The Logan Formation is the name given to a Lower Carboniferous (early

Osagean The Mississippian ( ), also known as Lower Carboniferous or Early Carboniferous, is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earlier of two subperiods of the Carboniferous period lasting from rou ...

)

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

and conglomeratic unit exposed in east-central Ohio and parts of western West Virginia, USA.

Stratigraphy and paleoenvironment

The Logan Formation was named by Andrews (1870) and originally described as a "buff-colored, fine-grained sandstone" above the Waverly Formation and below the Maxville Limestone. Bork and Malcuit (1979) concluded that the Logan Formation was deposited on a shallow marine shelf in a generally transgressing sea. The age of the Logan Formation has been established as early Osagean (Tn3) by the occurrences of

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s, ammonoids,

conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...

s and miospores (Clayton et al., 1998; Matchen and Kammer, 2006).

References

* * * * Image:LoganConglomerateWooster.jpg, Conglomerate in the Logan Formation exposed in Wooster, Ohio, USA. Image:LoganBrachiopodsWooster.jpg, Brachiopod internal and external molds in the Logan Formation in Wooster, Ohio. Image:Aviculopecten subcardiformis01.JPG, The bivalve '' Aviculopecten subcardiformis'' from the Logan Formation in Wooster, Ohio (external mold). Image:LoganFauna011312.jpg, Bivalves (''Aviculopecten'') and brachiopods (''Syringothyris'') in the Logan Formation in Wooster, Ohio. Image:Logan Formation Cross Bedding Scour.jpg, Cross-bedding and scour in the Logan Formation of Jackson County, Ohio. Image:Schizodus_medinaensis.JPG, ''Schizodus medinaensis''; a

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

from the Logan Formation in Wooster, Ohio (internal mold). Image:Syringothyris01.JPG, ''Syringothyris'' sp.; a spiriferinid brachiopod from the Logan Formation in Wooster, Ohio (internal mold). Image:Syringothyris bored Wooster Carboniferous.jpg, ''Syringothyris'' external mold with borings; Logan Formation; Wooster, Ohio. Image:Syringothyris texta Hall 1857 dorsal.jpg, ''Syringothyris texta'' (Hall 1857), dorsal view, internal mold. Lower Carboniferous of Wooster, Ohio. Image:Helminthopsis01.JPG, ''Helminthopsis'' ichnosp.; a

trace fossil A trace fossil, also called an ichnofossil (; ), is a fossil record of biological activity by lifeforms, but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of part ...

from the Logan Formation in Wooster, Ohio. Image:PlatyceratidMississippian.JPG,

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 ...

calyx from the Logan Formation in Wooster, Ohio, with a conical platyceratid gastropod (''Palaeocapulus acutirostre'') attached. Mississippian United States Carboniferous Indiana Carboniferous Ohio Carboniferous West Virginia Carboniferous southern paleotropical deposits Sandstone formations of the United States Siltstone formations of the United States Conglomerate formations Shale formations of the United States {{US-geologic-formation-stub