Hugo Beraldi 3 years, 1 month ago

These stromatolites formed ~72 Ma ago in an intra-arc basin within the Tarahumara Formation, which was emplaced during the Laramide orogeny in Northwestern Mexico (Sonora). The locality has been named the Huepac Chert because of the presence of thin and thick chert horizons. The chert is black and it contains a great variety of fossils, including angiosperm and gymnosperm pollen grains, fungal hyphae and spores, green algae, cyanobacteria, diatoms, arthropod remains, fruits, palm roots, aquatic plants (e.g. Haloragaceae), and numerous achritarchs.