Quaternary Sediments and Facies Relationships in the Sound of Iona, Western Scotland: ABSTRACT

Abstract

This study presents the sedimentological relationships between interbedded carbonate marine sediments and siliciclastic glacial deposit in the Sound of Iona. In this area there is an abrupt vertical and lateral facies transition between siliciclastic sediments deposited in turbid, cold water and biogenic limestones deposited in clear, warm water. The reason for this abrupt transition is that highly productive, carbonate-secreting organisms were rapidly deposited during the temperate-climate marine transgression. The carbonates abruptly cover preexisting glacial lowstand deposits. Terrigenous influx is low during the transgression because glacial erosion has removed siliciclastic sediment from coastal source areas. The Sound of Iona is carpeted by a Holocene deposit of carbonate sand, estimated from seismic data to be 3-5 m thick. Point-count data show that the sand averages 75% carbonate, with comminuted barnacle shells comprising over 50% of the sand. Four facies are recognized: (1) rippled carbonate sands lying on the margins of the sound, which grade laterally into (2) centrally located carbonate sand waves and sand ribbons, which lie downstream to (3) in-situ coralline algae deposits (maerl) which in turn overlie (4) relict glacial drift deposits. The sand-wave facies forms the thickest deposit ({approximately}5 m). The sand is localized over a bathymetric high formedmore » from an older deposit of glacial drift. Carbonate-sand deposits are thin or absent distal to the sand-wave facies; relict glacial deltaic deposits lie exposed in these outlying localities. The barnacle-rich, rippled carbonate-sand facies is deposited over preexisting glacial deposits, producing an abrupt vertical facies transition. These carbonate sands are transported by wind-generated wave and low-velocity tidal currents.« less