The Mullaghmore Sandstone Formation of north-west Ireland: a regional Mississippian lowstand deposit

Abstract:The Mullaghmore Sandstone Formation of north-west Ireland is a distinctive clastic unit of late Arundian age in an otherwise carbonate-dominant Mississippian succession. The distinctive base is erosive in the more proximal sections but is gradational in the successions deposited further offshore from the pre-Mullaghmore shoreline. The source area lay to the north-west and is interpreted to be dominated by felsic igneous and/or high grade metamorphic rocks due to the presence of large, first cycle feldspars that are common in all of the sandstones. The formation was deposited in the coastal zone with both fluvial and marginal marine deposits present in almost all sections. The fluvial channel deposits are most common in north-western sections and commonly show evidence for tidal currents in the coastal zone. Most of the coastal sediments are dominated by wave-generated structures. The formation is interpreted as the deposits of a deltaic coastal plain that was lobate in plan view. The top of the formation is interpreted as a regional transgressive surface. While there is local autocyclic repetition of facies, no higher-order sequences are detectable on a regional scale. The driving mechanisms for this regional lowstand are most likely regional tectonics rather than glacioeustasy, as the event is not readily correlated over any significant distance.