ABSTRACT Mississippian (Tournaisian–Viséan) carbonate mounds in the Compton and Pierson limestones, Ozark region, North America, have been called Waulsortian. However, European Waulsortian mounds contain features such as geopetals with multigenerations of carbonate mud (polymuds) and stromatactis cavity systems that are rare to absent in Ozark mounds. To determine similarities and differences, examine their origins, and clarify nomenclature, mounds in the Compton and Pierson limestones are compared with Waulsortian mounds in the Feltrim Limestone, Ireland. Features considered included mound size, geometry, style of aggradation, composition, depositional setting, and diagenetic history. Mounds in the Compton and Pierson limestones are <10 m (33 ft) thick and form singular knoll-form or aggregates with a strong lateral growth component. In contrast, individual Waulsortian mounds in the Feltrim Limestone range from 5 to > 30 m ( 16 – 100 ft ) thick, but coalesce and vertically aggrade to form complexes that exceed 500 m ( 1600 ft ) . Pierson mounds are crinoidal and grain-rich, whereas Compton and Feltrim mounds are bryozoan-rich and mud-dominated. All mounds have similar cement stratigraphy and diagenetic histories. Mud-rich Compton mounds and Feltrim mounds are interpreted as deeper water than skeletal-rich Pierson mounds. Limited accommodation constrained Compton and Pierson mound size and forced lateral aggradation. Subsidence-driven accommodation in the Dublin Basin allowed Feltrim mounds to grow larger, coalesce, and aggrade vertically. Three types of mounds are recognized: true Waulsortian in the Feltrim Limestone, mud-cored Waulsortian-type Compton and Pierson mounds, and Pierson transported bioaccumulation mounds. Small dimensions of Waulsortian-type Pierson and Compton mounds limit their potential as oil and gas reservoirs, whereas Pierson crinoidal sediment piles are known to form reservoir-size accumulations.

ABSTRACT Petrographic, geochemical, and fluid inclusion analysis of dolomite and calcite cements has been conducted on Mississippian carbonates collected from the surface and subsurface of the southern midcontinent of the United States (Oklahoma, Missouri, Kansas, and Arkansas). Fracture and vug, intergrain, and intragrain porosity are filled with calcite, authigenic quartz, and dolomite cements. Primary limestone porosity is filled partially by early marine and meteoric calcite cements. Equant (blocky) calcite cements were precipitated under seawater or mixed meteoric-seawater conditions in the phreatic zone and in the deep phreatic zone under late (burial) diagenetic conditions. Fracture- and breccia-filling saddle dolomite cements that were observed are late diagenetic and are likely related to the nearby Tri-State Mississippi Valley-type (MVT) mineral district. Carbon and oxygen isotope values of dolomite cements range from δ 18 O (VPDB) = −9.5 to −2.7‰ and from δ 13 C (VPDB) = −4.0 to −0.4‰. Values for calcite cements range from δ 18 O (VPDB) = −11.6 to −1.9‰ and from δ 13 C (VPDB) = −12.2 to +4.6‰. These values are consistent with three types of diagenetic fluids: seawater, seawater modified by meteoric water, and evolved basinal water. Analysis of fluid inclusions in late calcite, dolomite, and quartz cements indicates the presence of both dilute and high salinity end-member fluids. Homogenization temperatures (T h ) of fluid inclusions range from 57°C to 175°C and salinities range from 0 to 25 equivalent weight % NaCl. Fluid inclusion T h values and salinities are consistent with a saline basinal fluid variably diluted by fluids of meteoric or mixed seawater and meteoric origin. Petroleum inclusions were observed in late diagenetic calcite and dolomite cements.The late diagenetic cements filled porosity retained after early diagenetic cementation indicating that some original porosity in the Mississippian carbonate rocks remained open during petroleum migration. Elevated fluid inclusion T h values over a broad region, not just in the Tri-State Mineral District, imply that the regional thermal maturity of rocks may be higher than believed previously. This study indicates that the Mississippian carbonate resource play on the southern midcontinent has a very complex diagenetic history, continuing long after early diagenetic cementation. Possibly the most important diagenetic events affecting these rocks occurred during burial and basinal fluid migration through these strata.