| Field examples of the 787 to 732 million year old Neoproterozoic Beck Spring Dolomite that outcrop several miles from the Alexader Hills. The Beck Spring Dolomite yields some of the oldest skeletonized eukaryotic cells yet discovered in the US west. Image at bottome shows strontium-enriched giant ooids, characteristic of a specific horizon in the Beck Spring Dolomite. Ooids usually develop from concentric carbonate accretion around a minute sand fragment (or, a shell in modern oceans) in warm, shallow, extremely agitated marine intertidal environments. Photographs courtesy Robert Clyde Mahon. |