Composition of Mississippian carbonate mounds in the Ozark region, North America and Ireland

Scope and Method of Study: Mississippian crinoidal-bryozoan carbonate mounds in the Compton and Pierson Limestone, St. Joe Group, have been called Waulsortian or Waulsortian-type. Waulsortian mounds contain features such as polymuds, radial fibrous calcite cement filled cavities and specific grain-type assemblages (Lees and Miller, 1995). Conversely, those features are rare to absent in Ozark mounds. This study compares Ozark mounds to mounds in Ireland in order to classify the Ozark mounds and determine their depositional setting and diagenetic history relative to the "true" Waulsortian mounds.;Findings and Conclusions: Ozark mounds occur as knoll-form build-ups, may display minor stacking and have a strong lateral component, whereas Irish mounds display multiple stages of stacking and form larger and more vertically complex structures. The Compton and Irish Tournaisian mounds are interpreted to have formed in calmer, and moderate to deeper water, whereas Pierson mounds are interpreted to have formed at shallower depths as evidenced by more abraded skeletal fragments and a lower percentage of mud. Both Ozark and Waulsortian mounds have a similar diagenetic history. Compton and Irish Waulsortian mounds are bryozoan-rich, mud-dominated mounds whereas the Pierson mounds are crinoid-rich and grain-dominated. The mound-core facies of Irish Waulsortian mounds have >30% calcite cement compared to 10%-20% calcite cement in Compton mounds and 5%-30% calcite cement in Pierson mounds. Statistically, the Ozark and Irish mounds differ in the abundance of skeletal fragments and mud. Overall, Compton mounds and Benton County Pierson mounds are classified as Waulsortian-type and lime mud accumulation bioherms (Wilson, 1975). The grain-rich Delaware County Pierson mounds are classified as sediment piles (Wilson, 1975) due to their bedded mound-core facies, which are transported accumulations of skeletal fragments.