Thomas Webster's Tulip Alcyonium (Lamellaecylindrica, trace fossil) in the Upper Greensand Formation (Albian) of the Isle of Wight

Abstract

Large, ramified burrow systems with a thick lamination and bulbous enlargements are common in the Upper Greensand Formation (Albian) of Ventnor, Isle of Wight. From there, these trace fossils were first described by Thomas Webster more than two centuries ago. Although also characteristic outside their area of original description, these structures and Webster's fabulous documentation have fallen into oblivion and only recently were assigned to the ichnogenus Lamellaecylindrica. The two included ichnospecies, L. paradoxica and L. ludwigae reflect different behaviours of their trace maker (possibly a holothurian) in adaption to variations in the sedimentary conditions and current energy. A comparison of the associated ichnofauna with that of the Upper Greensand Formation at Lyme Regis, about 100 km to the west, reveals subtle but significant differences in the trace-fossil distribution, ichnodiversity and ichnoabundance, indicating a proximal (lower shoreface to offshore transition) to distal (inner shelf) depositional trend from west to east. Given the total bioturbation of the greater part of this shelf succession, these subtle variations in the ichnofauna provide valuable information for interpretation of the depositional environment and differences in the energy level where primary sedimentary structures are absent.