ABSTRACT Facies analysis utilizing a conodont biostratigraphic framework is a powerful tool for evaluating genetic relationships of Osagean–basal Meramecian strata within the Ozark region (Arkansas–Missouri–Oklahoma) of the southern midcontinent. This investigation builds upon previous work cited herein, and suggests that some lithostratigraphic divisions, although useful in differentiating strata in a localized setting, may not be suitable for regional correlations within the Boone Group. High-resolution conodont biostratigraphy demonstrates the diachronous nature of lithostratigraphic divisions within the Boone Group, with both the Reeds Spring Formation and Bentonville Formation (Burlington–Keokuk) clearly becoming younger as they are traced from southwestern Missouri into northern Arkansas and northeastern Oklahoma. Subsequent facies analysis shows that the Reeds Spring Formation represents deposition within outer ramp through proximal middle ramp settings (low to moderate energy), whereas the Bentonville Formation (Burlington–Keokuk) records deposition within proximal middle ramp to inner ramp settings (moderate to high energy). Integration of facies analysis and conodont biostratigraphy-based relative chronostratigraphy provides the basis for construction of four time-slice maps illustrating the distribution of time-correlative facies belts. Together, these time-slice maps deliver a clearer representation of the evolution of Boone Group carbonate ramp deposition during the Osagean, which was characterized by overall shallowing-upward and progradation to south and southwest.

ABSTRACT A succession of Ordovician and Mississippian carbonates, separated unconformably, is exposed across the southern flank of the Ozark Dome in southwest Missouri. Deposits of both periods exemplify typical facies of the Midwestern United States: carbonate tidal-flat assemblages for the Early Ordovician and carbonate shelf environments for the Early–Middle Mississippian. The basic stratigraphic sequence of these deposits has been known for over a century, but interesting features remain to be addressed. Thin discontinuous sandstones are present within the Early Ordovician Cotter Dolomite, but the informal Swan Creek sandstone member seems anomalous. This sandstone can exceed 5 m in thickness and is fairly continuous across southwest Missouri. Most Ordovician sandstones in Missouri mark major transgressions above regional unconformities, but not the Swan Creek, and there is no obvious source of the sand. Therefore, we hypothesize that the Swan Creek represents reworked eolian dunes blown across the broad peritidal environment. Clastic sandstone dikes, apparently sourced from the Swan Creek, cut across beds of Cotter Dolomite near faults. We propose that these dikes are evidence of local faulting and seismicity during the Early Ordovician. Early and Middle Mississippian limestones comprise a sequence of shelf deposits, although mud mounds and other facies changes near the Missouri-Arkansas line mark the edge of the Mississippian shelf and the transition to a ramp setting. Early Mississippian carbonate deposition was interrupted by a short and localized influx of siliciclastic sediment comprising the Northview Formation. The Northview has additional characteristics consistent with a river-dominated deltaic deposit, which we suggest as its origin. If correct, this hypothesis implies that the history of tectonic features in the Midwest is more complicated than yet known. Finally, facies changes within and between the local Mississippian formations may record an early crustal response to the impending Ouachita orogeny farther to the south.

ABSTRACT Lithologies, depositional environments, stratigraphic architecture, and conodont biostratigraphy of Lower to Middle Mississippian rocks in the western Ozarks comprise five depositional sequences in ramps on the southern Burlington shelf. Aggradational ramps in the Kinderhookian to early Osagean St. Joe group were relatively strongly overprinted by Ouachita-related tectonism involving inferred recurrent passage of fore-bulge highs and associated basins across central and southern parts of the outcrop area. Significant effects of tectonism are southward facies shallowing onto the broad Kanoka ridge paleotopographic high associated with locally extensive marine and lesser subaerial erosion, sediment thickening and deposition of generally northward down-lapping, resedimented wedges with dislodged reef blocks and conglomerates into relatively rapidly subsiding basins, and formation of a regionally extensive paleosol at the top of the group. Back-stepping subsidence due to middle Osagean foundering of the Kanoka ridge was followed by rapid, long-distance progradation of middle- and outer-ramp facies in the Bentonville and Reeds Spring limestones. Tectonism at this time resulted variously in local folding, uplift, marine and subaerial erosion, and reversal of shelf bathymetry. Southward erosion of the Reeds Spring and Bentonville occurred at least in Oklahoma on rejuvenated segments of the Kanoka ridge. Overlying lower Meramecian limestones are shallow-water deposits truncated by a major unconformity.

ABSTRACT Four conodont biozones, including three subzones, are interpreted within a revised lithostratigraphic framework for the upper Boone Group and Mayes Group in northeastern Oklahoma and adjacent parts of Missouri, Kansas, and Arkansas. Although revised lithostratigraphy is principally based on observed lithologic characteristics and stratigraphic relationships, conodont biostratigraphic data played an important role in correlation and final organization of units. Within the upper Boone Group, Biozone 1 (lower Meramecian) includes the Ritchey Formation and the Tahlequah limestone and Biozone 2 (middle Meramecian) includes the Moccasin Bend Formation and Quapaw Limestone. The Mayes Group spans Biozone 3 and Biozone 4. Biozone 3 (upper Meramecian) is represented by the Bayou Manard Member of the Pryor Creek Formation (new name). Biozone 4 marks the appearance of definitive Chesterian conodont fauna. The lower two subzones within Biozone 4 correspond to the Lindsey Bridge (Biozone 4L) and Ordnance Plant (Biozone 4M) members of the Pryor Creek Formation, whereas the upper subzone consists of the Hindsville Formation (Biozone 4U). Documentation of conodont taxa and recognition of the proposed biozones provides relative time constraints for genetically meaningful interpretations of regional geology and subsequent evaluation of the Mayes Group and upper Boone Group within a broader interregional context.

ABSTRACT The Early Mississippian Northview Formation is a siliciclastic deposit reaching 25 m in thickness along an east-west trend in southwest Missouri, USA. Along this trend, the formation coarsens upward from shale to coarse siltstone with shaley interbeds and channel fills. The siltstones have high concentrations of two trace fossils: Nereites missouriensis and Zoophycos . Thus, the ichnofauna is dominated by namesake genera of the two deepest marine ichnofacies. Nevertheless, the Northview was deposited on a shallow carbonate platform. The vertical succession of trace fossils is consistent with deltaic deposition. The lowest shale is dominated by common elements of the Phycosiphon prodelta ichnofacies, and the lowest overlying siltstone is dominated by elements of the Rosselia delta-front ichnofacies. N. missouriensis occurs abundantly and dominates the overlying siltstones, with Zoophycos covering bedding planes near the top, a pattern found within the lower plain of other Paleozoic deltas. Geochemical proxy measurements indicate paleosalinity decreasing upward through the formation and an approaching freshwater (fluvial) source, raising questions about Early Mississippian source areas and tectonics.

ABSTRACT Multiple orders of depositional cyclicity in the Mayes Group of northeastern Oklahoma are delineated by refined depositional facies associations and stratigraphic surfaces. Facies associations include deep subtidal facies, shallow subtidal facies (including distal and proximal subfacies), carbonate shoal facies, and shoal crest facies. The Mayes Group records a primary transgressive–regressive depositional cycle bounded below by a major unconformity (sub-Mayes unconformity) and above by an important provincial conodont biostratigraphic boundary and widespread flooding surface at the base of the Fayetteville Shale. Within the Mayes Group, two secondary transgressive–regressive depositional cycles are separated by an interpreted unconformity. The lower Mayes cycle comprises the Bayou Manard and Lindsey Bridge members of the Pryor Creek Formation, whereas the Ordnance Plant Member is grouped with the Hindsville Formation in the upper Mayes cycle. Present in both the lower and upper Mayes cycles are high-frequency shallowing-upward cycles bounded by flooding surfaces. Evaluating the distribution of facies and stratigraphic surfaces within a framework of multiple orders of depositional cyclicity is essential to interpreting the geologic evolution of the southern mid-continent during the Meramecian and Chesterian, and impacts oil and gas production by improving our understanding of reservoir compartmentalization.

ABSTRACT The Mississippian system in the midcontinent of the United States is a complex carbonate- and chert-dominated system with a large degree of reservoir variability and heterogeneity. An outcrop study was done in the state of Arkansas on the Middle Mississippian (Visean) Burlington-Keokuk Formation to analyze the depositional setting and high-resolution sequence stratigraphic architecture to better understand the reservoir distribution of similar units in the subsurface. The outcrop location, in the northwestern portion of the state of Arkansas, was studied using an integrated sequence stratigraphic approach, combining high-resolution photography for tracing bed boundaries and lithologic contacts along with facies determination from outcrop and thin section analysis. A range of skeletal packstones to grainstones dominated by crinoidal fragments and an abundance of void-filling syntaxial calcite cements comprised the majority of the outcrop facies. Nodular to bedded siliceous limestone to carbonate-rich chert facies were observed containing up to approximately 50% microporosity. Based upon facies assemblages and the presence of meter-scale sand waves with faint cross bedding on outcrop, these units were likely deposited in a high-energy sand shoal or sand bar in a proximal position on a distally steepened ramp. Within the outcrop, multiple shoaling upward packages were observed, consisting of siliceous limestones and cherts at the bases overlain by coarsening and thickening upward grainstone bodies. This stacking pattern was observed at two different scales. Larger-scale packages 15 to 35 feet (5–10 m) thick were mappable and continuous across the entire outcrop (1320 ft [400 m]), and are inferred to be controlled by eustatic sea-level change. A smaller-scale stacking pattern was observed on the meter (several feet) scale and were mappable for 165–500 ft (50–150 m) laterally. The lack of limited lateral correlation is inferred to be due to autocyclic controls within the active sand body. The observed shoaling upward patterns create a hierarchy of stacked reservoir and seal units with superimposed variability. These findings illustrate the potential for high-frequency sea-level change and autocyclic control on facies and reservoir distribution that may be seen in the subsurface. Two-dimensional geostatistical modeling further illustrates the need for this level of characterization, as variogram inputs are biased significantly by the segregation of high-frequency sequences and dominant eustatic or autocyclic controls on deposition.

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.