Aspects of Aktuo-Paläontologie of the rocky beaches of the eastern Isle of Mull, UK

Abstract

Conglomerates are, commonly, only poorly fossiliferous at best. Yet beaches with common lithic clasts can be used to model the taphonomy of fossils in conglomeratic settings. Four beaches on the east coast of the Isle of Mull, Inner Hebrides, are clast-rich, with lithic pebbles, cobbles and boulders, but poor in shells, many of which are poorly preserved. There is ample evidence of shells being bored and encrusted, yet many or most of these were infested after death of the host. Of the ‘boring trinity’ – Caulostrepsis Clarke, Entobia Bronn and Gastrochaenolites Leymerie – so typical of the Trypanites Ichnofacies around Britain's coasts, only the last ichnogenus was not present, most likely due to the absence of suitable mobile substrates (such as limestone cobbles and oysters). Encrusters including Balanus , serpulids and spirorbids, show different patterns of preservation, probably due to multiple factors. Bored wood ( Apectoichnus ) was only found at one locality, which may be due to hydrodynamic sorting. Whelk shells show a range of patterns of breakage, most probably due to mechanical damage. But conglomerates commonly preserve fossil snails either complete or not at all. The results from these sites suggest that they represent an intermediate condition rarely preserved in the rock record.