25 February 2017

Concretions in the Millboro Formation, Fort Valley

Posted by Callan Bentley

Yesterday was a gorgeous late spring day* in the Fort Valley, and I was delighted to engage in my first day of field work of 2017. Skies were clear, the temperature soared to a decadent 80°F, and I thrilled to be out geologizing!

I went out in the central Fort Valley with University of Virginia geologist Tom Biggs, who is mapping the Rileyville quadrangle. We stopped to examine some enormous concretions along the bedding plane in shale/siltstone of the Devonian Millboro Formation.

Here’s a double concretion, with a dump truck looming in the background:

These suckers are BIG. Here’s a single oblate** ellipsoid concretion, with a lens cap (upper right-center) for scale:

Concretions like these are typical of the Millboro. These behemoths are the largest I’ve seen, though.

I made a 3D model of this one:



* Not actually “late spring.” February 24th, actually. Still in the middle of winter. But, you know, global warming.

** As viewed, the diameter was about twice as wide as it is thick in the third dimension. The 3D model gives a sense of this.