The palaeoenvironmental and biological significance of marine carbonate depositional surfaces

Carbonate rocks form a substantial part of the ancient geological record, yet their reliability as archives of past environments and ecosystems has been questioned because of diagenetic alteration. This review investigates the potential of carbonate depositional surfaces – irregular or planar interfaces formed at the sediment–water or sediment–air boundary during deposition – to serve as records of ancient environments and ecosystems. These surfaces, commonly preserved in carbonate strata, provide valuable insights into sedimentary processes and ecosystems over varying timescales. Some carbonate depositional surfaces have the same features as siliciclastic examples, such as desiccation cracks, ripples, dunes and surfaces with trace and body fossils. Surfaces offer a glimpse into ordinary day-to-day deposition, such as ripples moving with the tide or mudcracks forming on an exposed tidal flat. Other depositional surfaces are unique to carbonate sediment, including hardgrounds, tepees, beachrock, reefs and microbialites. These surfaces represent cemented and/or condensed intervals of deposition, preserving significant differences in the duration of exposure and environmental conditions. Sedimentary factors, original mineralogy, biological and ocean chemical changes over Earth history and tectonic/burial history all impact the likelihood of preserving carbonate depositional surfaces.