AN ENIGMATIC LOBATE MAT-LIKE FOSSIL(?) IN THE KOPE FORMATION (UPPER ORDOVICIAN), KENTON COUNTY, KENTUCKY

A new, enigmatic, large fossil(?) object from a thin silty mudstone bed (up to 3 cm thick) underlain by siltstone was excavated from the lower Kope Formation (Economy Member, basal Pioneer Valley submember) near Covington, KY. The excavated object is roughly elliptical in outline, over 2 m long, with a parallel-fluted structure at one end that terminates in a complex of conjoined, flattened, ellipsoidal or spatulate concretion-like lobes at the other end. The lobes are about 10 cm and range to 45 cm long. Internally, some lobes show lamination, sometimes convoluted. The most perplexing feature of the lobe-like structures is a small-scale corrugation of the basal and upper surfaces that in places is cross-cut by secondary corrugation, producing a pattern of small polygonal, scale-like “reticles” in hyporelief. The reticles are elongate, about 5 mm long and 2 mm wide, with a peculiar beaded or “gooseflesh-like” surface. The reticulated texture of the basal surface is aligned with the minor axis of the elliptical lobes and wraps around to their upper surfaces. Clumps of aligned diplograptid graptolites occur in the sediment filling the lobes and some in situ bryozoan mounds occur on the upper surface, which is also bioturbated with Chondrites and Trichophycus. Small, articulated primaspid trilobites occur, adhered by their ventral sides, on the lower, corrugated surface. Primaspids, which occur elsewhere in the Cincinnatian adhering to bryozoan branches, might suggest that the corrugated surface texture represents an integument of some originally upright sac-like body or organism with lobate branches. Alternatively, the trilobites could have lived cryptically beneath a cohesive mat suspended above the substratum. The entire complex may represent deformed, gutter like features. Alternatively, the presence of reticulate patterning on both lower and upper sides of the lobes suggests a large mat-like fossil, possibly an alga or cnidarian with open spaces inside of a lobate body. In any case the 3-D structure of sediment fill has been preserved by early diagenetic concretionary cementation. This peculiar combination of features has never before been recognized in the Cincinnatian Series and its origin remains unresolved.