NEW AND UNEXPECTED CRYOGENIAN MICROFOSSIL FINDINGS FROM SOUTHEASTERN IDAHO AND THE DEATH VALLEY REGION OF CALIFORNIA

Organic-walled microfossils have recently been discovered in green argillite within the cap-carbonate sequence (ca. 665 Ma) of the Scout Mountain Member, Pocatello Formation, southeastern Idaho. The fossils are primarily compressed, organic spheres on the order of 100 microns in diameter; vesicles exhibit distinctive textures, and some specimens exhibit acanthomorphic processes. They are morphologically similar to other Neoproterozoic acritarchs, including those described from the Chuar Group (Grand Canyon, Arizona) and the Amadeus and Officer Basins (Australia). This is the first record of life during the late Neoproterozoic from this region. Although the Pocatello Formation has undergone greenschist facies metamorphism, identifiable organic material is preserved.

Vase-shaped microfossils have recently been discovered in gray shale in the upper Crystal Spring Formation of the Pahrump Group in the Death Valley region of California. These fossils constrain the depositional age of the upper Crystal Spring Formation as Neoproterozoic, and support correlations with the Chuar Group (ca. 742 Ma, Grand Canyon, Arizona).

The discovery of these elusive Neoproterozoic microfossils in unexpected facies provides optimism for generating a Cryogenian-Ediacaran fossil record in these areas, which will contribute to our understanding of Earth system interactions at the dawn of animal evolution.