About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 28 (1944)

Issue: 3. (March)

First Page: 301

Last Page: 325

Title: Geologic History of Northern Mexico and Its Bearing on Petroleum Exploration

Author(s): Lewis B. Kellum (2)

Abstract:

Buried platforms comparable with the Coahuila Peninsula of north-central Mexico are known to be present in several of the major downwarped areas in the central and coastal United States and beneath the coastal plain of eastern Mexico. It is believed that others may be present. The purpose of this paper is to point out certain criteria which may aid in their discovery.

A series of paleogeographic maps has been compiled to show the geologic development of Mexico during late Paleozoic and Mesozoic time. The stratigraphic section on the buried Coahuila Peninsula is in marked contrast to the deposits in the geosyncline on the south. This is due to the influence of the underlying massif on sedimentation throughout a long period of geologic time. It indicates that facies of deposition may be used as a guide in locating buried positive elements in the subsurface.

The influence of a buried massif on the structure of overlying strata is clearly demonstrated by the contrast between the relatively simple warping of Lower Cretaceous rocks over the Coahuila Peninsula and the tight, asymmetrical folding and overthrusting in the areas of the surrounding geosyncline. The physiography of the mountain ranges is an expression of the lithologic succession and geologic structure comprising them. Regionally it reveals the same contrast in underlying geology that marks the Coahuila Peninsula and the geosyncline. The area where great buried platforms, comparable with the Coahuila Peninsula, are likely to produce oil and gas in the future are the structurally downwarped provinces of the central United States and along the margins of the continent.

Text:

INTRODUCTION

Paleogeographic studies (FOOTNOTE 3) in the Cordilleran Basin region of the United States, by numerous geologists during the past quarter century, have demonstrated the presence of several landmasses which stood as islands in the Paleozoic seas. One of these (the Front Range Highland) persisted until late Mesozoic time (FOOTNOTE 4) and another (the Uinta element),(FOOTNOTE 5) which foundered at about the same time, has its structural continuation eastward concealed beneath a blanket of Cretaceous and

FOOTNOTE 3. Willis T. Lee, "Early Mesozoic Physiography of the Southern Rocky Mountains," Smithsonian Misc. Coll., Vol. 69, No. 4 (1918).

F. A. Melton, "The Ancestral Rocky Mountains of Colorado and New Mexico," Jour. Geology, Vol. 33, No. 1 (1925), pp. 84-90.

T. S. Lovering and J. Harlan Johnson, "Meaning of Unconformities in Stratigraphy of Central Colorado," Bull. Amer. Assoc. Petrol. Geol., Vol. 17, No. 4 (1933), pp. 353-74.

FOOTNOTE 4. T. S. Lovering and J. Harlan Johnson, op. cit. (1933), p. 373.

FOOTNOTE 5. W. A. VerWiebe, "Ancestral Rocky Mountains," Bull. Amer. Assoc. Petrol. Geol., Vol. 14, No. 6 (June, 1930), pp. 769, 773, 775.

End_Page 301------------------------------

Tertiary strata. Lovering (FOOTNOTE 6) has shown the influence of the Front Range Highland on Mesozoic and Cenozoic sedimentation in central Colorado. Several land areas of considerable relief and extent were present in California and Oregon during Mesozoic time.(FOOTNOTE 7) Their location is inferred from the lithology of sediments deposited in near-by troughs and basins to which they contributed large quantities of clastic sediments. The larger of these islands and peninsulas continued as positive elements of varying size and shape throughout the Tertiary.(FOOTNOTE 8) Read and Hollister (FOOTNOTE 9) concluded that the post-Jurassic structural evolution of southern California was dominated by the distribution of basement types. Sellards (FOOTNOTE 10) observed that structural conditio s on the Central Basin platform of West Texas, controlled to some degree the depositional facies in the Permian seas. In northern Mexico (FOOTNOTE 11) also it has been shown that the underlying basement had a profound influence both on the type of sediments laid down and on the type of regional folding which took place in overlying beds during a later geologic period of orogeny. Location of these old landmasses by geologic studies on the surface and others by subsurface investigations suggests the probability that similar ancient massifs exist elsewhere concealed beneath a cover of later sediments.

The basic principles of the interrelation of stratigraphy and structure developed by recent studies in northern Mexico may find an application in any large basin of deposition. Buried platforms comparable with the Coahuila Peninsula of north-central Mexico (FOOTNOTE 12) are known to be present in several of the major downwarped areas in the central and coastal United States and beneath the coastal plain of eastern Mexico. It is believed that others may be present. The purpose of this paper is to point out certain criteria which may aid in their discovery.

The Bellair-Champaign uplift (FOOTNOTE 13) in the Eastern Interior coal basin and the Central Kansas uplift (FOOTNOTE 14) in the Mid-Continent area are buried platforms similar in some respects to the Coahuila Peninsula. They were formerly peninsulas which projected southward into the Pennsylvanian seas just as the Coahuila Peninsula

FOOTNOTE 6. T. S. Lovering, "Geologic History of the Front Range, Colorado," Proc. Colorado Sci. Soc., Vol. 12, No. 4 (1929), pp. 75 and 84-109.

FOOTNOTE 7. F. M. Anderson, "Lower Cretaceous Deposits in California and Oregon," Geol. Soc. America Spec. Paper 16 (1938) pp. 11-17 and 87.

FOOTNOTE 8. R. D. Reed, Geology of California (Amer. Assoc. Petrol. Geol., 1933), pp. 250-54.

FOOTNOTE 9. R. D. Reed, and J. S. Hollister, "Structural Evolution of Southern California," Bull. Amer. Assoc. Petrol. Geol., Vol. 20, No. 12 (December, 1936), p. 1550.

FOOTNOTE 10. E. H. Sellards, "Structural Geology of Texas East of Pecos River," Univ. Texas Bull. 3401, Pt. I (January, 1934), p. 109.

FOOTNOTE 11. L. B. Kellum, R. W. Imlay, and W. G. Kane, "Relation of Structure, Stratigraphy and Igneous Activity to an Early Continental Margin," Evolution of the Coahuila Peninsula, Mexico, Part I, Bull. Geol. Soc. America, Vol. 47, No. 7 (1936), pp. 992-94, 1003, 1005-06.

FOOTNOTE 12. L. B. Kellum, "Paleogeography of Parts of Border Province of Mexico Adjacent to West Texas," Bull. Amer. Assoc. Petrol. Geol., Vol. 20, No. 4 (April, 1936), pp. 419-22.

FOOTNOTE 13. L. A. Mylius, "Oil and Gas Development and Possibilities in East-Central Illinois," Bull. Illinois Geol Survey 54 (1927), pp. 28, 30-31, Pls. I and XXI.

FOOTNOTE 14. L. C. Morgan, "Central Kansas Uplift," Bull. Amer. Assoc. Petrol. Geol., Vol. 16, No. 5 (May, 1932), pp. 483-84.

End_Page 302------------------------------

projected southward into the Mesozoic seas. There is one important difference, however, in that the seas which surrounded the Bellair--Champaign uplift and the Central kansas uplift were shelf seas whereas the seas which surrounded the Coahuila Peninsula were geosynclinal seas. This has made a great difference in the type of deformation which subsequently took place in the areas contiguous to the platforms.

The "Golden Lane" of the Mexican South fields (FOOTNOTE 15) is probably the most spectacular oil district that has ever been discovered, the East Texas field (FOOTNOTE 16) on the western edge of the Sabine uplift (FOOTNOTE 17) is the largest oil pool so far developed, the Central Basin platform (FOOTNOTE 18) in West Texas has produced many millions of barrels of oil. All are buried platforms which, like the Coahuila Peninsula, have influenced the character of deposition in overlying strata. The question which faces Gulf Coast geologists to-day is "Where are we going to find another of these great platforms which has controlled the distribution and accumulation of oil and gas?"

PALEOGEOGRAPHIC DEVELOPMENT

Every paleogeographic map is to some extent a composite picture of continuously changing shorelines. The faithfulness with which a given map portrays the true distribution of land and sea depends to a considerable degree on the brevity of the time interval selected for representation by the paleocartographer. The longer the interval the more generalized will be the resulting map; the shorter the interval the more limited are the available data. A compromise on a period of time long enough to furnish a wide distribution of localities and yet short enough to exclude more than one major transgression or regression of the sea is likely to yield a picture more nearly approaching the true appearance of the earth's surface at any time.

The sequence of events in the geologic history of northern Mexico is integrated with the geologic development of the oil-bearing regions of Texas and eastern Mexico. The mountainous region was the source of much of the clastic sediment deposited during Mesozoic and Cenozoic time in the oil- and gas-producing areas of the Gulf Coastal Plain. A series of paleogeographic maps have been compiled to show the geologic development of Mexico. Data for the earlier periods of the Paleozoic are too meager to permit an attempt to reconstruct the distribution of land and sea before Permian time.

FOOTNOTE 15. J. M. Muir, Geology of the Tampico Region, Mexico (Amer. Assoc. Petrol. Geol., 1936), pp. 203-25.

R. Leibensperger, "The Mexican Oil Fields," The Lamp (August, 1922), pp. 10-19.

FOOTNOTE 16. H. E. Minor and M. A. Hanna, "East Texas Oil Field, Rusk, Cherokee, Smith, Gregg, and Upshur Counties, Texas," Stratigraphic Type Oil Fields (Amer. Assoc. Petrol. Geol., 1941), pp. 600-60.

FOOTNOTE 17. E. H. Sellards, "Structural Geology of Texas East of Pecos River," Univ. Texas Bull. 3401 (January, 1934), pp. 45-48.

FOOTNOTE 18. Ibid., pp. 106-10.

R. E. King et al., "Resume of Geology of the South Permian Basin, Texas and New Mexico," Bull. Geol. Soc. America, Vol. 53, No. 4 (April, 1942), pp. 539-60.

End_Page 303------------------------------

Fig. 1. PERMIAN MEXICO

End_Page 304------------------------------

Cambrian strata, reported only from the Cabullona region in northeastern Sonora, is thought by N. L. Taliaferro (FOOTNOTE 19) who studied the area, to comprise a southward extension of the Balsa quartzite and the Abrigo limestone of Arizona. Upper Ordovician limestone, known from two localities in central Sonora (FOOTNOTE 20) has a thickness of 50 meters and bears a coral fauna of Richmond age correlated with the Montoya limestone of the El Paso region. Rocks of the Silurian have not been recognized anywhere in Mexico. The Upper Devonian Marine limestone of Arizona is thought by Taliaferro (FOOTNOTE 21) to extend southward into the Mustenas Mountains of the Cabullona area. Strata of Lower Mississippian age are reported from three widely spaced localities: (1) the Escabrosa limestone a Cabullona,(FOOTNOTE 22) (2) brachiopod-bearing limestone in the Sierra de Teras of northern Sonora,(FOOTNOTE 23) and (3) brachiopod-bearing shales at Peregrina Canyon (FOOTNOTE 24) in Tamaulipas. Fossiliferous strata of Pennsylvanian age are more widely distributed and better known than earlier Paleozoic formations. The Pennsylvanian is represented in the Cabullona area (FOOTNOTE 25) by the Naco limestone (2,500 feet thick) which includes both Pennsylvanian and Permian horizons; in the Huchita Hueca Mountains (FOOTNOTE 26) southeast of the Cabullona basin in northern Sonora, R. W. Imlay found 300 meters of limestone with fusulines comparable with the Cisco in the lower part and Leonard fusulines 30 meters below the top. C. L. Baker (FOOTNOTE 27) has described the Caborca group of Pennsy vanian age in the Altar region of northwestern Sonora; at Las Delicias in southern Coahuila Pennsylvanian shales and limestones have been described by R. E. King.(FOOTNOTE 28)

Permian limestones are widely distributed in Sonora. Fusulines of Leonard age from Sonora studied by C. O. Dunbar,(FOOTNOTE 29) have nothing in common with those from West Texas and the Las Delicias area. A western sea apparently invading southward from Arizona into Sonora, was separated by a land area from an eastern

FOOTNOTE 19. N. L. Taliaferro, "An Occurrence of Upper Cretaceous Sediments in Northern Sonora, Mexico," Jour. Geol., Vol. 41, No. 1 (January-February, 1933), pp. 16-18.

FOOTNOTE 20. R. E. King, "Geological Reconnaissance in Northern Sierra Madre Occidental of Mexico," Bull. Geol. Soc. America, Vol. 50, No. 11 (November, 1939), pp. 1641 and 1643.

FOOTNOTE 21. N. L. Taliaferro, op. cit., pp. 16 and 18.

FOOTNOTE 22. Ibid., p. 16.

FOOTNOTE 23. R. W. Imlay, "Paleogeographic Studies in Northeastern Sonora," Bull. Geol. Soc. America, Vol. 50, No. 11 (November, 1939), pp. 1730-32.

FOOTNOTE 24. G. H. Girty, "A New Area of Carboniferous Rocks in Mexico," Science, N. S., Vol. 63, No. 1628 (March, 1926), pp. 286-87.

FOOTNOTE 25. N. L. Taliaferro, op. cit., pp. 16, 18-19.

FOOTNOTE 26. R. W. Imlay, op. cit. (1939), pp. 1732-33.

FOOTNOTE 27. Charles Schuchert, Historical Geology of the Antillean-Caribbean Region, New York (1935), pp. 137-38.

FOOTNOTE 28. R. E. King, "Paleozoic Stratigraphy of Mexico," Proc. 8th Amer. Sci. Cong., Vol. IV (May 1940), pp. 112-14.

FOOTNOTE 29. C. O. Dunbar, "Permian Fusulines from Sonora," Bull. Geol. Soc. America, Vol. 50, No. 11 (November, 1939), pp. 1745-47.

End_Page 305------------------------------

Fig. 2. TRIASSIC CARNIAN MEXICO

End_Page 306------------------------------

sea in western Texas which extended southward into Coahuila and thence southeastward across Tamaulipas connecting with the Gulf of Mexico (Fig. 1). R. E. King (FOOTNOTE 30) who studied the Permian of West Texas and also of the Las Delicias area considers that the Las Delicias Permian was laid down in the southern continuation of the Texas Permian geosyncline. Marine Upper Triassic deposits are known in western Sonora (FOOTNOTE 31) and Zacatecas (Fig. 2).(FOOTNOTE 32) The faunas on opposite sides of the continent, although of the same age and having Mediterranean affinities, represent quite different facies. It seems unlikely that they had a direct marine connection. Probably an epeiric sea from the Gulf of Mexico invaded westward as far as Zacatecas for a short time during the Carnic tage while in Sonora an epi-continental sea from the west overlapped the margin of the present land area. The Carnic fauna in northwestern Sonora is closely related to the fauna which lived in California and Nevada at that time. Its Mediterranean element probably entered the Pacific by way of the Panama portal, migrated northward along the shoreline and into epeiric embayments such as that which invaded the Great Basin region. The Upper Triassic faunas of Sonora occur in limestone stringers in the lower part of the Barranca formation (FOOTNOTE 33) which is composed chiefly of fresh- and brackish-water clastic rocks, containing beds of coal and graphite. This eastward penetration of the sea marks the beginning of a marine portal in northern Sonora which may have connected the Pacific with the Mexican geosyncline at several stages of the Jurassic and Cretaceous.(FOOTNOTE 34)

By Lower Jurassic time the sea had withdrawn from Zacatecas and a new invasion had begun farther south in the Huasteca of Hidalgo, Puebla, and Vera Cruz (Fig. 3). In this downwarped area accumulated continental deposits with marine wedges from the Gulf of Mexico penetrating progressively farther west. A monograph prepared by C. Burckhardt on the paleontology and stratigraphy of this embayment is in press.(FOOTNOTE 35) In northern Sonora the western sea had developed a larger reentrant into a subsiding trough. Continental deposits of the Barranca formation continued to accumulate here, submerged from time to time, as repeated downwarping permitted the marine waters to invade eastward. Limestones

FOOTNOTE 30. R. E. King, "Permian of Southwestern Coahuila," Amer. Jour. Sci., 5th Ser., Vol. 27, No. 158 (February, 1934), p. 108.

FOOTNOTE 31. C. Burckhardt, "Etude synthetique sur le Mesozoique Mexicain," Mem. Soc. Paleont. Suisse, Vol. 49, No. 4 (1930), p. 6.

FOOTNOTE 32. C. Burckhardt, "La Faune Marine du Trias Superieur de Zacatecas," Bol. Inst. Geol. de Mexico, Nu. 21 (1905), pp. 1-41.

FOOTNOTE 33. R. E. King, "Geological Reconnaissance in Northern Sierra Madre Occidental of Mexico," Bull. Geol. Soc. America, Vol. 50, No. 11 (November, 1939), pp. 1645, 1655, 1657.

FOOTNOTE 34. L. B. Kellum, R. W. Imlay, and W. G. Kane, "Relation of Structure, Stratigraphy, and Igneous Activity to an Early Continental Margin," Evolution of the Coahuila Peninsula, Part I, Bull. Geol. Soc. America, Vol. 47, No. 7 (July, 1936), pp. 981-83.

See also: R. W. Imlay, "Possible Interoceanic Connections across Mexico during the Jurassic and Cretaceous Periods," Proc. 6th Pac. Cong. (1939), pp. 423-27.

FOOTNOTE 35. C. Burckhardt, "Etude synthetique sur le Mesozoique Mexicain," Mem. de la Soc. Paleont. Suisse, Vol. 49 (1930), p. 8.

End_Page 307------------------------------

Fig. 3. LOWER JURASSIC MEXICO

End_Page 308------------------------------

Fig. 4. UPPER JURASSIC MEXICO

End_Page 309------------------------------

Fig. 5. NEOCOMIAN LOWER CRETACEOUS MEXICO

End_Page 310------------------------------

bearing Lower Jurassic marine fossils are present in the upper part of the Barranca formation.(FOOTNOTE 36)

After Lower Jurassic time the seas spread rapidly from the area of their initial invasion of the Huasteca region. By Upper Jurassic they had filled the Mexican geosyncline and extended northward beyond the Rio Grande into West Texas at least as far as the Malone Mountains (Fig. 4). Their limit to the northwest is only vaguely known and further study may show that waters were present in the northern Sonoran portal at this time. From the Big Bend region of Texas a peninsula extended southward across western Coahuila and eastern Chihuahua as far as the Parras basin in southern Coahuila.(FOOTNOTE 37) Its mountainous topography is indicated by the coarse clastics contributed to the marginal seas adjoining it on three sides during Upper Jurassic and Lower Cretaceous (Neocomian) time. Northe st of the Coahuila Peninsula there is evidence of a smaller promontory projecting southeastward into the sea along the site of the Burro Mountains and their structural continuation, the Peyotes Hills and the Chancaca structure. The southeastern limit of this promontory is not known but it probably terminated before reaching the state line of Nuevo Leon where a well drilled by the Gulf Oil Company on the Escalera arch (southeast continuation of the Chancaca structure) in 1934 was reported to have encountered marine Jurassic strata from about 8,700 to 9,160 feet.(FOOTNOTE 38) A third promontory that may have influenced the position of the Upper Jurassic shoreline along the Rio Grande is indicated by data from the Ohio-Mexico Oil Company's Zambrano well, drilled in 1927 about 45 miles west f Villa Acuna, which started very near the top of the Georgetown limestone and went into granite wash at 3,200 feet. This well was located on a long prominent anticline that apparently is underlain by a granite ridge. It crosses the Rio Grande at a point 4 kilometers downstream from Jimenez, where its continuation to the southeast in Maverick County is known as the Chittim anticline. The shoreline of the Upper Cretaceous sea presumably passes around the nose of this feature and thence strikes northeast and north across central Texas to its known continuation in southern Arkansas. In southern Mexico the Mexican geosyncline was from time to time connected with the Pacific Ocean by the Balsas portal.(FOOTNOTE 39) The presence of this strait is indicated by the thick marine sections, and ste p folding in the mountainous belt of Michoacan, Jalisco and Colima north of the Sierra Madre del Sur which strikes east and west. This region has not been

FOOTNOTE 36. R. E. King, "Geological Reconnaissance in Northern Sierra Madre Occidental of Mexico," Bull. Geol. Soc. America, Vol. 50, No. 11 (November, 1939), pp. 1645, 1655, 1657, 1658.

E. Jaworski, "Eine Lias-Fauna aus Nordwest-Mexiko," Agh. Schweiz. Palaeont. Gesellschaft, Bd. 48, No. 4 (1929), pp. 1-12.

FOOTNOTE 37. L. B. Kellum, "Paleogeography of Parts of Border Province of Mexico Adjacent to West Texas," Bull. Amer. Assoc. Petrol. Geol., Vol. 20, No. 4 (April, 1936), pp. 418-22.

FOOTNOTE 38. F. K. G. Mullerried, "Neue Funde in Jura und Kreide Ost- und Sud-Mexicos," Eclogae Geologicae Helvetiae, Vol. 29, No. 2 (1936), p. 314.

FOOTNOTE 39. Charles Schuchert, Historical Geology of the Antillean-Caribbean Region, New York (1935), pp. 28, 150.

End_Page 311------------------------------

Fig. 6. ALBIAN LOWER CRETACEOUS MEXICO

End_Page 312------------------------------

studied in detail and the stages when this portal was open and closed are not definitely known.(FOOTNOTE 40)

During Lower Cretaceous time the seas continued to spread. Their encroachment caused the marginal landmasses to shrink in size. In the northwest the waters persisted beyond the Rio Grande into the Malone Mountain region of western Texas and extended into northeastern Sonora (Fig. 5). The Coahuila Peninsula was smaller in size than during the late Jurassic and probably the two promontories to the northeast of it were also smaller. The Balsas portal in the southwest appears to have been open during certain stages of the Neocomian. The Pacific waters spread eastward across western Sonora from the Gulf of California. By Albian (Lower Cretaceous) time marine waters covered most of Mexico (Fig. 6). A considerably shrunken landmass persisted in western Mexico surrounded by the sea. North of t the northern Sonoran portal was open connecting the Mexican geosynclinal sea with the Gulf of California. At the west lay the Gulf of California and the Pacific Ocean. To the southeast it was cut off by waters which filled the Balsas portal. The Coahuila Peninsula was first submerged in upper Aptian time and subsequently subsided so slowly that its surface remained at sea-level for a long period while lagoonal deposits accumulated to a thickness of 1,500 feet.(FOOTNOTE 41) By mid-Albian time it formed a submerged bank teeming with rudistids and foraminifera.(FOOTNOTE 42)

The seas continued to transgress northward from the Mexican geosyncline and the Gulf of Mexico and reached their maximum extent over the North American Continent in Turonian (Benton) time. Then they subsided during the remainder of the Upper Cretaceous except in downwarped embayments such as the Ojinaga basin of northeastern Chihuahua, the Muzquiz coal basin of northeastern Coahuila, the Parras basin of southern Coahuila, and the Cardenas area of San Luis Potosi. In the Parras basin accumulated 12,000 feet of shallow-water sandstones and shales during the Campanian stage alone.(FOOTNOTE 43) This basin must have subsided at least 20,000 feet after the close of the Lower Cretaceous when it was differentiated from the rest of the Mexican geosyncline south of the Coahuila Peninsula. Broad warping of the continent in Upper Cretaceous time marked the beginning of the Laramide revolution which reached its maximum intensity after Maestrichtian time and continued with decreasing vigor in the early Tertiary.

FOOTNOTE 40. R. W. Imlay, "Possible Interoceanic Connections across Mexico during the Jurassic and Cretaceous Periods," Proc. 6th Pac. Sci. Cong. (1939), pp. 423-27.

FOOTNOTE 41. W. A. Kelly, "Geology of the Mountains Bordering the Valleys of Acatita and Las Delicias," Evolution of the Coahuila Peninsula, Mexico, Part II, Bull. Geol. Soc. America, Vol. 47, No. 7 (July, 1936), pp. 1024-27.

FOOTNOTE 42. Ibid., pp. 1027-28.

FOOTNOTE 43. R. W. Imlay, "Stratigraphy and Paleontology of the Upper Cretaceous Beds along the Eastern Side of Laguna de Mayran, Coahuila, Mexico," Bull. Geol. Soc. America, Vol. 48, No. 12 (December 1937), p. 1800.

End_Page 313------------------------------

Fig. 7. LATE UPPER CRETACEOUS MEXICO

End_Page 314------------------------------

PETROLIFEROUS AREAS

The major oil fields of Mexico are situated on the Gulf Coastal Plain in the state of Vera Cruz between Tampico and Tuxpan. They belong to two groups: the Northern oil fields center along the Panuco River southwest of Tampico; and the South fields extend in an arc northward from the Tuxpan River for 51 miles to Dos Bocas on the coast. The formations penetrated by wells in these fields crop out in the coastal plain on the west or in the front range of the Sierra Madre Oriental. Most of the production in both areas comes from Lower Cretaceous limestones. In the northern fields the main producing formation is designated the Tamaulipas limestone (FOOTNOTE 44) from Sierra Tamaulipas which lies at the north and trends northward parallel with the coast. It is white, light gray, or brown in c lor and has a dense almost lithographic texture. Oil accumulation has taken place along joints, faults, or fracture zones crossing a broadly domed area. In the South fields the main producing formation is designated the El Abra limestone from the Sierra del Abra which is the front range of the Sierra Madre Oriental.(FOOTNOTE 45) It is coarsely crystalline white limestone made up largely of rudistid shells and the tests of miliolid foraminifera. The same facies forms the Sierra del Abra and is widely distributed over the Coahuila Peninsula in north-central Mexico. In the South fields it forms a buried fault block tilted east with oil accumulation along its higher western rim. The productive width is about 1 kilometer. Wells drilled a short distance west of the crest indicated a sharp drop off but wells east of the crest showed a relatively gentle slope of the El Abra limestone. The geologic history of this buried ridge is similar to that of the Sierra del Abra (FOOTNOTE 46) which forms a topographic ridge on the present land surface at the west side of the Tampico embayment. Both have an arcuate ground plan and lie on opposite sides of a depressed block with their steep convex side facing it. The El Abra limestone is clearly a reef limestone formed during Lower Cretaceous time on the shallow submarine banks of uplifted fault blocks. Between the two blocks a bathyal limestone facies was forming at the same time. It is the Tamaulipas limestone penetrated in the Northern oil fields.

STRATIGRAPHY AND STRUCTURE OF NORTHERN MEXICO

GEOLOGIC PROVINCES

Six physiographic and structural provinces present in northern Mexico are, with one exception, the southward continuation of provinces in the United States (Fig. 8).(FOOTNOTE 47) On the east, bordering the Gulf of Mexico, is the coastal plain underlain

FOOTNOTE 44. J. M. Muir, op. cit. (1936), pp. 23-36.

FOOTNOTE 45. Ibid., pp. 38-43.

FOOTNOTE 46. L. B. Kellum, "Similarity of Surface Geology in Front Range of Sierra Madre Oriental to Subsurface in Mexican South Fields," Bull. Amer. Assoc. Petrol. Geol., Vol. 14, No. 1 (January, 1930), pp. 73-91.

FOOTNOTE 47. N. M. Fenneman, "Physical Divisions of the United States." Map issued by the U. S. Geol. Survey.

E. Ordonez, "Principal Physiographic Provinces of Mexico," Bull. Amer. Assoc. Petrol. Geol., Vol. 20, No. 10 (October, 1936), pp. 1277-1307.

End_Page 315------------------------------

Fig. 8. PHYSIOGRAPHIC PROVINCES MEXICO

End_Page 316------------------------------

by gently folded Cretaceous and Cenozoic rocks. This is modified by isolated mountains or ranges of sedimentary and igneous rocks which rise above the general level of the plain to elevations locally of 4,000 feet or more. This relatively narrow province in Mexico is the southward continuation of both the Gulf Coastal Plain province and the Great Plains province in the United States. It is bordered on the west by the Sierra Madre Oriental, a belt of steeply folded Cretaceous limestone mountains which comprise the eastern margin of the Plateau Central province. The Sierra Madre Oriental and the Plateau Central together form the extension into Mexico of the Great Basin section of the Basin-and-Range province. The Plateau Central is made up largely of isolated mountain ranges of Cretaceo s and Jurassic rocks separated by broad intermontane, alluvium-covered plains. Tertiary lavas are locally present as hills and low ridges within the intermontane valleys. From the western margin of the Gulf Coastal Plain to the floor of the broad valleys on the Plateau Central there is a rise of about 3,500 feet. The Plateau Central province is bounded on the west by the Sierra Madre Occidental, a lofty mountain range of about 7,000 feet average elevation, composed of Tertiary lavas.(FOOTNOTE 48) Molten rocks poured out and buried the mountains and plains along the western side of the Plateau Central. Streams have since cut deep gorges through the nearly horizontal lavas, exposing the folded Mesozoic rocks beneath. At the northwest is the Sonoran Desert province extending from the state f Sonora into Arizona and southeastern California. Here erosion remnants of Paleozoic sedimentary and igneous rocks form island-like mountain ranges of the basin-and-range type, in the midst of great sandy wastes. This topography disappears toward the southeast beneath the lavas of the Sierra Madre which in mid-Tertiary time flowed into the southern part of the Sonoran Desert. West of it is the Gulf of California, a great down-dropped block which separates the peninsula of Lower California almost completely from the rest of Mexico. Lower California is a positive block comparable in structure and geologic history to the Sierra Nevada and Coast ranges. Intrusion of the batholiths, however, may have taken place in Lower Cretaceous time.(FOOTNOTE 49)

Intimate knowledge of the geologic history of northern Mexico has been gained by mapping numerous mountain ranges in Coahuila, Durango, Zacatecas, and Tamaulipas.

SAN CARLOS MOUNTAINS, TAMAULIPAS

Llanoria, the old landmass which occupied parts of Arkansas, Oklahoma, Louisiana, eastern Texas, and Mexico during most of the Paleozoic, became an active positive element in late Mississippian, Pennsylvanian, and Permian time.(FOOTNOTE 50) Subsequently, it foundered during the Mesozoic but all of the land was not submerged

FOOTNOTE 48. E. Ordonez, op. cit., pp. 1285-87.

FOOTNOTE 49. P. B. King, "Tectonics of Northern Mexico," Proc. 8th Amer. Sci. Cong., Vol. 4 (1940), p. 395.

FOOTNOTE 50. Charles Schuchert, op. cit. (1935), pp. 240-41.

C. Schuchert and C. O. Dunbar, Historical Geology, New York (1933), p. 280.

End_Page 317------------------------------

simultaneously. By Upper Jurassic time and possibly earlier, that part of Llanoria which extended into eastern Mexico had sunk beneath the sea. W. H. Hegwein discovered Upper Jurassic and Neocomian fossils in the Tamaulipas limestone of the San Carlos Mountains.(FOOTNOTE 51) Nevertheless, the influence of Llanoria is seen in the structure and lithology of Cretaceous and Jurassic sediments of the Gulf Coastal Plain. The Tamaulipas limestone appears to have been deposited in deep water, far from a source of clastic sediments, but not under geosynclinal conditions. In the coastal plain it did not undergo the intense deformation during the Laramide revolution which characterized the area farther west in the Sierra Madre Oriental and in part of the Plateau Central. Apparently the old land f Llanoria, although deeply submerged, acted as a buttress resisting the horizontal compression which crumpled the true geosynclines marginal to it.

An example of the stratigraphic and structural conditions which developed on Llanoria after its submergence is seen in the San Carlos Mountains in west-central Tamaulipas.(FOOTNOTE 52) It is an isolated range rising out of the coastal plain about midway between the Sierra Madre front and the Gulf Coast. It is at the north end of the Sierra Tamaulipas and separated from it by a broad saddle known as the Mesa de Solis. Mapping of the San Carlos Mountains was undertaken originally in connection with the oil possibilities of northeastern Mexico. The range is in the transition zone between the Tampico embayment and the Rio Grande embayment and its study has thrown some light on the problems of both areas.

The structure of the San Carlos Mountains is primarily a broad, low dome with two distinct types of secondary folding superimposed on it. The first is a series of gentle, parallel flexures trending eastward across the entire range. The second comprises a group of laccolithic intrusions of varying size which have domed the Cretaceous limestones in many parts of the mountains. Dikes radiate from the larger of these intrusions even beyond the margins of the range. That the folding of the anticlinal flexures preceded the igneous intrusions is indicated by the fact that the axes are not deflected as they approach the intrusions but head directly into them and terminate abruptly at the steeply tilted limestones of the domes.

VARIATION IN COLOR OF TAMAULIPAS LIMESTONE

The Tamaulipas limestone in the northern oil fields near Tampico, and also in the Sierra Tamaulipas, north of there, has a white to light gray or brown color. In the Sierra Madre Oriental, however, it is black or dark blue. This color change is thought to be of some significance since no oil has ever been found in the black or dark blue facies.

The San Carlos Mountains are much wider than the Sierra Tamaulipas and

FOOTNOTE 51. Carlos Burckhardt, op. cit. (1930), p. 266.

FOOTNOTE 52. L. B. Kellum et al., "The Geology and Biology of the San Carlos Mountains, Tamaulipas, Mexico," Univ. Michigan Studies, Sci. Ser., Vol. 12 (1937), 341 pp.

End_Page 318------------------------------

therefore afford an opportunity to study outcrops of the Tamaulipas limestone in a wider area east and west than is possible elsewhere east of the Sierra Madre front. Also they extend farther west and approach closer to the outcrops of Tamaulipas limestone in the Sierra Madre. It was observed that the limestone on the eastern side of the San Carlos Mountains is the same white or light gray dense facies that occurs in the Sierra Tamaulipas but that on the western side it is black or dark blue similar to the facies in the Sierra Madre Oriental. As one goes from east to west across the range it is noted that the white limestone becomes splotched with black color which increases in proportion westward until the limestone is all black.

On the eastern side wherever an igneous dike cuts the white limestone, the color is changed to black in a narrow zone immediately adjacent to the face of the dike. An inch or less from it the limestone is splotched black and white and a few inches away is entirely white. Also around the nephelite syenite intrusion at El Patado the limestone is black near the igneous contact and becomes white a short distance away from it. In the western part of the range where black limestone predominates, igneous activity is much more widespread. This suggests that the dark color of the limestone is the result of igneous metamorphism.

In the Sierra Madre Oriental, however, 40 miles west of the San Carlos Mountains, there is essentially no igneous activity and hence the dark color of the Tamaulipas limestone of that area can not be due to igneous metamorphism. It is, however, correlated with another striking geologic difference between that range and the Sierra Tamaulipas. In the Sierra Madre Oriental the limestone is intensely folded into sharp anticlines and synclines, whereas in the Sierra Tamaulipas it forms a broad, gently uplifted arch. This contrast in structure as well as in color suggests that the dark color of the Tamaulipas limestone in the Sierra Madre Oriental may be the result of regional metamorphism.

Dark color in limestone and shales is usually attributed to the presence of organic matter if dark colored minerals are not present to account for it. This is undoubtedly true but there is some evidence to suggest that the dark color may be due to the chemical condition of the organic matter rather than to its abundance. In El Abra quarry of the Sierra del Abra,(FOOTNOTE 53) west of Tampico, white crystalline limestone is very porous due to the abundance of rudistid fossils and to geodes. When freshly broken with the hammer a volatile, colorless oil runs out of the cavities and pore spaces. Here, therefore, the limestone contains an abundance of hydrocarbons but its color is white. Perhaps the heat of igneous metamorphism, or that generated by regional metamorphism, may cause a change in the chemical composition of the hydrocarbons resulting in the deposition of pure carbon or of some black hydrocarbon.

MAJOR ZONE OF CROSS-FOLDING

Regional studies have shown that the San Carlos Mountains with their eastward-trending

FOOTNOTE 53. J. M. Muir, op. cit., p. 38.

End_Page 319------------------------------

flexures are situated in a major zone of east-west folding traced for 200 miles from central Tamaulipas across Nuevo Leon, southern Coahuila, and northern Zacatecas to eastern Durango. This zone is about 25 miles wide, extends to the approximate center of the continent, and is a conspicuous feature in the structural plan of Mexico. Its origin and geologic history are closely related to the Coahuila Peninsula, another major structural element, lying north of it.

At the west end of this great zone of cross-folding is the Sierra de Jimulco,(FOOTNOTE 54) a high and rugged mountain knot. Highly fossiliferous marine Upper Jurassic and Cretaceous limestones, shales and sandstones are intensely folded into isoclinal folds whose axes incline at a steep angle to the south. Within this range the belt of east-west cross-folding passes into the normal northwest Rocky Mountain trend by a series of sharp bends, that is, horizontal buckling of the axes, which serve to accommodate the great mass of rock involved on the inside of the angle.

MEXICAN GEOSYNCLINE

The geologic history of the geosyncline south of the Coahuila Peninsula has been studied in numerous other mountain ranges of eastern Durango, southern Coahuila and northern Zacatecas.(FOOTNOTE 55) There we find continental Triassic (?) redbeds overlain by thick sections of marine Upper Jurassic and Cretaceous sediments intensely folded into steep anticlines and synclines, many of which are isoclinal. Locally fan folds are present and elsewhere thrust faulting has been recognized locally.

FOOTNOTE 54. L. B. Kellum, "Reconnaissance Studies in the Sierra de Jimulco, Mexico," Bull. Geol. Soc. America, Vol. 43, No. 3 (September, 1932), pp. 541-64.

FOOTNOTE 55. Carlos Burckhardt, "La Faune Jurassique de Mazapil, avec un appendice sur les Fossiles du Cretacique inferieur," Bol. Inst. Geol. de Mexico, Nu. 23 (1906), pp. 1-40.

Carlos Burckhardt, "Geologie de la Sierra de Concepcion del Oro (Mexico)," 10th Intern. Geol. Cong., Mexico, Guidebook 24 (1906), pp. 1-24.

Carlos Burckhardt, "Geologie de la Sierra de Mazapil et Santa Rosa (Mexico)," ibid., Guidebook 26, pp. 1-40.

Carlos Burckhardt, "Estudio geologico de la region de San Pedro del Gallo, Durango," Parergones Inst. Geol. Mexico, Tomo III, No. 6 (1910), pp. 307-57.

Carlos Burckhardt, "Faunes Jurassiques et Cretaciques de San Pedro del Gallo (Etat de Durango, Mexico)," Bol. Inst. Geol. de Mexico, Nu. 29 (1912), pp. 1-260.

Carlos Burckhardt, "Faunas Jurasicas de Symon (Zacatecas) y Faunas Cretacicas de Zumpango del Rio (Guerrero)," Bol. Inst. Geol. de Mexico, Nu. 33 (1919), pp. 1-135.

Emil Bose, "Algunas Faunas Cretacicas de Zacatecas, Durango y Guerrero," Bol. Soc. Geol. Mexico, Nu. 42 (1923), pp. 1-219.

Carlos Burckhardt, "Faunas del Aptiano de Nazas (Durango)," Bol. Inst. Geol. de Mexico, Nu. 45 (1925), pp. 1-71.

R. W. Imlay, "Geology of the Western Part of the Sierra de Parras," Evolution of the Coahuila Peninsula, Mexico, Part IV, Bull. Geol. Soc. America, Vol. 47, No. 7 (July, 1936), pp. 1091-1152.

L. B. Kellum, "Geology of the Mountains West of the Laguna District," Evolution of the Coahuila Peninsula, Mexico, Part III, ibid., pp. 1039-90.

Q. D. Singewald, "Igneous Phenomena and Geologic Structure near Mapimi," Evolution of the Coahuila Peninsula, Mexico, Part V, ibid., pp. 1153-76.

R. W. Imlay, "Geology of the Middle Part of the Sierra de Parras, Coahuila, Mexico," ibid., Vol. 48, No. 5 (May, 1937), pp. 587-630.

T. S. Jones, "Geology of Sierra de la Pena and Paleontology of the Indidura Formation, Coahuila, Mexico," ibid., Vol. 49, No. 1 (January, 1938), pp. 69-150.

R. W. Imlay, "Studies of the Mexican Geosyncline," ibid., Vol. 49, No. 11 (November, 1938), pp. 1651-94.

End_Page 320------------------------------

COAHUILA PENINSULA

Stratigraphic and structural conditions on the Coahuila Peninsula have been studied in the Las Delicias area (FOOTNOTE 56) and in the Sierra de Tlahualilo (FOOTNOTE 57) north of the Parras basin in western Coahuila. Here we find a basement of Permian sediments and lavas intensely folded and intruded by granite.(FOOTNOTE 58) Overlying the basement rocks unconformably Upper Aptian limestones are nearly horizontal. Above them is a section of interbedded gypsum and dolomite about 1,500 feet thick overlain by 500 feet of rudistid reef limestones of Albian age.

The gypsiferous deposits are believed to have accumulated in marginal lagoons which existed over the Coahuila Peninsula during early Albian time. The basement of the peninsula gradually subsided but its surface remained approximately at sea-level due to the deposition of evaporites in the lagoons. Periodically the sea swept across it enabling marine life to flourish temporarily and depositing calcareous sediments which gave rise to layers of fossiliferous dolomite interbedded with the gypsum. At the same time in the shallow waters surrounding the peninsula, where normal marine circulation prevailed, rudistids flourished in great profusion on the submarine banks. The accumulation of their shells formed

Click to view image in GIF format. Fig. 9. [Grey Scale] View S. 7° E. along crest of Sierra de Tlahualilo, Durango. This mature topography is more than 1,000 feet above level of broad intermontane valleys that surround range.

FOOTNOTE 56. W. A. Kelly, "Geology of the Mountains Bordering the Valleys of Acatila and Las Delicias," Evolution of the Coahuila Peninsula, Mexico, Part II, Bull. Geol. Soc. America, Vol. 47, No. 7 (July, 1936), pp. 1009-38.

FOOTNOTE 57. W. I. Robinson and L. B. Kellum, "Geology of Sierra de Tlahualilo Durango," Bull. Geol. Soc. America, Vol. 52, Pt. 2 (December, 1941), pp. 1930-31.

FOOTNOTE 58. R. E. King, "The Permian of Southwestern Coahuila, Mexico," Amer. Jour. Sci., 5th Ser., Vol. 27 (February, 1934), pp. 108-11.

End_Page 321------------------------------

the Aurora limestone. This bioherm rim was no doubt largely the cause for the maintenance of lagoonal conditions over the peninsula.

In mid-Albian time subsidence became more rapid and permitted the sea waters to circulate freely over the entire peninsula, thus causing the rudistid reefs to migrate inward from its margins. Myriads of foraminifera also inhabited these shallow banks and their tests contributed appreciably to the formation of the limestones.(FOOTNOTE 59)

To-day, in structurally downwarped areas on the peninsula, we find above the Aurora reef limestones remnants of the Indidura formation of late Lower and early Upper Cretaceous age. Its lithology, thickness, and fauna are very distinctive and are characteristic of environmental conditions which prevailed over the peninsula. The thin beds of buff platy limestone and shale have a total thickness of only about 100 feet in the type area.(FOOTNOTE 60) They are highly fossiliferous with a near-shore molluscan fauna in which pelecypods and echinoids are dominant.(FOOTNOTE 61) The well known forms of Gryphaea washitaensis, Hemiaster calvani, and Exogyra arietina, and others in the lower part indicate its Washita age, while Inoceramus labiatus in the upper part indicates beds equivalent to the agle Ford formation of Texas. These strata are in great contrast to the sediments which were being laid down at the same time in the deeper waters south of the peninsula. Along

Click to view image in GIF format. Fig. 10. [Grey Scale] View across central part of Sierro del Rosario Durango. Youthful topography and intense folding are characteristic of geosynclinal belt.

FOOTNOTE 59. L. B. Kellum, "Miliolid Limestone in North-Central Mexico," Proc. Geol. Soc. America, 1936 (June, 1937), pp. 82-83 (abstract).

FOOTNOTE 60. W. A. Kelly, op. cit., pp. 1028-29.

FOOTNOTE 61. T. S. Jones, op. cit., pp. 85-86.

End_Page 322------------------------------

the northern part of Sierra de Parras, strata referred to the Indidura formation are more than 2,500 feet thick.(FOOTNOTE 62) The section is dominantly gray shales interbedded with black limestone in thin ledges and contains few fossils. It has been subdivided into five members based chiefly on the relative proportion of limestone and shale present in different parts of the section. The environment of deposition of these beds south of the Coahuila Peninsula is so different from that in the type area of the Indidura formation that it would be useful to designate them by a different name.

CRITERIA FOR LOCATING BURIED PLATFORMS

The entire Cretaceous section in the area of the Coahuila Peninsula shows the influence of the underlying massif on sedimentation throughout a long period of geologic time. It indicates that facies of deposition may be used as a guide in locating buried positive elements in the subsurface where they would tend to localize the accumulation of oil.

Likewise, the influence of a buried massif on the structure of overlying strata is clearly demonstrated here by the contrast between the relatively simple warping of Lower Cretaceous rocks on the Coahuila Peninsula and the tight asymmetrical folding and overthrusting in the area of the surrounding geosyncline. This general relationship in the regional structure is another criterion for recognition of a positive block in the subsurface.

The physiography of the mountain ranges is an expression of the lithologic succession and geologic structure comprising them. Regionally it reveals the same contrast in underlying geology that exists between the Coahuila Peninsula and the geosyncline. Mountains in the peninsular area are dissected uplands with a mature, rolling topography over their broad summits (Fig. 9). This gives way abruptly at their margins to a youthful topography as the relief drops away rapidly to the level of the alluvium-filled, intermontane valleys. In the geosynclinal area the mountains are in topographic youth at their summits as well as on the flanks (Fig. 10).

CONCLUSIONS

This regional investigation of the geologic history of northern Mexico has demonstrated at least six periods of igneous activity since the beginning of Carboniferous time. During the same interval three periods of major diastrophism are recognized. In Coahuila where a large massif, once deeply buried, is now partly exposed on the surface, three types of criteria (lithology, structure, and physiography) would have revealed its presence in the subsurface even if the basement rocks were not exposed. In applying them to other areas where diastrophism has played a less important role due allowance must be made for degrees

FOOTNOTE 62. R. W. Imlay, "Geology of the Western Part of the Sierra de Parras," Evolution of the Coahuila Peninsula, Mexico, Part IV, Bull. Geol. Soc. America, Vol. 47, No. 7 (July, 1936), pp. 1126-32.

End_Page 323------------------------------

of intensity of folding and for various environmental conditions affecting the lithology.

Where and how are we to apply these criteria to find oil? Not on the Coahuila Peninsula because there practically all of the Mesozoic section is exposed on the surface; the Paleozoic section has some possibilities but it had undergone intense deformation and peneplanation before the Cretaceous was laid down on top of it. We would not expect to find oil on the Plateau Central and Sierra Madre Oriental which are the continuation of the Basin-and-Range province of the United States, for there, too, the Mesozoic sections are exposed, and faulting has not revealed any oil seepages. The Sierra Madre Occidental has little prospect for oil because the lava flows are too thick in most places, and where erosion has cut through them, the Paleozoic and Mesozoic strata exposed beneath are deformed into mountain folds like those on the Plateau Central and the Sonoran Desert. The Sonoran Desert with its metamorphosed, deeply dissected Paleozoic rocks and its continental or igneous Mesozoic and Tertiary rocks is unpromising for oil production. The peninsula of Lower California may have very limited oil possibilities in the areas of marine Tertiary and Upper Cretaceous strata, but it is largely made up of Tertiary volcanics with a basement of metamorphics and intrusive igneous rocks.

The areas where great platforms, comparable with the Coahuila Peninsula, are likely to produce oil and gas in the future are the structurally downwarped provinces of the central United States and along the margins of the continent. The Central Lowland and Great Plains provinces of the United States, the California trough and other structural depressions of the Pacific Coast, and especially the Gulf Coastal Plain of the United States and Mexico undoubtedly contain ancient landmasses not yet discovered beneath younger sediments.

In northern Mexico east of Sierra Tamaulipas, between the San Carlos Mountains and the Rio Grande, or in the Rio Grande embayment proper we may expect to find other great fault blocks comparable with that of the Mexican South fields, on which reef organisms have lived and built their limestone bioherms. North of the Rio Grande in the Coastal Plain of Texas, Louisiana, Mississippi, and Alabama, as well as in eastern Mexico, there may be other positive blocks of the same nature and origin as the Sabine uplift. It has been contended that the enormous thickness of Tertiary sediments known to be present in the coastal plain near the present Gulf Coast would preclude the possibility of reaching the Lower Cretaceous formations with the drill. This, however, is not necessarily the case becaus the presence of a platform of the Coahuila type is a positive element which resists subsidence and sediments can only accumulate over it to the extent that it does subside below sea-level. The great thickness of sediments in the coastal plain has accumulated in the surrounding negative areas, while a relatively thin section was built on the platforms. Furthermore the profusion of benthonic life necessary to build highly organic reefs may have lived in the clear waters on the shallow submarine banks at any time during the Upper Cretaceous or Tertiary so

End_Page 324------------------------------

that it would not be necessary to seek the El Abra limestone as the only prospective reservoir. In a study of submarine topography in relation to sedimentation off the coast of California, Revelle and Shepard (FOOTNOTE 63) observed that the banks and ridges, at whatever depth or distance from the shore, were receiving deposits of sand or of calcareous sediment or else had a rock bottom and that their sediments were notably coarser than those of the depressions and troughs. We may thus expect suitable sand reservoirs in the stratigraphic section above the buried platforms even if reefs of organic limestone are not present.

As shown in most of the large buried platforms already studied, they are reflected in the lithology and structure of overlying strata and may also have some topographic expression. Some of them may be located by geophysical methods; others may be discovered by stratigraphic methods. Systematic exploration by the stratigraphic methods will include the comparison of well and outcrop sections in regular profiles across the basins, with the principle in mind that the section will change appreciably and consistently over a buried platform. There should be close scrutiny of all the available surface and subsurface structural data over each of the basins as a whole, with the thought that any recognizable contrast in the regional structure may reveal the presence of an underlying massif.

FOOTNOTE 63. R. Revelle and F. P. Shepard, "Sediments off the California Coast," Recent Marine Sediments (Amer. Assoc. Petrol. Geol., 1939), p. 248.

End_of_Article - Last_Page 325------------

Acknowledgments:

(2) Director, Museum of Paleontology, University of Michigan.

Copyright 1997 American Association of Petroleum Geologists

Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Watermarked PDF Document: $14
Open PDF Document: $24

AAPG Member?

Please login with your Member username and password.

Members of AAPG receive access to the full AAPG Bulletin Archives as part of their membership. For more information, contact the AAPG Membership Department at [email protected].