CONODONTS OF THE DESMOINESIAN (MIDDLE PENNSYLVANIAN) LOST BRANCH FORMATION, MIDCONTINENT BASIN, OKLAHOMA AND KANSAS

The Lost Branch Formation represents the last Desmoinesian cyclothem in the Midcontinent Basin. The lower boundary of the formation is marked by the transgressive Homer School Limestone. The Nuyaka Creek Shale represents the deeper transgressive and regressive sequence. The formation is capped by the regressive Glenpool Limestone. The Nuyaka Creek Shale at the South Sasakwa section in Oklahoma is dominated by clay shales, not the classic black core shale. These clay shales allow for substantial conodont recovery and a more complete picture of the conodont fauna of the last Desmoinesian cyclothem.

The fauna of the Homer School Limestone at South Sasakwa is marked by the presence of Idiognathodus species A, Neognathodus dilatus, Adetognathodus latus, and Hindeodus minutus. The presence of both A. latus and H. minutus is indicative of a shallow environment. Specimens of I. species A have a rostral accessory lobe that extends down the rostral side of the element up to two thirds the length of the platform, whereas in I. expansus the rostral lobe is restricted to the ventral quarter of the platform.

In the lower meter of the Nuyaka Creek Shale, specimens of I. expansus including a deep water morphotype (having crenulated and disrupted ridges) are recovered. Swadelina nodocarinata, two additional species of Neognathodus, Gondolella magna and Gondolella denuda were also recovered in the lower meter of the Nuyaka Creek. The presence of Gondolella and Swadelina indicates deeper water conditions. At a height of 1.5 meters Gondolella and a deep water morphotype of Swadelina (more nodose than the common morphotype) are no longer recovered. It is likely that this was the deepest water represented in the section. Adetognathodus and Hindeodus are absent from a majority of the shale section until Adetognathodus reappears at 12 meters. At 12.5 meters from the base of the Homer School, Swadelina nodocarinata has its last occurrence. At 13.5 meters, just above the Glenpool Limestone, the three species of Neognathodus found in the South Sasakwa section have their last occurrences. I. species A and I. expansus are present to the top of the formation. The South Sasakwa section terminates at the base of the Seminole Sandstone. Similar results are found in the Little River and the Glenpool Sections of Oklahoma, and the Lost Branch Type Section of Kansas.