Facies models for rocky shorelines and their application to transgressed basement highs in the North Sea

Abstract

Rocky shorelines form where basement highs are eroded and flooded during marine transgressive events. Although the Mesozoic North Sea rift generated numerous platform margins and rotated fault blocks that acted as basement highs, rocky shoreline deposits have not previously been reported in this region. Rocky shoreline deposits are usually represented in the rock record by thin conglomerates overlying major unconformities. They are typically characterized by their ichnological aspects rather than by their depositional facies. This study used the sedimentological aspects of modern and Miocene rocky shorelines from Spain and Austria to create facies models, which were then applied to the recognition of rocky shorelines in the Mesozoic of the Central North Sea. Our results demonstrate that structureless, clast-supported, poorly to moderately sorted conglomerate–breccia deposits are associated with competent basement lithologies, which produce hard, resistant coastal cliffs around previously overlooked volcanic centres in the subsurface of the North Sea. The basement lithologies in most of the Central North Sea favoured the formation of softer coastal cliffs, with less resistant lithologies that did not generate or preserve gravel-sized particles. These softer coastal cliffs were mostly characterized by low-angle, unconformity-bounded sandstones and fine-grained deposits, precluding the preservation and recognition of Mesozoic rocky shores in much of the North Sea's stratigraphic record.