10 April 2014

Fusulinids and stylolites, Hueco Formation

Posted by Callan Bentley

My colleague Joshua Villalobos shared this image with me the other day – it’s a thin section of fusulinid-bearing limestone of the (Permian aged) Hueco Formation, from the Tom Mays Unit of Franklin Mountains State Park, Texas.

fus_mays_sm Click to enlarge

Note the scale bar at lower left. The big fusulinid in the middle is 3mm in diameter! And that’s not even it’s longest axis!

Fusulinids were big honking burrito-shaped protists (foraminiferids) that lived on the bottom of the sea. (They were benthic, like Cribratina). They each had one single cell. That’s it. Huge unicellular organisms – the wonders of a rigid skeleton!

The other beautiful thing about this image are the lovely stylolites (wiggly dissolution surfaces) that run from lower left to upper right. Notice that with some of the fusulinids on the top and bottom, significant portions of their bodies are missing along these dissolution surfaces.