Trace fossils and palaeoenvironments of the Middle Devonian Caherbla Group, Dingle Peninsula, southwest Ireland

• Published in: Geological journal (Chichester, England) England), 2012-01, Vol.47 (1), p.1-29
• Main Authors: Morrissey, Lance B., Braddy, Simon, Dodd, Chris, Higgs, Kenneth T., Williams, Brian P. J.
• Format: Article
• Language: English
• Subjects: aeolian; arthropod; Devonian; fluvial; ichnofauna; terrestrialisation
• ISSN: 0072-1050; 1099-1034
• DOI: 10.1002/gj.1324

Trace fossils from the Middle Devonian Caherbla Group of the Dingle Peninsula, southwest Ireland, record a diverse arthropod fauna inhabiting a hot‐arid intracontinental rift setting. Aeolian dunefield and coeval fluvial interdune deposits interfinger spatially and temporally with alluvial fan sedimentary rocks. Three distinct trace fossil assemblages are recognized. The Taenidium‐Scoyenia ichnocoenosis occurs in alluvial fan and fluvial channel deposits, and includes the large backfilled burrow Taenidium, interpreted as eoarthropleurid aestivation chambers. The Rusophycus‐Protichnites ichnocoenosis, composed of arthropod trackways and surface pits, occurs in an interdune ponded area that was susceptible to ephemeral fluvial flow, with Rusophycus showing preferred orientation into the oncoming palaeocurrent. Both the Taenidium‐Scoyenia and Rusophycus‐Protichnites ichnocoenoses are assignable to the globally recurring continental Scoyenia ichnofacies. They are clearly substrate‐controlled and moisture‐related due to the ephemeral nature of the fluvial system. The Palmichnium‐Entradichnus ichnocoenosis occurs in aeolian dune deposits, and includes Palmichnium, attributed to large stylonurid eurypterids, and Diplichnites, attributed to eoarthropleurids. These trackways represent the activities of dune pioneers that left their fluvial habitat to forage for detritus. Interface burrows (Entradichnus, Palaeophycus) were also constructed by arthropods moving just under the sand surface and vertical burrows (Cylindricum, Pustulichnus) were made by arthropods digging downward. Trace preservation in the aeolian environment was probably enhanced by heavy nocturnal dew‐fall or light rain. The Palmichnium‐Entradichnus ichnocoenosis is assigned to the globally recurring aeolian Octopodichnus‐Entradichnus ichnofacies. This aeolian facies, and associated ichnofauna described herein, represents the oldest development of a unique erg system in the Old Red Sandstone (Devonian) of the southern British Isles, and one of the oldest and most diverse aeolian ichnofaunas to be reported worldwide. Copyright © 2011 John Wiley & Sons, Ltd.