 1) sandstone 

toward the axis of the syncline; (3) erosion removed 

some of the sandstone of unit 1, locally exposing shale 

of the Walcott west of the axis of the syncline and 

widely exposing shale of the Walcott on the eastern 

limb of the syncline; (4) after moderate weathering of 

the Walcott shale, sandstone containing small rock 

fragments (unit 2) was deposited west of the axis of 

the syncline, and on the eastern limb of the syncline 

weathering of the Walcott continued, resulting in 

deep alteration; and (5) landsliding from the east disrupted sandstone strata of the Sixtymile in and west 

of the trough of the syncline. The last event recorded 

the first of two or more major structural pulses, 

reflecting large displacements on the Butte fault that 

presumably occurred during the course of strong regional uplift.

SIXTYMILE FORMATION

The Sixtymile Formation is subdivided into three 

informal members (fig. 2): (1) a lower sandstone and 

landslide breccia member; (2) a middle cherty quartzite member; and (3) an upper breccia-bearing sandstone and conglomerate member that exhibits an 

abrupt change in facies. The lower member, in and 

east of the trough of the Chuar syncline, is made up of 

landslide debris derived from the area and former 

scarp of the Butte fault. The polymict breccia passes 

into monomict breccia in the west limb of the 

syncline, where the materials consist of angular 

fragments of red sandstone derived from the subjacent 

basal unit of the Sixtymile. The landslide overlies red 

sandstone of the basal Sixtymile that is slumped toward the axis of the syncline and underlies red sandy 

siltstone at the top of the lower member of the Sixtymile. The stratigraphic and structural relations indicate that a progressive deepening of the Chuar 

syncline accompanied movement on the Butte fault 

and deposition of landslide material of the lower 

member.

The middle member is a laminated and thin-bedded 

very fine grained cherty quartzite. It probably was deposited in standing water, presumably a lake that occupied a topographic low in the syncline. The upper 

member, west of the axis of the syncline, consists of 

fine-grained fluviatile and fanglomeratic sandstone 

that grades abruptly into sandy conglomerate toward 

the axis of the syncline. In the lower member, the 

coarse materials were derived by landsliding from the 

east and northeast, from the area of the Butte fault. 

In the upper member, the coarse materials show the 

effects of stream transport and deposition along the 

axis of the syncline, and except for the basal bed of the 

upper member their deposition postdated folding on 

the syncline.

The Sixtymile Formation in the area of its type section is shown in a photograph of the north fork of Sixtymile Canyon (fig. 3). Most of the stratigraphic units 

shown in figures 2, 4, and 5 may be identified in the 

photograph. Figures 4 and 5 were drawn from a photograph that looks more directly down the axis of the 

Chuar syncline. The locations of the lines of section 

measured for the composite stratigraphic section (fig. 

3 and table 4) are shown in figure 5.

Thicknesses reported for the Sixtymile Formation 

show some variability because several of the units 

were deposited in an actively deepening trough. The 

stratigraphic interval along the lines of section on the 

west limb near the axis of the syncline (fig. 5) totals 

51 m. A composite stratigraphic section that includes 

the basal sandstone (unit 1; 6.4 m thick) preserved 

updip from the main line of section (fig. 5) and an estimated 1.5 m of strata strati graphically above the 

highest accessible beds of the upper member results in 

a reconstructed thickness of 59 m for the Sixtymile at 

the type section. Siltstone of unit 6 of the lower 

member may be about 5 m thicker at the axis of the 

syncline than where measured on the west limb. If so, 

the maximum reconstructed thickness of beds preserved in the syncline is about 64 m. The nominal 

thickness reported here for the Sixtymile is 60 m.

LOWER MEMBER

Six purplish-red units are recognized in the lower 

member (fig. 2). In ascending order they are unit 1, 

laminated hematitic sandstone; unit 2, thin-bedded 

micaceous sandstone containing rock fragments, 

which overlies weathered Walcott shale; unit 3, 

monomict and polymict breccia; unit 4, crudely bedded 

sandstone; unit 5, monomict and polymict breccia; and 

unit 6, thin-bedded soft sandy siltstone. These units 

record four intervals of sandstone deposition and two 

or more episodes of landsliding.

The contact relations of units 1, 2, and 3 with the 

Walcott Member have been summarized in the section 

"Development of Contact Relations." On the west, 

unit 3 breccia is monomict and crudely stratified and 

consists of disrupted angular fragments of welllithified sandstone derived mainly from unit 1. The 

breccia becomes polymict toward the axis of the 

syncline where it consists mainly of altered and silicified fragments derived from the Kwagunt Formation. 

A few fragments of sandstone made up of rounded 

grains of quartz are exotic to both the Kwagunt and 

Sixtymile Formations. Their source is not known. The 

polymict breccia in the trough of the syncline is not 

apparently stratified, and the various materials are 

chaotically distributed. Landslide material of unit 3 is 

8 m or more thick in the trough of the syncline, and 

two large exotic blocks, vertically oriented with respect to their bedding, rest side by side in the axis
STRATIGRAPHY 11

(figs. 2 and 5). Proceeding eastward, up the east limb 

of the syncline, a large buff-weathering carbonate 

body about 8 m thick and 40 m long crops out at the 

base of the unit 3 landslide. Judging from its lithology 

and thickness, this mass was derived from the upper 

of the doublet carbonate beds of the Walcott Member 

or else from another stratigraphically much lower 

carbonate bed. In the Walcott Member in the trough 

of the syncline, the upper of the marker beds lies 

about 70 m stratigraphically beneath the Sixtymile 

Formation. The landslide block has not been tumbled 

but rather arrived at its position by sliding on its 

basal surface down the east limb of the Chuar 

syncline. Presumably the bed was once exposed in the 

scarp on the upthrown side of the Butte fault. The upslope part of the landslide block rests on altered, 

weathered Walcott shale. Its downslope end overrides 

and rests on unaltered red transition beds of the Walcott.

The foregoing relations indicate that significant displacement occurred on the Butte fault early during 

the deposition of the Sixtymile. Just how much displacement had taken place by the time of deposition of 

landslide of unit 3 is not known. Displacement was at 

least 100 m and may have been much greater. A block 

of tan-weathering white quartzite at the base of the 

landslide mass in the axis of the syncline (figs. 2, 4, 

and 5) is foreign to the Chuar Group. The stratigraphically closest possible source is quartzite at the 

top of the Nankoweap Formation, some 2 km below 

the top of the Kwagunt Formation. Displacement on 

the Butte fault at the time of emplacement of the 

polymict landslide of unit 3 thus was at least 100 m 

and possibly was 2 km or more.

On the west side of the syncline (figs. 2 and 4), a 

poorly stratified and sorted sandstone (unit 4) overlies 

breccia (unit 3) and in turn is overlain by a dominantly monolithologic breccia (unit 5). The monolithologic breccia is made up of angular clasts of 

sandstone derived principally from unit 1. As is the 

case for unit 3, breccia of unit 5 becomes polymict toward the axis of the syncline, where no plane of separation between units 3 and 5 is apparent. Deposition 

of sandstone of unit 4 thus records a brief(?) interval 

between two large landslide events early in the deposition of the Sixtymile.

The record preserved in the lower member ends 

with deposition of soft thin-bedded sandy red siltstone 

(unit 6) that is exposed locally on the west side of the 

syncline. This unit is sharply and unconformably(?) 

truncated by the middle member, wedging out at the 

base up the limb of the syncline. Toward the axis of 

the syncline unit 6 is concealed by talus. A hiatus of 

unknown extent exists between deposition of unit 6 

and beds of the middle member of the Sixtymile. The

hiatus may have been geologically short, reflecting a 

change from mudflat to lacustrine deposition.

MIDDLE MEMBER

The middle member is a cherty quartzite, 25 m 

thick, which resists erosion and characteristically 

forms cliffs. It can be traced across the area of exposure of the Sixtymile Formation and is responsible for 

the preservation of the Sixtymile in the Chuar 

syncline. Its resistance to erosion led to the formation 

of small hills on either side of the syncline in late Precambrian time before deposition of the Tapeats 

Sandstone. The hills appear to have protected the 

lowest beds of the less resistant upper member from 

complete removal from the axis of the syncline before 

deposition of the Tapeats Sandstone. The middle member may be crossed, without resorting to technical 

climbing techniques, at one place in the trough of the 

syncline (fig. 5).

The quartzite of the middle member is thin bedded 

and finely laminated, and the grains are very fine 

sand to silt size. The lower part is purplish red, grading upward to a creamy mottled and streaked red. 

Chert is common to abundant, and the middle part 

contains numerous thin discontinuous beds of 

chalky-white chert. Breccia is sparse, one lens possibly of landslide origin occurring near the top. The 

very fine grain size, the thin regular bedding, and the 

bedded chert are evidence for deposition in quiet 

standing water, perhaps a lake along the axis of the 

Chuar syncline.

The middle member is folded on a moderately large 

scale, and the thin beds and laminations are crinkled 

in a manner that reflects slumping of the member toward the axis of the Chuar syncline. Slumping occurred after deposition of the member, because no 

internal folds independent of other folds were observed across the member. Folding probably occurred 

after deposition of the overlying basal sandstone bed 

of the upper member, which displays contorted bedding that may reflect the same slumping event. 

Slumping probably was in response to minor(?) renewed subsidence in the Chuar syncline, which in 

turn presumably reflected renewed displacement on 

the Butte fault. The slumping and subsidence produced a narrow trough in which strata of the upper 

member were deposited, and subsequently preserved.

The contact of the middle and upper members is 

sharp and unconformable. The basal sandstone of the 

sandstone facies of the upper member at one place 

truncates 1.5 m of beds of the middle member. Toward 

the axis of the syncline, in inaccessible exposures, 

conglomerate overlies the middle member with apparent unconformity. The length of the hiatus in deposition is not known, but possibly was not long geologically.
12 PRECAMBRIAN SIXTYMILE FORMATION AND OROGENY, ARIZONA

UPPER MEMBER

The upper member, about 12 m thick, is preserved 

in a narrow trough-shaped area in the axis of the 

Chuar syncline. Two fades, a sandstone facies and a 

conglomerate facies, are recognized. The sandstone is 

present southwest of the axis of the syncline (fig. 5), is 

pale red to brown, and contains scattered rock fragments that include chalky-white chert derived from 

the middle member. Some of the strata are fluvially 

crossbedded, and some of the sandstone is fanglomeratic. A siltstone bed 2 m thick is present in the lower 

part of the section. Parts of the sandstone facies grade 

laterally northeastward toward the axis of the 

syncline, over a distance of 3-4 m, into massiveweathering maroon conglomerate. Stratification in 

the conglomerate is obscure but where seen in a few 

lenses of contained sandstone is horizontal. Much of 

the coarsest detritus in the conglomerate is subangular and has undergone only comparatively short 

transport. However, some of the detritus in the conglomerate is subrounded, suggestive of moderate 

transport. The conglomerate and laterally equivalent 

beds of sandstone were deposited by a stream that 

once flowed along the trough of the syncline.

Sandstone and conglomerate beds at the top of the 

upper member, unlike beds near the base, are essentially flat lying. These uppermost beds of the Sixtymile dip 2° NW., identical to the dip of parallel laminated beds of the directly overlying Cambrian Tapeats 

Sandstone. This indicates that strata of the upper 

member record a simple filling of the synclinal trough 

and that folding on the Chuar syncline ceased before 

the end of deposition of the Sixtymile. The final increment of subsidence on the syncline, from the presence of a contorted breccia-bearing sandstone, occurred very early during deposition of the upper 

member (table 4). Strata above the basal brecciabearing sandstone of the upper member thus appear 

younger than disturbances related to the Grand Canyon orogeny, and these beds presumably record the 

deposition of an apron of detrital material shed from 

high-standing terrain onto and across downfaulted 

terrain. Judging from the 3 km of structural relief 

across the Butte fault, it is conceivable that the apron 

of material once was many hundreds of meters thick, 

following which it was nearly entirely removed by 

pre-Tapeats erosion.

TAPEATS SANDSTONE

The Tapeats Sandstone, of Early and Middle Cambrian age (McKee and Resser, 1945), was deposited 

across the region of the Grand Canyon about 570 m.y. 

ago as a consequence of west-to-east marine transgression. An irregular hilly terrain existed, and some 

hills had a topographic relief of more than 200 m. The 

highest hills were not buried until after the end of deposition of the Middle Cambrian Bright Angel Shale 

(table 1). During deposition of the Tapeats, a small 

amount of relief in the Sixtymile Canyon area was 

present as a consequence of the resistance to erosion 

of the middle member of the Sixtymile Formation (fig. 

4). Erosion and removal of the upper member of the 

Sixtymile from all but the central part of the syncline 

produced a swale or channellike depression, with 

20-30 m of erosional relief, between hills on both 

sides of the Chuar syncline. Red beds of the Tapeats 

were deposited across the area, and the original red 

coloration is preserved in the swale between the hills 

(fig. 4). These beds are nearly flat lying and dip 2° 

NW., indicating that the syncline is entirely of Precambrian age.

In the axis of the syncline, the contact of the 

Tapeats with the conglomerate and locally with 

sandstone of the upper member of the Sixtymile is a 

disconformity. A few meters to the south of the axial 

part of the syncline, an angular discordance between 

the formations of 6° to 10° can be seen. Within the 

Chuar syncline, about 20 m of the red beds and an 

estimated 5-10 m of overlying brown (bleached) beds 

of the Tapeats wedge out against beds of the middle 

member of the Sixtymile (fig. 4).

The basal unit of the Tapeats in the Chuar syncline 

is a parallel-bedded maroon sandstone, 2.5 m thick, 

that is not known elsewhere in the eastern Grand Canyon. It is similar to and presumably correlates with 

parallel-bedded maroon sandstone in the lower part of 

the Tapeats in the central Grand Canyon, seen opposite and slightly downstream from Deer Creek (river 

mile 136.5). If the parallel-bedded sandstone is correlative, the swale in the trough of the syncline was 

topographically low at the onset of deposition of the 

Tapeats.

Beds of unit 2 of the Tapeats are pale red to reddish brown and are typical of the color and stratification of unbleached sections of the Tapeats seen at 

places in the central Grand Canyon. The color of the 

red beds of units 1 and 2 in the topographic swale 

above the Chuar syncline probably was preserved because ground water did not percolate through these 

beds in Cenozoic time. Red sandstone is known to 

occur very locally at the base of the Tapeats at a few 

other places in the eastern Grand Canyon. In each 

case the lack of bleaching is seemingly related to a 

physical configuration that would have impeded 

Cenozoic ground water flow.
STRATIGRAPHY 13

TABLE 3.—Outline of depositional and structural events of Grand Canyon orogeny, Sixtymile Canyon, eastern Grand Canyon, Ariz.

Stratigraphy History

570 m.y.

Tonto Group:

Tapeats Sandstone

Great unconformity

Chuar Group:

Sixtymile Formation: 

Upper member:

Unit 4 

3 

2 

1

Unconformity 

Middle member.

Unconformity 

Lower member: 

Unit 6 __

830 m.y.

Unconformity

Fluviatile sandstone and conglomerate.

Fluviatile sandstone and breccia 

with contorted bedding.

_ Thin-bedded and laminated 

cherty quartzite.

Sandy red siltstone _______

Kwagunt Formation: 

Walcott 

Member

Landslide _______________

Red sandstone _________

Landslide ____________

Red sandstone with rock 

fragments resting on weathered Walcott shale.

Thin-bedded laminated red 

sandstone.

Transition beds _________. 

Black shale.

Pair of carbonate marker beds 

and intervening shale.

Awatubi 

Member

Thinning of lower marker 

bed and overlying shale, 

and pinchout of upper 

marker bed toward Butte 

fault to east. Disruption of 

upper marker bed on west 

side of Chuar syncline.

Black shale.

Flaky dolomite bed _______

Disruption by contemporary 

seafloor slumping.

Regional west-to-east Cambrian transgression. 

Chuar syncline was topographically as well as 

structurally low and received initial deposits 

characteristic of older strata of the Tapeats to the 

west.

Planation of the upthrown fault blocks; removal of 

nearly all of the late Precambrian de'trital deposits 

on the downthrown fault blocks as erosion cut 

deeply across the region. Preservation of Sixtymile Formation in a structural low.

Deposition of an apron of detrital deposits across 

downthrown fault block during subaerial erosion 

of high-standing fault block.

Filling of Chuar syncline with stream deposits.

Final erogenic pulse: Increment of subsidence in 

Chuar syncline resulted in slumping of the middle 

member toward axis of Chuar syncline and disruption of basal bed of upper member; subsidence 

accompanied by minor(?) faulting on Butte fault.

Interval of quiet deposition: Deposition of middle 

member in a lake localized along axis of Chuar 

syncline; small landslide breccia near top.

Mudflat deposition.

Main erogenic pulses accompanied by strong regional uplift:

d. Large displacement on Butte fault (1 km?), 

c. Brief(?) interval of deposition of sandstone, 

b. Major displacement on Butte fault (2 km?). 

a. Folding on Chuar syncline; slumping of unit 

1 sandstone accompanied by partial removal; exposure and weathering of shale 

of Walcott Member; deposition of unit 2 

sandstone.

Subaerial deposition at or near sea level.

Emergence accompanying regional uplift.

Uplift of the east limb of the Chuar syncline in response to faulting on the Butte fault. Structural 

relief was 20 m or more.

Possible initial faulting of Grand Canyon orogeny 

on preexisting Butte fault and initiation(?) of 

Chuar syncline.

______ Black shale.
14 PRECAMBRIAN SIXTYMILE FORMATION AND OROGENY, ARIZONA

HISTORY AND AGE

The Grand Canyon orogeny began during deposition 

of black shale and carbonate beds of the Walcott 

Member of the Kwagunt Formation (table 3). The first 

movements in the north-trending Chuar syncline and 

nearby Butte fault may have taken place as early as 

deposition of the flaky dolomite at the base of the 

Walcott Member. Contemporary slumping of the 

seafloor that has been suggested by Ford and Breed 

for the disruption of materials in this bed could have 

been triggered by displacement on the already existing Butte fault. However, the first direct evidence for 

deepening of the Chuar syncline is seen in an interval 

of strata that lies about 70-85 m below the top of the 

Walcott Member. The strata consist of two buffweathering dolomitic limestone beds separated by 

shale. In the Sixtymile Canyon area, the lower bed 

and the overlying shale thin eastward toward the 

Butte fault, and the upper bed pinches out. The thinning and pinchout record 20 m or more of relative 

structural uplift of beds near the Butte fault during 

deposition of the Walcott. The upper dolomite bed in 

the syncline locally appears disrupted and fragmented. Disruption and fragmentation of the possible 

algal laminations may have been due to some combination of desiccation and wave action or perhaps by 

an earthquake associated with movement on the 

Butte fault.

Regional uplift terminated deposition of the Walcott 

Member. This uplift is marked by the deposition of 

shale and siltstone that is transitional in color and 

lithology between black shale of the Walcott Member 

below and very fine grained red sandstone of the Sixtymile Formation above.

After emergence from the sea, at least 6 m of very 

fine grained thin-bedded and laminated red sandstone 

(unit 1 of lower member of Sixtymile) was deposited in 

the area of the Chuar syncline. Deposition was in 

quiet, standing water, presumably at or very near sea 

level. Aeration presumably caused the formation of a 

pervasive red hematite pigment.

The laminated basal sandstone strata of the Sixtymile then underwent slumping toward the axis of 

the Chuar syncline, presumably in response to a 

deepening of the syncline and the beginning of large 

displacements on the Butte fault. With uplift of the 

east limb of the syncline toward the Butte fault, erosion removed material of the Sixtymile, exposing the 

Walcott, and weathering and alteration of the black 

shales began. In the trough of the syncline, erosion 

removed much of the red sandstone of the Sixtymile 

and locally exposed Walcott shale low in the west 

limb, where minor weathering also took place. The 

transition beds of the Walcott in the trough of the

syncline escaped alteration. After exposure and minor 

alteration of Walcott shale on the west limb of the 

syncline, a local(?) red sandstone, 1.5 m thick, that 

contains sparse rock fragments and fresh white mica 

(unit 2 of lower member) was deposited downslope 

from slumped beds of unit 1. The contact of unit 2 

with the Walcott is a disconformity, and the sandstone wedges out with probable unconformity against 

unit 1.

After deposition of the two lower sandstone units of 

the Sixtymile, two strong episodes of faulting occurred 

on the Butte fault, accompanied by a deepening of the 

Chuar syncline and steepening of its limbs. Landslides cascaded westward down the east limb of the 

syncline. The first landslide contained a large stratigraphically coherent block derived from one of the resistant carbonate beds of the Chuar Group that was 

exposed in the upthrown block and detached from the 

fault scarp. Displacement on the Butte fault was at 

least 100 m and probably was much more. A quartzite 

block at the base of the landslide in the trough of the 

syncline is foreign to the Chuar Group and may have 

been derived from quartzite at the top of the Nankoweap Formation. If this is the case, displacement on 

the Butte fault at the time of the first landslide was at 

least 2 km. This is about two-thirds of the maximum 

stratigraphic displacement that can be deduced from 

the erosion of strata from the eastern upthrown block. 

Landslide material west of the axis of the syncline 

contains an increasing proportion of red sandstone 

fragments derived from the Sixtymile, and the landslide becomes monomict high on the west limb of the 

syncline. A poorly stratified red sandstone (unit 4) 

separates two episodes of landsliding and brecciation 

in the west limb (units 3 and 5). The two landslide 

units, however, could not be distinguished in the axis 

of the syncline, because the intervening sandstone is 

not present. If the first landslide reflects a large increment of displacement on the Butte fault, then the 

second landslide also presumably represents a major 

pulse of faulting. Soft sandy red siltstone (unit 6) was 

then deposited on the landslide, the last depositional 

event that is recorded for the lower member of the 

Sixtymile. From the relative paucity of breccia in 

overlying strata, most of the regional uplift, folding, 

and faulting of the Grand Canyon orogeny occurred 

during deposition of the lower member.

The middle member of the Sixtymile Formation, 25 

m thick, is a thin-bedded and laminated cherty 

quartzite that was deposited in standing water, probably a lake in the trough of the Chuar syncline. The 

middle member unconformably overlies the lower 

member and in turn is truncated with at least local angular unconformity by the basal unit of the upper member. The lengths of the hiatuses are not known, but
HISTORY AND AGE 15

they probably were short. The middle member displays 

folding that reflects slumping toward the axis of the 

Chuar syncline after deposition. Bedding of the overlying basal sandstone bed of the upper member also is 

contorted, and it reflects the last increment of slumping in the syncline, and by inference the last increment of Precambrian displacement on the Butte fault.

Strata of the upper member consist of fluviatile 

sandstone and conglomerate, 12+ m thick. Dips decrease upward and at the top are nearly horizontal. A 

dip of 2° NW. at the top is identical to the dip of directly overlying parallel-bedded sandstone of the 

Cambrian Tapeats Sandstone. The horizontal attitude 

and the lack of folding in these uppermost beds of the 

Sixtymile indicate that folding on the Chuar syncline 

and faulting on the Butte fault had ended. The 

fluviatile deposits simply aggraded in the synclinal 

trough produced at the time of slumping of the middle 

member and the basal sandstone of the upper 

member.

The record for the Grand Canyon orogeny thus is 

contained principally in the lower and middle members of the Sixtymile Formation and only to a minor 

extent in the underlying Walcott Member of the 

Kwagunt Formation. Two major increments of folding 

and faulting occurred during deposition of the lower 

member of the Sixtymile, and a third final increment 

of folding, and probably faulting, occurred shortly 

after the beginning of deposition of the upper member.

An age for the Sixtymile Formation, and the Grand 

Canyon orogeny, is estimated from reset K-Ar ages 

obtained from the Cardenas Lavas of the Unkar 

Group (table 1) and is believed to lie in the interval 

845-810 m.y. The age estimate is valid if argon loss 

accompanied deep burial and heating of the lavas and 

if argon retention began with a reduced geothermal 

regime after regional uplift, faulting, and the erosion 

of overlying strata. Geologic evidence for regional uplift and faulting, followed by erosion of a highstanding fault block, is developed in this study. 

Isotopic ages can be examined to see if they are compatible with the geologic history and with a reasonable model for argon loss and retention.

Flows of the Cardenas Lavas, the uppermost formation of the Unkar Group, lie about 2 km stratigraphically below the top of the Chuar Group (table 1). Samples from six different lava flows collected in Basalt 

Canyon, 11 km south-southwest of the Sixtymile Canyon area, have yielded a whole rock Rb-Sr isochron 

of 1,090± m.y. (McKee and Noble, 1976). This age of 

about 1.1 b.y. is probably the extrusion age of the 

lavas. Much younger K-Ar ages for samples from 

three different flows of the Cardenas were obtained by 

McKee and Noble (1976), who suggest the young ages 

may reflect an episode of heating about 800 m.y. ago.

McKee, when first reporting the results of the young 

K-Ar ages (McKee and Noble, 1974), proposed that 

they might represent the time of the Grand Canyon 

disturbance. The K-Ar ages, in descending stratigraphic order and starting with the topmost flow of the 

Cardenas, are 810±20, 790±20, and 781±20 m.y. The 

second and third ages are from flows in the upper- and 

lower-middle parts of the 300-m-thick section of flows. 

The progression in ages suggests that argon retention 

began at the top of the Cardenas earlier than in the 

lower-middle part of the section. Such a progression is 

consistent with the idea of a progressive removal of 

overlying strata following uplift and a progressive 

downward cooling of the section. Such would imply 

that the minimum age for the Grand Canyon orogeny 

is about 810 m.y.

Another K-Ar age of 832±30 m.y. was determined 

by M. L. Silberman (written commun., 1976) from a 

sample high in the Cardenas flow sequence in a structurally high block east of the Butte fault and south of 

the Palisades fault and Cedar Mesa monocline (Elston 

and Scott, 1976, fig. 1). This age also is in agreement 

with the argon retention model outlined before.

A K-Ar age of 845±15 m.y. is reported by Ford and 

others (1972) for a sample of basalt collected randomly 

in Basalt Canyon. This age, somewhat older than the 

two youngest K-Ar ages reported by McKee and Noble 

(1976), serves to place a maximum limit on the time of 

beginning of argon retention and would thus appear 

to represent a maximum age of the Grand Canyon 

orogeny. The spread in reset K-Ar ages allows a nominal age of about 830 m.y. to be provisionally assigned 

for the time of regional uplift and principal displacements on the Butte fault.

During the interval about 830-570 m.y., the beginning of Cambrian time (Geol. Soc. London, 1964), the 

region remained above sea level. After the accumulation of an unknown but perhaps substantial thickness 

of fanglomeratic deposits derived from high-standing 

blocks and deposited on downthrown fault blocks, erosion removed nearly all these deposits and then reduced the surface to an irregular rolling plain marked 

by scattered hills of the Shinumo Quartzite (Unkar 

Group) that stood as much as 200 m above the plain. 

In the area of Sixtymile Canyon, about 20-30 m of 

relief was developed on the resistant middle member 

of the Sixtymile Formation. A channellike swale was 

eroded in the Chuar syncline, principally by the removal of less resistant beds of the upper member of 

the Sixtymile Formation. Marine transgression from 

the west occurred in Early Cambrian time, marked by 

the deposition of parallel-bedded sandstone at the 

base of the Tapeats Sandstone in the central Grand 

Canyon, and similar beds were deposited in the channellike swale in the Chuar syncline. These beds are
16 PRECAMBRIAN SIXTYMILE FORMATION AND OROGENY, ARIZONA

not found at the base of the Tapeats elsewhere in the 

eastern Grand Canyon, which suggests that the swale 

was topographically low at the time of transgression.

CORRELATION

Stewart (1976, p. 14) has proposed that a marked 

change in the tectonic setting of North America occurred about 850 m.y. ago. The change was from deposition in scattered locally deep epicratonic troughs to 

deposition in miogeoclines that were marginal to and 

that extended almost continuously around North 

America. Stewart considered the Windermere Group, 

which occupies the stratigraphic position between the 

Precambrian Belt Supergroup and the earliest Cambrian rocks, to be the basal unit of the Cordilleran 

geosyncline. K-Ar ages from a small comparatively 

unmetamorphosed and unaltered area of greenstone 

(basalt) of the Windermere in northeastern Washington have been determined by Miller and others 

(1973), who reported that extrusion probably occurred 

between 827 and 918 m.y. ago. There is considerable scatter in the calculated ages, and several of 

the ages are less than 800 m.y. (Miller and others, 

1973, table 1). This very approximate age for the 

Windermere is fully compatible with the provisional 

830-m.y. age for the Sixtymile Formation and the 

Grand Canyon orogeny estimated from reset K-Ar 

ages from the Cardenas Lavas.

Structural and stratigraphic relations described for 

strata of the Purcell (Belt) and Windermere Supergroups in the southern Cordillera of Canada, particularly in southeastern British Columbia, are similar to 

the relations seen at the top of the Grand Canyon 

Supergroup. Gabrielse (1972, p. 528) regarded the east 

Kootenay orogeny of British Columbia as an episode 

of regional uplift accompanied by regional metamorphism and perhaps minor folding that terminated the long period of Purcell sedimentation in the 

southern Cordillera about 800 m.y. ago. Lis and Price 

(1976) reported that about 9 km of conglomeratic 

strata of the Windermere Supergroup (Young and 

others, 1973) was deposited on the northwest, 

downthrown side of a fault system that bounds the 

Purcell anticlinorium and that the maximum stratigraphic separation on Purcell strata was 13 km or 

more. Lis and Price (1976) proposed that the conglomeratic units represent fanglomerates that accumulated adjacent to a fault scarp separating the uplifted 

source area on the southeast and the deep structural 

basins on the northwest. They concluded that the 

magnitude of the stratigraphic separation associated 

with this late Precambrian faulting indicates that 

it represents a structure of crustal dimensions. As 

pointed out by Harrison and Reynolds (1976, p. 905),

the tectonics of the Western United States during 

the late Precambrian seem to have been characterized by vertical tectonics without the occurrence of 

either plate tectonics or collision.

The magnitude of faulting on the Butte fault in the 

eastern Grand Canyon is considerably less than that 

reported at the Purcell-Windermere boundary of 

southeastern British Columbia, but the structural 

senses of displacement, the changes in depositional 

conditions, and the timing appear similar. In both 

areas regional uplift was accompanied by high-angle 

block faulting, south and east sides up, about 800 m.y. 

ago, which resulted locally in the end of marine deposition and in the deposition of conglomeratic materials 

derived from fault-block mountains. The foregoing 

leads to the suggestion that pre-Sixtymile strata of 

the Chuar Group are correlative with strata of the 

upper part of the Belt (Purcell) Supergroup and that 

conglomeratic strata of the upper member of the Sixtymile Formation, deposited after Precambrian faulting had ended on the Butte fault, are correlative with 

conglomeratic strata of the basal parts of the Windermere Group (Supergroup in Canada). These correlations suggest that the Grand Canyon and East 

Kootenay orogenies are cogenetic.

On the east coast of North America, Rankin (1976) 

reported that Appalachian salients and recesses are 

inherited from the initial breakup of a continental 

mass beginning about 820 m.y. ago. The Grand Canyon and East Kootenay orogenies thus may be part 

of a major structural episode in the history of North 

America.

REFERENCES CITED

Breed, W. J., 1975, The Sixty Mile Formation: A slide breccia of 

younger Precambrian age, Grand Canyon, Arizona: Geol. Soc. 

America, Rocky Mountain Sec., 28th Ann. Mtg., Abs. with Programs, v. 6, no. 5, p. 590.

Breed, W. J., and Ford, T. D., 1973, Chapter two-and-a-half of 

Grand Canyon history, or the Sixty Mile Formation: Plateau, v. 

46, no. 1, p. 12-18.

Dutton, C. E., 1882, Tertiary history of the Grand Canyon district, 

with atlas: U.S. Geol. Survey Mon. 2, 264 p.

Elston, D. P., and Scott, G. R., 1976, Unconformity at the 

Cardenas-Nankoweap contact (Precambrian), Grand Canyon 

Supergroup, northern Arizona: Geol. Soc. America Bull., v. 87, 

no. 12, p. 1763-1772.

Ford, T. D., and Breed, W. J., 1972a, The Chuar Group of the Proterozoic, Grand Canyon, Arizona, in Sec. 1, Precambrian Geology: Internat. Geol. Cong., 24th, Montreal, 1972, Proc., p. 

3-10. , ———— 1972b, The problematical Precambrian fossil Chuaria, in Sec. 

1, Precambrian Geology: Internat. Geol. Cong., 24th, Montreal, 

1972, Proc., p. 11-18.

———1973, Late Precambrian Chuar Group, Grand Canyon, 

Arizona: Geol. Soc. America Bull., v. 84, no. 4, p. 1243-1260.

Ford, T. D., Breed, W. J., and Mitchell, J. S., 1972, Name and age of 

the upper Precambrian basalts in the eastern Grand Canyon: 

Geol. Soc. America Bull., v. 83, p. 223-226.
REFERENCES CITED 17

Gabrielse, Hubert, 1972, Younger Precambrian of the Canadian 

Cordillera: Am. Jour. Science, v. 272, p. 521-536.

Geological Society of London, 1964, The Phanerozoic time scale—A 

symposium: Geol. Soc. London Quart. Jour., v. 120, supp., p. 

260-262.

Harrison, J. E., and Reynolds, M. W., 1976, Western U.S. continental margin: A stable platform dominated by vertical tectonics in 

the late Precambrian: Geol. Soc. America, Abs. with Programs, 

1976 Ann. Mtg., v. 8, no. 6, p. 905.

Huntoon, P. W., 1971, The deep structure on the monoclines in 

eastern Grand Canyon, Arizona: Plateau, v. 43, no. 4, p. 148- 

158.

———1974, The post-Paleozoic structural geology of the eastern 

Grand Canyon, Arizona, in Breed, W. J., and Roat, E. C., eds., 

Geology of the Grand Canyon: Grand Canyon Natural History 

Assoc., Grand Canyon, and Museum of Northern Arizona, 

Flagstaff, Ariz., p. 82-115.

Huntoon, P. W., Billingsley, G. H., Jr., Breed, W. J., Sears, J. W., 

Ford, T. D., Clark, M. D., Babcock, R. S., and Brown, E. H., 

1976, Geologic map of the Grand Canyon, Arizona: Grand Canyon Natural History Assoc., and Museum of Northern Arizona, 

scale 1:62,500.

Huntoon, P. W., and Sears, J. W., 1975, Bright Angel and Eminence 

faults, eastern Grand Canyon, Arizona: Geol. Soc. America 

Bull., v. 86, no. 4, p. 465-472.

Lis, M. G., and Price, R. A., 1976, Large-scale block faulting during 

deposition of the Windermere Supergroup (Hadrynian) in 

southeastern British Columbia, in Report of activities, Part A: 

Geol. Survey Canada, Paper 76-1A, p. 135-136.

McKee, E. H., and Noble, D. C., 1974, Radiometric ages of diabase 

sills and basaltic lava flows in the Unkar Group, Grand Canyon: Geol. Soc. America, Rocky Mountain Sec., 27th Ann. Mtg. 

Abs. with Programs, v. 6, no. 5, p. 458.

———1976, Age of the Cardenas Lavas, Grand Canyon, Arizona: 

Geol. Soc. America Bull., v. 87, no. 8, p. 1188-1190.

McKee, E. D., and Resser, C. E., 1945, Cambrian History of the 

Grand Canyon region: Carnegie Inst. Washington Pub. 563, 

232 p.

Maxson, J. H., 1961, Geologic history of the Bright Angel quadrangle, in Geologic map of the Bright Angel quadrangle: Grand 

Canyon Nat. History Assoc., scale 1:24,000 (3d ed. ( rev. 1968).

———1967, Preliminary geologic map of the Grand Canyon and 

vicinity, Arizona, eastern section: Grand Canyon Nat. History 

Assoc., scale 1:62,500.

Miller, F. K., McKee, E. H., and Yates, R. G., 1973, Age and correlation of the Windermere Group in northeastern Washington: 

Geol. Soc. America Bull., v. 84, no. 11, p. 3723-3730.

Rankin, D. W., 1976, Appalachian salients and recesses: Late Precambrian breakup and the opening of the lapetus Ocean: Jour. 

Geophys. Research, v. 81, no. 32, p. 5605-5619.

Schopf, W. J., Ford, T. D., and Breed, W. J., 1973, Microorganisms 

from the Late-Precambrian of the Grand Canyon, Arizona: Science, v. 179, p. 1319-1321.

Sears, J. W., 1973, Structural geology of the Precambrian Grand 

Canyon Series, Arizona: Wyoming Univ., Laramie, Wyo., M. S. 

thesis, 100 p.

Stewart, J. H., 1976, Late Precambrian evolution of North America: 

Plate tectonics implication: Geology, v. 4, no. 1, p. 11-15.

Walcott, C. D., 1883, Pre-Carboniferous strata in the Grand Canyon 

of the Colorado, Arizona: Am. Jour. Sci., v. 26, p. 437-442.

———1890, Study of a line of displacement in the Grand Canyon of 

the Colorado in northern Arizona: Geol. Soc. America Bull., v. 

1, p. 49-64. 

-1894, Pre-Cambrian igneous rocks of the Unkar terrane,

Grand Canyon of the Colorado, Arizona, with notes on the petrographic character of the lavas by J. P. Iddings: U.S. Geol. 

Survey Ann. Rept. 14, pt. 2, p. 497-524.

Young, F. G., Campbell, R. B., and Poulton, T. P., 1973, The Windermere Supergroup of the southeastern Canadian Cordillera: 

Belt Symposium, 1973, Univ. Idaho, Moscow, Idaho, p. 181- 

203.
18 PRECAMBRIAN SIXTYMILE FORMATION AND OROGENY, ARIZONA

TABLE 4.—Description of strata at type section ofSixtymile Formation, north fork ofSixtymile Canyon, (36°12'42"N., 111°50'45"WJ, eastern

Grand Canyon, Arizona

Thickness 

(meters)

Cambrian:

Tapeats Sandstone:

3. Sandstone, coarse- to medium-grained; pale red (10R 6/2) to very pale orange (10YR 8/2) at top; quartzose; 

rounded coarse- to granule-size grains of pale-yellowish-orange (10YR 8/6) quartz are common; moderately 

well sorted; medium and thick bedded, parallel bedded, and cross laminated; forms cliff. Contains three 2.5- 

cm-thick beds of laminated red very fine grained silty sandstone enclosed by yellowish sandstone in upper 

0.75 m; these are the highest red beds in the Tapeats of the Sixtymile Canyon area ____________ 4.75

2. Sandstone; medium grained with subordinate beds ranging from fine to coarse grained and granule and pebble 

bearing; pale red (10R 6/2-5R 6/2) and moderate red (5R 5/4) subordinately streaked pale yellowish orange 

(10YR 8/6) to very pale orange (10YR 8/2); quartzose; grains subrounded to subangular; well cemented; subordinate interstitial silt; well to poorly sorted; scattered pebbles and granules of rock fragments are probably 

from Sixtymile Formation; dominantly thin and parallel bedded ana subordinately cross laminated. Conspicuous ledge-forming yellow-brown fine-grained sandstone bed, 2.9 m thick, is 5.06 m above base of unit; overlying 2.5 m consists of red and yellowish, soft and resistant, locally pebble-bearing sandstone; first appearance 

of yellow quartz that characterizes much of Tapeats occurs 0.5 m below top, in 5-cm-thick coarse-grained 

red-brown and yellow sandstone that contains angular pebble-size fragments _____________———___ 10.45

1. Sandstone; very fine grained and fine to medium grained with scattered coarse quartz grains and granules of 

rock fragments; locally pebble bearing in top 0.1 m; dominantly grayish red (5R 4/2), in part streaked pale 

red (5R 6/2); thin and parallel bedded, in part finely laminated; basal 0.3 to 0.4 m is conglomeratic sandstone 

reworked from directly underlying material of Sixtymile and distinguished from it only by character of 

stratification; hematite-rich very fine grained sandstone, 0.4 m thick, directly overlies reworked sandstone; 

hematite is somewhat less abundant in overlying 1.45-1.85 m of coarser grained beds; unit pinches out 

10-15 m to south against resistant beds of upper member of Sixtymile Formation that formed a ledge or step 

in the erosion surface ____________________________________________——_- 2.3-2.7

Thickness of Tapeats Sandstone ____________________________—____— ——— -___ 17.9+

Unconformity

Disconformable, becoming unconformable to south away from axis of syncline. 

Precambrian:

Chuar Group:

Sixtymile Formation:

Upper member—fluviatile sandstone and conglomerate:

Conglomerate facies; occupies axial part of syncline; grades abruptly southward into parts of sandstone

facies; inaccessible sharp lower contact on middle member to north marks probable unconformity: 

Silty conglomeratic sandstone and conglomerate; fine to coarse grained with angular to subangular 

granule-, pebble-, and scattered small boulder-size rock fragments; grayish red (5R 4/2) to light blackish red (5R 3/2), in part weathering pale red (5R 6/2); weathered or altered rock fragments impart a 

pale-yellowish-orange (10YR 8/6) and very pale orange (10YR 8/2) mottling and streaking; a few 

thin sandstone lenses are free of conglomeratic material; sandstone is quartzose; where medium 

grained and locally uncoated by silt, grains display pyramidal crystal faces; intergranular silt abundant. Crude subparallel stratification on centimeter and decimeter intervals with beds increasing in 

thickness toward axis of syncline; in places; abundant angular rock fragments are suspended in a 

fine-grained matrix with no hint of internal stratification, suggesting mudflow deposition. Fragments 

consist of fine-grained and aphanitic yellowish (weathered) quartzite, in part possibly exotic to the 

Sixtymile Formation, and reddish sandstone fragments apparently derived from the Sixtymile. Thickness approximately same as sandstone facies __________-______________--————— 1K+)

Sandstone facies:

4. Sandstone and sandy siltstone, in part breccia-bearing, irregularly bedded, thin- to mediumbedded, lenticular.

d. Siliceous, very fine grained silty sandstone, grayish-orange-pink (10R 8/2), faintly laminated, containing a few lenses of fine sand; resistant; forms ledge; slightly bleached 

and silicified beneath the Tapeats; 0.3 m thick.

c. Siliceous siltstone and very fine grained sandstone; pale red (10R 6/2); thin bedded to 

laminated, containing very fine to medium grains and 1-10-mm-thick discontinuous 

depositional layers of white very fine grained to aphanatic quartzite that impart the 

general aspect of a breccia; 0.24 m thick; units 4c and 4b occupy a swale in unit 4a and 

pinch out 2 m south where unit 4d rests on unit 4a.

b. Sandy siltstone, moderate-orange-pink (10R 7/4), thin-bedded and laminated; poorly 

sorted, containing fine- to coarse- and granule-size grains of white to grayish-orangepink (10R 8/2) rock fragments probably derived from middle member; 0.33 m thick, 

a. Sandstone, quartzose, fine- to medium-grained; pale red (10R 6/2) weathering moderate 

red (5R 5/4); grains subangular to subrounded; moderately well to poorly sorted; well 

cemented; moderate intergranular silt. Resistant; forms ledge. Locally contains coarse 

to very coarse, rounded to angular grains and fragments of rock; angular white chert 

fragments probably are from middle member; rounded to subrounded grains of very 

fine grained gray quartzite may be exotic to Sixtymile Formation, as are sparse fresh 

to moderately altered mafic grains whose source may have been a crystalline terrane. 

0.67 m thick at section measured, becoming 2 m thick 6 m to north where bed grades 

into conglomerate of conglomerate facies. 

(Thickness of unit 4 at measured section ________________________ 1.5)

About 5 m south of measured section, in an inaccessible face, 1.5 m of resistant irregularly bedded sandstone overlies unit 4d. The resistant sandstone was once exposed as 

a ledge against which beds of the Tapeats (unit 1 and lower part of unit 2) pinch out 

by onlap. 

Maximum thickness of unit 4 _____________________________ 3.0

3. Siltstone and very fine grained silty sandstone, pale-reddish-brown (10R 5/4); very finely and 

irregularly laminated; massive weathering; in 2-3 m to the north and to the south grades 

abruptly into purplish sandstone similar to overlying sandstone of unit 4a; pinches out 7 m 

to north ________________________________________________________ 2.0
TABLE 4 19

TABLE 4.—Description of strata at type section ofSixtymile Formation, north fork ofSixtymile Canyon, (36°12 '42"N., 111°50'45"W.), eastern

Grand Canyon, Arizona—Continued

Precambrian—Continued

Chuar Group—Continued

Sixtymile Formation—Continued

Upper member—fluviatile sardstone and conglomerate—Continued 

Sandstone facies—Continued

2. Sandstone, very fine to fine-grained, quartzose; silty to locally clean with scattered angular to 

subrounded rock fragments ranging from very coarse grained to small boulder size; grayish 

red (10R 4/2-5R 4/2), locally pale reddish brown (10R 4/2), pale red (10R 6/2), and moderate 

orange pink (10R 7/4); subordinate lenses and flakes of very pale orange (10YR 8/2) siltstone; 

poorly sorted and crudely stratified with some lenses of well-sorted sandstone. Angular fragments of chalky white chert and silicified sandstone from middle member are conspicuous _ 4.6 

1. Sandstone, medium- to fine-grained, pale-red (10R 6/2) to grayish-red (5R 4/2), mottled and 

swirled moderate-orange-pink (10R 7/4), quartzose; grains subangular to subrounded; well 

sorted with subordinate intergranular silt; laminae and flakes of moderate-orange-pink (10R 

7/4) siltstone common. Basal 0.5 m very fine grained siliceous fragmental sandstone, variably 

moderate red (5R 5/4) and grayish orange pink (10R 8/2), containing seams and fragments of 

whitish siliceous siltstone. Massive weathering; forms ledge. Bedding disrupted as a consequence of slumping toward axis of Chuar syncline where unit transects uppermost 1.5 m of 

beds of middle member. Disrupted stratification reflects youngest recognized increment of subsidence in syncline ________________________________________ 2.8

Thickness of upper member _____________________________________ 10.9-12.4(+)

Unconformity

Middle member—cherty quartzite:

1. Quartzite, very fine grained to silt-sized and aphanatic; pale red (10R 6/2) in lower 5-6 m and grayish orange pink (10R 8/2) mottled with pale red above; irregularly finely laminated and thin bedded 

with some medium-bedded layers. Abundant bedded chalky white chert begins about 5 m above 

base; hematite-rich beds about 15.5 and 20 m above base; breccia layer about 1 m thick 18.5 m 

above base contains angular clasts of sandstone of lower member and altered Kwagunt siltstone 

in disrupted matrix material of middle member. Resistant. Forms cliffs and ledges. Slumped on 

large and small scale toward axis of syncline, probably at time of disruption of overlying basal bed 

of upper member. 

Thickness of middle member _ ___ _____ _ ______ _____ ____ _ _____ _____ _ 25

Unconformity

Lower member—sandstone and landslide breccia:

6. Siltstone, finely laminated to very thin bedded; pale red (5R 6/2); hematite-rich; comparatively soft, 

weathering to a slope where not protected by resistant middle member of Sixtymile Formation. 

About 1.2 m exposed on updip end, where it can be seen to overlie unit 5 and wedge out beneath 

middle member; concealed by talus toward axis of syncline; may be present in unvisited exposure 

in axis where unit could be 6 m or more thick _______________________________- 1.2-6(?)

5. Landslide breccia. Similar to unit 3; well cemented where dominantly monolithologic on south limb 

of syncline, containing angular fragments and matrix derived from unit 1; exotic detritus derived 

from Kwagunt Formation increases toward axis of syncline _____________________ 9.1

4. Sandstone, fine- to coarse-grained with abundant hematitic intergranular silt; pale red (5R 4/2); 

poorly sorted and mostly crudely stratified; quartz grains angular to subrounded and dominantly 

amber; dark minerals sparse to locally abundant; upper % m in part thin bedded -_______ 1.5 

3. Landslide breccia:

Matrix: Sandstone, very fine to very coarse grained, pale-red to grayish-red (5R 6/2-5R 4/2), finely 

irregularly bedded to crudely stratified, contorted and slumped, moderately well cemented; 

material principally derived from units 1 and 2, but also contains grains derived from 

Kwagunt Formation ______________________________________ 1.8-2.4

Fragments; at line of section, west limb of syncline:

a. Siltstone, very pale orange (10R 8/2); weathering grayish-orange (10YR 7/4); compact; 

laminated to thin bedded. Similar to altered siltstone described in unit 4 of Kwagunt 

Formation.

b. Sandstone, quartzose, fine- to coarse-grained and silty; in part contains altered Kwagunt 

rock fragments and red sandstone of Sixtymile Formation; grayish orange pink (10R 

7/4) and mottled grayish red (5R 4/2); mostly poorly sorted; in part displays irregular 

disrupted stratification; medium to coarse quartz grains are well rounded and frosted, 

not characteristic of underlying sandstone of the Sixtymile, and perhaps derived from 

the disintegration of sandstone exposed in an upraised fault block.

Fragments; in axis of syncline at base of breccia, a and b are from large vertical blocks, and c 

is a breccia fragment:

a. Dolomite and dolomitic limestone, very fine grained, yellowish-gray (5Y 8/1) to lightolive-gray (5Y 6/1); weathering pale yellowish brown (10YR 6/2) to pale brown (SYR 

5/2); locally contains light-olive-gray chert; bed, 3-4 m thick and about 6 m high, 

possibly derived from one of brown-weathering carbonate beds of Walcott Member, 

b. Quartzite, very fine sand- to silt-size, white (N 9) to very pale orange (10YR 8/2); weathering light brown (5YR 6/4); well sorted and clean; finely porous; thin to mediumbedded; about 2 m thick and 3 m high. Exotic to Chuar Group. Source may have been 

Nankoweap Formation.

c. Quartzite, cryptocrystalline to very fine grained, very pale orange (10YR 8/2)^ weathering grayish orange (10YR 7/4) to light brown (5YR 6/4); thin bedded and finely laminated. Silicified and altered shale or siltstone from Chuar Group. 

2. Sandstone; directly underlies breccia and overlies altered shale of Walcott Member, west of axis

of syncline:

Sandstone, quartzose, silty and micaceous; fine to very fine grained with very sparse coarse-grained 

rock fragments; pale red (5R 6/2); white mica flakes are fresh and may have been derived from a 

newly exposed crystalline terrane; common to abundant opaque minerals; thin bedded; moderately
20 PRECAMBRIAN SIXTYMILE FORMATION AND OROGENY, ARIZONA

TABLE 4.—Description of strata at type section ofSixtymile Formation, north fork ofSixtymile Canyon, (36°12'42"N., 111°50'45"W.), eastern

Grand Canyon, Arizona—Continued

Precambrian—C ontinued

Chuar Group—Continued

Sixtymile Formation—Continued

Lower member—sandstone and landslide breccia—Continued 

Sandstone, quartzose, etc.—Continued

well sorted. Overlies altered or weathered material described under unit 4 of Walcott Member; 

alteration of underlying shale and presence of rock fragments and exotic minerals in the sandstone indicate an unconformity and deposition after unit 1 of lower member —_ ————— —— _— 1.5 

Unconformity 

1. Basal sandstone; preserved on west limb of syncline:

Sandstone, quartzose, very fine grained; pale and moderate red (5R 6/2-5R 5/4), and moderate pink 

(5R 7/4) near top; weathers grayish red to dusty red (5R 4/2-5R 3/4); laminated to very thin bedded; 

well sorted, compact, and firmly cemented, with laminae displaying various amounts of intergranular hematite and subordinate clay; no exotic materials observed. Contact with Walcott 

Member is concealed over interval of 2 m or more but probably grades into transition beds equivalent to those described in unit 3 of Walcott Member. Unconformably overlain by breccia of 

unit 5 ________________________._________________________--_______ 6.4(+)

Thickness of lower member __________________________________-_ 21.5-26.91+)

Thickness ofSixtymile Formation ________________________—__ ———— — -—— 57-641 + )

Kwagunt Formation: 

Walcott Member:

4. Altered (weathered?) shale. Underlies sandstone of unit 2 of lower member of Sixtymile Formation,

west of axis of syncline.

Siltstone and claystone, well-indurated; pale greenish yellow (10Y 8/2) with white flecks and seams 

and dusky-red 15R 3/4) very fine to coarse hematite grains; weathers grayish orange pink (SYR 

7/2) to yellowish gray (5Y 8/1). Thin bedded, in part very finely laminated and in part appears 

fragmental. Forms slightly resistant ledges ________________________-_-_ —1.5

3. Unaltered transitional beds in axis of syncline.

At base, shaly siltstone, light-olive-gray (5Y 6/1) to greenish-gray (5GY 6/1); gradational over 

about 10 cm with silty gray shale below; about 0.75 m above base grades upward into pale-red 

(5R 6/2) and grayish-red 15R 4/2) laminated and very thin bedded sandy siltstone that contains 

moderate intergranular clay and opaque minerals; red beds are similar to but slightly finer 

grained than basal sandstone (unit 1) of Sixtymile Formation. Forms slope. Separated from landslide (unit 3) of Sixtymile by slightly more resistant, 2-4-cm-thick interval of contorted compact 

siltstone that is mottled pale red (5R 6/2), grayish red 15R 4/2), grayish orange pink (10R 8/2), 

and dark yellowish orange 110YR 6/6). Contorted siltstone marks plane of landsliding _____ 1.5 

2. Shale, medium- to dark-gray (N 3/5) and bluish-gray (5B 5/1); chippy weathering; forms slope ____ —70

1. Upper bed of pair of brown-weathering carbonate beds near small flat, southwest side of Chuar syncline. Limestone, dolomitic, fine-grained; light olive gray (5Y 6/1); weathering pale yellowish 

brown (10YR 6/2); locally fragmental ranging from coarse-grained rounded oolitelike grains to 

subangular fragments of gray dolomite and very sparse angular pebbles of tan siltstone; fragmental material in part silica cemented. Forms ledge —————____—________________ ~ 8

GPO 689-035