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.

Natural fractures are common in the unconventional “Mississippian Limestone” play of the US Southern Mid-Continent region. Owing to their narrow width, vertical cores provide limited data on the distribution of fracture attributes (e.g., kinematic aperture, height, and spacing) in relation to fracture abundance. For the purpose of searching for an outcrop analog that provides an extensive view of lateral fracture distribution, this study uses an outcrop with Mississippian-aged strata in northwestern Arkansas. Targeting the Reeds Spring Formation, this study aims to characterize the type, attributes, and distribution of natural fractures and to test the outcrop’s suitability as a fracture analog for the subsurface. In the outcrop, planar and nodular beds of lime mudstone and chert contain near-vertical cemented fractures. Fracture types mainly include ptygmatic and opening-mode fractures. Ptygmatic fractures are the most common fracture type in both lime mudstone and chert, whereas the opening-mode fractures are present mostly in chert. Bedding structures, which are defined by lime mudstone–chert variations, affect fracture growth, as indicated by the observation that perfect bed-bounded, top- or base-bounded, and confined fractures collectively account for the majority of the fracture population. In terms of fracture intensity, chert shows a higher average value as compared with lime mudstone. Negative exponential and power law are present as the statistical patterns between cumulative frequency and fracture height, kinematic aperture, aspect ratio, and spacing. The best-fitting distribution pattern and the coefficient of determination vary with lithology, fracture type, and fracture height. These patterns likely point to a cooperative role of lithology, fracture type, and fracture-bedding relationships, as well as the dynamics of rock mechanical properties, in affecting these fracture attributes. In comparison with the cores, this outcrop may serve as a fracture analog for the Mississippian Limestone play in northernmost Oklahoma–southernmost Kansas where cherty facies are widespread, but not for the play areas in north-central Oklahoma, which are dominated by mixed carbonate–siliciclastic facies.

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.

A study of the McCourt Sandstone Tongue and the Glades coal bed of the Upper Cretaceous Rock Springs Formation in the Rock Springs coal field has provided valuable data for reconstructing an ancient coal-forming depositional environment. The sandstone and coal were deposited on a strand plain along the western shores of the Late Cretaceous interior seaway of North America. The McCourt Sandstone Tongue consists of a sequence of lenticular, eastward offtapping, north-northeast-trending, quartzose sandstone shoreline deposits. Lithofacies include lower and middle shoreface, surf, and forebeach, which are well preserved and are identifiable by their color, stratigraphic position, and sedimentary structures. The Glades coal bed formed in a narrow lagoon between two of the offlapping strand plain sandstones. Sedimentologic, palynologic, and maceral studies reveal that the coal was derived from organic debris that accumulated on the floor of a forest swamp that originally occupied the center of the lagoon and later expanded across the lagoon. The forest swamp was surrounded by a reed swamp. Landward of the reed swamp was an apron of sand that resulted from infilling of the western margin of the lagoon by detritus eroded from an older, abandoned strand-plain shoreline deposit. Initially, a large, open body of brackish water was situated at the eastern margin of the lagoon. The Snuggedy Swamp of the lower coastal plain of South Carolina is considered a modern analog of the depositional setting of the Glades coal bed.

Abstract In eastern California some rocks may be seen lying unconformably beneath Lower Cambrian strata which carry Olenellus . In the Inyo Range, for example, Kirk 1 has described the Deep Spring formation and Reed dolomite, the latter of which grades downward into still older sediments. The Deep Spring formation is unconformably overlain by the Lower Cambrian Campito sandstone. In the Bristol Mountains near Cadiz fossiliferous Lower Cambrian beds lie upon an eroded surface of a granite composed of large crystals of feldspar, smaller crystals of quartz, and a little brown biotite. The granite is said to form a considerable part of the range. 2 A few other occurrences of pre-Cambrian rocks have been recognized on fairly good evidence, but most of the rocks so designated are merely metamorphosed so as to look very ancient. In the Coast Ranges, in particular, where no rocks older than Jurassic carry more than traces of fossils, the age of the older rocks is everywhere in doubt. Part of them may be pre-Cambrian, but all may be Paleozoic or younger. In Chapter II the Paleozoic rocks of California have been grouped along with a variety of older and younger rocks as one type of basement, upon which has been laid the blanket of later sediments and volcanic rocks which are the chief subject of the present paper. This chapter summarizes a few of the scattered data concerning the basement rocks that are known or reasonably inferred to be of Paleozoic age. These are more, or less metamorphosed rocks

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.