Stratigraphic relationship between the late Jurassic Canelo Hills volcanics and the Glance Conglomerate, southeastern Arizona

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Authors Vedder, Laurel Kathleen

Publisher The University of Arizona.

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Link to Item http://hdl.handle.net/10150/558015 STRATIGRAPHIC RELATIONSHIP BETWEEN

THE LATE JURASSIC CANELO HILLS VOLCANICS

AND THE GLANCE CONGLOMERATE, SOUTHEASTERN ARIZONA

by

Laurel Kathleen Vedder

A Thesis Submitted to the Faculty of the

DEPARTMENT OF GEOSCIENCES

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

1 9 8 4 oil No. BINDING INSTRUCTIONS INTERLIBRARY INSTRUCTIONS W H ^ H W T

This thesis has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED:

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

2 (9 , / # / W. R. DICKINSON Date Professor of Geosciences ACKNOWLEDGEMENTS

Funding for this project was provided by the Laboratory of

Geotectonics, University of Arizona, and the Atlantic-Richfield

Corporation. I would like to thank the members of my thesis committee. Bill Dickinson, Bob Butler and Peter Coney for time spent combing hillsides and creekbeds for conglomerate outcrops and for prompt review of the manuscript.

My interest in the area was fostered by conversations with

Lucy Harding, Bob Butler and Chuck Kluth. In addition to a copy of his dissertation and an annotated map of the northern Canelo H ills,

Chuck Kluth generously donated a day's time in the field, replete with valuable comments on the results of my work.

My parents, Carrie Campen-Bell, and Steve May provided much appreciated assistance as well as good company during weeks spent in the field. Moral and creative support was ungrudgingly provided by

Steve May, who spent hours on logistics, Leroying, literary critique and lifting of the spirit.

My entire education has been lovingly supported by my parents and grandparents to whom I owe much of my appreciation of nature and curiosity concerning its works.

i l l TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS...... Vi

ABSTRACT ...... ix

1. INTRODUCTION...... 1

Statement of the Problem ...... 2 The "Lower" Member o f th e Canelo H ills Volcanics or "Mount Hughes Formation" . . . 3 The Glance Conglomerate ...... 4 The P r o b le m ...... 5 Study A r e a ...... 6 Method of Study ...... 6 Stratigraphic Framework ...... 8

2. NORTHERN CANELO HILLS ...... 12

P rev io u s W o r k ...... 12 G eneral S tru ctu re* ...... 15 M id-M esozoic S tr a tig ra p h y ...... 18 "Mount Hughes Formation" or Glance Conglomerate . 22 Canelo Ridge A r e a ...... 22 Red Meadow A r e a ...... 29 Canelo Pass Area ...... 36 Age C o n s t r a i n t s ...... 44 S u m m a ry ...... * ...... 48

3 . HUACHUCA MOUNTAINS...... 50

P rev io u s W o r k ...... 50 G eneral S tru c tu re ...... 52 M id-M esozoic S tra tig ra p h y ...... 54 Glance C onglom erate ...... 58 C e n tra l Huachuca M ountains ...... 58 Southern Huachuca Mountains ...... 66 Age C o n s t r a i n t s ...... 72 Summary ...... 75

4 . LONE MOUNTAIN...... 76

P rev io u s W o r k ...... 76 G eneral S tr u c tu re ...... 77 M id-M esozoic S tr a tig ra p h y ...... 82

iv TABLE OF CONTENTS— co n tin u ed Page

G lance C onglom erate ...... 85 N orthern Lone M ountain ...... 85 S outhern Lone M ountain ...... 100 Age C o n s t r a i n t s ...... 107 S u m m a ry ...... 109

DISCUSSION ...... 110

Evidence f o r C o rre la tio n ...... 110 S tr a tig r a p h ic R e la tio n s h ip s ...... 110 Lithologic Character ...... I l l F ie ld R e l a t i o n s h i p s ...... 114 C onclusions and im p lic a tio n s ...... 116 "Monkey Canyon Member"...... 116 Geochronology ...... 119 D e p o sitio n s! Environm ent ...... 121 Tectonic Environment ...... 124 LIST OF ILLUSTRATIONS

Figure Page

1. Location Map, Southeastern Arizona ...... 7

2. General Stratigraphic Column ...... 9

3. History of Mid-Mesozoic Stratigraphy ...... 14

4. Location Map, Northern Canelo H ills ...... 17

5. Geologic Map of the Canelo Ridge Area, Northern Canelo H ills ...... 23

6. Measured Section, Canelo Ridge ...... 24

7. Volcanic-clast Conglomerate, "Canelo Pass Member" . . . 28

8. Geologic Map of the Red Meadow Area, Northern Canelo H i l l s ...... 30

9. Measured Section, Red Meadow A re a ...... 31

10. "D ark Canyon M em ber", Red Meadow A rea ...... 33

11. Interbedded Maroon Mudstone and Arkosic Sandstones of th e M o rita F o r m a tio n , Red Meadow A rea ...... 37

12. Calcareous Mudstones Overlying the "Canelo Pass Member" a t Red M e a d o w ...... 37

13. Geologic Map of the Canelo Pass Area, Northern Canelo H i l l s ...... 38

14. Measured Section, Canelo Pass A rea ...... 40

15. Volcanic-clast Conglomerate of the "Canelo Pass Member" a t C an e lo P a s s ...... 43

16. Limestone-clast Conglomerate and Interbedded Subarkosic Sandstone, Upper "Canelo Pass Member", C an elo P a s s ...... 45

17. Volcanic-clast Conglomerate and Interbedded Subarkosic Sandstone, Upper "Canelo Pass Member", Canelo Pass ...... 46 v i v i i

LIST OF ILLUSTRATIONS— co n tin u ed Page

18. Location Map, Central to Southern Huachuca Mountains and Lone M o u n tain ...... 51

19. Geologic Map of the Central Huachuca Mountains Area . . . 59

20. M easu red S e c tio n , C e n t r a l H uachuca M o u n ta in s ...... 61

21. Carbonate-clast Conglomerate, Lower Glance Conglomerate Central Huachuca Mountains ...... 62

22. Limestone-clast Conglomerate, Upper Glance Conglomerate, C e n t r a l H uachuca M o u n ta in s ...... 6 5

23. Geologic Map of the Southern Huachuca Mountains Area . . 68

24. Measured Section, Southern Huachuca Mountains Area . . . 69

25. Lower Glance Conglomerate, Southern Huachuca M o u n t a i n s ...... 70

26. Upper Glance Conglomerate, Southern Huachuca M o u n t a i n s ...... 73

27. Geologic Map of the Lone Mountain Area, (Hayes and Raup, 1968) 78

28. Geologic Map of the Lone Mountain Area (This Study) . . . 80

29. A) Geologic Map of the Lone Mountain Area (1:12,000) in pocket B) S t r u c t u r e S e c tio n s ...... i n p o c k e t

30. Measured Section, Northern Lone Mountain ...... 87

31. Basal Contact, Lower Unit of the Glance Conglomerate on Welded Tuff Member of the Canelo H ills Volcanics, N o rth e rn Lone M o u n tain ...... 8 9

32. Subarkosic Sandstone, Middle Unit of the Glance Conglomerate, Northern Lone Mountain ...... 92

33. Volcanic Pebble Conglomerate, Middle Unit of the Glance Conglomerate, Northern Lone Mountain ...... 94

34. Sandy Conglomerate, Basal Part of the Upper Unit of the Glance Conglomerate, Northern Lone Mountain ...... 95 V iii

LIST OF ILLUSTRATIONS— co n tin u ed Page

35. Pebble to Boulder Conglomerate, Upper Part of the Upper Unit of the Glance Conglomerate, Northern Lone M o u n tain ...... 96

36. Measured Sections, Morita Transition Zone ...... 98

37. Maroon Mudstone with Limestone Nodules, Morita Transition Zone ...... 99

38. Coalesced Limestone Stringers, Morita Transition Zone . . 101

39. Laminated Limestone Bed with Chert, Morita Transition Z o n e ...... 101

40. Measured Section, Southern Lone Mountain ...... 102

41. Basal Contact, Glance Conglomerate on Welded Tuff Member of the Canelo Hills Volcanics, Southern Lone M o u n t a i n ...... 104

42. Boulder of Carbonate-clast Conglomerate within the Lower Part of the Glance Conglomerate, Southern Lone M o u n t a i n ...... 104

43. Mixed-clast Conglomerate, Glance Conglomerate, Southern Lone M ountain ...... 106

44. Revision of Mid-Mesozoic Stratigraphy, Southeastern A r i z o n a ...... 117

45. Map of Study Area and V icinity Showing Major Northwest- Trending Fault Systems and Paleocurrent Data from the G lan ce C o n g lo m e ra te ...... 123 ABSTRACT

Analysis of the sedimentary member of the Canelo H ills

Volcanics or "Mount Hughes Formation" in the northern Canelo H ills and at Lone Mountain, and of the Glance Conglomerate in the nearby

Huachuca Mountains, indicates that these conglomerate units are lithologically indistinguishable. At Lone Mountain, conglomerate previously mapped as "lower" sedimentary member of the Canelo Hills

Volcanics can be traced laterally into Glance Conglomerate. Both conglomeratic sequences are overlain conformably by the Morita

Formation. Correlation of these conglomerate units revises the age of in itial Glance Conglomerate deposition from Early Cretaceous to Late

Jurassic and suggests that the age of the base of the overlying Morita

Formation may be older than previously considered. The Jurassic-

Cretaceous period boundary is no longer represented by a regional unconformity in southeastern Arizona and must lie within the upper

Glance Conglomerate or lower Morita Formation.

i x CHAPTER 1

INTRODUCTION

Thick sequences of intermediate to silicic volcanic rocks and

coarse clastic sedimentary rocks dominate the mid-Mesozoic

stratigraphy of southeastern Arizona. However, specific lithologic units within local sequences can rarely be traced from one mountain

range to another across intervening basins. The basin and range

topography that is characteristic of the region obscures facies

changes, thus disguising the lim ited lateral extent and lenticular

nature of volcaniclastic strata and conceals the abrupt thickening and

thinning of sedimentary units that were deposited on surfaces of

moderate relief. The rarity of fossils and lack of reliable

radiom etric dates contribute to the difficulty of regional

correlation. Sequential overprinting by structural effects of Late

Cretaceous to Eocene Laramide orogeny, mid-Tertiary extensional

deformation, and Late Cenozoic block faulting impedes detailed

stratigraphic analysis by inhibiting accurate tracing of rock units

and their contacts over great distances. An understanding of the

Jurassic history of the region has probably been most hindered by the

marked sim ilarity of Jurassic, Lower Cretaceous and even Upper

Cretaceous conglomerates.

Closer scrutiny of Mesozoic conglomerates of southeastern

Arizona is necessary to determine the details of the geologic history

of the region, for they compose more than a third of the Mesozoic

1 2 stratigraphic column. Before detailed sedimentological and paleogeographic studies can begin, the conglomerate stratigraphy must be well understood. The Mesozoic conglomerates are extremely diverse in texture and composition. In the past, formation names have been applied on the basis of presence or absence of interbedded volcanic rocks, clast composition and inferred stratigraphic position. Until recently, few reliable radiometric dates have been available to constrain the ages of formations underlying or overlying the conglomerates, and no dates were available from volcanic units interbedded within the conglomerates.

This study involved re-examination of the stratigraphic relationship between two mid-Mesozoic conglomerate formations of

southeastern Arizona, the "Mount Hughes Formation" and the Glance

Conglomerate. As a result of this study, the two formations were

recognized to be a single formation, and the age of that formation,

the Glance Conglomerate, has been better constrained. The

conglomerates studied are of key geologic significance, because their

deposition may span the transition from an arc to a backarc tectonic

setting in southeastern Arizona.

Statement of the Problem

Mid-Mesozoic rocks of southeastern Arizona can be broadly

divided into two groups. The older group consists of Triassic (?) to

Jurassic igneous and sedimentary rocks associated with a magmatic arc

that was active along much of the southern Cordillera during Jurassic

time (Coney, 1978? Damon.and others, 1981; Dickinson, 1981). The 3 younger group, known throughout southeastern Arizona as the Bisbee

Group, is a Lower Cretaceous sequence of shallow marine and non-marine sediments which records a transgression into the Bisbee trough or

Sonoran embayment. It has been thought that these two groups of rock are separated by a major unconformity that supposedly spanned the

Jurassic-Cretaceous period boundary.

Recent work by Kluth (1982, 1983) in the Canelo H ills raised several questions concerning the stratigraphic relationship between these two groups of rocks. In particular, the distinction between the conglomerates of the Canelo H ills Volcanics, the youngest formation included within the Jurassic magmatic arc sequence, and the Glance

Conglomerate, the oldest formation included in the Bisbee Group, has been called into question.

The "Lower" Member of the Canelo H ills Volcanics or "Mount Hughes Formation"

A thick sequence of sedimentary rock, containing coarse conglomerates and interbedded welded tuffs, was included by Hayes and others (1965) in the lower member of the Canelo Hills Volcanics, part of the Jurassic magmatic arc sequence in southeastern Arizona. These sediments were thought to be overlain by a thick series of rhyolite flows and welded tuff comprising the upper two members of the Canelo

Hills Volcanics. A radiometric age date of 177+8 m.y. was available from welded tuffs of the upper member. Although a younger age of

147+6 m.y. had been obtained southwest of the Huachuca Mountains from rocks correlated with the lower member of the Canelo Hills Volcanics 4 by Hayes (1970a), the lower member. sediments were firmly believed to be latest Triassic or earliest Jurassic in age.

Recent detailed mapping in the northern Canelo Hills by Kluth

(1982) has shown that the "lower" sedimentary member of the Canelo

Hills Volcanics actually lies depositionally above the volcanic strata designated by Hayes and others (1965) as the "middle" and "upper" members of the Canelo H ills Volcanics. As a result, Kluth (1982) informally renamed the thick sedimentary sequence the "Mount Hughes

Formation". A paleomagnetic study of welded tuffs interbedded with the conglomerates of the "Mount Hughes Formation" has yielded a pole position which falls on the North American apparent polar wander path between the Summerville and lower Morrison poles (Kluth and others,

1982). The inferred late Jurassic age is consistent with a Rb-Sr

whole rock date on the same rocks of 151+2 m.y. (Kluth and others,

1982), and ages obtained from correlative rocks southwest of the

Huachuca Mountains.

The Glance Conglomerate

The Glance Conglomerate is a coarse sedimentary unit that is

widespread in southeastern Arizona. Regional recognition of the

Glance Conglomerate has been based only on its coarse conglomeratic

nature and relative stratigraphic position between the thick Jurassic

magmatic arc sequence and the fluvial sandstones and mudstones of the

Bisbee Group. At places in the Huachuca and Santa Rita Mountains

adjacent to the Canelo H ills, rocks correlated with the Glance

Conglomerate are interbedded with volcanic flows, breccias and 5 pyroclastic rocks (Bilodeau, 1979). Lithologic and textural characteristics at both microscopic and outcrop scale are nearly

identical for the Glance Conglomerate and the "Mount Hughes"

Formation. Both formations overlie the Jurassic volcanic rocks of the

"upper" and "middle” members of the Canelo H ills Volcanics.

The Problem

Misunderstanding of the stratigraphy in the Canelo Hills has

prompted previous workers to consider the "Mount Hughes Formation" or

"lower" member of the Canelo Hills Volcanics to be separated

stratigraphically from the Glance Conglomerate by several hundred

meters of Jurassic rhyolite flows and welded tuffs and by 15-30

million years of geologic time. Because this stratigraphic and

chronologic separation is no longer viable, the Glance Conglomerate

and "lower" Canelo H ills Volcanics or "Mount Hughes Formation" may be

correlative and a Late Jurassic age for the base of the Glance

Conglomerate is conceivable. The two previously defined conglomerate

units have never been mapped in stratigraphic juxtaposition. Where

both formations are assumed present, contacts between them have been

interpreted as faults. At the outset of this project, it was thought

that detailed study of the texture and composition of both formations

and examination of any suspected contacts between them might justify

their distinct formation names. However, the two formations cannot be

differentiated on these criteria. The implications for stratigraphy

in southeastern Arizona are significant, as both the Glance 6 Conglomerate and the Canelo H ills Volcanics have many correlatives within the region.

Study Area

The study was confined to an area southeast of Tucson encompassing the Canelo H ills and the Huachuca Mountains. The 190 square mile area is bounded on the northeast by the Sawmill Canyon—

Kino Spring fault system (Drewes, 1981) and on the southwest by the

Lampshire Canyon—Dove Canyon fault system (Kluth, 1982). Both fault systems are considered to have accomodated left-lateral strike-slip motion during the Mesozoic and may have been subsequently reactivated in Laramide time (Drewes, 1981). The fault zones converge in the

Sawmill Canyon area of the central Santa Rita Mountains. This area was not included in the study because major structural complications have been created by the proximity of the two complex faults. By

lim iting the study area to the Canelo H ills and Huachuca Mountains,

complications arising from any offsets of conglomerate units along

these fault traces were eliminated.

The study area extends southeast from the northern Canelo

Hills to the Huachuca Mountains and terminates at the Mexican border

south of Coronado National Monument at Montezuma Pass (Fig. 1).

Method of Study

Detailed lithologic descriptions of the "Mount Hughes Formation"

were made in the Canelo H ills. Local facies changes, petrology of

sandstone and volcanic interbeds, composition of conglomerate matrix,

sorting, roundness and lithological composition of conglomerate clasts 7

Tucson Rincon Mts

ARIZONA

Slerrlta Mts

ogales

10 is 20 25

Pig. 1. Location Map, Southeastern Arizona 8 were recorded. Exposures of the Glance Conglomerate and equivalents of the "Mount Hughes Formation" exposed along the southwestern flank of the Huachuca Mountains were studied with the same care. Special attention was given to previously mapped contacts of the conglomerates with underlying Jurassic volcanic rocks and overlying Bisbee Group s t r a t a .

A 5 square kilometer area including portions of Lone Mountain on the southwestern flanks of the Huachuca Mountains was mapped at a scale of 1:12,000 in order to illu strate the geologic relationships between the "lower" member of the Canelo H ills Volcanics and the

Glance Conglomerate in an area where they are juxtaposed.

Several sequences of conglomerate, associated sediments and ash flow tuffs were measured in the northern Canelo H ills and southwestern Huachuca Mountains. Thin sections were cut from representative conglomerate samples throughout each measured section in order to provide information about matrix and clast composition.

Stratigraphic Framework

Rocks ranging in age from Precambrian to Recent are exposed within the study area. A generalized stratigraphic column which incorporates the results of this study is presented in Figure 2. The youngest Paleozoic formations of the study area include the Lower

Permian Concha Limestone, a medium to dark gray, cherty, fossiliferous

limestone and the Lower Permian Rainvalley Formation which is composed of vari-colored lim estone, light colored dolomite and minor

intercalated brown sandstone. An invertebrate fauna from the AGE FORMATIONS

Quaternary Alluvium Tertiary Gravels and Basin Fill Salero Formation Late Cretaceous Fort Crittenden Formation Huachuca Mts Santa Rita Mts Turney Ranch Fm. Clntura Fm. Shelienberger Cyn. Fm. Early Cretaceous Mural Ls. Apache Cyn. Fm. Morlta Fm. Willow Cyn. Fm.

BISBEE GROUP Bathtub Fm. Glance CgL Temporal Fm. Jurassic Canelo Hills welded Tull Member Volcanics Rhyolitic Flow Member Gardner Canyon Formation Triassic Mount Wrlghtson Formation Rainvalley Formation Concha Limestone Permian Scherrer Formation Epitaph Formation Colina Limestone Earp Formation Pennsylvanian Horquilia Limestone Black Prince Limestone Misslssippian Escabrosa Limestone Devonian Martin Limestone Abrlgo Formation Cambrian Boise Quartzite Precambrian Granitic to Dlorltic Plutonic Rocks

Fig. 2. General Stratigraphic Column 10 Rainvalley Formation indicates a latest Wolfcampian or Leonardian age

(Drewes, 1981). The dominantly carbonate Paleozoic formations are

extensively disrupted by pre-Jurassic high-angle normal faults (Hayes,

1970a). A major unconformity divides the Permian Concha and

Rainvalley Formations from overlying Mesozoic strata. Volcanic rocks

of Triassic(?) to Jurassic age rest on formations as old as the

Pennsylvanian Horquilla Limestone, demonstrating that considerable

relief was developed on the Paleozoic basement.

The earliest Mesozoic rocks of southeastern Arizona consist of

thousands of meters of intermediate and silicic volcanic rocks

containing interbedded quartzite and sandstone. Together with several

granitic intrusions of Jurassic age, these volcanic rocks define the

eastern margin of a Jurassic magmatic arc. The arc can be traced

southward into Sonora, Mexico, where volcanic rocks are interbedded

with marine sediments of Jurassic age (Rangin, 1978).

A thick sequence of mudstone, sandstone and conglomerate with

intercalated volcanic flows and tuffs lies depositionally above the

Jurassic volcanic rocks. In some areas these sediments onlap older

Paleozoic rocks of Precambrian to Permian age. This package is

composed of poorly sorted pebble to boulder conglomerates of alluvial

fan origin, which locally thicken and thin abruptly, and show rapid

lateral changes in clast composition. These conglomerates and

interbedded volcanic rocks are discussed at length in the following

chapters. They include the former "lower" member of the Canelo Hills

Volcanics or "Mount Hughes Formation” and the Glance Conglomerate. 11 Resting depositionally on this sequence of conglomerates are the Morita Formation, the Mural Limestone and the Cintura Formation of the Bisbee Group. The Morita Formation is composed of light gray, arkosic, cross-bedded and bioturbated sandstones and massive maroon siltstones and mudstones, thought to represent a fluvial floodplain environment. The uppermost portion of the Morita Formation is interbedded with the Mural Limestone which consists of calcareous mudstones and limestones of shallow marine origin. The Mural

Limestone contains marine invertebrates which indicate an Aptian to

Albian age (Drewes, 1978). The overlying Cintura Formation is nearly indistinguishable from the Morita Formation and is recognized by its stratigraphic position above the Mural Limestone.

To the north and northwest of the study area in the Whetstone,

Empire, and Santa Rita Mountains, correlatives of the Bisbee Group are non-marine and more arkosic (Hayes, 1970b). CHAPTER 2

NORTHERN CANELO HILLS

The Canelo Hills are a northwest-trending set of discontinuous ridges which lie between the southern Santa Rita Mountains and the central Huachuca Mountains. The hills rise 700 feet above the surrounding alluvial plain, and attain a maximum elevation of 6,170 feet. Paleozoic to Mesozoic strata of the northern Canelo Hills are deformed into a northwest-trending faulted anticline.

Previous Work

The earliest description of sedimentary and volcanic rocks in the Canelo Hills was incorporated by Schrader (1915) in his review of the mineral deposits of the Santa Rita and Patagonia Mountains.

Schrader recognized four northwest-trending belts of rock composed of

limestone, conglomerate, andesite, and rhyolite. He considered the

southwest-dipping conglomerates and intercalated volcanics exposed

along the southwestern side of the northern Canelo H ills to be of

probable Tertiary age.

Peth (1947, 1948) assumed that the conglomerates, sandstones

and mudstones were of Cretaceous age based on their relative

stratigraphic position. On his map of the northernmost end of the

Canelo Hills, the Mesozoic sedimentary rocks were included in a unit

called the Canelo Redbeds. Believing the silicic volcanic rocks to be

12 13 younger than the sedimentary sequence, Feth (1947) did not contest

Schrader's original Tertiary age assignment (Fig. 3A).

The presence of pre-Cretaceous Mesozoic volcanic and

sedimentary rocks in southeastern Arizona was firmly established by

geologists from the United States Geological Survey who began

extensive research in southeastern Arizona about 1960. The silicic

volcanics and associated sedimentary rocks of the Canelo Hills were

described in detail by Hayes, Simons and Raup (1965), and were re­

assigned an early Mesozoic age based on a 177 + 8 m.y. K-Ar date on

biotite extracted from tuffs exposed just south of Canelo Pass. The

name Canelo H ills Volcanics was given by Hayes and others (1965) to

this series of rhyolitic flows, welded tuffs and associated sandstones

and conglomerates exposed in the Canelo H ills. The formation was

subdivided into a lower sedimentary member, which included the Canelo

Redbeds of Feth (1947), a middle rhyolitic flow member and an upper

massive welded tuff member; no type section was designated (Fig. 3B).

In succeeding years, maps and papers dealing with the Mesozoic

stratigraphy of surrounding mountain ranges (Hayes and Raup, 1968;

Hayes, 1970a, 1970b; Drewes and Cooper, 1963; Cooper, 1971; Drewes,

1968, 1971; Simons, 1972, 1974) followed the stratigraphic terminology

of the Canelo H ills Volcanics proposed by Hayes and others (1965).

Kluth (1982, 1983) recognized that the "lower" sedimentary

member of the Canelo Hills Volcanics rests depositionally above the

"upper" welded tuff member. He suggested that the "lower" member be

renamed the "Mount Hughes Formation". Paleomagnetic and radiometric 14

A B C Path (1948) Hayes and others (1965) Kluth (1 9 8 2 )

X O e rhyolite.c* 5 Q upper IL a n d e site . CO > 6 w elded < C an elo oc o tuff m mo tuff & R idge Mbr < & 3 m > minor member -j a cr a sa n d sto n e til Z Dark Cyn. Mbr m H b ed s o * < M onkey X a 2 W 5 -1 C y n . Mbr < S *o sh ale. oc o 3 o middle "upper* a sa n d sto n e. "3 XI > rhyolite O w elded e conglomerate e # oc flow c5 o tuff 1 member w? X c member ■ % thin o < m o s o m c lim estone 5 3 3 « CO e o o b eds c > OHI < m E o Q H S 5 < O x c conglomerate "middle* Ul low er 5 o OC CO % rhyolite o ■o sedimentary < c ® & m flow E member E o m H member c sa n d sto n e 3 z Z Z < < < 5 Snyder Hill Fm. 5 ec Concha Ls. 2 Concha Ls. m tu Ui CL a Q.

Pig. 3. History of Mid-Mesozoic Stratigraphy Northern Canelo H ills 15 studies of Kluth's "Mount Hughes Formation" support a Late Jurassic age for these rocks, clearly younger than that determined for the welded tuff member of the Canelo H ills Volcanics (Kluth and others,

1982). As discussed below, the "Mount Hughes Formation" is here correlated with the Glance Conglomerate of the Bisbee Group, and the latter name is preferred because of its clear priority in the

literatu re (Ransome, 1904). The informal name "Mount Hughes

Formation" is used in this chapter for clarity, to distinguish these newly correlated rocks from rocks previously mapped as Glance

Conglomerate in southeast Arizona.

General Structure

Pre-Tertiary rocks of the northern Canelo H ills have been

folded into a northwest-trending anticline dissected by a complex

system of steeply dipping normal and reverse faults (Kluth, 1982). The

most prominent of these faults strike northwest-southeast, and a less

conspicuous group of faults strike northeasterly, perpendicular to the

strike of the Mesozoic strata. The two sets of cross-cutting faults

are poorly exposed, and the magnitude of offsets can rarely be

established. However, three major fault zones are recognized in the

northern Canelo Hills.

The Lampshire Canyon fault is the major bounding structure

along the southwest side of the Canelo H ills. It is a vertical or

steeply northeast-dipping reverse fault, and may be a northwestern

extension of the Dove Canyon fault of Hayes and Raup (1968) and Simons

(1974) in the southern Canelo H ills (Kluth, 1982). The Lampshire 16 Canyon fault places the Jurassic "Mount Hughes" strata adjacent to the

Late Cretaceous Fort Crittenden Formation; the Dove Canyon fault places Jurassic rocks of the Canelo Hills Volcanics against the late

Jurassic (?) to Cretaceous rocks of Jones Mesa.

The Houston Ranch fault is a steeply dipping reverse fault exposed along the northeastern limb of the Canelo H ills anticline.

Acting in conjunction with the Lampshire Canyon fault, though not necessarily synchronously, this fault has displaced the core of the northern Canelo H ills anticline relatively upward to expose highly disrupted Paleozoic carbonate rocks (Kluth, 1982). The Houston Ranch fault parallels the Sawmill Canyon fault zone (Drewes, 1981), which purportedly lies beneath alluvium to the northeast of the Canelo Hills

(Fig. 45). The Houston Ranch fault places conglomerates of the "Mount

Hughes Formation" against conglomerates of the Upper Cretaceous Fort

Crittenden Formation.

The northeasterly trending Box Canyon fault zone runs

perpendicular to the trend of the h ills, and separates anticlinally

folded rocks of the northernmost Canelo H ills from gently dipping

homoclinal rocks to the south (Fig. 4).

Sm all-scale folding is developed primarily within Paleozoic

carbonate rocks exposed in the core of the Canelo H ills anticline;

however, minor folds also occur within the Mesozoic strata of the

limbs. These minor folds have axes that generally trend N30E to N50W

and plunge both to the northwest and southeast at angles of less than

25 degrees (Kluth, 1982). Fig. 4. Location Map, Northern Canelo H ills Explanation

QTg—Quaternary and Tertiary gravels Kfc—Fort Crittenden Formation Kc— Cintura Formation Km-— M orita Form ation

"Mount Hughes Formation"

Jcp—"Canelo Pass Member" Jcr—"Canelo Ridge Member" Jdc—"Dark Canyon Member" Jmc— "Monkey Canyon Member"

Canelo H ills Volcanics

J t ---- Welded T uff Member J r ---- R h y o lite Flow Member

Prv—Rainvalley Formation Pc---- Concha Limestone Ps---- Scherrer Formation Pu---- Paleozoic rocks undifferentiated

Strike and dip of bedding

Overturned bedding

Vertical bedding

Contact between rock units, dashed where approximate

Fault, dashed where approximate, dotted where inferred (bar and ball on downthrown side)

>> Thrust fault, dashed where approximate (teeth on upper plate) V" Anticlinal axis (showing direction of plunge) Synclinal axis 17

Canelo Ridge Area

Canelo Pass Area

Fig, 4. Location Map, Northern Canelo H ills (Modified from Kluth, 1982) 18 Mid-Mesozoic Stratigraphy

The southern portion of the Canelo Hills from Canelo Pass to

Parker Canyon Lake is underlain mainly by volcanic rocks of Jurassic age. These rocks were originally mapped as the "middle" rhyolite flow member and the "upper" welded tuff member of the Canelo H ills

Volcanics (Hayes and Raup, 1968; Simons, 1974). A combined thickness of 4600 m of volcanic strata was reported by Hayes and others (1965).

The rhyolite flow member, 600 m thick, is composed of flow- banded, sparsely porphyritic lava flows, but contains several interbeds of red to pinkish orange tuffs and rhyolite breccia. Lenses of tuffaceous sandstone and silicified mudstone are rarely interbedded with the pyroclastic strata. Large exotic blocks of Paleozoic limestone measuring several meters in thickness and tens of meters along strike are entrained in the rhyolite flow member. The overlying welded tuff member consists of 4000 m of uniformly massive porphyritic tuff that is light gray to light pink and pale orangish red. The tuff is rhyolitic in composition and is so homogeneous in appearance that bedding estim ates must be made on the basis of a remnant eutaxitic texture that parallels bedding in the overlying and underlying strata

(Kluth, 1982).

In outcrops north of Canelo Pass, the dominantly sedimentary rocks of the "Mount Hughes Formation" replace the dominantly volcanic

Jurassic lithologies observed to the south. The "Mount Hughes" strata are well exposed along the northeastern and southwestern limbs of the northern Canelo Hills anticline, and more highly disrupted beds crop

out at the northwestern end of the range. In the Canelo Pass area. 19 sedimentary and volcanic rocks of the "Mount Hughes Formation" lie depositionally on both the Permian Concha Limestone and the Canelo

H ills Volcanics. The contact between the latter two formations is concealed by the overlapping strata.

Kluth (1982) divided the "Mount Hughes Formation" into four members. From oldest to youngest, these are the "Monkey Canyon

Member", the "Dark Canyon Member", the "Canelo Ridge Member" and the

"Canelo Pass Member" (Fig. 3C).

The "Monkey Canyon Member", composed of red to purple sandstone, mudstone and rounded pebble conglomerate, is present only at the northwest end of the Canelo H ills, and thins abruptly to the southeast. It is poorly exposed and pervasively faulted, yet Kluth

(1982) reports a thickness locally in excess of 150 m. The "Monkey

Canyon Member" rests unconformably on Lower Permian carbonate rocks, but its stratigraphic relationship with the other members of the

"Mount Hughes Formation" is unclear. Lengthy unconformable contacts are mapped between the "Monkey Canyon Member" and the welded tuffs of the "Canelo Ridge Member", but a single "covered" contact, less than

150 m in length is the only unfaulted contact mapped between the

"Monkey Canyon Member" and the overlying "Dark Canyon Member".

Problems of correlation of the "Monkey Canyon Member" with the Glance

Conglomerate are discussed in the concluding chapter.

The "Dark Canyon Member" consists of red to orange cross- stratified sandstone and thin interbedded conglomerate. A maximum thickness of 100 m is exposed along the northeast flank of the 20 northern Canelo H ills. In places on the southwestern side of the hills the member contains a thin interbed of silicic welded tuff.

Resting unconformably on or faulted against Lower Permian Concha

Limestone and Rainvalley Formation, the "Dark Canyon Member" apparently thins to the southeast.

Light purple to reddish purple welded ash flow tuffs make up the "Canelo Ridge Member", which attains a maximum thickness of 200 m in the northern Canelo Hills. Welded ash flow tuff exhibiting spherulitic texture, and in some localities containing a thick lens of thinly bedded arkosic sandstone, help to distinguish this member from tuffs of the underlying Canelo Hills Volcanics. In most places, the

"Canelo Ridge Member" rests conformably on sandstones of the "Dark

Canyon Member"; however, locally along the southwestern flank of the

Canelo Hills it rests on Permian limestone and at the northernmost end of the Canelo Hills it apparently rests unconformably on mudstones of the "Monkey Canyon Member".

The "Canelo Pass Member” is composed of varying proportions of reddish brown to pale red conglomerate, sandstone and welded tuff.

Conglomerate clasts include granitic rocks of Precambrian age, quartzites, sandstones and carbonates of Paleozoic age and granitic, volcanic and sedimentary rocks of Jurassic age. The lithologic

characteristics of the "Canelo Pass Member" differ significantly

between each of several localities studied in the northern Canelo

Hills. Locally, the member lies conformably upon, intertongues with,

or scours into the underlying "Canelo Ridge Member". The "Canelo Pass

Member" is thickest, 600 m, just north of Canelo Pass where it 21 contains several volcanic interbeds. Rapid lateral thickness changes and truncation or erosion of the upper parts of the member in most outcrops do not allow assessment of regional trends in thickness.

Other sedimentary rocks of presumed Jurassic age are exposed in a fault-bounded block in the southern Canelo Hills in the vicinity of Parker Canyon (Fig. 18). In contrast to the Jurassic sediments of the northern Canelo H ills, these dominantly fine-grained clastic rocks are thinly bedded, very tuffaceous and contain highly silicified beds of red mudstone. Light purple welded tuffs are present and are sim ilar to those interbedded in the "Mount Hughes Formation" of the northern

Canelo Hills and to tuffs exposed a few kilometers to the southeast at

Lone Mountain.

Large exotic blocks of Permian limestone and older Jurassic volcanics are present within the "Monkey Canyon Member", "Dark Canyon

Member" and "Canelo Pass Member" of the "Mount Hughes Formation".

Some of the blocks are 40 to 50 m in length, but they rarely exceed 10 to 15 m in thickness. Similar exotic blocks are entrained in the

"middle" and "upper" members of the Canelo H ills Volcanics and several other Mesozoic units in southeastern Arizona. Originally believed to be tectonic klippe, these exotic blocks were once thought to indicate large scale thrusting of Paleozoic carbonate rocks over younger clastic rocks during the Late Mesozoic (Feth, 1947, 1948; Cetinay,

1967). The blocks were reinterpreted by Simons and others (1966) to be "megaclasts" transported by "gravity glide" mechanisms and enclosed in a matrix of Mesozoic detritus or rafted along by volcanic flows. 22 Slickensides and orientations of fold axes within surrounding strata indicate a northeast-to-southwest direction of block emplacement

(Davis and others, 1979).

Strata of the Bisbee Group are exposed in the cores of minor folds on the northeastern side of the Canelo Hills in the Red Meadow area and in an area north of the Canelo Ranger Station. They include beds assigned to the Cintura Formation by Kluth (1982) and to the

Morita Formation (this study). The Red Meadow area is the only

locality in the Canelo H ills where younger beds of the Bisbee Group

are in depositional contact with the underlying "Mount Hughes

Formation".

"Mount Hughes Formation" or Glance Conglomerate

Three representative sections of Jurassic sediments in the

northern Canelo Hills are briefly described to illustrate the regional

lithologic diversity encountered within the members of the "Mount

Hughes Formation". Such diversity is characteristic of the Glance

Conglomerate as w ill be described in the following chapters. Figure 4

shows the location of the areas discussed.

Canelo Ridge Area

Along the southwestern side of the Canelo H ills, the

moderately -dipping beds of the "Mount Hughes Formation" form a series

of hogbacks which define Canelo Ridge (Fig. 5). A section of "Mount

Hughes" strata 435 m thick was measured across central Canelo Ridge

(F ig . 6 ). Fig. 5. Geologic Map of the Canelo Ridge Area, Northern Canelo H ills Explanation

QTg—Quaternary and Tertiary gravels Kf c—Fort Crittenden Formation Kc---- Cintura Formation Km-— M orita F orm ation

"Mount Hughes Formation"

Jcp—"Canelo Pass Member" Jcr—-"Canelo Ridge Member" Jdc~"Dark Canyon Member" Jmc— "Monkey Canyon Member"

Canelo H ills Volcanics

J t — Welded T uff Member J r ——R h y o lite Flow Member

Prv—Rainvalley Formation Pc— Concha Limestone Ps— Scherrer Formation Pu---- Paleozoic rocks undifferentiated

Strike and dip of bedding

Overturned bedding

Vertical bedding / Contact between rock units, dashed where approximate

Fault, dashed where approximate, dotted where inferred (bar and ball on downthrown side)

Thrust fault, dashed where approximate (teeth on upper plate)

Anticlinal axis (showing direction of plunge) Synclinal axis 23

% -L- % i ml km

Pig. 5. Geologic Map of the Canelo Ridge Area, Northen Canelo H ills (Modified from Kluth, 1982) 24 CANELO RIDGE AREA Total 435 m faulted top v ^Canelo Pass Member: Subarkose

Sandy mixed-clast cgl

*

Volcanic-clast cgl with ss Senses

■ < > u 1 L > ^ Canelo Ridge Member: 7 ^ A - Llthic-rich tuff ^ > mm Sublltharenlte ••••. w " - : •. ■» ' w r 1 ‘ 7 ' a ' ‘•I'1 < ^ u ,Welded tuff, Includes porphyrltlc, \ f < •'r c ■* spherulltlc, eutaxitlc and llthic-rich ash flows meters A ^ A T r ^ 100 , < r v . A i- A r a a # ~ r L 4 A ^ r v _i *Dark Canyon Member; X-stratlfled quartzarenlte 50 - Welded tuff Subarkose i i i iiii i i i i ill Permian Concha Ls. i ll 1~ 1 I I I 0 -1 M l

Fig. 6. Measured Section, Canelo Ridge 25 Monkey Canyon Member". All members of the "Mount Hughes Formation" are present along the ridge; however, the "Monkey Canyon Member" is limited in outcrop, and is found only in fault contact with the underlying Permian strata to the southeast of the area shown in Fig. 5

(See Fig. 4). Along most of the ridge, the upper three members lie unconformably above Permian lim estone, and the "Monkey Canyon" mudstones are absent.

"Dark Canyon Member". Along Canelo Ridge, the "Dark Canyon Member" is composed dominantly of sandstone, and ranges in thickness from 0 to 50 m. Interbedded conglomerate and thin beds of mudstone characteristic of the member elsewhere are absent.

The "Dark Canyon Member" rests unconformably on the Lower

Permian Rainvalley Formation along the southeastern portion of the ridge, and on the underlying Concha Limestone to the northwest. An angular limestone- and chert-clast conglomerate fills shallow channels at the base of the member, and was probably derived locally from the underlying carbonate section. In unchanneled areas, the basal unit of the "Dark Canyon Member" is either thinly bedded, subarkosic sandstone or a reddish-purple welded ash flow tuff. In the case of the former, as much as 20 m of sandstone underlies this welded tuff, indicating that the "Dark Canyon Member” was deposited on a surface of moderate r e l i e f .

The tuff is . overlain by thickly bedded, volcanic

sublitharenite containing scattered angular fragments of light purple to pink crystal-lithic tuff. The sublitharenites grade upward into 26 massive, cross-stratified quartzarenite sandstones. These well- rounded, w ell-sorted, cross-bedded sandstones make up 10 to 15 m of the "Dark Canyon Member" at Canelo Ridge, but are absent in other a r e a s .

"Canelo Ridge Member". The "Canelo Ridge Member" rests conformably on quartzarenite sandstones of the "Dark Canyon Member", or in its absence, unconformably on Permian carbonate rocks. This largely volcanic member consists of up to 185 m of porphyritic welded ash flow tuffs ranging in color from grayish purple at the base to light pinkish orange near the top. Most of the tuffs are rich in volcanic

lithic fragments, display eutaxitic texture, and contain euhedral and

subhedral phenocrysts of quartz, plagioclase and sanidine in a

groundmass of flattened, devitrified glass shards. A tuff containing

sphericles up to 7 cm in diameter is present near the base of the

member, and is also present in exposures of the "Canelo Ridge Member"

on the northeastern side of the Canelo Hills.

Although absent in other exposures of the "Canelo Ridge

Member", up to 30 m of thinly bedded sublitharenite is present near

the middle of the member at Canelo Ridge. Some of the sandstone beds

are finely laminated, and several bedding planes show sm all-scale

scour features.

The upper contact of the "Canelo Ridge Member" with the

conglomerates of the "Canelo Pass Member" is sharp but conformable

along the central part of Canelo Ridge. These two members intertongue

to the southeast on a scale of tens of meters (see Fig. 5). 27 "Canelo Pass Member". The "Canelo Pass Member" of the Canelo Ridge area is composed of lenticular-bedded, pale red to maroon, subangular, pebble to small boulder conglomerate containing shallow channels filled with parallel laminated sandstone (Fig. 7).

Clasts in the basal part of the conglomerate are exclusively volcanic in composition and include dusky red welded tuff containing scattered quartz phenocrysts, gray to light purple aphanitic tuff and pinkish gray crystal-lithic tuff. The volcanic clasts are angular and elongate, suggesting short transport distances. Most are lithologically sim ilar to and may have been derived from tuffs of the

"Canelo Ridge Member". Clasts in the basal conglomerate are supported by a matrix of clay-rich volcanic litharenite, and show no consistent imbrication. Many of the clasts have^a hardened rind of matrix material coating their surface, a phenomenon characteristic of many of the Jurassic conglomerates studied.

Moving upsection, the volume of matrix decreases, clast composition becomes more heterogeneous and average clast size increases until some clasts measure more than a meter in diameter.

Approximately 50 m from the base of the conglomerate, rare rounded pebbles of limestone first appear and increase in abundance upsection.

Many of these clasts contain fragments of brachiopods, crinoids and bryozoa of Permian age. Chert, fine-grained dolomite and red-orange sandstone clasts are present higher in the section, where the matrix is composed of clean, moderately sorted, red-orange subarkose. Near the top of the "Canelo Pass Member", m atrix-supported conglomerates 28

Fig. 7. Volcanic-clast Conglomerate Canelo Pass Member 29 are again prevalent. In addition to the clast types that occur lower

in the section, clasts of red and white tuffaceous sandstone, maroon

mudstone, quartzite and red and black striped, flow-banded volcanics

are also present. The flow-banded clasts resemble the rhyolite flow

member of the Canelo Hills Volcanics. The sandy conglomerates at the

top of the unit grade upward into red-orange subarkose, exposed

locally at the top of the section. To the northwest, several exotic

blocks of both Jurassic volcanic rock and Permian limestone are

incorporated in the member, and to the southeast, interbedded welded

ash flow tuffs are present.

The upper beds of the "Canelo Pass Member" are truncated at

the base of Canelo Ridge by the Lampshire Canyon fault. In all, 200 m

of conglomerate are exposed.

Red Meadow Area

Red Meadow (Fig. 8) is an area of low topographic relief

located east of Papago Spring in the northeastern Canelo H ills (See

Figure 4). The "Mount Hughes Formation" strata exposed at Red Meadow

dip gently to the northeast and rest unconformably on the lower

Permian Concha Limestone. The "Monkey Canyon Member" is not present

in this area, but crops out in a fault block 1.5 km to the northwest.

The three upper members have a combined thickness of 450 m, and are

here overlain by interbedded maroon mudstones and arkosic sandstones

of the Morita Formation (Fig. 9).

"Dark Canyon Member". As at Canelo Ridge, the "Dark Canyon Member" of

the Red Meadow area rests unconformably on Permian carbonate rocks F ig . 8 . G eologic Map o f th e Red Meadow A rea, N o rth ern C anelo H i l l s Explanation

QTg—Quaternary and Tertiary gravels Kfc—Fort Crittenden Formation Kc---- Cintura Formation Km——Morita F orm ation

"Mount Hughes Formation"

Jcp—"Canelo Pass Member" Jcr—"Canelo Ridge Member" Jdc—"Dark Canyon Member" Jo e— "Monkey Canyon Member"

Canelo H ills Volcanlcs

J t ---- Welded T uff Member J r ---- R h y o lite Flow Member

Prv—Rainvalley Formation Pc---- Concha Limestone Ps—-Scherrer Formation Pu---- Paleozoic rocks undifferentiated

Strike and dip of bedding

76 Overturned bedding

Vertical bedding

Contact between rock units, dashed where approximate

Fault, dashed where approximate, dotted where inferred (bar and ball on downthrown side)

Thrust fault, dashed where approximate (teeth on upper plate) > / Anticlinal axis (showing direction of plunge) Synclinal axis F ig . 8 . G eologic Hap o f th e Red Meadow A rea, N o rth e rn Canelo H ills (Modified from Kluth, 1982) RED MEADOW AREA Total 4 50m

syncllne 1

Morita Fm. (?)

'Canelo Pass Member*: Sandy granitic-clast cgl

Welded tuff Mixed-clast cgl Volcanic clast cgl X-stratified subarkose Tuff breccia r * ^ a r a a ^ ^ > v

Canelo Ridge Member; > > Welded tuff, Includes porphyrltlc, eutaxltlc, and llthlc-rlch ash flows ® : m

W 4.

-I V - '.le Z C 4 Dark Canyon Member: meters Sublitharenite to lltharenite ss, 100-1 ms, and sandy cgl

50 -

\ i 1 i Permian Concha Ls. i 11 i r i i i

F ig . 9 . M easured S e c tio n t R ^i Meadow A rea 32 with an angular limestone and chert clast conglomerate developed locally at its base. The "Dark Canyon Member" is here composed of approximately 100 m of red silty sublitharenite to litharenite sandstone, mudstone and sandy pebble conglomerate (Fig. 10). No thick, cross-stratified subarkose is present. The sublitharenite sandstones thicken upsection, and a few lenticular volcanic pebble conglomerates are incorporated in the upper part of the member.

Subangular chert, mudstone and sandstone clasts are locally common within the matrix-supported conglomerates, which are dominantly composed of subangular clasts of welded tuff less than 2 cm in d ia m e te r.

"Canelo Ridge Member". The "Canelo Ridge Member" at Red Meadow is

sim ilar to that exposed at Canelo Ridge, except that it lacks the

interbedded sublitharenite sandstones. It rests conformably on the

"Dark Canyon Member" and consists of 260 m of cry stal-lith ic welded

ash flow tuffs ranging from grayish purple to reddish purple in color.

The spherulitic unit observed at Canelo Ridge is also present here,

near the base of the member. The ash flow tuffs contain sparse

biotite phenocrysts in addition to the feldspar and quartz phenocrysts

observed at Canelo Ridge. At the top of the member, reddish purple,

poorly sorted tuff breccias interfinger with pale red sandstones of

the overlying "Canelo Pass Member" over an interval of at least 5 m.

"Canelo Pass Member". The presence of granitic, pebble to cobble

conglomerate and cross-bedded subarkosic sandstone at the base of the 33

Fig. 10. "Dark Canyon Member", Red Meadow Area

Pale red silty sublitharenite to litharenite sandstone and mudstone. 34 sequence distinguishes the "Canelo Pass Member" exposed at Red Meadow from that exposed at Canelo Ridge. The "Canelo Pass Member" here is substantially thinner than at Canelo Ridge or Canelo Pass, measuring only 90 m in thickness.

At Red Meadow, the basal sandstones of the "Canelo Pass

Member" interfinger with volcanic tuff breccias of the "Canelo Ridge

Member", however, along strike to the northwest, the sandstone beds can be traced laterally into a high angle contact with welded tuffs of the "Canelo Ridge Member". Kluth (1982) interpreted this contact to be the steep wall of a channel cut into the tuff sequence and filled with the sedimentary rocks of the "Canelo Pass Member". He estimated the channel dimensions to be at least 100 m in depth and over 200 m in w id th .

A few meters above the interfingering basal contact, the subarkosic sandstones of the "Canelo Pass Member" display medium to large-scale cross-stratification. A total of 15 m of sandstone lies between the uppermost tongue of tuff breccia and the first conglomerate beds.

The basal conglomerate at Red Meadow is m atrix-supported volcanic pebble conglomerate containing clasts of pink and gray welded

tuff. The volcanic clasts increase in size and abundance upsection

where rounded pebbles of lim estone, granodiorite, dolom ite,

calcarenite and olive-green fine crystalline volcanic rock are also

p r e s e n t.

A thin gray tuff is present near the base of the member, and

is the only volcanic unit asssociated with the "Canelo Pass Member" at 35 Red Meadow. It contains euhedral and subhedral quartz crystals and scattered volcanic lithic fragments.

The mixed clast conglomerates near the base of the "Canelo

Pass Member" give way upsection to pale red, sandy, granitic pebble to cobble conglomerates. Cobble-size clasts are often segregated into discrete beds, but decrease in abundance upsection as the conglomerates become sandier. The subangular to subrounded clasts are dominantly granitic, although clasts of olive-green fine crystalline volcanic rock, dusky red welded tuff and limestone are commonly present. The light gray granitic clasts are granodiorite in composition and display a distinct foliation. Although of unknown provenance, thay are probably Jurassic in age. Very coarse feldspar grains incorporated in the matrix may have been derived from the characteristically coarse crystalline Precambrian granites of southeastern Arizona.

Several sandy siltstone and mudstone beds of variable lateral extent fill shallow channels cut into the conglomerates of the upper part of the member. These beds fine upward and contain scattered angular pebbles of welded tuff near their bases. Where overlying conglomerate beds have not scoured deeply into the tops of the mudstone beds, calcareous horizons are often visible.

Morita Formation. The sandy conglomerates of the "Canelo Pass Member" grade upward into a sequence of interbedded maroon mudstones and light gray, cross-bedded, bioturbated arkosic sandstones. In contrast to the underlying sediments, these beds have sharp tops and bottoms, are 36 of uniform lateral thickness and show well-preserved organic and sedimentary structures (Fig. 11).

Kluth (1982) included these rocks in the "Canelo Pass Member", but the striking change in lithology and bedforms does not occur in any other exposure of "Canelo Pass" strata. These rocks are here considered to belong to the Morita Formation of the Bisbee Group.

Fifteen meters of maroon mudstone containing abundant carbonate nodules (Fig. 12) and thin beds of pebbly sandstone form a transition zone between the massive lenticular beds of the "Canelo

Pass" conglomerates and the first sandstone beds of the Morita

Formation. Similar lithologies are observed at the transition between Glance Conglomerate and the overlying Morita Formation in the

Huachuca Mountains.

The arkosic sandstone of the Morita Formation at Red Meadow is fine-grained, subrounded, well-sorted and contains numerous mudchips.

It is cemented by calcite and minor hematite and clay minerals.

Upward thinning beds of maroon mudstone and pinkish gray to light gray and maroon sandstone compose 50 m of the section which terminates at a synclinal axis. Both the sandstone and mudstone beds fine upward and display planar laminations, ripple cross-stratification and scour surfaces. The tops of several sandstone beds show evidence of extensive bioturbation.

Canelo Pass Area

Canelo Pass (Fig. 13) is located on the Canelo-San Rafael

Valley Road north of Lookout Knob, the point of highest elevation in 37

>ig. 12. Calcareous Mudstones Overlying the "Canelo Pass Member" at Red Meadow Fig. 13. Geologic Map of the Camelo Pass Area, Northern Canelo H ills Explanation

QTg—Quaternary and Tertiary gravels Kfc—Fort Crittenden Formation Kc---- Cintura Formation Km---- Morita Formation

"Mount Hughes Formation"

Jcp—"Canelo Pass Member" Jcr—"Canelo Ridge Member" Jdc—"Dark Canyon Member" Jmc— "Monkey Canyon Member"

Canelo H ills Volcanics

J t — Welded T uff Member J r — R h y o lite Flow Member

Prv—Rainvalley Formation Pc---- Concha Limestone Ps— Scherrer Formation Pu---- Paleozoic rocks undifferentiated

Strike and dip of bedding

J'h- Overturned bedding

Vertical bedding

Contact between rock units, dashed where approximate

Fault, dashed where approximate, dotted where inferred (bar and ball on downthrown side)

Thrust fault, dashed where approximate (teeth on upper plate)

Anticlinal axis (showing direction of plunge) Synclinal axis 38

•It 24

J km

Fig. 13. Geologic Map of the Canelo Pass Area, Northern Canelo H ills (Modified from Kluth, 1982) 39 the Canelo H ills (Fig. 4). The stratigraphic relationships observed in the Canelo Pass area led Kluth (1982) to revise the stratigraphic nomenclature of the Canelo Hills Volcanics. The gently northwesterly dipping conglomerates and interbedded siliceous volcanics of the

"Mount Hughes Formation" rest depositionally on massive welded tuffs of the Canelo ,Hills Volcanics a few hundred yards east of the road.

The "Mount Hughes Formation" is over 600 m thick in this area, and the entire sequence was originally mapped by Kluth (1982) as the

"Canelo Pass Member". Subsequent field work has revealed that lithologies chracteristic of both the "Dark Canyon" and "Canelo Ridge" members are present immediately above the contact with the Canelo

Hills Volcanics (Fig. 14).

"Dark Canyon Member" and "Canelo Ridge Member". A fining-upward sequence of subarkosic sandstone 13 m thick is present at the base of the section. These sandstones are sim ilar to "Dark Canyon Member" subarkoses exposed to the northwest and display a vertical gradation from pale red, silty sandstone rich in volcanic lithics to pinkish gray, quartz-rich sandstone with a distinctive bimodal texture. In places, the sandstones contain large exotic blocks of Permian limestone and calcareous sandstone. Lenses of silicified breccia composed of angular pebbles and cobbles of pink and gray welded tuff are common above the contact with the Canelo H ills Volcanics.

A thick unit of lithic-rich welded tuff is exposed above the subarkosic sandstones. The light purple to orangish pink tuff 40 CANELO PASS AREA . TOTAL 545m

•roslenel top 'Canelo Pass Member* : Orange to rod a# La pebble cgl and orange aa

LI purple welded tuff

La pebble to cobble cgl

Volcanic pebble te cobble cgl

Pteddleh purple to It purple welded tuff

La pebble cgl

Maaelve red aa

nlc ble

Dark purple volcanic flow

Mlied elaat pebbla la cgl near top

La and miner volcanic pebble to boulder cgl

Purple welded tuff Paleozoic exotic block

Volcanic pebble to boulder cgl, rod alllafone and aa

Main

*Canslo Ridge Member*: m JOOn Gray tutfaceoua aa and brecclated exotic blocka of Scherrer Fm In red sa matrix Paleozoic exotic block

Volcanic breccia and purple welded tutf Dark Canyon Member": Mixed cleat pebble to boulder cgl SO- with Paleozoic exotic blocka Red to pink tuffaceeua aa

Canale Hllla Votcanlca Welded Tuff Member

0 J * * au2

Fig. 14. Measured Section, Canelo Pass Area 41 displays well-developed eutaxitic texture and contains quartz and euhedral feldspar crystals. The orangish pink color and lithic-rich composition of this tuff are similar to the upper tuffs of the "Canelo

Ridge Member" at Canelo Ridge.

Although considerably thinner, the "Dark Canyon" and "Canelo

Ridge" members at Canelo Pass are in the correct relative stratigraphic position, and are composed of the same lithologies observed elsewhere in these members. The volcanic breccias found near the contact with the Canelo H ills Volcanics may have resulted from the

same depositional conditions that produced the angular limestone

conglomerates above the Permian limestones in other exposures of the

"Dark Canyon Member".

"Canelo Pass Member". Rocks attributed to the "Canelo Pass Member"

are first encountered to the west of the Canelo Pass road, near Flower

Tank. A total thickness of 500 m of conglomerate and interbedded

silicic volcanic rocks are exposed before the erosional top of the

section is reached.

Several large exotic blocks of fossiliferous Permian

limestone, up to 50 m long, are present at the base of the section.

Several of these blocks are internally brecciated, and the angular

fragments are enclosed in a red volcanic-lithic siltstone or

crystalline calcite matrix.

Partially brecciated, cross-stratified quartzarenites of

probable exotic origin are also exposed at the base of the member.

Several bedding planes appear to dip more steeply than the regional 42 attitude; however, thin beds of tuffaceous sandstone conform with the regional dip. The fine-grained cross-stratified quartzarenites may have been derived from the lower Permian Scherrer Formation.

Over 450 m of interbedded conglomerate, breccia, siltstone and welded tuff overlie the sandstone and limestone exotic blocks exposed at the base of the member. Several additional limestone exotic blocks are distributed throughout the lower part of the member and, in contrast to exposures at Red Meadow, at least six distinct welded tuff units are recognized.

The welded tuffs are dispersed throughout the member; they range from pink to grayish purple in color and contain phenocrysts of quartz and feldspar in addition to minor amounts of volcanic-lithic inclusions. Many have well developed eutaxitic texture.

Near the base of the member, volcanic pebble to cobble conglomerates consisting of subangular to subrounded clasts of gray and purple welded tuff and sparse clasts of limestone, sandstone,

chert and granite are present (Fig. 15). Several welded tuff breccias

containing boulder size clasts of Permian limestone and cross-

stratified quartzarenite enclosed in a siliceous volcanic-litharenite

matrix are interbedded with the conglomerates. As at Canelo Ridge and

Red Meadow, many of the conglomerate and breccia clasts have a rind of

resistant matrix m aterial. Dpsection, sandstone and conglomerate

matrix compositions change from volcanic-litharenite to feldspathic

volcanic-litharenite to subarkose. Red sandy siltstones are also

common in the lower part of the member. Usually poorly exposed, these 43

Fig. 15. Volcanic-clast Conglomerate of the "Canelo Pass Member" at Canelo Pass

Scale is marked in feet. Core taken from clast of welded tuff was used in paleomagnetic conglomerate test (Kluth and others, 1982). 44 siltstones contain scattered subangular pebbles of varicolored welded t u f f .

Conglomerate beds composed of up to 90% pebble to boulder-size clasts of fossiliferous limestone are common in the middle part of the member. Such a concentration of limestone clasts is not found in the

"Canelo Pass Member" elsewhere in the northern Canelo H ills.

Graded and inversely graded conglomerate and sandstone packages are present at the top of the section. Bedding surfaces often show striations, tool marks and mudcracks. As at Canelo Ridge, red-orange subarkosic sandstones are present at the top of the member, but at Canelo Pass several lenticular beds of dominantly volcanic or dominantly limestone clast conglomerate are also present. These uppermost conglomerate beds are unique in that the lim estone-clast and volcanic—clast conglomerate beds alternate and are commonly intercalated with one another (Pigs. 16, 17).

Age C o n s tra in ts

The upper three members of the "Mount Hughes Formation"

overlie the Canelo H ills Volcanic*, and at Red Meadow underlie the

Morita Formation of the Bisbee Group. The upper welded tuff member of

the Canelo H ills Volcanics has yielded a 177+8 m.y. K-Ar date on

biotite from tuffs exposed just south of Canelo Pass (Marvin and

others, 1978), but the age of the overlying Morita Formation is poorly

constrained. In the type area of the Bisbee Group, the Mule

Mountains, fossil evidence indicates that the Aptian-Albian boundary

is in the lower member of the Mural Limestone which in places Fig. 16. Limestone-clast Conglomerate and Interbedded Subarkosic Sandstone, Upper "Canelo Pass Member", Canelo Pass 46

Fig. 17. Volcanic-clast Conglomerate and Interbedded Subarkosic Sandstone, Upper "Canelo Pass Member", Canelo Pass 47 intertongues with the upper Morita Formation. Fossils collected from the basal Mural Limestone in the Huachuca Mountains indicate a sim ilar age. On the basis of this evidence, the upper Morita Formation has been considered to be Aptian in age (Hayes, 1970b), but its age range is unknown.

Recent paleomagnetic and radiometric work by Kluth and others

(1982) supports a late Jurassic age for the "Mount Hughes Formation".

A paleopole position determined from the welded ash flow tuffs of the

"Canelo Pass Member" exposed north of Canelo Pass falls on the North

American apparent polar wander path between poles from the Summerville

and lower Morrison Formations, indicating an approximate age of 150

m.y. (Kluth and others, 1982). A whole rock Rb-Sr age of 151+2 m.y.

determined from the same series of ash flow tuffs confirms the

paleomagnetic results.

Paleomagnetic site mean directions determined from rocks in

the "Canelo Ridge Member" do not deviate significantly from site mean

directions measured in rocks from the "Canelo Pass Member" (R. Butler,

pers. comm.). Because rapid apparent polar wander during the Jurassic

would produce distinctly different directions if these rocks were of

appreciably different age, the sim ilarity in observed directions

indicates that the age of the "Canelo Ridge Member" is close to that

of the "Canelo Pass Member". A proximity in age is also supported

stratigraphically by the intertonguing of the two members along Canelo

R idge.

The "Dark Canyon Member" is undated, but it intertongues with 48 the "Canelo Ridge Member" at Canelo Ridge and is probably only slightly older than the overlying members.

The age of the "Monkey Canyon Member" is poorly constrained.

Since its stratigraphic relationship to the upper three members is unclear, it may not belong to the same depositional sequence.

Lithologically, it is similar to the Gardner Canyon Formation of the

Santa Rita Mountains (Drewes, 1971? Kluth, 1982). In any case, it is unknown whether the "Monkey Canyon" mudstones are younger, older or correlative with the Canelo Hills Volcanics.

The gradational contact between Late Jurassic conglomerates of the "Mount Hughes Formation" and the overlying Morita Formation at Red

Meadow casts doubt on the proposed late Early Cretaceous age of the

Morita Formation. The basal Morita Formation in this area may be latest Jurassic or earliest Cretaceous in age.

Summary

The members of the "Mount Hughes Formation" exhibit significant internal diversity and lateral variation. A heterogeneous assortment of clast lithologies in the conglomerates is common, yet at many localities a single clast type or combinations of two or three clast compositions dominate thick sequences of stratigraphy.

Although the members of the "Mount Hughes Formation" have been characterized by a particular lithology or collection of lithologies, each member contains lithologies characteristic of the other members.

The "Dark Canyon Member" and the "Canelo Ridge Member" intertongue at varying scales within the northern Canelo H ills, as do the "Canelo 49 Ridge Member" and the "Canelo Pass Member". The members were

apparently deposited on a Paleozoic surface of irregular relief, and

their thicknesses differ appreciably within distances of less than a

k ilo m e te r.

The combinations of lithologies and the lateral relationships

of the members indicate that they represent intricately intercalated

facies within the sequence of rock mapped in the Canelo Hills as the

"Mount Hughes Formation". Stratigraphically, the sequence is younger

than the Canelo H ills Volcanics and older than the interbedded

mudstones and sandstones of the Morita Formation. Paleomagnetically,

the age of the formation is fixed by a late Jurassic paleomagnetic

pole position confirmed by a Rb-Sr date of approximately 150 m.y.B.P.

Elsewhere in southeastern Arizona, an undated sequence of

coarse clastic and interbedded volcanic rocks resting unconformably

above Jurassic volcanic rocks and depositionally overlain by the

Morita Formation is mapped as the Glance Conglomerate. The Glance

Conglomerate is mapped in the Santa Rita Mountains northwest of the

Canelo Hills, in the Empire and Whetstone Mountains to the north of

the Canelo Hills and to the southeast along the southwestern flanks of

the Huachuca Mountains. Consequently, the "Mount Hughes Formation" is

here correlated with the Glance Conglomerate. As the latter name has

clear priority in the literatu re, the term "Mount Hughes Formation"

should be abandoned if the correlation is accepted. CHAPTER 3

HUACHUCA MOUNTAINS

Reaching up to 9,500 feet in elevation, the Huachuca Mountains are a northwest-trending range located a few kilometers southeast of the Canelo H ills and extending to the Mexican border. Mid-Mesozoic rocks are exposed along the crest and southwestern side of the mountains (Fig. 18), and lie mostly within the boundaries of the

Coronado National Forest.

P rev io u s Work

The first comprehensive geologic map of the Huachuca and

Mustang Mountains was compiled by Hayes and Raup (1968). Hayes was responsible for the majority of the mapping in the Huachuca Mountains, which he conducted in the years 1962 through 1965. The Mesozoic stratigraphy of the region was discussed in subsequent publications by

Hayes (1970a, 1970b).

Hayes mapped outcrops of both the Glance Conglomerate and the

"Mount Hughes Formation", or "lower" member of the Canelo H ills

Volcanics as it was then known, in the Lone Mountain area southwest of the main ridge of the Huachucas. In the Huachuca Mountains themselves, all conglomerate overlying Jurassic volcanics and overlain by the Morita Formation was mapped as Glance Conglomerate.

Bilodeau (1979) described the Glance Conglomerate of the

Huachuca Mountains, and compared it to exposures in other mountain

50 Pig. 18. Location Map, Central to Southern Huachuca Mountains and Lone Mountain Explanation

QTg—Quaternary and Tertiary gravels T i---- Tertiary intrusive rock Kfc--Fort Crittenden Formation Kc---- Cintura Formation Karo—Mural Limestone K*---- Morita Formation Jcg—Glance Conglomerate a—andesite member, Glance Conglomerate t—ash flow tuff. Glance Conglomerate Jg ---- Huachuca Quartz Monzonite

Canelo H ills Volcanics

Jt— welded tuff member Jr— rhyolite flow member

JTrv-"siliceous volcanics of the Huachuca Mountains" P------Permian rocks, undifferentiated Pu---- Paleozoic rocks, undifferentiated Peg—PreCambrian granitic rock —exotic blocks of Permian limestone and minor Jurassic v o lc a n ic s

Strike and dip of bedding

76 Overturned bedding

Vertical bedding

Contact between rock units, dashed where approximate

Fault, dashed where approximate, dotted where inferred (bar and ball on downthrown side) >- Thrust fault, dashed where approximate (teeth on upper plate)

Anticlinal axis (showing direction of plunge) Synclinal axis 51

(Modified from Hayes and Raup, 1968) Fig. 18. Location Map, Central to Southern Huachuca Mountains and Lone Mountain 52 ranges of southeastern Arizona. He hoped to gain insight into the mid-

Mesozic tectonic history of the region by comparing relative thicknesses and clast compositions of the conglomerate across northwest-striking Mesozoic discontinuities. He developed a depositional model in which thick sequences of Glance Conglomerate

were deposited in steep-sided northwest trending basins bounded by

structural highs covered by only a thin veneer of sediment (Bilodeau,

1983).

General Structure

A series of northeast-dipping thrust and reverse faults of

Laramide age on the east side of the Huachuca Mountains places

Precambrian to Jurassic rocks above an overturned syncline of Morita

Formation exposed in the core of the mountain range. Strata on the

west side of the range dip steeply to the southwest, or are

overturned, apparently as a result of the thrusting. Several

northwest-trending high-angle faults and associated folds of sim ilar

trend deform the rocks of the southwest side of the range (Hayes,

1970a? Bilodeau, 1979).

The Glance Conglomerate and overlying strata of the Bisbee

Group are exposed in a plunging anticline near Wakefield Camp on the

southwest side of the Huachuca Mountains. The southwest limb of this

west-northwest-trending anticline is truncated by the Lone Mountain

Fault, a major northwest-trending fault, on opposite sides of which

Canelo H ills Volcanics and Glance Conglomerate are exposed. The Lone

Mountain fault zone extends to the northwest, and may link up with 53 major normal faults In the southern Canelo Hills. To the southeast, a fault zone with sim ilar trend has been mapped just north of Montezuma

Pass in the southern Huachuca Mountains. This fault zone may be an extension of the Lone Mountain fault, although Hayes and Raup (1968) infer that the latter passes under alluvium southeast of Montezuma

Pass (Figs. 18, 45).

The Kino Spring fault is a major east-w est trending, left- lateral strike-slip fault that disrupts the generally northwest striking strata of the northernmost Huachuca Mountains. The fault places Jurassic volcanic and sedimentary rock on the north against folded and faulted rocks of Cambrian to Early Cretaceous age to the south. Both the Kino Springs fault and the northwest-trending faults of the Lone Mountain-Montezuma Pass area have been considered to be possible extensions of the Sawmill Canyon fault zone recognized in the

Santa Rita Mountains and northeast of the Canelo Hills. The Sawmill

Canyon fault is thought to be a complex fault repeatedly reactivated

in Mesozoic time (Drewes, 1981, Drewes, 1971, Titley, 1976, Davis and

others, 1979).

The Paleozoic rocks of the central Huachuca Mountains are cut

by numerous faults of post-Permian, pre-Middle Jurassic age. Repeated

uplift along these faults may have been a major factor in creating

topographic highs from which the exotic blocks so common in the

Jurassic section were derived. Bilodeau (1979) cites stratigraphic

evidence for Jurassic faulting near the head of Garden Canyon? some of

the high angle faults in the Paleozoic basement were traced by Hayes

and Raup (1968) into the lower Glance Conglomerate, suggesting 54 contemporaneous deformation and conglomerate deposition. Bilodeau also suggests that the unexposed contact between the "siliceous volcanics of the Huachuca Mountains" and the Paleozoic rocks in

Sawmill Canyon may be a Jurassic fault. A sim ilar relationship is observed at Canelo Pass where the welded tuff member of the Canelo

Hills Volcanics is juxtaposed against Paleozoic rocks along an apparently steep contact which is overlapped by conglomerates of the

"Mount Hughes Formation".

Mid-Mesozoic Stratigraphy

The Canelo Hills Volcanics and the "siliceous volcanics of the

Huachuca Mountains" of Hayes and Raup (1968) and Hayes (1970a) are the oldest Mesozoic form ations exposed in the Huachuca Mountains. The

"siliceous volcanics of the Huachuca Mountains" is an informally named sequence of poorly exposed and pervasively altered volcanic flows and tuffs which are intruded by the 167+7 m.y. (K-Ar, biotite) Huachuca

Quartz Monzonite (Hayes, 1970a; Marvin and others, 1978). In the southern Huachuca Mountains, a fault zone separates the "siliceous volcanics of the Huachuca Mountains" from the unaltered Canelo H ills

Volcanics. Hayes (1970a) assumed that the "siliceous volcanics of the

Huachuca Mountains" are correlative with the Canelo Hills Volcanics, but it is possible that the rocks represent an older volcanic assemblage.

As much as 1200 m of the "siliceous volcanics of the Huachuca

Mountains" are exposed in the upper plate of thrust faults in the southeastern Huachuca Mountains. The rocks are described as 55 predominantly pyroclastic, but lava flows and lenses of sedimentary rock have been identified within the unit (Hayes, 1970a). Internally brecciated exotic blocks of Paleozoic limestone are commonly incorporated in the volcanic rocks and are especially abundant near the southern end of the range. The unit rests unconformably on

Paleozoic limestone, both in the thrust plates of the eastern

Huachucas and in an irregular band of outcrop which parallels the crest of the range. In the central Huachuca Mountains, angular

limes tone-cobble conglomerates which grade laterally and vertically

into volcanic pebble conglomerates were included by Hayes (1970a) in

the "siliceous volcanics of the Huachuca Mountains". These sediments

rest on both Permian limestone and the "siliceous volcanics of the

Huachuca Mountains" in the Sawmill Canyon area, and probably represent

paleovalleys or erosional channels filled by Glance Conglomerate.

The Canelo H ills Volcanics are exposed only at the

southernmost tip of the Huachuca Mountains. Just north of the

international border, the rhyolite member of the Canelo Hills

Volcanics rests depositionally on lower Permian limestone of the Naco

Group. The Montezuma Pass area is the only place in southeastern

Arizona where this basal contact is exposed. The absence of a

sedimentary member below the rhyolite member at this contact supports

Kluth's (1982) stratigraphic revision of the Canelo H ills Volcanics.

Northwest of Montezuma Pass, the Canelo H ills Volcanics are in

inferred fault contact with the "siliceous volcanics of the Huachuca

Mountains" The Glance Conglomerate mapped as depositionally 56 overlying the welded tuff member of the Canelo Hills Volcanics in the

southern Huachuca Mountains is stratigraphically equivalent to the

"Mount Hughes Formation" of the Canelo H ills.

The rhyolite flow member of the Canelo H ills Volcanics is here

composed of 150 m of dark brown, reddish purple and gray rhyolitic

flows and flow breccias. Some of the gray flows have a distinctive

spherulitic texture which is recognized in clasts of conglomerate in

the Lone Mountain area to the northwest. Thin beds of red quartzose

sandstone, white tuffaceous sandstone and red siliceous mudstone occur

near the top of the member. Exotic blocks of Permian limestone up to 3

km in length are also present within the member; their bedding planes

are aligned parallel to flow banding in the enclosing volcanic rock.

The welded tuff member of the Canelo Hills Volcanics forms a

resistant cliff 75 m high above the rhyolite flow member in the

southern Huachuca Mountains. The pinkish orange, sparsely porphyritic

tuff displays crude columnar jointing and contains large boulders of

reddish purple rhyolite and pink welded tuff. The massive tuff grades

upsection into a coarse tuff breccia. The welded tuff member rests

conformably on the ryholite flow member and is overlain depositionally

by the Glance Conglomerate.

A conglomerate unit of supposedly Triassic to Jurassic age has

been mapped in the upper Garden Canyon area of the central Huachuca

Mountains (Hayes and Raup, 1968). The conglomerate is preserved in a

paleovalley cut into Permian limestone, and grades upward into Glance

Conglomerate. The only characteristic which differentiates this lower

conglomerate^from the overlying Glance Conglomerate is the presence of 57 volcanic as well as carbonate clasts. The same concentration of

volcanic clasts is found in basal Glance Conglomerate less than 2 km

to the southeast where it also lies in a deep paleochannel cut

sim ilarly into Permian limestone. The "Triassic to Jurassic"

conglomerates of Hayes and Raup (1968) thus are here considered to be

part of the Glance Conglomerate.

The Glance Conglomerate is exposed in a northwest-trending

band which extends for 20 km north of the international border along

the southwest side of the Huachuca Mountains. Small fault slivers of

Glance Conglomerate are also caught up along the thrust faults of the

eastern Huachuca Mountains, and at the northernmost end of the range,

deformed beds of Glance Conglomerate lie adjacent to the Kino Spring

'F a u l t .

In the central Huachuca Mountains, the Glance Conglomerate is

up to 1400 m thick and rests unconformably on both Paleozoic limestone

and volcanic rocks of the "siliceous volcanics of the Huachuca

Mountains". Bilodeau (1979) also reports Glance Conglomerate resting

nonconformably on Huachuca Quartz Monzonite in the Blind Canyon area.

At the southern end of the range, in the Montezuma Pass area,

the Glance Conglomerate lies depositionally on the welded tuff member

of the Canelo Hills Volcanics. Approximately 960 m of conglomerate

were measured in this area before the eroded top of the section was

re a ch e d .

Bilodeau (1979) divided the Glance Conglomerate into three

informal members: a lower conglomerate member, a middle andesite flow 58 member and an upper conglomerate member. This stratigraphy is only applicable where the andesite flow member is present. Within the

Huachuca Mountains, the Glance Conglomerate thickens and thins dramatically, reflecting the paleotopography on which it was deposited. The intercalated andesite flow member thins abruptly and pinches out to the northwest of Scotia Canyon, but is also present in fault blocks exposed at the northernmost end of the range.

The Morita Formation rests depositionally on the middle andesite member and on the upper conglomerate member of the Glance

Conglomerate. The latter contact is in most places gradational; in the Scotia Canyon area of the central Huachuca Mountains, mudstones of the Morita Formation and the Glance Conglomerate intertongue through a stratigraphic interval 30 to 40 m thick.

Glance Conglomerate

The mid-Mesozoic conglomerates exposed in the Huachuca

Mountains are very sim ilar to the sediments of the "Mount Hughes

Formation" exposed in the northern Canelo H ills. Two outcrop areas are described: the central Huachuca Mountains, where the conglomerate rests on rocks of late Paleozoic to Jurassic age, and the southern

Huachuca Mountains, where the conglomerate rests depositionally, perhaps conformably, on the welded tuff member of the Canelo H ills

V o lc a n ic s.

Central Huachuca Mountains

Conglomerates exposed in the central Huachuca Mountains were deposited on an irregular topographic surface (Fig. 19). The local T— aenr ad i avels e v ra g y r tia r e T and uaternary QTg—Q f— t it omation Form n e d n ritte C Kc rt o Kfc—P i T m —ua Lmestone Lim Rmu—Mural v-"sii cani of he Hahc Mountains" M Huachuca e th f o s ic n a lc o v s u o e ilic s " - rv T J r J t J Km Area ountains M Huachuca l tra n e C e th f o Map eologic G 19. . ig P Jg erate Conglom —Glance Jcg ocks of mi i one ad nor c i s s a r u J r o in m and e n to s e lim n ia rm e P f o s k c lo b c i t o x e — 0 ^ ------t — ash flow t u f f , G lance Conglom erate erate Conglom lance G erate , f f Conglom u t lance G flow member, ash — t ite s e d n a—a g—Precam brian g r a n itic rock rock itic n a r g brian g—Precam m ------nt a Fr ation rock Form e ra tu iv s in u C tr in y r tia r e T ie fo member flow member lite o y f h f r u t welded ation Form orita M eoz c r undi i ed te tia n e r e f d if d te n u tia n e r , s e f k c if ro d n u ic zo , o s le k a c P ro ian Perm onzonite M uartz Q Huachuca aeo ls Volcanics V ills H Canelo cani s ic n a lc o v X a i n tio a lan p x E 76 etre bedding verturned O i bedding l a tic r e V i i axis x a l a lin tic n A nat ewen ok dse wee prxmate approxim where dashed , s t i n u rock een betw ontact C bedding f o ip d and e ik tr S T h ru st f a u l t , dashed where approxim ate ate d e approxim r r e f where in dashed where d , t tte l o u d a f ate, st im ru x h ro T p ap where dashed lt, u a F i axis x a l a lin c n y S t h o upr at ) te la p upper on ) e id th s e (te downthrown on l l a b and r a (b so n di i pl ) e g n lu p f o n tio c e ir d ing (show

Fig. 19. Geologic Map of the Central Huachuca Mountains Area (Modified from Hayes and Raup, 1968) 60 relief of this surface is apparently greater where developed on

Paleozoic limestone than where developed on Jurassic volcanic rocks.

Several light orange to pale red and white beds of pebbly, tuffaceous

sandstone containing angular fragments of volcanic and sedimentary

rock are present just above the Paleozoic surface. A pale red

siltstone containing rare pebbles of well-rounded volcanic rock is

also locally present at the contact. These beds are variably

channeled into by the overlying conglomerate (Fig. 20).

Bilodeau's (1979) lower member of the Glance Conglomerate

contains several thin welded and non-welded tuffs ranging from

purplish red to light purple and gray in color. Four distinct welded

tuffs were recognized; several contain phenocrysts of quartz, sanidine

and biotite in a matrix of devitrified glass shards. The tuff beds

are discontinuous and restricted to lows in the paleotopography. A

breccia composed of clasts of sim ilar welded tuff is present above a

paleohill of Paleozoic strata north of the head of Scotia Canyon.

The lower conglomerate member, 500 m thick, is a poorly

bedded, poorly sorted, small pebble to boulder conglomerate of

laterally and vertically variable clast composition. In northernmost

outcrops, the conglomerate consists of up to 90% carbonate clasts. In

contrast to limestone conglomerate of the Canelo H ills, numerous

carbonate lithologies are represented. The heterogeneous carbonate-

clast conglomerate is very distinctive in outcrop (Fig. 21); it

contains clasts of very light to very dark gray fossiliferous 61 CENTRAL HUACHUCA MOUNTAINS Total 1260 m

M erita Fm.

Flalei upward ■ Ihaeslene-olaet e@l

M lsed-elaal cgl

1

Andesite flow

m e te rs 1 0 0 -t Coarsening upward me to mixed-clast cgl lens

SO — Andesite flow

o J BASE 1

Fig. 20. Measured Section, Central Huachuca Mountains 62

Fig. 21. Carbonate-clast Conglomerate, Lower Glance Conglomerate Central Huachuca Mountains 63 limestone, gray to pink dolomite, pale red and white sandy calcarenite and green to black chert.

To the southeast, the conglomerate is composed of up to 80% volcanic clasts composed of reddish purple to pale red porphyritic tuff and flow-banded rhyolite. The percentage of volcanic clasts increases upsection throughout the lower member, but is always greater in the southeast. The lower member conglomerate has a gray to pink, sandy, crystalline calcite matrix which grades upward and to the southeast into a reddish purple, calcareous sublitharenite. Granitic clasts derived from the Huachuca Quartz Monzonite appear in the upper half of the lower member and are also more abundant to the southeast.

The Ida Canyon exposures near Sutherland Peak contain up to 50% granitic clasts. The Huachuca Quartz Monzonite clasts become more common upsection in all areas, perhaps reflecting progressive unroofing of the pluton.

. The middle andesite member of the Glance Conglomerate reaches its maximum thickness of 600 m in the central Huachuca Mountains, where it is composed of at least two individual flows with a lens of andesitic breccia and sedimentary rock between them. This large lens of interbedded sandstone, mudstone and conglomerate extends for 1 km along strike and is about 50 m thick along Sunnyside Canyon, north of the Copper Glance Mine Road. The coarsening-upward clastic package contains andesite breccia and interbedded siltstones and mudstones at its base which grade upward into sandy volcanic conglomerate and finally into mixed volcanic- and lim estone-clast conglomerate. The character of the andesite on either side of this clastic lens is 64 different. The andesite below the lens is a reddish purple aphanitic rock containing fine laths of plagioclase. Above the sedimentary interval, the andesite is medium gray in color, and contains abundant coarse crystalline phenocrysts of altered feldspar.

Laterally, the Glance andesite changes character as well. In the Wakefield Camp area it is dusky red in color, rich in iron oxides and contains abundant calcite-filled amygdules. Phenocrysts altered to chlorite and iron oxide, originally pyroxene or hornblende, are also present. In the Wakefield Mine area, the Glance andesite is a purple to grayish purple aphanitic rock capped by a muddy andesite breccia.

The upper member of the Glance Conglomerate, 300 m thick, is a mixed volcanic- and lim estone-clast conglomerate, but the volcanic component decreases at different rates upsection. In the Scotia Canyon area only a thin layer of mixed-clast conglomerate is present at the base of the member and the remainder is composed of 80-90% limestone

(Fig. 22). Less than a mile to the southeast, in the Sunnyside Canyon area, mixed clast pebble conglomerates dominate the section. The upper member thins and pinches out to the southeast, but is again present in the major fold near Wakefield Camp. Here the clast assortment is almost exclusively volcanic. Parallel-lam inated sandstone interbeds are common in the upper member, and increase in frequency as the contact with the Morita Formation is approached. The lim estone-clast conglomerates of the upper member do not show the compositional diversity observed in the lower member. Light gray lim estone, occasionally containing fossil fragments identifiable as 65

Fig. 22. Limestone-clast Conglomerate, Upper Glance Conglomerate, Central Huachuca Mountains 66 Permian forms, is the dominant clast lithology. Many volcanic lithologies are represented in the volcanic-clast conglomerates to the southeast. They include flow-banded rhyolite; dusky red porphyritic tuff? pale red, white, and purple aphanitic tuff? fine crystalline andesite? and gray welded tuff breccia.

The Glance Conglomerate intertongues with the Morita Formation over several tens of meters in the Scotia Canyon area. Where the upper conglomerate pinches out to the southeast, in the vicinity of

Wakefield Mine, the Morita rests depositionally on the Glance andesite. In the Wakefield Camp area, the Morita Formation lies gradationally above the Glance Conglomerate. Beds of calcareous mudstone, laminated lim estone and w ell-sorted pebble conglomerate described in the following chapter are present at the transition from conglomerate to the finer grained sedimentary rocks of the Morita

Formation. These resistant transitional beds are also recognized at

Lone Mountain, where their presence is integral to the revision of stratigraphic and structural relationships in that area. In the Canelo

H ills, sim ilar beds are observed between the "Mount Hughes Formation" and suspected mudstones and sandstones of the Morita Formation at Red

Meadow.

Southern Huachuca Mountains

A thick section of Glance Conglomerate is exposed in the

Montezuma Pass area of the southern Huachuca Mountains. Like the

"Mount Hughes Formation" of the Canelo Pass area, the Glance

Conglomerate here rests depositionally on the welded tuff member of 67 the Canelo Hills Volcanics (Fig. 23). The contact is gradational, and is marked by alternating beds of welded tuff breccia with pyroclastic matrix and welded tuff-breccia with a reworked epiclastic matrix. The contact is arbitrarily placed where the reworked tuffs become the dominant rock type (Hayes, 1970a). Lithic inclusions of red siliceous mudstone are found in both rock types. The welded tuff, overlying breccias and basal conglomerate of the Glance Conglomerate all dip about 25° to the southeast. Thus the Glance Conglomerate of the

southern Huachuca Mountains appears to concordantly overlie the welded

tuff member of the Canelo H ills Volcanics, perhaps indicating that

little time is missing at this contact.

The basal beds of the Glance Conglomerate at Montezuma Pass

(Fig. 24) consist of conglomerates and breccias, many of which are

supported by a muddy volcanic-litharenite matrix. The lowermost of

these contain subangular to angular clasts of welded tuff and

rhyolite, lithologies derived from the underlying Canelo Hills

Volcanics. Scattered clasts of tan calcareous sandstone, red

siliceous mudstone and gray quartzite are also present.

Higher in the section, the poorly sorted pebble to cobble

conglomerate is poorly bedded and contains lenses of coarse grained

trough-crossbedded sandstone. Clast-supported conglomerates are

dominant and sparse limestone clasts occur in addition to previously

described clasts (Fig. 25). As also noted in the northern Canelo

Hills, many of the clasts are coated with a rind of siliceous matrix.

The volcanic clast suite becomes more diverse upsection and the

conglomerate becomes moderately well-bedded. Clasts of marbleized Fig. 23. Geologic Map of the Southern Huachuca Mountains Area Explanation

QTg—Quaternary and Tertiary gravels T i---- Tertiary intrusive rock Kfc—Fort Crittenden Formation Kc— Cintura Formation Kmu—Mural Limestone Km---- Morita Formation Jcg—Glance Conglomerate a—andesite member. Glance Conglomerate t —ash flow tuff. Glance Conglomerate Jg ---- Huachuca Quartz Monzonite

Canelo H ills Volcanics

J t ---- welded tuff member Jr—-rhyolite flow member

JTrv-"siliceous volcanics of the Huachuca Mountains" p_---- Permian rocks, undifferentiated Pu---- Paleozoic rocks, undifferentiated PGg—Precambrian granitic rock ■■ —exotic blocks of Permian limestone and minor Jurassic v o lc a n ic s

IS Strike and dip of bedding

76 Overturned bedding

Vertical bedding

Contact between rock units, dashed where approximate

% Fault, dashed where approximate, dotted where inferred (bar and ball on downthrown side)

Thrust fault, dashed where approximate (teeth on upper plate)

Anticlinal axis (showing direction of plunge) Synclinal axis 68

■iml

■J km

Pig. 23. Geologic Map of the Southern Huachuca Mountains Area (Modified from Hayes and Raup, 1968) SOUTHERN HUACHUCA MOUNTAINS Total 960 m

Volcanic flow breccia

Limestone-clast cgl

Fining upward volcanic-clast cgl with ss lenses

erosions# top •

Volcanlc-elest cgl

Tuff b r e c c ia

Welded Tuff Member, Canelo Hills Volcanlcs

F ig . 24. M easured Section, Southern Huachuca Mountains A rea 70

Fig. 25. Lower Glance Conglomerate, Southern Huachuca Mountains 71 limestone, sim ilar to exotic blocks within the "siliceous volcanics of the Huachuca Mountains" also occur.

The dip of the conglomerate increases upsection, and the conglomerate composition abruptly changes character as the middle volcanic member is approached. Although pebbles of heterogeneous volcanic lithologies are still abundant, subangular to angular cobble- to boulder-size clasts of limestone dominate the section.

The stratigraphic relationship of the middle volcanic unit to underlying and overlying conglomerates is unclear. It appears to be more steeply dipping than either of the conglomerate units, and may represent a brecciated fault zone incorporating exotic blocks of limestone, andesite and volcanic flow breccia. Large exotic blocks of

Permian Concha Limestone are common within the unit, and locally occupy its entire 60 m width. Patches of reddish purple aphanitic andesite are locally exposed beneath the exotic blocks, but cannot be traced laterally. Volcanic material surrounding the exotic blocks is of strikingly different character than that exposed elsewhere in the

Glance Conglomerate. Abundant subhedral quartz, feldspar and biotite

crystals and coarse sand to pebble-size lithic fragments of limestone,

chert, tuffaceous sandstone and welded tuff are enclosed in a pale red

felty groundmass. Further study is needed in order to fully

understand the origin of this unit.

Overlying the volcanic unit is a shallow-dipping, moderately

bedded conglomerate containing a heterogeneous clast assemblage.

Subangular to subrounded clasts of welded tuff, flow-banded rhyolite. 72 dusky red to grayish purple andesite, coarse orange porphyry, quartz monzonite, limestone, chert, calcareous sandstone and quartzite are present (Fig. 26). Lenses of red siltstone and matrix supported conglomerate become increasingly common upsection.

Because the top of the section is eroded at Montezuma Pass, the upper contact of the Glance Conglomerate with the Morita Formation is not exposed. However, this contact is visible to the northwest along the road between Montezuma Pass and the Ida Canyon area (see

Fig. 18). The Morita depositionally overlies the conglomerate at a gradational contact marked by the same characteristic transition zone briefly described in the central Huachuca Mountains. This zone will be described more fully in the following chapter.

Age C o n s tra in ts

In the southern Huachuca Mountains the Glance Conglomerate

rests depositionally, perhaps conformably, on the welded tuff member

of the Canelo Hills Volcanics in the Huachuca Mountains. As

previously noted, the welded tuff member has been dated at 177+8 m.y.

in the Canelo H ills (Marvin and others, 1978). In addition, a K-Ar

date of 169+6 m.y. on biotite from the welded tuff member of the

Canelo Hills Volcanics was reported by Marvin and others (1978) from

Lone Mountain, 9 km to the northwest of Montezuma Pass. Thus the

concordant contact between Glance Conglomerate and the welded tuff

member of the Canelo H ills Volcanics in the Montezuma Pass area

supports a Jurassic age for the Glance Conglomerate of the southern

Huachuca Mountains 73

Fig. 26. Upper Glance Conglomerate, Southern Huachuca Mountains 74 The Glance Conglomerate of the central Huachuca Mountains rests on rocks as young as the "siliceous volcanics of the Huachuca

Mountains" which are intruded by the 167+6 m.y. (K-Ar, biotite)

Huachuca Quartz Monzonite (Marvin and others, 1978). Clasts of the quartz monzonite are incorporated in the upper half of the lower member of the Glance Conglomerate, indicating that the upper half of

this member is younger than approximately 167 m.y. Neither the tuffs

exposed near the base of the Glance, nor the flows of the middle

andesite member have been successfully dated.

Hayes (1970a) tentatively correlated the Canelo H ills

Volcanics with the "siliceous volcanics of the Huachuca Mountains",

but it is possible that the latter could be an older volcanic

sequence. The Canelo H ills Volcanics of the Montezuma Pass area in

the southern Huachuca Mountains are not intruded by the Huachuca

Quartz Monzonite and no quartz monzonite clasts from this intrusion

have been identified within the Glance Conglomerate at this locality.

The Glance Conglomerate of the central Huachuca Mountains is

depositionally overlain by and intertongues with the Morita Formation.

In the southern Huachuca Mountains, approximately 2 km to the

northwest of Montezuma Pass, the Morita Formation rests depositionally

on conglomerate correlated with the upper member of the Glance

Conglomerate described at Montezuma Pass. The uppermost Morita beds,

in places 2000 m above the contact with the Glance Conglomerate, are

considered to be Aptian on the basis of fossil collections from the

lower member of the overlying Mural Limestone (Hayes, 1970a? Bilodeau,

1983) 75 Summary

The age of the Glance Conglomerate in the Huachuca Mountains is poorly constrained between approximately 175 m.y. and 108-115 m.y.

(Aptian). This age range includes the age of the equivalent "Mount

Hughes Formation". The welded tuffs near the base of the Glance

Conglomerate are sim ilar to tuffs of the "Mount Hughes Formation" and its fine-grained equivalent in the Parker Canyon area. The flows included in the andesite member of the Glance Conglomerate are restricted to the Huachuca Mountains, and map patterns indicate that they pinch out to the northwest.

As noted in the preceding chapter, the "Mount Hughes

Formation" and the Glance Conglomerate are lithologically indistinguishable. Both show a great degree of lateral and vertical variation in dominant clast type and texture. Both thicken and thin rapidly over underlying paleotopography, and both display gradational contacts with the overlying Morita Formation.

Intraformational scour is locally present, but no regionally recognized surface can be identified which separates the Glance

Conglomerate in the Huachuca Mountains from a supposedly older "Mount

Hughes Formation" equivalent, thus supporting the correlation of these formations. The relationship between the Glance Conglomerate and the former "lower" member of the Canelo H ills Volcanics is further explored in the Lone Mountain area, where these two conglomerate units were mapped by Hayes and Raup (1968) in juxtaposition. CHAPTER 4

LONE MOUNTAIN

Lone Mountain is an isolated northwest-trending ridge located on the southwestern flank of the central Huachuca Mountains (Pig. 18).

It lies 7 km north of the Mexican border and approximately 4 km southeast of the sim ilarly trending Canelo Hills. Measuring 5 km in length. Lone Mountain reaches a maximum elevation of 6,475 feet and rises up to 1000 feet above the surrounding alluvial surface. Stream incision along the southwest flank of the mountain, in response to uplift along northwest-trending normal faults, has produced extensive exposures of Jurassic to Cretaceous volcanic and sedimentary rock.

P rev io u s Work

The geology of the Lone Mountain area was previously mapped on the 1:48,000 scale geologic map of the Huachuca and Mustang Mountains

(Hayes and Raup, 1968). Interpretation of geologic relationships in the area was strongly influenced by the stratigraphy of the Canelo

H ills Volcanics as it was then understood (Hayes and others, 1965).

The Lone Mountain area was partially remapped for this study to illustrate stratigraphic and structural relationships in light of the revised Canelo Hills Volcanics stratigraphy of Kluth (1982).

Detailed descriptions of the Mesozoic formations are provided by Hayes (1970a), and outcrops of Glance Conglomerate in m ultiple fault blocks south of Lone Mountain were described by Bilodeau (1979).

76 77 General Structure

The Lone Mountain area has a pronounced northw est-trending structural grain, which may in part be inherited from discontinuities in the Precambrian crystalline basement (Titley, 1976). Drewes (1981) suggests that recurrent movement during the Triassic to Early

Cretaceous on northwest-trending faults, such as the Sawmill Canyon fault, played a major role in the tectonic development of the region.

He considers the northwest-trending Lone Mountain fault and parallel faults to be splay faults originating from the Sawmill Canyon fault zone where it arcs eastward to link with the Kino Spring fault.

The Lone Mountain fault zone parallels Lone Mountain Canyon on the northeast side of the mountain. Geologic relations exposed in a plunging anticline north of the fault have been discussed in the

Huachuca Mountains section. To the south of the fault, a sequence of steeply dipping to overturned volcanic and sedimentary rocks of the

Canelo Hills Volcanics and Bisbee Group are exposed in several fault blocks and north we st-trending folds.

On the southwest flank of Lone Mountain, Hayes and Raup (1968) mapped the "lower" sedimentary member of the Canelo H ills Volcanics in fault contact with and structurally overlying the rhyolite flow and welded tuff members. The "lower" sedimentary member was also shown in fault contact with the Morita Formation to the southwest and the

Glance Conglomerate to the southeast (Fig. 27). Remapping has demonstrated that both the lower contact with the welded tuff member of the Canelo H ills Volcanics and the upper contact with the Morita Fig. 27. Geologic Map of the Lone Mountain Area (Hayes and Raup, 1968)

Explanation

QTg—Quaternary and Tertiary gravels T i---- Tertiary intrusive rock Kfc—Fort Crittenden Formation Kc---- Cintura Formation Kira—Mural Limestone Km---- Morita Formation Keg—Glance Conglomerate of Hayes and Raup (1968) Jcg—Glance Conglomerate, this study a—andesite flow, Glance Conglomerate

Canelo H ills Volcanics

Jt—-welded tuff member J r ---- rhyolite flow member

H —exotic blocks of Permian limestone

Strike and dip of bedding

Overturned bedding

Vertical bedding

Contact between rock units, dashed where approximate

Fault, dashed where approximate, dotted where inferred (bar and ball on downthrown side)

Thrust fault, dashed where approximate (teeth on upper plate)

Anticlinal axis (showing direction of plunge) Synclinal axis 78

Fig. 27. Geologic Map of the Lone Mountain Area (Hayes and Raup, 1968) 79 Formation are actually depositional. In addition, evidence presented below indicates that no fault is present separating the "lower" member from Glance Conglomerate (Fig. 28, 29).

South of Lone Mountain, in the southern half of sec. 35, an arcuate fault mapped by Hayes and Raup (1968) between repeated "lower" sedimentary member and the Morita Formation, was also found to be a depositional contact. In addition, a welded tuff at the northern end o f Lone M ountain (NW1/4 sec . 27) mapped above th e "low er" member as

the "upper" welded tuff member of the Canelo H ills Volcanics is

actually a welded tuff interbedded with conglomerate.

It has thus been demonstrated that the "lower" sedimentary

member of the Canelo H ills Volcanics at Lone Mountain rests

depositionally above the original "middle" rhyolite member and "upper"

welded tuff member. The relative stratigraphic position of the member

confirms Kluth's observation in the Canelo Hills that the sedimentary

member of the Canelo Hills Volcanics is stratigraphically above the

volcanic members. The lithologic character of the sedimentary

sequence exposed at Lone Mountain is sim ilar to the "Mount Hughes

Formation" of the Canelo H ills. A re-examination of structural

interpretations at Lone Mountain has shown that many of the faults

mapped by Hayes and Raup (1968) are unnecessary when K luth's (1982)

version of the stratigraphy is applied. The "lower" sedimentary

member of the Canelo H ills Volcanics exposed on the southwest flank of

Lone Mountain and correlated with the "Mount Hughes Formation" of the

Canelo H ills, is here recognized as the Glance Conglomerate. Fig. 28. Geologic Map of the Lone Mountain Area (This Study) Explanation

QTg—Quaternary and Tertiary gravels T i-----T e r tia r y in tr u s iv e rock K fc— Fort Crittenden Formation K c-—Cintura Formation Kara—Mural Limestone Km---- Morita Formation Keg—Glance Conglomerate of Hayes and Raup (1968) J c g —Glance Conglomerate, this study a—andesite flow. Glance Conglomerate

Canelo H ills Volcanics

Jt— welded tuff member J r —-rhyolite flow member

—exotic blocks of Permian limestone

Strike and dip of bedding

Overturned bedding

> 1^ Vertical bedding

ontact between rock units, dashed where approximate

ault, dashed where approximate, dotted where inferred (bar and ball on downthrown side)

Thrust fault, dashed where approximate (teeth on upper plate)

Anticlinal axis (showing direction of plunge) Synclinal axis 80

Pig. 28. Geologic Map of the Lone Mountain Area (This Study) 81

Evidence for Late Jurassic faulting contemporaneous with conglomerate deposition is found at central and northern Lone

Mountain. An east-trending fault in the northern half of sec. 27 offsets welded tuffs at the base of the conglomerate, but fails to disrupt tuffs higher in the section. The fault was presumably active only during early Glance Conglomerate deposition. Further evidence of

syndepositional faulting is noted in central Lone Mountain (Nl/2 sec.

35, Sl/2 sec. 36), where a fault juxtaposes basal Glance Conglomerate and welded tuff of the Canelo Hills Volcanics, yet does not cut welded

tuffs higher in the section. The roughly east-west trend of these

faults parallels the trend of syndepositional faults recognized by

Bilodeau (1979) in the central Huachuca Mountains and discussed by

Davis (1981).

Abrupt lateral changes in clast composition across linear

features within the upper Glance Conglomerate indicate that faulting

continued throughout Glance deposition. A north-trending fault in the

northw est quarter of sec. 35 s e p a r a t e s 30 m of mixed lim estone- and

volcanic-clast conglom erate above volcanic conglomerate to the west

from exclusively volcanic conglomerate to the east. Both

conglomerates are depositionally overlain by the Morita Formation,

which is offset only 6 m to the south on the west side of the fault,

indicating recurrent movement on the fault. The welded ash flow tuffs

and associated sandstone interbeds off northern Lone Mountain thin to

the southeast, whereas the andesite flow and overlying conglomerates

of southern Lone Mountain thin to the northwest. These relations 82 imply the existence of a paleohigh in the area between. Coarse conglomerate of the lowermost Glance Conglomerate can be traced the length of Lone Mountain and are continuous over this paleohigh, which must have developed concurrently with Glance Conglomerate deposition.

Younger faulting has caused minor offsets of the contact between the Glance Conglomerate and the Morita Formation in sec. 35. i t Laramide or younger normal faulting repeats the conglomerates and overlying Bisbee sediments to the southwest of Lone Mountain (Davis,

1979).

Mid-Mesozoic Stratigraphy

The rhyolite flow member of the Canelo Hills Volcanics is the

oldest rock exposed at Lone Mountain. The base of the member is

truncated by the Lone Mountain fault zone on the north, but at least

300 m of flow-banded rhyolite and rhyolite breccia are preserved.

Several large exotic blocks of Permian Concha Limestone are entrained

in the rhyolite, in which bedding attitudes are difficult to measure

due to the contorted nature of the flow-banding. However,

intraform ational contacts of flow-banded rhyolite with rhyolite

breccia indicate a general northwest strike and steep southwest dip.

The reddish-brown to gray rhyolite lava is sparsely porphyritic,

containing phenocrysts of sanidine, quartz, plagioclase and biotite.

Some flows contain abundant volcanic lithic fragments. Hayes (1970a)

reports that tuffs within the member which resemble tuff of the

overlying welded tuff member. 83 The welded tuff member is at least 200 m thick at Lone

Mountain. Map patterns and field observations indicate interbedding of the welded tuff with rhyolite flow breccia included in the underlying member. Eutaxitic texture and flow structures in the pale orange to light pink porphyritic tuff indicate steeply southwest-dipping attitudes with an average strike of N60°W. The welded tuff contains coarse euhedral and subhedral phenocrysts of feldspar, quartz and biotite in addition to numerous pumice and lith ic fragments.

Lying depositionally above the welded tuff member are the conglomerates originally mapped by Hayes and Raup (1968) as "lower" member of the Canelo H ills Volcanics but here considered to be Glance

Conglomerate. The conglomerates crop out in a northwest-trending band along the southwest flank of Lone Mountain, and are partially repeated in a fault block to the south. Remapping has illustrated that these

conglomerates can be traced southeast into conglomerate originally

mapped as Glance Conglomerate by Hayes and Raup (1968).

At northern Lone Mountain, the conglomerate sequence is 900 m

thick and can be divided into three informal units: a lowermost unit

of coarse, poorly sorted, mixed-clast conglomerate that locally scours

into the welded tuff member of the Canelo H ills Volcanics; a middle

unit of interbedded tuffs, orange sandstone and volcanic pebble

conglomerate; and an upper unit of coarsening-upward, dominantly

volcanic-clast conglomerate. Conglomerate exposed at the southern end

of Lone Mountain lacks the numerous interbedded tuffs, but does

contain an andesite flow, which divides coarse conglomerate with 84 interbedded sand lenses stratigraphically below it from coarsening- upward conglomerate above.

The lower depositional contact of conglomerate on welded tuff can be traced from central Lone Mountain southeast to where it meets with the depositional contact mapped by Hayes and Raup (1968) between welded tuff and Glance Conglomerate. The upper contact with the

Morita Formation, although offset by several minor faults, is recognized by a zone of distinctive marker beds between the

conglomerate and finer grained Morita Formation. To the southeast,

this contact can be traced into that originally mapped between Glance

Conglomerate and overlying Morita Formation in the Bear Creek area

(Figs. 28, 29).

Thick sequences of Morita Formation sandstone and mudstone are

present in three fault blocks between Lone Mountain and the

international border. The upper part of the formation is missing

along a steeply dipping, northwest trending normal fault on the

southern flank of Lone Mountain, but the entire thickness is exposed

above the repeated conglomerate section to the south (Figs. 28, 29).

There the Morita Formation varies from 975 m to 1,280 m in thickness

(Hayes, 1970a), and is exposed in the northern limb of a northwest­

trending syncline, the southern limb of which is faulted against a

third sequence of conglomerate and overlying Morita Formation

extending into Mexico. 85 Glance Conglomerate

The conglomerates of the Lone Mountain area are described in two parts: conglomerate of northern Lone Mountain, originally mapped as the "lower" member of the Canelo H ills Volcanics and correlated with the "Mount Hughes Formation", and conglomerates at the southern end of Lone Mountain, originally mapped as Glance Conglomerate. Both conglomerates display sim ilar textural characteristics and lateral changes in clast composition. They differ only in the fact that the conglomerate of northern Lone Mountain contains interbedded welded ash flow tuffs, whereas the originally mapped Glance Conglomerate contains a single andesite flow.

Northern Lone Mountain

To aide in its description, the Glance Conglomerate of northern Lone Mountain is here divided into three informal units: a lowermost unit of coarse mixed-clast conglomerate; a middle unit of interbedded tuff, sandstone and volcanic pebble conglomerate; and an upper unit of coarsening-upward dominantly volcanic-clast conglomerate. Up to 10 m of epiclastic rock may underlie the coarse conglomerates of the lower unit, but more frequently the lower unit has channelled through these rocks into the welded tuff member of the

Canelo H ills Volcanics. At central Lone Mountain, the welded tuff

member is absent and the lower unit of the Glance Conglomerate rests

directly on the rhyolite flow member of the Canelo Hills Volcanics.

Where the basal contact of conglomerate and welded tuff is

best exposed, 300 m southeast of Mud Spring, 5—10 m of thin—bedded 86 volcanic breccia, tuffaceous sandstone and volcanic pebble conglomerate overlie the tuff and are channeled into by coarse, mixed- clast conglomerate (Fig. 30). This volcanic breccia contains clasts of pink porphyritic tuff? light gray to pale red aphanitic tuff? red flow-banded rhyolite and purple aphanitic lava in a red silicified volcanic-litharenite matrix. Pale red and green sandstones in this basal interval are thin-bedded, fine-grained, and well-indurated.

Thin beds of red silicified mudstones are often found at the top of these sandstones. Coarsening upward, fine pebble conglomerate containing subangular to subrounded tuff clasts in a tuffaceous sandstone matrix is also present within the sequence. Relief of up to

30 m is developed on the pre-conglomerate surface, where overlying conglomerates fill paleochannels cut into the basal volcanic breccia and tuffaceous sandstone sequence. This basal sequence is only locally preserved because the paleochannels often cut down into the welded tuff member of the Canelo H ills Volcanics.

Lower Unit. Poorly bedded, reddish purple, pebble to boulder conglomerate rests above the scoured contact. The lowermost of the three units recognized at northern Lone Mountain, it reaches a thickness of 320 m in section 26, where the welded tuff member of the

Canelo Hills Volcanics is absent and the unit rests on rhyolite breccia. To the northwest, this very coarse conglomerate pinches out against a paleotopographic barrier of welded tuff of the Canelo Hills

Volcanics. To the southeast the coarse conglomerate is offset to the

south by a fault which cuts the welded tuff member of the Canelo H ills 87 NORTHERN LONE MOUNTAIN

TOTAL 8 7 0 m

Si»«f #*###« •• w eieeeli

•lie# •leel. «eeHeeell» weleeele !•# $m#*ne*#**# •»** ICtfll* F* ••#•«••••

FlelieB *rey «• It #«*### t*M

Of#*#* • • ##4 w•»#••«# ##»&#* «•*

#*###*# »ef#«*

Of#### ## «*l««#t«

Of*### ## ••# #**#*#*# ##&#!# ##l It *•»**• **W#« teft Of*### •• **# v#l«#*»«

It •#f#l# I# #f#y ••«#♦# tetl

I# *#el*#f ##l •*»* #f#y #* <•«••• •••f *••#

€ * # ••• Mitt# V#l«##l«# Wet### Telt M*m**f

Fig. 30. Measured Secticn, Northern Lone Mountain 88 Volcanics; beyond this fault the lower unit can be traced directly into the basal Glance Conglomerate at the southeast end of Lone

M ountain.

Parallel-lam inated beds of gray to purple sandstone are observed in the conglomerate near its channeled base. The otherwise coarse conglomerate consists of 65% volcanic, 30% carbonate and 5% sandstone clasts, some of which are greater than 2 m in diameter (Fig.

31). Locally, the conglomerate may contain a higher percentage of volcanic or limestone clasts. As previously noted in the northern

Canelo Hills and Huachuca Mountains, many of these clasts are coated with a siliceous rind of matrix sediment.

Volcanic clasts include dark gray and red flow- banded rhyolite, light gray spherulitic rhyolite, dusky red porphyritic tuff,

light gray and purple crystal-lithic tuff, dark gray aphanitic lava, purple porphyritic lava, dark green porphyritic lava, and volcanic

flow breccia. All the clasts were apparently derived from the

underlying Jurassic volcanic section.

Carbonate clasts are composed of light to medium gray m icritic

limestone containing silicified echinoid spines and brachiopod

fragments, light gray m icritic limestone containing crinoid debris,

gray to pink dolomite, pink and medium gray sandy limestone and light

purple m icritic limestone. A gray intraclastic limestone with a pink

m icritic matrix is a rare clast type. Most of the carbonate clasts

could have been derived from Permian form ations now exposed in the

nearby Huachuca Mountains. 89

Fig. 31. Basal Contact, Lower Unit of the Glance Conglomerate on Welded Tuff Member of the Canelo Hills Volcanics, Northern Lone Mountain

Jt— welded tuff member, Canelo Hills Volcanics Jcg-Glance Conglomerate 90 Sandstone clasts include red siliceous volcanic litharenite, gray quartzite, cross-stratified white calcareous quartzarenite, and orange and purplish red sublitharenite. The cross-stratified quartzarenite was problably derived from the Permian Scherrer

Formation, the gray quarzite from Cambrian Bolsa Formation, and the red, orange and purple sandstones are likely of Jurassic origin.

The conglomerate matrix is fine to medium grained pale red silty sandstone of volcanic litharenite composition. Secondary calcite cement has partially replaced the original siliceous cement.

Notably, the lower conglomerate unit at Lone Mountain is lithologically sim ilar to basal Glance Conglomerate described by

Bilodeau (1979) in the Empire and Santa Rita Mountains.

Middle Unit. The middle conglomerate unit attains a maximum thickness of 270 m and consists of interbedded tuffs, sandstones and volcanic pebble conglomerates. At the northwest end of Lone Mountain the unit thins abruptly over a paleohigh of Canelo Hills Volcanics welded tuff member. To the southeast the unit gradually thins and can be traced without significant offset into sec. 35, where it is disrupted by local faulting. The unit pinches out against coarse conglomerate of the lower unit further to the southeast.

At least eight welded tuffs have been recognized in the middle unit. Even where well exposed, the tuffs are observed to coalesce and split along strike; thus, only certain tuffs of characteristic lithology or texture can be accurately traced the length of Lone

Mountain. Most of the tuffs are reddish purple to light purplish 91 gray, sparsely porphyritic, and exhibit eutaxitic texture. Many contain abundant volcanic lith ic fragments. The concentration of feldspar phenocrysts varies within single flows, which commonly contain scattered subhedral crystals of quartz and biotite.

A distinctive pinkish orange to gray welded tuff can be correlated with confidence along Lone Mountain. It is the uppermost tuff of the south-central area; in the north, it is overlain by at

least three tuffs. This tuff is 80 m thick near Sycamore Spring and

gradually thickens to 150 m in the northwest where it abruptly thins

to 40 m above the welded tuff member of the Canelo Hills Volcanics in

the northwest quarter of sec. 27. In central Lone Mountain, the tuff

is hidden by a h ill of alluvium, but is again exposed in the center of

sec. 35 where it is in fault contact with conglomerates of the upper

unit. To the southeast, the tuff gradually thins and pinches out

against a minor fault. This distinctive tuff is also present in the

repeated conglomerate sequence, south of Lone Mountain. The tuffs

within the conglomerates at Lone Mountain are sim ilar to those exposed

at Canelo Pass and in the Parker Canyon area of the Canelo Hills.

Red-orange sandstone beds intercalated with the tuffs are 20

to 50 cm in thickness, are of sublitharenite composition and display

both shallow trough cross-stratification and parallel laminations.

These sandstones resemble orange sublitharenites interbedded with

limestone- and volcanic-pebble conglomerates of the "Mount Hughes

Formation" at Canelo Pass (Fig. 32). Volcanic-pebble conglomerates

interbedded with the tuffs and sandstones at Lone Mountain are

composed of subangular clasts of varicolored porphyritic tuff enclosed 92

Fig. 32. Subarkosic Sandstone, Middle Unit of the Glance Conglomerate Northern Lone Mountain \

93 in a reddish purple sandy matrix (Pig. 33). Like the orange sandstones and welded tuffs, the volcanic-pebble conglomerates resemble

conglomerates of the "Mount Hughes Formation" in the Canelo H ills.

Upper Unit. The upper unit consists of a coarsening-upward package of

dominantly volcanic conglomerate, which reaches a maximum thickness of

320 m along central Lone Mountain. Numerous lenticular beds of pale

red, shallow trough-crossbedded sandstones are locally present near

the base of the unit (Fig. 34). Upsection the conglomerate becomes

more poorly bedded and very poorly sorted, clasts are pebble to

boulder size, and some boulders exceed 2 m in diameter (Fig. 35). To

the northwest, the unit is finer grained in central Lone Mountain a

mixed limestone and volcanic-clast conglomerate overlies the volcanic

pebble to cobble conglomerate. In central sec. 35, conglomerates of

the upper unit are faulted against conglomerates of the middle unit

which are directly overlain by Morita Formation. Two slivers of

conglomerate exposed in small fault blocks in this area are composed

of conglomerate of the upper unit which also grade upward into the

Morita Formation (Fig. 29).

The basal conglomerate of the upper unit is dominantly

composed of subangular pebbles of gray silicified tuff, clast

diversity increases upsection and includes: light gray porphyritic

tuff with phenocrysts of quartz, feldspar and biotite, dusky red

porphyritic tuff with abundant feldspar phenocrysts, red and gray

flow-banded rhyolite, pale red tuff and light purple tuff containing

sparse feldspar phenocrysts. These lithologies are all derived from 94

Fig. 33. Volcanic Pebble Conglomerate, Middle Unit of the Glance Conglomerate, Northern Lone Mountain 95

Fig. 34. Sandy Conglomerate, Basal Part of the Upper Unit of the Glance Conglomerate, Northern Lone Mountain 96 97 underlying tuffs of the middle unit or from the Canelo Hills

Volcanics. At the southern end of Lone Mountain, conglomerates

resting above the andesite flow in the Bear Creek area are identical

to fine basal conglomerates of the upper unit. In both areas the unit

is conformably overlain by the Morita Formation, which can be

recognized by a series of unique marker beds here called the Morita

transition zone.

Morita Transition Zone. The distinctive sequence of beds composing

the Morita transition zone is everywhere present at depositional,

gradational contacts between Glance Conglomerate and the interbedded

sandstones and mudstones of the Morita Formation. Figure 36

illustrates the stratigraphy of the transition zone as observed at

Lone Mountain, Wakefield Camp, and in the northern Canelo Hills. The

transition zone can be traced the entire length of Lone Mountain. It

has also been identified in fault blocks just south of Lone Mountain.

Three distinctive lithologies are found at the contact:

A) Maroon mudstones containing scattered nodules and stringers

of limestone of replacement origin are commonly associated with the

transition zone (Fig. 37). The limestone nodules are often encrusted

by light pink silica, a feature distinguishing them from limestone

pebbles derived from the Permian basement. Where these limestone

nodules weather out of the mudstone in areas of poor exposure, they

help to identify the Glance Conglomerate-Morita contact.

B) The limestone nodules and stringers locally thicken and

coalesce upsection to form beds of laminated limestone up to 70 cm lone m t n . n o . BEAR CREEK WAKEFIELD CAMP

OF MONTEZUMA PA SS RO. S O . CENTRAL LONE MTN. SO. LONE MTN. %W. HUACMUCA MTS.

i f l * c

w*» ■ IBMOO

F ig . 36 . Measured Sections, Morita Transition Zone A—Maroon mudstone with limestone nodules B—Laminated limestone - often contai ning chert C—Sandy pebble conglomerate 99

Fig. 37. Maroon Mudstone with Limestone Nodules, Morita Transition Zone

(Lithology A of Fig. 36) 100 thick (Fig. 38). Coarse sand-size grains of volcanic rock and quartzite are common in these laminated lim estones which commonly contain bands of red, green, or black chert (Fig. 39). These sandy, unfossiliferous, silica-rich limestone beds resemble fossil caliche profiles described by Steel (1974).

C) The third lithology unique to the Morita transition zone is a sandy pebble conglomerate. The light gray, resistant beds of coarse sand grains and very fine pebbles range from 50 cm t o 90 cm i n thickness and are composed of lim estone pebbles reworked from the caliche profiles; pink, red and green chert; pale red and gray silicified tuff; and gray to brown quartzite. The relatively w ell- sorted nature of these conglomerates distinguishes them from the underlying Glance Conglomerate.

Southern Lone Mountain

Conglomerate exposed at the southeastern end of Lone Mountain was mapped by Hayes and Raup (1968) as Glance Conglomerate. A section

315 m thick was measured where this conglomerate rests depositionally on the welded tuff member of the Canelo H ills Volcanics and is overlain conformably by Morita Formation (Fig. 40). The depositional nature of the lower contact was recognized by Hayes and Raup (1968),

who extended it for approximately 750 m to the west-northwest before truncating it against a west-trending normal fault (Fig. 27). The

contact, however, can be traced confidently beyond this point without

evidence of faulting through sections 35 and 36 to the Mud Spring area

of central Lone Mountain (Fig. 28, 29). 101

Fig. 39. Laminated Limestone Bed with Chert, Morita Transition Zone (Lithology B of Fig. 36) 102

SOUTHERN LONE MOUNTAIN

Total 315m

Merits Fm.

Sandy volcanic-clast egl Andesite flow

m Mixed-clast egl with ss lenses

meters 100 Volcanic-clast egl

Tuffaceous ss 50 - Tuff breccia

< r v Welded Tuff Member, Canelo Mills Volcanlcs 0-J

P ig . 40 Measured Section, Southern Lone Mountain 103 A volcanic flow breccia composed of angular clasts of porphyritic pinkish orange tuff and reddish brown rhyolite is present immediately above the welded tuff member of the Canelo Hills

Volcanics. This breccia and overlying thin-bedded pale red and green tuffaceous sandstones are characteristic of the basal Glance

Conglomerate contact, and are sim ilar to those locally observed at the

conglomerate-welded tuff contact at northern Lone Mountain (Fig. 41).

A massive volcanic cobble to boulder conglomerate containing clasts up

to 3.6 m in diameter channels into the tuffaceous sandstone and

volcanic breccia exposed in Lone Mountain Canyon. About 200 m to the

northwest, this conglomerate contains limestone and quartzarenite

clasts in addition to volcanic clasts, and channels through the

sandstone and breccia into the welded tuff member of the Canelo H ills

Volcanics. Conglomerates in this area also contain boulder-size

clasts of heterogeneous carbonate-clast conglomerate with a tan

crystalline calcite matrix, sim ilar to conglomerates described in the

lower Glance Conglomerate of the central Huachuca Mountains (Fig. 42).

Moving down Bear Creek and upsection, poorly bedded volcanic

pebble to cobble conglomerate containing several lenses of pale red

volcanic litharenite sandstone with poorly defined shallow trough

cross-bedding are present. Clast diversity increases upsection, both

among volcanic and sedimentary lithologies. Clasts of limestone and

orange sublitharenite sandstone become common approximately 100 ra from

the base of the section. Clasts of altered porphyritic tuff and fine

crystalline volcanics, both rich in secondary chlorite and epidote are

common in the poorly bedded, poorly sorted conglomerate exposed along 104

Fig. 41. Basal Contact, Glance Conglomerate on Welded Tuff Member of the Canelo Hills Volcanics, Southern Lone Mountain (tuff breccia on right, tuffaceous sandstone on left)

Fig. 42. Boulder of Carbonate-clast Conglomerate within the Lower Part of the Glance Conglomerate, Southern Lone Mountain 105 Bear Creek. Near the junction between Bear Creek and the Montezuma

Pass-Parker Canyon Road, sandstone interbeds occur more frequently and the conglomerate is composed of 60% volcanic clasts of mixed lithologies and 40% limestone clasts, predominantly of Permian types.

Rare pebbles of chert and quartzite are also present (Fig. 43).

A dark purple to reddish purple aphanitic andesite flow is ii interbedded in the upper conglomerates just south of the Montezuma

Pass-Parker Canyon Road bridge, in the northern half of sec. 1.

Approximately 30 m thick where it is exposed in Bear Creek, the flew can be traced to the northwest into the southwest quarter of sec. 36

where it grades laterally into an andesite flow breccia and eventually

pinches out. The andesite maintains a flow banded base and vesicular

top as it thins to the northwest, indicating a primary depositions!

thinning of the unit in this direction, rather than an erosional or

tectonic truncation.

The nearly monolithologic sandy pebble conglomerate above this

andesite flow is composed of subangular gray silicified tuff clasts in

a sandy volcanic—litharenite matrix. Shallow trough cross-stratified

sandstone beds are present near the base. This conglomerate is

identical to conglomerates in the basal part of the upper unit at

northern Lone Mountain. Although 20 m thick in Bear Creek, this

conglomerate steadily thins to the northwest and, like the andesite

flow beneath it, eventually pinches out. The thinning of the andesite

and overlying conglomerate indicates the presence of a paledhigh

northwest of the Bear Creek section. Since the lowermost coarse

conglomerate of the Glance Conglomerate is continuous over this 106

Fig. 43. Mixed-clast Conglomerate, Glance Conglomerate, Southern Lone Mountain 107 paleohigh, it must have been created by syndepositional faulting during Glance Conglomerate deposition.

Calcareous maroon mudstones, gray pebble conglomerates and silica-rich limestone beds of the Morita transition zone are well exposed in Bear Creek. The transition zone is appreciably thicker in this area, as are the individual cross-bedded and bioturbated sandstone packages of the basal Morita Formation (Fig. 36).

Age C o n s tra in ts

Biotite from the welded tuff member of the Canelo H ills

Volcanics at Lone Mountain has yielded a 169+6 m.y. K-Ar date (Marvin and others, 1978). This age is statistically concordant with the

177+8 m.y. date (K-Ar, biotite) obtained from the welded tuff member

in the Canelo Hills.

The welded tuffs and interbedded conglomerates of Lone

Mountain were originally mapped as the "lower" member of the Canelo

H ills Volcanics, and yielded radiometric dates younger than what Hayes

an others (1965) expected on the basis of their inferred stratigraphy.

These "aberrant" dates were attributed to alteration of the biotite

and loss of argon (Hayes, 1970a; Drewes, 1971). Since the

conglomerates and interbedded welded tuffs of Lone Mountain are now

recognized to lie depositionally above the Canelo Hills Volcanics, the

available radiometric dates are no longer inconsistent with the

stratigraphy. Marvin and others (1978) report a 147+6 m.y. K-Ar date

for biotite and a 149+11 m.y. Rb-Sr isochron date for one of the

welded tuffs at Lone Mountain. Both of these dates are statistically 108 ■ concordant with the 151+2 m.y. date obtained from tuffs interbedded with "Mount Hughes Formation" in the northern Canelo H ills (Kluth and others, 1981). Attempts at dating the andesite flow within the conglomerate at Bear Creek have been unsuccessful, but its relative stratigraphic position suggests a latest Jurassic or earliest

Cretaceous age.

Clasts of carbonate-clast conglomerate sim ilar to that exposed in the lower Glance Conglomerate of the central Huachuca Mountains are present within the basal Glance Conglomerate of southern Lone

Mountain. Such clasts suggest that older Glance Conglomerate sections have been reworked into younger sections, inferring that the Late

Jurassic conglomerates at Lone Mountain may not be the oldest exposures of Glance Conglomerate in southeastern Arizona.

It is unknown how much time is represented by the Morita transition zone. Fossil caliches are usually associated with stable alluvial fan and floodplain depositional environments (Steel, 1974).

Today caliche forms in arid to semi-arid climates which receive 10-60 2 5 cm. of annual precipitation and takes from 10 to 10 years to develop in areas of high surface stability or non-sedimentation.

Local relief hinders the process, but availability of a nearby source of CaCOg can accelerate it (Steel, 1974). M ultiple caliche profiles

such as those seen at Bear Creek and reworked horizons noted at Lone

Mountain indicate that the Morita transition zone is a condensed

stratigraphic section. The section could represent much of Early

Cretaceous time, however, since CaCOg was readily available from both 109 the Paleozoic basement and the lim estone-clast conglomerates , th e tim e represented by the zone may be appreciably shorter.

Summary

Detailed mapping at Lone Mountain has demonstrated the lateral equivalence of the Glance Conglomerate and "lower" member of the

Canelo H ills Volcanics. The "lower" member of the Canelo H ills

Volcanics lies depositionally on the welded tuff member at Lone

Mountain and in the Canelo H ills, where Kluth (1982) applied the name

"Mount Hughes Formation". Radiometric dates on tuffs from the "Mount

Hughes Formation" and "lower" member of the Canelo H ills Volcanics at

Lone Mountain are statistically concordant. This along with their lithological sim ilarity indicates that these units are correlative.

Ransome (1904) first proposed the name Glance Conglomerate for mid-

Mesozoic, coarse-grained conglomerates resting conformably below Lower

Cretaceous carbonates (Mural Limestone) and unconformably above

Precambrian to Jurassic rocks in southeastern Arizona. Since this

name has priority, the above correlated units should all be considered

Glance Conglomerate. CHAPTER 5

DISCUSSION

Mid-Mesozoic conglomerates and interbedded welded tuffs assigned to the "lower" member of the Canelo H ills Volcanics in southeastern Arizona (Hayes and others, 1965; Hayes, 1970a), and more recently to the "Mount Hughes Formation" in the Canelo Hills (Kluth,

1982), are here assigned to the Glance Conglomerate.

Evidence for Correlation

M isinterpretation of the stratigraphy of the Canelo Hills

Volcanics, the supposed late Early Cretaceous age of the Glance

Conglomerate, and the lack of volcanic units and abundant volcanic detritus in the type area of the Glance Conglomerate, hindered the recognition of the "Mount Hughes Formation" or "lower" member of the

Canelo H ills Volcanics as Glance Conglomerate. Several lines of

evidence now support this correlation.

Stratigraphic Relationships

The mid-Mesozoic conglomerates discussed in this study are all

found in the same relative stratigraphic position. The "Mount Hughes

Formation" or "lower" member of the Canelo H ills Volcanics and the

Glance Conglomerate both rest depositionally on rocks of Precambrian

to Jurassic age. The youngest dated underlying rocks include the

welded tuff member of the Canelo Hills Volcanics, which yields dates

of 177+8 m.y. in the Canelo H ills and 169+6 m.y. at Lone Mountain, and

1 1 0 I l l the Huachuca Quartz Monzonite in the central Huachuca Mountains, which has been dated at 167+6 m.y. (Marvin and others, 1978). At southern

Lone Mountain, the Glance Conglomerate apparently concordantly overlies the welded tuff member of the Canelo Hills Volcanics. This relationship seems to indicate that locally, no unconformity exists at the base of the Glance Conglomerate.

The identification of a series of interbedded cross-stratified and burrowed arkosic sandstones and maroon mudstones at Red Meadow in the Canelo H ills as the Morita Formation indicates that the "Mount

Hughes Formation" of the Canelo H ills, like the Glance Conglomerate of the central Huachuca Mountains, is depositionally overlain by the fine-grained sediments of the Bisbee Group. In addition, the former

"lower" member of the Canelo H ills Volcanics at Lone Mountain was observed to interfinger with mudstones of the Morita Formation. Thus, the conglomerates studied lie stratigraphically above a thick Jurassic volcanic sequence and below interbedded mudstones and sandstones of the Morita Formation.

Lithologic Character

The lithologic sim ilarity of the "Mount Hughes Formation" or

"lower" member of the Canelo H ills Volcanics to the Glance

Conglomerate was previously noted by Denney (1971), who tentatively correlated the Canelo Pass conglomerates with Glance Conglomerate outcrops in the central and northern Huachuca Mountains. This present study was originally designed to identify mappable lithologic differences within these conglomerates, but such an undertaking proved 1 1 2 impossible because of marked local variations in thickness, composition and texture. In overall character, however, the local variations in thickness, texture and composition are similar in all the conglomerates studied.

The Glance Conglomerate of the Huachuca Mountains is 90 m to

1400 m thick, but elsewhere thicknesses of up to 2000 m have been recorded (Bilodeau, 1982). The "Mount Hughes Formation" of the Canelo

H ills, here correlated with the Glance Conglomerate, is up to 600 m thick, which is a combined thickness of the upper three members (the

"Monkey Canyon Member" is not confidently correlated with the Glance

Conglomerate as discussed below). The "lower" member of the Canelo

H ills Volcanics at Lone Mountain ranges from 250 m to 900 m in thickness; the latter thickness was measured in central Lone Mountain where all three conglomerate subunits are present. Lateral variation in thickness over short distances is not unusual for any of the conglomerates studied, and is one of the major characteristics described for the Glance Conglomerate by Bilodeau (1979).

The textural .characteristics of the conglomerates are

strikingly sim ilar. They are generally poorly bedded, very poorly

sorted, clast-supported conglomerates consisting of subangular to

subrounded clasts. Lenticular bedding, channel-fillings and matrix-

supported beds are commonly observed in outcrop. The collective clast

suite consists of pebble to boulder-size clasts of Precambrian schist

and granite. Paleozoic sedimentary rocks, and Jurassic intrusive,

extrusive and sedimentary rocks. Although individual sections contain 113 only one or two dominant clast types, clast composition in the conglomerates varies both laterally and vertically and even alternates between stratigraphically juxtaposed beds. Clasts in the thicker, coarser sections of conglomerate are often enclosed in a silicified rind of matrix sediment, perhaps indicating a sim ilar diagenetic history. Very large exotic blocks derived from the Permian Colina,

Scherrer and Concha Formations as well as the underlying Jurassic volcanic sequence have been incorporated into the conglomerates and their interbedded volcanic units in both the Canelo H ills and the

Huachuca Mountains.

Sandstones interbedded with the conglomerates are commonly volcanic litharenite in compositon. However, beds of quartzarenite, sublitharenite and subarkose are locally present in the conglomerates of the Canelo H ills and at Lone Mountain. The volcanic litharenite sandstones commonly display parallel-lam ination and shallow trough cross-stratification. Thick sequences of the more mature sandstone types show large scale (1 to 3 m) cross-stratification. These better sorted and rounder sandstones are more common in the Canelo H ills outcrops, although they are present in the middle conglomerate unit at

Lone Mountain. Mudstones are rare within the conglomerates, but occur sparingly as thin beds associated with fining upward sandstone

sequences in the former "Dark Canyon Member" of the "Mount Hughes

Formation" and in the andesite member and upper member of the Glance

Conglomerate in the central and southern Huachuca Mountains.

The Glance Conglomerate of the central and southern Huachuca

Mountains contains thin silicic welded ash flow tuffs, andesite flows 114 and volcanic flow breccia. Glance Conglomerate desribed at Lone

Mountain contains a single andesite flow in southeastern exposures, and eight or more welded tuffs in northwestern exposures.

Intercalated volcanic rocks in the Glance Conglomerate of the Huachuca

Mountains were once considered unique (Hayes, 1970a); however,

Bilodeau (1979) correlated the Temporal and Bathtub Formations described by Drewes (1971) in the Santa Rita Mountains with the Glance

Conglomerate. These formations also contain intercalated rhyolite tuffs and andesite flows. At least eight welded tuffs and several volcanic flow breccias have been identified within the "Mount Hughes

Formation" of the northern Canelo Hills and three or four welded tuffs were observed in sediments mapped as "lower" member of the Canelo

H ills Volcanics in the southern Canelo H ills. Apparently, volcanic interbeds are not unusual in the Glance Conglomerate and its correlative formations, and are in fact common in western outcrops. A westward increase in volcanic interbeds is also noted in Glance

Conglomerate outcrops of northern Sonora, Mexico (Hayes, 1970b).

Field Relationships

The "Mount Hughes Formation" or "lower" member of the Canelo

Hills Volcanics and the Glance Conglomerate have never been mapped in

stratigraphic juxtaposition. The Glance Conglomerate was not recognized on Kluth's (1982) map of the northern Canelo H ills, and was

thought not to be exposed in that area despite its presence in the

surrounding Patagonia, Santa R ita, Empire, Whetstone, and Huachuca

Mountains. Ironically, wherever the "lower" member of the Canelo 115 Hills Volcanics or the "Mount Hughes Formation" has been mapped, the

Glance Conglomerate was supposedly not exposed due to faulting or

erosion, conversely, where the Glance Conglomerate has been mapped,

the "lower" member of the Canelo H ills Volcanics was faulted out or

missing along a supposed unconformity. The only locality where both

units are present is on the southwest flank of Lone Mountain where

they were mapped in structural juxtaposition. A high angle normal

fault was mapped by Hayes and Raup (1968) separating conglomerates

containing welded tuff from identical conglomerates containing a thin

andesite flow. The former were mapped as "lower" member of the Canelo

Hills Volcanics and the latter as Glance Conglomerate. In order for

the "lower" member to be in its position above the "middle" welded

tuff member of the Canelo H ills Volcanics, and below the Morita

Formation, faults were mapped at both its lower contact with the

welded tuff and upper contact with the Morita Formation.

Detailed mapping at Lone Mountain conducted for this study at

the 1:12,000 scale (Fig. 29) supports Kluth's (1982) revision of the

Canelo Hills Volcanics stratigraphy. What had originally been mapped

as the "lower" sedimentary member of the Canelo H ills Volcanics by

Hayes and Raup (1968) clearly rests depositionally on the underlying

welded tuff member and is depositionally overlain by the Morita

■. Formation. In addition, the "lower" member of the Canelo Hills

Volcanics can be traced directly into the Glance Conglomerate

originally mapped by Hayes and Raup (1968) at the southeast end of

Lone Mountain. The lower contact of the conglomerate on welded tuff

of the Canelo H ills Volcanics and the upper contact with the Morita 116 Formation can both be traced into their counterparts above and below the originally mapped Glance Conglomerate.

Conclusions and Implications

Since the Glance Conglomerate and the "lower" sedimentary member of the Canelo H ills Volcanics, renamed the "Mount Hughes

Formation" in the northern Canelo Hills, are indistinguishable, these conglomerates should be considered a single formation. The name

Glance Conglomerate, first proposed by Ransome (1904) for the reddish conglomerate at the base of the Bisbee Group has priority over all other names applied to the mid-Mesozoic conglomerates discussed in this study. Therefore, this name should be expanded to include outcrops of the "Mount Hughes Formation" and the "lower" member of the

Canelo H ills Volcanics. As a result, the Canelo H ills Volcanics is restricted to a predominantly volcanic sequence as its name implies.

To avoid confusion, the "middle " rhyolite flow member and "upper" welded tuff member of the Canelo H ills Volcanics should be referred to only by their compositional names and the incorrect "middle" and

"upper" prefixes dropped (Fig. 44).

"Monkey Canyon Member"

Lithologies sim ilar to those of the "Dark Canyon", "Canelo

Ridge" and "Canelo Pass" members of the "Mount Hughes Formation" have all been identified within the Glance Conglomerate although often in variable stratigraphic order. The correlation of the "Monkey Canyon

Member" is not so apparent. This 150 m sequence of red mudstones. 117

A B

(Hayes, 1870) (Kkm. 1882)

MORTTA FM.

A#e##e#

149+11 S»-4# we 1 5U 2 *»-S#we

147±6

Bettes 4 0 0 -

4 0 0 - 300-

3 0 0 - fmmm (?)

100- Pmm* o. CARBOMATESh

Fig# 44. Revision of Mid-Mesozoic Stratigraphy, Southeastern A rizona 118 siltstones, and rounded pebble conglomerates is not recognized elsewhere in the Glance Conglomerate and may represent an older clastic sequence.

Kluth (1982) originally speculated on the equivalence of the

"Monkey Canyon Member" and the Gardner Canyon Formation, a 300 m thick series of red mudstone, sandy siltstone and volcanic-chert pebble conglomerate described by Drewes (1971) in the Santa Rita Mountains.

Like the "Monkey Canyon Member" the Gardner Canyon Formation rests unconformably on the Rainvalley Formation and older Permian limestones

(Drewes, 1971); its relationship with the Mount Wrightson Formation, a thick volcanic sequence in the Santa Rita Mountains, is uncertain, but

it is believed to contain pebbles of Mount Wrightson lithologies

(Drewes, 1971). A Pb-alpha date of approximately 192 m.y. from

dacites interbedded (possibly intrusive) in the Gardner Canyon

Formation was reported by Drewes (1971), and a 170+35 m.y. Pb-alpha

date was obtained from interbedded volcanic rocks in the Gardner

Canyon Formation of the Empire Mountains (Marvin and others, 1973).

Recent discovery of a fossil tritylodont in the Gardner Canyon

Formation by J. Clark (personal communication, 1983) is consistent

with an Early Jurassic age. The Gardner Canyon Formation is

restricted to less than five square miles of scattered outcrops, and

its type area lies within the Sawmill Canyon fault zone. Apparently

conformably overlying the Gardner Canyon Formation in the Santa Rita

Mountains and the Empire Mountains are interbedded sandstones,

conglomerates and silicic volcanics of the "Mount Hughes Formation" or

"lower" member of the Canelo H ills Volcanics (Drewes, 1971? Finnell, 119 1970). Because the volcanic members of the Canelo Hills Volcanics are not present northwest of the northern Canelo H ills and the Gardner

Canyon Formation and the Mount Wrightson Formation are not known to the southeast of the Santa Rita and Empire Mountains, the stratigraphic relationships between these units and the "Monkey Canyon

Member" are uncertain.

Geochronology

Age dates obtained from the interbedded welded ash flows of the Glance Conglomerate in the Canelo H ills and at Lone Mountain indicate that Glance deposition extended back into Late Jurassic time.

A paleomagnetic study of the welded tuffs interbedded with the "Mount

Hughes Formation", now considered Glance Conglomerate, in the Canelo

Hills resulted in a paleopole which falls on the North American apparent polar wander path between poles from the Summerville and lower Morrison Formations, indicating an approximate age of 150 m.y. for these volcanic rocks. A whole rock Rb-Sr age of 151+2 m.y. determined from the same series of tuffs, confirms the paleomagnetic results (Kluth and others, 1982). This age is concordant with 147+6 m.y. (K-Ar, biotite) and 149+11 m.y. (Rb-Sr, whole rock) dates for welded tuffs interbedded with the Glance Conglomerate at Lone

M ountain.

The Glance Conglomerate is not entirely of Early Cretaceous age as suggested by previous workers. Not only does it extend back

into the Jurassic, but it may be entirely of Jurassic age in the

Canelo H ills and Huachuca Mountains. The widespread unconformity 1 2 0 separating Jurassic from Cretaceous rocks discussed by Hayes (1970b),

Bilodeau (1979) and Hayes and Drewes (1978) should no longer be considered a regional feature and may nowhere exist if the basal

Glance is everywhere Jurassic. The pre-Glance unconformity represents a portion of Jurassic time, rather than early Cretaceous time, therefore the base of the Glance Conglomerate can no longer be considered the horizon at which Cretaceous deposition begins. The

Jurassic-Cretaceous period boundary lies within the uppermost Glance

Conglomerate or the basal Horita Formation of the area studied, demonstrating that in southeast Arizona, as in central Mexico, lower

Cretaceous rocks lie with apparent conformity on Upper Jurassic strata

(Cordoba and others, 1971).

The revised age of the Glance Conglomerate im plies that the age of the lower Morita Formation may be older than previously estimated. An Aptian-Albian invertebrate fauna was described from the lower Mural Limestone, which is interbedded with the uppermost Morita

Formation in the Huachuca and Mule Mountains (Stoyanow, 1949). The late Early Cretaceous age of the unfossilif erous Morita Formation, which is up to 2 km thick in the Huachuca Mountains, is based on this relationship. Undoubtedly, the uppermost Morita beds are of Aptian age, but it remains uncertain how much time is represented by Morita sediments, the transition zone at the base of the Morita Formation, and the uppermost conglomerates above the volcanic units dated at

approximately 150 m.y.

The transition zone between the Glance Conglomerate and the

Morita Formation represents a condensed stratigraphic sequence. 1 2 1 although the length of time it represents is unknown. Steel (1974) estimates that caliche profiles take from 10^ to 10^ years to develop, depending on the availability of carbonate in the environment. It is concievable that the multiple caliche profiles and possible reworked profiles of the transition zone may represent a considerably longer period of time. Since the upper Glance conglomerates were probably deposited rapidly, it is not unreasonable to suggest that the transition zone and overlying Morita Formation represent most of Early

Cretaceous time, and may extend back into latest Jurassic time.

Depositional Environment

Although included as the basal formation of the Bisbee Group, the Glance Conglomerate is not necessarily related to the

transgressive facies of the Bisbee Sea, but represents alluvial fan

deposits that were shed into local fault-bounded basin's (Bilodeau,

1982). Thick accumulations of coarse pebble to boulder conglomerate,

with matrix-supported horizons represent proximal fan deposition,

alternating trough cross-stratified sandstones and finer pebble

conglomerates are indicative of mid-fan stream flow deposition, and

the large-scale cross-stratification of subarkosic and sublitharenite

sandstones of the northern Canelo Hills are characteristic of a distal

fan environment. Such texturally mature sands have been attributed to

the reworking of alluvial sediments by both braided stream and eolian

processes at fan margins (Cant, 1982; Nilsen, 1982).

Progradational cycles over 200 m thick are recognized in the

upper unit conglomerates at Lone Mountain, the conglomerates at Red 12 2 Meadow and the sandstone to conglomerate sequence at Canelo Ridge.

Such cycles probably represent outbuilding of alluvial fans along tectonically active basin margins (Miall, 1978).

The conglomerates studied all show rapid lateral and vertical

changes in clast composition over distances of less than a kilometer.

These lateral changes in clast composition are the result of

intertonguing of separate fans, each draining an individual source

region. Clastic wedges composed of such coalesced alluvial fan

deposits are commonly developed at the margins of fault-bounded basins

(N ilsen,1982).

Paleocurrent data derived from channel orientations, clast

imbrications, cross-stratification and bedding plane current

lineations in the Canelo H ills and at Lone Mountain have been combined

with data previously collected by'Bilodeau (1979) and Davis and others

(1979). Although no patterns are clearly evident in this preliminary

data, it is interesting to note that flow directions from the former

"lower" member and "Mount Hughes Formation" are not clearly different

from directions within the originally mapped Glance Conglomerate (Fig.

45). These paleocurrents are consistent with Davis and others (1979)

hypothesis that debris was shed off major northwest trending faults of

Jurassic age.

The fluvial deposits of the Morita Formation reflect

moderately stable crustal conditions associated with a northwest­

trending paleotroughi through which a shallow sea advanced from the

southeast, inundating the area by late Aptian time. If the basal

Morita Formation is of latest Jurassic age, the development of this 123

WHETSTONE MTS.

EXPLANATION

Paleocurrent Roses

23 Total measurements 4 Measurements per 30* interval: — >20 ------10—20 — — — •4 — 10 * - - - < 4

Structure Symbols

Anticline-arrow shows direction of plunge

Syncline- arrow shows direction of plunge

54 / Fault-dashed where approximate, dotted where inferred

miles

Fig. 45. Map of Study Area and V icin ity Showing Major Northwest-Trending Fault Systems and Paleocurrent Data from the Glance Conglomerate (Modified from Drewes, 1981; with data from Davis and others, 1979, and Bilodeau, 1979) 124 trough, the Bisbee basin, is coincident with the timing of marine transgressions in northern Mexico associated with rifting in the Gulf o f Mexico.

Tectonic Environment

U plift along basin margins may have been caused by differential vertical movement on reactivated northwest trending fault traces of pre-Jurassic, possibly Precambrian origin (Titley, 1976;

Davis, 1981; Drewes, 1981). Coarse breccias and boulder conglomerates were derived from uplifted blocks to form alluvial fans composed of locally derived clasts along the basin margins. Landslides and debris flows associated with active volcanism resulted in the emplacement of large Paleozoic exotic blocks within the section (Simons and others,

1966; Davis and others, 1979). Continued uplift and erosion caused the development of sedimentary wedges of coalesced alluvial fanglomerate and may have resulted in the reworking of earlier deposited conglomerate units as suggested by the boulders of

carbonate-clast conglomerate within the lower Glance Conglomerate at

Bear Creek. Intraformational unconformities recognized in the Glance

Conglomerate and its equivalents in the Santa Rita Mountains and

Canelo Hills and syndepositional normal faulting discussed by Bilodeau

(1979) in the Mule, Empire and Santa Rita Mountains and here

recognized w ithin the Glance Conglomerate at Lone Mountain suggest

continuous tectonic activity through Late Jurassic time.

A northwest-trending magmatic arc existed in southeast Arizona

between latest Triassic (?) and Late Jurassic time. By the Early 125 Cretaceous the arc had migrated southwest to the continental margin

(Coney, 1978). Therefore, the latest Jurassic to earliest Cretaceous can be considered a period of transition between sedim entation in a magmatic arc environment and sedim entation in a northw est-trending subaerial trough. Bilodeau (1979, 1982) and Bilodeau and Lindberg

(1983) interpreted the Glance Conglomerate as a backarc deposit based on its supposed Early Cretaceous age. Alternatively, the development of this trough may be related to regional tectonics associated with plate reorganizations in the Gulf of Mexico—Caribbean Sea area

(Coney, 1983).

Other coarse clastic units and interbedded volcanic rocks

mapped as "Triassic to Jurassic" in southeastern Arizona, may be

Glance Conglomerate. Re-examination of such outcrops in the Santa

Rita, Empire, Mustang and Patagonia Mountains, might lead to an

improved understanding of the nature and extent of Glance Conglomerate

d e p o s itio n REFERENCES CITED

Bilodeau, W. L., 1979, Early Cretaceous tectonics and deposition of the Glance Conglomerate, southeastern Arizona: unpublished Ph.D. dissertation, Stanford University, 145 p.

Bilodeau, W. L., 1982, Tectonic models for Early Cretaceous rifting in southeastern Arizona: Geology, v. 10, p. 466-470.

Bilodeau, W. L., 1983, Reply on "Tectonic models for Early Cretaceous rifting in southeastern Arizona": Geology, v. 11, p. 365-366.

Bilodeau, W. L., and Lindberg, F. A., 1983, Early Cretaceous tectonics and sedimentation in southern Arizona, southwestern New Mexico and northern Sonora, Mexico, in Reynolds, M. W. and Dolly, E. D., eds., Mesozoic Paleogeography of W est-Central United States, Rocky Mountain Section, S.E.P.M., p. 173-188.

Cant, D. J., 1982, Fluvial facies models and their application, in Scholle, P. A., and Spearing, D., eds.. Sandstone Depositions! Environments, Am. Assoc. Petroleum Geologists Mem. 31, p. 115- 137.

Cetinay, H. T., 1967, The geology of the eastern end of the Canelo H ills, Santa Cruz Co., Arizona: U niversity of Arizona, unpublished M.S. thesis, 54 p.

Coney, P. J., 1983, Un modelo tectonico de Mexico y sus relaciones con America del Norte, America del Sur y el Caribe: Revista del Institute Mexicano del Petroleo, v. 15, p. 7-15.

Coney, P. J., 1978, The plate tectonic setting of southeastern Arizona, in Callender, J. F., W ilt, J. C. and Clemons, R. E., eds.. Land of Cochise, New Mexico Geol. Soc., 29th Field Conf. Guidebook, p. 285-290.

Cooper, J. R., 1971, Mesozoic stratigraphy of the Sierrita Mountains, Pima County, Arizona: U. S. Geol. Survey Prof. Paper 658-D, 42 p.

Cordoba, D. A., Rodriguez-Torres, R., and Guerrero-Garcia, J., 1971, Mesozoic stratigraphy of the northern portion of the Chihuahua trough, in Seewald, L. and Sundeen, D., eds.. The Geologic Framework of the Chihuahua Tectonic Belt: West Texas Geol. Soc. Publ. 71-59, p. 83-97.

126 127 Damon, P. E., Shafiqullah, M. and Clark, K. F., 1981, Age trends of igneous activity in relation to metallogenesis in the southern Cordillera, in Dickinson, W. R., and Payne, W. D., eds., Relation of Tectonics to Ore Deposits in the Southern Cordillera, Ariz. Geol. Soc. Digest, v. 14, p. 137-154.

Davis, G. H., 1979, Laramide folding and faulting in southeastern Arizona: Am. Jour. Sci., v. 279, p. 543-569.

Davis, G. H., 1981, Regional strain analysis of the superposed deformations in southeastern Arizona and the eastern Great Basin, in Dickinson, W. R., and Payne, W. D., eds.. Relations of Tectonics to Ore Deposits in the Southern Cordillera, Ariz. Geol. Soc. Digest, v. 14, p. 155-172.

Davis, G. H., P hillips, M. P., Reynolds, S. J. and Varga, R. J., 1979, Origin and provenance of some exotic blocks in lower Mesozoic red-bed basin deposits, southern Arizona: Geol. Soc. America Bull., Part 1, v. 90, p. 376-384.

Denney, P. P., 1968, Geology of the southeast end of the Paleozoic portion of the Canelo H ills, Santa Cruz Co., Arizona: University of Arizona unpublished M.S. thesis, 105 p.

Denney, P. P., 1971, Relation of fossil landslides to geologic structure, Canelo H ills, Arizona: Ariz. Geol. Soc. Digest, v. 9, p. 213-233.

Dickinson, W. R., 1981, Plate tectonic evolution of the southern Cordillera, in Dickinson, W. R., and Payne, W. D., eds., Relations of Tectonics to Ore Deposits in the Southern Cordillera, Ariz. Geol. Soc. Digest, v. 14, p. 113-135.

Drewes, H. D., 1968, New and revised stratigraphic names in the Santa Rita Mountains of southeastern Arizona: U. S. Geol. Survey Bull. 1274-C, 15p.

Drewes, H. D., 1971, Mesozoic stratigraphy of the Santa Rita Mountains, southeast of Tucson, Arizona: U. S. Geol. Survey Prof. Paper 658-C, 81 p.

Drewes, H. D., 1981, Tectonics of southeastern Arizona: U. S. Geol. Survey Prof. Paper 1144, 96 p.

Drewes, H. D., and Cooper, J. R., 1973, Reconaissance geologic map of the west side of the Sierrita Mountains, Palo Alto Ranch Quadrangle, Pima Co., Arizona: U. S. Geol. Survey Misc. Field S tu d ie s Map MF-538.

Feth, J. H., 1947, The geology of the northern Canelo H ills, Santa Cruz Co., Arizona: U niversity of Arizona, unpublished Ph.D. dissertation, 150 p. 128 Feth, J. H., 1948, Permian stratigraphy and structure, northern Canelo H ills, Arizona: Am. Assoc, of Petroleum Geologists Bull., v. 32, p. 82-108.

Finnell, T. L., 1970, Preliminary geologic map of the Empire Mountains Quadrangle, Pima Co., Arizona: 0. S. Geol. Survey Open File Report 1971.

Hayes, P. T., 1970a, Mesozoic stratigraphy of the Mule and Huachuca Mountains, Arizona: 0. S. Geol. Survey Prof. Paper 658-A, 28 p .

Hayes, P. T., 1970b, Cretaceous paleogeography of southeastern Arizona and adjacent areas: U. S. Geol. Survey Prof. Paper 658-B, 42 p .

Hayes, P. T., and Drewes, H., 1978, Mesozoic depositional history of southeastern Arizona: New Mexico Geol. Soc. Guidebook, 29th Field Conf., Land of Cochise, p. 17-23.

Hayes, P. T., and Raup, R. B., 1968, Geologic map of the Huachuca and Mustang Mountains, southeastern Arizona: U. S. Geol. Survey Misc. Geol. Investigations Map 1-509.

Hayes, P. T., Simons, F. S., and Raup, R. B., 1965, Lower Mesozoic extrusive rocks in southeastern Arizona—the Canelo H ills Volcanics: U. S. Geol. Survey Bull. 1194-M, 9 p.

Kluth, C. F., 1982, The geology and mid-Mesozoic tectonics of the northern Canelo Hills, Santa Cruz Co., Arizona: University of Arizona unpublished Ph.D. dissertation, 245 p.

Kluth, C. F., 1983, Geology of the northern Canelo H ills and implications for the Mesozoic tectonics of southeastern Arizona, in Reynolds, M. W., and Dolly, E. D., eds., Mesozoic Paleogeography of the West-Central United States, Rocky Mountain Sec., S.E.P.M., p. 159-171.

Kluth, C. F., B utler, R. F., Harding, L. E., Shafiqullah, M. and Damon P. E., 1982, Paleomagnetism of Late Jurassic rocks in the northern Canelo H ills, southeastern Arizona: Jour. Geophys. Res., v. 87, p. 7079-7086.

Marvin, R. F., Naeser, C. W. and Mehnert, H. H., 1978, Tabulation of radiometric ages—including unpublished K-Ar and fission-track ages for rocks in southeastern Arizona and southwestern New Mexico, in Callender, J. F., W ilt, J. C., and Clemons, eds.. New Mexico Geol. Soc. Guidebook, 29th Field Conf., Land of Cochise, p. 243-252. 129 Marvin, R. F., Stern, T. W., Creasey, S. C., and Mehnert, H. H., 1973, Radiometric ages of igneous rocks from Pima, Santa Cruz and Cochise Cos., southeastern Arizona: U. S. Geol. Survey Bull. 1379, 27 p.

Miall, A. D., 1978, Tectonic setting and syndepositional deformation of molasse and other nonm arine-paralic sedimentary basins: Can. Jour. Earth Sci., v. 15, no. 10, p. 1613-1632.

Nilsen, T. H., 1982, Alluvial fan deposits, in Scholle, P. A., and Spearing, D., eds.. Sandstone Depositional Environments, Am. Assoc. Petroleum Geologists Mem. 31, p. 31-86.

Rangin, C., 1978, Speculative model of Mesozoic geodynamics, central Baja California to northeastern Sonora, Mexico, in Howell, D. ' G., and McDougall, K., eds., Mesozoic Paleogeography of the western United States: S.B.P.M., Pac. Sec., Pac. Coast Paleogeog. Symp. 2, p. 85-106.

Ransome, F. L., 1904, The geology and ore deposits of the Bisbee quadrangle, Arizona: U. S. Geol. Survey Prof. Paper 21, 168 p.

Schrader, F. C., 1915, Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona: U. S. Geol. Survey Bull. 582, 373 p.

Simons, F. S., 1972, Mesozoic stratigraphy of the Patagonia Mountains and adjoining areas, Santa Cruz Co., Arizona: U. S. Geol. Survey Prof. Paper 658-E, 23 p.

Simons, F. S., 1974, Geologic map and sections of the Nogales and Lochiel quadrangles, Santa Cruz Co., Arizona: U. S. Geol. Survey Misc. Invest. Series Map 1-762.

Simons, F. S., Raup, R. B., Hayes, P. T., and Drewes, H. D., 1966, Exotic blocks and coarse breccias in Mesozoic rocks of southeastern Arizona: U. S. Geol. Survey Prof. Paper 550-D, p. D12-D22.

Steel, R. J., 1974, Cornstone (fossil caliche)--its origin, stratigraphic, and sedimentological importance in the New Red Sandstone, Western Scotland: Jour. Geology, v. 82, p. 351- 369.

Stoyanow, A., 1949, Lower Cretaceous stratigraphy in southeastern Arizona: Geol. Soc. America Mem. 38, 169 p.

Titley, S. R., 1976, Evidence for a Mesozoic linear tectonic pattern in southeastern Arizona: Ariz. Geol. Soc. Digest, v. 10, p. 71-101.

111 m i l l 3 9C10 1III C1 1 8 4 9 3 4 9 7

UNIVERSITY OF ARIZONA LIBRARY

S p e c ia l Collections EXPLANATION

£ Qal Alluvium Z> S Contact between rock units o o o dashed where approximate ON c >- Mafic dike 0) a: O < Strike 8 Dip of bedding cr Microgranodior ite LU Overturned bedding h-

Vertical bedding Kfc Fort Crittenden Fm.

V) (showing direction of plunge) D Cintura Fm. O LU O < t- Kmu Mural Ls. S Fault- dashed where approximate LU a: o K m Morita Fm. A aZ Line of cross- section 1 Glance Conglomerate andesite ash flow tuff

V) CO < Canelo Hills Volcanics CL =) Welded tuff member Rhyolite flow member

T.23S Exotic blocks of Permian limestone

GEOLOGIC MAR of the LONE MOUNTAIN AREA Cochise County, Arizona

j z i

o LAUREL K. VEDDER c

mile

I kilometer

Scale: M2,000 Base enlarged from Miller Peak Contour Interval 25 feet 8 Huachuca Peak 7.5' U.SG.S. Topographic maps

Geology northeast of Lone Mountain Fault after Hayes 8 Raup (1968)

T.24S.

FIGURE 29 A

R 19 E. Laurel K. Vedder, M.S. Thesis Department of Geosciences University of Arizona, 1984

1800 'I 1700 --

1600- 1500- 5000

B m

Laurel K. Vedder, M.S. Thesis FIGURE 29B STRUCTURE SECTIONS Department of Geosciences University of Arizona, 1984