Crinoid calyx plate from the Mississippian of Ohio, USA. (millimeter scale)

The Maxville Limestone is the only Middle to Late Mississippian-aged stratigraphic unit in Ohio. Its outcrop belt is not extensive - it principally occurs in Muskingum County and Perry County in eastern and southeastern Ohio. The Maxville Formation can also be found as cobbles and pebbles in the basal Sharon Formation (Lower Pennsylvanian), which disconformably overlies Ohio's Mississippian rocks. Paleohills, or erosional outliers, of Maxville Limestone have also been identified.

Seen above is a small, weathered-out fossil from the Maxville Limestone at a quarry in western Muskingum County, Ohio. The quarry targets Maxville Limestone and crushes it for use as road gravel, fill, rip-rap, and erosion-control blocks. The Maxville here is an erosional outlier that is described in Stout (1918).

The exposed stratigraphy at this quarry includes basal Pennsylvanian sedimentary rocks disconformably overlying Mississippian Maxville Limestone:

1) ~4 to 5 feet of fissile black shale with smooth, slightly shiny concretions (paleopebbles?)

2) Sharon Conglomerate - quartz-pebble conglomerate

3) Black shale

4) Gray, non-fissile claystone with lumpy iron oxide concretions

5) Unconformity with minor paleotopography

6) Maxville Limestone - mostly lime mudstone (micritic limestone) with occasional lenses or pockets of fossil shell hash; some thin shale interbeds; one small apparent sandstone lens (= relatively thin, gray, clay-rich interval with sandy-silty grains); occasional coarsely-crystalline/coarse-grained limestone intervals with finely laminated argillaceous limestone; some slickenlined surfaces seen in the incompetent clay-rich intervals. Observed fossils include brachiopods (Composita subquadrata atrypids), bivalves, gastropods (Straparollus planodorsatus and Bellerophon sublaevis), and crinoids (even calyx material). Straparollus gastropods are common in the argillaceous intervals - they are compacted and compressed. One Straparollus fossil snail was seen with a healed shell fracture/break.

Notable Pennsylvanian float samples in the section: a Lepidodendron tree trunk with nice, diamond-shaped leaf scars and a coarse-grained rip-up clast breccia.

The small fossil shown here is a single, rounded-pentagonal plate from the head/calyx of a crinoid (possibly Cyathocrinus maxvillensis). Crinoids (also known as sea lilies) are sessile, benthic, filter-feeding, stalked echinoderms that are relatively common in the marine fossil record. They are also a living group, but are relatively uncommon in modern oceans. A crinoid is essentially a starfish-on-a-stick. The stick, or stem, is composed of numerous stacked columnals, like small poker chips. Stems and individual columnals are the most commonly encountered crinoid fossils in the field. Intact, fossilized crinoid heads (crowns, calices, cups) are unusual. Why? Upon death, the crinoid body starts disintegrating very rapidly. The soft tissues holding the skeletal pieces together decay and the skeleton falls apart.

Classification: Animalia, Echinodermata, Crinoidea

Stratigraphy: shaly limestone in the Maxville Limestone, Meramecian to Chesterian, Middle to Upper Mississippian

Locality: Pleasant Valley Limestone Quarry (spoils pile at the southwestern end of the quarry), southwest of Dillon Lake, Hopewell Township, western Muskingum County, eastern Ohio, USA (~vicinity of 39° 58' 49.64" North latitude, 82° 08' 05.74" West longitude)

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