Abstract Pennsylvanian (Atokan舑early Desmoinesian) parasequences in Indiana are thin (2舑13 m; 5舑40 ft) intervals that are composed of coal, siliciclastic, and carbonate-clastic units bounded by paleosols. Because the parasequences exhibit significant lateral and vertical lithologic variability and are so thin, they are difficult or impossible to discern on standard oil and gas geophysical logs. Therefore, in Indiana, regional correlations of this interval based primarily on geophysical logs and lithologic strip logs created from drill cuttings remain controversial. Detailed analyses of proprietary core from numerous locations in Daviess County in southwestern Indiana reveal that the most traceable of the parasequence facies in core are the paleosols which represent exposure surfaces that developed, in most cases, during apparent basinwide drops in relative sea level. Correlations are substantiated by detailed palynologic analyses of material collected from the bases of overlying marine-influenced flooding surfaces and by the use of thin, nearly continuous marker beds and the presence of certain biostratigraphically significant conodonts. Transgressive and regressive facies above the exposure surfaces are preserved with varying significance. The relative significance of the transgressive-regressive facies in a parasequence is, in part, related to the relative rates of changes in accommodation space and sea level. Detailed analyses of coal lithotypes and maceral compositions in two Atokan coal seams reveal that base-level rises during paleomire development were gradual in one and abrupt (catastrophic?) in another. Abrupt transgressions and the preservation of relatively thick transgressive sequences above the exposure surfaces were perhaps related to rates of mire collapse and compaction of the underlying peat (now coal) and soil (paleosol).

Abstract Well-developed tidal rhythmites associated with tidal mudflats overlie some of the lowest-sulfur Pennsylvanian coals in the eastern part of the Illinois Basin, U.S.A. Such an observation is seemingly at odds with the traditionally held view that low-sulfur coals are not typically associated with marine-influenced roof rock in the Illinois Basin and elsewhere. This association can be explained, however, if the tidal mudflats formed in a freshwater or low-salinity marine setting. Such deposits are known from modern systems but have not been adequately documented from the rock record. Geochemical, petrographic, and sedimentologic analyses of tidal deposits immediately above the low-sulfur (sulfur values <1%) Lower Block Coal Member of the Pennsylvanian Brazil Formation (Atokan), Daviess County, Indiana, confirm the potential for the preservation of extensive (>480 km 2 area) freshwater tidal flat deposits in the rock record. A strong tidal (marine) signal, manifested as tidal rhythmites preserving small-scale neap-spring cycles, is preserved within the laminated mudstone and interbedded sandstone and mudstone immediately above the Lower Block Coal. These cycles indicate deposition within a mixed, predominantly diurnal tidal system in which sedimentation rates were as high as 1 m/yr. Carbon to sulfur ratios, macerai types, and the dominance of terrestrial organic markers within the rhythmite facies reveal that the Lower Block peat (coal) was initially onlapped by a freshwater (low salinity) tidal flat. The presence of tidal rhythmites indicates that at least mesotidal conditions prevailed during transgression. The areal distribution, sedimentology, stratigraphy, petrography, and geochemistry of the succession from the Lower Block Coal to the next younger coal (Upper Block Coal Member of the Brazil Formation) suggest that the tidal flat facies formed within an embayed coastal setting that experienced significant rainfall and runoff typical of an ever-wet climate. The embayments likely formed by the collapse and transgression of the coastal peat mires (Lower Block Coal) and ultimately filled with mudflat and mixed sandflat and mudflat facies. Very high rainfall and associated runoff resulted in the formation of coast-hugging freshwater plumes. These plumes pushed the salt water wedge offshore and prevented it from entering the embayments until the coastal peats had already been covered by at least a meter of tidal flat mud. The results of this study may have implications for paleogeographic reconstructions in other Carboniferous basins. Similar tide-dominated facies may have gone unrecognized in some Carboniferous successions in Europe, and elsewhere, that are currently interpreted to be ancient nonmarine mud-dominated tropical systems. Such recognition would have important sequence stratigraphic and paleogeographic implications.

Abstract: Intra- and inter-basinal correlations between outcrop and subsurface over most of northern and central Wyoming indicate that chert-bearing conglomerates in the lower Cretaceous Cloverly Formation in the foreland of central Wyoming occupy three distinct stratigraphic levels. The two older conglomerates are in the lower Cloverly Formation in the western Wind River Basin and reflect northerly to northeasterly dispersal. The youngest conglomerate is in the upper Cloverly Formation in the eastern portion of the basin; gravels in this interval also were transported to the north and northeast. The two older conglomerates are separated from the youngest conglomerate by up to 35 m of purple to gray, smectite-rich mudstones that contain distinctive 10 to 90 cm-thick layers of white to dark green devitrified tuff, as well as silica and carbonate nodular beds. Fission-track ages of 125–128 Ma have been obtained from three samples of tuff in the Wind River Basin. These tuffs can be correlated to prominent tuffs further north in the Bighom Basin where a paleomagnetic stratigraphy has been established. Fission-track ages of zircons from devitrified tuff layers and magnetostratigraphy of mudstones suggest that the older two conglomerates in the Wind River Basin were deposited between 133 and 128 Ma and the youngest conglomerate at about 118 to 115 Ma. Three-dimensional, spatially controlled and temporally constrained reconstructions of paleodrainage systems for Cloverly conglomerates illustrate the complexity of fluvial drainage networks within the evolving Early Cretaceous foreland basin. Sand-body geometry and dispersal patterns within these fluvial networks were partially controlled by tectonic activity, which created a series of northeast-oriented horsts and grabens in the Wind River Basin. Location of trunk rivers was controlled by the positions of grabens within the basin.

Abstract The lower Pennsylvanian strata in Indiana, Illinois, and western Kentucky rests unconformably on Mississippian to Devonian deposits within the midcontinent Illinois Basin. These deposits fill a complex drainage network of sub-Pennsylvanian paleovalleys with as much as 140 m of shale, sandstone, coal, and mudstone. Paleovalley widths are variable ranging from a kilometer to several kilometers wide and trend roughly northeast to southwest. Timing of valley incision is difficult to constrain and may have been diachronous. Filling of the southern reaches of the drainage system commenced during earliest Pennsylvanian while incision may have continued in the more northern (upland) reaches in Indiana. The paleovalleys progressively filled from south to north during an overall transgressive sea-level rise. During sea-level rise, these valleys became the sites for estuarine deposition. Two relatively small paleovalleys (1 to 1.5 km wide) have been studied in detail in south-central Indiana. Lithofacies can be mapped down the valleys for several kilometers by using subsurface and outcrop data. Within these valleys, conglomerate and conglomeratic sand-dominated inner (upper) estuarine, mud-dominated estuarine central basin, and sand-dominated outer (lower) estuarine deposits can be identified. Central basin sediments overlie fluvial deposits. Direct evidence of tidal influence within the central basin deposits can be recognized by the presence of intertidal rhythmites that exhibit well developed neap-spring cycles. Outer estuarine deposits overlie the central basin deposits and accumulated during the final stages of valley-filling.

Cyclic laminations in gray shales are noted above many major coal seams in the Illinois Basin. These features, which are termed “tidal rhythmites,” indicate significant tidal influence during deposition of the roof strata. Many existing models, however, suggest fluvial dominance and crevasse splay deposition for such gray shales. Based on sedimentological and paleogeographical considerations, appropriate deposition models require micro- to mesotidal environments, limited wave reworking, and a mud-dominated, tropical setting. Following these requirements, tidally influenced estuarine/deltaic models can be generated for roof strata of many Illinois Basin coals. This model is based upon modern mud-rich tidally influenced estuaries and deltas in near equatorial settings and can be used to explain occurrence of shales that lack obvious marine influence (based upon paleontology) above low-sulfur coals in the Illinois Basin.