A frequent activity in my job is responding to public requests for identification of possible fossils. The majority of these turn out to not be fossils at all, but a few are, and some of those eventually make their way into a museum collection.
A few months ago, after reading some of my blog posts about thrombolites and stromatolites, Robin Boucher contacted me to confirm the identity of some possible stromatolites he had collected in Montgomery County, Virginia. Sure enough, Mr. Boucher’s identification was correct, and it turned out he had a large number of stromatolites with nice laminations visible in cross section:
Mr. Boucher arranged with the landowner, Cynthia Pitonyak, to have the specimens donated to VMNH, and delivered them personally a few weeks ago.
These stromatolites were collected from the Cambrian Elbrook Formation, which is older than the Conococheague Formation that produced the Boxley thrombolite, but probably deposited in a similar near-shore setting. It’s interesting that the older Elbrook specimens are laminated stromatolites, while the younger Conococheague specimens are non-laminated thrombolites. Walter and Heys (1985) suggested that in the Cambrian thrombolites became more common because increased burrowing destroyed stromatolitic laminations. If they’re correct, we may have caught the point in time in Virginia when burrowing increased enough that stromatolitic textures were being replaced by thrombolitic textures, resulting in the change in algal mounds we see from the Elbrook to the Conococheague.
Thanks to Mr. Boucher and Ms. Pitonyak for donating these interesting specimens to the museum.
Walter, M. R. and G. R. Heys, 1985. Links between the rise of the Metazoa and the decline of stromatolites. Precambrian Research 29:149-174.