Interpreting Specific Types of Paleowetlands; Examples from the Pennsylvanian of the Central Appalachian Basin

Coal beds are the deposits of peats, which are a type of wetland soil formed in mires. There are many types of mires. Increment sampling of coals allows for identification of vertical and lateral changes in palynomorphs, macerals, and geochemistry that can be attributed to changes in the specific types of mires that formed the coal bed. In the middle Pennsylvanian of the central Appalachian basin, compositional groups based on palynomorphs, petrography, ash yield, and sulfur content can be attributed to a range of modern peat-forming wetland types. In some cases, vertical successions of compositional groups exhibit a temporal decrease in ash yield, sulfur content, and petrography associated with a change in palynoflora from water-loving arborescent lycopsids to ferns and shrubbier lycopsids, analogous to topogenous to ombrogenous mire successions exhibited in modern tropical raised mires. By compensating for palynoflora changes through time, compositional group analyses can be useful for interpreting specific types of paleomires, and potential hydroseres.

Aside from coals, many non-peat-forming wetlands are also preserved. Rooting horizons below dark, carbonaceous shales, in situ Stigmaria, lycopod trunks or miner's “kettlebottoms,” and shales and siltstones containing compression floras often represent paleowetlands. The components of these non-peat-forming forest and shrub wetlands are often used as part of the criteria for identifying larger sedimentary facies. For example, rooting in interbedded sands and shales near a paleochannel may be part of the evidence for interpreting the larger sedimentary unit as a levee or proximal splay. But what is sometimes overlooked, is that the rooting horizon or buried stump horizon represents an individual paleowetland. If the extent and distribution of lateral and vertical sedimentary facies can be determined, then both peat- and non-peat-forming wetlands can be classified as estuarine, riparian, lacustrine, or paludal wetlands.