A Late Ordovician seafloor, preserved through repeated burial.
The Mt. Orab butter shale is a thin fossil-bearing interval within the Sunset Member. Its articulated fossils record several events, not one frozen moment for the entire bed.
| Age | Late Ordovician — Richmondian |
|---|---|
| Member | Sunset Member |
| Locality | Mount Orab, Brown County, Ohio, USA |
| Studied thickness | Approximately 0.46 m in the studied interval |
| Event beds | At least seven recognizable clay-silt couplets |
| Sediment | Repeated clay-silt couplets within the butter-shale interval |
The approximately 0.46 m measurement describes the studied Mt. Orab interval, not the thickness of the entire Arnheim Formation or a measurement of every Flat Run exposure.
The interval contains at least seven recognizable clay-silt couplets interpreted as stacked storm-generated event beds. More than one depositional event contributed to the assemblage.
The basal silt portions include transported skeletal debris and disarticulated trilobite remains. These are interpreted as parautochthonous: moved locally rather than necessarily buried exactly where they lived.
The clay-rich portions preserve articulated enrolled, prone and partially enrolled trilobites, alongside carcasses and molts. They are interpreted as largely autochthonous: organisms rapidly buried at or near where they lived. Enrolment alone does not establish how an individual died.
Documented fauna, comparison records and what I’ve personally found.
A checked box means I’ve personally found it. An unchecked box means I haven’t recorded a personal find here, not absence from the formation. These are read-only field-record markers, not visitor checkboxes or stock indicators.
This is a working selection, not an exhaustive census. Formation-wide records are not automatically Mt. Orab or Flat Run records. Occurrence evidence is stated separately on each entry; my personal identification is not being attributed to a paper that only identifies the genus.
Personally found
Trilobite · Calymenidae · Mt. Orab bed documented
I’ve personally found Flexicalymene retrorsa, which is also documented from the Mt. Orab bed. I record the identification and provenance of each specimen separately.
Sources: Hunda, Hughes & Flessa (2006) · PBDB: Mt. Orab collection 192315 / Key et al. (2010)
Personally found
Trilobite · Asaphidae · Formation-wide record; personal Mt. Orab find
I’ve personally found I. maximus at my home quarry. The UGA reference includes the Arnheim in its occurrence range. The Mt. Orab taphonomy paper records Isotelus at genus level; I’m not using that paper to establish the species of my find.
Sources: UGA Type Cincinnatian reference: Isotelus · Hunda, Hughes & Flessa (2006)
Personally found
Echinoderm · crinoid · My Arnheim find — my identification
I’ve found stems I identify as Cincinnaticrinus. I’m recording them at genus level, without assigning a species. The Mt. Orab paper supports crinoid occurrence generally, not my identification of these stems.
Sources: Hunda, Hughes & Flessa (2006)
Personally found
Echinoderm · crinoid · My Arnheim find — my identification
I identify the calyx I found as Pycnocrinus dyeri. An Arnheim specimen in the Geneseo collection is catalogued as Glyptocrinus dyeri, an alternative combination encountered in collection records. The UGA reference treats Pycnocrinus and Glyptocrinus as distinct genera; the names are not generally interchangeable. I count this as one find, not two.
Sources: UGA Type Cincinnatian reference: Pycnocrinus · Geneseo: Arnheim specimen catalogued as Glyptocrinus dyeri
Not yet recorded in my finds
Mollusc · bivalve · Mt. Orab bed documented
Recorded at genus level in the Mt. Orab assemblage. I haven’t recorded a personal find on this checklist yet.
Sources: Hunda, Hughes & Flessa (2006)
Not yet recorded in my finds
Colonial invertebrates · Mt. Orab bed documented
Bryozoans form part of the documented assemblage. The separate genus entries below are narrower published records, not additional finds of mine.
Sources: Hunda, Hughes & Flessa (2006)
Not yet recorded in my finds
Bryozoan · Mt. Orab collection record
PBDB collection 192315 records this genus, citing Key and colleagues (2010). That collection record does not mean I’ve personally found or identified it.
Sources: PBDB: Mt. Orab collection 192315 / Key et al. (2010)
Not yet recorded in my finds
Bryozoan · Mt. Orab collection record
Recorded in the same Mt. Orab PBDB collection, citing Key and colleagues (2010). Retained at genus level.
Sources: PBDB: Mt. Orab collection 192315 / Key et al. (2010)
Not yet recorded in my finds
Trace fossil · burrows · Mt. Orab bed documented
A recorded burrow trace, not the name of an identified body-fossil animal. Kept separate from the species-level fauna entries.
Sources: Hunda, Hughes & Flessa (2006)
Not yet recorded in my finds
Trilobite · Cheiruridae · Formation-wide Arnheim record
The UGA occurrence compilation includes the Arnheim, citing Ludvigsen (1977) and Babcock (1996). This does not establish a Flat Run or butter-shale occurrence.
Not yet recorded in my finds
Mollusc · gastropod · Formation-wide Arnheim record
The cited occurrence compilation includes the Arnheim. I haven’t marked it as a personal find or a confirmed Mt. Orab bed occurrence.
Not yet recorded in my finds
Mollusc · gastropod · Formation-wide Arnheim record
Listed from the Arnheim as well as other Cincinnatian units. The published range is broader than my home-quarry record.
Not yet recorded in my finds
Echinoderm · edrioasteroid · Formation-wide Arnheim record
An attached echinoderm included in the Arnheim occurrence compilation. This is not a crinoid, and my crinoid finds do not establish that I’ve found this animal.
Not yet recorded in my finds
Echinoderm · edrioasteroid · Formation-wide Arnheim record
The UGA compilation lists the Arnheim, citing Bell (1976). I’m not claiming a home-quarry occurrence or personal find here.
Not yet recorded in my finds
Mollusc · nautiloid cephalopod · Formation-wide Arnheim record, genus only
The compilation includes an Arnheim record at genus level. Its named species have different listed ranges; they are not assigned here. This is not a confirmed Mt. Orab butter-shale record.
Not yet recorded in my finds
Graptolite · Formation-wide Arnheim record
Listed from the Arnheim under this name; the reference notes the older combination Glyptograptus anacanthus. I haven’t recorded a personal find here.
Not yet recorded in my finds
Echinoderm · crinoid · Historical Arnheim record; taxonomic caution
The UGA compilation lists an Arnheim occurrence from Dalvé (1948), but explicitly questions the validity of this species. I include it as a qualified historical record, not as an identification of my crinoid material.
Not yet recorded in my finds
Trilobite · Asaphidae · Arnheim occurrence unverified in checked sources
I include it for comparison and leave it unchecked. The UGA reference lists the species but supplies no occurrence range for it. That gap is not proof of absence; a specific Arnheim or Mt. Orab record is still needed.
Not yet recorded in my finds
Trilobite · Lichidae · Arnheim occurrence I can confirm — fragments
I can confirm Allolichas fragments from the Arnheim, but I’m not marking them as a personal find. I use the species spelling given by Dry Dredgers; that overview does not establish the formation or identify these fragments to species.
Taxa documented in the Mt. Orab study, at the identification level supported by my working reference.
Trilobite · Calymenidae
The characteristic named trilobite of the Mt. Orab Lagerstätte. Enrolled, prone and partially enrolled individuals occur alongside carcasses, molts and disarticulated remains.
Trilobite · Asaphidae
Documented at genus level. Assigning I. maximus or I. gigas requires diagnostic specimen morphology; locality alone does not establish the species.
Crinoids
Crinoids are documented in the Mt. Orab fauna. Isolated stems and columnals do not by themselves establish a species identification.
Bivalve
Documented at genus level in the Mt. Orab faunal assemblage.
Bryozoans
Documented colonial animals in the Mt. Orab community; species names require additional evidence.
Trace fossil
A burrow trace recorded in the event beds, not the name of an identified body fossil.
Lingulids are also reported. Brachiopods are outside this guide’s main focus, not absent from the assemblage.
This section describes the limits of the cited literature; personal finds and occurrences I can confirm are recorded separately in the checklist above. An Arnheim or Cincinnatian record alone is not a butter-shale record.
Documented from the Arnheim Formation in the research draft, but not securely established from the Mt. Orab butter-shale horizon.
An Arnheim crinoid association is reported in the research draft. That does not establish a Flat Run butter-shale occurrence or a species identification.
Known in the wider Cincinnatian / Richmondian record. Locality-specific evidence remains weak. Use “orthoconic nautiloid cephalopod, indeterminate genus” for undiagnosed material rather than automatically calling it Orthoceras.
Cyclonema, Cyclora, Trepospira, Treptoceras, Glyptocrinus, Xenocrinus, Cupulocrinus, Ectenocrinus and rare trilobites such as Ceraurus remain comparative possibilities, not a confirmed Flat Run fauna list.
Cephalopod presence must not be inferred solely from healed injuries or bite marks; a fauna list needs body-fossil evidence.
Use the narrowest identification supported by the specimen. Formation-wide records do not establish a Mt. Orab or Flat Run occurrence. A locality study does not authenticate an individual lot.
Use Isotelus sp. when species is uncertain, Crinoidea indet. for unidentified crinoid material, and a species name only when diagnostic characters support it. F. retrorsa is documented in the bed; that is not an instruction to rename every existing Flexicalymene specimen.
Hunda, B. R., Hughes, N. C., & Flessa, K. W. (2006). Trilobite taphonomy and temporal resolution in the Mt. Orab Shale Bed (Upper Ordovician, Ohio, U.S.A.). PALAIOS, 21, 26–45.
The bed summary follows the supplied Mt. Orab working fauna research draft. The expanded checklist also cites formation-level reference pages and collection records, with occurrences I can confirm and my personal finds identified separately. These additional records are not all established by the Mt. Orab paper. Formation-wide evidence alone does not establish a home-quarry occurrence.
