Files
Abstract
The Bond Formation (Upper Pennsylvanian, Missourian) of the McLeansboro Group consists of shale, siltstone, and sandstone with subordinate layers of coal and limestone. A partial exposure of the Bond Formation is accessible along the Wabash River southwest of New Harmony at the Old Dam Site. Plant fossils were collected from a dark gray shale just below a thin coal deposit, most likely the Fairbanks Coal. Above the coal is a 5 cm bed of black shale with localized pyrite concretions, overlain by 50 cm of skeletal wackestone with disaggregated and abraded marine fossils; this latter unit is identified as the Riverview Limestone Member. The plant fossils were collected in late August 2024 by excavating approximately one square meter of shale. In the lab, the specimens were sealed with clear acrylic to preserve and enhance their durability. Plant fossils were identified to genus and/or species using a 10x hand lens, Olympus 20x to 40x binocular microscope, and by comparing morphological features to reference collections and published literature. The most common fossils are Medullosans, dominated by Neuropteris.
Multiple individual pinnules of Macroneuropteris scheuchzeri occur in samples dominated by N. flexuosa, N. ovata, and N. vermicularis. There is a moderate abundance of Calamites, Cordaites, and Cyclopteris, along with Annularia sphenophylloides and N. fimbriata. There are some trace occurrences of Sphenophyllum dubium, Sphenophyllum emarginatum, and Sphenopteris elegans. The genera identified are typical of the Late Pennsylvanian and are consistent with a wetland environment associated with a broad, river-dominated delta complex, but also indicate a paleoclimate with marginally drier conditions than the Early Pennsylvanian. This gradual shift in flora away from true ferns and lycophytes, which were absent in the collected samples, indicates an environment that is seasonally, or on average, much drier in comparison to the
tree-fern and lycopsid-rich swamps of the Lower Pennsylvanian.