As you may already know, the Houston Museum of Natural Science has long been digging up wonderful Permian fossils in Seymour, Texas. Curator of Paleontology Dr. Robert T. Bakker and his team of hot, tired and pink (from the dirt) volunteers have made major finds, but sometimes it’s the little things that count — like finding little amphibians, such as the boomerang-headed Diplocaulus and the snake-like Lysorophus, too.
The rock stars of the Seymour dig are people like Chris Flis, who finds bones everywhere. There are also geologists on the team, like Gretchen Sparks, who are interested in sedimentology (how the dirt got there) and who pick up interesting bits and wonder what they are.
This is a warty blob (that’s a technical term) that she found. It sort of looks like a bone or a burrow dug by something. I tested it and found that it is made of calcium carbonate.
To see more, I ground and polished the end. Now we can see that this is not a bone because it does not have a marrow cavity or bone lamellae. Warty surfaces like this are frequently found on the outsides of arthropod burrows because the animal lines the burrow with spit and sediments balls — but the warty parts of these structures are inside and on the exterior, so this is not a shrimp burrow.
The flowery appearance of the growth indicates that this is caliche, one of those sedimentary features that often get little attention.
Caliche is a hard-water deposit on steroids. Caliche forms in dry areas like North Texas when more water evaporates from the surface of the ground than falls as rain. Ground water dissolves minerals like calcium carbonate and gypsum from the soil and rock. When the water evaporates from the surface, these minerals are deposited in flowery growths called “efflorescences”.
The climate in Seymour is so dry that caliche is growing right now. During the Permian (about 250 million years ago), the climate must have been even dryer, because we find bands of caliche in the soil. Each band represents an ancient soil layer.
We can even tell the history of the caliche deposition. The interpretation is based on what covers what:
A. White layer was deposited in a nearly flat crack in the dirt. Note the white flowers.
B. The pink layer covers the white and has the same shape of flowers but contains more iron.
C. Layer B was partially covered by darker pink laminations. The laminations indicate that crystal growth was much slower.
D. The blob fractured and the dark red layer of sediment was deposited along with fragments of Layers A and B. This is a mini sedimentary dike.
E. Since Layer D is made of sediment and not hard caliche, it shrank and cracked in the process of drying. This crack was filled with a quickly-deposited rind of fine grained white material followed by very slow growing clear crystals, making the darker band inside the white. This looks like an agate filling but is still carbonate.
Were all these layers deposited 250 million years ago? That actually would be easy to tell, because young carbonate has a carbon delta C13 signature well within the 50,000 year sensitivity range for the method. It just costs money to have the analysis done, and there are probably better uses for the resources right now – like having more specimens mounted!
I conclude that the warty bone-looking thing is really an inorganic crystallization of carbonate and possibly gypsum. Did you know you could learn so much from gravel?