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I found some sedimentary rocks with fossils in the vicinity of Devil's Den State Park near Winslow, Arkansas yesterday. The rock is more like sandstone than limestone, and it is often sandwiched between thin layers of shale. Perhaps my geologist friends can help me out here? Ed. note: this appears to be in the vicinity of the Bloyd shale formation. The Bloyd shale is primarily sandstone, secondarily shale. Its time period is middle Pennsylvanian.
The rock is quite soft and porous. It also made of rather coarse particles, and the fossils are very thin and delicate. The actual fossils of what I believe are brachiopod shells often show little detail, with the cast being much better preserved.
Here's a particularly well-preserved example of one of the small coiled shells, 1/4" in size. It appears to be the same species as the larger example appearing in the previous entry. They make up 80% of the fossils found in the rock.
The rock frequently features sealed cavities, filled with a fine dirt. They at first appeared to be relatively huge fossils.
Note the toothlike structures on this bivalve, each about 1/3 mm.
This crumbling crinoid stem fragment is typical of the extremely delicate fossils found in this particular rock.
I'm particularly interested in getting an identification of the coiled shells. Anyone have any ideas?
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