ALLOCHTHONOUS CRINOID MATERIAL FROM ECHINODERM-POOR LITHOFACIES IN THE UPPER ORDOVICIAN GRANT LAKE FORMATION OF NORTHERN KENTUCKY

Crinoids (Phylum Echinodermata) represent major components of fossil assemblages in the type Cincinnatian (Upper Ordovician: Katian) of the greater Cincinnati Arch region. However, certain shallow marine lithofacies are characterized by a nonexistent to depauperate crinoid fauna, being instead dominated by trilobites, bryozoans, gastropod and modiolopsid mollusks and, in some layers, solenoporid algae(?) and stromatoporoids. One such setting is represented by the Grant Lake Formation, equivalent to the upper Corryville and Mt. Auburn members of the McMillan Formation of Ohio, as exposed south of Flemingsburg, Fleming County, northern Kentucky. Herein, we describe an articulated crinoid crown (Anomalocrinus?) from this otherwise crinoid-poor interval. If assigned to the correct genus, this would represent a relatively small Anomalocrinus crown, probably belonging to a juvenile. A more important issue is the reason for crinoid skeletal material in deposits generally lacking the remains of such organisms. One potential explanation is that the crinoid-bearing units represents a brief interval where conditions were more amenable to occupation by crinoids, possibly corresponding to a minor flooding surface. However, a more likely explanation involves transportation of skeletal remains from nearby, more offshore areas that contained crinoids in greater abundance. Allochthony of the crinoid is supported by the absence of in situ attachment structures and rarity of disarticulated column material at the study site. This study illustrates the value of echinoderm remains in paleoenvironmental analysis, the significance of crinoidal material in taphonomic interpretation of Paleozoic argillaceous carbonate deposits, and the sensitivity of crinoid fossils as indicators of allochthony or autochthony.