Hindia parva?-Sphenothallus-Apycnodiscus Communityof the Elgin (Ordovician of the United States)

Where: Allamakee County County, Iowa (43.3° N, 91.4° W: paleocoordinates 19.7° S, 61.3° W)

• coordinate based on political unit

• outcrop-level geographic resolution

When: Elgin Member (Maquoketa Formation), Maysvillian (452.0 - 449.5 Ma)

• Basal 15 cm phosphorite in Elgin Member, Maquoketa Formation, at Dubuque Formation contact.

• group of beds-level stratigraphic resolution

Environment/lithology: deep subtidal ramp; lithified, dolomitic, pyritic phosphorite

• The strong tendency for some groups to be preserved articulated while echinoderms are not suggests a rather low sedimentation accumulation rate, but this is not a true starved basin situation. The pitted and mineralized Maquoketa-Dubuque contact resembles many other corrosion surfaces in the Upper Mississippi Valley Galena Group (Witzke, 1985b), and likely formed in a submarine, not subaerial environment. If the suggestion of Brown (1974) that upwelling of oxygen-poor, phosphate-rich waters into a typical carbonate shelf edge produced the diminutive Maquoketa faunas is correct, then this community, with a significant but small echinoderm component, marks the transition from the highly affected Palaeoneilo fecunda-Nuculites neglectus Community (with almost no echinoderms) to the more normal marine Thaerodonta recedens-Iowacystis sagittaria Community. Benthic assemblages have not been defined for many Ordovician communities as yet, but a position analogous to BA 3-4 is probable (see also Witzke & Glenister, 1987, for further discussion).
• The lithology is a poorly consolidated to pyrite-cemented dolomitic phosphorite ranging in thickness from 0.1 to 0.3 m. Most common are small (<2 mm) subsphaeroidal concentrically laminated hydroxylapatite clasts, but less well rounded phosphate clasts up to 15 cm in length and phosphatized fossils are also abundant. Locally quartz geodes ranging in size from 1 cm to more than 25 cm in length are common, e.g., at the type locality. The geodes contain minor sulfide mineralization (wire marcasite) and common calcite, ferroan dolomite, fluorite, and selenite crystals in the often largely hollow interiors... This community appears to have been subject to some current activity, but not frequently enough to remove selectively particular size clasts. The deposit is very poorly sorted, at least basally, with clay to gravel-sized clasts intermixed, some or all of which may be phosphatized.

Preservation: replaced with phosphate

Primary reference: T. J. Frest, C. E. Brett, and B. J. Witzke. 1999. Caradocian-Gedinnian echinoderm associations of Central and Eastern North America. Paleocommunities--a case study from the Silurian and Lower Devonian 638-783 [M. Foote/K. Koverman/P. Wagner]more details

Purpose of describing collection: paleoecologic analysis

PaleoDB collection 13261: authorized by Michael Foote, entered by Kimberly Koverman on 04.02.2002

Creative Commons license: CC BY (attribution)

Taxonomic list

Trilobita indet. Walch 1771 trilobite
Ostracoda indet. Latreille 1802 ostracod
 Orthida - Platyorthidae
Diceromyonia sp. Wang 1949
 Acrotretida - Scaphelasmatidae
Scaphelasma sp. Cooper 1956
 Acrotretida - Acrotretidae
Conotreta sp. Walcott 1889
 Lingulida - Obolidae
 Lingulida - Lingulidae
 Protobranchia -
Nuculites neglectus Hall 1862 clam
Palaeoneilo fecunda Hall 1862 clam
Gastropoda indet. Cuvier 1797 snail
 Trochonematoidea - Lophospiridae
"Loxoplocus (Lophospira) depauperata" = Lophospira depauperata
"Loxoplocus (Lophospira) depauperata" = Lophospira depauperata Hall and Whitney 1862 snail
 Euomphalina - Platyceratidae
"Cyclora minuta" = Cyclonema minuta
"Cyclora minuta" = Cyclonema minuta Hall 1845 snail
 Bellerophontida - Bellerophontidae
Bucanopsis lirata Ladd 1925 snail
 Bellerophontida - Bucanellidae
 Murchisoniina - Eotomariidae
Liospira micula Hall and Whitney 1862 snail
 Murchisoniina - Hormotomidae
"Murchisonia (Hormotoma) sp." = Hormotoma
"Murchisonia (Hormotoma) sp." = Hormotoma Salter 1859 snail
 Orthocerida - Proteoceratidae
Isorthoceras sociale Hall in Miller 1877
 Paleoloricata -
Bryozoa indet. Ehrenberg 1831
Conodonta indet. Eichenberg 1930 conodont
 Diplograptoidea - Diplograptidae
Orthograptus truncatus Lapworth 1876 diplograptoid
Orthograptus truncatus peosta
 Bireclinata -
Climacograptus pumilis climacograptid
Climacograptus typicalis Hall 1865 climacograptid
Climacograptus typicalis putillus
  - Cyclocystoididae
Apycnodiscus sp. Smith and Paul 1982
Asteroidea indet. de Blainville 1830 sea star
undetermined starfish plates
Crinoidea indet. Miller 1821 Sea lily
undetermined crinoid plates
 Streptosclerophorida - Hindiidae
Hindia ? parva demosponge