Edrioasteroids on corals: Taphonomic feedback and sedimentary processes control the ecology of a Late Ordovician (Katian: Cincinnatian, Richmondian) community in central Kentucky, USA

Abstract

Communities of organisms that encrusted hardgrounds and skeletal material developed and became widespread during the Great Ordovician Biodiversification Event, and this community structure was a well-established part of the marine ecosystem by the Late Ordovician. Here we describe and investigate an example of skeletal encrustation from the Bardstown Member of the Drakes Formation (Upper Ordovician, Katian, Richmondian) near Mount Washington, Kentucky. This occurrence exhibits three dense coral beds near its base which primarily contain the problematic colonial organism Tetradium, the colonial rugose coral Cyathophylloides, and the solitary rugose corals Grewingkia and Streptelasma, as well as several species of stromatoporoids, bryozoans, brachiopods, cephalopods, and trilobites. In one locality, the corals in the uppermost bed are fragmented, reoriented, and encrusted, demonstrating reworking and taphonomic feedback of the skeletons. Tetradium skeletons created hard-substrate clasts that were exploited by a community of sclerobionts including stromatoporoids, bryozoans, and edrioasteroid echinoderms. The skeletons of Cyathophylloides, abundant in the underlying coral beds, are in life orientation and host a lower diversity of encrusters. Corals at other exposures of the Bardstown Member are not significantly reworked and do not host encrusters, suggesting localization of submarine erosion. Here, we describe the stratigraphy, paleoecology, and comparative taphonomy of the Bardstown coral beds at two localities to assess: 1) the burial and taphonomic feedback of the coral skeletons; 2) the community structure and evolution, attachment strategies, and substrate preferences of the encrusting community; and 3) the spatial patterns of submarine erosion and disturbance at the Bardstown coral bed horizons.