SEPM Strata

regressive surface of marine erosion

Subaqueous surface of marine erosion formed during a relative sea-level fall. As sea level falls, wave base and the upper shoreface zone of current transport drops, too, and planes off the seafloor sediments that formerly lay below wave base and the upper shoreface currents. Such a fall usually is followed by the superposition of coarser-grained upper shoreface deposits sharply overlying finer-grained lower shoreface or shelf deposits associated with the following trangression. The glossifungites ichnofacies may be present within this surface associated with material deposited or reworked during fall or during the following transgression. This ichnofacies is environmentally wide ranging but only develops in firm unlithified substrates such as dewatered, compacted muds. This dewatering results from burial of offshore muds. As the overlying sediments above the sewatered muds are stripped off by submarine erosion during a lowering of wave base into the deeper shelf setting, the firm substrates are laid bare to the seafloor and made available to the organisms that form these trace fFossils. Burrowers excavate open burrows in the firm muds and leave behind traces such as Rhizocorallium, Diplocraterion, Thalassinoides, Skolithos, etc. The burrows commonly remain open and are subsequently filled with coarser-grained shallow water sediments related to the downward shift in sea level, or the shallow water sediments of the subsequent sea level rise.

Catuneanu (2002) explains that during a forced regression of the shore the shoreface maintains its equilibrium with the wave energy with its concave-up shape (Bruun, 1962; Plint, 1988; Dominguez and Wanless, 1991; Plint and Nummedal, 2000). This leads to scouring of the lower shoreface by waves and the formation of a regressive surface of marine erosion. Plint (1988) demonstrated how shoreface deposits may be separated from the basal surface of forced regression by a sharp based contact with the forced regressive shelf sediments. Catuneanu (2002) indicates how the "landward portion of the regressive surface of marine erosion is likely to rework the basal surface of forced regression, in which case it becomes a systems tract boundaformry. The formation of the regressive surface of marine erosion requires a shallow gradient of the sea floor, smaller than the average gradient of the shoreface profile. This is often the case in shelf settings, where the average gradient of the sea floor is about 0:03. In contrast, slope settings have a steeper sea floor topography relative to what is required by the shoreface to be in equilibrium with the wave energy, and hence no scouring is generated in the lower shoreface during forced regressions. These steep sea floor slopes are prograded by Gilbert-type deltas whose delta front facies are not sharp-based (sensu Plint, 1988). ). A synonymous term for the regressive surface of marine erosion is the regressive ravinement surface (Galloway, 2001)" or regressive wave ravinement (Galloway, 2005).

References
Bruun, P., 1962. Sea-level rise as a cause of shore erosion. American Society of Civil Engineers Proceedings, Journal of the Waterways and Harbors Division 88, 117–130.
Catuneanu,O., 2002, sequence stratigraphy of clastic systems: concepts, merits, and pitfalls Journal of African Earth Sciences, Volume 35, Issue 1, Pages 1-43
Dominguez, J.M.L., Wanless, H.R., 1991. Facies architecture of a falling sea-level strandplain, Doce River coast, Brazil. In: Swift, D.J.P., Oertel, G.F., Tillman, R.W., Thorne, J.A. (Eds.), Shelf Sand and Sandstone Bodies: Geometry, Facies and sequence stratigraphy, vol. 14. International Association of Sedimentologists Special Publication, pp. 259–281.
Galloway, W.E., 2001. The many faces of submarine erosion: theory meets reality in selection of sequence boundaries. A.A.P.G. Hedberg Research Conference on sequence Stratigraphic and allostratigraphic Principles and Concepts, Dallas, August 26–29, Program and Abstracts Volume, pp. 28–29.
Galloway, W.E., 2005, Gulf of Mexico basin depositional record of Cenozoic North American drainage basin evolution: International Association of Sedimentologists Special Publication 35, p. 409-423.
Plint, A.G., 1988. Sharp-based shoreface sequences and offshore bars in the Cardium formation of Alberta; their relationship to relative changes in sea level. In: Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C., Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. (Eds.), Sea Level Changes––An Integrated Approach, vol. 42. SEPM Special Publication, pp. 357–370.
Plint, A.G., Nummedal, D., 2000. The falling stage systems tract: recognition and importance in sequence stratigraphic analysis. In: Hunt, D., Gawthorpe, R.L. (Eds.), Sedimentary Response to forced regression, vol. 172. Geol. Soc. London Speci. Publ, pp. 1–17.
Posamentier, H.W., Allen, G.P., 1999. Siliciclastic sequence stratigraphy: concepts and applications. SEPM Concepts in Sedimentology and Paleontology no. 7, 210 p