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AGENDA DE LA EXCURSIÓN (Continuación) LUNES, 26 De Mayo

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AGENDA DE LA EXCURSIÓN (Continuación) LUNES, 26 De Mayo Estratigrafía Jurásico-Cretácica del Arco de Monterrey de la Sierra Madre Oriental y . 33 AGENDA DE LA EXCURSIÓN (Continuación) LUNES, 26 de Mayo un espesor más potente de litofacies de ambiente de plataforma abierta (Taraises-Tamaulipas Inferior). El ANTICLINAL DE POTRERO CHICO, borde del Sistema Sedimentario Cupido está ausen- NUCLEADO POR EVAPORITAS te al oriente de la Sierra Minas Viejas. En la Sierra Minas Viejas la Formación La Parada 2-1 Peña es más gruesa respecto a la Sierra del Fraile, sin embargo, la zonificación paleontológica no revela La primera Parada (2-1) del segundo día de ausencia de taxones de amonitas entre ambas locali- la excursión se encuentra a 1 hr, 45 min y 57 km de dades, por lo que se considera que en Potrero Chico la ciudad de Monterrey sobre la carretera Monterrey- está condensada esta formación. Monclova. En esta Parada de la excursión se aborda- En el Potrero Minas Viejas, en la base de la rán aspectos regionales de la Estratigrafía y Geología Formación Taraises, aflora un cuerpo de caliza wacke- Estructural porción sur de la Cuenca de Sabinas en stone y packstone de edad Valanginiano Inferior, su sector sur de anticlinales nucleados por sal. conocido en el Noreste de México como miembro El objetivo de la Parada 2-1 es: Mostrar los Nogales y correlacionable en Texas con la unidad elementos estratigráficos y estructurales alrededor del ‘‘Knowles’’, estas litofacies corresponden a una se- área en una vista panorámica del flanco frontal del cuencia transgresiva de segundo orden (Fig. 1). Anticlinal Potrero Chico y sur del Pliegue Minas Vie- jas, enfatizando sobre las variaciones de la geometría PANORÁMICA SOBRE LA ESTRUCTURA del primero. Se demostrará que los anticlinales Gar- DE ANTICLINALES NUCLEADOS POR SAL cía y Potrero Chico forman una enorme estructura de despegue tipo caja con un sinclinal colgado. Posible- La relevancia de los relieves estructurales de mente, este anticlinal represente la flexura de despe- los pliegues nucleados por sal, será un tema para se- gue más grande en la región. ñalar, debido a la escala de estas trampas estructu- rales que también son desarrolladas en el Golfo de PANORÁMICA SOBRE LA ESTRATIGRAFÍA DEL México, aunque la columna estratigráfica involucra- ANTICLINAL DE POTRERO CHICO da en ambos casos tiene una diferencia importante. Y SIERRA DE MINAS VIEJAS Se observará cómo el flanco frontal del Anti- clinal de Potrero Chico cambia notablemente, debido En la Sierra de Minas Viejas las capas más a la rotación de echados a lo largo de la estructura gruesas en la cima de la montaña pertenecen a la ca- hacia el buzamiento occidental y oriental de la naríz liza ‘‘Cupidito’’ y corresponden a la secuencia trans- estructural del pliegue (Fig. D2-2). gresiva colocada sobre la discordancia 124 Ma. El modelo estructural que explica este cam- La estratigrafía de Potrero Chico es similar bio de geometría del pliegue atendiendo los datos a la descrita para el Potrero García con la diferencia de superficie adquiridos por Echanove, 1965, pero de que entre ambas localidades la base de la For- actualizado con conceptos estructurales y datos re- mación Cupido tiene mayor espesor de parches del gionales es el de un anticlinal con falla tardía (Mo- Complejo “Arrecifal” Cupido. Una sección de corre- delo 1), el cual presenta fallas inversas tardías en la lación litoestratigráfica del intervalo Neocomiano- porción central del flanco norte del anticlinal que se Aptiano entre el Cañón Huasteca, los potreros de propagan hacia ambas terminaciones de éste (Figs. García, Chico y la Sierra de Minas Viejas (Fig. D2-1) D2-3 y D2-4); estas fallas producen la rotación de muestra que en las primeras localidades la posición un segmento central del flanco norte del pliegue. de parches de “arrecife” estratigráficamente están en Muchos ejemplos de pliegues despegados con 1 ó la base y subyacen a litofacies que denotan ambiente 2 fallas tardías se pueden observar en el subsuelo lagunar, mientras que en la Sierra de Minas Viejas del Golfo de México, siendo más común los plie- el “arrecife” es más joven, la litofacies lagunar cam- gues tipo pop-up de este tipo de estilo estructural bia de espesor y el Complejo “Arrecifal” sobreyace a que pliegues no fallados. Mario Aranda García et al. 34 Figura D2-1.- Sección de corre- lación entre el Cañón Huasteca, Potrero Chico y Sierra Minas Viejas. El borde del Sistema Se- dimentario Cupido prograda ha- cia el NE las litofacies de cuenca de las formaciones La Peña y Taraises aumentan su espesor y la Formación ‘‘Cupidito’’ es una secuencia transgresiva a partir de la discordancia 124 Ma (sec- ción modificada de Wilson et al., 1984). SE NW a. b. NW SE c. 02Km Figura D2-2.- Vistas panorámicas del flanco norte de la Sierra de Potrero Chico, viendo al noroeste (a.) y al sur (b.). Imagen Spot de la Sierra de Potrero Chico mostrando los rasgos dominantes del anticlinal del mismo nombre. Estratigrafía Jurásico-Cretácica del Arco de Monterrey de la Sierra Madre Oriental y . 35 Figura D2-3.- Secciones estructurales de Echa- nove 1965 (a.) y modifi- cada de Echanove (b.), ubicación de la sección en el mapa de Echanove, 1965 (d.). Imagen Spot del Anticlinal de Potrero Chi- co con sus principales rasgos estructurales (c). Corte geológico interpre- tando la geometría en el subsuelo (e) a partir de la sección (b). El desarrollo de fallas tardías en los pliegues frontal para explicar el recostamiento de la estrati- de despegue, es el mecanismo de deformación que grafía en la porción central del pliegue (Modelo 2). explica el acortamiento máximo en este tipo de es- La secuencia del desarrollo de los pliegues de este tructuras, acomodando a través de estas fallas una modelo fue primero el desarrollo de los pliegues de vergencia en dirección del acortamiento y otra con un despegue superior, ubicado hacia la cima en dirección opuesta, la deformación contraccional, de la columna del Cretácico Inferior, esta posición incrementando el relieve estructural por el ascenso estratigráfica corresponde a niveles plásticos dentro de la estratigrafía en la rampa de la falla del bloque de la Formación Cupido y después el desarrollo del alto de la estructura por un empuje vertical dominan- pliegue principal despegado en evaporitas jurásicas temente. afectó y rotó los pliegues superiores, explicando el Existe la posibilidad de la sobreposición de cambio lateral de ángulos de buzamiento en el flanco dos niveles de plegamiento disarmónico en el flanco frontal. a0. a1. b. 02Km Figura D2-4.- Secciones estructurales transversales del Anticlinal de Potrero Chico (modificada de Echa- nove, 1965). Las secciones (a0.) y (a1.) corresponden al Modelo 1 de un anticlinal de despegue nucleado por evaporitas con fallas tardías. La sección (b.) corresponde al Modelo 2 que involucran dos niveles de plegamiento disarmónico. Mario Aranda García et al. 36 MECANISMO DEL NUCLEAMIENTO y Potrero Chico) 35.4 y 18.2 km2 bajo la base del DE ANTICLINALES POR EVAPORITAS Kimmeridgiano. Adicionalmente se propone que el bloque de basamento bajo los pliegues referidos res- La figura D2-5 ilustra cómo las geometrías ponde al acortamiento invirtiendo fallas antiguas de de los pliegues de García, Potrero Chico y Minas Vie- un graben sin-rift, este modelo proporciona el meca- jas son estados de evolución diferente de pliegues de nismo para explicar deformación vertical de evapo- despegue nucleados por sal. El volumen de evapori- ritas actuando con el mecanismo contraccional de ta en el núcleo corresponde en cada caso a: (García manera simultánea o desfasada. Anticlinorio de la Anticlinal de Sierra del Fraile Minas Viejas Figura D2-5.- Sección transversal de los anticli- nales de García y Potrero Chico (ver figura 13, sección 2c, página 66.) para la ubicación. Mo- delo de Anticlinal nucleado por sal con inver- a sión de basamento. La inversión de basamento introduce las evaporitas en los anticlinales (a). Panel de la Estratigrafía de un graben jurásico con relleno syn-rift de evaporitas (b). La línea roja punteada es la posición del despegue thin- skin, las líneas moradas son fallas jurásicas que limitaron el graben, y después fueron invertidas modificando el despegue. 01Km 0 b 01Km 0 PANORÁMICA SOBRE LA ESTRUCTURA DOMO DIAPÍRICO AL ESTE DEL DOMO DE MINA DE LA CUENCA LA POPA La figura D2-6 muestra la expresión morfo- Parada 2-2 lógica típica de estructuras dómicas subyacidas por evaporitas, numeradas a continuación: La segunda Parada (2-2) del segundo día a) La relación proporcional de longitud y de la excursión se encuentra a 10 min y 10 km de la amplitud en el eje de la estructura es no- primera Parada sobre la misma carretera Monterrey- toriamente en una relación 1:1.5. Monclova. En esta Parada de la excursión se aborda- b) El arreglo de fracturas del Domo de rán aspectos locales de la Geología Estructural por- Mina es más parecido a los ejemplos de ción sur de la Cuenca de Sabinas donde existe otra la figura xx e, cuya expresión y arreglo estructura halocinética no reportada como tal. geométrico es como el modelo de do- El objetivo de la Parada 2-2 es: Mostrar los mos por diapirismo activo con la cima elementos estratigráficos y estructurales del área del de la sal sin fallar y fallamiento simétrico Diapiro de Mina en su posición norte, adyacente al en el domo. Pliegue de Minas Viejas. Se enfatizará sobre las va- La figura D2-7 (a.) muestra una sección riaciones y magnitudes del relieve estructural. transversal que incluye los diversos estadios de es- Estratigrafía Jurásico-Cretácica del Arco de Monterrey de la Sierra Madre Oriental y . 37 tructuras halocinéticas, los diapiros del Lineamiento Cara y Cuna, el Diapiro de Mina y el Anticlinal nu- cleado por sal de Minas Viejas.
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