Abstract

Lower Cenomanian ammonites have been described from the Pawpaw Formation, the Main Street Limestone, the Grayson Formation, the Del Rio Claystone, the upper part of the Georgetown Limestone, and the Buda Limestone of Texas and northern Mexico. The fauna of the Buda Limestone, in particular, is dominated by a distinctive group of lyellicerid ammonites of the genera Faraudiella and Budaiceras.

The greatest number of lyellicerids in Texas consists of 13 species from the Buda Limestone (zone of Budaiceras hyatti). These species occur with Mantelliceras sp. cfr. batheri Spath, M. sp. cfr. hyatti Spath, and M. cantianum Spath (=M. budaense Adkins), all of which have been collected from the Buda Limestone. They represent the cantianum zone and probably the upper part of the martimpreyi zone of western Europe.

In Europe lyellicerids (Stoliczkaia) do not range above the martimpreyi zone, and Faraudiella is said not to range higher than the Albian. There are mantellicerid species common to Texas and Europe, but there are no Cenomanian lyellicerid species common to Texas and Europe. If the Mantelliceras species are used for correlation, the Budaiceras fauna of Texas and northern Mexico would seem to represent a relict lyellicerid group that lived in the restricted environment of that area after lyellicerids had disappeared from the rest of the world.

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