The Brassfield Formation, named by A.F. Foerste in 1906, is a

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

and dolomite formation exposed in Arkansas, Ohio, Kentucky, Indiana, Tennessee and West Virginia in the United States.Foerste, A.F. 1906. The Silurian, Devonian, and Irvine formations of east-central Kentucky, with an account of their clays and limestones. ''Geological Survey of Kentucky, Bulletin'' 7, 369 p. It is Early

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

(Aeronian, Llandoverian) in age and well known for its abundant

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

s and stromatoporoids.Schneider, K.A. and Ausich, W.I. 2002. Paleoecology of framebuilders in Early Silurian reefs (Brassfield Formation, southwestern Ohio). ''Palaios'' 17: 237-248. In Ohio, where the unit has escaped

dolomitization Dolomitization is a geological process where magnesium ions replace calcium ions in the mineral calcite, resulting in the formation of dolomite. Dolomitization conditions are present in Abu Dhabi, the Mediterranean Sea, and some Brazilian hyp ...

, the Brassfield is an encrinite biosparite with numerous

crinoid Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...

species.Ausich, W.I. 1984. Calceocrinids from the Early Silurian (Llandoverian) Brassfield Formation of southwestern Ohio. ''Journal of Paleontology'' 58: 1167-1185.Coogan, A.H. 1996. Ohio's surface rocks and sediments, in Feldmann, R.M., and Hackathorn, M., eds., ''Fossils of Ohio: Ohio Department of Natural Resources, Division of Geological Survey Bulletin'' 70: 31–50. File:BrassfieldEncrinite042112.jpg, Close view of Brassfield Formation near Fairborn, Ohio, showing grains mainly composed of crinoid fragments. File:Phaenopora superba Silurian Brassfield.jpeg, ''Phaenopora superba'', a

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

n from the Brassfield Formation. File:BrassfieldEncrinite041915.JPG, Encrinite from the Brassfield Formation (Silurian) near Fairborn, Ohio.

References

Silurian System of North America Silurian Arkansas Silurian Indiana Silurian Kentucky Geologic formations of Ohio Silurian Tennessee Geologic formations of West Virginia Silurian southern paleotemperate deposits Rhuddanian Aeronian Telychian Limestone formations of the United States Dolomite formations {{US-geologic-formation-stub