Upper Proterozoic and Cambrian 

Rocks in the Caborca Region, 

Sonora, Mexico Physical 

Stratigraphy, Biostratigraphy, 

Paleocurrent Studies, and 

Regional Relations

u.s. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1309
Upper Proterozoic and Cambrian 

Rocks in the Caborca Region, 

Sonora, Mexico Physical 

Stratigraphy, Biostratigraphy, 

Paleocurrent Studies, and 

Regional Relations

By JOHN H. STEWART, MARK A. S. McMENAMIN, 

and JUAN MANUEL MORALES-RAMIREZ

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1309

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1984
DEPARTMENT OF THE INTERIOR 

WILLIAM P. CLARK, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

Stewart, John Harris 1928-

Upper Proterozoic and Cambrian rocks in the Caborca region, Sonora, Mexico physical stratigraphy, biostratigraphy, 

paleocurrent studies, and regional relations.

(U.S. Geological Survey Professional Paper 1309)

Includes bibliographical references.

Supt. of Docs no.: I 19.16:1309

1. Geology, stratigraphic Precambrian. 2. Geology, stratigraphic Cambrian.3. Geology Mexico Heroica Caborca.

I. McMenamin, Mark A. S. II. Morales-Ramirez,Juan Manuel. III. Title. IV. Series: United States. Geological

Survey. Professional Paper 1309. 

QE653.S68 1984 551.7'15'097217 84-600060

For sale by the Distribution Branch, Text Products Section, 

U.S. Geological Survey, 604 South Pickett St., Alexandria, VA 22304
CONTENTS

Abstract. _____ 

Introduction __ 

Previous work _ 

Present studies

Page

1

1

2

3

Acknowledgments ________________________________ 3

Physical stratigraphy of upper Proterozoic and

Cambrian rocks ________________________________ 5

El Arpa Formation ____________________________ 7

Caborca Formation.___________________________ 10

Clemente Formation.__________________________ 10

Pitiquito Quartzite ____________________________ 11

Gamuza Formation-___________________________ 12

Papalote Formation ___________________________ 14

Tecolote Quartzite ____________________________ 15

La Cienega Formation _________________________ 15

Puerto Blanco Formation-______________________ 15

Proveedora Quartzite __________________________ 16

Page

Physical stratigraphy of upper Proterozoic and

Cambrian rocks Continued ______________________ 17

Buelna Formation ____________________________ 17

Cerro Prieto Formation ________________________ 17

Arrojos Formation ____________________________ 17

Tren Formation ______________________________ 17

Biostratigraphy _ _________________________________ 17

Paleocurrent studies ______________________________ 22

Regional correlations _____________________________ 25

Southern Great Basin _________________________ 25

San Bernardino Mountains _____________________ 28

Sierra Agua Verde ____________________________ 29

Tectonic and paleogeographic setting ________________ 30

Model A_____________.________________ 30

Model B_______________________________ 31

Model C____________________._______.__ 32

References cited _________________________________ 33

ILLUSTRATIONS

Page

FIGURE 1. Index map showing location of Caborca region, Mexico, and localities mentioned in text _________________ 1

2. Map of Caborca region, Mexico, showing locations of outcrops of upper Proterozoic and Cambrian rocks _ _ _ _ 2

3. Reconnaissance map of the Cerro Rajon area, Mexico _____________________________________________ 4

4. Chart showing correlation of nomenclature used in the Caborca region, Mexico ________________________ 6

5. Stratigraphic column in the Cerro Rajon area, Mexico-____________________________________________ 7

6. Photomicrograph of oolitic dolomite from the Clemente Formation, east side of Cerro Calaveras___-_______ 11

7. Photographs showing drag marks, and possible flute casts in in the Clemente Formation in the Cerro Rajon

area------__-__-_---_____----______--________________________________________________ 11

8. Photographs of conical stromatolites in the upper unit of the Gamuza Formation in the Cerro Rajon area __ 13

9. Diagram showing distribution of fauna and flora in upper Proterozoic and Cambrian strata in the Caborca

region, Mexico ________________________________________________________________________ 18

10. Photograph of possible metazoan trace fossils from unit 6 of the Clemente Formation, Cerros de la Cienega 20

11. Photograph of dimpled mound structure from unit 6 of Clemente Formation, Cerros de la Cienega-________ 20

12. Photograph of unornamented tabular shelly fossils from unit 1 of the La Cienega Formation in the Cerro

Rajon area ___________________________________________________________________________ 21

13. Map showing paleocurrent directions in upper Proterozoic and Lower Cambrian rocks in the Caborca

region, Mexico ________________________________________________________________________ 23

14. Map showing paleocurrent directions and paleogeography in the Western United States and northern

Mexico from Late Proterozoic to Late Cambrian time. ________________________________________ 24

15. Correlation chart for Middle Proterozoic to Cambrian rocks from California to Mexico ___________________ 26

16. Diagram showing correlation of part of the Clemente Formation and the Pitiquito Quartzite in the Caborca

region with part of the Johnnie Formation and the Stirling Quartzite in the Death Valley region_____ 27

17. Stratigraphic column in the Sierra Agua Verde, Sonora, Mexico ____________________________________ 30

18. Tectonic and paleogeographic models of the Southwestern United States and northern Mexico____________ 31

19. Map showing generalized distribution of the Zabriskie Quartzite in Nevada and California and of the

correlative Proveedora Quartzite in northern Mexico and possible left-lateral offset ________________ 32

in

UPPER PROTEROZOIC AND CAMBRIAN ROCKS 

IN THE CABORCA REGION, SONORA, MEXICOPHYSICAL STRATIGRAPHY, BIOSTRATIGRAPHY, 

PALEOCURRENT STUDIES, AND REGIONAL RELATIONS

By JOHN H. STEWART, MARK A. S. MCMENAMIN,' 

and JUAN MANUEL MORALES-RAMIREZL)

ABSTRACT

Exposed upper Proterozoic and Cambrian rocks in the Caborca region, Sonora, Mexico, consists of a shallow-water miogeoclinal sequence of quartzite, siltstone, dolomite, limestone, 

and minor amounts of conglomerate and greenstone. A revised 

stratigraphic sequence is divided into 14 formations, 11 of which 

have been previously named and 3 of which are named here. 

The sequence is as much as 3,300 m thick and rests unconformably on a basement terrane of 1,600- to l,750-m.y.-old metamorphic and igneous rocks, intruded by l,400-m.y.-old porphyritic granite and l,100-m.y.-old granite. The sequence 

contains a wide assortment of fossils that include algallike 

filaments, possible trace fossils, and conical stromatolites (Conophyton and related forms) in the upper Proterozoic rocks; a 

primitive shelly fauna in the lowermost Cambrian rocks; and 

archaeocyathids, trilobites, Salterella, Hyolithes, Gimanella, 

gastropods, and brachiopods in the overlying Cambrian rocks. 

Paleocurrent measurements in six different formations reveal 

no dominant trend, although individual studies characteristically show a single dominant direction or oppositely directed 

paleocurrents suggestive of the ebb and flow of tides.

The revised stratigraphic sequence in the Caborca region 

is correlated, much of it unit for unit, with stratigraphic sequences in the southern Great Basin region of eastern California and southern Nevada, in the San Bernardino Mountains 

of southern California, and in the Sierra Agua Verde of central 

Sonora, Mexico.

The upper Proterozoic and Cambrian rocks of the Caborca 

region have long been recognized as a southward extension of 

the Cordilleran miogeocline, but interpretations have varied 

as to whether or not many of these rocks have been tectonically 

displaced. The position of the Caborca rocks to the southeast 

of correlative rocks in the Southwestern United States may be 

due to an eastward curvature of the Cordilleran miogeocline 

into northern Mexico, to major left-lateral offset along the 

Mojave-Sonora megashear, or to a combination of both these 

factors. A complex pattern of tectonic disruption involving leftlateral and subsequent right-lateral offset is also possible.

INTRODUCTION

Upper Proterozoic and Cambrian rocks in the 

Caborca region (figs. 1, 2) have long been recog1 Department of Geology, University of California, Santa Barbara, CA 93106. 

2Consejo de Recursos Minerales, Nogales, Mexico.

nized as important in understanding the tectonic 

framework of North America. These rocks are generally considered to be a southward extension of 

shallow-water shelf deposits of the Cordilleran miogeocline (Eardley, 1951, pi. 2; Stewart, 1970, fig. 

36; Poole and Hayes, 1971; Stewart and Poole, 1975; 

Cameron, 1981; Dickinson, 1981; Stewart, 1982), 

but interpretations have varied as to how much 

they have been tectonically displaced. Silver and 

Anderson (1974) and Anderson and Silver (1979) 

suggested that the Precambrian and Paleozoic 

rocks of the Caborca region have been offset 700 

to 800 km along a left-lateral fault, the Mojave119°

\ NEVADA

"V,^ ^Mount Dunfee 

^o£° \ SOUTHERN

\ \

\GREAT 

Death \ i 

Valley \

CALIFORNIA BASIN \

Victorville,. Mojave Desert

^Drd Mountains 

Los Angeles N San Bernardino 

Mountains

UTAH

-I

Las 

, Vegas I ARIZONA

PACIFIC

Phoenix

'^s,

^^

Tucson

_ OCEAN Cabo

SONORA \

Area of

figure 2 Sierra

Agua Verde i

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Hermosillo < '

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300 KILOMETERS

_I

FIGURE 1. Index map showing location of Caborca region, 

Mexico, and localities mentioned in text.

1
PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

Sonora megashear, from the Western United 

States. Part of the evidence for this possible offset 

is the similarity of the Cambrian rocks in the Caborca region and those in the Western United 

States. Other geologists (Stewart and Poole, 1975; 

Peiffer-Rangin, 1979; Stewart, 1982) have speculated that the Cordilleran miogeocline may curve 

eastward in northern Mexico, to account for the 

position of the rocks in the Caborca area. A clear 

understanding of the stratigraphy of the rocks in

the Caborca area is needed before these concepts 

can be evaluated. The present report describes new 

information from the Caborca region that corrects 

errors in the previously described stratigraphic 

section and allows precise correlations with rocks 

in the Western United States.

PREVIOUS WORK

The presence of Cambrian and Precambrian 

rocks in the Caborca region was first reported by

:erro Llano 

Verde 

/

20 KILOMETERS

FIGURE 2. Map of Caborca region, Mexico, showing outcrops of upper Proterozoic and Cambrian rocks. In part after 

Merriam and Eells (1979) and Longoria and others (1978). Stippled areas, outcrops; double line, major road; dashed 

line, secondary road. See figure 1 for location.
PRESENT STUDIES

Stoyanow (1942) on the basis of fossils collected by 

Isauro G. Gomez and L. Torres. This discovery led 

to a joint investigation of the Precambrian and 

Paleozoic stratigraphy of the region by A. R. V. 

Arellano of the Institute de Geologia, Universidad 

Nacional Autonoma de Mexico, and G. A. Cooper 

of the U.S. National Museum, sponsored in part 

by the Smithsonian Institution. Arellano and 

Cooper and their colleagues described and named 

the Cambrian formations of the Caborca region 

and studied the fauna (Arellano, 1946,1956; Cooper 

and Arellano, 1946, 1952; Lochman, 1948, 1952,

1953. 1956; Cooper, 1952; Cooper and others, 1952,

1954. 1956; Johnson, 1952; Okulitch, 1952; Stoyanow, 1952). Arellano (1946) and Cooper and Arellano (1946) also briefly described the stromatolite-bearing Precambrian rocks in the Caborca 

region.

Damon and others (1962) and Livingston and 

Damon (1968) dated the crystalline basement rocks 

of the Caborca region and briefly described the 

overlying Precambrian sedimentary rocks. Fries 

(1962) described the general occurrence of Precambrian and Paleozoic rocks in the region.

In the 1970's, studies of crystalline basement 

rocks in the Caborca region were made by Anderson and Silver (1970, 1971), Cserna (1970), and Anderson and others (1978, 1979). These geologists 

also described the relations of these rocks to the 

overlying upper Proterozoic sequence.

In 1972, J. L. Eells made the first detailed study 

of the upper Proterozoic rocks of the Caborca region. He mapped parts of the Cerros de la Cienega, 

Cerro Calaveras, Cerro Aquituni, and Cerro San 

Clemente areas and divided the upper Proterozoic 

rocks into 12 units. Eells' results were summarized 

by Anderson and others (1978, 1979).

Stratigraphic studies and regional mapping in 

several areas of the Caborca region were undertaken in the late 1970's by J. F. Longoria and coworkers (Longoria and others, 1978; Longoria and 

Perez, 1979; Longoria, 1980, 1981; Gonzalez, 1981; 

Longoria and Gonzalez, 1981; Mendoza, 1981; and 

Perez, 1981). Longoria and his colleagues named 

five formations and one group in the Precambrian 

succession.

Precambrian stromatolites in the Caborca region were studied by Benmore (1978), Gamper and 

Longoria (1979), Weber and others (1979), CevallosFerriz and Weber (1980), Weber and Cevallos-Ferriz 

(1980), Cevallos-Ferriz (1981), and Cevallos-Ferriz 

and others (1982).

Correlations of the Caborca rocks with similar 

rocks in the Western United States were made by

Lochman (1956), Eells (1972), Fritz (1975), Palmer 

and Halley (1979), Cameron (1981), and Stewart 

(1982). The Cambrian strata at Caborca were compared with the Cambrian strata in Argentina by 

Baldis and Bordonaro (1981).

Part of the Caborca region was mapped in reconnaissance by Merriam and Eells (1979).

PRESENT STUDIES

The senior author first studied the upper Proterozoic rocks in the Caborca area during a 3-day 

trip in 1977. He returned in 1978 on a field trip 

organized as a part of the "Primer Simposio sobre 

la Geologia y Potencial Minero en el Estado de 

Sonora" (Roldan and Salas, 1978), and again in 1981 

in connection with the Geological Society of America's Cordilleran Section Annual Meeting (Longoria, 1981). After the 1981 meeting, the senior 

author and J. M. Morales-Ramirez spent 5 days in 

the region, measuring paleocurrent directions and 

studying the stratigraphy of the upper Proterozoic 

and Lower Cambrian rocks. In March 1982, all 

three authors of this report were in the field together for 16 days. During this time, the Cerro 

Rajon stratigraphic section was measured and 

compared with sections measured by Eells (1972) 

and Longoria and coworkers (Longoria, 1981). Additional paleontologic collecting was done in December 1982 by M. A. S. McMenamin, and a field 

trip to check correlations was made in February 

1983 by the senior author, Jaime Roldan-Quintana, 

Sergio Cevallos-Ferriz, and Alfonso Salcido-Reyna.

ACKNOWLEDGMENTS

Our work in Mexico was sponsored by the Consejo de Recursos Minerales. We thank G. P. Salas, 

past Director General of the Consejo, and J. L. LeeMoreno, Gerente de Estudios Especiales of the 

Consejo, for their support and help in carrying out 

the fieldwork. T. H. Anderson, A. R. Palmer, and 

L. T. Silver have been extremely helpful in indicating important localities and in discussing the 

regional relations of the rocks. Jose Longoria 

kindly showed the senior author parts of the upper 

Proterozoic stratigraphic section and indicated localities that were suitable for current-direction 

studies. Sergio Cevallos-Ferriz, Alfonso SalcidoReyna, and Jaime Roldan-Quintana showed us outcrops of the Proterozoic rocks in Cerro Llano 

Verde, Cerro Clemente, and the Sierra del Viejo. 

S. M. Awramik helped in collecting and identifying 

fossils, and provided valuable discussions concern-
PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

30° 2 7'

30°24'

QTa

Contour interval 

100 meters

FIGURE 3. Reconnaissance map of the Cerro Rajon area, Mexico. See figure 2 for location and figure 5 for descriptions of

measured sections.
PHYSICAL STRATIGRAPHY OF UPPER PROTEROZOIC AND CAMBRIAN ROCKS

ing the age of the stromatolites. D. L. Kidder and 

W. K. Gross provided valuable field assistance in 

December 1982. C. S. Cameron helped by freely 

sharing his knowledge of the stratigraphic section 

in the San Bernardino Mountains, Calif., and by 

discussions of correlations of the rocks in the San 

Bernardino Mountains with those in the Caborca 

region. R. E. Powell and J. C. Matti provided logistic support in the San Bernardino Mountains 

and pointed out important problems with the stratigraphic relations there.

PHYSICAL STRATIGRAPHY OF UPPER PROTEROZOIC AND CAMBRIAN ROCKS

The stratigraphy we describe in this report is 

based primarily on exposures of rocks in the Cerro

Rajon area (fig. 3), which contains the most complete upper Proterozoic and Lower Cambrian 

stratigraphic section in the Caborca region. The 

section is well exposed and relatively little faulted 

and is a standard with which less complete, less 

well exposed, and more highly faulted sections in 

the Caborca region can be compared (fig. 4). Figure 

5 shows a stratigraphic column of the Cerro Rajon 

section, details on which have been reported by 

Stewart (1984).

The Cerro Rajon area was first mapped by Longoria and others (1978) and Longoria and Perez 

(1979), who described a lower Precambrian sequence of granodiorite and pegmatite and an upper 

Precambrian sequence that they divided into two 

formations, the Pitiquito Formation and the overEXPLANATION

Cerro Prieto and 

Buelna Formations

Includes small outcrop of 

Arrojos Formation

Puerto Blanco Formation

La Cienega Formation

QUATERNARY

AND 

UPPER TERTIARY

- MESOZOIC

MIDDLE

AND

LOWER

CAMBRIAN

Basement complex

Igneous and metamorphic

rocks

UPPER 

PROTEROZOIC

MIDDLE

AND

LOWER

PROTEROZOIC

LOWER 

CAMBRIAN

Contact

High-angle fault

Bar and ball on downthrown side 

Dotted where concealed

Line of measured section

UPPER 

PROTEROZOIC

Papalote and Gamuza Formations

FIGURE 3. Continued.
PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

Cooper and 

Arellano 

(1952)

Trcn 

Formation

Arrojos 

Formation

Ccrro Pricto 

Formation

Buelna 

Formation

Provccdora 

Quartzite

Puerto Blanco 

Formation

not exposed

Eells (1972) 

Cerro 

Calaveras

Tren 

Formation

Arrojos 

Formation

Cerro Prieto 

Formation

Buelna 

Formation

Proveedora 

Quartzite

Puerto Blanco 

Formation

Unit 12

Unit 11

Unit 10

Unit 9

UnitS

Unit 7

not 

exposed

Eells (1972) 

(section 3, pi. 4) 

Cerro de la 

Cienega

not exposed

Unit6

UnitS

Unit 4

Unit 3

Mctamorphic 

rocks

Eells (1972) 

Southern 

Cerro 

Aquituni

not exposed

UnitS

Unit 2

Unit 1

not 

exposed

Longoria 

(1981)

El Tren 

Formation

Arrojos 

Formation

Cerro Prieto 

Formation

Buelna 

Formation

Proveedora 

Quartzite

Puerto Blanco

Gachupin 

Group

Papalote 

Formation

Gamuza 

Formation

Pitiquito 

Formation

^-- ? "^^

Caborca 

Formation

El Arpa 

Formation 

TAMIT

Bamori metamorphic 

complex and 

Aibo Granite

This report

Tren 

Formation

Arrojos 

Formation

Cerro Prieto 

Formation

Buelna 

Formation

Proveedora 

Quartzite

Puerto Blanco

La Cienega 

Formation

Tecolote 

Quartzite

Papalote 

Formation

Gamuza 

Formation

Pitiquito 

Quartzite

Clemente 

Formation

Caborca 

Formation

El Arpa 

Formation 

*^^s ^^ - ^ ^ ^ 

Basement 

complex

FIGURE 4. Correlation of nomenclature used in the Caborca region, Mexico.
PHYSICAL STRATIGRAPHY OF UPPER PROTEROZOIC AND CAMBRIAN ROCKS

lying Gamuza Formation. They mapped the contact of the Pitiquito and Gamuza with the lower 

Precambrian igneous rocks as a thrust fault and, 

in addition, showed the Pitiquito and Gamuza Formations to be repeated three times by major thrust 

faults. However, we found no evidence for any of 

these thrust faults. The contact between the lower 

Precambrian and upper Precambrian rocks is, in 

our view, a sedimentary contact. Our work further 

indicates that the Pitiquito and Gamuza Formations are not duplicated three times; instead, the 

rocks in each of the three "thrust plates" mapped 

by Longoria and others (1978) and Longoria and 

Perez (1979) are different and in stratigraphic continuity with rocks in the adjacent "thrust plates." 

Longoria and coworkers also showed the Gamuza 

Formation in the Cerro Raj on area as structurally 

overlain along the Rajon fault by the Rajon Group 

of Jurassic age. However, we found no evidence of 

the Rajon fault. The lower units of the Rajon 

Group as mapped by Longoria and others (1978) 

and Longoria and Perez (1979) are clearly upper 

Proterozoic to Middle Cambrian rocks (Puerto 

Blanco, Proveedora, Buelna, Cerro Prieto, and Arrojos Formations) in continuity with older upper 

Proterozoic strata.

Our work also indicates errors in the sequence 

of units described by Eells (1972), who recognized 

a succession of 12 numbered units and several 

named formations in the Cerros de la Cienega, 

Cerro Calaveras, Cerro Aquituni, and Cerro San 

Clemente areas. As indicated in figure 4, some of 

Eells' units are repeated three times.

In this report, we recognize 14 upper Proterozoic 

and Cambrian formations, 11 of which have been 

previously named and 3 of which we name here 

(fig. 4). The formational names used here appear 

to be applicable to the upper Proterozoic and Cambrian rocks throughout the Caborca region. In the 

Sierra del Viejo, which is presently being studied 

by Sergio Cevallos-Ferriz, Alfonso Salcido-Reyna, 

and Andres Pelayo-Ledesma, all the formations we 

describe here are recognized, although some are 

much thicker than elsewhere in the Caborca region 

and one is present only in the southern part of the 

sierra.

EL ARPA FORMATION

The El Arpa Formation was named by Longoria 

(1980, 1981) for outcrops on the east flank of the 

northernmost part of the Cerro El Arpa area (fig. 

2). In the type area, the El Arpa is 190 m thick 

and consists of a basal sequence about 20 m thick

of cross-stratified sandstone, quartzite, conglomerate, and sandy dolomite, with an overlying 170 

m thick sequence of medium-gray and light-brown 

dolomite which is locally silty or sandy. In the 

Cerro El Arpa area, the El Arpa Formation overlies the Aibo Granite, dated at 1,110 ±10 m.y. (Anderson and others, 1978, 1979). The contact between the Aibo and the El Arpa was considered a 

fault by Earl Ingerson (in Arellano, 1956) and Longoria (1981), and as a sedimentary contact by Damon and others (1962), Cserna (1970), and Anderson and others (1978, 1979). We agree with the 

latter group that the contact is sedimentary because of the presence of granitic clasts in conglomerate of the basal unit (Damon and others, 1962;

EXPLANATION

Conglomerate

and conglomeratic

quartzite

Greenstone

0

Trace fossils

Oncolites

("Girvanella")

Salterella

a

Skolithos

Trilobites

Archeocyathids

Shelly fossils

Domal stromatolites

Conical stromatolites

(Conophyton and

related forms)

Silty dolomite

FIGURE 5. Stratigraphic column in the Cerro Rajon area, 

Mexico. See figure 3 for locations of sections.
PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

FORMATION 

(AGE)

RAJON GROUP 

(JURASSIC)/

ARROJOS 

FORMATION 

(MIDDLE 

CAMBRIAN)

CERRO PRIETO 

FORMATION 

(LOWER 

CAMBRIAN)

BUELNA 

FORMATION 

(LOWER 

CAMBRIAN)

PROVEEDORA 

QUARTZITE 

(LOWER 

CAMBRIAN)

PUERTO 

BLANCO 

FORMATION 

(LOWER 

CAMBRIAN)

LA CIE'NEGA 

FORMATION

(LOWER 

CAMBRIAN) 

(TYPE 

SECTION)

THICKNESS 

(METERS)

NOT 

MEASURED

93.0

INCOMPLETE

82.0

77.5

201.0

717.0

78.0

141 f

117.5

173.0

cOO.O

27.0

37.5 

37.5

76.0

LITHOLOGY FOSSILS

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DESCRIPTION

Boulder conglomerate, pale red, composed of pebbles to boulders as large as 

1 m of quartzite. Only basal part examined.

Siltstone, pale red, fine to medium silt. Minor amounts of pale-yellowishbrown, very pale orange, and light-gray very thin to thin beds of limestone.

Limestone, light gray to medium gray, thin bedded. Abundant oncolites 

(Girvanella) in lower half, sparse in upper half.

Mixed rock types. Siltstone, greenish gray to yellowish gray, coarse silt. 

Quartzite, yellowish brown, fine to medium grained, laminated and cross 

stratified. Limestone and dolomite, sandy in part, light gray, commonly 

weathering moderate brown, laminated and cross stratified.

Quartzite, pinkish gray, fine to medium grained, scattered coarse grains, 

laminated to very thin bedded; common very thin tabular planar sets of lowangle cross strata. Abundant Skolithos in lower 90 m. Sparse siltstone

layers in lower 83 m.

Unit 4. Siltstone, greenish gray and grayish orange, common tracks, trails, 

and burrows in upper 44 m. Limestone to silty limestone, medium gray, 

laminated to very thin bedded, common cross strata. Quartzite, very pale 

orange to yellowish gray, very fine to fine grained, laminated to thin bedded,

common Skolithos. Dolomite, medium gray, weathering light brown, laminated to 

thin bedded, common cross strata. Archeocyathids , possibly reworked clasts, 

occur in lower one-fourth of unit. Shelly trash beds occur in limestone 

locally.

Unit 3. Archeocyathid-bearing yellow-gray to light-gray indistinctly thin 

bedded limestone at base and at top of unit. Middle part of unit is 

yellowish-gray and greenish-gray siltstone, yellowish-gray very fine to fine 

grained quartzite, and minor sandy limestone, limestone, and siltstone.

Unit 2. Siltstone, yellow gray, dusky yellow, and grayish red, micaceous, 

abundant borrows, tracks, and trails. Quartzite, very fine grained, evenly 

laminated. Sparse limy siltstone to silty limestone beds.

Unit 1. Volcaniclastic sandstone to boulder conglomerate, brownish gray, 

composed of greenstone, dolomite, sandy dolomite, and siltstone clasts set in 

a silty fine to very coarse grained sand matrix. Greenstone, greenish gray, 

altered mafic minerals in chloritic matrix. Quartzite, pale red and olive 

gray, mostly very fine to fine grained, sparse fine- to medium-grained parts, 

evenly laminated. Siltstone, in parts intergradational with very fine grained 

quartzite, olive gray. Sparse silty dolomite.

sparse intraclast conglomerate.

Unit 3. Siltstone, pale olive, laminated. Quartzite, yellowish gray, very 

fine to medium grained, laminated and cross stratified. Common dolomite and 

sandy dolomite. Greenstone (1.5 m thick) in middle. 

Unit 2. Dolomite, medium gray, indistinctly laminated to thin bedded. Common

cross-stratified sandy dolomite in top 7.5 m. 

Unit 1. Dolomite and sandy dolomite, light brown, fine to medium quartz 

grains, laminated and cross stratified. Quartzite, pinkish gray, fine to 

medium grained, laminated to thin bedded and cross stratified. Minor 

siltstone, silty dolomite, and greenstone.

FIGURE 5. Continued.
PHYSICAL STRATIGRAPHY OF UPPER PROTEROZOIC AND CAMBRIAN ROCKS

FORMATION 

(AGE)

CONTINUE

TECOLOTE 

QUARTZITE 

(UPPER 

PROTEROZOIC) 

(TYPE 

SECTION)

PAPALOTE 

FORMATION 

(UPPER 

PROTEROZOIC)

GAMUZA 

FORMATION 

(UPPER 

PROTEROZOIC)

PITIQUITO 

QUARTZITE 

(UPPER 

PROTEROZOIC)

CLEMENTE 

FORMATION 

(UPPER 

PROTEROZOIC) 

(TYPE 

SECTION)

CABORCA 

FORMATION 

(UPPER 

PROTEROZOIC)

EL ARPA 

FORMATION 

(UPPER

BASEMENT 

COMPLEX

THICKNESS 

(METERS) LITHOLOGY FOSSILS

) FROM BOTTOM OF PREVIOUS PAGE

168.5

404.5

35.C

Ifi7 (1

31.5

157.0

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20.0

31.5 

60.0

4,5 

70.5

77.0

210.3

126.6

89.7

81.0

^ 

12./.

33.0

18^ 

63.0

45.0

81.6

37.5

43.2

9.0 "

NOT 

MEASURED

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DESCRIPTION

Quartette, pinkish gray, medium to coarse grained, evenly laminated, sparse 

cross-stratified parts. Sandy dolomite and dolomite, medium gray, weathering 

light brown, fine to coarse quartz grains. Sandy dolomite occurs mostly in 

thin trough and tabular planar sets of cross strata; dolomite is mostly 

laminated to thin bedded.

Unit 6. Dolomite, medium light gray, weathering light olive gray, 

indistinctly laminated to thin bedded. Sparse small-scale cross strata, 

intraclast conglomerate, and intraclast microconglomerate. Contains minor 

amounts of moderate red siltstone from 12 to 22 m above base.

strata. Sandy dolomite to dolomite,, grayish red, weathering light brown, fine 

to coarse quartz grains, laminated, sparse cross strata.

Unit 4. Dolomite, medium light gray, evenly laminated to thin bedded. Common 

sandy dolomite from 42 to 45 m above base. Domal stromatolites from 15.0 to 

15.5 m above base.

Unit 3. Silty dolomite to dolomitlc siltstone, pale red to pale reddish 

brown, evenly laminated. 

Unit 2. Dolomite, medium light gray, laminated.

dolomite. 

Upper unit. Stromatolitic dolomite, medium gray, weathers medium gray with 

irregular grayish orange mottling, composed of conical stromatolites 

(Conophyton and related forms) mostly 5 to 20 cm in diameter.

Lower unit. Dolomite, medium gray, laminated to thin bedded, common wavy 

laminae suggestive of algal mats. Basal 13.5 m contains common dolomitic 

siltstone and 1-m-thtck bed of quartz granule conglomerate.

Quartzite, pale red, fine to medium grained, sparse medium- to coarse-grained 

parts, laminated to thin bedded, common thin trough and tabular planar sets of 

small-scale cross strata. Sparse dolomitic sandstone.

Unit 6. Siltstone to very fine grained sandstone, pale red and greenish gray, 

common drag marks, flute casts, and ripple marks. Basal 30 m contains two 

beds of intraclast conglomerate containing siltstone clasts as large as 

15 cm.

Unit 5. Oolitic dolomite, aphanitic dolomite, and intraclast conglomerate 

composed of oolitic dolomite clasts, very pale orange.

Unit 3. Siltstone to very fine grained quartzite, pale red, laminated to very 

thin bedded. Sandy limestone to dolomite in middle.

Unit 2. Quartzite to granule conglomerate composed mostly of quartz clasts, 

pale red, laminated, and' cross stratified.

Unit 1. Siltstone to very fine grained quartzite, pale red to grayish red, 

laminated to very thin bedded. Minor amounts of light-brown dolomite in basal 

5 m.

Upper unit. Dolomitic limestone and dolomite, dark gray, laminated to thin 

bedded, common low-angle cross strata. Common microchip conglomerate composed 

of 2- to 6-mm-wide plates of dolomite in a lime mud matrix. Sparse intraclast

Lower unit. Dolomite to dolomitic limestone, medium gray, laminated to very 

thin bedded. Minor amounts of silty to sandy dolomite, siltstone, and

Unit 3. Dolomite and minor dolomitic limestone, medium light gray, laminated 

to thin bedded.

Unit 2. Dolomite, sandy dolomite, quartzite, sandstone, and siltstone. A 

1.7-m-thick greenstone occurs in upper part.

Unit 1. Arkosic sandstone, yellow gray, medium to coarse grained, laminated 

to thin bedded and cross stratified. Basal 10 cm contains clasts of 

megacrysts from underlying porphyritic granite.

Porphyritic granite, greenish gray with pinkish-gray orthoclase phenocrysts as 

long as 4 cm in very coarse grained matrix of quartz and chloritized mafic 

minerals, 1,400+20 m.y. old (L. T. Silver, oral commun., 1982). Common 

irregular masses of greenstone.

FIGURE 5. Continued.
10 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

Anderson and others, 1978, 1979) and because of 

the lateral continuity of this basal unit along the 

outcrop.

In the Cerro Raj on area (fig. 5), the El Arpa 

Formation is 89.7 m thick and consists of a lower 

unit of arkosic sandstone and conglomerate about 

9 m thick; a 43.2-m-thick slope-forming middle unit 

of dolomite, sandy dolomite, quartzite, sandstone, 

siltstone, and thin greenstone (possibly a sill); and 

a 37.5-m-thick cliff-forming upper unit of mediumlight-gray dolomite. The basal sandstone and conglomerate unit rests depositionally on middle Proterozoic porphyritic granite containing megacrysts as much as 4 cm long. The occurrence of 

clasts of these large megacrysts in conglomerate 

of the basal unit of the El Arpa Formation clearly 

demonstrates that the base of the El Arpa in the 

Cerro Raj on area is a sedimentary contact. The 

age of the pre-El Arpa porphyritic granite is 

1,400 ±20 m.y. (L. T. Silver and T. H. Anderson, 

oral commun., 1982). Pre-El Arpa granitic and metamorphic rocks elsewhere in the Caborca region, 

except for the l,110-m.y.-old Aibo Granite, range 

in age from about 1,600 to 1,750 m.y. (Anderson 

and Silver, 1970, 1971; Anderson and others, 1978, 

1979; recalculated using new decay constants by 

L. T. Silver and T. H. Anderson, oral commun., 

1982).

The El Arpa Formation also occurs in the Cerros 

de la Cienega (fig. 2), where it forms the lower part 

of unit 3 of Eells (1972). There, the distinction between the El Arpa and the overlying Caborca Formation is less clear than in the Cerro El Arpa and 

Cerro Rajon areas. In section 3 of Eells (1972, pi. 

4), in the Cerros de los Cienega, the El Arpa and 

Caborca Formations were described as a single 

unit by Eells. We were able to distinguish the two 

formations in Eells' section 3, although the two 

formations are, indeed, similar. In the Cerros de 

la Cienega, Eells (1972) showed his map unit 3 in 

fault contact with underlying metamorphic rocks 

of the crystalline basement. Although our work 

was not complete enough to demonstrate the nature of this contact, the lowest unit in the El Arpa 

Formation along Eells' section 3 is a quartzite similar to the basal unit of the El Arpa Formation in 

the Cerro El Arpa and Cerro Rajon areas. The 

presence of this probable basal unit in Eells' section 3 suggests that the basal contact of the El 

Arpa Formation in the Cerros de la Cienega may, 

at least locally, be a sedimentary contact.

CABORCA FORMATION

The Caborca Formation was named by Longoria 

(1980, 1981) for outcrops on the east flank of the 

northernmost part of the Cerro El Arpa area,

where it is 105 m thick. In the type area, it consists 

of two major units a slope-forming lower unit 

about 85 m thick of greenish-gray and pale-red 

siltstone and minor amounts of gray and brown 

dolomite, and a cliff-forming upper unit about 20 

m thick of dark-gray dolomite. The upper unit is 

distinguishable from a distance by well-defined 

thin to thick bedding.

In the Cerro Rajon area, the Caborca Formation 

is 126.6 m thick and contains the same two units 

as in the Cerro El Arpa area. The lower unit, which 

is 81.6 m thick in the Cerro Rajon area, is composed 

primarily of medium-gray to light-brown dolomite 

and dolomitic limestone and relatively minor 

amounts of sandy to silty dolomite, siltstone, and 

sandstone, in contrast to the dominant siltstone 

within the unit in the Cerro El Arpa area. The 

upper unit, which is 45 m thick in the Cerro Rajon 

area, is lithologically similar to the upper unit in 

the Cerro El Arpa area. In Cerro Rajon and, less 

abundantly, in Cerro El Arpa, the upper unit contains microchip conglomerate composed of 2- to 6- 

mm-wide plates of dolomite in a lime-mud matrix.

The Caborca Formation also occurs in Eells' section 3 in the Cerros de la Cienega, where it forms 

the upper part of his unit 3 and is composed largely 

of dolomite. Minor units of siltstone and very fine 

grained sandstone in the upper part of Eells' unit 

3 appear to be correlative with the lower unit of 

the Caborca Formation. The cliff-forming upper 

unit of the Caborca Formation is well defined at 

the top of Eells' unit 3.

The lowest unit exposed on the east side of Cerro 

Calaveras (fig. 2) unit 7 of Eells (1972) also is 

correlative with the Caborca Formation. This unit 

is 150 m thick and consists of a lower 90-m-thick 

subunit of thin-bedded limestone and an upper 60- 

m-thick subunit of thin-bedded to laminated dolomite. These two subunits apparently correspond 

to the lower and upper units of the Caborca recognized elsewhere. The Caborca Formation is the 

lowest unit exposed on Cerro Calaveras, but its 

base is not exposed there.

CLEMENTE FORMATION

The name "Clemente Formation" is proposed 

here for a 210.3 m-thick unit of siltstone, sandstone, 

quartzite, conglomerate, and minor dolomite exposed in the Cerro Rajon area. The type section 

(composite) is 2.3 km south-southeast of Cerro Rajon (El Prieto quad., H12A77, l:50,000-scale map) 

at lat 30°24.4' N., long 111°56.4' W. The name is 

derived from Cerro Clemente, 11 km south-southwest of the type section (El Prieto quadrangle map) 

(fig. 2).
PHYSICAL STRATIGRAPHY OF UPPER PROTEROZOIC AND CAMBRIAN ROCKS 11

The Clemente Formation in the type section can 

be divided into six distinctive units. Unit 1 is 63 

m thick and consists of pale-red to grayish-red siltstone to very fine grained quartzite and minor 

amounts of light-brown dolomite in the basal 5 m. 

Unit 2 is 18 m thick and consists of pale-red to 

grayish-orange-pink cross-stratified quartzite to 

granular conglomerate composed mostly of quartz 

clasts. Unit 3 is 33 m thick and consists of palered to light-brownish-gray siltstone to very fine 

grained quartzite with a medial sandy-limestone 

to dolomite layer. Unit 4 is 12.7 m thick and consists 

of greenish-gray siltstone. Unit 5 is a distinctive 

2.6 m thick very pale orange to pale-red oolitic 

dolomite (fig. 6), aphanitic dolomite, and conglomerate composed of rounded clasts of the oolitic dolomite. Unit 6 is 81 m thick and is composed of 

pale-red and greenish-gray siltstone to very fine 

grained sandstone and, in the lower half of the 

unit, two distinctive intraclast conglomerate beds 

composed of tabular clasts of siltstone as large as 

15 cm across. Drag marks, flute casts, and ripple 

marks (fig. 7) are common on bedding-plane surfaces of the siltstone and sandstone of unit 6.

The Clemente Formation is missing owing to 

faulting in the Cerro El Arpa area except for a 

small outcrop in the northernmost part of the 

range, where about 110 m of strata correlative with 

unit 6 of the Clemente Formation is recognized. 

The Clemente is also recognized on the east side 

of Cerro Calaveras, where it forms all but the top 

30 m of unit 8 of Eells (1972), and in the Cerros de 

la Cienega, where it forms unit 4 of Eells (1972, 

sec. 3, pi. 4). All six units of the Clemente Formation are recognized on Cerro Calaveras and in 

the Cerro de la Cienega, although the thicknesses 

and dominant lithology of the units vary somewhat

1mm

FIGURE 6. Photomicrograph of oolitic dolomite from unit 5 of 

the Clemente Formation, east side of Cerro Calaveras. Specimen number MM-82-63. Photograph by S. M. Awramik.

from locality to locality. The Clemente Formation 

also crops out in the Cerro Clemente and Cerro 

Llano Verde areas, as was pointed out to us by 

Sergio Cevallos-Ferriz and Alfonso Salcido-Reyna.

PITIQUITO QUARTZITE

The name "Pitiquito Formation" was introduced 

by Longoria and others (1978, fig. 1) and Longoria 

and Perez (1979, p. 125 126). The holostratigraphic 

type (type section) is on the east flank of the extreme northern part of the Cerro Gamuza area 

(fig. 2), and the parastratigraphic type (reference 

section) is in the eastern and northern parts of the 

Cerro El Arpa area (Longoria, 1980, 1981). The 

holostratigraphic type of the Pitiquito Formation 

consists of 89 m of white to reddish-brown fine- to 

medium-grained thick-bedded cross-stratified

B

10cm

FIGURE 7. Drag marks (A) and possible flute casts (B) in unit 

6 of the Clemente Formation in the Cerro Raj on area.
12 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

quartzite. The lower contact as mapped by Longoria (1980, 1981) and Gonzalez (1981) is in fault 

contact with the structurally underlying Chino 

Group of Jurassic age. At the parastratigraphic 

type section, the Pitiquito Formation is more completely exposed than at the holostratigraphic type 

and consists of a lower 110-m-thick unit of interbedded phyllite, orthoquartzite, and sandy dolomite, and an upper 175 m-thick unit of homogeneous cliff-forming quartzite. The contact of the 

Pitiquito Formation and the underlying Caborca 

Formation in the Cerro El Arpa area is a low-angle 

fault according to Longoria (1980, 1981) and Gonzales (1981), although Anderson and others (1978, 

1979) showed it as a high-angle fault. Our observations agree with the latter interpretation.

We here modify Longoria's definition of the Pitiquito Formation by restricting it entirely to a 

quartzite sequence and by referring to it as the 

Pitiquito Quartzite rather than the Pitiquito Formation. In the Caborca region, the quartzite that 

we here define as the Pitiquito Quartzite is a distinctive unit, easily distinguishable from the siltstone and very fine grained quartzite of the underlying upper part of the Clemente Formation 

and the dolomite of the overlying Gamuza Formation. The Pitiquito Quartzite, as defined here, 

is an easily mappable unit that we believe should 

stand alone as a formation. Our definition of the 

Pitiquito is in harmony with the holostratigraphic 

type, where the formation is almost entirely 

quartzite (Longoria, 1980, 1981). In the parastratigraphic type in the Cerro El Arpa area, however, 

Longoria (1980,1981) included a 110-m unit of phyllite, orthoquartzite, and sandy dolomite in the 

lower part of his Pitiquito. We here include this 

110-m unit in the Clemente Formation. In the 

Cerro Raj on area, our definition of the Pitiquito 

contrasts with that of Longoria and Perez (1979, 

p. 125-126, figs. 4, 5), who included in the Pitiquito 

a sequence of phyllite and quartzite below the 

main cliff-forming quartzite. We include this phyllite and quartzite in our Clemente Formation and 

restrict the name "Pitiquito" to the cliff-forming 

quartzite.

In the Cerro Raj on area, the Pitiquito Quartzite 

of our definition is 77 m thick and consists of palered fine- to medium-grained quartzite. It is laminated to thin bedded and contains common thin 

tabular planar and trough sets of small-scale cross 

strata. The lower part contains a few light-brownweathering dolomitic sandstone layers.

In addition to the exposures in the Cerro El 

Arpa, Cerro Gamuza, and Cerro Rajon areas described above, the Pitiquito Quartzite also occurs 

in the Cerro San Clemente and Cerro Aquituni 

areas (fig. 2), where, as noted by Longoria and 

others (1978, fig. 1), Longoria and Perez (1979, fig. 

2), and Longoria (1980, 1981), it forms map unit 1 

of Eells (1972). In the Cerros de la Cienega, it forms 

map unit 5 of Eells (1972). On the east side of Cerro 

Calaveras, it forms the top 30 m of map unit 8 of 

Eells (1972). The Pitiquito also crops out low on 

the west side of the Cerro Pitiquito area, but the 

quartzite high in the Cerro Pitiquito area is probably the Tecolote Quartzite, not the Pitiquito as 

mapped by Mendoza (1981). The Pitiquito also 

crops out in the Cerro Llano Verde and Cerro Clemente areas and in the southern part of the Sierra 

del Viejo. Alfonso Salcido-Reyna (written commun., 1983) has indicated that the Pitiquito 

Quartzite is missing in the northern part of the 

Sierra del Viejo in sequences that otherwise contain all the formations from the El Arpa to the 

Papalote.

GAMUZA FORMATION

The name "Gamuza Formation" was introduced 

by Longoria and others (1978) and Longoria and 

Perez (1979). The holostratigraphic type (type 

section) of the formation is on the east flank of the 

northernmost part of the Cerro Gamuza area (fig. 

2; Longoria, 1980, 1981). The parastratigraphic 

type (reference section) is on the east flank of the 

northernmost part of the Cerro El Arpa area 

(Longoria, 1980, 1981).

The name "Gamuza beds," according to Arellano 

(1956), was originally used in the Caborca area by 

W. T. Keller and F. E. Wellings in 1922. This name 

was then, and in several subsequent papers (Arellano, 1956; Anderson and others, 1978,1979; Weber and others, 1979), used as a general term to 

describe the stratigraphic section that Longoria 

(1980, 1981) included in the El Arpa through Papalote Formations. Because the name "Gamuza" 

is now used to describe a formation, we believe 

that the broader usage in the term "Gamuza beds" 

should be abandoned.

In the type area, the Gamuza Formation consists 

of dark-gray dolomite containing abundant conical 

stromatolites in the upper half. The formation 

forms a distinctive dark-gray resistant unit that 

contrasts with the underlying reddish-brown relatively nonresistant Pitiquito Quartzite and the 

overlying light-gray relatively nonresistant Papalote Formation. Longoria (1981) reported that 

the holostratigraphic type of the Gamuza For-
PHYSICAL STRATIGRAPHY OF UPPER PROTEROZOIC AND CAMBRIAN ROCKS 13

mation consists of a lower 390 m of dark-gray thickbedded sandy dolomite and an upper 114 m of medium- to thick-bedded black stromatolitic dolomite. 

He reported that the parastratigraphic type is only 

80 m thick and consists dominantly of gray dolomite containing stromatolites in the upper part. Our 

work on the Gamuza Formation suggests that it 

is fairly uniform in thickness and lithology 

throughout the Caborca region and that it probably is generally 100 to 150 m thick. Thus, we think 

that the thickness of 514 m reported by Longoria 

(1981) for the Gamuza Formation in Cerro Gamuza 

is in error and that the 80 m reported by him for 

the formation in the Cerro El Arpa area is closer 

to its true thickness.

In the Cerro Rajon area, the Gamuza Formation 

is 135 m thick and consists of three distinctive 

units. The lower unit is 70.5 m thick and consists 

of medium-gray laminated to thin-bedded cliffforming dolomite containing intraclast conglomerate and irregular laminae suggestive of algal 

mats. The middle unit is 4.5 m thick and consists 

of gray-red dolomite, siltstone, and minor chert, 

and forms a nonresistant unit between the cliffforming lower and upper units. The upper unit is 

60 m thick and consists of medium-gray stromatolitic dolomite with irregular grayish-orange mottling. The stromatolites (Gamper and Longoria, 

1979; Weber and others, 1979) consist of vertical 

conical structures (Conophyton and related forms) 

that generally range in diameter from 5 to 20 cm 

(fig. 8).

The three units recognized in the Gamuza Formation in the Cerro Rajon area are widespread in 

the Caborca region. We have noted them on the 

east side of Cerro Calaveras and in the Cerros de 

la Cienega (sec. 3 of Eells, 1972). In the Cerro El 

Arpa and Cerro Pitiquito areas and near La Union 

in the Sierra del Viejo, we recognized the lower 

and upper units but not the middle unit.

10cm

FIGURE 8. Conical stromatolites in upper unit of the Gamuza Formation in the Cerro Rajon area. A, Conophyton, section 

parallel to axis of vertical stromatolite column. Specimen MM-62-33. B, Conophyton and Jacutophyton, section viewed from 

top perpendicular to vertical axis of stromatolite column. Hammer is 35 cm long.
14 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

The Gamuza Formation is widely exposed in the 

Cerros de la Cienega, Cerro Calaveras, Cerro Aquituni, and Cerro San Clemente areas mapped by 

Eells (1972), although Eells did not recognize the 

equivalence of units now known to be the Gamuza. 

The Gamuza Formation is correlated with the 

lower 110 m of unit 9 of Eells (1972) in Cerro Calaveras, with unit 6 of Eells (1972, pi. 4, sec. 3) in the 

Cerros de la Cienega, and with unit 2 of Eells (1972) 

in the Cerro Aquitini area. Longoria and others 

(1978, fig. 1), Longoria and Perez (1979, p. 126, fig. 

2), and Longoria (1980,1981) previously noted that 

Eells' unit 2 is the Gamuza. The Gamuza Formation also crops out in Cerro Llano Verde, Cerro 

Clemente, Cerro Pitiquito, and the Sierra del Viejo.

PAPALOTE FORMATION

The name "Papalote Formation" was introduced 

by Longoria and others (1978) and Longoria and 

Perez (1979). The holostratigraphic type (type 

section) is in the northernmost part of the east 

flank of the Cerro El Arpa area, and the parastratigraphic type (reference section) is in the Cerro 

Gamuza area (Longoria, 1980,1981).

In the holostratigraphic type in the Cerro El 

Arpa area (Longoria, 1980,1981), the Papalote Formation is 188 m thick and consists of light-gray 

laminated to thick-bedded dolomite, commonly containing algal-mat structures. In the Cerro El Arpa 

area, the Papalote Formation conformably overlies the Gamuza Formation, but the top is not exposed. In the parastratigraphic type in the Cerro 

Gamuza, the Papalote Formation is overlain by 

the Gachupin Group of Longoria (1980, 1981), although Longoria did not clearly indicate where he 

placed the contact of the Papalote Formation and 

Gachupin Group.

We here define the Papalote Formation as lying 

conformably above the Gamuza Formation, as did 

Longoria (1980, 1981), and below the Tecolote 

Quartzite as defined in this report. Such a definition is a departure from the usage of Longoria 

(1980,1981) who apparently included what we here 

include in the upper part of the Papalote Formation within his Gachupin Group. We believe that 

this modified definition of the Papalote is justified 

because most of what we now call the Papalote is 

lithologically similar dolomite. The Papolote as we 

define it is an easily mappable unit lying between 

the distinctive stromatolite-bearing upper unit of 

the Gamuza Formation and equally distinctive 

light-colored quartzite and sandy dolomite of the 

Tecolote Quartzite. We also believe that the name

"Gachupin Group" is not needed, and so we do not 

use it in this report. As defined by Longoria (1981, 

1982), the Gachupin Group contains several distinctive units that should, in our opinion, be defined as separate formations. The Gachupin Group 

of Longoria (1980, 1982) includes what we here 

define as the upper part of the Papalote Formation, the Tecolote Formation, and part of the La 

Cienega Formation.

As defined here, the Papalote Formation in the 

Cerro Rajon area is 404.5 m thick, consists mostly 

of dolomite, and is divided into six units. Unit 1 is 

about 31.5 m thick and consists of slope-forming 

poorly exposed pale- to moderate-red siltstone and 

quartzite and medium-gray dolomite. Unit 2 is 

about 20 m thick and consists of cliff-forming lightgray laminated dolomite. Unit 3 is 7.5 m thick and 

consists of slope-forming pale-red to pale-reddishbrown silty dolomite to dolomitic siltstone. Unit 4 

is 157 m thick and consists of ledge-forming lightgray evenly laminated to thin-bedded dolomite. 

Domal stromatolites occur in the lower part of unit 

4, but no conical Conophyton-like stromatolites 

were noted. Unit 5 is 31.5 m thick and consists of 

pinkish-gray fine- to medium-grained laminated 

cross-stratified quartzite and sandy dolomite to 

dolomite. Unit 6 is 157 m thick and consists of 

medium light-gray to light olive gray indistinctly 

laminated to thin bedded dolomite, with sparse 

moderate red siltstone in the lower part.

In addition to its occurrence in the Cerros El 

Arpa, Gamuza, and Rajon areas described above, 

the Papalote Formation has also been identified 

in the Cerro Pitiquito area (Longoria and others, 

1978; Longoria and Perez, 1979; Mendoza, 1981; 

our observations in 1982); in the Cerro Aquituni 

and Cerro San Clemente areas (Longoria and others, 1978; Longoria and Perez, 1979; Longoria, 

1980, 1981), where it forms unit 3 of Eells (1972); 

and on the east side of Cerro Calaveras, where it 

forms the upper 30 m of unit 9 and all of unit 10 

of Eells (1972). On Cerro Calaveras, the Papalote 

Formation contains six units, the same as those 

in the Cerro Rajon area, although the thickness 

and lithology of these units on Cerro Calaveras 

differ somewhat from those in the Cerro Rajon 

area. In particular, unit 1 on Cerro Calaveras contains more quartzite, and unit 5 is thicker and 

contains more quartzite than in the Cerro Rajon 

area. Granule conglomerate also occurs in unit 1 

on Cerro Calaveras, whereas it is absent in the 

Cerro Rajon area. The Papalote Formation is also 

extensively exposed in the Sierra del Viejo, where 

it appears to be at least twice as thick as in the
PHYSICAL STRATIGRAPHY OF UPPER PROTEROZOIC AND CAMBRIAN ROCKS 15

Cerro Raj on area and forms much of the high crest 

of the range (Alfonso Salcido-Reyna, oral commun., 

1983).

TECOLOTE QUARTZITE

The Tecolote Quartzite is here named for outcrops in the Cerro Rajon area. The type section is 

1.3 km southeast of Cerro Rajon at lat 30°24.9' N., 

long 111°56.7' W. The unit is named for Cerro El 

Tecolote (fig. 2), 8.2 km south-southeast of the type 

section (El Prieto quad., H12A77, l:50,000-scale 

map).

In the type section, the Tecolote Quartzite is 

168.5 m thick and composed of pinkish-gray and 

yellowish-gray medium- to coarse-grained quartzite and sandy dolomite, and minor amounts of very 

finely crystalline dolomite. The quartzite and 

sandy dolomite are evenly laminated to thin bedded and contain common thin trough and tabular 

planar sets of cross strata.

The Tecolote Quartzite is also recognized on the 

east side of Cerro Calaveras, where it forms the 

lower 70 m of Eells' unit 11. It also occurs 3 km 

southeast of Cerro Clemente at lat 30°18' N., long 

111°58.5' W. The quartzite in the upper part of the 

Gachupin Group of Longoria (1980, 1981) in Cerro 

Gamuza may also be the Tecolote Quartzite, but 

we have not examined the rocks in this area with 

enough detail to be sure. We have also noted the 

Tecolote Quartzite near the crest of the Cerro Pitiquito area; these rocks were mapped erroneously, we believe as the Pitiquito Formation 

by Mendoza (1981). The Tecolote Quartzite also 

crops out on Cerro Llano Verde and in the Sierra 

del Viejo (Alfonso Salcido-Reyna, oral commun., 

1983).

LA CIENEGA FORMATION

The La Cienega Formation is here named for 

outcrops in the Cerro Rajon area. The type section 

(composite) is 1 km southeast of Cerro Rajon at 

lat 30°25' N., long 111°56.8' W. (El Prieto quad., 

H12A77, l:50,000-scale topographic map). The formation is named for the village of La Cienega, 

located 24.6 km south of the type section (La Cienega quad., H12A87, l:50,000-scale topographic 

map).

In the type section, the La Cienega Formation 

is 178 m thick and is divided into four major units. 

Unit 1 is 76 m thick and consists of a mixture of 

rock types, including dolomite, sandy dolomite, 

silty dolomite, quartzite, siltstone, and greenstone,

and forms a slope with minor ledges. Unit 2 is a 

37.5 m thick ledge-forming medium-gray dolomite, 

with common sandy dolomite in the top 7.5 m. Unit 

3 is 37.5 m thick and consists of a slope-forming 

sequence of dolomite, sandy dolomite, siltstone, 

quartzite, and greenstone. Unit 4 is 27 m thick and 

consists of ledge-forming medium-light-gray 

dolomite.

The La Cienega Formation is also recognized 

near and along the crest of Cerro Calaveras, where 

it forms the upper 180 m of unit 11 of Eells' (1972). 

It also occurs near the crest of Cerro Pitiquito, 

where it was mapped erroneously by Mendoza 

(1981) as either the Gamuza or Papalote Formation. The La Cienega also crops out 2.1 km southwest of Cerro Clemente at lat 30°18.5' N., long 

112°0.6' W., and probably also 3 km southeast of 

Cerro Clemente at lat 30°18' N., long 111°58.5' W.

PUERTO BLANCO FORMATION

The Puerto Blanco Formation was named by 

Cooper and Arellano (1952, p. 4) for outcrops on 

the west side of Cerro de la Proveedora, 11 km west 

of Caborca (fig. 2), where it consists of about 293 

m of green shale, sandstone, and limestone, containing diagnostic Lower Cambrian fossils. The 

base of the Puerto Blanco Formation is not exposed on Cerro de la Proveedora. In the Cerro Calaveras and Cerro Aquituni areas, Eells (1972) 

studied a more complete succession of upper Proterozoic and Lower Cambrian rocks than that exposed on Cerro de la Proveedora. He defined the 

Puerto Blanco Formation as a siltstone, quartzite, 

and limestone unit lying between his volcaniclastic 

unit 12 below and the Proveedora Quartzite above. 

His unit 12 is 90 m thick and composed of volcaniclastic boulder conglomerate, litharenite, and, in 

places, porphyritic olivine basalt.

Longoria (1981), although he did not discuss 

Eells' (1972) definition of the Puerto Blanco Formation, included basalt flows, volcanic agglomerate, and volcanic breccia in his Puerto Blanco. 

These volcanic and volcaniclastic units mentioned 

by Longoria (1981) are, in part, equivalent to unit 

12 of Eells (1972). Thus, Longoria (1981) broadened 

the original definition of the Puerto Blanco. In the 

present report, we follow Longoria's usage and 

include the volcanic and volcaniclastic units, including unit 12 of Eells, in the Puerto Blanco Formation. Such a usage seems useful because, in the 

Cerro Rajon area, basalt (greenstone) and volcaniclastic rocks are interstratified with siltstone and 

quartzite similar to those included by Eells (1972)
16 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

in his Puerto Blanco Formation. A similar relation 

was observed about 3.5 km southeast of Cerro 

Clemente at lat 30°18' N., long 111°58' W., where a 

black vesicular basalt occurs within a sequence of 

siltstone and very fine grained sandstone similar 

to rocks included in the Puerto Blanco Formation 

by Eells (1972). Finally, the volcaniclastic rocks 

here included in the Puerto Blanco Formation are 

generally nonresistant and topographically 

weather to form valleys along with the remainder 

of the Puerto Blanco Formation.

In the Cerro Rajon area, the Puerto Blanco Formation is 717 m thick and is divided into four major 

units. Unit 1 is 285.5 m thick and characterized 

mainly by the presence of volcaniclastic rocks and 

greenstone. The volcaniclastic rocks include sandstone to boulder conglomerate composed of greenstone, dolomite, sandy dolomite, and siltstone 

clasts set in a silty fine to very coarse grained sand 

matrix. The greenstone contains altered mafic 

minerals set in a chloritic matrix. Unit 1 also contains nonvolcanigenic siltstone and quartzite, including, in the middle, 80 m of pale-red fine-grained 

quartzite and minor siltstone. Unit 2 is 173 m thick 

and consists of greenish-gray to yellow-gray siltstone and minor very fine grained quartzite. Unit 

3 is 117.5 m thick and is divided into three parts, 

Archaeocyathid-bearing limestone occurs in the 

upper and lower parts, and siltstone, quartzite, 

and minor limestone in the middle part. Unit 4 is 

141 m thick and consists of well-bedded limestone, 

silty limestone, siltstone, quartzite, and minor 

amounts of dolomite. Skolithos (= Scolithus, a vertical burrow) is common in the quartzite of unit 4.

The Puerto Blanco Formation changes facies 

markedly from one locality to another in the Caborca region. At one locality 3.5 km southeast of 

Cerro Clemente, the Puerto Blanco Formation consists of fine- to coarse-grained cross-stratified sandstone in the lower part, of siltstone and very fine 

grained sandstone in the middle part, and of limestone in the upper part. No volcaniclastic rocks 

occur in the lower part hi contrast to the Cerro 

Rajon section, and the only volcanic rock is a vesicular basalt less than 20 m thick that occurs in 

the middle siltstone and very fine grained sandstone of the formation.

In the Cerro Calaveras and Cerro Aquituni 

areas, Eells (1972) divided the Puerto Blanco Formation into three members. As mentioned above, 

we also include unit 12 of Eells (1972) in the Puerto 

Blanco Formation, and so the Puerto Blanco Formation, as we define it in Eells' study area, is 

divided into four units. These four units are comparable to, but differ considerably in detail from, 

the four units in the Cerro Rajon area. Unit 1 (unit 

12 of Eeels, 1972) in the Cerro Calaveras and Cerro 

Aquituni areas is 90 m thick and consists of volcaniclastic boulder conglomerate, litharenite, and, 

locally, porphyritic olivine basalt (Eells, 1972). Unit 

2, Eells' lower member of the Puerto Blanco Formation, is 194 to 288 m thick and consists of siltstone and very fine grained to fine-grained sandstone and quartzite. Unit 3, Eells' middle member 

of the Puerto Blanco Formation, is 68 to 126 m 

thick and consists entirely of limestone on Cerro 

Calaveras and of archaeocyathid-bearing limestone, quartzite, and dolomite in the Cerro Aquituni area. Unit 4, Eells' upper member of the 

Puerto Blanco Formation, is 90 to 100 m thick and 

consists of very fine grained to fine-grained quartzite in the lower part and of siltstone in the upper 

part. Skolithos (a vertical burrow) is common in 

the quartzite of unit 4. The largely siliciclastic unit 

4 of the Cerro Calaveras and Cerro Aquituni areas 

contrasts with the largely carbonate unit 4 of the 

Cerro Rajon area.

More study is needed to document and interpret 

the facies changes in the Puerto Blanco Formation. Our work clearly indicates that significant 

facies changes occur but is insufficient to understand their regional distribution and origin.

PROVEEDORA QUARTZITE

The Proveedora Quartzite was named by Cooper 

and Arellano (1952, p. 4) for outcrops on Cerro de 

la Proveedora, 11 km west of Caborca. The Proveedora consists of pinkish-gray fine- to mediumgrained vitreous quartzite that in most areas 

forms a conspicuous ridge or ledge. The quartzite 

is laminated to very thin bedded, although in most 

places stratification is difficult to see, and contains 

minor amounts of very thin tabular planar sets of 

low-angle cross strata. Micaceous coarse-grained 

siltstone occurs in thin to thick sets in the lower 

part of the formation. Skolithos (a vertical burrow) 

is common m quartzite in the lower half of the 

formation. The Proveedora Quartzite is 223 m thick 

in the type area, 201 m thick in the Cerro Rajon 

area, and 224 m thick in the Cerros Calaveras area 

(Eells, 1972). It also occurs in the Cerro Clemente 

area, in the Cerros de la Cienega (Eells, 1972), and 

in the southernmost part of the Sierra del Viejo 

(A. R. Palmer, written commun., 1981).

BUELNA FORMATION

The Buelna Formation was named by Cooper 

and Arellano (1952, p. 4, 7,12) for Cerro de Buelna,
BIOSTRATIGRAPHY 17

about 14 km northwest of Caborca. The Buelna 

consists of limestone, dolomite, sandy limestone 

and dolomite, and minor quartzite and siltstone. 

The formation is 101 to 121 m thick in the type 

area, 77.5 m thick in the Cerro Raj on area, 68 m 

thick in the Cerro Calaveras area (Eells, 1972), and 

104 m thick in the Cerro de la Cienega area (Eells, 

1972). It also occurs in the Cerro Clemente and 

Cerro Pozo Serna areas.

CERRO PRIETO FORMATION

The Cerro Prieto Formation was named by 

Cooper and Arellano (1952, p. 7) for Cerro Prieto, 

about 2 km southwest of Caborca. The Cerro Prieto 

Formation is characterized by massive cliff-forming medium-gray limestone containing abundant 

spherical oncoliths (Girvanella), about 1 to 2 cm in 

diameter. Its dark color and resistant weathering 

contrast with the lighter colored and relatively 

nonresistant overlying and underlying Buelna and 

Arrojos Formations. The Cerro Prieto Formation 

is 100 m thick in the type area, 82 m thick in the 

Cerro Raj on area, and 88 m thick in the Cerros de 

la Cienega. The Cerro Prieto Formation also occurs 

in the Cerro Clemente area and in the southernmost part of the Sierra del Viejo.

ARROJOS FORMATION

The Arrojos Formation was named by Stoyanow 

(1942, p. 1264) but was more completely described 

by Cooper and Arellano (1952, p. 9). It is named 

for the Cerros de los Arrojos, about 19 km westsouthwest of Caborca. The Arrojos Formation consists of nonresistant thin-bedded limestone, limy 

siltstone, and siltstone. It is 310 m thick on Cerro 

de la Proveedora (Cooper and others, 1952, fig. 6) 

and 201 m thick in the southern Cerros de la Cienega (Eells, 1972). Only the lower 93 m is exposed 

in the Cerro Raj on area.

TREN FORMATION

The Tren Formation was named by Cooper and 

Arellano (1952, p. 9) for outcrops in the Cerros de 

los Arrojos, 19 km west-southwest of Caborca. It 

consists of massive medium-gray dolomite and 

limestone, and forms a conspicuous resistant unit 

on Cerro de la Proveedora and in the Cerro de los 

Arrojos. A complete section is not known in the 

Caborca region. The exposed part is 490 m thick 

in the type area. Eells (1972) reported that the 

lower 100 m is exposed in the Cerro Calaveras area.

BIOSTRATIGRAPHY

The upper Proterozoic and Cambrian rocks in 

the Caborca region contain a wide assortment of 

fossils (fig. 9) that include algal filaments in the 

El Arpa Formation, possible trace fossils from the 

Clemente Formation, Conophyton and related stromatolites from the Gamuza Formation, a primitive 

shelly fauna from the La Cienega Formation, archaeocyathids, trilobites, and brachiopods from 

the Puerto Blanco Formation, and various trilobites and brachiopods from the Buelna through 

Tren Formations. A detailed description of some 

of these fossils has been given by McMenamin 

(1984).

A silicified microbiota of blue-green algallike filaments occurs in the El Arpa Formation in black 

silicified wackestone chert collected from the Cerro 

El Arpa area (McMenamin and others, 1983). Two 

filament morphologies are present: narrow darkwalled tubes and thicker translucent tubes. The 

first filament is a tubular nonseptate form, 2 to 3 

(xm in diameter, as large as 120 |xm long, with thin 

(less than 0.2 (Jim) dark walls. These filaments are 

found between and within peloids in the wackestone. Aside from the absence of septae, they most 

closely resemble the Late Proterozoic genus Eomycetopsis (Schopf, 1968). The other filament is larger 

(avg diameter, 5 (xm) and is unlike that of any 

previously described Proterozoic morphology.

At the base of unit 6 of the Clemente Formation, 

traces suggestive of metazoan activity (fig. 10; 

McMenamin and others, 1983, fig. 3e) and dimpled 

mound structures (fig. 11) which are probably pitand-mound fluid-escape structures occur in a red 

sandy siltstone in the Cerros de la Cienega. These 

traces (fig. 10) are too complex to be easily discounted as sedimentary structures, and a metazoan origin seems most likely. Nevertheless, we 

note that the Clemente Formation contains various unusual sedimentary structures (flute casts, 

tool markings, dewatering structures, and traillike 

scratches) and so caution must be exercised when 

interpreting fossillike markings (Cloud, 1973).

Conical stromatolites that occur in unit 3 of the 

Gamuza Formation have received a good deal of 

study (Gamper and Longoria, 1979; Weber and others, 1979; Cevallos-Ferriz and Weber, 1980; Weber 

and Cevallos-Ferriz, 1980; Cevallos-Ferriz, 1981; 

Cevallos-Ferriz and others, 1982). The assemblage 

is dominated by Jacutophyton and Conophyton (fig. 

8) and by Platella. Many of the conical stromatolites are large (as much as 1 m wide and as much 

as 2 m high).
18 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

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Based in part on Cooper and others (1952), Lochman (1953), Rowell (1962), Fritz (1975), Weber and others (1979), 

Yochelson (1981), A. R. Palmer (written communs., 1981-82), S. M. Awramik (oral commun., 1982), and McMenamin 

and others (1983). See figure 5 for explanation of lithologic symbols.
BIOSTRATIGRAPH Y 19

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20 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

Weber and others (1979) suggested a middle Riphean (Middle or early Late Proterozoic) age for 

these stromatolites, equivalent to the Riphean R2 

(or possibly R3) stromatolite biostratigraphic zone 

of Keller and Semikhatov (1976, table 1). I. N. 

Krylov (written commun. to S. M. Awramik, 1982) 

believed this to be a plausible age assignment, but 

he cautioned that both Jacutophyton and Conophyton are known from the Vendian and Early 

Cambrian, and the microstructure of these Ca10 mrn

FIGURE 10. Possible metazoan trace fossils from unit 6 of the 

Clemente Formation, Cerros de la Cienega. Specimen MM82-79.

I

30mm

I

FIGURE 11. Dimpled mound structure (probably pit-andmound fluid-escape structures) in unit 6 of the Clemente 

Formation, Cerros de la Cienega. Specimen MM-82-79b.

borca stromatolites is unlike that of Riphean conical stromatolites of the Siberian platform. Keller 

and Semikhatov (1976) showed both Jacutophyton 

and Conophyton ranging into the lower Vendian, 

and a recent report from China (Gao and others, 

1982) described Conophyton from the Chigebrak 

Formation, which is probably Vendian in age.

Considering the possible occurrence of trace fossils well below the stromatolites, a post-middle Riphean age (possibly Vendian) seems most likely for 

the Mexican stromatolites. We emphasize, however, that a Vendian age for this distinctive Jacutophyton-Conophyton stromatolite assemblage 

would be quite anomalous and would necessitate 

an important revision of stromatolite biostratigraphy. If these stromatolites are middle Riphean, 

they seriously challenge our interpretation of the 

traces in the Clemente Formation as trace fossils 

(pre-middle Riphean trace fossils have never been 

unambiguously documented) and our correlation 

(discussed below) of the Clemente Formation with 

the Johnnie Formation (of Vendian age) of California and Nevada. Before our discovery of possible trace fossils and units resembling the Rainstorm member of the Johnnie Formation below the 

Caborca stromatolites, the Gamuza Formation 

was thought (Benmore, 1978) to correlate with the 

Conophyton-bearing Crystal Springs Formation 

(Roberts, 1974) and with the 'tConophyton-bearing 

Beck Spring Formation (D. Pierce, written commun., 1983) of the Pahrump Group in the Death 

Valley region.

Stromatolites were also noted in the Papalote 

Formation, but these are sparse and consist of low 

domal "Co^ema"-like forms.

A pre-trilobitic small shelly fauna occurs in unit 

1 of the La Cienega Formation. The fauna consists 

of millimeter-size tubular and conical shells preserved as discontinuous channel-lag horizons (as 

much as 20 cm thick) and coquina in a sandy dolomitic limestone approximately 50 m above the 

base of unit 1 of the La Cienega Formation. Associated 10-cm-thick crossbeds and very coarse 

sand grains attest to conditions of high-energy deposition. The tubular fossils are generally broken 

to less than 10 mm in length, but at least five 

different morphologies are still recognizable 

(McMenamin and others, 1983). Unornamented 

tubes weathering out of the carbonate matrix (fig. 

12) may belong to the genus Sinotubulites (Chen 

and others, 1981), known from sedimentary rock 

near the Sinian-Lower Cambrian boundary in the 

Yangtse Gorge, China. Other fossils from the La 

Cienega Formation include regularly annulated
BIOSTR ATIGR APH Y 21

tubes (tube diameter, commonly 1.2 1.8 mm); 

smooth-walled forms with multiple wall layers, possibly nested hyolithids (diameter, commonly 2.0- 

3.0 mm); and robust tubes with irregular annulations, also possibly Sinotubulites (avg diameter, 

2.4 mm). The affinities of these shells are uncertain 

at present.

A similar fauna of probable earliest Cambrian 

age has been recently reported from the uppermost 

part of the Reed Dolomite and the lowermost part 

of the Deep Spring Formation at Mount Dunfee, 

Esmeralda County, Nev. (Gevirtzman and others, 

1982). This fauna includes small calcareous shelly 

fossils, tentatively identified as Coleoloides Walcott, Coleolella Missarzhevskii, and Salanytheca 

Missarzhevskii, as well as other, undescribed 

forms (Signer and others, 1983). The irregularly 

annulated robust tube and smooth single-walled 

tubes of the Caborca shelly fauna may also be 

present in the Nevada fauna. The stratigraphic 

positions of the Mexican and Nevadan shelly-fossil 

occurrences are virtually identical. The shelly fossil Wyattia reedensis, described from the Reed Dolomite in the White-Inyo Mountains, Calif. (Taylor, 

1966), may be correlative with both the Nevada 

and Sonora pre-trilobitic faunas. In fact, both 

faunas contain Wyattia-like fossils. Cribricyathidlike tubular shelly fossils (if these poorly preserved 

specimens are, indeed, fossils), reported from the 

D member of the Stirling Quartzite (Langille, 

1974), are smaller (mean diameter, 0.52 mm) than 

tubes from Caborca and Mount Dunfee, and their 

stratigraphic position suggests that they represent a somewhat older fauna.

FIGURE 12. Unornamented tabular shelly fossils from unit 1 

of the La Cienega Formation, Cerro Raj on area. Possibly 

genus Sinotubulites Chen, Chen, and Qian, 1981. Specimen 

MM-82-84.

A possible specimen of the trace fossil IRusophycus was recovered from pale-olive shale of unit 

3 of the La Cienega Formation. Rusophycus is 

thought to be a trilobite resting trace, and trace 

fossils ascribed to the activities of trilobitelike organisms are known to occur below the oldest trilobite body fossils in the White-Inyo Mountains and 

Death Valley regions (Alpert, 1977).

The shelly faunas from the La Cienega, Reed, 

and Deep Spring Formations appear to belong to 

the pre-trilobitic-shelly-fossil bio stratigraphic interval known from many parts of the world. These 

faunas are commonly referred to as "Tommotian" 

in age by correlation with pre-trilobitic faunas 

from the Tommotian Stage of the Siberian platform, but their age equivalence is far from being 

definitively established. Albert (1977) suggested 

that Tommotian-equivalent sediment can be recognized in western North America by the occurrence of trilobite ichnofossils (such as Rusophycus) 

below the lowest trilobite body fossils. Thus, the 

La Cienega Formation may correlate, in part, with 

Siberian strata of Tommotian age and should be 

considered the pre-Fallotaspis Zone of Fritz (1972).

The Puerto Blanco Formation contains trilobites 

(Lochman, 1948, 1952, 1953, 1956; A. R. Palmer, 

written commun., 1982, 1983) assigned to the Bonnia-Olenellus, Nevadella, and Fallotaspis Zones of 

Fritz (1972, 1975), as well as archaecyathids (Okulitch, 1952), Salterella (Lochman, 1952), hyolithids 

(Lochman, 1952), the trace fossils Planolites, Scolicia, Bergaueria, Cruziana, and Rusophycus, linguloid and obolelloid brachiopods (Cooper, 1952), 

possible nisusiid brachiopods, Hyolithellus (McMenamin and others, 1983), tommotiids, helcionellid and pelagiellid gastropods, and Microdictyon sp. (M. gen. and sp. indet. of Mathews and 

Missarzhevskii, 1975).

In the Cerro Raj on area, siltstone in unit 1 of 

the Puerto Blanco Formation contains Planolites 

and ?Scolicia, but no body fossils are known. Brachiopods (possibly nisusiids) occur 30 m above the 

base of unit 2. Similar brachiopods are known from 

the Fallotaspis Zone of the White-Inyo Mountains 

(Rowell, 1977). Microdictyon sp. (M. gen. and sp. 

indet. of Mathews and Missarzhevskii, 1975) occurs 

65 m above the base of unit 2; this fossil is known 

from sedimentary rocks of Atdabanian and 

younger age (S. Bergtson, oral commun., 1983). The 

Atdabanian Stage of the Siberian platform was 

correlated by Gangloff (1975) with the Fallotaspis 

zone of Fritz (1972). A partial trilobite cephalon 

with long genal spines (comparable to Fallotaspis 

but possibly not belonging to this genus) was found
22 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

by S. M. Awramik in an olive shale approximately 

120 m above the base of unit 2. Considering these 

biostratigraphic data in the Cerro Raj on area, an 

Atdabanian age (Fallotaspis zone) for unit 2 seems 

reasonable.

Archaeocyathids occur in limestone at the top 

and bottom of unit 3 of the Puerto Blanco Formation in the Cerro Rajon area. Nevadiid trilobites 

from the shale beds between the archaeocyathidbearing limestone beds have the long eyes of the 

genus Nevadia but possess a much narrower cephalon the pleural regions are not so wide as the 

forms illustrated by Nelson (1976), from the WhiteInyo Mountains of eastern California (A. R. Palmer, written commun., 1983). These trilobites are 

tentatively considered to be part of the Fallotaspis 

zone because they appear to be generally similar 

to the trilobites within the Fallotaspis zone in the 

Montenegro Member of the Campito Formation of 

the White-Inyo Mountains (A. R. Palmer, written 

commun., 1983).

Olenellid trilobite fragments, IWanneria, and 

Linguella have been reported from the Proveedora 

Quartzite (Cooper and others, 1952). Except for the 

abundant trace fossil Skolithos in the lower half 

of the Proveedora, however, fossils are generally 

rare.

The Buelna, Cerro Prieto, Arrojos, and Tren Formations contain an extensive trilobite fauna 

(Lochman, 1948, 1952, 1953, 1956; Stoyanow, 1952; 

Fritz, 1975), as well as: Girvanella oncolites (Johnson, 1952) in the Buelna, Cerro Prieto, and Arrojos 

Formations; hyolithids, Salterella, and archaeocyathids in the Buelna Formation (Lochman, 1952; 

Okulitch, 1952); and brachiopods in the Buelna, 

Arrojos, and Tren Formations (Cooper, 1952). The 

Cerro Prieto and Buelna Formations are assigned 

to the Bonnia-Olenellus Zone of Fritz (1972, 1975). 

The transition to the Middle Cambrian (PagiuraPoliella! and Albertella Zones) occurs near the base 

of the Arrojos Formation (Fritz, 1975). Fritz indicated that the boundary between the Albertella 

and Glossopleura Zones is about 200 m above the 

base of the Arrojos Formation on Cerro 

Proveedora.

Johnson's (1952) description of calcareous Girvanella filaments from oncolites in the Buelna Formation (G. mexicana, filament diameter^ 20-28 |xm) 

and the Arrojos Formation (G. of. sinensis, filament diameter, 9-12 |xm) indicates that these 

Lower Cambrian oncolites can be properly referred 

to as Girvanella oncolites. Stratigraphers should 

be wary of identifying all nonmicrofossiliferous oncolites as Girvanella, because other blue-green algallike micro-organisms besides Girvanella can 

participate in the construction of oncolites (Rezak, 

1957; Brown, 1981).

PALEOCURRENT STUDIES

We made a total of 321 individual measurements 

of the dip directions of cross strata in upper Proterozoic and Lower Cambrian rocks in the Caborca 

region (fig. 13). These readings were at 14 localities 

and included data from six different stratigraphic 

units: the El Arpa Formation, the Pitiquito 

Quartzite, the Tecolote Quartzite, the Puerto 

Blanco Formation, the Proveedora Quartzite, and 

the Buelna Formation. The measurements were 

corrected for tilt imposed by the structural dip of 

units, but no attempt was made to correct for rotation caused by plunging folds. Most measurements were made in strata with a structural dip 

of less than 60°, which would result in an angular 

error of 10° or less, regardless of the plunge of folds 

(Ramsey, 1961). The units in which measurements 

were made are generally fine to coarse grained 

quartzite or dolomitic sandstone that contain tabular planar sets, and a lesser number of trough 

sets, of small-scale cross strata.

A considerable variation of paleocurrent direction as determined from cross strata is evident in 

the Caborca region (fig. 13). Overall, no dominant 

direction is evident ("all readings" insert, fig. 13). 

Studies at individual localities, however, characteristically show a dominant paleocurrent direction or oppositely directed paleocurrent directions 

suggestive of currents generated by the ebb and 

flow of tides.

The absence of a dominant paleocurrent direction in the Caborca region was a disappointment 

because we had expected that paleocurrent directions might be fairly consistent, judging from such 

a consistency in many regions of the United States. 

The overall pattern in the United States (fig. 14) 

shows flow directions generally westward in Idaho 

and Nevada, southwestward in Arizona, southwestward to southward in New Mexico and western Texas, and southward to southeastward in central Texas. Stewart (1982) suggested that these 

paleocurrent directions are generally at right angles to the continental margin; if so, then the 

southwesterly, southerly, and southeasterly transport directions in the Southern United States 

would indicate a generally easterly trend of the 

continental margin across the Southern United 

States and northern Mexico. We had hoped that 

paleocurrent data in the Caborca region would
REGIONAL CORRELATIONS 23

30°45'

112°00'

30°30' 

30°15' 

EXPLANATION

Buelna Formation 

Proveedora Quartzite 

Puerto Blanco Formation 

Tecolote Quartzite 

Pitiquito Quartzite 

F.I Arpa Formation

n = 1 0 Number of readings 

1 2 3

Number of readings in 

a 10-degree segment

 Strike of inferred paleoslope

Number of readings in 

10-degree segment

10

I.

15 KILOMETERS

FIGURE 13. Paleocurrent directions in upper Proterozoic and Lower Cambrian rocks of the Caborca region, Mexico.
24 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

,' NEVADA ' ' ' '. ' V-.' |;V'A':f£#U ' \ : '.-< : . ' vV-:^7-- ' . . ^ i^

CALIFORNIA--

'

% > ' :V'-V ' n%'': '.' 

 ' .-^.. :- .-^-x-.. -.

^@?&il O --^^L 

' %- SONORA

EXPLANATION

Barb indicates current direction. Line

indicates inferred strike of paleoslope

at right angles to current direction.

Generalized in areas of abundant data

Cambrian cratonal rocks, partly restored.

Upper Proterozoic rocks probably do not

occur in these areas

Bimodal-bipolar current directions. Line 

indkates inferred strike of paleoslope 

at right angles to current directions

Upper Proterozoic and Cambrian rocks absent

Anadarko-Ardmore aulacogen

Miogeoclinal upper Proterozoic and Cambrian rocks

\\\\

Ouachita geosynclinal rocks, allochthonous.

Lower(?), Middle(?), and Upper Cambrian rocks are

present (Nicholas and Pozendal, 1975), but

distribution is uncertain

FIGURE 14. Paleocurrent directions and paleogeography from Late Proterozoic to Late Cambrian time in the Western United 

States and Sonora, Mexico. Paleocurrent studies in miogeoclinal belt are from upper Proterozoic and Lower Cambrian 

strata. Studies in cratonal areas are in clastic units at the base of the Cambrian sequence in each area. These basal rocks 

young progressively toward the interior of the continent and range in age from Early Cambrian adjacent to the miogeocline 

to Late Cambrian in interior cratonal areas. Data from McKee (1940), Wilson (1962), Seeland (1968, 1969), Stewart (1970), 

Hereford (1977), and Thompson and Potter (1981); figure 13 of this report; and fieldwork by J. H. Stewart in the San 

Bernardino Mountains, Calif. Additional current-direction data, though not used here, were reported by Diehl (1974, 1979), 

Williams and others (1974), Moore (1976), Benmore (1978), and Wertz (1982).
REGIONAL CORRELATIONS 25

help evaluate this concept, but the results are 

inconclusive.

REGIONAL CORRELATIONS

Upper Proterozoic to Middle Cambrian strata in 

the Caborca region can be correlated in detail with 

strata of the southern Great Basin in eastern California and southern Nevada, of the San Bernardino Mountains in southern California, and of the 

Sierra Agua Verde in central Sonora (fig. 1).

SOUTHERN GREAT BASIN

Upper Proterozoic to Middle Cambrian strata in 

the southern Great Basin consist, in ascending 

order, of: the Noonday Dolomite, the Johnnie Formation, the Stirling Quartzite, the Wood Canyon 

Formation, the Zabriskie Quartzite, the Carrara 

Formation, and the lower part of the Bonanza 

King Formation (fig. 15). Eells (1972) indicated that 

the Puerto Blanco Formation of the Caborca region correlates with part of the Wood Canyon Formation; the Proveedora Quartzite, with the Zabriskie Quartzite; the Buelna, Cerro Prieto, and 

Arrojos Formations, collectively, with the Carrara 

Formation; and the Tren Formation, with the 

lower part of the Bonanza King Formation (fig. 

15). We propose here that units 4 to 6 of the Clemente Formation correlate with the Rainstorm 

Member of the Johnnie Formation; the Pitiquito 

Quartzite, the Gamuza Formation, the Papalote 

Formation, and the Tecolote Quartzite, with the 

Stirling Quartzite; and the La Cienega Formation, 

with the lower member of the Wood Canyon Formation (fig. 15). Precise correlations of the El Arpa 

and Caborca Formations and of units 1 to 3 of the 

Clemente Formation are not possible, although 

these rocks are lithologically similar to some parts 

of the Noonday Dolomite and the Johnnie Formation, to which they may be related.

In previous discussions by Cameron (1981, 1982) 

and Stewart (1982), the sequence of rocks below 

the Puerto Blanco, and, in part, the Puerto Blanco 

itself were considered to significantly differ lithologically from strata presumably within the same 

stratigraphic interval in the southern Great Basin. 

These supposed dissimilarities were based on comparisons with a stratigraphic section in the Caborca region that is now known to be partly in 

error. The new information presented in this report reveals a close similarity of the pre-Puerto 

Blanco strata in the Caborca and southern Great 

Basin regions.

The correlation of units 4 to 6 of the Clemente 

Formation of the Caborca region with the Rainstorm Member of the Johnnie Formation of the 

southern Great Basin is based on strong lithologic 

similarities as well as on a similar sequence of 

units (fig. 16). Unit 4 of the Clemente Formation 

is a greenish-gray siltstone that strongly resembles the lower part of the siltstone unit of the 

Rainstorm Member. This part of the Rainstorm 

Member is extensively exposed in the Death Valley 

region, where it has been considered to be possibly 

an altered tuff (Wright and Troxel, 1966). Unit 5 

of the Clemente Formation consists of a distinctive 

oolite or oolitic intraclast conglomerate that is correlated with a lithologically identical oolite ("Johnnie oolite") in the siltstone unit of the Rainstorm 

Member in the southern Great Basin area (fig. 6). 

The "Johnnie oolite" is extensively exposed in the 

southern Great Basin region (Stewart, 1970), 

where it is everywhere less than 4 m thick and is 

so distinctive that it can be recognized out of context of the surrounding rocks. The oolite unit of 

the Clemente Formation is somewhat unusual in 

that it everywhere contains and, in most places, 

is composed entirely of intraclast conglomerate 

composed of clasts of the oolite. Such intraclast 

conglomerate, however, also occurs in the "Johnnie 

oolite" in the southern Great Basin (Benmore, 

1978, p. 81-84), although it is not so common as in 

the Caborca region. Unit 6 of the Clemente Formation consists predominantly of pale-red and 

greenish-gray siltstone to very fine grained sandstone and minor silty limestone, containing abundant drag marks, flute casts, and ripple marks (fig. 

7). The siltstone and sandstone and their characteristic drag and flute marks are similar to siltstone, limy siltstone, and limestone of the carbonate unit of the Rainstorm Member of the Johnnie 

Formation of the southern Great Basin (Stewart, 

1970, 1974) and correlative units which have been 

recognized throughout a large area of eastern California, southern and eastern Nevada, and western 

Utah (Stewart, 1974; Christie-Blick, 1982).

The Pitiquito Quartzite, the Gamuza Formation, 

the Papalote Formation, and the Tecolote Quartzite are correlated with the Stirling Quartzite of 

the southern Great Basin on the basis of the presence of quartzite (Pitiquito and Tecolote Quartzites) similar to that in the Stirling. This correlation 

is supported by the position of the Pitiquito-Gamuza-Papalote-Tecolote sequence between the 

Clemente Formation below (correlated with the 

upper part of the Johnnie Formation) and the La 

Cienega Formation above (correlated with the
26 PROTEROZOIG AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

lower member of the Wood Canyon Formation) (fig. 

15). The predominant carbonate sequence of the 

Gamuza and Papalote Formations differs from the 

predominant quartzitic sequence of the Stirling 

Quartzite. The Stirling, however, does contain 

some carbonate the D member of the Stirling 

Quartzite in the northern Death Valley region contains 78 m of largely carbonate rock. In addition, 

the D member thickens northwestward (Stewart, 

1970) to form the 520 m thick Reed Dolomite of the 

White-Inyo Mountains of eastern California.

The correlations presented here are based on 

physical stratigraphy and disagree with correlations based on stromatolite zonation. Conophyton

1

NOPAH RANGE, DEATH VALLEY SAN BERNARDINO MOUNTAINS CABORCA

LU <

§ m

KM ;

r 3

- 2

o

2

BE < 

LU (£

O ^

u 0

Bonanza

King 

Formation

Carrara 

Formation

Zabriskie 

Quartzite

Wood

Canyon

Formation

Stirling 

Quartzite

Johnnie 

Formation

Noonday 

Dolomite

Cerro Prieto Fm 

Buelna Formation 

Proveedora 

Quartzite

Bonanza King 

Formation

Arrojos 

Formation

Carrara Formation

Zabriskie Quartzite

 __

Wood Canyon Formation

La Cienega 

Formation D member 

C member 

B member 

A member

Formation 

(may be too 

thick due to 

repetition of 

units)

Tecolote 

Quartzite

Rainstorm 

Member Papalote 

Formation

carbonatebearing member

Moonridge 

Siltstone member Quartzite

Lower carbonate-bearing member

Quartzite member

Lightning

Gulch 

Transitional member Formation

Wild horse

> Meadows

Quartzite

Baldwin 

Gneiss

of 

Guillou (1953)

LU <

a: <

LU OC 5*

o ^

-I <

o

Pitiquito Quartzite

Clemente 

Formation

Caborca 

Formation

El Arpa Formation 

Basement 

complex

ai O 

a. oc

§0

oc o

LU QC

FIGURE 15. Correlation of Middle Proterozoic to Cambrian rocks from California to Mexico. Nopah Range section after Stewart 

(1970), San Bernardino Mountains section after Cameron (1981,1982), and Caborca section after figure 5 of this report and 

Cooper and others (1952). Lithologic symbols same as in figure 5.
REGIONAL CORRELATIONS 27

Death Valley, 

California

METERS 

400 -l

Stirling 

Quartzite

300 -

200 -

Johnnie 

Formation

100 -

o-1

member

Rainstorm 

Member

Upper 

carbonate -

bearing 

member

Siltstone < member

(af 

197C

Siltstone 

and 

quartzite" 

unit

Carbonate 

unit "

Siltstone 

unit

ter Stev\ 

, p. 12:

O 0 OQ O O

 ^-^.

------

__ . __ . _

^ f S7-1

__.__._

Ip:

_ . __ . _. ._

 . . 

T: -. 

_:_:_

^r. _ .cj x*" >*" /"

^ x s

 s-s- / 

/ / /L

 / -S- -f-

/ S

 '/ / 

:_'.j_.'_

 ; 

 . . ^

 ._._

U/^J

/art, Ce 

3-126)

Pale-red fine- to

^-v. medium-grained

^\s^ quartzite

Pale -red and ^^^v^^

greenish-gray siltstone ^^^^ 

to very fine grained sandstone;^^^

and silty limestone in Death Valley 

region. Common ripple marks, 

drag marks, and flute casts 

in carbonate member of Johnnie 

Formation and in unit 6 of 

Clemente Formation

Oolitic dolomite ("Johnnie oolite")\^^

Light-greenish-gray siltstone

rro Rajon, 

Sonora

/ r

f /

/ / /

/ / /

/ /

} /

f / t-

/ /

f /

c / /~

/ / /

/ s

/ /

/ / /

:7_~_:

- '-' -

ca i= t=a

 

_ . _ . _

'o 'o 'o 'o

a o o o

-- ;-

]/ 'x*

/ /

/ /

-r 1 I l

1

4

 Unit 6 

- Unit 5

> Unit 4 

- Unit 3

 Unit 2 

- Unit 1

Gamuza 

Formatio

Pitiquito 

Quartzite

Clemente 

Formatio

Caborca 

Formatior

FIGURE 16. Correlation of part of the Clemente Formation and the Pitiquito Quartzite in the Caborca region with 

part of the Johnnie Formation and the Stirling Quartzite in the Death Valley region. Lithologic symbols same as in 

figure 5.
28 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

and associated stromatolites in the Gamuza Formation of the Caborca region are commonly considered to be Middle Proterozoic (middle Riphean) 

(Weber and others, 1979), whereas stromatolites 

(Cloud and Semikhatov, 1969) in the Johnnie Formation of the southern Great Basin, a unit considered to be older than the Gamuza in our correlations (fig. 15), are considered to be Late 

Proterozoic (Vendian). However, as discussed in 

the section above entitled "Biostratigraphy," Conophyton may range into the Vendian; and the occurrence of possible metazoan trace fossils below 

Conophyton supports a post-middle Riphean age 

for these stromatolites.

The correlation of the La Cienega Formation 

with the lower member of the Wood Canyon Formation is based on the similar lithology of these 

two units, which consist largely of greenish-gray 

siltstone, very fine grained to medium-grained 

quartzite, and dolomite. The two cliff-forming dolomite units (units 2, 4) of the La Cienega Formation are considered to be the same as the upper 

two conspicuous dolomite units in the lower member of the Wood Canyon Formation.

Unit 1 of the Puerto Blanco Formation locally 

contains grayish-red cross-stratified fine- to medium-grained sandstone and quartzite similar to 

that in the middle member of the Wood Canyon 

Formation, with which unit 1 is correlative in part. 

Much of unit 1, however, is composed of volcanogenie conglomerate and greenstone unlike any 

rocks in the middle member of the Wood Canyon 

Formation. The volcanogenic rocks in unit 1 are 

mostly coarse conglomeratic strata that are locally 

derived and probably of little use in establishing 

regional correlations.

Units 2, 3, and 4 of the Puerto Blanco Formation 

are correlated with the upper member of the Wood 

Canyon Formation. This correlation is supported 

by the dominance of siltstone and very fine grained 

quartzite in units 2 through 4 and in the upper 

member of the Wood Canyon Formation, as well as 

by the occurrence of archaeocyathid-bearing limestone in both sequences. The threefold division of 

unit 3 is similar to the threefold division of the 

Poleta Formation, a unit equivalent to part of the 

upper member of the Wood Canyon Formation 

(Stewart, 1970), in the White-Inyo Mountains region and adjacent areas of the southern Great 

Basin. Unless these units are time transgressive, 

however, correlation of unit 3 with the Poleta does 

not seem to be valid because the trilobites (see 

section above entitled "Biostratigraphy") in unit

3 most closely resemble those in the Montenegro 

Member of the Campito Formation that underlies 

the Poleta Formation.

The lithologies of the Proveedora Quartzite and 

the correlative Zabriskie Quartzite are remarkably similar. Both formations are composed of pinkish-gray fine- to medium-grained quartzite containing generally small scale low-angle cross 

strata. Skolithos ( = Scolithus) tubes are characteristic of the lower parts of these correlative 

quartzite units.

The Buelna, Cerro Prieto, and Arrojos Formations consist of interstratified siltstone and limestone, with minor amounts of sandy dolomite, 

sandy limestone, and quartzite lithologically similar to the correlative Carrara Formation of the 

southern Great Basin. These correlative rocks contain faunas of the Bonnia-Olenellus, Plagiura-Poliella, Albertella, and Glossopleura Zones (Fritz, 

1972,1975; Palmer and Halley, 1979). In detail, the 

Cerro Prieto Formation can be correlated (A. R. 

Palmer, written commun., 1981), on the basis of 

stratigraphic relations and fossils, with the Gold 

Ace Limestone Member of the Carrara Formation 

of the southern Great Basin and with the laterally 

equivalent Mule Spring Limestone of the WhiteInyo Mountains of California.

The Tren Formation and the correlative Bonanza King Formation consist of thick sequences of 

carbonate of comparable age (Eells, 1972).

SAN BERNARDINO MOUNTAINS

Upper Proterozoic and Cambrian rocks crop out 

in the San Bernardino Mountains and in the Victorville area of southern California (Stewart and 

Poole, 1975; Tyler, 1975,1979; Cameron, 1981,1982; 

Miller, 1981). The most complete sequence occurs 

in the San Bernardino Mountains, where the sequence was divided by Cameron (1982) into the 

following units, in ascending order: the Wildhorse 

Meadows Quartzite, the Lightning Gulch Formation, the Moonridge Quartzite, the Green Spot Formation, the Delamar Mountain Formation, the 

Wood Canyon Formation, the Zabriskie Quartzite, 

the Carrara Formation, the Bonanza King Formation, and the Nopah(?) Formation. The Wildhorse Meadows Quartzite was considered by Cameron (1981, 1982) to rest unconformably on the 

Baldwin Gneiss of Guillou (1953), a unit of gneiss 

and schist at least 1,750 ± 15 m.y. old (Silver, 1971). 

The sequence of units in the San Bernardino 

Mountains is difficult to determine because of me-
REGIONAL CORRELATIONS 29

tamorphism, complex structure, and poor outcrops, and some uncertainty exists about the exact 

sequence of units in that area. We accept the section described by Cameron (1981, 1982), although 

further work might require revisions to it.

We here propose that the Pitiquito Quartzite of 

the Caborca region correlates with the Moonridge 

Quartzite of the San Bernardino Mountains, the 

Gamuza and Papalote Formations with the Green 

Spot Formation, and the Tecolote Quartzite with 

the Delamar Mountain Formation (fig. 15). Correlations of higher units, the La Cienega through 

Tren Formations with the Wood Canyon Formation 

through Bonanza King Formations, which also occur in the southern Great Basin, were discussed 

above in connection with correlations with the 

southern Great Basin region.

The correlation of the Pitiquito, Gamuza, Papalote, and Tecolote with units in the San Bernardino Mountains is based primarily on similar 

lithology and sequence of units. This correlation 

is also strongly supported by the occurrence in 

both sequences of conical stromatolites in comparable parts of the stratigraphic section (fig. 15). 

In Caborca, these stromatolites consist of Conophyton and related forms in the Gamuza Formation. In the San Bernardino Mountains, the stromatolites (Cameron, 1981, 1982) occur in the lower 

part of the Green Spot Formation and consist of 

conical and columnar forms, possibly including 

Conophyton. On the west slope of the nearby Ord 

Mountains, a conical and columnar stromatolite 

was collected by C. Meisling from a carbonate unit 

which may be the Green Spot Formation.

Correlation of the units below the Moonridge 

Quartzite (fig. 15) is uncertain. The Lightning 

Gulch Formation is lithologically similar to some 

parts of the Clemente Formation of the Caborca 

region and to the partly correlative Rainstorm 

Member of the Johnnie Formation of the southern 

Great Basin region. Drag marks and flute casts, 

typical of unit 5 of the Clemente Formation and 

of the Rainstorm Member, were not seen in the 

Lightning Gulch Formation in the San Bernardino 

Mountains, although metamorphism may have obliterated such features. No oolitic unit similar to 

the "Johnnie oolite" of the southern Great Basin 

or the correlative oolite in the Clemente Formation 

was noted in the San Bernardino Mountains. The 

Wildhorse Meadows Quartzite has no lithic equivalents at the base of the upper Proterozoic stratified sequence in the Caborca or southern Great 

Basin regions.

SIERRA AGUA VERDE

A section of Cambrian rocks in the Sierra Agua 

Verde about 100 km east of Hermosillo in central 

Sonora was discovered in February 1982 by J. H. 

Stewart, A. K. Armstrong, and F. G. Poole. This 

Sierra Agua Verde section is important because it 

contains Lower to Upper Cambrian rocks in a region where none had previously been recognized. 

These rocks are, in part, a continuation of the formations recognized in the Caborca region.

The Cambrian sequence in the Sierra Agua 

Verde consists, in ascending order, of: an equivalent of the Puerto Blanco Formation, the Proveedora Quartzite, equivalents of the Bonanza King 

Formation and the Dunderberg Shale, and, possibly, a thin overlying carbonate unit (fig. 17). The 

equivalent of the Puerto Blanco Formation consists of yellow-gray, medium-gray, and pale-red 

siltstone to phyllitic siltstone, with minor amounts 

of yellow-gray very fine grained to fine-grained 

quartzite, yellow-brown fine- to coarse-grained 

quartzite to pebble conglomerate, and mediumgray limestone. These rocks are poorly exposed and 

locally structurally contorted, and the thickness 

of the sequence of units was not determined. The 

top 80 m of the equivalent of the Puerto Blanco 

Formation is exposed in apparent stratigraphic 

continuity with the overlying Proveedora Quartzite and contains the brachiopod Obolella and the 

Lower Cambrian trilobite Nevadella (A. R. Palmer, 

written commun., 1982). The presence of Nevadella 

assures a time equivalent of these rocks in the 

Sierra Agua Verde with the Puerto Blanco Formation of the Caborca region, although the lithology is not exactly the same. The Proveedora 

Quartzite of the Sierra Agua Verde closely resembles the Proveedora Quartzite of the Caborca region and contains Skolithos ( = Scolithus) in its 

lower part, as does the Proveedora in the Caborca 

region. Siltstone interstratified with quartzite of 

the Proveedora in the Sierra Agua Verde contains 

the Lower Cambrian trilobite Olenellus gilberti (A. 

R. Palmer, written commun., 1982), a fossil that 

occurs in the upper part of the Zabriskie Quartzite 

(the correlative of the Proveedora in the southern 

Great Basin) or in the overlying lower part of the 

Carrara Formation in the southern Great Basin. 

Middle and Upper Cambrian rocks in the Sierra 

Agua Verde consists of rocks considered to be 

equivalents of the Bonanza King Formation and 

the Dunderberg Shale, as well as, possibly, a thin 

sequence of carbonate rock overlying the Dunder-
30 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

berg Shale (fig. 17). The Bonanza King Formation 

equivalent may, in part, be correlative with the 

Tren Formation of Caborca, but this correlation is 

uncertain because only the lower part of the Tren 

is exposed in the Caborca region and only the upper 

part of the Bonanza King equivalent is exposed in 

the Sierra Agua Verde. The only fossils in the Middle and Upper Cambrian sequence in the Sierra 

Agua Verde are found in the Dunderberg Shale 

equivalent, within which linguloid and acretretid 

brachiopods (Angulotreta) and hexactinellid 

sponge spicules occur (A. R. Palmer, written commun., 1982). Angulotreta is Late Cambrian in age

METERS 

1500 -

1000-

500-

Upper 

Cambrian

Middle 

Cambrian

Lower 

Cambrian

Equivalent

of

Dunderberg 

Shale

Equivalent

of 

Bonanza <

King 

Formation

I P Lower Ordovician 

conodonts

J

Linguloid and 

acrotretid brachiopods

(Angulotreta) 

Hexactinellid sponge 

 -^^A spicules 

I I \

Not exposed

Thickness of missing

strata uncertain

Proveedora 

Quartzite

Equivalent

of

Puerto 

Blanco

Formation

_. - . '-ZT ( Olenellus gilbert! 

Skolithos

Nevadella, Obolella

o-1

FIGURE 17. Stratigraphic column in the Sierra Agua Verde, 

Sonora, Mexico.

and characteristic of the lower part of the Dunderberg Shale in the southern Great Basin (A. R. 

Palmer, written commun., 1982). Early Ordovician 

conodonts, identified (John Repetski, written commun., 1983) from carbonate rocks 69 m above the 

Dunderberg equivalent, indicate that, at most, 

only a thin sequence of Cambrian rock occurs 

above the Dunderberg Shale equivalent in the 

Sierra Agua Verde.

TECTONIC AND PALEOGEOGRAPHIC SETTING

The thick terrigenous detrital and carbonate 

rocks of Upper Proterozoic and Cambrian age in 

the Caborca region are part of a widespread miogeoclinal sequence interpreted as a continentalterrace deposit along the margin of the North 

American Continent (Stewart and Poole, 1974;. The 

miogeoclinal deposits and the trend of the inferred 

continental margin are well defined in most of the 

Western United States (fig. 14), but uncertainties 

exist about the trend of the margin and the extent 

of its tectonic disruption in the Southwesternmost 

United States and northern Mexico.

Three tectonic and paleogeographic models are 

considered here.

MODEL A

Model A (fig. ISA) shows the changing trend of 

upper Proterozoic and Paleozoic rocks and curving 

of the continental margin eastward in northern 

Mexico (Eardley, 1951; Stewart and Poole, 1975; 

Stewart, 1976; Peiffer-Rangin, 1979). The margin 

may extend eastward across northern Mexico and 

join with the Ouachita margin in the South-Central United States (Stewart, 1970, 1982; PeifferRangin, 1979). This model, though appealing in its 

simplicity, fails to account for the remarkable similarity of the stratigraphic sequence in the Caborca 

region to those in the San Bernardino Mountains 

and the southern Great Basin similarities which 

suggest that these regions were once closer together and subsequently disrupted tectonically. 

The model also fails to explain independent evidence of left-lateral disruption of crystalline basement rocks (Silver and Anderson, 1974; Anderson 

and Silver, 1979) in the Southwestern United 

States and northern Mexico.

MODEL B

Silver and Anderson (1974) and Anderson and 

Silver (1979) proposed that a major Mesozoic left-
TECTONIC AND PALEOGEOGRAPHIC SETTING 31

lateral megashear (the Mojave-Sonora megashear) 

extends southeastward from the southern Inyo 

Mountains, across the eastern Mojave Desert region, into Sonora, Mexico, and beyond. They noted 

that Precambrian orogenic and magmatic rocks 

ranging in age from 1,600 to 1,800 m.y. are disrupted by this shear zone. From the similarities 

between the stratigraphic columns in the Inyo 

Mountains/Death Valley region and the Caborca, 

Mexico, region on opposite sides of the megashear, 

they suggested that these areas originally were 

closer together and have subsequently been displaced left laterally about 700 to 800 km to their 

present positions.

121° 117° 113° 109° 121° 11

However, the concept of the megashear as presented by Silver and Anderson (1974) and Anderson and Silver (1979) does not account for the presence of Cordilleran miogeoclinal rocks in the San 

Bernardino Mountains-Victorville area (Stewart 

and Poole, 1975; Cameron, 1981,1982; Miller, 1981). 

The presence of these rocks suggests that the Cordilleran miogeoclinal belt once extended southwestward across the Mojave Desert region to the 

San Andreas fault (Stewart and Poole, 1975; Davis 

and others, 1978; Burchfiel and Davis, 1981; Cameron, 1981, 1982; Miller, 1981). If so, major leftlateral offset on the Mojave-Sonora megashear is 

impossible, unless the San Bernardino Mountains113°

37°

B

113° 109°

300 KILOMETERS

EXPLANATION

Upper Proterozoic and Paleozoic miogeoclinal strata

Paleozoic siliceous and volcanic rocks

Approximate leading edge of allochthonous

Paleozoic siliceous and volcanic rock

Queried where position uncertain

FIGURE 18. Tectonic and paleogeographic models of the Southwestern United States and northern Mexico. A, Major facies 

and tectonic belts curve around the Southwestern United States and northern Mexico, unbroken by major left-lateral faults. 

B, Facies and tectonic belts are offset to southeast into northern Mexico along a major left-lateral fault. Fault as shown 

corresponds in Mexico to the Sonora-Mojave megashear of Silver and Anderson (1974) and Anderson and Silver (1979), but 

lies west of their proposed megashear in southern California. C, Facies and tectonic belts are offset to southeast into northern 

Mexico along a major left-lateral fault corresponding to the Mojave-Sonora megashear as originally defined. Later movement 

along a major right-lateral fault offsets western part of the Caborca block northwestward into southern California. SAF, 

San Andreas fault. Terrane west of San Andreas fault in western California and Baja California is not shown because of 

uncertainties in palinspastic reconstruction (Gastil and Miller, 1981).
32 PROTEROZOIC AND CAMBRIAN ROCKS, CABORCA REGION, MEXICO

Victorville rocks reached their present position by 

complex postmegashear displacements, such as 

tectonic transport along low-angle faults (L. T. Silver, oral commun., 1982), from a position east of 

the megashear, or as transport as a block northward from a position originally west of the 

megashear.

A possible interpretation (fig. 18B; Cameron, 

1981, 1982; Stewart, 1982) is that the megashear, 

if it exists, lies south of the San Bernardino Mountains, a position compatible with the distribution 

of the Zabriskie Quartzite and the correlative Proveedora Quartzite (fig. 19). Although the Zabriskie 

Quartzite in the San Bernardino Mountains-Victorville area is on line with outcrops of the Zabriskie in the southern Great Basin region, the 

correlative Proveedora occurs to the southeast in 

a position that could indicate southeastward offset 

relative to the Southwestern United States. Such 

an offset also accounts for the similarity of the 

Caborca rocks to those in the Southwestern United 

States.

The concept of the Mojave-Sonora megashear or 

a related left-lateral fault does not rule out the 

possibility that the upper Proterozoic and Paleozoic continental margin of North America extended across northern Mexico. The distribution 

of upper Proterozoic and Paleozoic rocks in northern Mexico (fig. 18) suggests that an eastward 

trend of this margin would exist, even if the Mexican rocks were palinspastically restored to their 

presumed original positions before left-lateral 

movement. This eastward trend is also inferrable 

from paleocurrent studies (Stewart, 1982) that 

show a progressive change in trend from westerly 

in Idaho and Utah, through southerly in New Mexico, to southeasterly in Texas (fig. 14).

MODEL C

Comparison of the upper Proterozoic and Cambrian rocks of the Caborca, San Bernardino, and 

southern Great Basin regions suggests a third 

model (fig. 18C) in which the Caborca rocks were 

displaced southeastward along the left lateral Mojave-Sonora megashear, situated where Silver and 

Anderson (1974) originally placed it across the eastern Mojave Desert and Sonora. After this offset, 

a tectonic block that includes the San Bernardino 

Mountains-Victorville area was detached from the 

southwest side of the Caborca block and moved 

right laterally northwestward to its present position. This concept is appealing because some 

parts of the the Caborca sequence appear to be

more closely tied lithologically to the sequence in 

the southern Great Basin than to that in the San 

Bernardino Mountains. In the Caborca region, 

rocks correlative with the Rainstorm Member of 

the Johnnie Formation of the southern Great 

Basin, including a distinctive 2.6 m thick oolite (the 

"Johnnie oolite"), indicate a close tie to the southern Great Basin. In the San Bernardino Mountains, however, this oolite is absent, and the Rainstorm Member, even if it is present, is not clearly 

defined. These correlations suggest that some 

parts of the Caborca sequence are more closely 

allied to the southern Great Basin than to the San 

Bernardino Mountains. Such comparisons are, 

nonetheless, risky because part of the Caborca and 

San Bernardino sequences are very similar. The 

Pitiquito-Gamuza-Papalote-Tecolote sequence of 

the Caborca region and the Moonridge-Green SpotDelamar Mountain sequence of the San Bernardino Mountains are similar lithologically and have 

a similar order. The occurrence of conical stromatolites in the Gamuza Formation and of similar 

stromatolites in the lower part of the Green Spot 

Formation also indicates a similarity. However, 

these relations are all compatible with the idea

39°

119°

31 C

\ NEVADA

\ 

\

UTAH

-IARIZONA

\"* -\ UN1TED_SJATES 

^ -\ " "MEXICO \- X ^

SONORA

Sierra

AguaiVerde

FIGURE 19. Generalized distribution of the Zabriskie Quartzite in Nevada and California and of the correlative Proveedora Quartzite in northern Mexico (stippled areas), showing 

possible left-lateral offset.
REFERENCES CITED 33

that the strata of the Caborca region are intermediate in facies between strata of the southern 

Great Basin and San Bernardino Mountains. If so, 

a complex pattern of disruption, such as that in 

model C (fig. 18C), is possible.

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