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. It is apparently
a distinct stromatolite rather than a part of a large bacrobial
mat. 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.
|