Abstract

OMANA, Lourdes; GONZALEZ-ARREOLA, Celestina  and  RAMIREZ-GARZA, Blanca Margarita. Barremian planktonic foraminiferal events correlated with the ammonite zones from the San Lucas Formation, Michoacán (SW Mexico). Rev. mex. cienc. geol [online]. 2005, vol.22, n.1, pp.88-96. ISSN 2007-2902.

We studied the Tiringueo section from the San Lucas Formation, located in the state of Michoacán, SW Mexico. The section is a flysch sequence consisting of a rhythmic deposit of shale, siltstone, and fine to medium graded sandstone interbedded with limestone. The sequence contains ammonites, foraminifera and radiolarians.

The biostratigraphic analysis, based on the planktonic foraminifera and ammonites, permitted the recognition of the biostratigraphic units established on both fossil groups, for first time in SW Mexico. Although the planktonic foraminifera are scarce and poorly preserved, some important events such as the first occurrence of Hedbergella similis, Globigerinelloides blowi and Globigerinelloides aptiensis were correlated with the ammonite zones. By means of these foraminiferal events, the Zones of Hedbergella similis and Globigerinelloides blowi partim (early and late Barremian) were identified. The faunal assemblage and distinctive lithological characteristics suggest that the San Lucas Barremian sequence was deposited in pelagic conditions.

Keywords : planktonic foraminifera; Barremian; San Lucas Formation; Michoacán; Mexico.