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vol.22 número1Hacia una zonación estándar de ammonites para el Aptiano (Cretácico Inferior) del norte de MéxicoAmmonites y bivalvos del Jurásico Superior de la Formación Cucurpe, Sonora (México) índice de autoresíndice de materiabúsqueda de artículos
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Revista mexicana de ciencias geológicas

versión On-line ISSN 2007-2902versión impresa ISSN 1026-8774

Rev. mex. cienc. geol vol.22 no.1 Ciudad de México abr. 2005

 

Artículos

Maastrichtian shallow-water ammonites of northeastern Mexico

Ammonites de agua somera del Maastrichtiano del noreste de México

Christina Ifrim1 

Wolfgang Stinnesbeck1 

Armin Schafhauser1 

1Institut für Regionale Geologie, Universität Karlsruhe, D-76131 Karlsruhe, Germany. christina.ifrim@bio-geo.uni-karlsruhe.de


Abstract

In northeastern Mexico, extensive deltaic and prodeltaic sediment complexes developed during Maastrichtian times, known as the Difunta Group and Escondido Formation in Coahuila and the Northwest of Nuevo León, and the Cárdenas Formation in San Luis Potosí. These sediments contain abundant and diverse invertebrate assemblages, among them the last ammonites in the area, prior to their extinction. Sphenodiscus (S. lobatus, S. pleurisepta) and Coahuilites sheltoni are the dominant elements of this paucispecific fauna and clearly favored shallow water coastal environments. Ammonites other than sphenodiscids are rare and restricted to occasional Baculites ovatus and a single Pachydiscus (Pachydiscus) neubergicus. This early (and possibly early late) Maastrichtian assemblage differs notably from the coeval ammonite fauna of the distal prodeltaic and open marine Méndez Formation in eastern Nuevo León. The latter assemblage is far more diverse (23 species referred to 18 genera) and includes, in addition to typical Gulf of Mexico faunal elements, many Tethyan, cosmopolitan, and even southern high latitude Indopacific species previously unknown from Mexico. Faunal differences between the two nearby outcrop areas are thus clearly related to paleobathymetry and not to paleobiogeography, being Baculites ovatus the only conspecific element.

Key words: ammonites; paleobathymetry; Maastrichtian; Upper Cretaceous; Mexico

Resumen

Durante el Maastrichtiano, complejos deltaicos y prodeltaicos extensos se desarrollaron en el Noreste de México, y se conocen como grupo Difunta y formación Escondido en Coahuila y el Noroeste de Nuevo León, y formación Cárdenas en el Estado de San Luis Potosí. Los sedimentos contienen asociaciones abundantes y diversas de invertebrados, entre ellos los últimos ammonites en la región, previos a su extinción. Sphenodiscus (S. lobatus, S. pleurisepta) y Coahuilites sheltoni son los elementos dominantes de esta fauna pauciespecífica y claramente favorecieron ambientes costeros someros. Ammonites que no pertenecen a los sphenodiscidos son mucho más escasos y se restringen a Baculites ovatus y un sólo ejemplar de Pachydiscus ( Pachydiscus) neubergicus. Esta asociación caracteriza al Maastrichtiano temprano (y posiblemente la parte temprana del Maastrichtiano tardío) . Difiere notablemente de la fauna coetánea de la formación Méndez del Este de Nuevo León, la cuál fue depositado en ambientes prodeltaicos distales y de mar abierto. La fauna de la formación Méndez es mucho más diversa (23 especies pertenecientes a 18 géneros) e incluye, aparte de elementos faunísticos típicos del Golfo de México, especies tethysianas, cosmopolitas, y hasta especies indopacificas de latitudes australes altas. Estos elementos habían sido desconocidos en México hasta la fecha. Las diferencias faunísticas entre las dos regiones cercanas del Noreste de México se deben, por lo tanto, a diferencias en la paleobatimetría y no a la paleobiogeografía. El único elemento idéntico es Baculites ovatus.

Palabras clave: ammonites; paleobatimetría; Maastrichtiano; Cretácico Superior; México

Texto completo disponible sólo en PDF.

ACKNOWLEDGMENTS

We are greatly indebted to John D. Cooper for showing us around the Eagle Pass area and the Escondido Formation in southern Texas. We also thank José Guadalupe López Oliva, Arturo González González, and Stefan Götz for discussions on the geology and fossil invertebrate fauna of northeastern Mexico. The Facultad de Ciencias de la Tierra of the Universidad Autónoma de Nuevo León, Linares, and the Museo del Desierto de Coahuila, Saltillo, offered logistical and technical support, and the Instituto Nacional de Antropología y Historia in Mexico City kindly authorized sampling and temporal expedition of the fossil material. Research was supported by the Deutsche Forschungsgemeinschaft grants STI 128/7 and STI 128/9.

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Received: January 02, 2004; Revised: September 01, 2004; Accepted: September 12, 2004

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