| The Arco Hills Formation of east-central Idaho is a mixed carbonate-siliciclastic unit which is Late Mississippian (Latest Chesterian) in age and contains abundant well-silicified brachiopods. Fifteen genera (twenty-four species) of brachiopods occur in the Arco Hills Formation; Orbiculoidea, Rugosochonetes, Werriea, Schuchertella, Schizophoria, Inflatia, Diaphragmus, Flexaria?, Pugnoides, Leiorhynchus, Punctospirifer, Anthracospirifer, Torynifer?, Composita, and Cleiothyridina.; The brachiopods and associated other taxa are found as both in situ communities and biostratinomic accumulations. Factors such as quantitative community analysis, functional morphology, and taphonomic features provide the basis for water depth interpretation. Five biofacies are found in the Arco Hills Formation; (A) low specific diversity Orbiculoidea wyomingensis, (B) high diversity Productoidea /Orthotetoidea, (C) low diversity tempestites with Anthracospirifer and Composita, (D) encrinite grainstones with broken brachiopods, and (E) high diversity mixed brachiopod-bivalve community.{09}The articulate brachiopod communities of the Arco Hills flourished in normal salinity, well-oxygenated, ramp conditions. Orbiculoidea occurs in dysaerobic environments which other forms cannot tolerate. |
