For more than 100 years, Pennsylvanian permineralized peats have been studied for their exceptionally preserved plant remains. Late Atokan-early Desmoinesian coal balls from the Williamson # 3 deposit in south-central Iowa were preserved by the permineralization of soluble carbonate into pores in the peat and plant cells creating carbonate nodules. These nodules, referred to as coal balls, protect the plant remains from the compaction associated with coal allowing for the analysis of anatomically preserved plants from Pennsylvanian. The Williamson #3 deposit is unusual because it is dominated by a diverse assemblage of gymnosperms. Other deposits of similar age in Iowa are dominated by a mixture of cordaitalean gymnosperms, tree-ferns, and medullosan gymnosperms; while, other North American deposits are dominated by lycopsids with tree-ferns and seed-ferns as the subdominant vegetation. Because vegetation types differ with environment, analysis of the Alethopteris pinnules from the Williamson #3 Mine provides insight into the ecology of a peat-producing swamp during the Pennsylvanian, and allows for the comparison of this deposit to others in North America. The focus of this study is the description of a distinct morphotype of Alethopteris from the Williamson #3 Mine. Alethopteris pinnules described from other mines were used to compile a traits list and compare measured and descriptive characteristics. The objective of this study is to gain a better understanding of changes in swamp vegetation during the Pennsylvanian, and the effect of environmental variation on the dominant vegetation in peat swamps.

The Eastern Shelf was a constructional platform developed on the margin of the sediment-starved Midland Basin during Late Pennsylvanian and Early Permian time. A mixed terrigenous-carbonate sedimentary province characterized the shelf during most of its history. Sediments were derived from highlands to the east and northeast. Along the outcrop in Eastland, Stephens, Young, and Jack counties, uppermost Pennsylvanian beds compose the Harpersville Formation, a boundary-defined rock stratigraphic unit within the Cisco Group. Harpersville facies extend westward into the subsurface 50 to 60 miles, where they grade into equivalent shelf margin carbonate and slope terrigenous facies. Preserved relief between the shelf margin and basin floor ranges from 600 to 1100 feet with dips of up to five degrees. Three depositional systems are recognized on the basis of gross lithologic composition and position relative to the shelf edges. They are the Cisco fluvial-deltaic system, the Sylvester shelf edge bank systern, and the Sweetwater slope system. The Cisco fluvial-deltaic system is composed of dip-fed fluvial-deltaic facies and associated strike-fed interdeltaic embayment facies. Eight deltaic lobe complexes have been mapped. The Sylvester slope system is composed of several slope wedges or fans each of which includes shelf margin, slope trough, and distal slope sandstone facies, as well as slope mudstone facies. Terrigenous sediments were transported across the shelf by prograding fluvial-deltaic channels, which locally extended through the shelf edge bank system and onto the slope where submarine fans were constructed into the basin. The Eastern Shelf prograded into the Midland Basin by local upbuilding through fluvial, deltaic, and shelf edge bank deposition contemporaneous with outbuilding by slope fan deposition. Sites of shelf construction shifted through time in response to sedimentary and structurally controlled abandonment of delta lobes. Extrabasinal controls such as eustatic sea level changes were of secondary importance in developing the depositional fabric of the shelf. / text

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The Alleghanian orogeny was a collision between the Gondwanan and Laurentian continents that produced the Pangean supercontinent. Mechanical and kinematic models of collisional orogens are believed to follow a critical taper geometry, where the tectonic imbrication of continental crust begins nearest to the edge of continental plate and advances toward the craton in a break- forward sequence. Studies of shear zones within the Alleghanian collisional orogen, however, suggest that most of the early deformation was translational. Propagation of craton-directed thrusts into the foreland did not occur until the latest Pennsylvanian in the southern Appalachians, and the middle-late Permian in the central Appalachians. Radiometric sedimentary provenance proxies have been applied to the late Mississippian-early Permian strata within the Appalachian foreland basin to determine the crustal composition and structural evolution of the orogen during the continental collision. U-Pb ages of detrital zircons from the early to middle Pennsylvanian sandstones suggest that most of the detritus within the Appalachian basin was recycled from Mesoproterozoic basement and Paleozoic strata of the Laurentian margin. The presence of Archean and late Paleoproterozoic age detrital zircons is cited as evidence of recycling of the Laurentian syn-rift and passive-margin sandstones. Detrital zircon ages from early-middle Permian-age sandstones of the Dunkard Group do not contain any Archean or Paleoproterozoic detrital-zircon ages, implying a source of sediment with a much more restricted age population, possibly the igneous and metamorphic internides or middle Paleozoic sandstones from the Appalachian basin. The persistance of 360-400 Ma K/Ar ages of detrital white mica suggest that the sediment was supplied from a source that was exhumed during the Devonian Acadian orogeny. Detrital-zircon and detrital-white-mica ages from Pennsylvanian-age sandstones indicate that the late Paleozoic orogen did not incorporate any significant synorogenic juvenile crust. The 87Sr/86Sr ratios of middle Pennsylvanian-early Permian lacustrine limestones within the Appalachian basin show a slight enrichment through time, suggesting that labile 87Sr-rich minerals in the Alleghanian hinterland are being exposed. Stable isotopic data from the lacustrine limestones also corroborates that the Appalachian basin became much more arid through time.

The primary factors that influence stratigraphy are tectonic subsidence, eustasy, and sediment supply. Change in any of these factors potentially produces a similar response in the form of a change in accommodation space. Accordingly, distinguishing the origin of a stratigraphic response is difficult, but theoretically possible by analysis of temporal and spatial extents of the accommodation signal. Correlation is critical for distinguishing eustasy from tectonism. Upper Pennsylvanian strata of the Pedregosa and Orogrande basins (southern Ancestral Rocky Mountains) were deposited during a time of continental collision and extensive continental glaciation, and contain a composite record of changing tectonism, eustasy, climate, and sediment supply. High-frequency stratigraphic cyclicity expressed as repetitive stacks of lithofacies at the scale of 10¹ m pervades all sections and displays features that collectively imply a primary glacioeustatic origin, notably: (1) abrupt juxtaposition of dissimilar lithofacies, signaling a rapid rate of baselevel change, (2) apparent intrabasinal, interbasinal and, provisionally, interregional correlation of high-frequency cycles across and between contrasting tectonic environments, and (3) cycle frequencies that approach the 413 ka periodicity of orbital eccentricity, the probable forcing mechanism for Pennsylvanian glaciations. Glacial-interglacial climate change expressed as precipitation and circulation fluctuations in the equatorial Pedregosa and Orogrande basins accompanied Pennsylvanian glacioeustasy. Intensified aridity and wind strength during peak glacials led to decreased fluvio-deltaic sedimentation and increased eolian activity where siliciclastics were available. Conversely, increased precipitation during interglacials reactivated and/or intensified fluvio-deltaic sediment yield. Eustasy dictated fluvial aggradation versus degradation and coastal sediment trapping versus bypassing. Coupled glacioeustatic-glacioclimatic change was sufficiently severe to reconfigure environments between climatic extremes, which implies that Pennsylvanian stratigraphic cycles should be viewed in at least partially non-Waltherian terms. Each cycle potentially recorded contrasting facies mosaics that were to some degree temporally exclusive. Multiple-cycle trends in facies and/or thickness also occur to define low-frequency stratigraphic patterns at the scale of 10² m. Qualitative analysis of these trends implicates distinct eustatic and tectonic processes as contributing influences. The eustatic component may derive from low-frequency glacioeustasy as well as tectonoeustasy related to evolving continental paleogeography. The tectonic component probably reflects late Paleozoic Marathon-Ouachita collisional orogenesis.

We analyzed detrital zircons in Lower-Middle Pennsylvanian strata collected from seven sandstones in the Forest City Basin and seven sandstones in the Illinois Basin. In these basins, Lower-Middle Pennsylvanian strata unconformably overlie Mississippian and Devonian strata and reflect a renewed influx of detritus after a significant depositional hiatus. In the total combined dataset (n=3,106), U-Pb ages of approximately 66% of zircons match ages interpreted to be derived from the Appalachian region, including Grenville (1.3-1.0 Ga), Pan-African (530-620 Ma and 750 Ma), Taconic (440-490 Ma), Acadian (350-420 Ma), and Alleghenian (330-270 Ma) ages. Subordinate populations of grains consist of Granite-Rhyolite (1300 -1500 Ma), Yavapai and Mazatzal Terrane (1600- 1800 Ma), Penokean and Trans-Hudson orogens (1800-1900 Ma), and Superior Province (>2.0 Ga) ages. Proportions of grains matching Appalachian sources increased in the Illinois Basin from ~46% to ~79% between our stratigraphically lowest and highest samples, respectively. The Forest City Basin exhibited a similar upsection increase in Appalachian derived grains, which increased from ~52% in our stratigraphically lowest sample to ~70% in our stratigraphically highest sample. Proportions of grains from northern sources (the Canadian Shield and Penokean Province) diminished upsection as these source areas and recycled sediments containing associated grains become covered with Appalachian-derived sediments. Overall, these shifts are interpreted to reflect an increased flux of Alleghenian erosional detritus across the Laurentian craton as a result of the overfilling of the Appalachian foreland region. These results supplement our understanding of the stratigraphic and provenance records left by fluvially dominated large-scale sedimentation events that occur during the formation of supercontinents.

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The Red Mountain formation (Lower Pennsylvanian?) of the Chilliwack group (Carboniferous) was mapped in five areas of northwestern Washington. Except for a few outcrops of Devonian strata, the formation represents the oldest known sedimentary rocks in this region. It consists primarily of argillite, graywacke, chert, tuff and limestone, and is overlain by conglomerate of the Black Mountain formation (Lower Permian). The base of the formation is nowhere exposed. Correlation of the Red Mountain formation is dependent essentially on the presence of large crinoid stems, foraminifera, and similarity of stratigraphic relationships. Limestones of the upper portion of the formation represent deposition under conditions of marked tectonic stability, whereas enclosing strata are indicative of deposition in an unstable, subsiding realm. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate