PALEOECOLOGY AND TAPHONOMY OF TENTACULITIDS FROM THE BIRDSONG SHALE MEMBER OF THE ROSS FORMATION (DEVONIAN), WESTERN TENNESSEE

The Birdsong Shale Member (Lower Devonian, Lochkov) is the shale-dominated portion (~20m thick) of a mixed carbonate-siliciclastic sequence exposed in a north-south trending outcrop belt in western Tennessee. Previous studies have determined that the mixed nature of the sequence results from a combination of storm winnowing and obrution on a level bottom seafloor. While most of the fauna is dominated by epibiont-rich brachiopods, bryozoans, echinoderms, and trilobites, a 1.2 meter section of interbedded thin packstone/wackestone and shale preserved an unusually rich accumulation (over 1000 per 10 m²) of the tentaculid Tentaculites aculus at a single locality. At least 15 different packstone/shale interbeds occur suggesting alternating conditions at this locality; however, the tentaculid bed is not traceable to other areas. Two scenarios to explain the accumulation are examined. Either the tentaculid accumulation is a series of mass kills that occurred in the same general region repeatedly (due to some form of endemism?) over a protracted interval of time or the entire 1.2 meter accumulation is one mass kill event, which suggests that much of the Birdsong itself may be a short-term sediment accumulation.