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 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 An understanding of regional orogenic, climatic, and eustatic processes is critical to interbasinal correlation of Paleozoic strata in eastern North America. Tectonic activity associated with the culmination of Appalachian orogenic events has been shown to have regional influence on paleostructure and sediment dispersal in the Appalachian foreland basin and adjacent intracratonic Illinois and Michigan Basins. The culmination of the Acadian orogeny at the end of the Devonian represents the beginning of a period of general tectonic quiescence extending throughout the early and middle Mississippian in eastern North America. Early Mississippian strata in the Michigan Basin are distinctive and mark the transition from marine shale and carbonate-dominated sedimentation during much of the Late Ordovician through Late Devonian to siliciclastic-dominated deposition throughout much of the Carboniferous. The Osagean Stage Marshall Formation constitutes an important coarse-grained siliciclastic formation in the Michigan Basin. Despite numerous outcrop studies and early subsurface investigations, the Marshall Formation remains poorly understood in terms of depositional controls and stratigraphic relationships to related Mississippian strata in Michigan and correlative strata in adjacent basins. This work documents sedimentological and sequence stratigraphic relationships in early–middle Mississippian, generally clastic-dominated strata of the Marshall and lower Michigan Formations (as described in previous literature). Utilizing 535 well logs and core-to-log calibration in conjunction with detailed descriptions of seven cored intervals spanning the Michigan Basin, new stratigraphic relationships are presented suggesting the Marshall Formation and informal stray sandstone units are genetically related and reflect tectonic, eustatic, and climatic processes that occurred in the Michigan Basin during the early Carboniferous.

Abstract This field trip provides an overview of geological features in southwestern Missouri that are related to the American Civil War and to human culture. This includes the geology and history of the Wilson’s Creek National Battlefield (where the second important battle of the American Civil War was fought on 10 August 1861), Zágonyi’s Charge (25 October 1861), the Battle of Springfield (8 January 1863), and the gravestones and monuments of the National Cemetery in Springfield in which many of those who fought at Wilson’s Creek and other Civil War conflicts are buried. Other stops include the Springfield Underground and the quarries and facilities at what was once the town of Phenix (which, along with Carthage, Missouri, was the home of some of the largest dimension-stone quarries west of the Mississippi River); and a reconstructed mill site in Point Lookout, just south of Branson. Most of the field trip involves outcrops, quarries, and bedrock composed of the Mississippian Burlington-Keokuk limestones (undivided), providing numerous chances to examine outcrops and products made of limestone and chert.

Evidence for eustasy at the Kinderhookian-Osagean boundary is presented here in a new synthesis based on detailed analysis of the boundary in the central Appalachian Basin and regional mapping of the Kinderhookian-Osagean boundary unconformity in the conterminous United States. Detailed stratigraphic analysis within the central Appalachian Basin shows that coarse-grained, fluvial sandstones (Black Hand, Burgoon, Big Injun, Purslane) are associated with valley incision up to 60 m and a widespread sequence boundary (SB2) that is inferred to have resulted from a forced regression during the Kinderhookian-Osagean boundary interval. The extent of unconformity at the boundary was evaluated by mapping the inferred positions of shorelines during the Kinderhookian, Kinderhookian-Osagean boundary interval, and early Osagean based on stratigraphic data from Correlation of Stratigraphic Units of North America (COSUNA) charts. This analysis shows areas of extensive unconformity at the Kinderhookian-Osagean boundary across the United States inferred to be the result of sea-level fall and recovery during a period of ~2 m.y. or less, based on missing conodont zones. The Kinderhookian-Osagean boundary is equivalent in age to the global Tn2-Tn3 boundary, and supporting evidence for global regression and eustasy at this boundary is also reviewed. The combination of this evidence for eustasy with recently reported middle to early late Tournaisian (Tn2a-Tn3b) diamictites in South America permits the inference of continental glaciation at this time. Previous studies of oxygen and carbon isotope data from marine carbonates and fossils have shown strong positive anomalies suggestive of global cooling at the Kinderhookian-Osagean and Tn2-Tn3 boundary, providing further support for the hypothesis of continental glaciation in the late Tournaisian.