Taphonomy of a Mississippian crinoid pluricolumnal, Newton Grange, Derbyshire, UK

摘要

The Mississippian (Lower Carboniferous) succession of Derbyshire contains numerous crinoid specimens, but they remain poorly documented. Although these well-lithified limestones may include abundant crinoids, they are difficult to study; better results can be obtained from weakly lithified mudrocks, as seen elsewhere. A moderately long pluricolumnal of 29 columnals has been collected from the mudrock of the Newton Grange crinoid bed of the Hopedale Limestone Formation, Peak Limestone Group; it most likely comes from high in the formation (=Brigantian) and was deposited in the deeper water of the Widmerpool Gulf. The pluricolumnal is part of the mesistele of either a cladid or a camerate crinoid. The pluricolumnal was originally circular in section, but has been deformed into an ellipse. A second elongate structure, probably a second pluricolumnal (not preserved), was adpressed into the surface, and calcite of the endoskeleton lost on this and the opposite side of the pluricolumnal to expose the axial canal. All these post-burial modifications were probably under the influence of the weight of overburden, but indicate a complex scenario for the preservation of a simple specimen.