U.S. GEOLOGICAL SURVEY CIRCULAR 943 

Petroleum Geology and Resources 

of Northeastern Mexico 
• ·~ I 
Petroleum Geology and Resources 

of Northeastern Mexico 

By James A. Peterson 

U.S. GEOlOGICAl SURVEY CIRCUlAR 943 

Potentially ma;or petroleum deposits, 

primarily gas, in northeastern 

Mexico occur in carbonate and 

clastic reservoirs of Cretaceous 

and Jurassic age 

7985 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Library of Congress Cataloging-in-Publication Data 

Peterson, James A. 

Petroleum geology and resources of northeastern Mexico 

(Geological Survey circular; 943) 

Bibliography: p. 27 

Supt. of Docs. no.: I 19.4/2:943 

1. Gas, Natural-Geology-Mexico. 2. Gas, Natural-Mexico. 3. Petroleum-Geology-Mexico. 4. Petroleum-Mexico. I. Title. 

II. Series. 

TN882.M6P47 1985 553.2'8'09721 85--600110 

Free on application to Distribution Branch, Text Products Section, 

U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 
PREFACE 

The World Energy Resources Program of the U.S. Geological Survey (USGS) intends to 

develop reliable and credible estimates of undiscovered recoverable petroleum resources throughout the world. Initial program efforts have focused on the major producing areas of the world in 

order to gain a broad understanding of the geologic characteristics of petroleum occurrence for 

purposes of resource assessment as well as for analysis of production potential. Investigations of 

production potential are carried out in cooperation with other U.S. Government agencies; specifically, the studies of the main free-world exporting nations, of which this study is a part, are 

carried out in cooperation with the Foreign Energy Supply Assessment Program of the Department of Energy. The estimates represent the views of a U.S. Geological Survey study team and 

should not be regarded as an official position of the U.S. Government. 

The program seeks to investigate resource potential at the basin level, primarily through 

analogy with other petroleum regions, and does not necessarily require, therefore, current exploration information that is commonly held proprietary. In conducting the geological investigations, 

we intend to build a support base of publicly available data and regional geologic synthesis 

against which to measure the progress of exploration and thereby validate the assessment. Most 

of these investigations will lead directly to quantitative resource assessments; to be effective, 

resource assessment, like exploration, must be an ongoing process taking advantage of changing 

ideas and data availability-the results produced being progress reports reflecting a state of 

knowledge at a point in time. Because the program is coordinated with the USGS domestic 

assessment program and both utilize similar techniques for assessment, the user can be assured 

of a thread of consistency permitting comparisons between the various petroleum basins of the 

world, including those of the United States, that have been assessed in the overall USGS 

program. 

In addition to resource estimates, the program provides a regional base of understanding for 

in-country exploration analysis and for analysis of media reports regarding the exploratory 

success or failure of ventures in studied areas. 

USGS open-file reports related to the assessment of undiscovered conventionally recoverable 

petroleum resources include: 

81-0986-Assessment of conventionally recoverable petroleum resources of Persian Gulf basin 

and Zagros fold belt (Arabian-Iranian basin) 

81-1027 -Assessment of conventionally recoverable petroleum resources, Volga-Urals basin, 

U.S.S.R. 

81-1142-Assessment of conventionally recoverable petroleum resources of Indonesia 

81-1143-Assessment of conventionally recoverable petroleum resources of northeastern Mexico 

81-1144-Assessment of conventionally recoverable petroleum resources of southeastern Mexico, northern Guatemala, and Belize 

81-114 5-Assessment of conventionally recoverable petroleum resources of Trinidad 

81-1146-Assessment of conventionally recoverable petroleum resources of Venezuela 

81-1147-Assessment of conventionally recoverable petroleum resources of the West Siberian 

Basin and Kara Sea Basin, U.S.S.R. 

81-0296-Assessment of undiscovered conventionally recoverable petroleum resources of the 

Middle Caspian basin, U.S.S.R. 

82-1027-Assessment of undiscovered conventionally recoverable petroleum resources of the 

East Siberian Basin, U.S.S.R. 

82-1056-Assessment of undiscovered conventionally recoverable petroleum resources of North 

Africa 

82-1057-Assessment of undiscovered conventionally recoverable petroleum resources of the 

Timan-Pechora basin, U.S.S.R., and Barents-northern Kara shelf 

83-0598-Assessment of undiscovered conventionally recoverable petroleum resources of northwestern, central, and northeastern Africa 

83-0801-Assessment of undiscovered conventionally recoverable petroleum resources of onshore China 

Ill 
84-0094-Assessment of undiscovered conventionally recoverable petroleum resources of the 

northwest European assessment region 

84-0158-Assessment of undiscovered conventionally recoverable petroleum resources of New 

Zealand 

84-0214-Assessment of undiscovered conventionally recoverable petroleum resources of 

Australia 

84-0328-Assessment of undiscovered conventionally recoverable petroleum resources in Tertiary sedimentary basins of Malaysia, Brunei 

84-0329-Assessment of undiscovered conventionally recoverable petroleum resources in offshore Tertiary sedimentary basins of The People's Republic of China 

84-0330-Assessment of undiscovered conventionally recoverable petroleum resources in Tertiary sedimentary basins of Thailand 

84-0852-Assessment of undiscovered conventionally recoverable petroleum resources of South 

Asia 

These reports are available from Open File Services Section, Branch of Distribution, USGS, Box 

25425, Federal Center, Denver, CO 80225. Prices are available on request. 

USGS Circulars related to the assessment of undiscovered conventionally recoverable petroleum 

resources include: 

C-760-Petroleum geology and resources of southeastern Mexico, northern Guatemala, and 

Belize 

C-881-Assessment of undiscovered recoverable resources of the Arabian-Iranian basin 

C-885-Petroleum geology and resources of the Volga-Urals province, U.S.S.R. 

C-899-Assessment of undiscovered conventionally recoverable petroleum resources of 

Indonesia 

C-922-A-Assessment of undiscovered conventionally recoverable petroleum resources of the 

Northwest European Region 

Circulars are available free from the Distribution Branch, Text Products Section, U.S. Geological 

Survey, 604 South Pickett Street, Alexandria, VA 22304. 

IV 
CONTENTS 

Abstract - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Page 

Petroleum Geology -Continued 

Tertiary, Burgos Basin -Continued 

Page 

Geography---------------------------------------- Traps------------------------------------------ 20 

Information sources - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 

Acknowledgments - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 

Analogs ---------------------------------------- 20 

Upper Cretaceous----------------------------------- 20 

Lower Cretaceous- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 20 

Reservoirs- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 21 

Regional geology - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 

Structure - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 

Stratigraphy- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10 

Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10 

Basement--------------------------------------- 10 

Triassic - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10 

Jurassic - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 0 

Lower Cretaceous - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 14 

Upper Cretaceous--------------------------------- 16 

Source rocks - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 21 

Regional cap rocks -------------------------------- 21 

Traps------------------------------------------ 21 

Analogs ---------------------------------------- 22 

Jurassic ------------------------------------------ 22 

Reservoirn--------------------------------------- 22 

Sourcerocks------------------------------------- 22 

Tertiary---------------------------------------- 17 Traps------------------------------------------ 22 

Quaternary-------------------------------------- 18 

Petroleum geology ------------------------------------ 18 

Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 18 

Tertiary, Burgos Basin - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 19 

Reservoirs- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 19 

Analogs ---------------------------------------- 22 

Resource assessment - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 23 

Procedures---------------------------------------- 23 

Assessment --------------------------------------- 23 

Comments - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 24 

Source rocks - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 20 

Regional cap rocks - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 20 

Selected references - - - - - - - - - - - - -- - - - - - -- - - - -- - --- - - - - - 27 

FIGURE 1. 

2. 

3. 

4. 

5. 

6. 

ILLUSTRATIONS 

Page 

Index maps of northeastern Mexico showing main basins and uplifts and outline of 

assessment area - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 

Stratigraphic correlation chart of northeastern Mexico and adjacent area -- - - -- - 4 

Map of northeastern Mexico showing main structural features, oil and gas fields, 

important dry holes, and outcrop areas of Lower Cretaceous and Tertiary 

sedimentary rocks and Tertiary igneous rocks - - - - - - - - - - - - - - - - - - - - - - - - 5 

Map of Mesozoic paleostructure showing regional basin and uplift features active 

during Jurassic and Cretaceous deposition --------------------------- 6 

North-south structural-stratigraphic cross section A-A', southwestern Texas to 

Sierra Madre Oriental south of Monterrey, Mexico, showing Cretaceous and 

Jurassic sedimentary facies, structural features, and productive intervals --- 7 

Southwest-northeast structural-stratigraphic cross section B-B', Sierra Madre 

Oriental south of Parras, Mexico, to Gulf Coast south of Corpus Christi, Tex., 

showing Cretaceous and Jurassic sedimentary facies, structural features, and 

productive intervals - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 8 

7. West-east structural-stratigraphic cross section C -C ', Sabinas basin to Gulf Coast 

at mouth of Rio Grande, showing Cretaceous and Jurassic sedimentary facies, 

structural features, and productive intervals- - - - - - - - - - - - - - - - - - - - - - - - - - 9 

8-12. Maps showing: 

8. Approximate thickness in feet, partly restored, Jurassic System, and approximate distribution of pre-Oxfordian salt, postsalt Upper Jurassic main 

sedimentary facies, and gas fields producing from Upper Jurassic reservoirs - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 11 

9. Approximate thickness in feet, partly restored, Coahuilan Series, Lower Cretaceous, and main sedimentary facies and gas fields producing from rocks of 

Coahuilan Series- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 12 

10. Approximate thickness in feet, partly restored, Comanchean Series, and main 

sedimentary facies and gas fields producing from rocks of Comanchean Series--------------------------------------------------·------ 13 

v 
FiGURE 

TABLE 

Page 

11. Approximate thickness in feet, partly restored, Gulfian Series and main sedimentary facies and gas and oil fields producing from rocks of Gulfian Series - - - - 14 

12. Approximate thickness in thousands of feet, Tertiary System, and gas and oil 

fields producing from Tertiary rocks in Mexico and from productive trends in 

south Texas - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 15 

13-14. Graphs showing: 

13. Aggregate recoverable oil in Burgos and Sabinas-Parras basins, Mexico----- 25 

14. Aggregate recoverable total gas in Burgos and Sabinas-Parras basins, 

Mexico - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 25 

TABLES 

Page 

1. Estimates of conventionally recoverable petroleum resources of northeastern Mexico, including those of the Sabinas, Parras, and Burgos basins --- - -- - - -- -- 23 

2. Data and information summary - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 24 

3. Summary of assessment factors - - - - -- - - -- - - - - - - -- - --- - - -- - - -- - - - - - - -- - 26 

4. Supplementary and comparative data supporting the resource estimates for northeastern Mexico - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 27 

ABBREVIATIONS USED IN THIS REPORT 

BBO-Billion barrels of oil 

BBOE-Billion barrels of oil equivalent 

BCF-Billion cubic feet 

BD-Barrels per day 

DOE-Barrels of oil equivalent 

CFD-Cubic feet per day 

MMBO-Million barrels of oil 

MMCF-Million cubic feet 

TCF-Trillion cubic feet 

VI 
Petroleum Geology and Resources of 

Northeastern Mexico 

By James A. Peterson 

ABSTRACT 

Petroleum deposits (primarily gas) in northeastern Mexico occur in 

two main basins, the Tertiary Burgos basin and the Mesozoic Sabinas 

basin. About 90 gas fields are present in the Burgos basin, which has 

undergone active exploration for the past 30-40 years. Production in 

this basin is from Oligocene and Eocene nearshore marine and deltaic 

sandstone reservoirs. Most of the fields are small to medium in size 

on faulted anticlinal or domal structures, some of which may be 

related to deep-seated salt intrusion. Cumulative production from 

these fields is about 4 trillion cubic feet gas and 100 million barrels 

condensate and oil. Since 1975, about 10 gas fields, some with large 

production rates, have been discovered in Cretaceous carbonate and 

Jurassic sandstone reservoirs in the Sabinas basin and adjacent Burro-Picachos platform areas. The Sabinas basin, which is in the early 

stages of exploration and development, may have potential for very 

large gas reserves. 

The Sabinas basin is oriented northwesterly with a large number 

of elongate northwest- or west-trending asymmetric and overturned 

Laramide anticlines, most of which are faulted. Some of the structures may be related to movement of Jurassic salt or gypsum. Lower 

Cretaceous and in some cases Jurassic rocks are exposed in the 

centers of the larger anticlines, and Upper Cretaceous rocks are 

exposed in much of the remainder of the basin. A thick section of 

Upper Cretaceous clastic rocks is partly exposed in tightly folded and 

thrust-faulted structures of the west-east oriented, deeply subsided 

Parras basin, which lies south of the Sabinas basin and north of the 

Sierra Madre Oriental fold and thrust belt south and west of 

Monterrey. 

The sedimentary cover of Cretaceous and Jurassic rocks in the 

Sabinas and Parras basins ranges from about 1,550 m (5,000 ft) to 

9,000 m (30,000 ft) in thickness. Upper Jurassic rocks are composed 

of carbonate and dark organic shaly or sandy beds underlain by an 

unknown thickness of Late Jurassic and older redbed clastics and 

evaporites, including halite. Lower Cretaceous rocks are mainly platform carbonate and fine clastic beds with some evaporites (gypsum 

or anhydrite) deposited in two main rudist reef-bearing carbonate 

cycles. Upper Cretaceous rocks are mainly continental and marine 

clastic beds related to early development of the Laramide orogeny. 

This Upper Cretaceous sequence contains a marine shale and deltaic 

clastic complex as much as 6,000 m (20,000 ft) or more thick in the 

Parras basin, which grades northward and eastward to open marine, 

fine clastic beds. The Burgos basin, which is an extension of the Rio 

Grande embayment of the western Gulf of Mexico basin province, 

contains an eastward-thickening wedge of Tertiary continental and 

marine clastics. These beds are about 1,550 to 3,000 m 

(5,000-10,000 ft) thick in the outcrop belt on the west side of the 

basin and thicken to more than 16,000 m (50,000 ft) near the Gulf 

Coast. 

1 

INTRODUCTION 

GEOGRAPHY 

The assessment area considered in this report covers 

about 330,000 km2 (125,000 mi2

) in the northeastern 

part of Mexico. The area includes the Burgos basin 

(primarily a Tertiary gas province), including its ,offshore part to the 1,000-m depth; the Sabinas basin 

where recent Mesozoic gas discoveries have been made; 

the adjacent Sierra Madre frontal basins (Parras and 

Magiscatzin basins); and the northern part of the Sierra Madre Oriental fold and thrust belt (fig. 1). Topography of the area is characterized by the flat-lying Gulf of 

Mexico coastal plain, the plateau regions along the Rio 

Grande and in western Coahuila State, the isolated 

ranges or sierras of central Nuevo Leon and eastern 

Coahuila (basins and ranges provinces of Humphrey, 

1956), the rugged mountain belt along the front of the 

Sierra Madre Oriental, and the northern part of the 

Central Mesa region south of the Sierra Madre front. 

The climate is semiarid to arid in most of the region. 

Annual precipitation is about 25 to 50 em (10-20 inches) in most parts of Coahuila State and part of Nuevo 

Leon State and about 50 to 75 em (20-30 inches) in the 

coastal plain region of Tamaulipas State. In the high 

sierras south of Monterrey, precipitation may be to 100 

em (40 inches) or more in places. 

INFORMATION SOURCES 

Data and information used in preparing this report 

were compiled primarily from Mexican journals and 

other publications on petroleum geology and general 

geology of the area. Of particular value were publications by Lopez-Ramos (1980), Charleston (1974, 

1981), Humphrey (1956), Smith (1970, 1971, 1981), 

Gonzales Garcia (1979), Wilson and Pialli (1977), 

McBride and others (197 4), articles from the Oil and 

Gas Journal and World Oil, and the information files 

of Petroconsultants, S.A. Additional references are 
104° 96° 88° 

28° 

GULF OF MEXICO 

20° 

EXPLANATION 

--BOUNDARY 

AREA 

OF THRUST BELT 

0 100 200 

100 200 300 KILOMETERS 

FIGURE 1.-Index maps of northeastern Mexico; cities shown are D.R., Del Rio, Texas; L, Laredo; M, 

listed in the bibliography. Work on the report was completed in June 1981. Geological and other data made 

available after that date are not incorporated in the 

study. 

The nomenclature used in the Texas area in this 

report was summarized from many reports; some has 

been adopted by the U.S. Geological Survey and some 

has not. 

ACKNOWLEDGMENTS 

This report benefited from constructive reviews and 

discussions by R. L. Miller, K. C. Bayer, J. W. Clarke, 

and C. D. Masters, U.S. Geological Survey. The resource assessment was prepared in collaboration with 

the Resource Appraisal Group of the Branch of Oil and 

Gas Resources, U.S. Geological Survey. 

2 

REGIONAL GEOLOGY 

STRUCTURE 

The main basin areas of northeastern Mexico are the 

Burgos basin, which is part of the Rio Grande embayment of the western Gulf of Mexico basin; the Sabinas 

basin (or "Gulf of Sabinas"); the Magiscatzin or Linares 

basin; and the Parras and La Popa basins (figs. 1-4). 

The Burgos basin occupies the eastern part of the assessment area and is filled with a thick sequence of 

Tertiary clastic rocks, which wedge-out rapidly updip to 

the west in the vicinity of Reynosa. West of the Tertiary wedge-out, the sedimentary cover comprises mainly 

Cretaceous marine carbonate rocks, which make up 

most of the surface exposures in Coahuila and Nuevo 

Leon, and a relatively unknown thickness of marine 
28° 

20" 

104° 

~O.R RIO 

EXPLANATION 

----BOUNDARY OF 

ASSESSMENT 

AREA 

of Thrust Belt 

0 100 I I I I 0 100 200 

200 

I I 

96° 

GULF 

300 KILOMETERS 

88° 

OF M E X I C 0 

Monterrey, Mexico; P, Parras, Mexico. A, Political boundaries and assessment area; B, Main basins and uplifts. 

Jurassic carbonate, clastic, and evaporite rocks (fig. 2, 

cols. 1-3). The Burgos basin is bounded on the west by 

the Tamaulipas platform (arch) and the southeastern 

extension of the Burro-Picachos platform. The Sabinas 

basin or "Gulf of Sabinas" lies west of this platform 

belt and merges with the Parras and La Popa basins 

around the southeast extension of the Coahuila platform. The broad Coahuila platform or "peninsula" 

forms the southern and western boundaries of the 

Sabinas basin and the north boundary of the Parras 

basin. The Parras basin occupies a relatively narrow 

west-east-trending tightly folded outcrop belt north of 

the Sierra Madre thrust and fold belt and merges on 

the east with the Magiscatzin (Linares) basin southeast 

of Monterrey. Together, these two basins form a relatively narrow, Late Cretaceous-Tertiary foredeep 

trough adjacent to the Sierra Madre Oriental, which is 

3 

a broad belt of thick tightly folded and thrust-faulted 

Cretaceous and Jurassic platform carbonate deposits. 

To the south, the Magiscatzin basin joins the Tampico 

basin and the Chicontepec basin (fig. IB). 

Early growth of the Tamaulipas, Burro Picachos, 

and Coahuila platforms occurred in Triassic and Early 

Jurassic time as part of the regional tensional stresses 

associated with initial development of the ancestral 

Gulf of Mexico province. At this time, redbed clastics 

and evaporites were deposited in the Sabinas Gulf (ancestral Sabinas basin) and parts of the ancestral Gulf of 

Mexico basin (figs. 5-7). Intense growth of these paleostructures diminished after Triassic time, but moderate growth continued through most of the remainder of 

Mesozoic time and influenced depositional processes 

and distribution of both clastic and carbonate sedimentary facies. Growth of salt structures probably began 
I. 2. 3. 4. 5 SIERRA PARRAS 

AGE MADRE 

SABIN AS BASIN- B U R G 0 S BURRO -

PICACHOS 

QUATERN- PLEISTOCENE ARY 

PLIOCENE 

MIOCENE 

>- OLIGOCENE 

a::: 

<{ 

1-

a::: 

w 

1-

(/) 

liJ 

EOCENE 

PALEOCENE 

MAESTRICHIAN 

ORIENTAL BASIN 

Dl FUNTA MENDEZ 

COAHUILA PLATFORM BASIN 

CONTINENTAL BEDS IN VALLEYS LISSIE FM. 

ESCONDIDO 

OLMOS 

FM. ~\"' 

"'I- F M. 0 

\"' 

GOLIAD FM. 

~~ LAGARTO FM 

f.JC)··~ ~ OAKVILLE FM 

ANAHU~FM . 

• NORMA CGL. 

FRIO.~. 

IJ I CI<SBURG FM 

JACKSON FM. 

hr.- ...I.-· F'!i YEGUA FM. 

~ - COOK ·-MTN !J1 dM,'I~N~ 

WIL~ox-A 

M 1 ow;V1::~ 

• MENDEZ 

SH. GP 

SAN M I G U E L F M ) 0'-5- ~ r-~~~u~pFs~o7.N~~F"M-.~~~\ a: SH. liJ CAMPANIAN (/) 

SANTONIAN 

z 

::! CONIACIAN 

u.J TITHONIAN 

1-

CUPIDO 

LS. 

TARAISES 

FM 

LA CASITA FM. LA CAJA FM. 

(La Catitol 

OLVI DO FM. 

SAN 

FM. FELIPE 

FM. 

A G U A 

FM. • NUEVA FM. 

• • LOWER LA- LA 

PATUL VIRGEN MULA CUPIDO LOWER 

EVAP. SH. LS . TAMAUL IPAS AMAULI PAS ARI< 

AOI~~~G~E FM. ? FM. 

SAN MARCOS BARRIL VIEJO? 

ARKOSE ~aFM;,-.:>TARAIFS:_s~ 

~NCHAC~·~ ~ ? LA CASITA FM .... LA CASITA 

- FM.. 

0 ~ KIMMERIDGIAN OLVIOO FM. _.J 

(f)w 

(f).J 

OXFORDIAN ZULOAGA FM. ZULOAGA FM LA GLORI~ ZULOAGA L S. ~ SMAC)(OVER LS. 

CALLOVIAN LA JCYA FM MINAS VIEJAS FM 

<{ 0 1-----+..--r? -,- a::: ~ BATHONIAN 

~ :::!: BAJOCIAN 

--;) 

EARLY 

TRIASSIC 

PALEOZOIC 

HUIZACHAL 

or La BOCA FM. 

NAZAS FM . 

METAMORPHOSED 

SEDIMENTS 

MINAS VIEJAS 

REDBEDS AND EVAPORITES 

REDBEDS 

METAMORPHIC AND IGNEOUS 

R 0 C K S 

a OIL PRODUCT I ON • GAS PRODUCTION ~ SOURCE ROCK • REGIONAL SEAL 

REDBEDS ? 

? 

PLATFORM 

~ " AUSTIN <I> 

• j -FM. -' 

-· => 

0 

EAGLE F~ 0 

"' BUDA LS. 

CUPIDO L S 

HOSSTON 

(COLORADAl 

ss 

METAMORPH lC1 

IGNEOUS 

ROCKS 

FIGURE 2.-Correlation chart, northeastern Mexico and adjacent area. 1. , after Lopez-Ramos, 1980, 

Wilson and Pialli, 1977; 2., after Lopez-Ramos, 1980, McBride and others, 1974; 3., after Smith, 

C. I., 1981, Lopez-Ramos, 1980, Wilson and Pialli, 1977, Charleston, 1974; 4., after Lopez-Ramos, 

1980; 5., after Smith, C. I., 1981, Lopez-Ramos, 1980, Gonzalez Garcia, 1979. 

4 
• 

3:)0 -

\ 

\ ')3" 

I 

MARATHON, UPLIFT 

EXPLANATION 

+Anticline 

Z Mo}or left-lateral fault 

~ Thrust fault 

m Normal fault 

Outcrop, Lower Cretaceous rocks 

Outcrop, Tertiary rocks 

IQ n eo us, mainly Terti or y 

,, l 

ASSESSMENT AREA 

2,.)( 

0 Gas field 

• Oil tiel~ 

0 Oil and QOS field 

Dry hole 

y 

MAVERICK 

~ 

6~ 8ASIN 

LIST OF NUMBERED FIELDS AND WELLS 

1. Buena Suerte-Monclova 9. Laredo 17. 

2. Ulua 10. Oasis 18. 

3. Lampazos 11. La Presa 19. 

4. Anahuac 12. Culebra 20. 

5. Garza 13. Panalva 21. 

6. Polvorin 14. Mision 22. 

7. Tribolites 15. Comitas 23. 

8. Totonaca 16. Reynosa 

J- ' 

- 26° 

- 25" 

- 24 

I - 23° 

Monterrey 

Francisco Cano 

Trevino 

Brasil 

18 de Marzo 

Matamoras 

Lerna 

FIGURE 3.-Map of northeastern Mexico showing main structural features, oil and gas fields, important dry holes, and outcrop areas 

of Lower Cretaceous and Tertiary sedimentary rocks and Tertiary igneous rocks. Outcropping rocks are not shown in Sierra 

Madre Oriental in which mainly Cretaceous and some Jurassic rocks are exposed in fold and thrust structures. Lines of cross 

sections of figures 5, 6, and 7 are shown. Data are primarily from Charleston (1974, 1981), Lopez-Ramos (1980), and Corpus 

Christi Geological Society (1978, 1979). Significant fields or discoveries are numbered. Cities shown in Mexico: C, Chihuahua; 

C.V., Ciudad Victoria; Mo, Monclova; Mu, Muzquiz; N.L., Nuevo Laredo; P, Parras; S, Saltillo; Sb, Sabinas; S.H., Sabinas 

Hidalgo; T, Torreon; cities shown in Texas: C.C., Corpus Christi; D.R., Del Rio; E.P., Eagle Pass; L, Laredo; S.A., San 

Antonio. 

5 
25° -

A 

\'fiP.Rp.\'r\0~ 

?\..If\ 

~ 0 0

1

3

"r E XJA S 

........... 

EXPLANATION 

~ THRUST FRONT 

-- -- -- ASSESSMENT AREA 

0 50 100 150 mi 

10 50 IOC 200 250 k"n 

00° 

ORATO'N 

- - 29° 

- 2?0 

'"=> '\ 

-26° ""-· C' 

- 25° 

- 24° 

I 

98° - 23° 

FIGURE 4.-Mesozoic paleostructure map showing regional basin and uplift features active during Jurassic and Cretaceous deposition. Lines of cross sections of figures 5, 6, and 7 are shown. Cities shown in Mexico: C, Chihuahua; C.C., Cuatro Cienegas; 

C.V., Ciudad Victoria; M, Monterrey; Mo, Monclova; Mu, Musquiz; N.L., Nuevo Laredo; P, Parras; R, Reynosa; S, Saltillo; 

Sb, Sabinas; S.H., Sabinas Hidalgo; T, Torreon; cities shown in Texas: D.R., Del Rio; E.P., Eagle Pass; L, Laredo; S.A., San 

Antonio. Sources of data: Humphrey (1956), McBride and others (1974), Gonzalez Garcia (1979), Lopez-Ramos (1980), Charleston (1974, 1981), and Smith, C. I. (1971, 1981). 

by Late Cretaceous time and continued into early Tertiary time. Regional uplift during middle and late Tertiary time resulted in widespread erosion and exposure 

of Mesozoic rocks throughout most of northeastern 

Mexico, except for the Burgos basin, which underwent 

rapid subsidence throughout Tertiary time. 

The Burgos structural basin is a part of the Rio 

Grande embayment, which forms the western part of 

6 

the Gulf of Mexico basin. The basin area contains a 

thick sequence of Tertiary and upper Mesozoic deposits, 

which are cut by a series of normal fault zones displaced downward on the Gulf Coast side and roughly 

parallel to the coastline (fig. 3). Most of these are 

growth faults active during Tertiary deposition. Numerous faulted anticlinal or domal folds are present, 

some of which may be related to deep-seated salt 

structures. 
" 

A 

... ·-

5,000 II. 2. 3 

[. 

- .~ CRET.

~[ - _ . ---=--- - -~-, 

~ sea level -

- 5,000 

-10,000 

-20,000 

A 

B 

LIST OF CONTROL POINTS 

1. Squaw Peak, Texas 

2. Fort Lancaster, Texas 

3. Pandale, Texas 

4. Pecos River, Texas 

5. Zambano No. 1 

TEXAS GRATON 

EXPLANATION 

MAIN LITHOLOGIC FACIES 

~ 

~ 

lZ2Zl 

ITI . 

. 

a 

-~ 

~ 

~ 

~ 

mm 

I 

t 

1\1 

Conolomerote 

Sa ndstone 

Arkosic sandstone or conolomerote 

Redbeds 

Morine sha le, gray/black 

Ltmutone 

Dolomite 

Anhydrite or gypsum 

Salt 

Gas production 

Oi 1 production 

Normal Fault 

~ 3. 

I 

Well 

Surface 

6. Trevino No. 

7. Chupadero No. 

8. Tribolites No. 1 

9. Peyotes No. 2-A 

10. Lomerio de Peyotes 

t,000m14,000ft 

2,000 

0 0 

0 tOO 200ml. 

0 100 200 300km. 

11 . Silencio No. 1 

12. Gato No. 1 

13. Ulua No. 1 

14. Sierra Laja 

15. Sierra La Gavq 

16. Paredon 

17. Saltillo section 18. Sierra de Sombreratilio 

c 18 A' 

SIERRA 

MADRE OR lEN TAL 

POPA 

OVERTHRUS T 

BELT 

FIGURE 5.-N orth-south structural-stratigraphic cross section A- A', southwestern Texas to Sierra Madre Oriental south of Monterrey, Mexico, showing Cretaceous and Jurassic 

sedimentary facies, structural features, and productive intervals. Top of La Casita Formation is the top of the Jurassic. Datum for lower cross section B is estimated 

sea level at close of Cretaceous time; datum for upper cross section A is present-day sea level. Cross section is based on available published data and is partly schematic, 

particularly in older and deeper parts of section. Data are mainly from Humphrey (1956), Charleston (1974, 1981), Smith, C. I. (1970, 1971, 1981), Lopez-Ramos (1980), 

and Gonzalez Garcia (1979). Line of cross section A-A 'is shown on figures 8--11. 
00 

A 

19. Sierras de Simon and Ramirez 

20. Sierra de Parras 

21. Sierra de Los Alamitos 

22. Sierra de San Marcos 

8 19. 

S,OOOft. 

sea ltvtl 

B 

J,000m1 4'000ft. 2,000 

0 0 

2QI 

PARRAS 

b. 

0 100 200mi 

0 100 200 300km. 

21. 

LIST OF CONTROL POINTS 

23. Sierra de Barril Viejo 27. Lampazas No. 1 31. Laredo Field 

24. Potrero de Menchaca 28. Reforma No. 1 32. Humble No. 1 Benavides, Texas 

25. Buena Surete No. 1 29. Anahuac Field 33. Philips, Nueches No. 1, Texas 

26. Monclova No. 1 30. Ambrosia No. 1 34. Continental, No. 16 Driscoll, Texas 

24 . c s' 

~~, ..b' ~ ,, ~ ,, ,, <}"-,, I ~J/1-f,t.\\\.~~~~ YfiUl FN~ c:z::::: ~agorto P'111 Pllocen• PJtlttOOtll• MOiwel 

spoo 

1~000 

35. Sun, No. 117 Canales, Texas 

36. Humble, No. J-7 Kenedy, Texas \I\ -25,000ft. 

37. Mobil, No.1 St. Tr 1006-5, Texas 

11 ~ 111 

GULF OF MEXICO BASIN 

FIGURE 6.-Southwest-northeast structural-stratigraphic cross section B-B', Sierra Madre Oriental south of Parras, Mexico, to Gulf Coast south of Corpus Christi, Tex., showing 

Cretaceous and Jurassic sedimentary facies, structural features, and productive intervals. Datum for lower cross section B is estimated sea level at close of Cretaceous 

time; datum for upper cross section A is present-day sea level. Cross section is based on available published data and is partly schematic, particularly in older and deeper 

parts of section. Sources of data are same as for figure 5. Lithologic explanation is on figure 5. Line of cross sectionB-B' is shown on figures 8-12. 
"' 

c c/ 

5,000 fl 

Sea level Sea level LIST OF CONTROL POINTS 

14. Sierra Laja 

38. Sierra Sabinas -10,000 -10,000 39. Sierra de Picachos 

40. Los Ramones No. 1 

41. Los Herreras No. 1 

-2 0.000 ·20.,000 42. Santa Monica No. 1 

43. El Pato No. 1 

A ·-· ... -·· -30,000 

44. Zacate No. 101 

45. El Charro No. 1 

46. Reynosa No. 1 

47. Trevino No. 1 

,!...... ---- ~ ___ 1,_ __ ._

1 

__ "'i __ ,_ r ~Pt!:O~III!!_t ..._t~lf,!.f:.._ ~ :.!.ft!.!! _Er~G,!Of! ._ .-,:'- __ ,_ _ 48. Cardenas No. 1 

49. Texas No. C-1 

50. Santa Fe No. 1 

B 

FIGURE 7.-West-east structural-stratigraphic cross section C-C', Sabinas basin to Gulf Coast at mouth of Rio Grande, showing Cretaceous and Jurassic 

sedimentary facies, structural features, and productive intervals. Datum for lower cross section B is estimated sea level at close of Cretaceous time; 

datum for upper cross section A is present-day sea level. Cross section is based on available published data and is partly schematic, particularly in older 

and deeper parts of section. Sources of data are same as for figure 5. Lithologic explanation is shown on figure 5. Line of cross section C-C' is shown 

on figures 8-12. 
The Tamaulipas and Burro- Picachos platforms are 

broad and relatively gentle uplifts with superimposed 

north- or northwest-trending anticlines (fig. 3) that may 

have formed as a result of northeast-directed compressive Laramide stresses during the development of 

the Sierra Madre thrust and fold belt (Humphrey, 

1956; Charleston, 1974). 

The Sabinas basin is an elongate northwest-oriented 

basin .with numerous northwest-trending local uplifts 

or sierras of exposed Cretaceous rocks (fig. 3), some of 

which have a narrow elongate belt of exposed Jurassic 

rocks in their centers (figs. 5-7). In the northern part 

of the basin, local uplifts are primarily elongated, relatively narrow, asymmetric anticlines, some of which are 

overturned and faulted (fig. 3). In the central and 

southern part of the basin, the folds are similar but 

tend to be broader to domal in shape with sharply 

plunging axes. These structures may be related in part 

to movement of underlying Jurassic salt and(or) gypsum (Weidie and Martinez, 1972; Gonzalez Garcia, 

1979). Lower Cretaceous rocks are exposed in the centers of several larger structures, and in a few cases 

Upper Jurassic rocks are exposed (figs. 3, 5, 6, 7). 

The Parras and La Papa basins (figs. 1, 3, 4) are 

characterized by surface exposures of thick Upper Cretaceous clastic sedimentary rocks and east-west oriented elongate anticlines that become more tightly folded 

and thrust faulted to the south toward the Sierra Madre Oriental thrust belt (Weidie and Murray, 1967; McBride and others, 197 4). The small La Papa basin lies 

between the Sabinas basin on the north and the Parras 

basin on the south, but in many respects it is simply an 

extension of the Sabinas basin. Structures in the La 

Papa basin are similar to those of the Sabinas and are 

elongated northwest-southeast. The Parras is a narrow 

east-west basin lying between the Coahuila platform on 

the north and the Sierra Madre fold and thrust belt on 

the south, although thrusts related to the Sierra Madre 

belt extend into the younger rocks of the Parras basin. 

Structures in the northeastern part of the Parras basin 

are broad, domal folds or open, elongate folds, with 

minor thrust faults displaced toward the north. In the 

main part of the basin nearer the Sierra Madre front, 

folds are highly elongated east-west, tight, overturned, 

and thrusted toward the south, dipping away from the 

main Sierra Madre mass (Krutak, 1965; McBride and 

others, 197 4). 

STRATIGRAPHY 

INTRODUCTION 

The sedimentary cover of northeastern Mexico consists primarily of Mesozoic rocks in the States of Coa10 

huila and western Nuevo Leon (Sabinas basin and adjacent area) (fig. 2). Mesozoic sedimentary rocks are 

1,550 to 6,000 m (5,000-20,000 ft) thick in the 

Sabinas basin (fig. 6) and up to more than 9,000 m 

(30,000 ft) thick in the Parras and La Papa basins 

(figs. 5, 6, 8, 9, 10, 11). On the Burro-Picachos and 

Coahuila platforms and in the Sierra Madre thrust belt, 

Mesozoic rocks are about 1,550 to 4,650 m 

(5,000-15,000 ft) thick, except where partly removed 

by erosion in the main uplift areas. Except for a thin 

Paleocene section in the Parras and Magiscatzin basins, 

Tertiary rocks are present only in the Burgos basin, 

where they range in thickness from about 1,550 to 

3,000 m (5,000-10,000 ft) in the outcrop belt on the 

west side of the basin to more than 15,500 m (50,000 

ft) near the Gulf Coast (fig. 12). Total thickness of the 

sedimentary cover in the deeper part of the Burgos 

basin is not known but probably ranges to more than 

21,000 m (70,000 ft) of Tertiary and Mesozoic rocks. 

BASEMENT 

The oldest rocks exposed in the area are scattered 

exposures of upper Paleozoic metamorphosed sedimentary rocks in the Burro-Picachos and Coahuila platform 

areas. Little is known of the basement rocks in the 

basins. According to Gonzalez Garcia (1979), the basement is probably composed of Permian-Triassic 

metasedimentary and intrusive rocks, but some areas 

of unmetamorphosed upper Paleozoic sedimentary 

rocks may be present in downfaulted blocks of the 

basement. 

TRIASSIC 

Unmetamorphosed rocks of Triassic age are known 

to overlie the basement in a few places around the 

borders of the assessment area, but little is known of 

their character except that they are primarily redbeds 

where observed, and they may underlie much of the 

area. South of Monterrey in the Linares trough, 2,000 

m or more of Triassic redbeds (La Boca Formation) are 

present in exposures on the flanks of the Tamaulipas 

platform. 

JURASSIC 

The Jurassic Sabinas basin or Gulf of Sabinas was 

bordered by the ancestral Burro-Picachos and Tamaulipas platforms on the north and east and the Coahuila 

platform on the west. The ancestral basin opened on 

the southeast into the Tampico basin and on the east, 

through an opening between the Tamaulipas and Burro-Picachos platforms, into the ancestral Gulf of Mexico basin (figs. 1B, 3, 4). The Jurassic sequence in 
• 

\ 

\ 

l 

\ I 

( 

---. ~ 

( 

26°-

Sandy 

Carbonate 

I 

\ 

\ 

' ,J A-· 

II 

I I 

I 

----~ La Casita dark organic shale 

.ti:E3:I::l Pre-Oxfordian Salt 

0 50 100 150 m1 

0 50 100 200 250 km 

--- Boundary of Assessment Area 

'l'l' 

00° 

98' 

98° 

0 

0 

- 29° 

- 28° 

- 25° 

- 24° 

I - 23° 

FIGURE B.-Approximate thickness in feet, partly restored, Jurassic System, showing approximate distribution of pre-Oxfordian 

salt, post salt Upper Jurassic main sedimentary facies, and gas fields producing from Upper Jurassic reservoirs. Lines of cross 

sections of figures 5, 6, and 7 are shown. Sources of data: Humphrey (1956), Erben (1957), Weidie and Wolle ben (1969), Gonzalez 

Garcia (1979), Lopez-Ramos (1980), and Newkirk (1971). 

northeastern Mexico consists of, in ascending order, 

the Minas Viejas (and its equivalent, the La Joya), the 

Zuloaga (and its equivalent, the La Gloria), and the 

Olvido and La Casita Formations (fig. 2). The Minas 

Viejas is a thick unit of redbeds, gypsum or anhydrite, 

and salt with minor interbeds of shale, carbonate, and 

sandstone. These beds are exposed in the centers of 

11 

several diapiric anticlines in the southeastern part of 

the Sabinas basin and have been penetrated in several 

wells. The formation may be approximately equivalent 

in age to the Louann Salt and the Werner Formation of 

the western Gulf of Mexico basin. Exact distribution 

and thickness of the salt section is not known, but 

original depositional thickness may have been as much 
\. 

\ 

' \ 

• 

26°-

EXPLANA liON 

,_--,r THRUST FRONT 

MAIN FACIES 

~ 

.. 0 0"" Son Morcos-Potulo arkosic 

.:EII:::.::;: sandstone a conglomerate 

----....;..a. Hosston Sandstone 

~ La Mula Shale 

~ La Virgen Evaporite 

~ Cupido Backreef Dolomite 

--.....:::c:. Cupido Reef 

00 51 

20t , 5f I 

Bounoory of Assessment Area 

A 

- 29° 

- 25° 

- 24° 

I 

98° - ?Y 

FIGURE 9.-Approximate thickness in feet, partly restored, Coahuilan Series, Lower Cretaceous, showing main sedimentary facies 

and gas fields producing from rocks of Coahuilan Series. Lines of cross sections of figures 5, 6, and 7 are shown. Sources of 

data: Humphrey (1956), Krutak (1965), Smith, C. I. (1971, 1981), Charleston (1974, 1981), Gonzalez Garcia (1979), Wilson and 

Pialli (1979), Lopez-Ramos (1980), Bebout (1977), Scott and Kidson (1977), and Rainwater (1971). 

as 1,550 m (5,000 ft) or more in the southeastern part 

of the Sabinas basin. The Minas Viejas probably grades 

to redbeds of the La Joya Formation around the periphery of the salt basin; it is absent on the Coahuila platform (figs. 5-6). 

The Zuloaga Limestone is a fossiliferous and oolitic 

limestone unit of middle to late Oxfordian age (fig. 2). 

12 

It is equivalent to the Smackover and Norphlet Formations of the U.S. Gulf Coast area (Imlay, 1980) and is 

widely distributed in northeastern Mexico (figs. 5-7). 

The Zuloaga has been identified in surface exposures in 

several breached anticlines in the Sabinas basin and in 

outcrops in the Sierra Madre Oriental fold and fault 

belt south of Monterrey. The Zuloaga grades westward 
\. 

'4-o 103° 

30° -

\ 

.......... 

• c 

25° -

EXPLANATION 

A 

101" 

I 

-""\ 

\ \ 

98" 

I 

97° 

1- 30° 

- 27° 

- 25° 

• • THRUST FRONT ~ CARBONATE REEF AND MOUND I \ TT "''T .,.,... PRODUCTIVE BELT, 

_.1...1- _1,..l.. SOUTH TEXAS 

_.1...1-

FACIES 

~ EVAPORITE FACIES \ \ r->-) 

0 GAS FIELD1 

Comanchean reservoir 

1! t "'+/-' 

i/ \ t VAL ES

0 

0 

Boundary of Assessment Area 

/ P~A TFORM I 

I looo I sao I 

- 23° 

FIGURE 10.-Approximate thickness in feet, partly restored, Comanchean Series, showing main sedimentary facies and gas fields 

producing from rocks of Comanchean Series. Lines of cross sections of figures 5, 6, and 7 are shown. Sources of data: Humphrey 

(1956), Gonzalez Garcia (1979), Lopez-Ramos (1980), Rainwater (1971), and Fisher and Rodda (1969). 

into sandstone and conglomerate of the La Gloria 

Sandstone, which is composed of lithologies reworked 

from underlying beds during the transgressive advance 

of the Upper Jurassic seaway. A limy transitional facies 

assigned to the Olvido Formation may be present between the Zuloaga or La Gloria and the overlying La 

Casita Formation. 

13 

The La Casita Formation is Kimmeridgian and 

Tithonian in age, equivalent to the Cotton Valley Group 

(Schuler and Bossier Formations) and to the Buckner 

Formation of the U.S. Gulf Coast (Imlay, 1980). The 

unit is about 300 to 1,000 m (975-3,250 ft) thick and is 

mostly black carbonaceous shale, marl, siltstone, and 

minor limestone in the lower part grading up to sand-
30° -

• c 

25° -

" \ 

105° \ 

I 

\ 

04° 

I 

¥ ¥ THRUST FRONT 

0 

0 50· 

PROOUCTIVE BELT, 

SOUTH TEXAS 

50 100 

W GAS F[ELD, 

Gulfion reservoir 

150 m1 

100 200 250 km 

Boundary of assessment area 

I ' < 00° 

I 

100° 

99° 99° 

I 

99° 

- 29° 

- 27" 

- 25° 

- 24° 

I - 23° 

FIGURE H.-Approximate thickness in feet, partly restored, Gulfian Series, showing main sedimentary facies and gas and oil fields 

producing from rocks of Gulfian Series. Lines of cross sections of figures 5, 6, and 7 are shown. Sources of data: Humphrey 

(1956), McBride and others (1974), Gonzalez Garcia (1979), Lopez-Ramos (1980), Holcomb (1971). 

stone with some conglomerate and limestone in the 

upper part. The La Casita Formation occupies the main 

part of the Sabinas and Parras basins and extends 

southward into the Sierra Madre Oriental and Tampico 

basin areas where it becomes a more limy facies than in 

the Burgos basin (figs. 1, 8). In the vicinity of the 

Coahuila platform, the unit becomes much more sandy 

and in places is conglomeratic (fig. 6). In the Sabinas 

basin, the contact between the La Casita and the overlying Lower Cretaceous beds is transitional. 

14 

LOWER CRETACEOUS 

Lower Cretaceous deposition in northeastern Mexico 

and adjacent Texas is dominated by two main marine 

transgressive cycles of reef-bearing carbonate facies 

deposition, the Cupido and Sligo Formations of Coahuilan age and the Glen Rose and Edwards or the Aurora 

and Cuesta del Cura Limestones of Comanchean age 

(figs. 2, 9, 10). The overlying Upper Cretaceous sequence is dominated by marine and continental clastic 
'"' " 

• c 

\. 

' \ 

os• \ 

I 

\ 

TEXAS, ,J ........... ...__..·.~ v 

r"' MEXICO . S' . "1...-<1 

( ., DR 

.· I 

.\ \. 

'·:t/. \ 

/j 

I I 

I I 

/ I 

\ I 

I 

\ 

I 

\ 

\ 

\ \ 

\ \ 

"" \ >' 

\ \ ~ ) I 

~\ 

• Mu • Sb 

a Mo 

\.... 

L. 

) 

) 

./ ~ '\_ \ ,_~.....____ / 

100• 

I 

2.50 - l.____ \/ "- . ) 

0 

,o 

105° 

EXPLANATION 

~Thrust front 

• Oil field, Tertiary reservoirs 

Q Gas field, Tertiary reservoirs 

_ _ Boundary assessment area 

50 

50 100 

I 

100 

200 I 

"~- - - - -.......:... ~ I --......... ~ 

'\ \ 

150 011 

250 km 

I \ w l 

\ ~ ) 

I ' (~ \ \ . 5"-)-- ~-

100° 

99° 

I 

98° 

I 

0 

97" 

i- 30° 

- 24° 

I - 23° 

FIGURE 12.-Approximate thickness in thousands of feet, Tertiary System, showing gas and oil fields producing from Tertiary rocks 

in Mexico and from productive trends in south Texas. Sources of data: Guzman and others (1955), Beebe (1968), Fisher and 

McGowen (1967), Lofton and Adams (1971), Shinn (1971), Tipsword and others (1971), and Lopez-Ramos (1980). 

deposits of Gulfian age that include substantial thicknesses of deltaic deposits and some coal beds in the 

upper half (figs. 2, 11). 

Lower Coahuilan (lower Neocomian) lowermost Cretaceous deposits are dark shale and shaly limestones of 

the Taraises and Menchaca Formations, which are conformable with the underlying La Casita Formation. The 

Taraises and Menchaca were deposited in the main 

area of the Sabinas basin and part of the Parras basin. 

15 

These formations grade laterally into the lower part of 

the San Marcos Arkose near the Coahuila platform and 

into the Colorado Sandstone (equivalent to the Hosston 

Formation of Texas) near the Burro-Picachos platform 

(figs. 2, 5, 6, 9). In the vicinity of Monterrey in the 

southeastern part of the Sabinas basin, the upper part 

of the Taraises grades into the lower part of the Cupido 

Limestone, which may represent the initial depositional 

stages of the Cupido-Sligo platform margin reef belt. 
To the south and east, equivalents of the Taraises are 

in the lower part of the Tamaulipas Formation, which is 

a deeper water offshore or basinal shaly carbonate and 

shale. 

Middle Coahuilan beds in the central and southeastern part of the Sabinas basin are represented by the 

marine shales and marls of the Barril Viejo Formation, 

which grade upward into the fossiliferous rudist-bearing limestone and dolomite beds of the Padilla Tongue 

(Sacramento Limestone of Charleston, 197 4), a westward-extending tongue of the Cupido platform limestone facies. The upper part of the Padilla contains 

oolitic and bioclastic beds in places. Along the southwestern flank of the basin, adjacent to the Coahuila 

platform, these beds grade into the green and red 

shales of the lower La Mula Shale, which grades farther southwest into part of the San Marcos and Patula 

Arkoses. To the east, Barril· Viejo and Padilla grade 

into the main facies belt of the lower Cupido Limestone, 

which extends in a broad north-south belt along the 

east side of the Sabinas basin (figs. 5, 6, 9). 

Upper Coahuilan beds in the main Sabinas basin 

area are represented by the limy and shaly shell-fragment beds of the upper La Mula Shale and the gypsum 

or anhydrite and limy or dolomitic beds of the La 

Virgen Evaporite. These beds grade southwestward into the Patula Arkose and eastward into the middle part 

of the Cupido Limestone. The La Mula and La Virgen 

Formations apparently represent a back-bank facies of 

the Cupido platform margin carbonate buildup. In Barremian time, organic bank and reef beds of the middle 

Cupido were deposited along a southwest-northeast 

belt between Saltillo in Coahuila State, and Laredo, 

Tex., across western Nuevo Leon State (fig. 9). This 

facies continues eastward into Texas as the Sligo Formation. In Nuevo Leon State, Cupido bank margin beds 

grade eastward to lime mudstone and shale of the lower Tamaulipas basinal facies. Lower Aptian (upper part 

of the Coahuilan Series) beds represent progradation 

and maximum development of the Cupido platform carbonate facies, which at this time covered most of the 

western part of Nuevo Leon and central to eastern 

Coahuila. The main platform margin Cupido-Sligo reef 

facies developed at this time and extended across 

Nuevo Leon between Laredo, Tex., and Monterrey. 

From here, the trend of the bank margin facies is uncertain, but it apparently continues southward for a 

short distance and then may continue westward into 

the Sierra Madre Oriental fold and thrust belt south of 

Saltillo (Gonzalez Garcia, 1979; Smith, 1981; Conklin 

and Moore, 1977; Wilson and Pialli, 1977). 

Lower Comanchean shale and siltstone beds of the 

widespread upper Aptian La Pena Formation overlie 

the Cupido Limestone throughout the Sabinas basin 

16 

and adjacent area (figs. 5-7). These beds, which are 

about 25 to 100m (80-325 ft) thick, represent deepening and transgression of the Cretaceous seas and termination of Cupido carbonate platform deposition and 

related organic bank and reef growth. At this time, 

widespread deposition of dark open-shelf shale, marl, 

and nodular limestone occurred across the submerged 

platform. To the east and southeast, the La Pena 

grades to open marine basinal thin-bedded argillaceous 

and cherty limestone and shale of the Otates Formation. The La Pena beds apparently represent the early 

stages of major transgression and foundering of the 

Cupido platform by basinal deposits of lime mudstone 

(upper Tamaulipas Formation) as the Cretaceous seas 

deepened and platform carbonate deposition shifted toward shallow-water areas to the west in the vicinity of 

the partly submerged Coahuila platform and to the 

north in the general area of the submerged BurroPicachos platform (figs. 4, 10). The Sabinas basin 

formed an embayment (Ocampo embayment) where the 

shaly facies of the upper Tamaulipas and the lime mudstone facies of the Aurora were deposited farther to the 

west at this time. These beds grade laterally into rudist 

banks and reefs of the Aurora Limestone deposited in 

shallow-water environments in the vicinity of the Burro-Picachos platform (equivalent to the Glen Rose 

Limestone, a shelf deposit) (Smith, 1981). 

Late Comanchean time was marked by submergence 

and transgression of the Cupido platform during early 

Albian time and the beginning of the second main Cretaceous carbonate cycle or reef belts, which included 

the Glen Rose, Edwards, Stuart City, and Devils River 

Limestones (figs. 5, 6, 10). Reef and organic bank facies growth continued in the vicinity of the submerged 

Coahuila platform and along the south border of the 

Texas craton from where the bank margin expanded 

and prograded basinward, with the total complex forming the successively deposited Glen Rose and lower 

Aurora Limestone, followed by the Stuart City, Devils 

River, and middle Aurora organic carbonate units, and 

finally in late Albian time, by the upper Aurora and 

upper Devils River bank carbonate units (figs. 6, 10). 

Farther south, in the Tampico basin area, the El Abra 

Limestone and equivalent reef and bank margin facies, 

and in southeastern Mexico, the main reef and bank 

margin facies of the Sierra Madre Limestone, were deposited in late Albian time. 

UPPER CRETACEOUS 

Following deposition of the Aurora Limestone and 

upper part of the Tamaulipas Formations and equivalent beds, marly beds of late Albian age were deposited 

across much of the Sabinas basin or Cupido platform 
area (Georgetown Limestone of the Washita Group and 

Kiamichi Formation of the Fredericksburg Group and 

Sue Peaks or Sombreratillo Marl of Smith, 1981). 

Along a broad belt between Laredo and Monterrey, 

these beds grade upward into the Cuesta del Cura 

Limestone, a sequence of thin-bedded, cherty limestones, which were deposited approximately along the 

trend of the previously deposited Cupido bank margin 

facies. The Cuesta de Cura beds are partly equivalent 

to the Del Rio Clay and Buda Limestone of southwestem Texas and northern Coahuila. 

Deposition of the Cuesta del Cura and equivalents 

was followed by an influx of fine calcareous clastics 

and argillaceous carbonates of the Cenomanian or basal Upper Cretaceous Agua Nueva or Indidura Formations, which probably represent the initial clastic influx 

related to Larmide orogenic activity (Smith, 1981). Organic carbonate production was greatly diminished at 

this time as terrigenous clay and silt covered the entire 

platform province. 

The Parras Shale is a thick (1,000-2,000 m; 

3,250-6,500 ft) sequence of dark-gray marine shale 

and siltstone overlying the limy Indidura beds. The Parras becomes more sandy in the upper part and is present throughout much of the Sabinas, Parras, and La 

Popa basins (figs. 5-6). Eastward, toward the Gulf 

basin, these beds grade into the lower part of the Mendez Shale (fig. 6), which is deeply buried beneath the 

Gulf Coastal Plain. 

The Difunta Group conformably overlies the Parras 

or Mendez Shale and occupies most of the Parras, La 

Popa, and southern part of the Sabinas basins, except 

where removed by late Cenozoic erosion in the main 

uplift areas. The Difunta is a group of seven formations, which are thickest in the Parras and La Popa 

basins where they are 3,000 to 5,000 m (9,750-16,000 

ft) or more thick, and is also present in the southern 

part of the Sabinas basin (figs. 5-6). This sedimentary 

complex represents the accumulation of a series of 

prograding and retrograding deltas into the Upper Cretaceous and Paleocene Gulf seaway by terrigenous detritus from highland areas in the vicinity of and southwest of the Sierra Madre Oriental and the Coahuila 

platform. Deltaic, nearshore, and marine-shelf environments are recognized in this complex intertonguing of 

sandstone, siltstone, redbeds, marine gray shale, and 

minor limestones deposited in the strongly subsided 

Parras and La Popa basins. The main part of the 

Difunta Group is of latest Cretaceous (CampanianMaestrichtian) age, but the upper part is probably Paleocene (McBride and others, 1974). Eastward, these 

beds grade to the upper part of the Mendez Shale in the 

Gulf Coastal Plain region. The Difunta is partly removed by late Cenozoic erosion in the main uplift areas 

17 

of the Sabinas basin and is absent within and south of 

the Sierra Madre Oriental, which was rising at this 

time. 

TERTIARY 

Except for probable Paleocene rocks in the uppermost beds of the Difunta Group, Tertiary rocks in 

northeastern Mexico are present only in the Burgos 

basin, which lies east of the trend of the Mesozoic 

Tamaulipas platform (fig. 12). West of here, Tertiary 

rocks are absent by erosion or nondeposition. The Burgos basin contains an eastward-thickening and offlapping wedge of Cenozoic open marine and nearshore 

marine, deltaic, and continental deposits 1,550 to 

15,000 m (5,000-50,000 ft) or more thick. These beds 

are of Paleocene through Holocene age and are continuous with similar sequences of the western Gulf basin 

in Texas. However, some of the Tertiary formation 

names whose type localities are in Texas are no longer 

used in Texas even though they are valid in Mexico. 

Paleocene rocks (lower part of Midway Formation of 

Mexico, lower part of Midway Group of Texas) crop out 

in a narrow belt along the western border of the Burgos 

basin, and a thin section of Paleocene beds also crops 

out in the Linares or Magiscatzin basin southeast of 

Monterrey. In the Burgos basin subsurface, these beds 

comprise a lower sequence of marine sandstone and 

glauconitic sandstone and shale grading upward to primarily marine shale in the upper part. The beds thicken 

eastward and are probably about 600 to 1,550 m 

(2,000-5,000 ft) thick near the Gulf coastline, where 

they are at depths greater than 12,000 m ( 40,000 ft). 

Eocene rocks crop out along the western border of 

the Burgos basin but are in part overlapped by Pleistocene and younger beds. Eocene rocks are primarily a 

marine sandstone and shale sequence of six main formations, thickening eastward to more than 6,150 m 

(20,000 ft) near the Gulf Coast. The lithologic framework of subsurface Eocene rocks was worked out by 

industry geologists and others from the extensive drilling activity in the U.S. Gulf Coast area. Most of these 

lithologic divisions are also recognized in the Burgos 

basin of Mexico (fig. 2). All of the units thicken rapidly 

eastward from the outcrop belts along the west side of 

the basin. 

The Wilcox Group is the basal Eocene unit and consists of alternating beds of marine shale and sandstone 

with some lignitic beds near the center. The Wilcox is 

about 770 to 1,230 m (2,500-4,000 ft) thick and is 

overlain by the Claiborne Group, which in ascending 

order consists in the Burgos basin of the Mount Selman, Cook Mountain, and Y egua Formations, all of 

which thicken eastward in the subsurface. 
The Carrizo Formation, which conformably overlies 

the Wilcox, is a unit of fine- to medium-grained nearshore marine sandstone and shale, which thins and disappears southward in the Burgos basin. 

The Mount Selman Formation (a term no longer used 

in Texas) is primarily marine and nearshore sandstone 

and shale 310 to 1,230 m (1,000-4,000 ft) thick. A 

deltaic unit (Queen City Sand) north of the embayment 

is an important reservoir section in south Texas. 

The Cook Mountain Formation (a term used in the 

Burgos basin and in Texas north of the Rio Grande 

embayment) is a marine glauconitic sandstone and 

gray shale unit, which is probably several thousand feet 

thick in the deep subsurface to the east. 

The Y egua Formation is a marine and nearshore 

marine or continental carbonaceous sandstone and 

shale unit 110 to 1,100 m (350-3,500 ft) thick. 

The Eocene Jackson Group in Texas or Jackson Formation in the Burgos basin conformably overlies the 

Y egua Formation of the Claiborne Group and is a sequence of marine sandstone and sandy shale about 310 

to 2,000 m (1,000-6,500 ft) thick. 

Oligocene rocks thicken from about 310m (1,000 ft) 

in the outcrop area on the west to more than 6,100 m 

(20,000 ft) in the eastern Burgos basin subsurface and 

represent continental beds on the west grading to nearshore marine and basin deposits to the east. A narrow 

band of outcropping Oligocene rocks extends from just 

west of Reynosa southeastward to near the Gulf Coast 

east of Ciudad Victoria (figs. 3, 11). 

The Vicksburg Formation of earliest Oligocene age is 

mainly marine shale in the Burgos basin subsurface 

with beds of volcanic ash and some nearshore sandstone units in the western area. Vicksburg beds are 

about 3,000 m (9, 750 ft) thick in the Reynosa Oriente 

No. 1 well and are thicker eastward toward the Gulf 

basin. 

The Oligocene Frio Formation, which overlies the 

Vicksburg, is primarily a relatively thin continental facies in outcrop sections in southwestern Texas and 

northeastern Mexico, but it thickens and changes rapidly to a thick sequence of nearshore marine sandstone 

and shale in the subsurface. The marine sandstone and 

shale facies of the Frio reaches maximum thickness, as 

much as 2,000 m (6,500 ft) in the subsurface, along a 

northwest-southeast belt passing east to Reynosa. East 

of there, the formation grades to a basinal shale sequence more than 3,000 m (9,750 ft) thick. 

The Norma Conglomerate, which unconformably 

overlies the Frio in the Burgos basin to the west, is a 7 5 

to 300 m (250-975 ft) or more unit of lenticular conglomerate and sandstone deposited as a large alluvial 

fan. The unit grades basinward to marine sandstone 

and shale representing a regressive unit at the top of 

18 

the Frio. The Norma represents coarse continental beds 

deposited during development of the regional mid-Oligocene unconformity. 

The Anahuac Formation is an upper Oligocene subsurface unit of variable thickness (50-150m; 160-485 

ft) overlying the Norma in southwestern Texas. It is a 

marine unit of foraminiferal shale and poorly consolidated sandstone that probably extends to the southwest into the Burgos basin subsurface. 

Miocene rocks crop out in a relatively broad band 

lying east of the Oligocene outcrop belt. They are in 

part overlapped by Quaternary beds in the eastern part 

of the Burgos basin. 

The Fleming Group of Mexico includes the Oakville 

and Lagarto Formations, and it unconformably overlies 

the Anahuac and equivalent beds, thickens rapidly eastward from less than 100m (325ft) in the outcrop area 

to 3,000 m (9,750 ft) or more in the subsurface near 

the Gulf Coast. In south Texas the Oakville and 

Lagarto are not assigned to a group, and the Fleming 

Formation is not used. These beds are primarily a continental and nearshore marine sandstone, conglomerate, 

and shale facies on the west and grade eastward to 

marine shale and sandstone toward the Gulf of Mexico. 

Pliocene rocks comprise a sequence of about 10 to 35 

m (33-110 ft) of outcropping continental sandstone, 

gravel, and clay beds assigned to the Goliad Sand along 

the eastern border of the Miocene outcrop belt. These 

beds thicken in the subsurface to as much as 200 m 

(650 ft) or more near the Gulf Coast. 

QUATERNARY 

Continental gravels and clay overlie the Pliocene 

beds and onlap older Tertiary beds in a broad area 

extending from the Gulf Coast as far west as Reynosa. 

These beds thicken to more than 300 m (975 ft) near 

the mouth of the Rio Grande. Relatively thin deposits of 

Quaternary gravels are also present in topographically 

low areas throughout northeastern Mexico, particularly 

in the Sabinas basin, where they usually overlie Upper 

Cretaceous beds. 

PETROLEUM GEOLOGY 

INTRODUCTION 

Exploration for petroleum in northeastern Mexico 

was stimulated during the 1920's and 1930's by the 

possibility of extending the producing zones of the Texas Gulf Coast southward into Mexico. Geophysical 

work, following surface geological studies in the upper 

Tertiary outcrop belt west and south of Reynosa, identified several subsurface structures, which resulted in 
early drilling activity and the discovery of a small accumulation of gas in Eocene lenticular sandstone at the 

La Presa field (fig. 3) west of Reynosa in 1931. During 

the period 1931 to 1937, three other relatively small 

gas fields were discovered, all productive from Eocene 

sandstone reservoirs, including the Laredo field near 

Nuevo Laredo about 122 km (75 mi) northwest of the 

La Presa field. These discoveries, which demonstrated 

a significant potential for hydrocarbons in northeastern 

Mexico, led to additional seismic work in the coastal 

plain area south of the Rio Grande. Between 1945 and 

1955, 21 additional gas fields with some oil production 

were discovered, including the largest (Reynosa, about 

2 TCF) and the six other most important fields. The 

main production from these fields was from sandstone 

reservoirs in the Oligocene Frio Formation, which extended the Frio productive belt of Texas southward 

some distance into the Burgos basin of Mexico. A total 

of about 90 gas and gas-condensate fields and a few 

small oil fields has been found in the Burgos basin with 

cumulative production (about 1970) of approximately 4 

TCF gas and 100 MMB oil and condensate. Estimated 

total ultimate recoverable reserves from these fields is 

about 5 TCF gas and 400 MMB oil and condensate. 

An early period of petroleum exploration in the 

Sabinas basin, based on field geology, resulted in the 

drilling of two unsuccessful wells in the northwestern 

part of the basin. Further field work was conducted by 

Imlay (1936, 1940, 1944, 1953), Kellum and others 

(1936), Humphrey (1949, 1956), and by PEMEX (Petroleos Mexicanos) geologists between 1940 and 1960. 

A geophysical and drilling program was then organized, which resulted in the drilling of two unsuccessful 

wildcats, Minas Viejas (1968) and Anhelo (1969), in 

the southeastern part of the basin. In 1976, gas was 

discovered in Jurassic and Cretaceous rocks in the 

northwestern part of the basin at the Buena Suerte No. 

1 well (fig. 3). Since then, a total of at least 10 gas 

fields has been discovered producing from Cretaceous 

carbonate and Jurassic sandstone reservoirs, with 

many of the wells producing at high rates. A small 

discovery in Upper Cretaceous beds was made at Garza 

No. 1 well in 1957 on the eastern border of the basin 

about 75 km (45 mi) west of Nuevo Laredo (fig. 3). 

TERTIARY, BURGOS BASIN 

Gas and condensate production in the Burgos basin 

is from sandstone and siltstone reservoirs of the Frio, 

Anahuac, and Vicksburg Formations of Oligocene age 

and of the Mount Selman, Jackson, and Y egua Formations of Eocene age, and Wilcox Formation of Eocene 

and Paleocene age (fig. 2). Minor gas is also produced 

19 

from Miocene sandstone reservoirs, and some oil is produced from Frio and Vicksburg reservoirs. Production 

occurs in relatively well defined belts extending into 

Mexico from productive trends in southwestern Texas, 

arranged generally from oldest (Eocene) on the west to 

youngest (Miocene or late Oligocene) on the east (fig. 

12). 

RESERVOIRS 

Lower Miocene sandstone reservoirs are productive 

over a relatively wide area along the Gulf Coast in 

Louisiana and Texas. In southwestern Texas and 

northeastern Mexico, a few fields produce from these 

beds in the vicinity of the Rio Grande delta. The reservoir sands are mainly discontinuous deltaic and delta 

fringe sand bodies probably deposited by the ancestral 

Rio Grande delta. 

The Oligocene reservoir section of the Vicksburg, 

Frio, and Anahuac Formations is thickest along a belt 

about 50 km (30 mi) wide between Reynosa and 

Matamoras extending southward into the Burgos basin. Approximately within this belt the main production 

occurs, with maximum production from the Frio sands. 

Reservoirs are discontinuous and lenticular deltaic 

fringe sandstone and siltstone bodies interbedded with 

marine and nonmarine shale beds. Some localized conglomeratic beds are present in the Frio, and overall the 

sandstone sequence tends to be more shaly and silty 

than equivalents in southwestern Texas. Reservoir 

quality in the Oligocene beds diminishes southward into 

the Burgos basin; permeability is generally reported as 

poor to medium; porosity is highly variable but ranges 

as high as 20-25 percent in some cases. Gross pay 

thickness ranges from less than 3m (10ft) to as much 

as 155 to 310m (500-1,000 ft) in some cases. Production rates range from 1 MMCFD or less to as much as 5 

MMCFD or more in a few cases from Frio reservoirs. 

Cumulative production from Oligocene reservoirs as of 

about 1970 was somewhat over 2 TCF and about 30 

MMB oil and condensate, almost all from Frio sandstone and siltstone reservoirs. 

Eocene reservoirs in the Burgos basin include sandstone and siltstone beds of the Wilcox, Mount Selman, 

Yegua, and Jackson Formations, which produce gas 

and some condensate in about 60 fields. Total production, however, is much less than that from the Oligocene reservoirs. Nearshore marine and nonmarine discontinuous sandstone beds are gas reservoirs in the 

upper Eocene Jackson Formation at a few fields in the 

northwestern part of the Burgos basin, but production 

is relatively minor. The bulk of Eocene production is 

from deltaic and nearshore marine sandstone reservoirs 

of the Claiborne Group (Yegua, Cook Mountain, and 
Mount Selman Formations). These reservoirs are best 

developed within a belt between Laredo, Tex. , and 

Reynosa, Mexico, extending across the Rio Grande 

southward into the Burgos basin. Basal Eocene reservoirs are deltaic, fringe, and barrier bar sandstones 

deposited during a major regressive cycle (Rainwater, 

1967; Fisher and McGowen, 1967). The main belt of 

sandstone development passes southward into Mexico a 

short distance east of Nuevo Laredo. Distribution of 

sandstone beds and thickness of the Wilcox are influenced greatly by a growth fault system downdropped 

toward the Gulf of Mexico. General reservoir quality of 

Eocene reservoirs decreases southward into the Burgos 

basin. Reported permeability is generally poor to medium, and porosity values are highly variable. Gross pay 

thicknesses range from less than 3m (10ft) to 30 to 60 

m (100-200 ft) in a few cases. Production rates range 

from 0.5 MMCFD or less to more than 10 MMCFD in 

one case. Almost all of the production is from Mount 

Selman sandstone and siltstone reservoirs. As of about 

1970, cumulative .production from the Mount Selman 

was about 300 BCF with about 50 BCF from Jackson 

Y egua, and Wilcox reservoirs. ' 

SOURCE ROCKS 

Marine argillaceous rocks, interbedded with deltaic 

and nearshore marine sandstone reservoirs, are believed to be the main source rocks for oil and much of 

the gas accumulations in Tertiary reservoirs. Carbonaceous deltaic and nearshore lagoonal or swamp-deposited argillaceous beds are also probable source rocks for 

some of the gas. 

REGIONAl CAP ROCKS 

Thick and widespread marine, and in some cases 

nonmarine, shale facies of the Gulf basin Tertiary sequence, which intertongue with and overlie the sandy 

reservoir facies, form numerous regional seals for the 

petroleum accumulations. 

TRAPS 

Most traps in Burgos basin Tertiary fields are associated with combined structural-stratigraphic relationships incident to complex facies patterns of the deltaic 

and related nearshore environments of deposition, 

growth faults, and faulted domal or anticlinal folds, 

which in some cases may be related to deep-seated salt 

structures. Except in the updip beds near the outcrop 

belts, few of the structures are expressed at the 

surface. 

20 

ANAlOGS 

The stratigraphic and structural aspects of the Burgos basin productive province are essentially the same 

as those of the analogous western Gulf basin U.S. 

province. 

UPPER CRETACEOUS 

Only minor production (gas) has been found in Upper 

Cretaceous rocks, mainly in fractured limestone beds of 

the San Felipe Formation at the Lerna field in the 

southeastern part of the Burgos basin and in limy beds 

of the Eagle Ford (Boquillas) Formation at the Garza 

field on the northeastern flank of the Sabinas west of 

Nuevo Laredo (fig. 3). Gas production from fractured 

Eagle Ford (Boquillas) beds is also reported northwest 

of Nuevo Laredo on the Burro-Picachos platform 

(Zwanziger, 1978). These are small accumulations, and 

thus far prospects for significant petroleum deposits in 

Upper Cretaceous beds have not been promising in the 

Burgos and Sabinas basins. In the Burgos basin, Upper 

Cretaceous beds are of the open-basin shaly marine 

facies, probably without reservoir development, and in 

most cases are buried to depths greater than 7,200 m 

(25,000 ft). The potential of the Upper Cretaceous section in the Sabinas basin is limited by the severe erosion 

and the probability that these beds have not been buried to thermal maturity depths, although some possibility for biogenic gas may exist in the coaly parts of the ~ 

section in the Sabinas coal basin (fig. 3). The thick 

Upper Cretaceous sequence in the Parras and La Pop a 

basins has not yet been explored, and several parts of 

this section may be attractive for gas prospects. Much 

of this section is an intertonguing marine and 

nonmarine facies with thick reservoir and potential 

source-rock beds, many fold and fault structures with 

good trap possibilities, and regional cap-rock facies. 

The upper part of this section has not been buried to 

thermal maturity depths in parts of these basins, but 

some of the shallower beds could be prospects for biogenic gas accumulations in the deltaic and nearshore 

marine facies. In the deeper parts of these basins, the 

lower half of the sequence has been buried to depths 

beyond the thermal maturity range. 

LOWER CRETACEOUS 

Lower Cretaceous fractured limestone and dolomite 

beds are productive of gas at about 10 fields in the 

Sabinas basin and Tamaulipas platform area. Reservoir 

facies are present in the carbonate beds of the Aurora 

Limestone, Monclova facies (upper Aurora Limestone 

or Actita Evaporite), Cupido Limestone and its Padilla 
Tongue, La Virgen Evaporite, and Menchaca Limestone, in sandstones of the Barril Viejo Formation, and 

in fractured argillaceous limestone facies of the La 

Pena Formation (fig. 2). 

RESERVOIRS 

The Aurora Limestone and Monclova facies are 

equivalent to the Stuart City Limestone of Texas, a 

platform and rudist bank facies of Albian Age generally present in western Coahuila in the vicinity of the 

Coahuila platform (fig. 10). Good porosity is observed 

in outcrops of these beds (Gonzalez Garcia, 1979), and 

the potential for matrix and fracture porosity and permeability is good where structures in the area are covered by Upper Cretaceous shaly beds. 

The La Pena argillaceous limestone or shale is present throughout northeastern Mexico (fig. 2). These 

beds are fractured reservoirs in the Sabinas basin and 

Burro-Picachos platform areas. 

The Cupido (and its stratigraphic equivalent in Texas, the Sligo) platform limestone facies covers much of 

the Sabinas basin, Tamaulipas platform, and thrust 

belt area and contains the major shelf margin rudist 

reef and mound belt of the Lower Cretaceous. Gas 

shows are reported from these beds (Gonzalez Garcia, 

1979), and although good matrix porosity has not been 

observed in wells drilled so far, fractured reservoirs are 

a good possibility as is the local development of matrix 

porosity in reef or back-reef dolomitized beds. 

The limestone, dolomite, and evaporite beds of the 

La Virgen Evaporite are a platform interior facies 

equivalent to the platform margin facies of the Cupido 

Limestone (figs. 2, 5, 6). These beds are productive in 

the Buena Suerte, Monclova, and Ulua gas fields (fig. 

3) from porous, finely crystalline dolomite beds, which 

are interbedded with nonporous limestone and anhydrite beds. The La Virgen is in facies relationship with 

the La Mula Shale, which is a probable good sourcerock facies. Fracturing is an important factor in reservoir quality because of the fine-grained and generally 

low matrix permeability of the dolomites. 

The Padilla Tongue represents a relatively widespread platform limestone tongue of the lower Cupido, 

which underlies and intertongues with the La Virgen 

Evaporite and La Mula Shale (figs. 2, 5, 6). The Padilla 

contains a thick section (up to 80 m; 260 ft) of porous 

dolomitized reef and back-reef facies with good reservoir quality (Gonzalez Garcia, 1979); the section has 

been saltwater bearing in several wells. 

The Barril Viejo Formation, Patula Tongue, and San 

Marcos Arkose are a continental to marine coarse clastic facies present in the central and southwestern part 

21 

of the Sabinas basin and adjacent areas. The sandstone, carbonate, and shale beds of the Barril Viejo 

Formation underlie the Padilla Tongue of the Cupido in 

the central part of the Sabinas basin. These beds grade 

westward into parts of the San Marcos and Patula 

Arkoses. The sandstone units of the Barril Viejo are of 

interest as potentially good reservoirs, although lack of 

control prevents a complete assessment at this time. 

Good gas shows are reported in Barril Viejo sandstones 

in the Colmar No. 1 and Dolomita No. 1 wells (Gonzalez Garcia, 1979). 

The Menchaca Limestone is the basal Cretaceous 

shelf limestone and marl unit in the central and northern parts of the Sabinas basin. These beds grade eastward into marly and sandy beds of the Taraises Formation and southward into the lower San Marcos Arkose. 

Fractured Menchaca Limestone flowed gas under high 

pressure for a short time at the Buena Suerte No. 1 

well (fig. 4), but the test was considered inconclusive 

(Gonzalez Garcia, 1979). 

SOURCE ROCKS 

Potential Lower Cretaceous source rocks are present 

in the La Pena, La Virgen, La Mula, Barril Viejo, 

Menchaca, and Taraises Formations. All these formations are marine shale or shaly carbonate beds with 

varying amounts of organic content. In most cases, 

they are in stratigraphic association with potential reservoir beds. Geochemical data are not available on any 

of the Cretaceous units, and in places the Lower Cretaceous rocks may not have been buried to thermal maturity depths. However, in areas where the Upper Cretaceous beds are present, the Lower Cretaceous section 

should have been buried to sufficient depth, particularly 

in the southern part of the area north and east of the 

Sierra Madre Oriental fold and thrust belt and in most 

of the Sabinas basin. 

REGIONAl CAP ROCKS 

Impermeable regional facies that are suitable as 

seals for Lower Cretaceous reservoirs include the widespread Upper Cretaceous argillaceous beds and the 

Lower Cretaceous shale and shaly carbonate beds of 

the La Pena Shale, upper Tamaulipas Formation, La 

Virgen Evaporites, La Mula Shale, and the Barril Viejo 

Formation and Menchaca Limestone. These units vary 

in regional distribution, but in general several of them 

are present in most parts of the assessment area. 

TRAPS 

Thus far, gas discoveries in the Sabinas basin and 

adjacent area are on anticlinal structures, most of them 
faulted and most with large closures. Many similar 

structures are as yet undrilled; some are intruded by 

salt or gypsum but many may not be. Many potential 

fault and fractured reservoir traps should be present on 

the flanks of large structures. Facies changes are common in the Lower Cretaceous section with good possibility of stratigraphic traps; many of the accumulations 

appear to be combination structure, fracture pattern, 

and stratigraphic traps. Probably the most favorable 

structures are those over which the Upper Cretaceous 

shaly section is preserved. Accumulations may depend 

on the specific combination of the above factors. 

ANALOGS 

Stratigraphic analogs for the Lower Cretaceous section are found in much of the carbonate and evaporite 

section of similar age in the U.S. Gulf basin, the Tampico basin, and the southeastern Mexico-Guatemala basins. Structural styles in these areas are in the main 

somewhat different from those of the Sabinas and associated basin and uplift areas, where the structural 

styles are more directly related to the effects of 

Laramide folding and thrusting of the Sierra Madre 

Oriental. However, similarities are found in the presence of evaporite intrusion structures in some cases and 

in the high degree of fracturing in tightly folded structures. An important difference between the northeastern Mexico Mesozoic provinces and those of other Mesozoic productive regions of the Gulf of Mexico is the 

absence or thinning by erosion or nondeposition of the 

Upper Cretaceous and Tertiary cover in the Sabinas 

basin and related basins and uplifts. 

JURASSIC 

RESERVOIRS 

The La Casita Formation contains sandstone and 

siltstone units, which are interbedded with high-organic shale beds in much of the Sabinas basin area. The 

sandstone facies is best developed in the vicinity of the 

Coahuila platform and the Tamaulipas platform paleostructures. Sandstone beds in the La Casita are productive of gas in the Lampazos field (fig. 3) and have had 

good gas shows in several other wells. The sandstones 

are composed of calcite-cemented quartz and carbonate 

grains, and interstitial porosity thus far has been low. 

However, their reservoir quality may improve in other 

parts of the basin depending on facies changes and 

paleostructure position. Fracturing also is important on 

the tightly folded Sabinas basin structures. 

The Upper Jurassic Zuloaga Limestone includes the 

oolitic carbonate beds and evaporites of the Upper Ju22 

rassic Olvido Formation. The Zuloaga is present in the 

central part of the Sabinas basin and grades into the 

sandy facies of the La Gloria Sandstone around the 

basin borders. The oolitic beds of the Zuloaga so far 

have not been porous where drilled, but facies changes 

could improve porosity, and fracturing is important on 

structural prospects. The La Gloria Sandstone beds are 

also of potential reservoir quality, although they are 

suspected in most areas to have low matrix porosity. 

The presalt redbed clastics are probably widespread 

in the area and may be very thick in downwarped graben areas of the basement. Good matrix porosity and 

adequate associated source rocks would not be expected in this facies, but in anomalous structural situations they could be of interest. 

SOURCE ROCKS 

The Upper Jurassic La Casita Formation contains a 

substantial thickness (as much as 310 m; 1,000 ft or 

more) of dark organic shaly beds which underlie the 

Cretaceous section throughout most of the Sabinas basin. The La Casita has been buried to depths of more 

than 4,600 m (15,000 ft) in parts of the basin area, and 

there is some indication that these beds may have undergone severe thermal alteration (Gonzalez Garcia, 

1979). Igneous activity, as well as burial depths, may 

have also contributed to the thermal effects. Excessive 

thermal activity may explain the high methane and C02 

content of most of the gases, as well as the lack of 

significant oil indications in the fields discovered so far. 

In addition, there seems to be evidence that the basin is 

primarily a dry-gas basin. Condensate and some oil 

shows, however, have been encountered in a few wells, 

and current drilling density precludes an accurate assessment of these factors. 

The Zuloaga Limestone, which is reported as black 

and argillaceous in places, may also contain a less important Upper Jurassic source-rock facies. 

TRAPS 

Petroleum deposits in Jurassic reservoir beds should 

be associated with the same kinds of traps as those of 

the Lower Cretaceous reservoirs that occur in folded 

and faulted structures having an important fractured 

reservoir factor and some possibility of stratigraphic 

trapping, particularly on the flanks of large structures. 

ANALOGS 

The Jurassic stratigraphic section in northeastern 

Mexico is similar in most respects to that of the north-
ern regions of the U.S. Gulf basin, except that the 

carbonate beds in the Zuloaga Formation do not appear 

to contain porous reservoir facies as extensive as those 

of the Smackover Formation. The La Casita and La 

Gloria beds are similar in most respects to clastic facies 

of the Cotton Valley Group in the northern Gulf basin 

and contain a significant thickness of dark high-organic facies and sandstone beds similar to equivalent productive reservoirs in Texas and Louisiana. 

RESOURCE ASSESSMENT 

PROCEDURES 

The resource assessment was conducted by the Resource Appraisal Group (RAG) of the U.S. Geological 

Survey, Branch of Oil and Gas Resources, following the 

standard procedures developed since 197 4 for domestic 

petroleum resource analysis. The technique, briefly, requires study of a given area paying particular attention 

to the geologic factors controlling the occurrence, quality, and quantity of the petroleum resource. Standardization of critical elements of the investigations is 

achieved by the preparation of data forms for each 

basin; the forms call for specific volumetric, areal, and 

rock-quality measurements, as well as the determination of basin analogs for comparison purposes. In addition, finding-rate histories and projections are constructed when possible. From these data and analyses, 

various analytical techniques are used to calculate a set 

of resource numbers. Not considered in this assessment 

are resources of heavy oil deposits, tar deposits, and oil 

shales; gas in low-permeability reservoirs, in geopressured shales and brines, and in natural gas hydrates; 

and gas occluded in coal. 

The assessment process itself is subjective; the results of the geological investigation and of the resource 

calculations are presented to a team of U.S. Geological 

Survey assessment specialists who make their personal 

estimates conditional upon recoverable resources being 

present. Initial assessments are made for each of the 

assessed provinces as follows: 

(a) A low resource estimate corresponding to a 95-

percent probability of more than that amount; this 

estimate is the 95th fractile (F95). 

(b) A high resource estimate corresponding to a 5-

percent probability of more than that amount; this 

estimate is the 5th fractile (F5). 

(c) A modal ("most likely") estimate of the quantity of 

resource associated with the greatest likelihood of 

occurrence. 

The individual estimates are then posted and averaged, and the results debated from the perspective of 

23 

the personal experiences of the individual assessors; a 

second and third iteration of the procedure may follow 

depending on consensus. If no commercial oil has been 

heretofore discovered in the basin, then a marginal 

probability is subjectively assessed reflecting the 

probability that any commercial oil will ever be 

discovered. 

The results of the final estimates are averaged, and 

those numbers are computer processed using probabilistic methodology (Crovelli, 1981) to show graphically 

the resource values associated with a full range of 

probabilities and to determine the 95th fractile, the 5th 

fractile, and the mean, as well as other statistical 

parameters. 

ASSESSMENT 

The locations of the northeastern Mexico basins are 

shown in figure 1. Unconditional estimates by the U.S. 

Geological Survey of oil and gas resources in these 

basins are given in table 1 and figures 13 and 14. Data 

and summary information supporting these estimates 

are supplied in tables 2-4. 

TABLE 1.-Estimates of conventionally recoverable petroleum 

resources of northeastern Mexico, including those of the 

Sabinas, Parras, and Burgos basins 

[Unconditional resource assessment by U.S. Geological Survey as of June 23, 1981; 

see also figures 13 and 14] 

Crude oil Natural gas 

in billions of barrels in trillions of cubic feet 

Probability of occurrence (percent) 

95 5 Mean 95 5 Mean 

Sabinas and Parras basins1 

0 2.9 0.8 18 122 55 

Burgos basin 

0.1 1.2 0.5 1.6 12.5 5.5 

Combined Sabinas, Parras, and Burgos basins2 

0.2 3.5 1.3 23 

4 

126 61 

BBOE at 

6,000 ft3/barrel* 

21 10 

1 A marginal probability of 0.85 is assigned to the occurrence of commercial oil in 

these basins. 

2 Totals are derived by statistical aggregation; only the mean total equals the sum 

of the component parts. 

* In PEMEX reports, conversion to BBOE is made at 5,000 ft3fbarrel, but the 

6.000 ft3fbarrel is used here for comparison with other U.S. and world numbers. 
COMMENTS 

• Exploration in the Sabinas basin is in its very initial 

stages. So far, we have reports on four successful 

wildcats, each of which is reported to be capable of 

production in excess of 10,000,000 ft3

/d. Though no 

oil has yet been reported, the geologic investigation 

suggests that oil in some part of the basin is likely. 

• Giant fields are likely in the Sabinas and Parras basins owing to structural development, including salt 

and probable favorable Jurassic source rock. Overall 

stratigraphic thickness of Mesozoic units may be 

30,000 to 40,000 ft. 

• The Sabinas and Parras basins reflect geologic conditions similar to those in the western United States 

from the overthrust belt east to the North American 

craton. Production from Jurassic and Cretaceous 

units will predominate. 

• The Burgos basin is an extension of the U.S. Western Gulf basin. Substantial production has been established from lower Tertiary rocks on both sides of 

the U.S.-Mexico border. Production from Eocene and 

Oligocene rocks will predominate. 

• Giant fields are not likely in the Burgos basin owing 

to the state of maturity for exploration and the deltaic environment. Overall stratigraphic thickness of 

Tertiary rocks may exceed 50,000 ft. 

TABLE 2.-Data and information summary 

Geologic province: Mesozoic and Tertiary continental 

basins. 

Areas included in assessment: 

Burgos basin 

Sabinas basin and adjacent uplifts 

Parras, La Popa, and Magiscatzin basins 

Northern and eastern borders of Sierra Madre Oriental 

overthrust belt. 

Total area of province: 330,000 m2 (125,000 mi2) 

Prospective intervals: 

Tertiary continental-marine clastic sequence, Burgos 

basin. 

Upper Cretaceous continental-marine clastic sequence, 

Parras, La Popa, and southern Sabinas basins. 

Lower Cretaceous marine platform carbonate sequence, 

Sabinas, Parras, La Popa, and Magiscatzin basins; 

Burro-Picachos, Tamaulipas, and Coahuila platforms 

and Sierra Madre Oriental overthrust belt. 

Upper Jurassic marine clastic and carbonate sequence 

Pre-Upper Jurassic continental-marine clastic and evaporite sequence. 

Source beds: 

Tertiary marine, lagoonal, and deltaic carbonaceous 

shales and siltstones. 

Upper Cretaceous marine and deltaic carbonaceous shales 

and siltstones. 

Lower Cretaceous marine organic shale and argillaceous 

limestone. 

Upper Jurassic marine organic shale and argillaceous 

limestone. 

Prospective trap types: 

Tertiary and Upper Cretaceous marine, deltaic, and continental sandstones. 

Cretaceous and Jurassic reef, back reef, and fracture pattern porosity-permeability variations. 

Asymmetric, thrust-faulted, and normal faulted anticlines 

and domes, some related in part to salt or gypsum 

movement. 

Combination structural and stratigraphic traps 

Exploration stage of province: Mature in Tertiary Burgos 

basin; early in province. 

Number of fields: About 90 small to intermediate gas and 

gas-condensate fields in Burgos basin; about 10 dry gas 

fields in Sabinas basin and adjacent Burro-Picachos platform, some of which may be large. 

Cumulative production: About 4 TCF gas and 100 MMB 

condensate and oil. 

Average depth of undiscovered resources: About 4,500-6,000 m 

( 15,000-20,000 ftl in Burgos basin; about 3,300-4,500 m 

( 10,000-15,000 ft) in Sabinas-Parras-La Popa basins. 

Recoverable basin richness: At mean, undiscovered estimate 

assuming 330,000 mi3 of sediments=43,000 BOE/mi3. 

Analogs: Gulf basin, United States; Tampico basin, Mexico 

24 
1.0 

=\ ESTIMATES 

MEAN -

~ MEDIAN - 0.8 

I 

1-

w 

0:: 

~ 0.6 

-

-

- \ 95% -

75% -

50% -

25% -

u. 

0 

>-

-

-

-

1- 0.4 

::J 

Ci) -

<( - ca 

0 -

g: 0.2 

-

-

-

0.0 

1.0 

~ 0.8 

I 

1-

w 

0:: 

0 0.6 ~ 

u. 

0 

>- !::: 0.4 _J 

Ci) 

<( 

ca 

0 

g: 0.2 

0.0 

0.0 

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

0.0 

\ 5% -

MODE - (j -

\ 

f\ 

~ r--_ 

1.4 2.8 4.2 5.6 7.0 8.4 9.8 11.2 12.6 

RECOVERABLE OIL, IN BILLIONS OF BARRELS 

FIGURE 13.--Aggregaterecoverable oil in the Burgos and Sabinas-Parras basins, Mexico. 

\ ESTIMATES 

\ MEAN -

MEDIAN -

\ 95% -

75% -

50% -

25% -

\ 5% -

MODE -

(j -

' 

~ "' ~ 

30.0 60.0 90.0 120.0 

----

150.0 180.0 210.0 240.0 270.0 

RECOVERABLE GAS, IN TRILLION CUBIC FEET 

FIGURE 14.-Aggregate recoverable total gas in the Burgos and Sabinas-Parras basins, Mexico. 

25 

1.31 

0.93 

0.24 

0.55 

0.93 

1.55 

3.51 

0.41 

1.34 

14.0 

60.55 

52.20 

22.77 

37.03 

52.20 

74.74 

126.37 

40.21 

35.55 

300.0 
Sedimentary 

section 

Reservoirs 

Source rocks· 

Structure 

Paleostructure 

Time of migration 

and 

hydrocarbon 

generation 

Depth of burial 

Geothermal 

gradient 

Preservation 

history 

Size of area 

Exploration stage 

TABLE 3.-Summary of assessment factors 

Burgos basin 

85 percent marine; primarily Tertiary and Upper 

Cretaceous clastics; some Lower Cretaceous 

and Jurassic carbonates, evaporites, and 

clastics in lower part at great depths. 

Mainly Tertiary deltaic and longshore marine 

sands, somewhat discontinuous; some 

possibility of Cretaceous and Upper Jurassic 

carbonate and Upper Jurassic clastic 

reservoirs at depth. 

Tertiary marine shales, maiPly gas; Cretaceous 

and Upper Jurassic marine black shales and 

shaly carbonates. 

Anticlines and domes, faulted, and vertical faults; 

possibly deep salt-structure influence. 

General continental border basin subsidence with 

down-to-gulf growth faults. 

Good. 

Shallow in much of upper Tertiary with biogenic 

gas; moderate in remainder of Tertiary and 

Cretaceous but rapidly reaching excessive 

depths in coastal plain and offshore area. 

Normal. 

Good. 

Small-14,000 mi3, 113,000 mi3 of sediment; 

about 118 the size of western U.S. Gulf basin. 

Mature, except in deep part of basin where 

probability of good reservoir section is low. 

26 

Sabinas basin area 

95 percent marine; primarily Lower and middle 

Cretaceous carbonates; Upper .Jurassic 

carbonate and clastics; Upper Cretaceous 

clastics in south part; Jurassic and some 

Triassic clastics and evaporites in lower part. 

Mainly Cretaceous and Upper Jurassic 

carbonates, with reef, mound, or fractured 

carbonate reservoirs; clastic reservoirs in 

Upper Cretaceous and Upper Jurassic. 

Upper Jurassic black shales; Lower and middle 

Cretaceous gray and black shales and shaly 

limestones; Upper Cretaceous marine gray 

shales. 

Elongate anticlines and regional uplifts, many 

evaporite structures; common vertical faults; 

major thrust belt in south part. 

Regional Mesozoic paleostructures inherited from 

Paleozoic; major continental border evaporite 

basin subsidence in center; Laramide thrust 

belt growth in south part. 

Good. 

Shallow in much of Upper Cretaceous with 

possibility of biogenic gas; moderate in 

remainder Cretaceous and Upper Jurassic in 

most of area, probably reaching 

postmaturation depths in central part of 

area. 

Probably high in parts of area, particularly 

western part, because of Cenozoic igneous 

activity and overthrust activity. 

Upper Cretaceous exposed over much of area; 

Lower and middle Cretaceous exposed in 

main structural areas; Upper Jurassic 

exposed in small areas of main salt anticlines 

and in parts of south thrust belt. 

Intermediate-80,000 mi 2, 218,000 mi3 of 

sediment; slightly smaller than Permian 

basin of Midcontinent areas, United States. 

Early; 65 or more important structures are as yet 

undrilled. 
TABLE 4.-Supplementary and comparative data 

supporting the resource estimates for 

northeastern Mexico 1 

Crude oil Natural gas 

(billion barrels) (trillion cubic feet) 

Cumulative production to Jan. 1, 1980 

Sabinas/Parras - - - - - - - - - - - - - 0 

Burgos - - - - - - - --·- - - - - - - - - - - .1 4.0 

Measured reserves 3 to Jan. 1, 1980 

Sabinas/Parras - - - - - - - - - - - - - 0 

Burgos -------------------- .3 

Original recoverable resources 

(ultimate) of the two basins 

+2 

5.0 

Oil 

BBOE at 

6,000 ft3/barrel 

Cumulative production ----- 0.1 4.0+ 

Identified reserves - - - - ------ .3 5.0+ 

Undiscovered resources 

(mean) ------------------ 1.3 61.0 

Total - - - - - - - - - - - - - - - - 1. 7 70.0+ 

12+ 

Total14+ BBOE 

Recoverable basin richness: At mean, undiscovered estimate 

assuming 330,00 mi3 of sediments=43,000 BOE/mi3. 

1 Cumulative production and reserves are composited estimates from various 

sources. 

2 Quantity positive, but data unavailable. 

3 Follows terminology outlined in "Principles of a Resource/Reserve Classification 

for Minerals," 1980, U.S. Geological Survey Circular 831, by U.S. Bureau of Mines 

and U.S. Geological Survey, 5 p. 

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27 

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