Unique Cretaceous Oncolite Stromatolites Mexico

This unique stromatolite comes from an inland freshwater lake in the State of Chihuahua, Mexico, probably a hypersaline aquatic environment. In terms of geologic time, this is very young stromatolite (Cretaceous). While Phanerzoic stromatolite such as this is far less common than in the Proterozoic, it is distributed worldwide; recently a 12 foot tall, living stromatolite dome was discovered in a freshwater, hypersaline lake in Africa.
In this specimen, the microbial colony began on a still intact host rock of volcanic origin and then grew in ever-expanding bands. Such forms are often called Oncolite, and are typically found in ancient lakes. The form is typical of younger stromatolite owing to the vast number of life forms that would feed on the bacteria as compared to the Precambrian when stromatolite was at its zenith on Earth, and had little competition.

This specimen has been cut along one horizontal plane and highly polished one side to show the intricate detail.

Of interest from a scientific perspective is the young age. This dinosaur-age, Cretaceous stromatolite was formed long, long after stromatolite-building organisms had to compete with other life forms, and hence had become uncommon on earth, similar to modern times. The microorganism(s) that form this stromatolite is unknown. Perhaps it was photosynthetic cyanobacteria, other prokaryotic bacteria, Eukaryotic algae (often considered a simple plant), or perhaps some combination of these types of organisms competing to survive in a not-so-friendly aquatic environment.