IRC.760S

GEOLOGICAL SURVEY CIRCULAR 760

Petroleum Geology and 

Resources of 

Southeastern Mexico, 

Northern Guatemala, and 

Belize
Petroleum Geology and 

Resources of 

Southeastern Mexico, 

Northern Guatemala, and 

Belize

By James A. Peterson 

GEOLOGICAL SURVEY CIRCULAR 760

Major reserves of oil occur in Cretaceous 

and Paleocene microfractured dolomite 

reservoirs on salt structures in the 

Reforma and offshore Campeche areas of 

southeastern Mexico

1983
United States Department of the Interior

WILLIAM P. CLARK, Secretary

Geological Survey

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

Peterson, James A.

Petroleum geology and resources of southeastern Mexico, northern Guatemala, and Belize.

(Geological Survey circular ; 760)

Bibliography: p.

Supt. of Docs, no.: I 19.4/2:760

1. Petroleum Mexico. 2. Petroleum Guatemala. 3. Petroleum Belize. I. Title. II. Series.

QE75.C5 no. 760 557.3s [553.2'82'0972] 83-600170 [TN873.M6]

Free on application to Distribution Branch, Text Products Section, 

U. S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304
ASSESSMENT OF RECOVERABLE ENERGY RESOURCES

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 to gain a broad geological understanding of the 

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; resource assessment, like 

exploration, to be effective, must be an ongoing process taking advantage of changing 

ideas and data availability the results produced being progress reports reflecting on a 

state of knowledge at a point in time. Because this 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 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.

Other U.S. Geological Survey publications relating to the assessment of 

undiscovered conventionally recoverable petroleum resources include the following:

Open-File Report 81-0986 "Assessment of conventionally recoverable petroleum resources of Persian Gulf

basin and Zagros fold belt (Arabian-Iranian basin)" 

Open-File Report 81-1027 "Assessment of conventionally recoverable petroleum resources, Volga-Urals

basin, U.S.S.R."

Open-File Report 81-1142 "Assessment of conventionally recoverable petroleum resources of Indonesia" 

Open-File Report 81-1143 "Assessment of conventionally recoverable petroleum resources of northeastern Mexico" 

Open-File Report 81-1144 "Assessment of conventionally recoverable petroleum resources of southeastern

Mexico, northern Guatemala, and Belize"

Open-File Report 81-1145 "Assessment of conventionally recoverable petroleum resources of Trinidad" 

Open-File Report 81-1146 "Assessment of conventionally recoverable petroleum resources of Venezuela" 

Open-File Report 81-1147 "Assessment of conventionally recoverable petroleum resources of the West

Siberian basin and Kara Sea basin, U.S.S.R." 

Open-File Report 82-0296 "Assessment of undiscovered conventionally recoverable petroleum resources of

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

These reports are available from the Open File Services Section, Branch of Distribution, USGS, Box 25425, 

Federal Center, Denver, CO 80225.
CONTENTS

Abstract .__...._--._.._---_------------ J

Introduction ....._..._................... 1

Geography ..........__......_......._ 1

Sources of data ....................... 2

Regional geology ......................... 2

Introduction ____......_____........_.. 2

Stratigraphy ____........__........._. 4

Paleozoic ......................... 8

Lower Mesozoic .................... 8

Upper Jurassic ..................... 8

Cretaceous ....................... 8

Tertiary ......................... 9

Structure ........................... 16

Sierra Madre del Sur ................ 19

Sierra Madre Oriental ................ 19

Yucatan platform ................... 20

Gulf Coast Tertiary basins ............ 20

Veracruz basin .................. 20

Isthmus Saline basin ......___..... 21

Comalcalco basin ................ 21

Macuspana basin ................ 21

Reforma shelf ..................... 21

Campeche shelf _._......._......... 22

Offshore salt structure province ......... 22

Peten basin ....................... 22

Petroleum geology --.._......__........... 23

Introduction -.....__....._............ 23

Tertiary clastic deposits ................. 23

Isthmus Saline and Comalcalco basins ..... 23

Macuspana basin ._._-......._...... 23

Petroleum geology Continued

Tertiary clastic deposits -Continued

Veracruz basin ..................... 24

Reservoirs __.......-__.__..__----. 24

Source rocks ......__........--.._. 24

Regional cap rocks _........___-_.--. 24

Traps .._......._-_-......._----- 26

Analogs ..__......._-_._....-_-.-- 26

Mesozoic and lower Tertiary carbonate complex . 27

Reforma shelf ........-........---- 27

Campeche shelf ......_._____..._--. 27

Rubelsanto area (Guatemala) ___________ 32

Reservoirs ___________.______.__--. 34

Source rocks ______________________ 35

Regional cap rocks ......__-.----..-_ 36

Traps ................._.--.--... 36

Analogs _..____----..------------- 36

Pre-Oxfordian Mesozoic clastic deposits ....... 36

Paleozoic rocks ____.-.-._-.----------_- 36

Giant fields ....................... ^.. 37

Tertiary basin fields _________________ 37

Reforma fields ..........-....-.---- 37

Offshore Campeche fields __________.-. 37

Summary ___________-_-._-___------- 37

Genesis of the petroleum deposits ------- 37

Information summary ________________ 39

Resource assessment ___._-.._------------- 40

Procedures _____..._----------------- 40

Assessment ....--..-.---------------- 4^

Comments ____--__.-.--_.------._---- 40

Selected references ___.._------.----------- 43

ILLUSTRATIONS

FIGURES 1. Map showing location of southeastern Mexico, northern Guatemala, and Belize assessment region .. 2

2. Map showing location of oil and gas fields, important dry holes, and recently reported discoveries, northwestern Guatemala and southeastern Mexico _..___-______._.-----.--._----------- 3

3. Regional structure map of southeastern Mexico, Guatemala, and Belize ..........-.----..-._ 4

4. Stratigraphic correlation chart of southern Mexico and Guatemala _.__.-_.-----.--.-------- 6

5. South-north structural-stratigraphic cross section A-A', southern Chiapas State to offshore Tabasco

State, Mexico ........................................................... 7

6. West-east structural-stratigraphic cross section A'-B, offshore Tabasco State to Yucatan Peninsula . 10

7. South-north structural-stratigraphic cross section C-C", southern Guatemala to eastern Tabasco State,

Mexico ................................................................ 11

8. West-east structural-stratigraphic cross section D-D', Veracruz basin ______________________ 12

9. Northwest-southeast structural-stratigraphic cross section E-E', Sigsbee Knolls area to Yucatan

Peninsula ______________________________________________________________ 13
Page

FIGURES 10-14. Isopach maps showing:

10. Approximate thickness in meters, partly restored, of pre-Oxfordian Jurassic and Triassic rocks,

southeastern Mexico, Guatemala, and Belize ........................._--.... 14

11. Approximate thickness in meters, partly restored, Upper Jurassic Oxfordian through Tithonian

rocks, southeastern Mexico, Guatemala, and Belize .....................__.... 15

12. Approximate thickness in meters, partly restored, total Cretaceous rocks, southeastern Mexico,

Guatemala, and Belize .._......................_...-_..._--._.-_-__-_ 16

13. Approximate thickness in meters, lower Tertiary (Paleocene, Eocene, and Oligocene) rocks,

mostly restored, in Sierra Madre del Sur, Mexico, and Guatemala-Belize areas ........ 17

14. Approximate thickness in meters, upper Tertiary (Miocene and Pliocene) rocks, mostly restored,

in Sierra Madre del Sur, Mexico, and Guatemala-Belize areas........__..__._.___ 18

15. Structure of top of Miocene Encanto Formation, Cinco Presidentes oil field .................. 25

16. Structure of top of Miocene Amate Formation, Jose Colomo-Chilapilla gas field, Macuspana basin .. 26

17. Seismic structural map, Reforma area, top of Cretaceous Cenomanian ...................... 28

18. Structure of top of Upper Cretaceous, A. J. Bermudez Complex oil field, Reforma area ......... 31

19. Seismic structural map, offshore Campeche area, top of lower Paleocene ..--..--.---..---.-. 32

20. Structure of Paleocene reservoir section, Cantarell Complex oil field, offshore Campeche area ..... 33

21. Structural cross section A-A', Cantarell Complex oil field, offshore Campeche area -....-.-..-. 34

22. Southeast Mexico, northern Guatemala, and Belize recoverable oil --..----.--------.--.--- 41

23. Southeast Mexico, northern Guatemala, and Belize recoverable total gas ...-..-.---..---..-. 41

TABLES

Page

TABLE 1. List of main oil and gas fields shown on figure 2--..--.-.------..---.-----------------.-- &

2. Data on giant fields assessment area, southeast Mexico ........................_-.._--..--_ 29

3. Generalized stratigraphic columns in Reforma area and offshore Campeche area ......_......-...._ 30

4. Assessment of conventionally recoverable petroleum resources of southeastern Mexico, northern Guatemala,

and Belize ...................................................-.....-..._-. 42

5. Supplementary and comparative data supporting the resource assessment for southeastern Mexico, northern

Guatemala, and Belize .___.___.___.______...__..___._._.__.--__-.-------.-.-- 42

ACKNOWLEDGMENTS

The resource assessment for this report was prepared in collaboration with the 

Resource Appraisal Group of the USGS Branch of Oil and Gas Resources.

VI
Petroleum Geology and Resources of Southeastern Mexico, 

Northern Guatemala, and Belize

By James A. Peterson

ABSTRACT

Petroleum deposits in southeastern Mexico and Guatemala 

occur in two main basinal provinces, the Gulf Coast Tertiary 

basin area, which includes the Reforma and offshore Campeche 

Mesozoic fields, and the Peten basin of eastern Chiapas State 

(Mexico) and Guatemala. Gas production is mainly from Tertiary sandstone reservoirs of Miocene age. Major oil production, in order of importance, is from Cretaceous, Paleocene, 

and Jurassic carbonate reservoirs in the Reforma and offshore 

Campeche areas. Several small oil fields have been discovered 

in Cretaceous carbonate reservoirs in west-central Guatemala, 

and one major discovery has been reported in northwestern 

Guatemala. Small- to medium-sized oil accumulations also 

occur in Miocene sandstone reservoirs on salt structures in the 

Isthmus Saline basin of western Tabasco State, Mexico. Almost all important production is in salt structure traps or on 

domes and anticlines that may be related to deep-seated salt 

structures. Some minor oil production has occurred in Cretaceous carbonate reservoirs in a buried overthrust belt along the 

west flank of the Veracruz basin.

The sedimentary cover of Paleozoic through Tertiary rocks 

ranges in thickness from about 6,000 m (20,000 ft) to as much 

as 12,000 m (40,000 ft) or more in most of the region. Paleozoic 

marine carbonate and clastic rocks 1,000 to 2,000 m (3,300 to 

6,500 ft) thick overlie the metamorphic and igneous basement 

in part of the region; Triassic through Middle Jurassic red beds 

and evaporite deposits, including halite, apparently are present 

throughout the region, deposited in part in a Triassic graben 

system. Upper Jurassic (Oxfordian) through Cretaceous rocks 

make up the bulk of the Mesozoic regional carbonate bank complex, which dominates most of the area. Tertiary marine and 

continental clastic rocks, some of deep water origin, 3,000 to 

10,000 m (10,000 to 35,000 ft) thick, are present in the coastal 

plain Tertiary basins. These beds grade eastward into a 

carbonate sequence that overlies the Mesozoic carbonate complex on the Yucatan platform.

During the past 10 years, about 50 large oil fields were 

discovered in the Reforma and offshore Campeche areas. Oil is 

produced from intensely microfractured Cretaceous, 

Paleocene, and Upper Jurassic dolomite reservoirs on blockfaulted salt swells or domes. Most fields are located in the

Mesozoic carbonate-bank margin and forebank talus (Tamabra) 

facies, which passes through the offshore Campeche and onshore Reforma areas. Oil source rocks are believed to be organic-rich shales and shaly carbonate rocks of latest Jurassic 

and possibly Early Cretaceous age. At least six of the Mesozoic 

discoveries are giant or supergiant fields. The largest is the 

Cantarell complex (about 8 billion to 10 billion barrels (BB)) in 

the offshore Campeche area and the Bermudez complex (about 

8 BB) in the Reforma onshore area. Oil columns are unusually 

large (from 50 m to as much as 1,000 m, or 160 ft to 3,300 ft). 

Production rates are extremely high, averaging at least 3,000 

to 5,000 barrels of oil per day (bo/d); some wells produce more 

than 20,000 bo/d, particularly in the offshore Campeche area, 

where 30,000- to 60,000-bo/d wells are reported.

Tertiary basin fields produce primarily from Miocene 

sandstone reservoirs. About 50 of these are oil fields ranging 

from 1 million barrels (MMB) to 200 MMB in size, located on 

faulted salt structures in the Isthmus Saline basin. Another 30 

are gas or gas-condensate fields of a few billion cubic feet to 3 

trillion to 4 trillion cubic feet (Tcf) located on salt structures or 

probable salt structures in the Macuspana, Comalcalco, Isthmus Saline, and Veracruz basins. Source rocks for the gas are 

believed to be carbonaceous shales interbedded with the 

sandstone reservoir bodies.

Identified reserves in the southeastern Mexico-Guatemala 

area, almost all in the Mesozoic fields, are about 53 BB of oil, 

3 BB of natural gas liquids, and 65 Tcf of gas. The estimated 

undiscovered resources are about 78 BB of oil and 24 Tcf of 

gas. Estimated total original recoverable resources (ultimate) 

are about 177.5 billion barrels of oil equivalent (BBOE). At 

least 75 onshore structures and more than 150 offshore structures are yet to be tested.

INTRODUCTION

GEOGRAPHY

The petroleum provinces of southeastern 

Mexico, northern Guatemala, and Belize cover an 

area of about 840,000 km2 (325,000 mi2), which includes the northern part of Central America and
100 200 mi 

Boundary of assessment 

area

FIGURE 1. Location of the southeastern Mexico, northern Guatemala, and Belize assessment region.

the land and offshore area in and adjacent to the 

southern Gulf of Mexico (figs. 1, 2, 3; table 1). The 

region includes the southern Gulf coastal plain, 

the Yucatan Peninsula and the adjacent offehore 

area of southern Mexico, the Sierra Madre de 

Chiapas, approximately the northern half of 

Guatemala, and Belize. The topography of this region ranges from the sea-level Gulf coastal plain 

and the generally flat, low-relief Yucatan Peninsula to the high-relief Sierra Madre Oriental, the 

Sierra Madre de Chiapas, the Sierra Madre del 

Sur, and the ranges of central Guatemala. Climate 

ranges from tropical rain forest with precipitation 

of more than 200 cm/yr (80 in./yr) in central 

Chiapas and Guatemala to a savannah climate on 

the Yucatan Peninsula, where precipation ranges 

from less than 50 cm/yr (20 in./yr) to about 125 

cm/yr (50 in./yr). Parts of the area are low lying 

and swampy, particularly in northern Guatemala 

and easternmost Tabasco, Mexico. The region lies 

in the northern equatorial belt between latitudes 

15 and 25 N.

SOURCES Of DATA

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 Viniegra-0. (1971, 

1981), Lopez-Ramos (1979), Acevedo and Dautt 

(1980), Bishop (1980), articles from "The Oil and 

Gas Journal" and "World Oil," and the information 

files of Petroconsultants, S.A. Additional references are listed in the section "Selected References/'

REGIONAL GEOLOGY

INTRODUCTION

The main basins of southeastern Mexico-northern Guatemala (northern Central America) include 

the Veracruz, Isthmus Saline, Comalcalco, and 

Macuspana Tertiary basins of the Mexican coastal 

plain and the Peten basin of Guatemala and east-
18' 

Sierra Madre Front

Gas field, Tertiary clastic reservoirs

Oil field. Tertiary clastic reservoirs

Oil field, Mesozoic or Pileocem carbonate

FIGURE 2. Oil and gas fields, important dry holes, and recently reported discoveries (44, 45), northwestern Guatemala and 

southeastern Mexico. Numbers refer to main oil and gas fields. See table 1 for listing. From Viniegra-0., 1971, 1975a, b, 

1981; Mossman and Viniegra-0., 1976; Lopez-Ramos, 1979; Acevedo and Dautt, 1980; Bishop, 1980; and Petroconsultants.

ern Chiapas, Mexico. The Veracruz, Isthmus 

Saline, Comalcalco, and Macuspana basins contain 

thick deposits of Cenozoic marine clastic deposits 

(fig. 4) and extend northward into the offshore 

area of the southern Gulf of Mexico where they 

merge with the main offshore salt structure province. This coastal plain Tertiary basin province is 

bounded on the south by the front ranges of the 

Sierra Madre Oriental and the Sierra Madre de 

Chiapas fold and fault belt, which contain extensive exposures of thick Cretaceous carbonate 

rocks, narrow infolded bands of Tertiary clastic 

rock remnants, and some Cenozoic igneous bodies. 

The mountainous area to the south (the Sierra 

Madre del Sur) is an elongate belt of Paleozoic or 

Precambrian intrusive and metamorphic rocks and 

of Cenozoic volcanic rocks. This belt includes the 

Chiapas Massif of Mexico and the fault-bounded 

igneous and metamorphic province of southern 

Guatemala. The Peten basin lies north of the 

Polochic fault zone (which forms the northern 

boundary of the Guatemalan metamorphic, intrusive, and volcanic belt). This basin includes the 

Chapayal and north subbasins, which are separated by the east-trending La Libertad anticline 

(arch) (fig. 2). The Yucatan platform in the northeastern part of the province includes the Yucatan 

Peninsula and the surrounding shallow-water 

offshore shelf extending approximately out to the 

200-m (650-ft) water depth. The platform is 

bounded by a steep underwater escarpment, with 

relief of 2,000 to 3,000 m (6,500 to 10,000 ft); the 

escarpment is particularly prominent on the 

northwestern, northern, and eastern sides of the 

platform. The southwestern part of the Yucatan 

platform includes the Campeche shelf, which contains the major offshore petroleum deposits of the 

area. The salt structure province covers a large 

segment of the southwestern Gulf of Mexico including the offshore Campeche production area 

(fig. 3) and extends southward onshore to include 

the main area of Tertiary oil and gas fields in the 

Isthmus Saline basin and the giant Cretaceous oil 

fields in the Reforma area (fig. 2, table 1).
EXPLANATION 

V»» *^ Sierra Madre Front

T ~T~ ~T Fault

H Major cities

FIGURE 3. Regional structure map of southeastern Mexico, Guatemala, and Belize. From Viniegra-0., 1971, 1975a; Dengo and 

Bohnenberger, 1969, Mossman and Viniegra-0., 1976; Lopez-Ramos, 1979; Bishop, 1980; and Martin, 1980.

STRATIGRAPHY

The basement complex of the appraisal area 

consists of Precambrian and lower to middle 

Paleozoic igneous and metamorphic rocks, which 

are overlain by a thick section of upper Paleozoic, 

Mesozoic, and Cenozoic sedimentary rocks (see 

figs. 4^9) (Viniegra-O., 1971, 1981; Lopez-Ramos,

1979; Bishop, 1980). Sedimentary rocks of late 

Paleozoic age are locally metamorphosed in outcrops in the southern part of the region, but little 

is known of their character in the subsurface, 

where they have been penetrated by relatively 

few wells. The total sedimentary cover in the 

Sierra Madre de Chiapas, northern Guatemala, 

Belize, and on the Yucatan platform is about 3,000
TABLE 1. List of main oil and gas fields shown in figure 2

[Number in parentheses following oil or gas field name corresponds to oil or gas field number used in figure 2]

Area Oil or gas field name

Isthumus Saline basin

Comalcalco basin 

Reforma areaOffshore Campeche -

Macuspana basin 

Veracruz basin -

Peten basin 

Santa Ana (1) 

Magallanes-San Ramon (2) 

Cinco Presidentes (3) 

Tonala (4) 

Soldadas (5) 

El Plan (6) 

Ogarrio-Otates (7) 

Nanchital (8)

Mecoacan (9) 

Arrastradero )10)

A. J. Bermudez Complex (11)

Cactus (12)

Sitio Grande (13)

Agave (14)

Cacho Lopez (15)

Mundo Nuevo (16)

Paredon (17)

Iris (18)

Fenix (19)

Giraldas (20)

Sunapa (21)

Copano (22)

Bacaab (23)

Maloob (24)

Ku (25)

Ek (26)

Cantarell Complex (27)

Takim (28)

Ixtoc (29)

Kanaab (30)

Abkatun (31)

Hormiguero (32) 

Jose Colomo (33) 

Chilapilla (34)

Tres Higueras (35) 

Mata Pionche (36) 

Casa Blanca (37) 

Angostura (38) 

Cocuite (39) 

Mirador (40) 

Mata Verde (41) 

Jesus Carranza-1 (42)

Tortugas (43)

Rubelsanto (44)

Chinaja (45)

Hispanoil 1981 discovery, Yalpemech No. 1 (46)

Tertiary-Mesozoic discovery, 1979? (47)

Northwest Guatemala Texaco discovery, 1981, Xan No. 1 (48)
YUCATAN 

1ATFORVI TAMPICO 

BASIN

VERACRUZ

BASIN

MACUSPANA 

BASIN

Eratnem, 

system, 

series, stage GULF OF 

MEXICO

CONTINENTAL DEPOS Nonmarine

and 

Marine 

Clastic

TUXPAN-Filisola

Deposit 

La Laja 

Horcones

Escolin 

Gxjtzintlas

Pnlmn (toil

DepBsl 

La Laja

Nanchital

Fm.

Macuspano 

Misopa Mexican

Ridges

unit

Chapopote 

Tantoyuca 

Guayakal 

Araaon

Chcpopote 

Guayabal 

Aragon

SIERRA

MAD RE

LIME S*TONE

'/////*

TEPEXIC RED BEDS

and 

SALTS

LOWER

IURASSIC RED BEDS AND SALT

METAMORPHC

SANTA 

ROSA GP

METAMORPHIC SEDIMENTARY 

ROCKS?

EXPLANATION

 Oil Production ~^*- Source Rock 

A Gas Production Regional Seal

FIGURE 4. Stratigraphic correlation chart of southern Mexico and Guatemala. From Vinson, 

1962; Richards, 1963; Viniegra-0., 1971; Burkart and others, 1973; demons and others, 1974; 

Lopez-Ramos, 1979; and Bishop, 1980.
CHIAPAS MASSIF SIERRA MADRE DE CHIAPAS COASTAL P

REFORMA SH

Chiapas Synclinorium Chiapas Anticlinorium 

uripache 

10, 000m LEXPLANATION

A

Carbonate rocks 

Mainly Limestone

Carbonate rocks 

Mainly Dolomite

Anhydrite

Salt

Igneous and Metamorphic rocks

Intrusive rocks

A/V\/\A Unconformity

00=00 Conglomerate

c=j CD Breccia

Oil Accumulation 

Contact, dashed where 

approximate

Fault, arrows show 

direction of relative 

movement

T-Tertiary

Tm Miocene

To-Oligocene

Te-Eocene

Ti Tertiary intrusive rocks

Tp-Paleocene

Tv-Tertiary volcanic rocks

K-Cretaceous

Ku-Upper Cretaceous

KI-Lower Cretac

J Jurassic

Ju-Upper Jurass

Js-Jurassic salt

1 Triassic

Us-Todos Sant

ft-Paleozoic

FIGURE 5. South-north structural-stratigraphic cross section A-A', southern Chiapas State to offshore Tabasco State, Mexico

shown. From Gutierrez-Gil and Thompson, 1956; Viniegra-0., 1971, 1981; Herrara, 1973; Hernandez, 1973; Garcia, 1973; M

enheim, 1974; Vargas, 1978; Lopez-Ramos, 1979; Bishop, 1980; and Acevedo and Dautt, 1980.
to 10,000 m (10,000 to 35,000 ft) thick and consists 

largely of Mesozoic carbonate and evaporite rocks 

(figs. 10-12). Tertiary carbonate rocks overlie 

Mesozoic carbonate and evaporite rocks on the 

Yucatan platform. Mesozoic rocks are thinner in 

the subsurface of the Gulf coastal plain but are 

overlain by a thick section of Tertiary marine clastic rocks. The total thickness of the sedimentary 

cover in the coastal plain basins, primarily of 

marine Tertiary rocks, is at least 6,000 m (20,000 

ft) in most places and ranges as high as 10,000 m 

(35,000 ft) or more (figs. 13, 14).

PALEOZOIC

An unknown thickness of marine Paleozoic carbonate and clastic rocks, which are metamorphosed in varying degrees, underlies the Mesozoic 

in most of the region (figs. 4, 5, 7). These rocks 

comprise the Santa Rosa Group in Guatemala and 

eastern Chiapas, Mexico, where relatively unmetamorphosed sequences are present. The Santa 

Rosa Group consists of marine fossiliferous Permian and Pennsylvanian carbonate, dark shale, 

and sandstone beds that are considered to have 

petroleum potential (Garcia, 1973; Bishop, 1980).

LOWER MESOZOIC

Rocks of late Paleozoic age are overlain unconformably by red beds and conglomerates of the 

Todos Santos Formation, which grade upward to 

intertonguing red beds and evaporite deposits, including halite, of probable Middle to Late Jurassic 

age. The Todos Santos is 1,000 m or more (^3,300 

ft) thick in parts of Guatemala, Chiapas, the coastal plain, and offshore Campeche areas (fig. 10). 

Clastic source areas for these sediments were the 

Chiapas Massif and uplifts in southern Guatemala, 

Belize, and possibly eastern Yucatan. The conglomerate facies is thickest in Guatemala and 

southeastern Chiapas, where it is observed to fill 

grabenlike troughs of probable Triassic age.

The known or projected distribution of pre-Oxfordian Jurassic salt and the area of important salt 

structures are shown in figure 10. The precise age 

and the original depositional thickness of the salt 

section are not known; it may have been deposited 

at different times in the early Mesozoic basins of 

southern Mexico and Guatemala (fig. 4). Thickness 

patterns must have been influenced by the position of local areas of subsidence, such as the early

Mesozoic grabenlike troughs where large thicknesses of both red beds and salt probably accumulated. Some authors believe that the present distribution of known salt structures generally coincides with the areas of greater salt deposition 

(Bishop, 1980). Viniegra-O. (1981) shows five 

areas of maximum salt accumulation, two of which 

are offshore and three onshore in eastern Veracruz, Tabasco, and Chiapas, Mexico.

UPPER JURASSIC

Upper Jurassic beds are as much as 1,000 m or 

more (^3,300 ft) thick (fig. 11) and represent the 

early development (Oxfordian) of the platform carbonate facies that dominated the area through the 

remainder of Mesozoic time (Great Carbonate 

Bank of Yucatan) (Viniegra-O., 1981). The exact 

distribution of the Upper Jurassic platform 

carbonate belt is not known, but the platform 

facies has been penetrated in the Reforma and 

offshore Campeche wells. The facies also may be 

present around the border of the Yucatan platform and may extend westward along the south 

flanks of the Isthmus Saline and Veracruz basins 

and probably into eastern Chiapas and central 

Guatemala. This section contains a substantial 

thicljiess of oolitic and bioclastic carbonate beds 

similar to the limestone facies of the Smackover 

Formation of the U.S. Gulf Coast and northern 

Mexico. Back-bank evaporite beds, possibly including some halite, are present in Guatemala and 

eastern Chiapas.

In the coastal plain and offshore Gulf of Mexico, 

the carbonate bank facies grades into and is overlain by organic-rich, deeper water black shale and 

shaly limestone beds. The upper part of this section extends southward into Chiapas, and possibly 

Guatemala, and is believed to be the main sourcerock section for oil in the Reforma and offshore 

Campeche fields.

CRETACEOUS

Shelf carbonate rocks of Cretaceous age as 

much as 3,000 m or more (^10,000 ft) thick make 

up the major part of the Great Carbonate Bank of 

Yucatan (figs. 4, 12). Three carbonate facies, similar to those of the Tampico basin-Golden Lane 

area, have been recognized (Viniegra-O., 1981) in 

the southeastern Mexico region: (1) the El Abra 

facies, which includes the relatively narrow plat-
form-edge reef belt and the associated widespread 

back-reef fine-grained carbonate and evaporite 

beds, (2) the Tamabra facies, which comprises a 

relatively narrow belt of forereef talus or slump 

breccia on the seaward border of the El Abra 

facies, and (3) the Tamaulipas facies, a deeper 

water basinal facies of fine-grained argillaceous 

limestone and limy shale. The back-reef El Abra 

facies occupies the entire Yucatan platform, much 

of Guatemala, and the Sierra Madre de Chiapas. 

The main reef belt of this facies is believed to be 

present around the entire periphery of the platform as far south as northern Belize. From here, 

its distribution is not well known, but it may extend to the west from Belize across Guatemala 

and the Sierra Madre de Chiapas in more than one 

belt (Viniegra-O., 1975b, 1981; Bishop, 1980; Garcia, 1978). The reef and forereef breccia facies passes through the offshore Campeche area and continues along the platform border through the Reforma area. From there, it is projected to continue 

westward along the southern border of the Isthmus Saline and Veracruz basins (Viniegra-O., 

1981). The reef rocks of the El Abra facies are

composed of rudist, coral, and other shell debris 

and are commonly dolomitized, particularly in the 

western Yucatan and Reforma areas. These beds 

are similar in composition to the Edwards and associated reef facies of the U.S. Gulf of Mexico 

area and northern Mexico. Reef growth was 

greatest in the "middle" Cretaceous (Aptian-Albian and Cenomanian), which is overlain unconformably by Upper Cretaceous beds. The unconformity represents a period in which the Cretaceous reef section underwent widespread 

emergence, karstification, possibly dolomitization, 

and erosion, with the consequent development of 

erosional debris accumulations, particularly on the 

seaward side of the reef belt. At this time, a carbonate detritus or calcarenite fan was deposited in 

the Reforma area (Viniegra-O., 1981), where 

these beds make up an important part of the productive reservoir section. The Tamabra reef-talus 

facies has been recognized in the subsurface of the 

Reforma and offshore Campeche districts, where 

it is a major reservoir facies. The facies is projected to be present along most of the oceanward 

border of the reef belt. The Tamaulipas basinal 

facies is reported in wells in the northern part of 

the Reforma and the western part of the Campeche productive areas and is believed to be

widely distributed in the Gulf of Mexico basinward 

of the reef facies.

Rocks of Late Cretaceous age (Agua Nueva, 

San Felipe, and Mendez Formations) are mainly 

pelagic marine marl and calcareous shale in the 

Mexico coastal plain region. To the south, in the 

Sierra Madre de Chiapas and central Guatemala, 

part of the Upper Cretaceous section is absent in 

places because of Cenozoic erosion. However, fossiliferous bank carbonate deposits are recognized 

in outcrops and in the subsurface in Guatemala 

and Chiapas, and shelf limestone, dolomite, and 

anhydrite beds are present in Yucatan, indicating 

the continued deposition of the El Abra facies during this time. Nearshore clastic beds are reported 

at the top of the Cretaceous (Campanian-Maestrichtian) in Guatemala and southern Chiapas 

(Bishop, 1980), and Paleocene clastic rocks locally 

overlie "middle" Cretaceous carbonate rocks in 

the Reforma subsurface (Viniegra-O., 1981).

TERTIARY

Rocks of Tertiary age are believed to be as 

much as 8,000 to 10,000 m (25,000 to 35,000 ft) 

thick in the coastal plain and nearby offshore Gulf 

area of Tabasco and Veracruz (figs. 13, 14). In this 

area, Tertiary beds are primarily a fine-grained 

offshore marine clastic facies, which grades southward into coarser grained marine sandstone, conglomerate, and shale in the Veracruz, Isthmus 

Saline, and Macuspana basins and finally to 

coarse-grained continental and nearshore marine 

beds in the Sierra Madre provinces of Veracruz 

and Chiapas and in central Guatemala (figs. 13, 

14). Thick, lower Tertiary, deepwater beds with 

turbidite deposits are common toward the basin 

centers. This facies grades upward to shallowwater nearshore deposits in the Miocene, which 

contain the main reservoir sand facies in the coastal plain basins.

Tertiary beds are absent in much of the Sierra 

Madre and Guatemala areas because of middle to 

late Cenozoic erosion but are preserved in elongate northwest-trending downwarped belts in the 

fold and fault belt of Chiapas. Mixed continental 

and marine beds of early and late Tertiary age are 

described in outcrop areas north of the Chiapas 

Massif (Frost and Langenheim, 1974; LopezRamos, 1979) and in Guatemala (Vinson, 1962; 

demons and Burkart, 1971; Burkart and others,
A YUCATAN

GULF OF MEXICO CAMPECHE SOU^D

SEA 0 

LEVEL

10,000 m

FIGURE 6. West-east structural-stratigraphic cross section A'-B, offshore Tabasco State to Yucatan Peninsula. Main oil fields 

explanation on figure 5. From Viniegra-0., 1971, 1981; Garcia, 1978; Lopez-Ramos, 1979; and Acevedo a
PETEN BASIN

SEA 

LEVEL

0 -i

5000 m 

10,000 m

C

S

Chisec-1 Rubelsanto San 

LA LIBERTAD ANTICLINE "NORTH BASIN" 

La Pita-1

N/ / f» «^ II 1 \ 

' / - /W / ^ / / /

FIGURE 7. South-north structural-stratigraphic cross section C-C', southern Guatemala to eastern Tabasco State, Mexico. M

Lithologic explanation on figure 5. From Vinson, 1962; Richards, 1963; Viniegra-0., 1971, 1981; Anderson and others, 1973

1975; Wilson, 1974; and Bishop, 1980.
SIERRA MADRE CASA 

BLANCA

FIELD MATA 

{Buried ovcrthrust belli MC-I J-l ESPINOSA

FIELD

FIGURE 8. West-east structural-stratigraphic cross section D-D', Veracruz basin. Main oil fields and deep wells are sho

5. From Viniegra-0., 1965; Mossman and Viniegra-0., 1976; Cruz-Helu and others, 1977; and L
CO

FIGURE 9. Northwest-southeast structural-stratigraphic cross section E-E', Sigsbee Knolls area to Yucatan Peninsula. Main oil fields and deep wells are shown. 

Lithologic explanation on figure 5. From Lopez-Ramos, 1975, 1979; Watkins and others, 1976; Martin, 1980; and Viniegra-0., 1981.
f

SANTOS""RED BEDS

150 km

FIGURE 10. Approximate thickness in meters, partly restored, of pre-Oxfordian Jurassic and Triassic rocks, southeastern 

Mexico, Guatemala, and Belize. From Viniegra-0., 1971, 1975a, 1981; Lopez-Ramos, 1975,1979; Bishop, 1980; Martin, 1980.

1973). Restored-thickness maps indicate that original depositional thickness of lower Tertiary rocks 

(Paleocene, Eocene, and Oligocene) was greatest 

in a northwest-trending elongate foredeep trough 

north of the Chiapas Massif (>5,000 m or > 16,000 

ft), whereas the upper Tertiary (Miocene and 

younger) beds are thickest (>6,000 m or >20,000 

ft) in the coastal plain area of Tabasco (figs. 13, 

14). These thickness relations are compatible with 

the concept of a northward-shifting depositional 

axis as the Laramide tectonic belt developed.

The Tertiary clastic facies becomes progressively more calcareous toward the east. On the 

Yucatan platform, Tertiary beds are primarily 

carbonate rocks and marls with some evaporite 

deposits. These beds represent continued building 

of the great carbonate bank of Yucatan during the 

Tertiary. The platform-edge reef belt of the platform border remained in essentially the same position during Tertiary time, and reef growth continued in much of the belt into Holocene time. 

Paleocene and possibly Eocene reef and forereef

14
EXPLANATION

Oil Accumulation, 

Upper Jurassic Rocks

FIGURE 11. Approximate thickness in meters, partly restored, Upper Jurassic Oxfordian through Tithom'an rocks, southeastern 

Mexico, Guatemala, and Belize. From Viniegra-0., 1971, 1975a, 1981; Lopez-Ramos, 1975, 1979; Bishop, 1980; and Martin, 1980.

talus facies have been penetrated in offshore Campeche wells, where these beds make up an important part of the reservoir facies. The Tertiary carbonate facies covers the entire Yucatan platform 

and grades westward to fine-grained, deeper 

water clastic rocks west of the Campeche shelf 

and approximately along the eastern border of 

Tabasco. Southward, the carbonate facies grades 

into clastic beds just south of the La Libertad 

arch in Guatemala (fig. 13). Upper Tertiary rocks

are absent on much of the Yucatan Peninsula, apparently owing to post-Oligocene emergence.

STRUCTURE

The structural complexity of the southeastern 

Mexico, Guatemala, and Belize area has evolved 

through at least seven episodes of tectonic activity 

(Viniegra-O., 1971, 1981; Bishop, 1980; Dengo and 

Bohnenberger, 1969; Paine and Meyerhoff, 1970):

15
EXPLANATION

Oil Accumulation, 

Cretaceous Racks

FIGURE 12. Approximate thickness in meters, partly restored, total Cretaceous rocks, southeastern Mexico, Guatemala, and 

Belize. From Vinson, 1962; Richards, 1963; Viniegra-O., 1971, 1975a, 1981; Burkart and others, 1973; Anderson and others, 

1973; Wilson, 1974; Lopez- Ramos, 1975, 1979; Mora and others, 1975; and Bishop, 1980.

1. Middle Paleozoic (Devonian?) tectonic and 

igneous activity with batholith emplacement in the Chiapas metamorphic complex 

(Guzman and de Cserna, 1963).

and associated volcanic activity in the 

Sierra Madre del Sur area and deposition of 

thick red bed and evaporite sequences in 

the depressions.

2. Late Paleozoic (Pennsylvanian-Permian) tec- 4. Late Jurassic to Late Cretaceous development

tonic and igneous activity with folding and 

metamorphism in some areas. 

3. Triassic to Middle Jurassic uplift, together 

with formation of intermontane grabens,

of the Mesozoic geosyncline and platform 

and an associated uplift belt along the 

Sierra Madre del Sur belt. Slow subsidence 

of platform areas in a major part of eastern

16
I I

~ 15°

EXPLANATION

^ Oil Accumulation, Paleocene Carbonate Rocks 

e» Minor Gas Accumulation, Lower Tertiary Rocks

FIGURE 13. Approximate thickness in meters, lower Tertiary (Paleocene, Eocene, and Oligocene) rocks, mostly restored, in 

Sierra Madre del Sur, Mexico, and Guatemala-Belize areas. From Castillo, 1955; Vinson, 1962; Viniegra-0., 1965, 1971, 

1975a; Burkart and others, 1973; Frost and Langenheim, 1974; Mossman and Viniegra-O., 1976; Cruz-Helu and others, 1977; 

and Lopez-Ramos, 1979.

5.

Mexico, Guatemala, Belize, and the Yucatan 

platform occurred, with associated deposition of the thick platform carbonate sequence. In Chiapas and Guatemala, a narrow foredeep immediately north of the 

southern land mass was present during 

Jurassic and Early Cretaceous time. 

Possible "middle" Cretaceous orogeny and 

igneous intrusion along the Sierra Madre

del Sur belt (Paine and Meyerhoff, 1970). 

6. Late Cretaceous-early Tertiary (Laramide) 

orogeny (the Mexican orogeny) with uplift 

of the Sierra Madre del Sur and folding and 

thrust faulting directed north or northeast 

and decreasing northward in the Sierra 

Madre Oriental and Sierra Madre de 

Chiapas. Tectonic activity of this phase culminated in the Eocene.

17
- 20°

EXPLANATION

9 Oil accumulation, Miocene rocks 

O Gas accumulation, Miocene rocks 

TT Fault

FIGURE 14. Approximate thickness in meters, upper Tertiary rocks (Miocene and Pliocene), mostly restored, in Sierra Madre 

del Sur, Mexico, and Guatemala-Belize areas. From Castillo, 1955; Vinson, 1962; Viniegra-0., 1965, 1971, 1975a; Burkart 

and others, 1973; Frost and Langenheim, 1974; Mossman and Viniegra-0., 1976; Cruz-Helu and others, 1977; and LopezRamos, 1979.

7. Late Tertiary widespread epeirogenic tectonic 

activity, not as intense as earlier episodes, 

with further development of normal or 

strike-slip fault systems, followed by volcanism in the Sierra Madre del Sur. Strong 

subsidence of the Gulf Coast Tertiary basins occurred with deposition of several

thousand meters of clastic sediments, 

mainly of Miocene age. Final growth of salt 

pillows and diapirs probably occurred at 

this time.

The pre-Pennsylvanian tectonic history of the 

area is poorly known. Guzman and de Cserna 

(1963), Lopez-Ramos (1969), Dengo and Bohnen18
berger (1969), and Viniegra-0. (1971) postulated a 

Paleozoic miogeosynclinal province (Huasteca 

geosyncline) extending southeast across eastern 

Mexico and continuing eastward across 

Guatemala. The southwestern part of Mexico and 

the southern border of Guatemala are thought to 

have been an emergent land mass during most of 

pre-Pennsylvanian time, generally occupying the 

present belt of the Sierra Madre Occidental and 

Sierra Madre del Sur. Much of this miogeosynclinal province is now buried beneath a thick section 

of Mesozoic and Tertiary rocks. Pre-Pennsylvanian rocks are highly metamorphosed, and little is 

known of the Pennsylvanian and Permian sequence except for a few outcrops and well penetrations in eastern Chiapas and Guatemala. The 

Yucatan platform, which has a pre-Mesozoic igneous and metamorphic basement, may have been a 

separate block that came to its present position 

sometime during late Mesozoic and Tertiary time. 

The subdivision of southeastern Mexico and 

Guatemala into tectonic provinces is difficult due 

to overlapping tectonic patterns, differences in 

tectonic history, and lack of data in some areas. 

Agreement and consistency are not found in the 

literature, but the area in general can be subdivided into about eight main structural provinces, which, in varying degrees, have relatively 

distinct structural styles.

SIERRA MADRE DEL SUR

The Sierra Madre del Sur province, which is an 

extension of the Sierra Madre Occidental of northern and central Mexico, includes the mountain 

ranges along the Pacific side of southern Mexico 

and extends eastward across southern Guatemala 

south of the Polochic fault zone (fig. 3). This uplifted belt is the ancestral core of northern Central 

America and is composed mainly of metamorphic, 

granitic, and volcanic rocks, as well as some remnant belts of Paleozoic and Mesozoic sedimentary rocks. During much of its geologic history, 

the belt was above sea level and was a major clastic source area in the Mesozoic, the Cenozoic, and 

probably part of the Paleozoic. In southern 

Chiapas, the Sierra Madre del Sur is dominated 

by the Chiapas Massif. In Guatemala, the volcanic 

ranges and plateaus and the Pacific volcanic chain 

occupy the southern part of the province.

SIERRA MADRE ORIENTAL

The Sierra Madre Oriental mountain chain is an 

extension of the main belt of early Cenozoic folding and thrust faulting in northern and east-central Mexico. It lies along the western border of 

the Veracruz basin, merges with the Sierra Madre 

de Chiapas in central Chiapas State, and continues 

eastward to include the ranges immediately north 

of the Polochic fault zone in Guatemala and Belize. 

The entire belt consists mainly of uplifted thick 

Cretaceous carbonate rocks that are tightly folded 

and thrust faulted toward the Gulf of Mexico. 

Some outcrops of upper Paleozoic rocks present in 

southeastern Chiapas and Guatemala and lower 

Tertiary clastic rocks occupy elongate northwestsoutheast troughs within the folded belt. In 

Chiapas, the Sierra Madre de Chiapas is separated into the southeast-trending Chiapas 

synclinorium, which lies just north of the Chiapas 

Massif (figs. 4, 5), and the Chiapas anticlinorium; 

the latter extends southeast across north-central 

Chiapas and continues eastward into central 

Guatemala (Chiapas-Guatemala tectonic belt). The 

Laramide fold and thrust belt also is cut by many 

normal faults and by southeast- or east-trending 

left-lateral transcurrent fault zones with horizontal displacements as great as several kilometers 

(Viniegra-0., 1971, 1981; Lopez-Ramos, 1979). 

The Chiapas synclinorium contains erosional remnants of thick lower Tertiary continental beds 

that were deposited in a narrow foredeep north of 

the Chiapas Massif during the Laramide tectonic 

cycle (fig. 5). The Chiapas anticlinorium is characterized by a complex system of high-angle thrust 

or reverse faults and elongate southeast-trending 

folds recumbent toward the northeast; the folds 

become wider and gentler in the northwestern part 

of the belt.

The Chiapas anticlinorium merges northeastward into an intermediate structural zone of less 

intense folding, which lies between the Yucatan 

platform and the Sierra Madre de Chiapas. The intermediate structural zone extends eastward into 

the Chapayal subbasin and the west extension of 

the La Libertad arch in the Peten basin. The 

Sierra Madre de Chiapas belt narrows toward the 

northwest against the Chiapas Massif and is separated from the main Sierra Madre Oriental by the 

left-lateral Salina Cruz fault. This fault also displaces the northwest part of the Chiapas Massif 

and continues northward across the isthmus near

19
the boundary between the Veracruz and Isthmus 

Saline basins; at this point, the fault is downdropped on the west by several hundred meters (Salas, 

1967).

YUCATAN PLATFORM

The Yucatan platform lies approximately between latitude 18 and 24 N. and between longitude 86 1/2 and 92 1/2 E. (fig. 3). It is bordered 

on the west, north, and east by a steep underwater escarpment that begins approximately at the 

200-m (650-ft) water depth contour. The southern 

boundary is not well defined; some authors extend 

it as far south as the La Libertad arch, others to 

about latitude 18 N., just north of the Guatemala 

border. The latter boundary appears to be near 

the approximate north edge of the north subbasin 

of the Peten basin and seems to be a more logical 

choice (fig. 7). The offshore eastern border of the 

platform is very abrupt and is probably controlled 

by a zone of north-trending vertical step faults 

downdropped to the east into the deep Yucatan 

Channel. The western and northern borders of the 

platform also may be controlled by vertical fault 

systems, although information about the deep subsurface in the offshore area is not available. The 

Campeche bank, which includes the offshore Campeche oil fields, forms the southwestern segment 

of the platform; it is bounded on the west by the 

steep-sided Campeche submarine canyon and on 

the south by an east-west fault zone forming the 

northern border of the Comalcalco and Macuspana 

basins. The southwestern corner of the platform is 

bounded by the deep Tertiary Macuspana basin. 

The platform border there probably is also fault 

controlled (Bishop, 1980), although data about the 

subsurface are not available.

Mesozoic rocks rest on a basement of 

metamorphosed Paleozoic sedimentary and igneous rocks that are structurally highest in the 

northeastern part of the Yucatan Peninsula. From 

there, the platform is tilted toward the west (fig. 

6), resulting in westward thickening of the 

Mesozoic and Tertiary sedimentary cover from 

about 600 to 1,000 m (2,000 to 3,300 ft) in northeastern Yucatan to more than 6,500 m (21,000 ft) 

in the offshore Campeche area on the west side of 

the platform (Vmiegra-0., 1981). Except for the 

eastern border, the sedimentary cover on most of 

the Yucatan Peninsula is only mildly disturbed. 

Exceptions are a northwest-trending fault zone

(the Sierra de Ticul) in the north-central part of 

the peninsula and a north- to northeast-trending 

fold and fault zone (the Sierra de Bolonchan) in 

central Campeche State in the southwestern part 

of the peninsula (fig. 3).

GULF COAST TERTIARY BASINS

The Gulf Coast Tertiary basins consist of a belt 

of thick Tertiary sedimentary rocks north and 

northeast of the Sierra Madre Oriental front and 

occupy the general position of the coastal plain in 

the States of Veracruz, Tabasco, and western 

Campeche (figs. 1, 3). On the basis of subsurface 

exploration, the coastal plain region has been subdivided into several basins, although in some 

places basin boundaries are not clearly defined.

Veracruz Basin

The Veracruz basin is a deep Tertiary downwarp with more than 8,500 m (28,000 ft) of 

Paleocene through Holocene sedimentary rocks in 

its southeastern part (Cruz Helu and others, 

1977). The basin is bounded on the southwest by 

the Sierra Madre Oriental fold and thrust belt and 

is separated from the Tampico basin on the north 

by the Teziutlan Massif (Santa Ana uplift) (figs. 3, 

8). The basin opens into the Gulf of Mexico basin 

toward the northeast and merges with the Isthmus Saline basin near the Tuxtla Massif.

The subsurface structure of the southwestern 

flank of the basin is dominated by a buried thrust 

plate of Mesozoic carbonate rocks; the plate consists of westward-dipping and closely spaced imbricate thrust sheets and tight folds (Mossman 

and Viniegra-0., 1976). Toward the basin center, 

the leading edge of the buried thrust plate is as 

deep as 3,500 m (11,000 ft) and is marked by a 

high-angle reverse fault. From there, the thrust 

plate is progressively overlapped southwestward 

by marine and nonmarine clastic beds ranging in 

age from Eocene to Holocene. Toward the southeast, it merges with the exposed overthrust front 

of the Sierra Madre Oriental. East of the buried 

thrust plate, a narrow grabenlike trough runs 

parallel to the thrust front. This trough, containing more than 6,000 m (20,000 ft) of Tertiary 

rocks, appears to mark the axis of the basin. To 

the east beyond the trough, steeply dipping faults 

downthrown toward the Gulf of Mexico are pre20
sent. Many local folds also are present in the 

basin, some of which may be related to deep-seated salt structures or shale diapirs. Beneath the 

main thrust belt, Viniegra-O. (1981) postulates 

that major folds involving salt structures overlain 

by Mesozoic rocks may occur at depth beneath the 

buried thrust plate (fig. 8). The age of the thrust 

faulting is thought to be Eocene, and the main 

overthrust plate is cut by numerous left-lateral 

transcurrent vertical faults, probably also of 

Eocene age, which are oriented perpendicular to 

the thrusts (Mossman and Viniegra-O., 1976). 

Similar transcurrent fault zones have been observed in outcrops in the Sierra Madre Oriental on 

the southwestern border of the basin (ViniegraO., 1965).

Isthmus Saline Basin

The Isthmus Saline basin lies east of the Veracruz basin and is bounded on the south by the 

Sierra Madre Oriental and on the east by the Reforma shelf or the Villahermosa horst (figs. 2, 3). 

The basin extends northward offshore into the 

Gulf of Mexico shelf and merges to the northeast 

with the Comalcalco basin. Structures in the basin 

include many complexly block-faulted salt domes 

or massifs that are at shallow depths (about 100 to 

1,000 m or 325 to 3,250 ft) in the western part of 

the basin and are deeper and more widely spaced 

in the eastern part. Most salt structures are relatively broad, high-relief features with salt rise on 

the order of 1,000 to 3,000 m (3,300 to 10,000 ft) 

to as much as 5,000 m (16,000 ft). Piercement 

structures are common in the western part of the 

basin; in some cases, rocks as old as Eocene, Cretaceous, or Jurassic have been brought to shallow 

depths or are exposed at the surface. The age of 

salt uplift is unknown; estimates in the literature 

range from Laramide (Late Cretaceous-early Tertiary) to Miocene.

Comalcalco Basin

The Comalcalco basin is an area of thick Tertiary sedimentary rocks oriented northeast-southwest along the Gulf coastal plain and extending 

into the offshore area north of the Reforma shelf 

(fig. 3). To the west, it merges with the Isthmus 

Saline basin and to the northeast with the northern extension of the Macuspana basin. The northern limit may be defined by an east-trending fault

zone marking the southern boundary of the Campeche shelf. Numerous anticlines or domes are 

present that may be related to deep-seated salt 

structures. The basin contains a great thickness of 

Tertiary rocks; minimum depth to the Cretaceous 

is about 6,000 to 7,000 m (20,000 to 23,000 ft).

Macuspana Basin

The Macuspana basin is bounded on the west by 

the Villahermosa horst and extends offshore to 

the north where it apparently merges with the 

eastern extension of the Comalcalco basin (figs. 2, 

3). The southern and eastern boundaries are not 

well defined. The basin appears to terminate at 

the northern boundary of the Sierra Madre de 

Chiapas. Eastward, it may merge with the southwestern corner of the Yucatan platform, although 

Acevedo and Dautt (1980) indicate that the eastern border is a northeast-trending fault zone. 

Some evidence suggests that the thick Tertiary 

section defining the basin may extend eastward or 

southeastward into the northern segment of the 

Peten basin in Guatemala (figs. 7, 13, 14). Numerous domal and anticlinal structures are present in 

the Macuspana basin and may represent deep-seated salt structures, although salt has not been 

penetrated by wells except in the extreme southern part of the basin. These structures generally 

are oriented northeast-southwest in the northern 

part of the basin and more easterly in its southern 

part.

REFORMA SHELF

The Reforma shelf (Jalpa Anticlinorium of Viniegra-O., 1981), which includes the main Mesozoic 

productive area in northwestern Chiapas and 

southwestern Tabasco, occupies the southern part 

of the Villahermosa horst. This feature is a northnortheast-trending block oriented roughly parallel 

with the west coast of the Yucatan Peninsula (figs. 

2, 3, 5). The general structure of the horst block 

is that of a shelf tilted toward the north and west 

and cut by numerous northwest-trending steeply 

dipping normal faults. These form a system of 

horst and graben structures, which are accentuated by closely faulted salt swells and are down 

stepped to the north into the Comalcalco basin 

(fig. 5). The detailed structural pattern is very 

complex, as the rocks also are cut by southwestdipping reverse faults and by northwest-trending 

wrench faults with left-lateral displacements

21
(Acevedo and Dautt, 1980; Viniegra-0., 1981). 

The Reforma shelf, which lies immediately north 

of the Sierra Madre front, makes up the southern 

part of the Villahermosa horst and is interpreted 

by Viniegra-0. (1981) to be the downfaulted 

northwesterly plunging nose of the Chiapas anticlinorium. It may be related to the system of 

northwest-oriented left-lateral wrench faults identified in surface mapping in the Sierra Madre de 

Chiapas (Viniegra-0., 1971, 1981; Lopez-Ramos, 

1979), which have also been identified in the Reforma subsurface. Left-lateral movement on the 

wrench faults during the orogeny may have offset 

the Mesozoic carbonate-bank sequence northwesterly in the Reforma area. Concurrent sediment 

loading and downwarping north of the rising 

Sierra Madre de Chiapas resulted in salt movements that produced the horsts and grabens of the 

Villahermosa horst. The Villahermosa horst underwent relatively continuous growth throughout 

the Tertiary, perhaps in part a consequence of 

great sediment loading and downwarping in the 

Tertiary Macuspana, Comalcalco, and Isthmus 

Saline basins. In contrast, Tertiary rocks are considerably thinner in the Reforma area than they 

are in the basin areas on its west, north, and east 

flanks.

CAMPECHE SHELF

The offshore Campeche area of recently discovered giant oil fields is referred to by Viniegra-0. 

(1981) as the "Campeche shelf." The exact boundaries of this province are not yet known; it lies 

along the western border of the Yucatan platform 

and is bounded on the south by an east-trending 

zone of normal and possibly strike-slip faults 

downdropped to the south (figs. 3, 6). On the 

west, the shelf drops abruptly into the Campeche 

submarine canyon at about the 200-m (650-ft) 

water depth, and on the north it merges with the 

main scarp of the platform border. The overall 

structure is that of a shelf tilted toward the west 

and cut by north-trending normal faults that form 

a system of horsts and grabens accentuated by 

salt pillows similar to those on the Reforma shelf. 

The detailed structure on the productive section is 

similar to that at Reforma; it is complicated by severe faulting and fracturing due to salt movement, 

as well as by numerous southwest-dipping reverse 

faults and some left-lateral wrench faults.

OFFSHORE SALT STRUCTURE PROVINCE

The main offshore salt structure province in the 

Gulf of Campeche is a complex of salt domes, 

ridges, and large salt massifs mobilized mainly by 

sediment loading (Martin, 1980). Salt structures in 

the onshore coastal plain province along the south 

border of the Gulf of Campeche are much smaller 

in diameter and are mainly high-relief domes and 

anticlines. Mobilization of the salt may have been 

initiated as early as the Late Cretaceous by sediment overburden (Contreras and Castillon, 1968; 

Salas, 1967; Bishop, 1980) or by combined overburden and Laramide compressive stresses directed from the southwest (Viniegra-0., 1981). 

Salt uplift must have continued during deposition 

of the thick clastic sequence of Paleocene, Eocene, 

and Oligocene ages in the coastal plain area but 

may have been near completion some time during 

the Miocene, as suggested by the presence of 

Miocene beds, although thinned, over most of the 

domal structures. Some authors, however, propose that salt structure growth continued from 

late Mesozoic through late Tertiary time (Ladd 

and others, 1976; Martin, 1980).

PETEN BASIN

The Peten basin lies south of the Yucatan platform, occupying most of northern Guatemala and 

part of the State of Chiapas, Mexico (figs. 3, 7). 

Its southern boundary is the east-trending 

Polochic fault zone. The northern limit is uncertain because of lack of subsurface control, but its 

eastern limit is reasonably well defined by the 

Maya Mountains block in Belize although to the 

south the basin opens eastward into the Caribbean 

through the Sartsun portal. On the west, the 

basin province merges with the Chiapas anticlinorium and the adjacent intermediate structural 

province to the north. The Peten basin is divided 

by the east-trending La Libertad arch into a 

northern segment (the "north basin") and a larger 

southern segment designated as the Chapayal 

basin by some authors. Subsurface control is lacking, but some evidence indicates that the north 

subbasin may open westward into the southern 

part of the Macuspana basin, perhaps through an 

east-west grabenlike trough. The La Libertad 

arch dominates the internal structure of the basin, 

but several large subsidiary folds in the main 

basin areas and salt pillows or piercement domes 

in the south segment also are reported (Bishop,

22
1980). Some evidence indicates that salt of Early 

Cretaceous or Jurassic age may lie at depth in the 

north basin area and that salt structures also may 

be present (Lopez-Ramos, 1973).

PETROLEUM GEOLOGY

INTRODUCTION

Early interest in the petroleum possibilities of 

southern Mexico was stimulated by the presence 

of numerous oil seeps in the State of Tabasco and 

other parts of the Isthmus of Tehuantepec. Oil 

was first discovered in 1904 at the San Cristobal 

field in eastern Veracruz State in the southwestern part of what is now known as the Isthmus 

Saline basin. Exploration subsequently spread 

through much of the southeastern Mexico coastal 

plain, and by the late 1960's about 80 fields had 

been discovered, almost all producing from 

Miocene sandstone reservoirs (the Encanto, Concepcion, and Amate Formations) in the Isthmus 

Saline and Macuspana basins (fig. 2). Most of 

these fields are on salt structures or on anticlines 

and domes that may be related to deep-seated salt 

structures.

The possibilities for Mesozoic oil in southeastern 

Mexico had long been considered by Pemex 

geologists (Guzman and others, 1955; LopezRamos, 1979; Viniegra-0., 1971, 1981). Abundant 

oil seeps were known along the front of the Sierra 

Madre de Chiapas, and in 1960 oil was found in 

Lower Cretaceous dolomite reservoirs at the 

Cerro de Nachital field (later abandoned), located 

in the southern part of the Isthmus Saline basin 

near the Sierra Madre de Chiapas front (fig. 2). 

Active exploration for Mesozoic oil in the southeastern Mexico area began during the 1960's and 

resulted in drilling of several wells in the Sierra 

Madre de Chiapas province and on the Yucatan 

Peninsula. None of these wells was productive 

from Mesozoic rocks, but the stratigraphic information gained from the drill holes led to the identification of Cretaceous reef and backreef facies, 

similar to those present in the Tampico basinGolden Lane area. An active geophysical exploration program was then undertaken to the north in 

the coastal plain area, which resulted in the mapping of several deep seismic structures near Villahermosa, Tabasco State. Subsequent drilling 

there led to the discovery in 1972 of the Sitio

Grande and Cactus oil fields, producing from Cretaceous carbonate reservoirs of the Sierra Madre 

Limestone (Acevedo and Dautt, 1980; ViniegraO., 1981).

The Reforma discoveries were followed by discoveries in the offshore Campeche area, which had 

been explored by extensive marine seismic surveys that identified a large number of structures 

on the offshore Campeche shelf. Chac No. 1, the 

discovery well in 1976, produced 20° API (American Petroleum Institute) oil from a Paleocene 

dolomite breccia reservoir and bottomed in Jurassic (Oxfordian) carbonate and shale beds.

TERTIARY CLASTIC DEPOSITS

Of the approximately 80 fields that have been 

found in Tertiary clastic reservoirs in southeastern Mexico, about 50 are oil, or oil and gas, and 

30 are gas or gas-condensate fields (figs. 2, 13, 14).

ISTHMUS SALINE AND COMALCALCO BASINS

Fields in the Tertiary Isthmus Saline and Comalcalco basins are oil or combination oil and gas 

fields. Most of the oil production is from Miocene 

sandstone and siltstone reservoirs of the Encanto 

and Concepcion Formations on salt structures (fig. 

4). Most of these fields are small to medium in 

size, but several are classed as giants (Acevedo 

and Dautt, 1980). AD large fields are associated 

with diapiric salt structures, which are complexly 

block faulted by salt intrusion (figs. 15, 16).

MACUSPANA BASIN

Most of the Tertiary gas and gas-condensate 

fields are in the Macuspana basin; all are located 

on block-faulted domes or anticlines, some of 

which may be related to deep-seated salt intrusion, although salt has not been penetrated in the 

basin except in shallower structures in its southern part. Almost all production is from lower 

Miocene sandstone bodies of the Amate Formation 

(fig. 4). Some gas also is produced from middle 

Miocene sandstones of the Zargazal and Encajonada Formations. Three giant gas and gascondensate fields are located in this basin: Jose 

Colomo (about 3 to 4 Tcf), Chilapilla (fig. 16), and 

Hormiguero (Acevedo and Dautt, 1980). Small 

amounts of oil are produced from Miocene reservoirs in the southern part of the basin.

23
VERACRUZ BASIN

Of the 8 to 10 small Tertiary gas fields in the 

Veracruz basin, most produce from sandstone and 

conglomerate reservoirs of Miocene age near the 

basin center (Encanto and Concepcion Formations). The productive Miocene reservoirs occur in 

a conglomerate, sandstone, and shale sequence 

about 1,000 m (3,300 ft) thick deposited in a deepwater environment (Cruz Helu and others, 1977). 

Conglomerate beds are composed of coarse fragments of Cretaceous limestone with some 

metamorphic and igneous material derived from 

the uplifted Sierra Madre province to the west. A 

similar deepwater turbidite facies occurs in the 

Oligocene and Eocene sequence but is located 

farther west, closer to the basin border. Some 

minor production and noncommercial gas shows 

have also been encountered in these older beds. 

Average porosity of the Miocene reservoirs is 

about 6 to 8 percent. The matrix is generally 

shaly, and permeabilities are not high, but some 

sandstone beds are as thick as 100 m (350 ft). Exploration success in Tertiary reservoirs in this 

basin thus far has been disappointing, but the 

basin is not heavily drilled and is structurally complex. The possibilities for finding large stratigraphic traps may be good (Cruz-Helu and others, 

1977).

RESERVOIRS

Miocene reservoirs are primarily discontinuous, 

regressive-marine, nearshore sandstone and 

siltstone bodies interbedded and intertongued 

with marine and brackish-water shale; some carbonaceous and lignitic beds occur in the upper 

part of the oil-bearing strata (figs. 4, 8). The total 

Miocene section is at least 5,000 m (16,000 ft) 

thick in parts of the Isthmus Saline, Comalcalco, 

and Macuspana basins but is much thinner over 

salt structures, which probably were growing at 

this time. Sandstone beds vary greatly in thickness, but some are very thick. Porosities and permeabilities range widely, but porosity values of 15 

to 25 percent and intermediate permeability 

values are commonly reported. In the Jose Colomo field, producing reservoirs of the lower part 

of the Amate Formation are exceptionally thick, 

about 200 m (650 ft), and porosity values of 10 to 

30 percent are reported. Reserves of this field 

were reported in 1963 to be about 2.75 Tcf 

(Beebe, 1968).

Sandstone and conglomerate bodies interbedded 

with shale occur in the Paleocene, Eocene, and 

Oligocene sequence in the southern part of the Isthmus Saline basin and in outcrops along the 

Sierra Madre front. To date, no important production has occurred in these beds, although oil seeps 

in outcrops and some shows in wells are reported 

(Guzman and others, 1955). In some cases, these 

beds are tightly cemented and of low porosity. In 

the basin area, much of this sequence was deposited under deepwater conditions, and most 

coarse-clastic beds probably are turbidite deposits. Few wells within the Isthmus Saline and 

Macuspana basins have penetrated these beds; in 

most cases, they probably are deeply buried in 

low areas between salt structures but should provide deeper prospects for flank accumulations ondiapiric structures. The sequence becomes more 

limy toward the east, where reservoir quality is 

diminished (fig. 13)1 .

SOURCE ROCKS

Source rocks for most oil and gas in the Tertiary clastic sequence of southeastern Mexico are 

considered to be shales of the marine and lagoonal 

Miocene sequence associated with the reservoir 

sands (Guzman and others, 1955; Guzman and de 

Cserna, 1963). However, most of the Isthmus 

Saline basin fields contain oil or combination oil 

and gas accumulations, whereas the Macuspana 

basin fields are gas or gas-condensate fields. This 

raises the question of possible differences in 

source rocks. The Isthmus Saline basin fields are 

associated with complexly faulted diapiric salt 

structures, whereas the Macuspana basin gas 

fields are on nondiapiric domes and anticlines. 

These relations suggest the possibility that the oil 

deposits in the Isthmus Saline basin fields may not 

be derived entirely from Tertiary source rocks but 

may include in part oil that migrated upward from 

underlying Upper Jurassic or Cretaceous basinal 

source rock facies into Tertiary reservoir beds on 

the complexly faulted salt structures.

REGIONAL CAP ROCKS

The thick Tertiary shale sequence interbedded 

with sandstone reservoir facies provides an effective seal for both structural and stratigraphic ac-

'From Guzman and others, 1955; Contreras and Costillo, 1968; Lopez-Ramos, 

1979; Acevedo and Dautt, 1980.

24
/ ./- fjouvn

% - 

x EXPLANATION

OIL AND GAS PRODUCER WELL 

DRY WELL 

DRILLING WELL

SALT

1000

SCALE

zooo

FIGURE 15. Structure (depth in meters) of top of Encanto Formation (Miocene), Cinco Presidentes oil field. Location of field,

lat 18°11'30" N., long. 94°00'30" W. (After Acevedo and Dautt, 1980.)
EXPLANATION

GAS PRODUCER WELL 

O DRY WELL

FIGURE 16. Structure (depth in meters) of top of Amate Formation (Miocene), Jose Colomo-Chilapilla gas field, Macuspana 

basin. Location of field, lat. 17°58' N., long. 92°28' W. (After Acevedo and Dautt, 1980.)

cumulation throughout most of the Tertiary basin 

province. Diapiric salt masses should be good 

updip seals for Tertiary sandstone reservoirs on 

the flanks of piercement structures, where fractured reservoirs are also important.

vidual structures; some good structures have not 

yet proven productive. The discontinuous nature 

of the Tertiary sand bodies implies that stratigraphic trapping may be important to future discoveries. A stratigraphic exploration program has 

not yet been undertaken.

TRAPS

Most traps in known Tertiary accumulations are 

structural, either anticlinal or domal folds or fault 

traps associated with salt structures. However, 

distribution patterns and thickness of clastic reservoir facies are also important in determining 

reserves and production characteristics on indiANALOGS

Probably the best stratigraphic and structural 

analog for the southeastern Mexico Tertiary basin 

productive province is the Gulf Coast Tertiary 

basin of the United States, where many fields are 

related to similar reservoir, trap, and source rock 

conditions.

26
MESOZOIC AND LOWER TERTIARY CARBONATE COMPLEX

The great petroleum potential of southeastern 

Mexico and Guatemala is directly related to deposition of the "Great Carbonate Bank of Yucatan" 

(Viniegra-O., 1981), the thick sequence of reef and 

bank carbonate and evaporite beds of Late Jurassic (Oxfordian) through early Tertiary age (figs. 

11, 12). The bank complex, which is present on 

the Yucatan platform, in Guatemala, throughout 

the Sierra Madre Oriental and Sierra Madre de 

Chiapas, and part of the subsurface to the north, 

is generally from 1,000 to 2,000 m (3,300 to 6,600 

ft) thick and reaches thicknesses of more than 

3,000 m (10,000 ft) in Yucatan, Guatemala, and 

Chiapas.

REFORMA SHELF

After the 1972 discoveries of the Cactus and 

Sitio Grande oil fields, intensified exploration and 

development drilling during the next few years resulted in several other significant discoveries and 

elevated the Reforma area to Mexico's leading oil 

province. As of January 1981, 36 fields had been 

discovered, most producing from "middle" and 

Upper Cretaceous and Upper Jurassic carbonate 

reservoirs (figs. 2, 17, tables 2, 3) at depths between 4,000 and 6,000 m (13,000 and 20,000 ft) 

(World Oil, 1981). Minor production in some of the 

fields is from Tertiary sandstones. Approximately 

75 to 100 onshore structures are yet to be tested 

(World Oil, 1980). The new fields are located on 

the Reforma shelf, a segment of the Villahermosa 

horst, which separates the Isthmus Saline and 

Macuspana Tertiary basins. Production in the 

Mesozoic Reforma fields is primarily from a reef 

bank-edge dolomitized detrital carbonate facies 

(the Tamabra facies) on salt pillow or salt swell 

structures that have caused intense microfracturing of the dolomite reservoirs (figs. 5, 12). Depths 

to the top of the reservoir section range from 

3,800 to 4,500 m (12,000 to 15,000 ft). Regional 

cap rocks for these fields are Tertiary shales and 

to a lesser extent Cretaceous shales. The producing column is unusually thick in many of the fields, 

averaging more than 300 m (1,000 ft) and ranging 

as high as 900 m (3,000 ft) or more at the Sitio 

Grande field (fig. 5). Matrix porosity averages 

about 8 to 10 percent, but effective porosity is 

considerably higher because of intense microfracturing. Permeability values are very high, ranging 

up to as much as 8,000 mD (Acevedo and Dautt,

1980). Average production rates are reported to 

be 3,000 to 5,000 bbl/d; some are as much as 

10,000 to 20,000 bbl/d. Gravity of the oils ranges 

from 25° to 45° API; gas-oil ratios are about 

1,500:1. The main source beds for the Mesozoic 

oils in the Reforma area are organic-rich black 

shale and shaly limestone beds of Late Jurassic 

(Kimmeridgian and Tithonian) age (Viniegra, 

1971, 1981). Dark-colored, shaly rocks in the 

Lower and "middle" Cretaceous section may also 

be the source of some of the oil. As of January 

1981, 185 wells were producing 953,394 bbl/d of 

oil, 133,216 bbl/d of condensate, and 2.038 Ecf/d 

(billion cubic feet per day) of gas (World Oil, 

1981). The largest of the Mesozoic fields is the A. 

J. Bermudez complex (fig. 18), reported as about 

8 BBOE ultimate recoverable reserves (Acevedo 

and Dautt, 1980).

CAMPECHE SHELF

Since 1976, about 15 major fields have been discovered on the Campeche shelf, some of which 

have now been combined into single-field complexes (figs. 2, 6, 19; tables 2, 3). All fields are located on sharply defined and complexly faulted 

structural domes or anticlines with exceptionally 

large closures, associated with salt pillows or 

domes. In most cases, oil columns are very large 

(50 to >500 m or 160 to > 1,600 ft), and reservoirs 

are intensely microfractured dolomites of 

Paleocene and Cretaceous age. Oil saturation is 

also reported in Uppe* Jurassic sandstones at 

some of the wells. The stratigraphic section penetrated thus far includes carbonate and clastic 

rocks of Late Jurassic age, carbonate rocks of 

Cretaceous and Paleocene age, Eocene carbonate 

rocks and evaporite deposits, and post-Eocene 

marls. Bank carbonate beds have been identified 

in the Jurassic, Cretaceous, Paleocene,and upper 

Eocene sections. Heavy dolomitization of the carbonate rocks has hampered precise age identification by Pemex geologists, but parts or all of the 

Cretaceous section apparently are absent in some 

wells. The major production thus far has been 

from dolomitized forereef talus (Tamabra) facies, 

similar to that at Reforma.

The source rocks for the oil in the offshore Campeche province are believed to be the same as 

those of the Reforma area, primarily post-Oxfordian Jurassic organic-rich black shale and carbonate beds and secondarily Lower Cretaceous dark

27
93°00'

EXPLANATION

pa7;.| LIMIT OF THE GREAT CARBONATE BANK 

F^q EXPLORED AREA. 1974-1975 J

L8°30' 

I | REGIONAL FAULT AND LIMIT OF THE 

=== VILLAHERMOSA HORST

FRONT OF SIERRA MADRE

SEISMIC CONTOURS. TOP OF CENOMANIAN

DIRECTION OF SEISMIC DIP

MINOR FAULTS

PRODUCTIVE AREAS (CLASTIC CARBONATE 

ROCKS). ALBIAN-CENOMANIAN

PRODUCTIVE AREAS (ALB. CENO. ABSENT OR 

IN DEEP-WATER SEDS.) APTIAN THRU U.JURASSIC 

DOLOMITE IS PRODUCTIVE

WRENCH FAULT

\COMALCALCO

TERTIARY

COMALCALCO

BASIN

18°00' 

TERTIARY

MACUSPANA

BASIN

17°30' 

FIGURE 17. Seismic structural map, Reforma area Chiapas-Tabasco States, top of Cretaceous Cenomanian. (After

Viniegra-0., 1981.)

shale and shaly limestone beds. The proximity of 

the Jurassic source rock section is believed to be 

a principal requisite for major oil accumulations in 

all parts of the section, including those in the Cretaceous and Paleocene reservoirs. Cap rocks for 

the fields appear to be upper Paleocene shales.

The largest accumulation is in' the Cantarell 

complex (figs. 6, 19, 20, 21), which includes the 

Chac, Akal, and Nohoch fields, reportedly containing from 8 to 10 BB of ultimate recoverable 

proven reserves (Acevedo and Dautt, 1980; World 

Oil, 1981). The effective oil column at this complex 

averages about 800 m (2,600 ft); the thickest encountered so far is about 1,000 m (3,300 ft) at the 

Nohoch No. 2 well. The combined Abkatun, 

Kanaab, Taratunich, and Ixtoc structures are predicted to become a second giant complex as drilling progresses (Acevedo and Dautt, 1980).

28
TABLE 2. Data on giant fields;assessment area, southeast Mexico

[MMBO, million barrels of oil; MMBOE, million barrels of oil equivalent; BBO, billion barrels of oil; BBOE, billion barrels of oil equivalent; Tcf, trillion cubic feet; mD, m

Field name and Structure 

discovery date

(Yucateco) 1960.

Jose Colomo-Chilapilla Faulted salt (?) dome 

(1951).

No. of 

prod, 

wells

246

146

(1977)

Depth 

to top 

of pay

1,800- 

1,900m

1,400- 

1,500 m

Reservoir (age and lithology) Jhickness 

of pay

and silt.

Early Miocene sandstone 

Porosity and 

permeability

- 10-30 percent 

75-3,000 mD

Cumulative 

production

227 MMBO 

300 Tcf gas

50 MMBO 

and condensate 

2 Tcf gas

D~ j 

Proved

ultimate G

production 

3 Tcf 45-5

A. J. Bermudez Complex Faulted salt swell 

(1973) (Samaria, iride, 

Cunduacan, Ojaicaque).

96 3,000- Middle Miocene sand- 500 m aver- 8 percent avg. 

(1980) 4,500 m stone; Early, "middle," age-up 7,800 mD avg. 

and Late Cretaceous dolo- to 2,000 m 

mite; Late Jurassic dolomite.

SitioGrande(1972) Faulted salt domeCactus(1972) Faulted salt dome __ 

Iris-Giraldas Complex Faulted salt dome 

(1977)

Cantarell Complex Faulted salt structure 

(1976) Chac, Akal, Nohoch).

Abkatun-Kanaab Faulted salt structure 

Taratunich-Ixtoc Complex 

(1979).

26 3,700- "Middle" and Late Cre- 

(1980) 4,000 m taceous dolomite.

57 3,700- "Middle" and Late Cre- 

(1980) 4,500 m taceous dolomite.

100-200 m 8 percent avg. 

3,080 mD avg.

up to 7 percent avg. 

1,000 m 6,228 mD avg.

4 "Middle" Cretaceous 400 m _________

(1980) dolomite. average

>20 1,100- Paleocene and Greta- 50-1,300 m 10-12 percent 

4,000 m ceous dolomite; Late Juras- > 8,000 mD 

sic sandstone.

 About Paleocene and Late Cre3,100 m taceous dolomite.

>2 BBO 7 BBO 14-2

3 Tcf 17.5 Tcf (M

assoc. gas 28-3

(Cr

164 MMBO 765 MMBOE 30-3

0.3 Tcf (1980)

258 MMBO 1.5 BBOE 35-3

>1 Tcf (1980)

7 MMBO > 1.5 BBO 33-3

(1980) > 1 Tcf

 8-10 BBOE 19-2

Probable 

super giant.
TABLE 3. Generalized stratigraphic columns in Reforma area and offshore Campeche area

Reforma area Offshore Campeche area

Unit Thickness Lithology Thickness Lithology

Miocene 3,200 m maximum (Sitio 

Grande).

Oligocene 450 m maximum

Eocene 400-800 m

Paleocene 300-400 m

Upper 

Cretaceous.

Middle 

Cretaceous.

._ 70-400 m

120-700 m 

(AptianCenomanian 

absent in 

Northern part 

of area).

Lower 200-600 m 

Cretaceous.

Upper - 

Jurassic.

.__ 800-1,600 m

Nearshore marine gray and green 

shale, sandstone (some pebbly), 

and siltstone.

Offshore marine gray shale and 

thin sandstone beds.

Offshore marine shale with thin 

beds of sandstone.

Marine calcareous shale, minor 

sandstone beds with limestone 

fragments breccia at base.

Marine marl, fine-grained argillaceous limestone and thin 

shale beds; x'line and finegrained limestone and chert 

in lower part.

Marine platform and basin dolomite and dolomitic limestone, 

vuggy, with porous dolomitic 

breccias and fractures; some 

black chert beds.

Marine dolomitic limestone and 

dolomite, fractured, porous; 

some black chert beds.

Marine platform dark gray 

oolitic, pelletal, and bioclastic 

limestone, in part dolomitized, 

with anhydrite and shale beds 

and much dark brown and gray 

shale.

600-2,600 m 

(thickens rapidly west to 

east)

12-165 m

95-170 m

>200m

Total Cretaceous 

is about 425 m 

(irregularly 

absent in parts 

of the offshore 

productive 

area).

Tithonian=>81

m 

Kimmeridgian=

>160m

Oxfordian= 

>280m

Pre-Upper 

Jurrasic and 

Triassic.

?(not penetrated) Red beds, salt, and anhydrite? ?(not penetrated)

Upper 

Paleozoic?

?(not penetrated) Metamorphosed marine carbonate, shale, and sandstone?

?(not penetrated)

Mainly marls and shales.

Marine green-gray shale and 

marl.

Marine green-gray bentonitic 

shale, some bank carbonate 

upper part.

Marine shale and limestone breccia underlain by dolomitic brecwith fractured and dissolution 

cavities (shale in upper part is 

seal for fields).

Identification of Cretaceous subdivisions is difficult because of 

dolomitization and intense microfracturing; lithology is x'line 

dolomite with fractures and 

dissolution cavities.

Argillaceous limestone, shale, 

and some sandstone.

Oolitic limestone, shale, and dolomite with some anhydrite 

beds.

Dark gray shale, red-brown siltstone, and argillaceous, partly 

oolitic limestone and sandstone; 

some dolomite and anhydrite; 

complete section not penetrated.

Red beds, salt, and anhydrite, 

grading to red beds to east?

Metamorphosed marine carbonate shale and sandstone? Possibly some intrusive igneous 

bodies?

30
XX OJIACAQUE

rvf i i /^ Jj\.

EXPLANATION

OIL AND GAS 

PRODUCER WELL

DRY WELL 

(D DRILLING WELL

M

FIGURE 18. Structure (depth in meters), top of Upper Cretaceous, A. J. Bermudez Complex oil field, Reforma area. Location

of field at lat 18° N., long 93°06' W. (After Acevedo and Dautt, 1980.)

31
19°30'

92°00' 

I

EXPLANATION

Regional fault

Seismic contours 

i Minor faults

Productive areas, Pateocene

Productive areas, Upper Jurassic-Lower Cretaceous, 

! Wrench faults Arrows show direction of relative^ 

movement

JW

V

1

\

v~

^\' ^*«~- ,x ^>

V'JS^^v ^"-^V "-

FIGURE 19. Seismic structural map, offshore Campeche area, top of lower Paleocene. (After Viniegra-0., 1981.)

Some of the oils are relatively low gravity (20° 

API), particularly in the Cantarell complex, but 

lighter oils (30° to 33° API) were found in some of 

the more recently discovered fields (Abkatun, 

Kanaab, Ku, and Ixtoc) (Acevedo and Dautt, 

1980). Matrix porosity in most of the fields averages somewhat higher than that at Reforma. Because of intense microfracturing caused by salt 

movement, permeability values are exceptionally 

high and are somewhat greater than those recorded at Reforma (Viniegra-O., 1981). Initial production rates are some of the highest ever encountered (30,000 bbl/d at Ixtoc and 50,000 to 60,000 

bbl/d at some Cantarell complex wells). As of July 

1980, 20 wells were on production at an average 

per well rate of 32,700 bbl/d (World Oil, 1981).

Geophysical surveys have identified more than 

200 structures in the offshore area. About 20 had

been drilled by early 1981, 5 of which were nonproductive. Of these 200 known offshore structures, Pemex estimates that 60 eventually will be 

productive (World Oil, 1981).

RUBELSANTO AREA (GUATEMALA)

The central and northern Guatemala and Belize 

area occupies the distal portion of the early 

Mesozoic evaporite trough, which extends southeastward from the southwestern Gulf of Mexico 

(figs. 3, 9). The Cretaceous reef or bank-edge belt 

that passes through the Reforma-Campeche area 

and around the offshore periphery of the Yucatan 

platform (fig. 12) may continue southward across 

Belize and possibly into south central Guatemala 

(Viniegra-O., 1971, 1975b, 1981; Garcia, 1978). Interest in exploring this reef belt began some time

32
N

A

EXPLANATION c-ftor

 Oil and gas producer well

T,

2) Dry well 

(D Drilling well

8 KILOMETERS

FIGURE 20. Structure (depth in meters), Paleocene reservoir section, Cantarell Complex oil field, offshore Campeche. Location 

of field at lat 19°39' N., long 92°20' W. (After Acevedo and Dautt, 1980.)

33
AKAL- 2 AKAL-1 NOHOCH-1 CHAC-2

FIGURE 21. Structural cross section A-A ', Cantarell Complex oil field, offshore Campeche area. (After Acevedo and Dautt,

1980.)

ago when numerous wells were drilled in onshore 

and offshore Belize. None of these were productive, and the earlier wells drilled in Guatemala 

also were disappointing. In 1974, oil was discovered at Rubelsanto in west-central Guatemala, 

and three other fields since have been found in the 

vicinity of Rubelsanto (figs. 2, 7). All are apparently on salt structures and produce from the 

"middle" Cretaceous carbonate and evaporite section. The total recoverable reserves of these fields 

are small about 50 MMB (World Oil, 1981). Recently, a significant discovery was announced in 

the northwestern corner of Guatemala (fig. 2), and 

this, plus a reported discovery in southeastern 

Chiapas near the Guatemalan border, adds further 

interest in the possibilities of the Peten basin.

RESERVOIRS

The important reservoirs in the Mesozoic and 

lower Tertiary carbonate fields at Reforma and 

Campeche are in the dolomitized and intensely 

microfractured high-energy bank-edge (Tamabra) 

facies of Cretaceous and Paleocene age (figs. 5, 6, 

12, 13). Much of this facies is a brecciated reef-derived talus. Primary porosity is not necessarily 

high and is related to original pore spaces in reefal 

organisms and interparticle detritus. Secondary 

porosity is related to dolomitization, solution 

cavities, and intense brecciation caused by movement of underlying salt. This facies is projected to 

be present in the subsurface along the seaward 

side of the El Abra reef and back-reef bank facies

34
around most of the Yucatan platform and to extend west from Reforma along the southwest flank 

of the Veracruz basin (Viniegra-0., 1981). However, according to some authors (Castillo, 1955; 

Benavides, 1960; Viniegra-0., 1971; Bishop, 1980), 

this facies probably was removed by erosion in the 

western part of the Isthmus Saline basin where all 

or part of the Cretaceous is thin or missing. It 

may be present in the subsurface near the southern edge of the basin and in subthrust position at 

depth adjacent to the Sierra Madre Oriental along 

the southwestern margin of the Veracruz basin 

(fig. 8).

The lower part of the Sierra Madre Limestone 

in southern Chiapas is dolomitized, and dolomite 

also is common in the upper part of the formation 

(Mora and others, 1975). Thick beds of crystalline 

dolomite and thick limestone breccias are reported 

in the lower part of the Cretaceous outcrop sequence in Guatemala (Hillbank Dolomite and other 

units) (demons and Burkart, 1971; Anderson and 

others, 1973; Bishop, 1980). These breccias were 

interpreted as possibly intraformational or collapse breccias rather than forereef breccias 

(Blount and Moore, 1969). Fractured dolomite 

beds interbedded with anhydrite in the Peten 

basin are the reservoirs in the Rubelsanto area oil 

fields.

Porous and fractured carbonate beds of reservoir quality are common in the Sierra Madre belt 

of southeastern Mexico and Guatemala and on the 

Yucatan Peninsula. However, throughout most of 

this tropical rain forest area, parts of the thick 

Cretaceous carbonate sequence are exposed and 

probably flushed by meteoric waters. In the subsurface of eastern Chiapas and Guatemala, however, carbonate units are interbedded with anhydrite, or a Tertiary cover is present. Flushing 

should be less effective here, and impermeable 

seals are also present for trapping petroleum.

Upper Jurassic (Oxfordian) bank carbonate beds 

were penetrated by several wells at Reforma and 

offshore Campeche, where oil-saturated reservoirs 

of dolomitized oolitic and bioclastic units are reported. This facies, as much as 500 to 1,000 m or 

more (1,600 to >3,300 ft) thick (fig. 11), is similar 

to the Limestone facies of the Smackover Formation of the U.S. Gulf Coast and the Zuloaga 

Limestone of northern Mexico. Its areal extent in 

southern Mexico and Guatemala is speculative, 

but it may underlie much of the area where the 

the Cretaceous El Abra-Tamabra bank margin 

and talus facies are present.

SOURCE ROCKS

The organic-rich black shale and limestone 

source-rock facies of Late Jurassic (KimmeridgianTithonian) age in the Reforma and offshore Campeche areas may be present throughout much of 

the main salt area in the Gulf Coast basins and 

along the western border of the Yucatan platform. 

This facies was deposited under restricted basin 

conditions and thus also may have been deposited 

in other Mesozoic evaporite basins. A similar 

facies of the same age overlies a Jurassic evaporite sequence in other parts of the Gulf of Mexico 

province and may be present in much of the Jurassic salt area in southern Mexico and Guatemala.

Lower Cretaceous dark shale and shaly limestone beds also are probable source beds for oil in 

Cretaceous and Paleocene reservoirs (Viniegra-0., 

1981; Bishop, 1980; Acevedo and Dautt, 1980). 

These beds are not as organically rich as those of 

the Upper Jurassic but, in places, may be of substantial thickness. Because of similarities in depositional history, the distribution of these beds 

should be similar to that of the Upper Jurassic organic-rich beds. Other potential source beds may 

include the Tamaulipas facies offshore from the 

main bank-edge belt, although these beds are not 

reported to have a significantly high organic content. Similar Upper Cretaceous deeper water 

beds may be present locally within the main bank 

carbonate complex and in the foredeep area north 

of the Sierra Madre del Sur in Guatemala.

REGIONAL CAP ROCKS

The Tertiary shale facies of the Reforma and 

Campeche areas is present everywhere north of 

the Sierra Madre Oriental and should extend 

around the periphery of the Yucatan platform, 

where these beds are probably mainly marls. On 

the Yucatan platform, Tertiary beds are primarily 

carbonate rocks and, except for some anhydrite 

beds, probably do not contain adequate cap rocks. 

Except for local areas of preservation, the Tertiary shale facies is absent in much of Chiapas, although it is somewhat more widespread but thinner in eastern Chiapas and Guatemala. Anhydrite 

beds, interbedded with carbonate beds in the 

Lower and "middle" Cretaceous sequence in 

Guatemala and much of Chiapas, should be 

efficient seals for the underlying reservoirs of 

folded carbonate or clastic beds.

35
TRAPS

Almost all of the carbonate Mesozoic oil accumulations in the Reforma and Campeche shelf provinces have been found on complexly faulted salt 

structures. Originally, both areas may have been 

giant stratigraphic accumulations (Viniegra-0., 

1981) that were remigrated and segmented by 

Laramide structural growth and subsequent 

episodes of salt movement. Thrust or reverse and 

normal fault traps are documented on many of the 

structures, and local stratigraphic traps also may 

be present within the structural complexes. At 

least 200 undrilled structures in the Tabasco and 

offshore Campeche areas with probable salt cores 

are reported. Fields in the Rubelsanto area of 

Guatemala also are on salt structures, but these 

appear to be less complex. Salt structures also 

may be present in much of the remainder of the 

Peten basin, including the north basin where a 

significant discovery was recently announced 

(World Oil, 1981). The numerous broad domal or 

anticlinal structures mapped on the Yucatan 

Peninsula and to the north on the offshore Yucatan platform may be flushed by meteoric waters 

from the exposed carbonate sequence on the 

peninsula. Likewise, the complex of anticlinal and 

fault structures in the Sierra Madre de Chiapas 

have undergone massive flushing of the carbonate 

reservoirs because of exposure and lack of adequate stratigraphic seals.

ANALOGS

Facies analogs to the Mesozoic-Tertiary carbonate bank province of southern Mexico and 

Guatemala are found in most of the equivalent age 

carbonate complex surrounding the Gulf of Mexico 

basin. The processes of organic carbonate buildups, postdepositional history, dolomitization, 

karstification,and brecciation by salt movements 

have in varying degrees similarly affected this reservoir and source rock facies in many other productive areas, including the Tampico-Golden 

Lane, Sabinas basin, and U.S. Gulf Coast areas.

PRE-OXFORDIAN MESOZOIC CLASTIC DEPOSITS

Thick sandstone and conglomerate beds are present in outcrops of the Todos Santos (red bed) 

Formation in Chiapas and Guatemala. These beds 

are pre-Oxfordian Jurassic and probably Triassic 

in age and may be in part as young as Early Cretaceous in southeastern Chiapas and Guatemala 

(Bishop, 1980; Vinson, 1962; Viniegra-0., 1971, 

1981). In places, this section contains marine fossils, particularly in the upper part, and porous 

sandstones are present, although their distribution and reservoir character in the subsurface is 

relatively unknown because of lack of control. The 

facies apparently occurs throughout most of the 

region, having been reported in the subsurface as 

far north as offshore Campeche, Reforma, and the 

western part of the Isthmus Saline basin, as well 

as in wells on the Yucatan Peninsula. Much of the 

Todos Santos sequence is continental in origin and 

is unlikely to contain beds with sufficient organic 

material to serve as source rocks for petroleum. 

However, the upper, more marine part may contain more organic matter in places, particularly in 

the more basinal or graben-trough areas of the depositional province. The possibility of nonindigenous petroleum in these beds should be greater in 

structurally high areas where the underlying 

upper Paleozoic marine section may include 

source-rock beds, particularly in northern 

Guatemala and eastern Chiapas (Bishop, 1980). 

Evaporites, which are interbedded with or overlie 

the Todos Santos in most of Chiapas, Guatemala, 

the Gulf coastal plain, and the offshore Campeche 

areas, provide a regional seal for these beds.

PALEOZOIC ROCKS

Pre-Pennsylvanian sedimentary rocks are 

metamorphosed wherever observed and, except 

for the possibility of anomalous fracture reservoirs, are unlikely to contain hydrocarbons. However, a sequence of marine Pennsylvanian and 

Permian rocks 2,000 m or more ( 6,600 ft) thick in 

places is known from outcrop studies in southeastern Chiapas and Guatemala and probably is widespread in the subsurface of Chiapas and 

Guatemala (figs. 5, 7) (Bishop, 1980; Paine and 

Meyerhoff, 1970; Garcia, 1973; Lopez-Ramos, 

1969; Anderson and others, 1973; demons and 

others, 1974). These beds are metamorphosed in 

places but may be unmetamorphosed in much of 

the subsurface. The lower part of the sequence 

consists of basal conglomerate, sandstone, and 

marine shale beds overlain by fossiliferous limestone and shale, some of which apparently have 

source-rock quality. Oil seeps are present in outcrops of these beds in Chiapas (Bishop, 1980). The 

section is essentially unexplored for petroleum

36
and is deeply buried in much of southeastern 

Mexico and Guatemala but is considered to have 

good potential for hydrocarbons in Chiapas and 

parts of Guatemala (Garcia, 1973; Bishop, 1980). 

Regional cap rocks may not be present in the 

Paleozoic section, but the overlying Todos Santos 

clastic and evaporite beds should provide an adequate seal on structures.

Insufficient data are available for satisfactory 

analog comparisons with the upper Paleozoic section. However, this marine sequence was deposited in the Paleozoic geosyncline of Mexico, which 

is an extension of the Pedregosa and Delaware 

basin depositional province of southwestern 

United States and northern Mexico. There may be 

some similarities between the carbonate and clastic reservoir facies and potential source-rock facies 

of these two areas.

GIANT FIELDS

TERTIARY BASIN FIELDS

Acevedo and Dautt (1980) report five giant oil 

fields (more than 100 MMB) in the Tertiary Isthmus Saline basin and three giant gas fields 

(more than 0.6 Tcf) in the Macuspana basin (fig. 

2). Cumulative production through 1980 in the 

larger Isthmus Saline basin fields is as follows: 

Cinco Presidentes (fig. 15) (227 million barrels of 

oil (MMBO)), El Plan (147 MMBO), Magallanes 

(126 MMBO), Orragio (119 MMBO), and Tonala'- 

El Burro (95 MMBO). Production in these fields is 

from Tertiary sandstones, mainly the lower 

Miocene Encanto Formation, on complexly faulted 

diapiric salt domes. The largest Macuspana basin 

fields are Jose Colomo, Chilapilla (fig. 16), and 

Hormiguero, all of which produce from faulted 

anticlines that may be related to deep-seated salt 

structures. These fields produce gas and condensate from sandstone reservoirs in the middle 

Miocene Amate Formation. Specific data on the 

Cinco Presidentes and Jose Colomo-Chilapilla 

fields are summarized in table 2.

REFORMA FIELDS

By January 1981, 36 fields had been discovered 

in the Reforma area. Four of these (Sitio Grande, 

Cactus, A. J. Bermudez complex, and Iris Giraldas complex) are reported as giant or supergiant 

fields (Acevedo and Dautt, 1980). Production is 

from Cretaceous and Upper Jurassic microfractured dolomite reservoirs on complexly faulted 

salt structures. The A. J. Bermudez complex is a 

combination of four fields discovered between 1973 

and 1977, which with further development drilling, turned out to be part of a giant accumulation 

on a complexly faulted salt structure (fig. 18). Production is from microfractured Cretaceous and 

Upper Jurassic dolomite reservoirs with pay 

thickness as much as 1,200 m (4,000 ft). By mid1980. the complex had produced more than 2 BB 

of oil and more than 3 Tcf of gas. Because the reservoirs are undersaturated, an intensive waterflood project was set up early in the history of the 

field, and in 1981 more than 1,000,000 bbl/d of 

water were being injected (World Oil, 1981). Detailed reservoir and production data for the main 

Reforma fields are summarized in table 2, and the 

general stratigraphic column of the area is shown 

in table 3.

OFFSHORE CAMPECHE FIELDS

By July 1980, production from the offshore 

Campeche fields was 784,000 bbl/d from 24 wells 

averaging more than 32,000 bbl/d each; in March

1981. production had increased to 1.3 million bbl/ 

d, mainly from the Cantarell complex. The Cantarell complex includes the Akal, Nohoch, and 

Chac fields, which make up a single supergiant accumulation (figs. 6, 19, 20, 21). Production is from 

Paleocene and Cretaceous microfractured and 

vuggy brecciated dolomite reservoirs with pay 

thicknesses as much as 1,000 m (3,300 ft) or more. 

Production rates of individual wells are extremely 

high because of the intense fracturing of the reservoir rock. The structure of the Cantarell complex 

is complicated by normal, reverse, and wrench 

faults related to movement of the salt. All or parts 

of the Cretaceous section are missing in places 

(Acevedo and Dautt, 1980). Another group of 

fields, the Abkatun-Kanaab-Taratunich-Ixtoc complex, is in the early stages of development but is 

predicted to be a second supergiant accumulation 

in this offshore area (Acevedo and Dautt, 1980).

Data pertinent to these two largest productive 

complexes are summarized in table 2, and the general stratigraphic column of the area is shown on 

table 3.

SUMMARY

GENESIS OF THE PETROLEUM DEPOSITS

The sequence of geological events that resulted

37
in the accumulation of major deposits of petroleum 

in southern Mexico can be summarized as follows:

1. Deposition of a sequence of upper Paleozoic 

marine clastic and fossiliferous carbonate 

beds 2,000 m or more (>6,600 ft) thick in 

the Mexico geosyncline north of the Sierra 

Madre del Sur province.

2. Seafloor and continental-margin spreading 

around the border of the North American 

continent and development of a Triassic 

graben trough system. Deposition of Triassic and Lower Jurassic continental and 

marine red beds, conglomerates, and 

evaporite deposits occurred and eventually 

spread across most of the southeast 

Mexico-Guatemala area, but deposition was 

thickest in elongate fault-bounded troughs 

of the Early Triassic structural complex.

3. Deposition of a thick sequence of Middle and 

lower Upper Jurassic evaporite deposits 

with halite and gypsum interbedded with 

red beds, mostly in the vicinity of the main 

graben troughs inherited from the Triassic 

tensional structural event.

4. Late Jurassic (Oxfordian-Kimmeridgian) 

marine transgression and wide-spread deposition of marine carbonate and dark shaly 

beds within the entire Gulf of Mexico province. This event marked the early building 

of the bank carbonate complex in shallowwater marine areas around the Gulf of 

Mexico basin.

5. Latest Jurassic (Kimmeridgian-Tithonian) 

marine regression and deposition of organic-rich dark shale, silt, and argillaceous 

carbonate beds, primarily in trough areas 

where the main sequence of Jurassic evaporite deposits had previously been deposited.

6. Transgressive-regressive cyclic deposition of 

unusually thick platform and bank organic 

carbonate and evaporite beds of the major 

Cretaceous transgressive cycle. In the 

main platform areas of the Gulf of Mexico 

province, the El Abra bank and reef-carbonate and backreef evaporite beds were deposited, and deeper water dark calcareous 

shale and argillaceous carbonate beds 

(Tamaulipas facies) accumulated in the 

main Gulf of Mexico basin. Along the platform borders and at places within the platform, the forereef or bank-edge talus deposits (Tamabra facies) formed, mainly during low sea-level (regressive) stages of the 

cycle, with a particularly important and 

widespread development of this facies at 

the close of the "middle" Cretaceous (Aptian-Albian). Solution, karstification, and 

early dolomitization of the bank carbonate 

sequence probably occurred with regional 

emergence of the carbonate complex, particularly around the platform borders 

where seepage-reflux and basinal dolomitization processes were effective.

7. Laramide tectonic movements, beginning 

sometime during the Late Cretaceous, with 

north- and northeast-directed compressive 

stresses, causing uplift of the Sierra Madre 

del Sur, development of an adjacent 

foredeep trough immediately to the north, 

and imbricate folding and thrust faulting in 

the Sierra Madre Oriental and Sierra 

Madre de Chiapas. As interpreted by Viniegra-0. (1971, 1981) and Lopez-Ramos 

(1979), regional left-lateral transcurrent 

normal faulting occurred in association with 

the compressive Laramide stresses, and 

parts of the thick carbonate-bank complex 

were displaced toward the west or northwest, particularly in the Veracruz, Reforma shelf, and Campeche shelf areas, and 

perhaps in other parts of the platform.

8. Laramide structural activity accompanied by 

increased clastic influx into the basin areas. 

Thick deposits of shallow- and deepwater 

Upper Cretaceous and lower Tertiary 

marine and nearshore continental beds 

were deposited along the Cretaceous platform carbonate front and adjacent deepwater areas of the Gulf of Mexico (Veracruz, 

Isthmus Saline, Macuspana, and Comalcalco basins). Deposition of these beds on 

the Reforma shelf, Campeche shelf, and the 

Veracruz thrust front caused further sagging of these offset blocks and deeply 

buried the Mesozoic sequences within the 

main coastal basin province. Vertical faulting along the borders of the blocks may 

have begun at this time, initiating the delineation of the Villahermosa horst, as well 

as the Macuspana, Comalcalco, and other 

basin-border faults.

38
9. At some time during the early Tertiary, maturation of the Upper Jurassic and Lower 

Cretaceous organic-rich argillaceous beds 

due to burial depths. Also at this time or 

perhaps earlier, burial depths and post- 

"middle" Cretaceous sediment thickness 

differences were sufficient to cause extensive vertical salt movement, although salt 

movement may have begun earlier, 

perhaps in part stimulated by Laramide 

compressive stresses. Petroleum generation and migration probably began at this 

time, with early migration directed out of 

the more deeply buried basinal areas and 

toward the shelf areas such as the Reforma 

shelf, the Campeche shelf, and the carbonate-bank border. At the same time, salt 

movement would have been directed toward areas of shallower burial within the 

salt province (Reforma shelf, Campeche 

shelf, western Isthmus Saline basin area 

near the Salina Cruz fault and others). 

Brecciation of overlying dolomitized carbonate beds also occurred, enhancing the 

movement of generated petroleum into the 

salt-uplift areas.

10. Deposition of thick offshore and nearshore 

marine clastic rocks in the coastal basin 

province, resulting in further vertical salt 

movement and continuation of Mesozoic 

source-bed maturation, at least through 

most of the Miocene. Intensified microfracturing of carbonate reservoirs and redistribution of earlier petroleum deposits in 

the Mesozoic reservoirs continued until the 

present-day accumulations were essentially 

formed. During this time, deep burial of 

much of the lower and middle Tertiary 

marine sedimentary rocks reached the 

thermal-maturity stage. Gas, condensate, 

and some oil were generated and migrated 

into adjacent sandstone beds of the lower 

and middle Miocene nearshore sand and 

carbonaceous shale reservoir-source rock 

complex. These petroleum accumulations 

were further redistributed during the final 

phases of salt-structure growth. At some 

time during the middle Tertiary, as salt 

movement reached a maximum, salt piercement structures probably began to form in 

the western part of the Isthmus Saline

basin, resulting in upward migration into 

Miocene sandstone reservoirs of Mesozoic 

oil from earlier formed fractured Mesozoic 

reservoirs on the main salt structures. 

11. Continued burial of salt structures and of 

earlier formed Laramide structures in the 

coastal plain province during latest Tertiary time, resulting perhaps in some minor 

redistribution of previously formed petroleum deposits.

INFORMATION SUMMARY

Geologic province:

Mesozoic-Tertiary continental margin basin 

Area:

325,000 mi2 

Volume of sediment:

1,100,000 mi3 

Prospective intervals:

A. Upper Paleozoic carbonate-clastic beds

B. Pre-Oxfordian Jurassic clastic beds

C. Oxfordian-Tithonian (Jurassic) carbonate-clastic beds

D. Cretaceous carbonate fades

E. Paleocene-Eocene carbonate fades

F. Lower and upper Tertiary Paleocene-Miocene clastic

beds 

Source beds:

A. Upper Jurassic dark shale and carbonate beds

B. Lower and "middle" Cretaceous dark shale and carbonate 

beds

C. Tertiary marine shales 

Prospective trap types:

A. Reef, forereef talus, back-reef carbonates, porosity-permeability variations

B. Marine sandstones lense, channel, bar, and porositypermeability variations

C. Salt swells and domes, anticlines, fault traps

D. Combination traps 

Principal plays:

A. Structure to immediate northwest and southwest of Cantarell, including possible horst block high in the depression between Cantarell and Reforma

B. Undrilled structures in Reforma area

C. Possible reef area in Guatemala

D. North basin area of Guatemala where Tertiary cover is 

present

E. Southeastern Chiapas-western Guatemala where Tertiary 

cover is present

F. Buried thrust play in Veracruz basin

G. Stratigraphic play seaward and against the Yucatan escarpment

H. Sediment troughs in offshore salt structure area 

I. Deep Paleozoic gas in Chiapas and Guatemala 

Exploration stage of province:

A. Intermediate in Tertiary basins

B. Early in deeper onshore Mesozoic and offshore provinces 

Number of fields:

About 125 oil or oil and gas; about 30 to 35 gas fields

39
Average depth of undiscovered resources:

A. Oil-^,500 to 5,500 m

B. Gas 5,000 to 6,000 m 

Analogs:

Tampico basin, Mexico; Persian Gulf; Permian basin, U.S.; 

western Gulf basin, U.S.; Arctic slope, U.S.

RESOURCE ASSESSMENT

PROCEDURES

The resource assessment of this region was conducted by the Resource Appraisal Group (RAG) of 

the USGS, Branch of Oil and Gas Resources, following the standard procedures developed since 

1974 for analysis of domestic petroleum resources. 

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, which include 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 where 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, as well as gas in low permeability reservoirs, in occlusions in coal, in geopressured shales 

and brines, and in natural gas hydrates.

The assessment process itself is subjective; the 

results of the geological investigation and of the 

resource calculations are presented to a team of 

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:

(1) A low resource estimate corresponding to a 

95-percent probability of more than that 

amount; this estimate is the 95th fractile 

(F95).

(2) A high resource estimate corresponding to a 

5-percent probability of more than that 

amount; this estimate is the 5th fractile 

(F5).

(3) 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 are debated from the 

perspective of 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 that reflects the probability 

that any commercial oil will ever be discovered. 

The results of the final estimates are averaged, 

and those numbers are computer processed by 

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 southeastern Mexico, northern Guatemala, and Belize basins are shown in 

figure 1. Unconditional estimates by the USGS of 

oil and gas resources in these basins are shown in 

table 4 and in figures 22 and 23. Data supporting 

these estimates are supplied in table 5.

COMMENTS

The Reforma-Campeche reservoirs are salt assisted and apparently require assistance for fracturing.

The production between Reforma and Campeche is limited by a deep trough that places potential source rocks below oil or gas generation 

levels. An uplifted structural block is, however, 

inferred in the area, which is part of the exploration potential.

North of the offshore Campeche fields, production is limited by (1) loss of salt assist, (2) loss of 

seal (Tertiary deltaic and offshore marine sands 

and shales derived from the south), and (3) possible flushing from the Yucatan high to CretaceousJurassic outcrops on the seafloor.

The Ixchel well north of offshore Campeche, 

earlier reported as a discovery and later reported 

not to have been drilled, clouds the assessment of 

the north Yucatan platform area. This assessment 

assumes the well does not exist.

Most of northern Guatemala appears to be in a 

back-reef facies and probably not in a position to 

contain major resources. Inferences of reef development, however, lend some encouragement.

40
Assessment date: April 3, 1981

STANDARD - 

DEVIATION

0.0 40.0 80.0 120.0 160.0 200.0. 240.0 280.0 320.0 360.0 400.0

RECOVERABLE OIL, IN BILLION BARRELS

FIGURE 22. Unconditional estimates of recoverable oil in southeast Mexico, northern Guatemala, and Belize (assessment date,

April 3, 1981).

Assessment date: April 3, 1981

MEANS

MEDIAN

95%

75%

50%

25%

5%

MODE

119.92

103.14

41.80

71.22

103.14

149.37

254.50

76.30

STANDARD 71.13

DEVIATION

0.0 55.0 110.0 165.0 220.0 275.0 330.0 385.0 440.0 495.0 550.0

RECOVERABLE GAS.TRILLION CUBIC FEET

FIGURE 23. Unconditional estimates of recoverable total gas in southeast Mexico, northern Guatemala, and Belize (assessment

date April 3, 1981).

41
A buried overthrust play in Veracruz basin is 

deep but promising.

Oil occurrence and entrapment in the area is a 

combination of many factors, each of which has 

unique areal limits; therefore, it is not reasonable 

to count structures and assume a percentage of 

discoveries.

TABLE 4. Assessment of conventionally recoverable 

petroleum resources of southeastern Mexico,

northern Guatemala, and Belize

[Unconditional resource assessment by USGS as of April 3,1981; see figures 22 and 

23 also]

Crude oil

Probability of occurrence, in percent

Billions of barrels 

(BB)

95 - 

5 -

Mean -

26

168

78

Natural gas

Probability of occurrence, 

in percent

Trillions of cubic feet 

(Tcf)

Billions of barrels of oil

equivalent (BBOE)

at 6,000 ftVbbl1

95 ________

Mean 

42

254

120

7

42

20

'Pemex commonly reports barrels of oil equivalent at 5,000 ft'/bbl, but the 6,000:1 

conversion is used here for comparability with other assessments made by USGS.

TABLE 5. Supplementary and comparative data supporting the resource assessment 

for southeastern Mexico, northern Guatemala, and Belize1

Crude oil Natural gas 

Billions of barrels (BB) Trillion cubic feet (Tcf)

Cumulative production to 1/1/80

Identified reserves to 1/1/80*

Demonstrated 27 

Inferred 26

53

__ Original recoverable resources (ultimate) of assessment area

Cumulative 5

Identified reserves 563

Undiscovered resources (mean) 78

139 

Total BBOE 171

Recoverable basin richness, at mean estimate assuming 1,100,000 mi* of 8ediments=161,000 BOE/mi*

Original recoverable resources (ultimate) BBOE:

Cumulative production/oil 5.0 

Cumulative production/gas 

Identified reserves/oil 53.0 

Identified reserves/liquid 3.0 

Identified reserves/gas 

Mean undiscovered resources/oil 78.0 

Mean undiscovered resources/gas 24.0 

Total BBOE 177.5

45

20

65

BBOE 11

8

65

120

193 

BBOE 32

'Cumulative production and reserves are composited estimates from various sources.

'Follows terminology outlined in USGS Circular 831. Demonstrated is equivalent to API Proved and Indicated Additional. Inferred represents anticipated field growth in 

existing fields. 

'Included 3 BB natural-gas liquids.

42
SELECTED REFERENCES

Acevedo, J. S., 1979, Petroleum geology of Campeche offshore 

area, southeastern Mexico (abs): American Association of 

Petroleum Geologists Bulletin, v. 63, p. 697.

Acevedo, J. S., and Dautt, O. M., 1980, Giant fields in the 

southeast of Mexico: Transactions Gulf Coast Association 

of Geological Societies, v. 30, p. 1-31.

Alvarez, M., Jr., 1949, Tectonics of Mexico: American Association of Petroleum Geologists Bulletin, v. 33, p. 1319-1335.

Anderson, T. H., Burkart, B., and demons, R. E., 1973, Geology of the western Altos Cuchumatanes, northwestern 

Guatemala: Geological Society of America Bulletin, v. 84, 

p. 805-826.

Beebe, B. W., 1968, The occurrence of natural gas in Mexico: 

American Association of Petroleum Geologists Memoir 9, 

p. 209-232.

Benavides, G. L., 1960, Notas sobre la geologiade la Cuenca 

Salina del Istmio (Notes on the Geology of the Isthmus 

Saline Basin): Soc. Mex. Mec. Suelos, v. 5, p. 98-101.

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44