Abstract In response to rising concerns about atmospheric carbon dioxide (CO 2 ) levels and likely regulations on emissions, investigations into geologic carbon storage options across the United States are underway. In the Midwest, Cambrian sandstones are major targets for potential geologic carbon storage. In some localities, the overlying Cambrian–Ordovician Knox Group is also being investigated as a possible target for primary and secondary storage of CO 2 . The thick dolomitic succession contains intervals that may function as both reservoirs and seals. Gas storage fields in Knox carbonates in Kentucky and Indiana demonstrate that methane can be safely stored in paleotopographic highs along the Knox unconformity surface. Numerous injection wells have also been completed in the Knox Group for brine disposal. More significantly, at least seven class 1 injection wells have used the Knox as all or part of a storage reservoir for industrial wastes. Many of these wells have injected millions of gallons of liquid waste annually into Knox reservoirs. The relative scale of these injection operations can be used to estimate the types and sizes of potential reservoirs within the Knox succession in the Midwest. Specific data on the Knox interval relative to its carbon storage and confining potential are currently being collected from wells drilled as part of U.S. Department of Energy administered carbon storage projects, as well as state-administered carbon storage programs. In this chapter, initial results of carbon storage tests are summarized from the Battelle 1 Duke Energy well, Kentucky Geological Survey 1 Blan well, Battelle-American Electric Power (AEP) 1 Mountaineer well, and Battelle-Ohio Geological Survey 1 CO 2 well. The AEP Mountaineer Power Plant will host the nation’s first commercially integrated carbon capture and geologic storage project, and the storage reservoirs will be in the Knox Group. Because the Knox Group is widespread at depth across much of the Midwest, it will be an important part of sequestration programs as confining interval and reservoir.

Abstract In the eastern mid-continent United States, the Cambrian Mt. Simon Sandstone is a likely deep-saline reservoir target for CO 2 sequestration. The overlying Cambrian–Ordovician Knox carbonate section will be an important part of the confining interval for the Mt. Simon, as much of the Knox is dominated by dense (<0.01 md), well-cemented dolomites with little or no permeability. The Knox, however, does contain discrete zones of porosity and permeability and is locally an important oil and gas producer, as well as gas storage unit. The Knox needs to be considered in any sequestration project in the region because in some localities carbonate and sandstone zones within the unit have better reservoir characteristics than the underlying Mt. Simon or overlying St. Peter Sandstone. An example of such a locality is the DuPont waste-injection site at Louisville, Kentucky, where a thick Mt. Simon section was tested and then abandoned in favor of a fractured, vuggy dolomite facies in the overlying lower Knox with an injectivity rate as high as 568 liters per minute (150 gallons per minute). Thick, dense carbonates of the Knox enveloped the reservoir effectively sealing the porous and permeable zones within the same stratigraphic unit. This is not an exceptional circumstance because several deep tests of Cambrian–Ordovician clastics in the region have encountered tight sandstone in the target horizon but vuggy and fracture porosity in overlying Knox carbonates. Analyses of known Knox enhanced oil recovery operations, waste-injection wells, and gas storage fields illustrate that liquids and gases can be effectively and safely retained within Knox reservoirs. However, porous and permeable zones within the units that constitute the local reservoirs are discontinuous and heterogeneous, and data describing the detailed characteristics of these reservoirs are sparse. More deep subsurface data are needed to better characterize the Knox and similar carbonates in other regions for their use as potential carbon sequestration reservoirs. Some of these data are currently being collected through the U.S. Department of Energy’s Carbon Sequestration Regional Partnership programs.

Various orders of marine flooding surface–bounded depositional sequences are recognized in coal-bearing, Pennsylvanian-age strata of the greater Appalachian Basin. The best preserved of these from the Lower Pennsylvanian are in the southern and central Appalachians; Middle Pennsylvanian cyclothemic sequences are best preserved in the central Appalachians; and Upper Pennsylvanian cyclothemic sequences are best preserved in the northern Appalachians. Palynological and lithostratigraphic correlations to global time scales have been used to infer eustatic controls on accumulation of cyclothem-scale sequences in each of these areas, albeit with significant tectonic and climatic overprints. New U-Pb absolute age dates from upper Lower Pennsylvanian and Middle Pennsylvanian tonsteins in the central basin can be used to infer an average maximum duration of 0.1 m.y. for minor transgressive-regressive depositional cycles, which supports the possibility of short eccentricity-driven eustatic influences on sedimentation. Although glacial eustasy influenced Pennsylvanian sedimentation throughout the basin, the thickness, lateral continuity, and constituent facies of high-frequency depositional cycles were strongly influenced by changing rates of tectonic accommodation in at least three depocenters, sediment flux, and changing paleoclimate.

The fossil record of wetlands documents unique and long-persistent floras and faunas with wetland habitats spawning or at least preserving novel evolutionary characteristics and, at other times, acting as refugia. In addition, there has been an evolution of wetland types since their appearance in the Paleozoic. The first land plants, beginning in the Late Ordovician or Early Silurian, were obligate dwellers of wet substrates. As land plants evolved and diversified, different wetland types began to appear. The first marshes developed in the mid-Devonian, and forest swamps originated in the Late Devonian. Adaptations to low-oxygen, low-nutrient conditions allowed for the evolution of fens (peat marshes) and forest mires (peat forests) in the Late Devonian. The differentiation of wetland habitats created varied niches that influenced the terrestrialization of arthropods in the Silurian and the terrestrialization of tetrapods in the Devonian (and later), and dramatically altered the way sedimentological, hydrological, and various biogeochemical cycles operated globally. Widespread peatlands evolved in the Carboniferous, with the earliest ombrotrophic tropical mires arising by the early Late Carboniferous. Carboniferous wetland-plant communities were complex, and although the taxonomic composition of these wetlands was vastly different from those of the Mesozoic and Cenozoic, these communities were essentially structurally, and probably dynamically, modern. By the Late Permian, the spread of the Glossopteris flora and its adaptations to more temperate or cooler climates allowed the development of mires at higher latitudes, where peats are most common today. Although widespread at the end of the Paleozoic, peat-forming wetlands virtually disappeared following the end-Permian extinction. The initial associations of crocodylomorphs, mammals, and birds with wetlands are well recorded in the Mesozoic. The radiation of Isoetales in the Early Triassic may have included a submerged lifestyle and hence, the expansion of aquatic wetlands. The evolution of heterosporous ferns introduced a floating vascular habit to aquatic wetlands. The evolution of angiosperms in the Cretaceous led to further expansion of aquatic species and the first true mangroves. Increasing diversification of angiosperms in the Tertiary led to increased floral partitioning in wetlands and a wide variety of specialized wetland subcommunities. During the Tertiary, the spread of grasses, rushes, and sedges into wetlands allowed for the evolution of freshwater and salt-water reed marshes. Additionally, the spread of Sphagnum sp. in the Cenozoic allowed bryophytes, an ancient wetland clade, to dominate high-latitude mires, creating some of the most widespread mires of all time. Recognition of the evolution of wetland types and inherent framework positions and niches of both the flora and fauna is critical to understanding both the evolution of wetland functions and food webs and the paleoecology of surrounding ecotones, and is necessary if meaningful analogues are to be made with extant wetland habitats.

Dedicated to the memory of William T. Holser, colleague and friend. A gap in the fossil record of coals and coral reefs during the Early Triassic follows the greatest of mass extinctions at the Permian-Triassic boundary. Catastrophic methane outbursts during terminal Permian global mass extinction are indicated by organic carbon isotopic (δ 13 C org ) values of less than –37‰, and preferential sequestration of 13 C-depleted carbon at high latitudes and on land, relative to low latitudes and deep ocean. Methane outbursts massive enough to account for observed carbon isotopic anomalies require unusually efficient release from thermal alteration of coal measures or from methane-bearing permafrost or marine methane-hydrate reservoirs due to bolide impact, volcanic eruption, submarine landslides, or global warming. The terminal Permian carbon isotopic anomaly has been regarded as a consequence of mass extinction, but atmospheric injections of methane and its oxidation to carbon dioxide could have been a cause of extinction for animals, plants, coral reefs and peat swamps, killing by hypoxia, hypercapnia, acidosis, and pulmonary edema. Extinction by hydrocarbon pollution of the atmosphere is compatible with many details of the marine and terrestrial fossil records, and with observed marine and nonmarine facies changes. Multiple methane releases explain not only erratic early Triassic carbon isotopic values, but also protracted (∼6 m.y.) global suppression of coral reefs and peat swamps.

Early Silurian (Llandoverian) macrofossils from the lower Massanutten Sandstone at Passage Creek in Virginia represent the oldest known terrestrial wetland communities. Fossils are preserved as compressions in overbank deposits of a braided fluvial system. Specimens with entire margins and specimens forming extensive crusts provide evidence for in situ preservation, whereas pre-burial cracks in the fossils demonstrate subaerial exposure. Developed in river flood plains that provided the wettest available environments on land at the time, these communities occupied settings similar to present-day riverine wetlands. Compared with the latter, which are continuously wet by virtue of the moisture retention capabilities of soils and vegetation, Early Silurian flood-plain wetlands were principally abiotically wet, depending on climate and fluctuations of the rivers for moisture supply. Varying in size from <1 cm to >10 cm, fossils exhibit predominantly thalloid morphologies but some are strap-shaped or form crusts. Their abundance indicates that a well-developed terrestrial groundcover was present by the Early Silurian. Morphological and anatomical diversity of specimens suggests that this groundcover consisted of several types of organisms and organismal associations, some characterized by complex internal organization. Earlier microfossil finds at Passage Creek corroborate an image of systematically diverse but structurally simple communities, consisting only of primary producers and decomposers. Ten to fifteen million years older than the oldest previously known complex terrestrial organisms (e.g., Cooksonia ), they provide a new perspective on the early stages of land colonization by complex organisms, whereby the earliest terrestrial communities were built by a guild of thalloid organisms and associations of organisms comparable to extant biological soil crusts.

The Trout Valley Formation of Emsian–Eifelian age in Baxter State Park, Maine, consists of fluvial and coastal deposits that preserve early land plants (embryophytes). Seven facies are recognized and represent deposits of main river channels (Facies 1, 2), flood basin (Facies 4), storm-influenced nearshore shelf bars (Facies 3), a paleosol (Facies 5), and tidal flats and channels (Facies 6, 7). The majority of plant assemblages are preserved in siltstones and are allochthonous and parautochthonous, with only one autochthonous assemblage identified in the sequence above an apparent paleosol horizon. Taphonomic analysis reveals that plant material within allochthonous assemblages is highly fragmented, poorly preserved, and decayed. Plant material within parautochthonous assemblages shows evidence of minimal transport, is well preserved, and shows signs of biologic response after burial. The one autochthonous assemblage contains small root traces. Trimerophytes ( Psilophyton and Pertica quadrifaria ), rhyniophytes (cf. Taeniocrada ), and lycopods ( Drepanophycus and Kaulangiophyton ) are the most common taxa in estuarine environments. Psilophyton taxa, Pertica , cf. Taeniocrada , and Drepanophycus are found also in fluvial settings. The presence of tidal influence in deposits where parautochthonous and autochthonous assemblages occur shows that these plants occupied coastal-estuarine areas. However, the effects on the growth and colonization of plants of the physical conditions (e.g., salinity) that exist in these settings in the Early to Middle Devonian are unknown.

The Late Devonian Red Hill locality in north-central Pennsylvania contains an Archaeopteris -dominated plant fossil assemblage, a diverse fossil fauna, and an extensive sedimentary sequence ideal for investigating the landscapes and biotic associations of the earliest forest ecosystems. Sedimentological analysis of the main plant-fossil bearing layer at Red Hill indicates that it was a flood-plain pond. A seasonal wet-and-dry climate is indicated by well-developed paleovertisols. The presence of charcoal interspersed with plant fossils indicates that fires occurred in this landscape. Fires appear to have primarily affected the fern Rhacophyton . The specificity of the fires, the distribution profile of the plant remains deposited in the pond, and additional taphonomic evidence all support a model of niche partitioning of the Late Devonian landscape by plants at a high taxonomic level. At Red Hill, Archaeopteris was growing on the well-drained areas; Rhacophyton was growing in widespread monotypic stands; cormose lycopsids grew along the pond edge; and gymnosperms and Gillespiea were possibly opportunists following disturbances. Tetrapod fossils have been described from Red Hill—therefore, this paleoecological analysis is the first systematic interpretation of a specific site that reflects the type of wetland environment within which the earliest tetrapods evolved.

The Horton Group (late Famennian to Tournaisian) of Atlantic Canada provides an unusually complete record of Early Mississippian wetland biota. Best known for tetrapod fossils from “Romer's Gap,” this unit also contains numerous horizons with standing vegetation. The taphonomy and taxonomy of Horton Group fossil forests have remained enigmatic because of poor preservation, curious stump cast morphology, and failure to recognize the unusual sedimentary structures formed around standing plants. Four forested horizons within the Horton Group are preserved as cryptic casts and vegetation-induced sedimentary structures formed by the interaction of detrital sediment with in situ plants. Protostigmaria , the lobed base of the arborescent lycopsid Lepidodendropsis , occur as sandstone-filled casts attached to dense root masses. Mudstone-filled hollows formed when a partially entombed plant decayed, leaving a void that was later infilled by muddy sediment. A scratch semi-circle formed where a current bent a small plant, causing it to inscribe concentric grooves into the adjacent muddy substrate. Obstacle marks developed where flood waters excavated erosional scours into sandy sediment surrounding juvenile Lepidodendropsis . These cryptic lycopsid forests had considerably higher densities than their Pennsylvanian counterparts. Vegetation-induced sedimentary structures are abundant in Horton Group strata and could easily be misidentified as purely hydrodynamic or soft-sediment deformation structures without careful analysis. Recognition of these structures in early Paleozoic strata has great potential to expand our knowledge about the distribution of early land plants.

The Fayetteville Formation of northwestern Arkansas (upper Mississippian/middle Chesterian) contains two compression plant fossil assemblages (one in situ) that represent plant communities, and an allochthonous permineralized assemblage recovered from marine strata that represents the landscape. This preservation of spatial ecological subunits (communities) nested within a larger subunit (landscape) provides a snapshot of vegetation patterns within a Late Mississippian clastic swamp. Fifteen whole plants are recognized. Seed ferns are the most speciose group and lycopsids account for most biomass. Seed fern taxa known only as permineralized specimens include one canopy tree ( Megaloxylon ), two understory trees, and five herbaceous layer plants. Two herbaceous layer seed ferns are observed only as compressions. Lycopsids are represented as two canopy trees that are known from both permineralizations and compressions. Archaeocalamites is also known from both permineralizations and compressions but was an understory tree. Ferns are rare and are preserved only as fragments of permineralized rachises from two species. As revealed by the in situ compression assemblage, the two species of lycopsid canopy trees co-occur and they formed communities that occupied ever-wet bottomlands, with Archaeocalamites occupying the understory, and a single species of seed fern comprising the herbaceous layer. Lycopsids do not co-occur with Megaloxylon . Megaloxylon probably formed a second community type in somewhat water-stressed areas of the swamp with an understory of small arborescent seed ferns, some Archaeocalamites , and an herbaceous-layer seed fern. Ferns probably formed a third type of community in disturbed sites.