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

Rocky shorelines form where basement highs are eroded and flooded during marine transgressive events. Despite the Mesozoic North Sea rift generated numerous platform margins and rotated fault blocks which acted as basement highs, rocky shoreline deposits have not been previously reported. In the rock record rocky shoreline deposits are usually represented by thin conglomerates overlying major unconformities, and are typically characterised by their ichnological aspects, rather than their depositional facies. This study uses the sedimentological aspects of modern and Miocene rocky shorelines from Spain and Austria, to create facies models which are 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 size particles, being mostly characterised by low-angle, unconformity-bounded sandstone and fine-grained deposits and precluding the preservation and recognition of Mesozoic rocky shores in much of the North Sea's stratigraphic record.