Drift stratigraphy and buried morphology beneath the Forth at Rosyth

Abstract

Synopsis During work under contract to the Institute of Geological Sciences, over 500 old bore records have become available for a small area at Rosyth, the majority relating to the area below low water mark. They show that till and patchy fluvioglacial deposits are covered by fine late-glacial marine sediments whose maximal recorded thickness exceeds 60 m. In the western parts of the area a glacial readvance or halt stage is indicated particularly by ‘boulder clay’ inter-bedded with the late-glacial marine sediments. Sea-level when glacier ice last extended into the Rosyth area was about 35 m above present. Later in late-glacial times the sea fell below its present level and marine sediments deposited earlier were extensively planated, the coarser (ice-rafted) constituents of these sediments and the coarser constituents of the interbedded ‘boulder clay’ (where present) being left as a layer of stones and boulders sloping gently seawards. This coarse stratum now lies beneath a layer of silt and shells. The drift sequence in the Rosyth area can be correlated with that at Bo’ness and Grangemouth, enabling the gradient of the shoreline limiting the main period of late-glacial marine erosion to be provisionally calculated as between 0.20 and 0.25 m/km.