New findings of Late Jurassic charophyte gyrogonites and gastropods from the San Juan Formation, NW Oaxaca, Mexico

Limestone samples were collected from the San Juan Formation, which consists of a mixed marine and non-marine deposit located in the Tlaxiaco Basin, Oaxaca, Mexico. These beds contain a fresh-water assemblage of charophyte gyrogonites and gastropods, and a shallow-water marine association with larger foraminifera Labyrinthina mirabilis Weynschenk, 1951, Everticyclammina sp. a Rivulariacean-like cyanobacteria and Cladocoropsis mirabilis Felix, 1907. An Oxfordian–Kimmeridgian age has been assigned based on the stratigraphic range of the larger foraminifera Labyrinthina mirabilis Weynschenk, and Everticyclammina sp. The mudstone textured limestone and the fossil association with charophytes and gastropods suggest a continental fresh-water environment. The grainstone-packstone with larger foraminifera Labyrinthina mirabilis Weynschenk, Rivulariacean-like cyanobacteria and Cladocoropsis mirabilis Felix suggests a shallow-water marine milieu.