ABSTRACT

The Berriasian-Valanginian Taraises Formation in the subsurface of northeastern Mexico consists of an intercalation of argillaceous limestone and shale. This formation is divided into two members, based on lithologic characteristics defined from electric and radioactivity logs from oil wells in northeastern Mexico. In addition, two small ammonite groups of the subfamily Olcostephaninae (upper Valanginian) collected at Potrero de Garca, Nuevo Len, northeastern Mexico, are described: (1) Capeloites neoleonense n. sp. and (2) Garcites potrerensis n. gen. and sp. and G. cavernensis n. gen. and sp. The presence of Dichotomites (Dichotomites) sp. in the same beds supports an late Valanginian age for these strata. One specimen of Capeloites obtained from a core of the La Laja-8 well, south of Tampico City, eastern Mexico, designates an late Valanginian age for the interval drilled (2556-2562 m) in the so-called Lower Tamaulipas Formation in this area. Global geographic distribution of Capeloites is restricted to France, Spain, and Peru; its presence in Mexico supports a biogeographic link between Europe and America.