Old Red Sandstone sedimentation and basin development in the Dingle Peninsula, southwest Ireland.

Abstract

Abstract The Dingle Peninsula exposes the most complete Old Red Sandstone (ORS) succession in Ireland, ranging from Late Silurian to Early Carboniferous in age. It lies within 20 km of several ENE-WSW aligned lineaments, including the Dingle Bay Lineament immediately to the south, and the putative trace of the Iapetus Suture to the north. These were formed in a regime of sinistral transpression in the Late Silurian to Early Devonian. It also forms part of the northern margin of the Munster Basin formed by Late Devonian N-S extension. The sequence is divided into five groups: the Dingle Group, the Caherbla Group, the Smerwick Group, the Pointagare Group and the Glengarriff Harbour Group in ascending order. The Dingle Group records initially lacustrine dominated sedimentation followed by deposition in laterally and axially draining fluvial systems within the NE-SW aligned Dingle basin. Generation and inversion of the Dingle basin, and subsequent deposition of the Caherbla Group — composed of alluvial fan and aeolian dunefield deposits — may be related to sinistral strike-slip displacements along the Dingle Bay Lineament. The Smerwick and Pointagare Groups, also consisting of fluvial and aeolian facies, are interpreted to have been deposited in small half grabens restricted to the north of the peninsula. Further Late Devonian extension and subsidence allowed the more widespread deposition of the Glengarriff Harbour Group comprising braided river sediments. Thus the lower part of the ORS of the Dingle Peninsula is interpreted to reflect the Late Silurian to Early Devonian development of localised basins adjacent to sinistral strike-slip faults that were active during the final oblique convergence within the British and Irish Caledonides. In the later Devonian these lineaments were reactivated as normal faults during N-S extension to form the northern margin of the more extensive Munster basin. This change in tectonic regime is also reflected in the swing of major fluvial drainage from an early NE-SW along-basin alignment to a later southerly directed paleoflow.