Lecathylus gregarius-Sphenothallus Community, Mosalem Formation (Silurian to of the United States)

Where: Iowa (42.3° N, 90.4° W: paleocoordinates 19.7° S, 57.2° W)

• coordinate based on political unit

• local area-level geographic resolution

When: Mosalem Formation, Rhuddanian to Rhuddanian (443.4 - 438.5 Ma)

• "Early Silurian (early Llandovery), based on graptolites, i.e. zones 16-19 of the British succession (Berry and Boucot 1970)." [I.e., acuminatus through gregarius Zones, which would imply an age range of Rhuddanian through early Aeronian.]

• formation-level stratigraphic resolution

Environment/lithology: lagoonal or restricted shallow subtidal; burrowed, gray, argillaceous, cherty/siliceous, carbonaceous dolomite

• Plants and other carbonaceous material noted, as well as soft-bodied "worms". Contact with underlying Maquoketa unconformable, with deeply eroded Maquoketa surface. "A nearshoe environment, equivalent to BA 1, seems indicated, although the presence of Leptaena would indicate at least BA 2 to 3 for at least one bedding plane...possible halite pseudomorphs and rare ripple marks low in the Iowa Mosalem section.." This is seen as the shallower-water variant of the Lecthyalus Community Group. Compare with PBDB coll. 25861.
• "Witzke states that 'the Mosalem is the most argilalceous unit noted in the Silurian of Iowa and is primarily characterized by dense, thin-bedded argillaceous dolomites.' the unit is most shaly basally and more dolomitic at the top. Color varies from gray to brown. Locally there are chert nodules in the middle or upper portions. Major parts show a mottled coloration when weathered due to burrowing. Other parts are distinctly laminated, with laminations often less than 1 mm..."

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 26860: authorized by Michael Foote, entered by Michael Foote on 06.11.2002

Creative Commons license: CC BY (attribution)

Taxonomic list

Lecathylus gregarius
The genus is variably spelled "Lecthyalus" and "Lecthaylus" in this reference, but the correct form is "Lecathylus" according to Treatise on Invertebrate Paleontology, volume W.
 Strophomenida -
 Strophomenida - Rafinesquinidae
Leptaena "rhomboidalis" Wahlenberg 1818
 Rhynchonellida -
 Lingulida - Lingulidae
Lingula cuneata Conrad 1839
"Pelecypoda indet." = Bivalvia
"Pelecypoda indet." = Bivalvia Linnaeus 1758 clam
Gastropoda indet. Cuvier 1797 snail
 Diplograptoidea - Diplograptidae
 Dendroidea -
Dendroidea indet. Nicholson 1872 graptolite
  - Pyrgocystidae
Pyrgocystis sp. Bather 1915
Plantae indet. Haeckel 1866
spores, filaments