Bol. Soc. Mexicana XXXVII (1): 11-17, Junio, 1976

The Tamuin Member of the Mendez Shale along the Eastern Flank of the Sierra de El Abra, San Luis Potosí, East México.

J. Eduardo Aguayo C. and Kunio Kanamori

Institute for Geosciences, University of Dallas



The Tamuin Member, is proposed herein as a new member of the Mendez Shale, it is exposed along the eastern flank of the Sierra de El Abra in the Tampico Region in East Mexico.

Lithologically, the Tamuin Member consists of finely laminated, black argilaceous limestone displaying graded bedding, possibly deposited by means of turbidity currents.

The planktonic foraminiferal assemblage in the Tamuin Member indicates that the member is late Campanian in age. thereofre. is equivalent to the middle part of the Mendez Shale.



Se propone un nuevo miembro de la Formación Méndez con el nombre de: Miembro Tamuin, el cual se encuentra expuesto a lo largo del flanco Oriental de la Sierra de El Abra, en la región de Tampico, al este de México.

Litológicamente, el Miembro Tamuin, consiste de calizas argilaceas de color negro, finamente laminadas y con estratificación gradual, posiblemente depositadas por corrientes de turbidez.

El Miembro Tamuin es asignable al Campaniano Superior, de acuerdo con su contenido de foraminiferos planctórticos, y por lo tanto es equivalente a la parte media de la Formación Méndez.


1. Introduction

A field sun'ey was carried out in 1975, in order to examine formational units overlying the El Abra Limestone. As a result of those investigations a new member of the Mendez Shale, the Tamuin Member, was discovered.


2. Description of the Tamuin Member

2.1. Type Locality

The type locality is located north 40 degrees west, twelve kilometers from Tamuin at the "Cementos Anáhuac" quarry, at foothills of the Sierra de El Abra (Figura 1).

 Figura 1. Locality map showing the sample zones.

Figura 2. Stratigraphic column of the eastern
most portion of the Valles, San Luis PotosíPlatform in the Tampico Region.


2.2. Thickness

The maximum measured thickness of the Tamuin Member is about 40 meters measured at the type locality.


2.3. Lithology

The Tamuin Member consists of hard, black, finely laminated, pyritic, argillaceous limestone which weathers buff to brown splintery fragments.


2.4. Contacts

The Tamuin Member overlies the El Abra Limestone in angular unconformity and thins to the west. Usually, the upper contact is uncertain due to soil caver or erosion.

At the "Taninul" quarry, the Tamuin Member is in fault contact with the San Felipe Formation (Figura 3).

Figura 3. Generalized sketch showing the stratigraphic position of the El Abra-Limestone, San Felipe Fm y Tamuin Member.


2.5. Depositional Environment

Small-scale structures such as toolmarks, current  lineations, graded bedding, cross-bedding, horizontal lamination and convolute bedding, suggest a distal turbidite deposit along the eastern flank ofthe Sierra de El Abra.


2.6. Distribution

The Tamuin Member is exposed at leat at two localities, one is the type locality at "Cementos Anáhuac" quarry, and the other is the "Taninul" quarry about 9 kilometers southward from the type locality. At both localities, the dip of the Tamuin Member is about 40 degrees east (Figura 3).


2.7. Paleontology

The Tamuin Member ineludes a rich planktonic foraminiferal fauna and rather scarce benthonic foraminifers. Samples, from the Tamuin Member are very indurated thus extraction of individual planktonic foraminifera is limited utilizing existing techniques. Therefore, the following new technique was used for extracting calcareous Foraminifera (See Pessagno, 1976).

1) Crush sample

2) Place crushed sample in concentrated HF in plastic beaker for 48 hours.

3) Pour off concentrated HF.

4) Wash, and sieve the resulting residue.

5) Place the residue in concentrated HF for five minutes.

6) Pour off concentrated HF, wash, and sieve the residue.

7) Place the residue in ultrasonic cleaner with water for 10 minutes.

8) Sieve the residue again.

Calcareous Foraminifera are replaced by fluorite using this technique. The method is effective in extracting calcareous Foraminifera from hard shale and from argillaceous limestone.

In addition to the examination of matrix-free individuals, some microfossils were also identified in thin sections. The following planktonic foraminiferal assamblage was recognized at each locality of the Tamuin Member.

Locality I: "Cementos Anahuac" quarry:

Pseudotextularia elegans (Rzehak), Globotruncana arca (Cushman), G. bulloides Vogler, G. elevata (Brotzen), G. fornicata PIummer, G. hilli Pessagno. G. lapparenti Brotzen, G. linneiana (d'Orbigny), G. loeblichi Pessagno, G. rosetta (Carsey), G. stephensoni Pessagno, G. stuartiformis Dabiez stuartiformis Dabiez and G. ventricosa White.

Locality II, "Taninul" quarry:

Heterohelix globulosa (Ehrenberg), Pseudoguembelina costulata (Cushman), Pseudotextularia elegans (Rzehak), Globigerielloides bolli Pesagno, Archaeoglobigerina blowi Pesagno, A. Cretacea (d'Orbigny), Globotruncana arca (Cushman), G. Bulloides Vogler, G. elevata (Brotzen), G. fornicata Plummer, G. hilli Pesagno, G. lapparenti (Brotzen), G.  linneiana (d'Orbigny),  G. cf rosetta (Carsey), G. stephensoni Pessagno, G. stuartiformis Dalbiez and G. ventricosa White.

These planktonic foraminiferal assemblages are assignable to the GlobotTuncana fornicata - stuartiformis Assemblage Zone, G. elevata Subzone, G. calcarata Zonule of Pessagno (1967, 1969) and are indicative of a late Campanian age.


3. Discussion

A controversy exists concerning the disignation of formations overlying the El Abra Limestone along the southeastern flank of the Sierra de El Abra. Kellum (1930) pointed out that the upper part of the Mendez Shale overlies the El Abra Limestone in this area. Muir (1936), however, stated that the middle Mendez red shales were down-thrown on the east againt the El Abra Limestone by a faulted contact at "Taninul" Cave. Several kilometers north of "Las Palmas" dam the contact between the El Abra Limestone and Mendez Shale "seemed to be an overlap" (Ojo de Agua de Ponce).

Bonet (1952) pointed out that the Mendez marls exposed along the escarpment, rests unconformably on the El Abra Limestone, except to the southeast at Tallinul Station, where the San Felipe Formation crops out. There, he slated that the San Felipe Formation dips to the west in fault contact with the El Abra Limestone. Pessagno (1969) suggested that Campanian Mendez strata are in contact with the El Abra Limestone due to a thrust fault. The San Felipe Formation differs from the Tamuin Member in that it consists of an alternation of limestone and marl. Although both are similar when weathered.

The Tamuin Member can be distinguished from the Mendez Shale (1) by showing darker color, (2) by being more limy and harder, (3) by being broken into slabs as apposed to subangular fragments and semispheroidal lumps. However, the Tamuin Member corresponds in age with the midole Mendez Shale. Therefore, we include tentaively such member as part of the Mendez Shale herein. The writers have also examined the planktonik foraminiferal assemblage in the San Felipe Formation. The assemblage fouud is listed below.

Type locality of the San Felipe Formation: the outcrop west of San Felipe at the point 541.37 kilometers in the National Railroad,

Heterohelix globulosa (Ehrenberg), Pseudotextularia elegans (Rzehak),  Globotruncana arca (Cushman), G. Bulloides Vogler, G. fornicata Plummer, G. lapparenti (Brotzen), G.  linneiana (d'Orbigny),  G. cf rosetta (Carsey), G. stephensoni Pessagno and G. stuartiformis Dalbiez

This assemblage is correlative with the Globotruncana fornicata - stuartiformis Assemblage Zone, Archaeoglobigerina blowi Subzone D. multicostata Zonule of Pessagno (1967, 1969). These assemblages are indicative of an early Campanian age.

The sample from locality II was taken close to the transition zone between the Mendez Shale and the San Felipe Formation, at the "Taninul" quarry. It contained the following planktonic species:

Heterohelix globulosa (Ehrenberg), H. pulchra (Brotzen), H. striata (Ehrenberg), H. ultimatumida (White), Pseudoguembelina costulata (Cushman), Pseudotextularia elegans (Rzehak), Globigerinelloides multispina (Lalicker), G. prairiehillensis Pessagno, Archacoglobigerina blowi Pessagno, A. cretacea (d'Orbigny), Globotruncana arca (Cushman), G. bulloides Vogler, G. elevata (Brotzen), G. fornicata Plummer, G. lapparenti Brotzen, G. linneiana (d' Orbigny), G. loeblichi Pessagno, G. rosetta (Carsey), G. stephensoni Pessagno, G. stuartiformis Dalbiez and G. ventricosa White, Rugoglobigerina rugosa (Plummer).

This assemblage is asignable to the G. fornicata stuartiformis Zone G. elevata Subzone (P. elegans Zonule) of Pessagno (1967, 1969) and is thus younger than the sample of the type locality of the San Felipe Formation. These assemblages are indicative of an early to late Campanian age. However, they are still older than the assemblage from the Tamuin Member and below the first occurrence biohorizon of Globotruncana hilli and of Globigerinelloides bollii



The aulhors offer special thanks to Dr. Emile A. Pessagno Jr. for suggestions during field work and for helpful criticism of the manuscript.



Bonet, F., 1952, La Facies Urgoniana del Cretácico Medio de la Región de Tampico: Bol. Asoc. Mex. Geol. Petrol., IV, 5-6, 151-262. 50 figs.

Bonet, F., 1956,  Zonificación Microfauníslica de las calizas cretácicas del este de México: Bol. Asoc. Mex. Geol. Petrol., XX Congreso Geológico Internacional, 3 cuadros, 4 figs. láms. XXXI

Bonet, F., 1963, Biostratigraphic Notes on the Cretaceous of Eastern Mexico: Corpus Christi Geol. Soc. Annual Field Trip Guidebook, pp. 36-48.

Bonet, F.; Heim. A., Vollbrechthausen. A. U., 1956, Map (fig. 9) in Estratigrafía del Cenozoico y del Mesozoico a lo largo de la carretera entre Reynosa, Tamps. y México D.F., Tectónica de la Sierra Madre Oriental, Vulcanismo en el Valle de México, Congreso Geológico Internacional, XX Sesion, 323 pp. 15 figs., tablas IX.

Carrillo, J., 1971, La Plataforma  Valles - San Luis Potosí. Bol. Asoc. Mex. Geol. Petrol., XXIII 1-6, 102 pp.

Coogan, A. H.; Bebout, D. G., Maggio, C., 1972, Depositional Environments and Geological History of Golden Lane and Poza Rica Trend, Mexico: en Alternative View. Am. Assoc. Petroleum Geologists Bull. 56 (8): 1419-1447, 21 figs.

Hinojosa, A., 1972, Excursión Geológica Tampico, Tam.-Zacatecas, Zac., Etapa No. 2 Tramo: Tamuin-Río Verde, S. L. P. Petróleos Mexicanos

Imlay. R. W., 1944, Cretaceous Formations of Central America and Mexico: Am. Assoc. Petroleum Geologists Bull. 28, 8, 1077-1195, 16 figs.

Kellum L. B., 1930, Similarity of Surface Geology in Front Ranges of Sierra Madre Oriental to Subsurface in Mexican South Fields: Am. Assoc. Petroleum Geologists Bull. 14 (t), 73-91, 3 figs., table I.

Moya, F., 1974, Estudio Estratigráfico y Sedimentológico de los Sedimentos cretácicos Depositados en el Área Pre-arrecifal de la Margen Oriental de la Plataforma Valles - San Luis Potosi: Asoc. Int. Petróleos Mexicanos, XII Congreso (1974): 14 pp.

Muir, J. M., 1936,  Geology of the Tampico Region, México: Am. Assoc. Pretroleum Geologists, Tulsa, 280 pp.

Pessagno, E. A. Jr., 1967, Upper Cretaceous planktonic  Soraminifera from the Western Gulf Coastal Plain: Paleontographica  Americana, 5, 37, 245-445, pls. 48-101, figs, 1-63-

Pessagno, E. A. Jr., 1969,  Upper Cretaceous Stratigraphy of the Western Gulf Coast Area of Mexico, Texas and Arkansas. Geol Soc. Am., Mem., 111, 139 pp., pis. 1-60.

Pessagno, E. A. Jr., 1976, Upper Jurassic Radiolaria an Radiolarian Biostratigraphy of the California Coast Ranges, in press.


Plate 1

1 . Photograph showin, the contact between the Taninul Member (7) and the El Abra Limestone (A) at the "Cementos Anáhuac" quarry. Scale bar-5 meters.

2. Same as above. Notioe the massive aspect of the Taninul Member. Scale bar-2 meters.

3. Close-up of the Taninul Member at the type locality. Notice parallel current lineations oriented north-south. See pen for scale.

4-5. Pseudotextularia elegans (Rzehak)

4: Lateral view. 5: Apertural view. Scale bar. 150 microns.



Plate 2

1-3. Globotruncana formicata Plummer.

The specimen replaced by fluorite.
1: Spiral view. 2: Side view. 3: Umbilical view.
Scale bar-150 microns. 

4-6. Globotruncana elevata (Brotzen)

The specimen replaced by fluorite.
4: Spiral view. 5: Side view. 6: Umbilical view.
Scale bar-200 microns.

7-2. Globotruncana hilli Pessagno.

The specimen replaced by fluorite.
7: Spiral view. 8: Sidie view. 9: Umbilical view.
Scale bar·120 microns.