Patterns of isostatic land uplift during the Holocene: evidence from mainland Scotland

Abstract

Preliminary results of a lengthy and detailed investigation into middle- and late-Holocene raised shorelines in mainland Scotland indicate that three shorelines are sufficiently widely distributed to permit an examination of their extent and of the patterns of uplift which they indicate. The shorelines are the Storegga Tsunami Shoreline, reached at c. 7100 14C years BP, at the culmination of the Main Postglacial Transgression; and the Blairdrummond Shoreline, reached after the Main Postglacial Shoreline, at c. 2000–4200 14C years BP, at the time of a tsunami believed to have been caused by the Second Storegga submarine slide; the Main Postglacial Shoreline, reached at c. 5800–6850 14C years BP. The Main Postglacial Shoreline, previously believed to be the highest Holocene raised shoreline in Scotland, is now believed to be overlapped around the periphery of the uplifted area by the later Blairdrummond Shoreline. Isobase models, based upon quadratic trend surface analysis of available comparable height data consisting of altitudes on former estuarine surfaces and related to the local High Water Mark of Ordinary Spring Tides, depict the pattern of uplift for each shoreline. These models are probably more accurate than previous models of land uplift for the period studied, and indicate a consistent and unchanging uplift pattern during the middle and late Holocene.