Wave-ravinement surfaces: Classification and key characteristics

The wave-ravinement surface (WRS) is a surface of sequence-stratigraphic significance that forms in shallow-water settings during transgression. It develops progressively landward during shoreface retreat due to wave action, which erodes the substrate and leads to sediment bypass in the offshore direction. The WRS may rework previously formed surfaces, such as the maximum regressive surface (also known as the transgressive surface) and the subaerial unconformity, becoming a systems tract and/or sequence boundary. Due to the associated lithological contrast between underlying and overlying deposits and the presence of lags and/or shell pavements, the WRS has a very good appearance in both outcrop and cores and is often used as the boundary of shallow-marine stratigraphic sequences. The WRS, therefore, represents an important lithological and paleo-environmental break, and its recognition is significant for reconstructing stratigraphic architectures and the history of relative sea-level change, as well as for reservoir characterization. Several controlling factors govern the development of the WRS and of the associated deposits; they include the accommodation to sedimentation (A/S) ratio, environmental energy, topographic gradient, roughness and lithology of the substrate. Relatively low rates of relative sea-level rise and sediment supply, high wave energy, steep topographies and easily erodible substrates favor the development of the WRS. These factors interact, leading to a high variability in the amount of erosion, shape, length along depositional dip and deposits associated with these surfaces. WRSs may be classified based on either underlying or overlying deposits, or a combination of both. A classification based on the deposits that underlie the WRS helps to determine the location of the studied outcrop along depositional dip, whereas a classification based on the deposits that overlie the WRS afford insights into the physical conditions that accompanied its formation. However, the best description of the WRS in terms of location of a considered outcrop, physical conditions under which the WRS developed and their lateral variability, type of substrate, as well as its practical significance for reservoir modeling is achieved with a combination of the two criteria.