Structural traverse across the Sierra Madre Oriental fold-thrust belt in east-central : Alternative interpretation and reply

Alternative interpretation

JOSE F. LONGORIA The University of at Dallas, Programs in Geosciences, Box 830688, Richardson, Texas 75083-0688

INTRODUCTION

The of Mexico is enigmatic mainly because of the lack of For example, in his sections a and c, the lithic package overlying the field work addressing basic aspects of geological research, including re- Las Trancas is referred to as the " Formation" [sic !]. On the gional stratigraphy and paleogeographic analysis, which are fundamental basis of pioneering studies by Segerstrom (1956,1961a, 1961b, 1962), as to unraveling the structure and tectonics of the Mexican Cordillera. In my well as my own regional studies (Longoria, 1975,1984a, 1984b), there are opinion, it is necessary to have a proper stratigraphic framework before the no outcrops of Tamaulipas Limestone to the west or the east of the "El structure of the Sierra Madre Oriental can be correctly balanced. Although Doctor bank"; instead, a near time equivalent of it, the Santuario, was Suter's paper (1987) represents an excellent attempt to display the geologic defined by Segerstrom in 1961 to include those carbonate rocks. Substitu- complexity of part of the Sierra Madre Oriental, there are basic strati- tion of the Tamaulipas for the Santuario should be documented in com- graphic and structural aspects that deserve further treatment because they parative field studies of both stratotypes and should follow the precepts may yield an alternative interpretation to Suter's structural analysis, as established by the North American Stratigraphic Code (North American well as to his attempt to extrapolate the surface features to the basement. Commission on Stratigraphic Nomenclature, 1983). Distinguishing be- In his paper, Suter (1987), in addition to describing the structures of tween coeval lithic units should not be viewed as a mere nomenclatural an area in east-central Mexico, attempted to construct balanced cross procedure; rather, more significantly, their separation has direct influence sections and area-balanced sections using the technique originally de- on the paleogeographic reconstruction of the under study, which scribed by Dahlstrom (1969) and later developed by Suppe (1983,1985). according to Dahlstrom (1969, p. 753), is the ultimate check of a balanced As presented by Dahlstrom (1969), balanced cross sections are success- cross section in deformed terranes. It is my opinion that if the Tamaulipas fully achieved in areas where sufficient stratigraphic documentation is Limestone, originally described from northeastern Mexico, is demon- available, including (1) a standard lithostratigraphy, (2) accurate thickness strated to be present on top of Las Trancas at any locality in east-central of formations, (3) facies relationships, and (4) temporal relationships of the Mexico, its occurrence represents a major tectonic juxtaposition that must units. Knowledge of the Mexican Cordillera, however, is still in its infancy be considered in the balance of the Sierra Madre Oriental. and does not allow the application of quantified geometric methods be- The assignment of the pelitic flysch to the Agua Nueva and San cause most of the aforementioned data are not available. An unbalanced Felipe Formations of his section e contradicts lithostratigraphic schemes of stratigraphy may have been used to obtain balanced cross sections. east and east-central Mexico previously established by Wilson and others (1955), Bodenlos (1956), Segerstrom (1961, 1962), Bonet (1956a), and STRATIGRAPHY Longoria (1984b) and requires lithostratigraphic documentation. The lith- ic packages he referred to as the "San Felipe" (for example on p. 260, first Lithostratigraphy column, bottom paragraph: "tectonic contact of the Chapulhuacan Forma- tion with the San Felipe beds" [nc!]) are related to the as described The lithic units identified by Suter (his Fig. 2, 1987) as Las Trancas, by Heim (1940). Suter, however, repeatedly used the base of the Agua Pimienta, Chapulhuacan, Tamaulipas, EI Doctor, El Abra, Agua Nueva, Nueva as a reference horizon to estimate the shortening of his balanced and San Felipe do not correspond to those formations. These units are of segments between the Maguey-2A and the lower Xilitla thrust (see primary importance in Suter's analysis because they were used as reference p. 260), thereby adding uncertainty to his balanced cross section because horizons in constructing the balanced cross sections of the region. The no lithologies of the Agua Nueva are seen in this region. Suter's reference lithic features described by Suter, however, differ radically from those in to the San Felipe (p. 254) as composed of "pelagic limestone, platform- the original definitions. derived carbonate exoclasts, shale, sandstone, and graywackes of a wide compositional range" reflects his misuse of lithostratigraphic terms, as the above-mentioned lithic features do not characterize the San Felipe. For a characterization of the San Felipe, the reader is referred to Pessagno (1969, p. 36-42). Although this lithic package is coeval with the San Felipe, it The article discussed appeared in the Bulletin, v. 98, p. 249-264. belongs in a different paleogeographic domain (Longoria, 1984b).

Geological Society of America Bulletin, v. 102, p. 261-266, 2 figs., February 1990.

261

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Biochronology central Mexico is that synsedimentary thickness variations of the Pimienta Formation, from about 55 m (Ahuacatlan area) to more than 800 m On page 249, third column, fourth paragraph, a biochronologic (Cuetzalan area), do occur, but thickness variation is independent of tec- datum is displayed by Suter; he states, "the exposed part of Las Trancas is tonic deformation. The question is, how does Suter distinguish between Kimmeridgian to Barremian age (Carrillo-Martínez and Suter, 1982)," differences in original thickness and tectonic thinning of the Pimienta? giving the impression that the reader will find biostratigraphic information Even if formal aspects of stratigraphy are put aside, the simple analy- to support that chronostratigraphic assignment of Las Trancas. In Carrillo sis of the vertical succession, as illustrated by Suter in his Figure 2, gives and Suter (1982, p. 3), however, one finds only citations of the original evidence of abrupt changes in sedimentary facies, implying obvious con- work by Segerstrom (1961b) and reference to unpublished personal com- trasts in sedimentary environments for which the superposition likely indi- munications. The chronostratigraphic position of Las Trancas is thus not cates the occurrence of unconformities, and thickness variations as documented beyond the original assignment by Segerstrom in 1961. Con- recorded by López Ramos (1980, p. 331-343). The deposition of the sequently, Suter's stratigraphic columns need to be documented in terms vertical succession, represented in his section d by the Pimienta, El Abra, not only of lithic characters but also of their chronostratigraphic position. and Soyatal, reflects dynamic changes in the stratigraphic record with The only biochronologic information in Suter's paper is his reference consequent thickness variations. This type of vertical relationship, that is, to the presence of a planktonic foraminifer. Interestingly enough, he wrote Las Trancas/Tamaulipas and Pimienta/El Abra contacts, complicates the (p. 253, first column), "platform-carbonate production, however, probably construction of balanced cross sections (compare with Dahlstrom, 1969, lasted until early Campanian near the present site of Highway 120, where p. 754) because they represent abrupt paleobathymetric fluctuations, from the lower part of the Soyatal Formation corresponds to the Globotruncana bathyal in Pimienta to inner neritic in El Abra. elevata planktonic foraminiferal zone sensu stricto (Suter, 1984)." In his 1984 paper, no reference is given to this important biochronologic finding STRUCTURE that allowed him to postulate the continuous sedimentation of the succes- sion represented in his 1987 section d on page 251. Thrust Faults The chronostratigraphic position of the well-known El Abra and El Doctor Formations has been treated loosely by Suter, who regarded the Very little or no stratigraphic field documentation was actually pro- first as Barremian-Coniacian and the second as Aptian-Cenomanian. vided by Suter to establish the existence of ten thrust faults beyond their There are no published records of Barremian, Turonian, and Coniacian assumed geometric attributes. It is impossible to review in this discussion fossils in the El Abra in spite of the fact that detailed microfacies and all the thrust faults, but a discussion of the Xilitla and Frontal thrusts will micropaleontologic investigations have been carried out by Petróleos Mex- provide some insight into the controversy involved in the recognition of icanos (Pemex) geologists (Carrillo-Bravo, 1971). Furthermore, Suter's these thrust faults in the fold-thrust belt of the Mexican Cordillera in statement (p. 252), "where the Valle de Guadalupe-1 well was drilled, east-central Mexico platform deposits had begun to accumulate in the Barremian (Carrillo- The Xilitla Thrust. The Xilitla thrust, together with the "Frontal Bravo, 1971)," leads one to believe that Carrillo-Bravo established the thrust," was one of the first two thrust faults postulated in the literature of Barremian position of the El Abra. Contrary to that, Carrillo-Bravo (1971, east-central Mexico by Heim more than 40 yr ago (Heim, 1926,1940). It p. 34, 36,40) clearly established its Albian-Cenomanian position. has a complicated history in the literature, which is summarized as follows: (1) In its original definition, "Xilitla thrust" implies the tectonic contact Unconformities between the lower Xilitla (above) and the San Felipe (below). (2) Later work by Bonet (1956) mapped the Xilitla thrust as the tectonic contact Suter's inadequate biochronologic control of the sections leads to between the Pimienta (above) and the Xilitla (below), exposed on High- another fundamental aspect of sedimentary geology, that is, the existence way 120, about 2 km west of Xilitlilla. (3) According to Suter (1987, of breaks in the stratigraphic succession. In 1926, pioneering stratigraphic Fig. 11), the Xilitla thrust is defined by the tectonic contact between the work by Muir in east Mexico demonstrated the existence of a hiatus in the San Felipe (below) and the Tamaulipas/Tamabra (above). (4) In his stratigraphic record of this region whereby El Abra is unconformably previous Geological Society of America paper (1984, p. 1389, Figs. 4 and overlain by Campanian terrigenous shales of the San Felipe. Recent strati- 5), Suter had recognized the units involved at the fault contact as the graphic studies by López Ocampo and others (1986) in the states of Chapulhuacan Formation (above) and the San Felipe (below). (5) Suter Queretaro and have shown two unconformities in Las Trancas of (1980) had also identified the "upper" Tamaulipas (above) and the San the Sierra Madre Oriental in east-central Mexico corresponding to the Felipe (below) as the formations involved at the fault contact. In his three upper Tithonian and Aptian. These breaks may indeed correspond to papers, Suter not only assigned different lithic units at the fault contact of tectonic events described by Longoria (1984a, 1984b) from east-central the same outcrop (Peña de San Antonio) but also failed in giving any lithic and and should be considered in balancing the cross description of the units involved in the Xilitla thrust, as well as the features sections of the Sierra Madre Oriental. that allowed him to radically change the assignment of lithic units, making it impossible for other workers to attempt any lithic correlation between Sedimentary Environments the packages (formations) he identified and those formations previously established in the region. Suter assumed a "layer cake" stratigraphy in his structural traverse of On the basis of my regional stratigraphic studies (Longoria, 1984b), the Sierra Madre, ignoring the thickness variations and facies changes. On the units exposed at Peña de San Antonio are Chapulhuacan, Ahuacatlan, page 260, first column, second paragraph, he wrote, "the Pimienta beds El Doctor, and Xilitla; however, more than 90% of the surface is covered were, in the latter case, thinned in the limbs from whence the material by soil and heavily vegetated (Fig. 1). A lot of room is left for speculation flowed into the fold cores, which resulted in a wide range of thicknesses on the internal structure and geometry of this range. It is likely that the from 150 to 750 m for this formation." My experience in dealing with field Peña de San Antonio range is the flattened core of a large box anticline stratigraphic work of Jurassic units in the Mexican Cordillera of east- developed in response to a blind thrust. This blind thrust corresponds to

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N

Figure 1. Cross section of Peña de San Antonio range, showing the exposed lithic packages and their topographic expression. The lack of strati- graphic data, such as thickness and attitude of lithic packages, plus covered intervals hinder geometric reconstruction of the structure and the kinematics of deformation. Arrow indicates covered the location of the Xilitla thrust according to Suter. SCALE Xllitlilla (Meters)

covered 500

Bonet's (1956) original thrust, that is, the tectonic contact between Pi- the tectonic contacts. Moreover, the geological features observed in the mienta and Xilitla, which is exposed at lower topographic at km traverse along the Moctezuma River revealed the existence of another 255 of Highway 120, west of Xilitlilla, and about 3 km from the town of thrust, herein referred to as the "Xaltipa thrust," to the west of the Frontal San Antonio. thrust and east of the Agua Zarca thrust. The mathematical calculations Frontal Thrust. The history of the Frontal thrust is summarized as given by Suter on the areal shortening of the segment between the Agua follows: (1) Heim (1940, p. 343) first observed the tectonic contact be- Zarca and border (Frontal) faults are immaterial because he failed in tween the Tenestipa (the Chapulhuacan of Bodenlos, 1956) and the Upper recognizing other thrusts, such as the Xaltipa behind the Frontal thrust, Cretaceous, regarding it as local thrusting. (2) Later, in 1956, Bodenlos that change the balanced structural sections. (1956, p. 212) demonstrated that this thrust is expressed by the overriding of the Chapulhuacan on the Xilitla. (3) Suter (1987, p. 260) has wrongly Extrapolation of the Surface Geometry down to the Basement considered that the Frontal thrust involves the tectonic contact between the Chapulhuacan (above) and the San Felipe (below). Furthermore, he Suter's extrapolation of the geometry of the structure down to the calculated a translational component due to the Frontal thrust of 1,950 m. basement is not based on observed, surface features and inherits the lack A structural traverse along the Moctezuma River (Fig. 2) between the of stratigraphic control of his surface geology. For example, between the towns of Taman, type locality of the Taman Formation, and Vega Larga Xilitla thrust and the Maguey-2A and Valle de Guadalupe-1 wells where and parallel to Bodenlos' cross section revealed the structural relations of Suter (p. 260) calculated the distance between the detachment fault and the Jurassic and Cretaceous succession. This profile (Fig. 2) shows the the stratigraphic level of the reference horizon (the Agua Nueva Forma- first-order structures of the succession, which if compared with Suter's tion), he concluded that his calculated depth to detachment of 19,286 m is section C-C (Fig. 5), suggest that his "balanced structural sections" in "totally inconsistent with the stratigraphic thickness of the sedimentary addition to being theoretical (speculative) are not compatible with the sequence below the reference bed, which measures only 1,048 m in the exposed structure. Maguey-2A well but at least 1,500 m in the Tancuilin Canyon southwest Suter's quantified shortening along the thrusts needs to be re- of the Xilitla thrust" (p. 261). Consequently, he concluded that a "blind examined in light of the lithostratigraphic units he identified as involved at thrust" above the sole fault must occur in the Maguey-2A well. Lopez-

E3 EE51 ESS EE53 M E33 Santiago Tamán Pimienta Chapulhuacan Ahuacatlán Xilitla

Figure 2. Geologic profile along the Moctezuma River from Taman to Vega Larga, showing the stratigraphic units observed and their structure. (1) Xaltipa thrust, (2) Frontal thrust.

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Ramos (1972) showed, however, that the well penetrated an uninterrupted Carrillo-Bravo, J., 1971, La Plataforma Valles-San Luis Potosí: Asociación Mexicana de Geoiógos Petroleros Boletín, v. 22, p. 1-102. Cretaceous-Jurassic section. There is further controversy over Suter's pro- Carrillo, M., and Suter, M., 1982, Tectónica de los alrededores de Zimapan, Hidalgo y Queretaro: Sociedad Geológica Mexicana, Convención Nacional, 6tb, México D.F., Excursión a la region de Zimapan y areas circundantes, jected stratigraphic succession of the Valle de Guadalupe-1 well (Fig. 11). Libreto Guía, p. 1-20. Paleontologic, stratigraphic, and structural studies by Pemex geologists (for Dahlstrom, C.D.A., 1969, Balanced cross sections: Canadian Journal of Earth Sciences, v. 6, p. 743-757. Gignoux, M., 1950, Stratigraphic geology: San Francisco, California, W. H. Freeman, 682 p. example, Betanzos Gomez, 1980) showed that contrary to Suter's interpre- Heim, A., 1926, Notes on the Jurassic of Tamazuachale (Sierra Madre Oriental, Mexico): Eclogas Geologicae Helvetiae, v. 20(1), p. 84-87. tation of three thrust faults, the Valle de Guadalupe-1 well penetrated a 1940, The front ranges of the Sierra Madre Oriental, Mexico, from to Tamazunchale: Eclogae continuous Cretaceous-Jurassic section with a high-angle reverse fault in Geologicae Helvetiae, v. 33, p. 313-352. Longoria, J. F., 1975, Estratigrafía de la Serie Comancheana del Noreste de México: Sociedad Geológica Mexicana the Lower Cretaceous part of the section; the stratigraphic succession was Boletín, v. 36, p. 31-59. 1984a, Stratigraphic studies in the Jurassic of northeastern Mexico: Evidence for the origin of the Sabinas Basin: identified as Lower Cretaceous, Pimienta, Taman, and Santiago (in which Society of Economic Paleontologists and Mineralogists, Gulf Coast Section, Annual Research Conference Proceed- the well terminated). ings, p. 171-193. 1984b, Mesozoic tectostratigraphic domains in east-central Mexico, in Westermann, G.E.G., ed., Jurassic- Cretaceous biochronology and paleogeography of : Geological Association of Canada Special Paper 27, p. 65-76. CONCLUSIONS 1985, Tectonic transpression in the Sierra Madre Oriental, northeast Mexico: An alternative model: Geology, v. 13, p. 343-345. 1986, Mesozoic plate tectonic reconstruction of Mexico: Evidence from the stratigraphic record, in Sager, W., and Stratigraphic studies are vital in regional structural interpretations of Scotese, C. R., conveners, Mesozoic and Cenozoic plate reconstructions: Geodynamics Symposium, Texas A&M University, College Station, Texas, 3 p. the Mexican Cordillera. The lack of a proper stratigraphic framework Longoria, J. F., and Davila, V., 1979, Estratigrafía y microfacies del Cerro de La Silla, SE de : Universidad de Sonora Departamento de Geología Boletín, v. 2, p. 65-95. leaves Suter's balanced cross sections of the Sierra Madre Oriental as mere López Ocampo, E., Guzman Vega, M. A., and Moreno Hentz, P., 1986, Las relaciones discordantes de la Formación Las geometric essays. The words by Maurice Gignoux (1950, p. 11) were as Trancas en los estados de Queretaro e Hidalgo: Sociedad Geológica Mexicana, Convención Geológica Nacional, 8th, 30 de Julio-1 de Agosto, 1986, México, D. F., Resúmenes, p. 85-86. inspiring 39 yr ago as they are relevant today: "Thus, it is truly tectonics López Ramos, E., 1972, Estudio del basamento ígneo y metamòrfico de las Zonas Norte y Poza Rica (entre Nautla, Ver. y Jiménez, Tamps.): Asociación Mexicana de Geoiógos Petroleros Boletín, v. 24, p. 267-323. which governs stratigraphy, and the two branches of geologic sciences are 1980, Geología de México, Tomo II: Tesis Resendiz, S. A., 454 p. inseparable. A structural geologist who is not a stratigrapher is only a Muir, J. M., 1936, Geology of the Tampico region, Mexico: Tulsa, Oklahoma, American Association of Petroleum Geologists, 280 p. geometer, not a geologist, for he reasons about abstract surfaces and vol- North American Commission on Stratigraphic Nomenclature, 1983, North American Stratigraphic Code: American Association of Petroleum Geologists Bulletin, v. 67, p. 841-875. umes, emptied of their history; and a stratigrapher who never concerned Pessagno, E. A., Jr., 1969, Upper Cretaceous stratigraphy of the western Gulf Coast area of Mexico, Texas, and Arkansas: himself with tectonics would produce only a dead stratigraphy." Geological Society of America Memoir 111,139 p. Segerstrom, K., 1956, Ruta: México, D. F.-Zimapan, Hgo., in Maldonado-Koerdell, M., ed., Estratigrafía del Cenozoico y del Mesozoico a lo largo de la Carretera Reynosa, Tamps. y México, D. F. Tectónica de la Sierra Madre Orientai. Vulcanismo en el Valle de México: Congreso Geológico Internacional, Vigésima Sesión, Excursiones A-14 y C-6, ACKNOWLEDGMENTS p. 167-215. 1961 a, Geología del Suroeste del Estado de Hidalgo y Noroeaste del Estado de México: Asociación Mexicana de Geoiógos Petroleros Boletín, v. 13, p. 147-168. I thank Tom Anderson, University of Pittsburgh, for his valuable 1961b, Geology of the Bernal-Jalpan area, Estado de Queretaro, Mexico: U.S. Geological Survey Bulletin 1104-B, p. 19-83. comments on my manuscript. 1962, Geology of south-central Hidalgo and northeastern Mexico: U.S. Geological Survey Bulletin 1104-C, p. 87-162. Suppe, J., 1983, Geometry and kinematics of fault-bend folding: American Journal of Science, v. 283, p. 684-721. 1985, Principles of structural geology: Englewood Cliffs, New Jersey, Prentice-Hall, 537 p. REFERENCES CITED Suter, M., 1980, Tectonics of the external part of the Sierra Madre Oriental foreland thrust-and-fold belt between Xilitla and the Moctezuma River (Hidalgo and San Luis Potosí States): Universidad Nacional Autónoma de México Aguayo, J. E., 1978, Sedimentary environments and diagenesis of a Cretaceous reef complex, eastern Mexico: Universidad Revista, v. 4, p. 19-31. Nacional Autónoma de México, Centro de Ciencias del Mar y Limnología Anales, v. 5, p. 93-140. 1984, Cordilleran deformation along the eastern edge of the Valles-San Luis Potosi carbonate platform, Sierra Betanzos Gomez, A., 1980, Tamazunchale-Río Verde, S.L.P., in Evaluación Geológica Petrolera, Plataforma de Valles- Madre Oriental fold-thrust belt, east central Mexico: Geological Society of America Bulletin, v. 95, p. 1387-1397. San Luis Potosí, XI Excursión Geológica, Junio de 1980, Petroleos Mexicanos Superintendencia de Distritos de 1987, Structural traverse across the Sierra Madre Oriental fold-thrust belt in east-central Mexico: Geological Exploración Petrolera, Zona Norte, p. 54-83. Society of America Bulletin, v. 98, p. 249-264. Bodenlos, A. J., 1956, Notas sobie la Geología de la Sierra Madre en la sección Zimapan-Tamazunchale, in Maldonado- Wilson, B. W., Hernández, P., and Meave-Torrescano, E., 1955, Un arrecife Cretácico en la parte oriental de Queretaro-. Koerdell, M-, ed-, Estratigrafía del Cenozoico y del Mesozoico a lo largo de la Carretera Reynosa, Tamps. y Sociedad Geológica Mexicana Boletín, v. 18, p. 1—10. México, D. F. Tectónica de la Sierra Madre Oriental. Vulcanismo en el Valle de México: Congreso Geológico Internacional, Vigésima Sesión, Excursiones A-14 y C-6, p. 293-309. Bonet, F., 1956, Ruta: Tamazunchale-Taninul, in Maldonado-Koerdell, M., ed., Estratifrafía del Cenozoico y del Meso-

zoico a lo largo de la Carretera Reynosa, Tamps. y México, D. F. Tectónica de la Sierra Madre Oriental. MANUSCRIPT RECEIVED BY THE SOCIETY MAY 6,1987 Vulcanismo en el Valle de México: Congreso Geológico Internacional, Vigésima Sesión, Excursiones A-14 y C-6, REVISED MANUSCRIPT RECEIVED MARCH 31,1988 r. 217-240. MANUSCRIPT ACCEPTED SEPTEMBER 2,1988

Reply

MAX SUTER Instituto de Geología, Universidad Nacional Autónoma de México, Apartado 70-296, México DF 04510, México

Longoria's Alternative Interpretation of my structural analysis of the several shortcomings in the introductory stratigraphic as well as in the Sierra Madre Oriental fold-thrust belt in east-central Mexico (Suter, structural parts of my paper. 1987a) boils down to (i) his opinion that the present state of knowledge of Contrary to Longoria's opinion, I contend that the stratigraphic and the stratigraphic framework of east-central Mexico does not favor the paleogeographic record of the area under discussion is not only well doc- construction of balanced structural cross sections and (ii) his claim of umented but probably even the best studied of all Mexico. This can be

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mainly attributed to the vicinity of the oil fields of the Tampico-Misantla 1984b, Fig. 10; 1987a) is not representative for this formation. In fact, the foredeep in the Tampico-Tuxpan area. The Mesozoic rocks in my traverse San Felipe Formation shows facies and thickness changes perpendicular to area are the outcrops closest to these hydrocarbon deposits, the discovery the margin of the VSP platform (Suter, 1988). These changes certainly of which initiated an extensive exploration effort in the first half of this merit further petrographic and stratigraphic analysis, which, however, was century (Heim, 1926, 1940; Burckhardt, 1930; Muir, 1936) that was not an objective of my essentially structural work in that area. Besides, the renewed in the period of the 20th International Geological Congress thickness of this formation, 100 to 150 m, is very small in comparison to (Bodenlos, 1956a, 1956b; Bonet, 1956a, 1956b). Subsequent surveys by the thickness of the whole detached sedimentary sequence of 5,000 m, the Mexican oil company Petróleos Mexicanos are summarized in which suggests that these facies changes do not have much influence on the Carrillo-Bravo (1965) and were followed by stratigraphic and sedimen- structural style. tologic-paleogeographic studies by Petróleos Mexicanos and by the Mexi- 3. Longoria's statement that there is no evidence in the references can Petroleum Institute. The latter include detailed descriptions of the given in my paper (Suter, 1987a) for the time ranges I assigned to the Las sediments of the Cretaceous Valles -San Luis Potosí (hereinafter abbre- Trancas (Kimmeridgian to Barremian; Carrillo-Martínez and Suter, 1982, viated as VSP) carbonate platform (Carrillo-Bravo, 1971; Aguayo, 1978) p. 3, lower part of left column) and the base of the Soyatal Formations and of the Tamabra foreslope deposits (Carrasco, 1977), as well as sedi- (early Campanian; Suter, 1984b, p. 1392, last paragraph and Fig. 10A) is mentologic (Aguayo, 1977; Pedrazzini and Basáñez, 1978) and strati- simply false and could have been avoided, had he or the reviewers of his graphic studies of the Middle and Upper Jurassic. More recently, Paul Alternative Interpretation read those references more carefully. Enos (1974,1986) and his graduate students (Ward, 1979; Minero, 1983; 4. The same can be said for Longoria's comment that I refer wrongly Bitter, 1986) have contributed to our understanding of the sedimentology to Carrillo-Bravo (1971) when I state that the base of the VSP platform is and paleogeography of east-central Mexico. of Barremian age in the area of the Valle de Guadalupe-1 well. From The major remaining knowledge gap, not mentioned by Longoria, Carrillo-Bravo (1971, p. 24 and 25), the core of the Valle de Guadalupe concerns, from my point of view, the Lower-Middle Jurassic normal anticline contains a >300-m-thick sequence of Aptian-Barremian age (his faults known from outcrops in the Huayacocotla anticlinorium and from "calizas de plataforma sin nomenclatura formal") that cannot be distin- subsurface data in the nearby Tampico-Misantla foredeep (Suter, 1987a, guished lithologically from the overlying El Abra platform-interior facies. 1987b, 1988). The geometry of these faults and the associated synsedimen- My assignment of a Late Cretaceous age for the upper limit of the El tary record are still poorly constrained, and we do not know to what Abra Formation, also criticized by Longoria, is based on (i) the existence extent the faults became reactivated in the subsequent Cordilleran shorten- of an intercalation of platform-edge facies inside the Soyatal Formation ing phase. near El Lobo that overlies pelagic rocks with microfossils of the Globo- Even if the stratigraphic record were as poorly known as Longoria truncana elevata planktonic foraminiferal zone s.s. (Suter, 1984b, p. 1392) believes it to be, I still could not agree that this would make modeling the and (ii) the documentation of Upper Cretaceous carbonates in the central subsurface geometry futile. The uncertainty of the results of such models part of the VSP platform by Carrillo-Bravo (1971, Fig. 9), the southern depends not only on the stratigraphy but on the quality and distribution of limit of which he places close to my study area. the observational and experimental data in general, and certainly also on 5. Longoria contends that I ignored thickness variations and facies the complexity of the structure and deformation path to be modeled changes in my sections, only to remark in his next sentence that he dis- (Suter, 1984a). The judgment of what degree of uncertainty is acceptable agrees with the tectonic nature of the thickness changes of the Pimienta will depend on the objective of the modeling process. For example, a level Formation documented in the folds of the Huayacocotla anticlinorium of confidence acceptable to a petroleum explorationist in a frontier area (Suter, 1987a, Fig. 5). A more careful reading of my paper, however, will probably not satisfy a geologist working on a well-to-reservoir scale. would have shown the following, (i) The thickness and facies variations of In my opinion, the paper under discussion contains right now the the Lower Cretaceous are clearly marked on the structural sections, for best-documented cross-sectional data set of the Mexican Cordillera, and example across the Maconi syncline (Suter, 1987a, Fig. 5). In fact, the the balanced traverse section is the first and so far only one of this kind documentation that the structural style of the study area is controlled by across the Cordillera between the -North American plate the horizontal lithology variations of the Lower Cretaceous rocks is one of boundary and the Mexico-United States border. We have enough the key results of the paper and is emphasized in the abstract, (ii) The confidence in this data set to use selected parts of it in tests of an algorithm stratigraphic thickness changes of the Upper Jurassic are documented in for the numerical simulation of cross-sectional deformation sequences that the stratigraphic sections (Suter, 1987a, Fig. 2). Both the Pimienta and we are presently developing (Contreras and Suter, 1988a, 1988b). Tamán Formations show a significant thickness increase from east to west, The following part of my Reply concerns the more parochial aspects toward the later VSP platform (Suter, 1988). On a larger scale, the Pi- of Longoria's Alternative Interpretation. mienta and Tamán Formations fill an epicontinental basin delimited in 1. Longoria is opposed to the use of the term "Tamaulipas Forma- the west by a volcanic arc and arc-derived clastic rocks, and in the east by tion" (Carrillo-Martínez and Suter, 1982; Suter, 1987a) for the Lower shallow-water carbonates in the area of the present Cretaceous basin facies west of the VSP carbonate platform. He suggests (Carrillo-Martínez and Suter, 1982, Fig. 6). (iii) There is no evidence for a using "Santuario Formation" instead, a term introduced by Segerstrom stratigraphic origin, as suggested by Longoria, for the local thickness (1962). Unfortunately, the type area of this formation, north of Cardonal, changes of the Pimienta Formation in the Huayacocotla anticlinorium. Hidalgo, is in reality an outcrop of the lithologically similar Upper Cre- Tectonic accumulation of the Pimienta Formation is clearly associated taceous Soyatal Formation, as documented by Kiyokawa (1981), which with the cores of the folds formed by the detachment of the overlying makes the use of "Santuario Formation" obsolete. Moreover, Ross (1979) sedimentary sequence on the Pimienta Formation (Suter, 1987a, Fig. 5). has shown that the Tamaulipas can be correlated around the northern tip 6. In Longoria's present interpretation, the ramp anticline or fault- of the VSP platform. I therefore think that it is valid to use this term for the bend fold associated with the Xilitla thrust corresponds to the "flattened coeval Lower Cretaceous basin facies on either side of the VSP platform. core of a large box anticline." This interpretation is truly an alternative to 2. I agree with Longoria that the lithology described for the San Longoria's former allochthonistic interpretation in Tardy and others Felipe Formation from the edge of the underlying VSP platform (Suter, (1975), wherein a connection is suggested for the Xilitla thrust with a

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thrust observed east of San Luis Potosi, about 190 km farther west- REFERENCES CITED northwest in the Sierra Madre Oriental fold-thrust belt. The distance be- Aguayo, J. E., 1977, Sedimentación y diagénesis de la Formacion Chipoco (Jurásico Superior) en afloramientos, Estados de Hidalgo y San Luis Potosí: Instituto Mexicano del Petróleo Revista, v. 9, p. 11-37. tween the two outcrops and the north-northwest trend of the structures 1978, Sedimentary environments and diagénesis of a Cretaceous reef complex, eastern Mexico: Universidad Nacional Autónoma de México, Centro de Ciencias del Mar y Limnología Anales, v. 5, p. 83-140. located between them would require a transport > 150 km for the Xilitla Bitter, M. R., 1986, Sedimentology and petrology of the Chícontepec Formation, Tampico-Misantla basin, eastern Mexico thrust, which corresponds to about twice the shortening of the Helvetic [M.Sc. thesis]: Lawrence, Kansas, University of Kansas, 174 p. Bodenlos, A. J., 1956a, Notas sobre la geología de la Sierra Madre en la sección Zimapán-Tamazunchale: International Alps (Hsu, 1979). Neither of Longoria's interpretations is documented, Geological Congress, 20th, México D.F., Guidebook, Excursions A-14 and C-6, p. 293-309. 1956b, Itinerario Zimapán, Hgo.-Tamazunchale, San Luis Potosí: International Geological Congress, 20th, Méx- however, and the fact that he calls the Indian hamlet of San Antonio ico D.F., Guidebook, Excursions A-14 and C-6, p. 179-215. Xalcuayo a "town" in his Alternative Interpretation suggests that he has no Bonet, Federico, 1956a, Itinerario Taninul-Tamazunchale: International Geological Congress, 20th, México D.F., Guide- book, Excursions A-14 and C-6, p. 93-118. first-hand knowledge of the area. 1956b, Zonificación microfaunística de las calizas cretácicas del este de México: International Geological Con- gress, 20th, México D.F., Monograph, 102 p. Contrary to Longoria's latest interpretation, the Xilitla thrust exists Burckhardt, Charles, 1930, Etude synthetique sur le Mesozoique mexicain: Soc. Paleont. Suisse Mem. 49-50, 280 p. and is well exposed and structurally relatively simple, as the reader can Carrasco, Baldomero, 1970, La Formación El Abra (Formación El Doctor) en la plataforma de Valles-San Luis Potosí: Instituto Mexicano del Petróleo Revista, v. 2, p, 97-99. convince him or herself from my documentation of that structure. The 1977, Albian sedimentation of submarine autochthonous and allochthonous carbonates, east edge of the Valles- San Luis Potosí platform, Mexico, in Cook, H. E., and Enos, Paul, eds., Deep-water carbonate environments: exposed horizontal slip component of the thrust is 3,600 m (Suter, 1984b), Society of Economic Paleontologists and Mineralogists Special Publication 25, p. 263-272. whereas modeling of the subsurface geometry resulted in a shortening of Carrillo-Bravo, José, 1965, Estudio geológico de una parte del anticlinorio de Huayacocotla: Asociación Mexicana de Geólogos Petroleros Boletín, v. 17, p. 73-96. 17,200 m (Suter, 1987a, Fig. 11). 1971, La plataforma Valles-San Luis Potosí: Asociación Mexicana de Geólogos Petroleros Boletín, v. 23, p. 1-102. 7. Concerning Longoria's rumbling comments on semantics of the Carrillo-Martínez, Miguel, and Suter, Max, 1982, Tectónica de los alrededores de Zimapán, Hidalgo y Querétaro: Sociedad geológica Mexicana, Convención geológica nacional, VI, Excursión a la región de Zimapán y áreas stratigraphic units in the Xilitla thrust plate, I would like to reply the circundantes. Guidebook, p. 1-20. following, (i) The definitions of the Chapulhuacan Formation by Bodenlos Contreras, Juan, and Suter, Max, 1988a, Simulación numérica de secuencias de deformación geológica [abs.]: GEOS, Unión Geofísica Mexicana Boletín (in press). (1956a, p. 301) and of the Ahuacatlan Formation by Bonet (1956a) 1988b, Numerical simulation of cross-sectional geological deformation sequences [abs.]: EOS (American Geophys- ical Union Transactions), v. 69 (in press). suggest that these terms can be used as synonyms of the terms (in the sense Enos, Paul, 1974, Reefs, platforms, and basins of middle Cretaceous in northeast Mexico: American Association of of Muir, 1936) "Tamaulipas Inferior" and "Tamaulipas Superior," respec- Petroleum Geologists Bulletin, v. 58, p. 800-809. 1986, Diagénesis of Mid-Cretaceous rudist reefs, Valles platform, Mexico, in Schroeder, J. H., and Purser, B. H., tively (Suter, 1980, 1984b, 1988). (ii) Longoria's unfamiliarity with the eds., Reef diagenesis: New York, Springer-Verlag, p. 160-185. Heim, Arnold, 1926, Notes on the Jurassic of Tamazunchale (Sierra Madre Oriental, Mexico): Eclogae Geologicae stratigraphic literature for the locality is also shown by his use of the term Helvetiae, v. 20, p. 84-87. "El Doctor" for the foreslope deposits in the upper plate of the Xilitla 1940, The front ranges of Sierra Madre Oriental, Mexico, from Ciudad Victoria to Tamazunchale: Eclogae Geologicae Helvetiae, v. 33, p. 313-352. thrust (his Fig. 1). Since 1971, all papers about this area have used the Hsü, K. J., 1979, Thin-skinned plate tectonics during neo-Alpine orogenesis: American Journal of Science, v. 279, p. 353-366. term "El Abra Formation" for the carbonates of the VSP platform, accord- Kiyokawa, Motomu, ed., 1981, Geological survey of the Pachuca-Zimapán area, central Mexico: Metal Mining Agency of ing to the definition by Carrillo-Bravo (1971), and "Tamabra Formation" Japan and Consejo de Recursos Minerales, Estados Unidos Mexicanos, 194 p. (unpub.). Minero, C. J., 1983, Sedimentary environments and diagenesis of the El Abra Formation (Cretaceous), Mexico [Ph.D. for the foreslope deposits, whereas the term "El Doctor Formation" ap- thesis]: Binghamton, New York, State University of New York, 367 p. Muir, J. M., 1936, Geology of the Tampico region: Tulsa, Oklahoma, American Association of Petroleum Geologists, plies to the carbonates of a different platform located about 100 km west 280 p. of Xilitla (Carrasco, 1970). (iii) Longoria's use of the term "Xilitla Forma- Pedrazzini, Carmen, and Basáñez, M. A., 1978, Sedimentación del Jurásico Medio-Superior en el anticlinorio de Huaya- cocotla-Cuenca de Chícontepec, Estados de Hidalgo y , México: Instituto Mexicano del Petróleo Revista, tion" is even more obsolete. Heim (1940, p. 326) used that term as a v. 10, p. 6-25. Ross, M. A., 1979, Stratigraphy of the Tamaulipas limestone, northeastern Mexico [M.Sc. thesis]: Arlington, Texas, synonym for "Agua Nueva Formation"; however, most if not all subse- University of Texas, 96 p. quent papers stayed with the term "Agua Nueva." Segerstrom, Kenneth, 1962, Geology of south-central Hidalgo and northeastern México: U.S. Geological Survey Bulletin 1104-C, p. 87-162. 8. Longoria's alternative section across a part of the Huayacocotla Suter, Max, 1980, Tectonics of the external part of the Sierra Madre Oriental foreland thrust-and-fold belt between Xilitla and the Moctezuma River (Hidalgo and San Luis Potosí States): Universidad Nacional Autónoma de México, anticlinorium in the Moctezuma River valley (his Fig. 2) sets us back Instituto de Geología Revista, v. 4, p. 19-31. 1984a, Secciones estructurales con balanceo de masa [abs.]: Sociedad geológica Mexicana, Convención geológica more than 60 yr; it has structurally less resolution than Heim's section of nacional, Vil, México D.F., Resúmenes, p. 125. 1926. Furthermore, the villages Xaltipa and Tlacuilola of his Figure 2 do 1984b, Cordilleran deformation along the eastern edge of the Valles-San Luis Potosí carbonate platform, Sierra Madre Oriental fold-thrust belt, east-central Mexico: Geological Society of America Bulletin, v. 95, p. 1387-1397. not exist in the area of his section. Xaltipa is located 13 km northwest of 1987a, Structural traverse across the Sierra Madre Oriental fold-thrust belt in east-central Mexico: Geological Society of America Bulletin, v. 98, p. 249-264. Vega Larga in the Tancuilin Canyon (Mexican Federal Mapping Agency, 1987b, Fallas jurásicas normales en el área de la Hoja Tamazunchale (Estados de Hidalgo y San Luis Potosí): INEGI, 1:50,000 topographic sheet F14D31), in a syncline that cannot be Universidad Nacional Autónoma de México, Instituto de Geología, Simposio de Geología Regional de México, II, México D.F., Resúmenes, p. 29-30. projected into Longoria's section but passes about 6 km west of its 1988, Hoja Tamazunchale 14Q-e(5) con Geología de la Hoja Tamazunchale, Estados de Hidalgo, Querétaro y San Luis Potosí: Universidad Nacional Autónoma de México, Instituto de Geología, Carta geológica de México, southwestern end (Suter, 1980, Fig. 2). Tlacuilola lies totally beyond the serie de 1:100,000 (in press). section trace, approximately 12 km northwest of Taman (INEGI, 1:50,000 Tardy, Marc, Longoria, J. E., Martinez, Juventino, Mitre, L. M., Patiño, Manuel, Padilla, Ricardo, and Ramírez, Calixto, 1975, Observaciones generales sobre la estructura de la Sierra Madre Oriental; la aloctonía del conjunto Cadena topographic sheet F14C49) in the western flank of the Pisaflores anticlino- Alta-Altiplano Central, entre Torreón, Coah., y San Luis Potosí, S.L.P., México: Universidad Nacional Autónoma de México, Instituto de Geología, Revista (oíd series), no. 1, p. 1-11. rium (Suter, 1988). Ward, J. A., 1979, Stratigraphy, depositional environments, and diagenesis of the El Doctor platform, Queretaro, Mexico In conclusion, then, Longoria's Alternative Interpretation contains no [Ph.D. thesis]: Binghamton, New York, State University of New York, 172 p. factual information and is certainly not a contribution to Mexico's need for MANUSCRIPT RECEIVED BY THE SOCIETY AUGUST 12, 1988 basic geologic research, emphasized at the beginning of his essay. MANUSCRIPT ACCEPTED SEPTEMBER 2,1988

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