PETROLOGY, PETROGRAPHY AND CONODONT BIOSTRATIGRAPHY OF THE LADDSDALE COAL INTERVAL, ALONG WHITEBREAST CREEK, BAUER, IOWA

A cut-bank on White Breast Creek 1 mile north of Bauer, Iowa exposes three coals distributed through about 14 meters (45 ft) of strata. The section looks very similar to the type Laddsdale outcrop, at the base of the Floris Formation (Cherokee, Desmoinesian), on Soap Creek in northeastern Davis County, about 105 km (65 miles) to the southeast. The lower two coals seen at the type section, are not exposed at Bauer, and the upper two coals are thinner than those at the type section. The lowest exposed coal thickens in an incised valley at the north end of the outcrop and thins to the south over a topographic high. Marine units above the lower coal only occur in the incised valley and consist of light to medium gray, highly fossiliferous shales and a fossiliferous, lenticular septarian limestone. The limestone is a medium to dark gray, organic-rich, pyritic, skeletal lime mudstone to wackestone. The only fossil seen in the limestone was the brachiopod Desmoinesia muricata. The shales below the septaria contain an abundant open marine fauna consisting of ten species of brachiopods, gastropods, clams, ammodiscoid and other forams, ostracodes, bryozoa, crinoids, fish debris, coprolites, scolecodonts, and conodonts. Terrestrial plant spores and carbonized wood are also common. The conodont Idiognathodus podolskensis has been identified, as well as other morphotypes that have been described from similar shales at the type Laddsdale. These morphotypes have also been seen at the type Inola Limestone in Oklahoma and the type Hackberry Branch Limestone in Missouri. We propose that the strata exposed at the outcrop north of Bauer are equivalent to most of those exposed at the type Laddsdale. The marine units above the lower coal are equivalent to the Inola Limestone of Oklahoma and the Hackberry Branch Limestone of Missouri. This would make the coal underlying the marine units, equivalent to the Bluejacket Coal of Oklahoma. We also propose, since the type Laddsdale is very difficult to access, that this outcrop be designated as a reference section for the Laddsdale interval in Iowa.