Any Ideas?

[jgcox]

While we were at U-dig in Utah, Kim found this looks cool but does anyone have any idea what it could be?

[Oxytropidoceras]

This an example of weathering that is often found calcareous shales at the you-DIG site in Millard County, Utah. The sides of this slab were the surfaces of parallel fractures that formed a block of shale before it was split along bedding planes. While it was still in the ground, groundwater flowed through these fractures and aqueous solutions from these fractures filtered through the shale. As these solutions filtered through the shale, the block of shale was altered progressively deeper from these fracture surfaces to create concentric shells of rocks that consist of less weathered rock with depth into the block. When the block of shale was broken along a bedding plane, it revealed a cross-section of these concentric shells of progressively less weathered rock and the weathering front that created them. The process that created these color bands is similar to the process that results in spheroidal weathering of large blocks of rock.

Similar features in other rock types can be seen in Big Bend National Park along The Grapevine Hills Trail in
http://prism.texarkanacollege.edu/bbvirtual/grapevine/sphero-weath05.jpg at http://prism.texarkanacollege.edu/bbvirtual/grapevine/grapevine.html

A couple of papers about this process are:

Heald, M. T., T. J. Hollingsworth, and R. M. Smith, 1979. Alteration of sandstone as revealed by spheroidal weathering. Journal of Sedimentary Petrology. vol. 49, pp. 901–910.

Sarracino, R., and G. Prasad, 1989, Investigation of spheroidal weathering and twinning. GeoJournal. vol. 19, no. 1, pp 77-83.

Yours,

Paul H.