Transgressive rocky coasts in the geological record: Insights from Miocene granitic rocky shorelines and modern examples

• Published in: Sedimentary geology 2023-03, Vol.446, p.106344, Article 106344
• Main Authors: Puig López, Josep M., Howell, John, Roetzel, Reinhard, Poyatos-Moré, Miquel
• Format: Article
• Language: English
• Subjects: Conglomerates; Granitic basement; Joint-cut coves; Pocket beaches; Rocky shorelines; Transgressive
• ISSN: 0037-0738; 1879-0968
• DOI: 10.1016/j.sedgeo.2023.106344

Rocky shorelines are commonly punctuated, with alternating high relief cliffs and incised embayments which host “pocket beaches”. While multiple cases of ancient rocky shorelines associated with low relief ravinement surfaces have been documented in the geological record, deposits formed in pocket beaches and joint-cut coves are more rarely described. This poses the question “are high relief rocky coastlines and their associated deposits not preserved or have they been previously overlooked? Here we document exhumed examples of ancient granitic rocky shoreline systems of diverse morphologies from the Early Miocene of northern Austria, and compare them with modern systems in UK, Corsica, Spain and Norway. The preserved ancient examples offer a good opportunity to characterize these sedimentary systems, provide diagnostic criteria for their recognition and discuss the main controls on their occurrence and preservation in the rock record. From their stratigraphic and sedimentological analysis, and its comparison with modern examples, we interpret that these rocky shorelines form and get preserved during rapid rates of combined tectonic and eustatic sea-level rise, along lithological, structural and weathered “weakness” zones affected by normal low wave energy conditions interrupted by storms. These results provide a mechanism for predicting their potential occurrence and distribution during transgression of rocky coasts, with implications for exploration around structural highs and coastal management. •Miocene rocky shoreline deposits on top of granitic basement are described.•The deposits are interpreted to be formed in pocket beaches and joint-cut coves.•Deeply incised and shallow, scoop shaped, incisions are preserved.•The sedimentary infill is dominated by conglomerates and sandstones.•Their preservation potential and distribution can be predicted.