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 roughly ...
)
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.Blatt ''et al.'' 1980, p ...
,
sandstone 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
brachiopods,
ammonoid
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
s,
conodont
Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which ...
s and miospores (Clayton et al., 1998; Matchen and Kammer, 2006).
References
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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 (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
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 from the Logan Formation in Wooster, Ohio.
Image:PlatyceratidMississippian.JPG, Crinoid 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
{{US-geologic-formation-stub