Aeolian sedimentation from the Galtymore Formation (Devonian), Ireland

Abstract

Summary The Galtymore Erg (Devonian) of the Galtee Mountains, southern Ireland can be reconstructed by the coupling of field relationships with current hypotheses and observations from other ancient aeolian sequences and modern ergs. Stratigraphical relationships show that the Galtymore Erg formed at the northern, fault-controlled, margin of the Munster Basin. Northern sequences, close to the basin margin, are dominated by northerly derived, proximal braided stream deposits. Two types of aeolian-dominant sequences occur within the Galtymore Formation. A marginal erg facies, characterized by simple crescentic dunes showing S-N palaeocurrents is interbedded with fluvial deposits. To the S an erg facies is developed which is characterized by the vertical repetition of cosets of large-scale cross-strata and thin horizontal deposits. The cosets are interpreted as representing the downwind migration and climbing of large dunes and interdune areas, respectively. The geometrical relationship of the hierarchy of bounding surfaces suggests that the dunes of the erg facies were compound crescentic in form, with enclosed interdune areas. The distribution of stratification types and foreset dip dispersion similarly suggest crescentic dunes. Estimates of compound dune wavelength and some dune and interdune dimensions can be made. Crescentic dunes (simple and compound) were moved by south-southeasterly palaeowinds towards the foot of alluvial fans.