Abstract

Upper Silurian carbonate rocks on Somerset, Cornwallis and Devon islands contain numerous trace fossils. A Polarichnus-Bergaueria ichnoassociation characterizes limestones and dolostones deposited in the intertidal zone (Cape Storm and Leopold formations), a Fuersichnus-Uchirites ichnoassociation characterizes limestones deposited under shallow subtidal conditions (Douro Formation), and a Neonereites ichnoassociation characterizes basin-slope limestones (tongue of ?Cape Phillips Formation). Trace fossils in planar-bedded calcisiltite and dolosiltite were preserved through toponomic processes, which resulted in diverse ichnoassemblages similar to those reported from contemporaneous shallow marine siliciclastic rocks. In contrast, trace fossils in bathymetrically equivalent rubbly (nodular) calcilutite were preserved through diagenetic processes, which resulted in ichnoassemblages largely restricted to infaunal feeding and dwelling traces. The susceptibility of carbonates to early and late diagenetic processes can significantly affect the nature of the ichnocoenose. Characters resulting from formational and preservational processes of trace fossils suggest that the calcilutite substrates were generally firm, whereas calcisiltite substrates ranged from firm to thixotropic. Simple, "non-diagnostic" burrows such as Palaeophycus can contribute a wealth of information on substrate consistency, much of it not readily available from more traditional environmental indicators.--Modified journal abstract.

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