Paper No. 9
Presentation Time: 3:45 PM
AN EDRIOASTEROID-ACROTHORACIC BARNACLE-DOMINATED COMMUNITY ATTACHED TO PENNSYLVANIAN EXTRAFORMATIONAL CONGLOMERATE CLASTS
Although extraformational conglomerates occur throughout Earth history, these hard substrates are rarely preserved with associated biota. A locality from the Lower Pennsylvanian (Morrowan) Golf Course Formation in south-central Oklahoma is interpreted to be a marine, synorogenic conglomerate deposited in a shallow lagoonal setting with bored and encrusted clasts eroded from many of the Lower and Middle Paleozoic units during the Criner Uplift. The low-diversity fauna is dominated by hard-substrate taxa including four genera of edrioasteroids (highly unusual for the Pennsylvanian: Neoisorophusella, Ulrichidiscus, Postibulla, and Parapostibulla), acrothoracic barnacle borings, serpulid tube worms, and fewer solitary rugose and alloporid corals, ramose and encrusting bryozoans, and several species of pediculate brachiopods. Associated soft-substrate fauna includes the stemless crinoid Paragassizocrinus tarri, several species of ostracodes and conodonts, isolated crinoid, holothuroid, and echinoid ossicles, and a single rostroconch mollusk. The hard-substrate fauna attached to some of the isolated clasts at the locality shows several types of preserved interactions. Even though a single clast, typically large pebble to small cobble in size, can have an edrioasteroid concentration of over 4,000 individuals per square meter, edrioasteroids are never preserved overgrowing members of their own species but rather become polygonal in crowded conditions. However, the edrioasteroids Ulrichidiscus and Parapostibulla are preserved overgrowing other elements of the fauna including serpulid worms, corals, bryozoans, and the edrioasteroid Neoisorophusella. Also, very small serpulids are preserved overgrowing Neoisorophusella but not the other three edrioasteroids. Edrioasteroid colonization shows little preference for clast size, shape, or lithology. Acrothoracic barnacles prefer carbonate clasts and to a lesser degree siltstone and sandstone. Although they have no clast size preference, acrothoracic barnacles tend to bore into the edges of subangular clasts and show preference for softer lithologies in larger clasts. Some clasts have been rolled and bored or encrusted on both sides.