base level

corelative conformity

forced regression

regressive surface of erosion

unconformity

This was defined by Hunt and Tucker (1992) as the surface that underlies the marine sedimentary wedge that builds seaward during a forced regression of the shoreline. Catuneanu (2002) and Catuneanu et al (2011) suggest that this surface replace "the correlative conformity of Posamentier et al. (1988), and that it represents the paleo-sea floor" at the shoreline at the onset of base level fall. He points out the in "shallow marine successions, the basal surface of forced regression may be conformable", making it difficult to identify as the correlative conformity. Similarly it may be reworked by the regressive surface of marine erosion. Hunt and Tucker (1992) suggest that the basal surface of forced regression may be traced into the deepwater setting under the prograding submarine fan complex. Catuneanu (2002) indicates that "it matches the scour cut by the earliest gravity flows associated with the forced regression of the shoreline". He explains "that during the growth of the prograding submarine fan complex, individual submarine fans may gradually onlap the sediment-starved continental slope (Vail and Wornardt, 1990; Kolla, 1993; Embry, 1995)". He concludes that this "portion of the basal surface of forced regression is also known as the "regressive slope onlap surface" (Embry, 2001). "

References
Catuneanu,O., 2002, Sequence stratigraphy of clastic systems: concepts, merits, and pitfalls Journal of African Earth Sciences, Volume 35, Issue 1, Pages 1-43
Catuneanu, Octavian, William E. Galloway, Christopher G. St. C. Kendall, Andrew D. Miall, Henry W. Posamentier, André Strasser, and Maurice E. Tucker, 2011, "Sequence stratigraphy: Methodology and Nomenclature", Newsletters on Stratigraphy, Stuttgart, Vol. 44/3, 173–245
Embry, A.F., 1995, Sequence boundaries and sequence hierarchies: problems and proposals. In: Steel, R.J., Felt, V.L., Johannessen, E.P., Mathieu, C. (Eds.), Sequence stratigraphy on the Northwest European Margin, vol. 5 (Special Publication). Norwegian Petroleum Society (NPF), pp. 1–11.
Embry, A.F., 2001, The six surfaces of sequence stratigraphy.A.A.P.G. Hedberg Research Conference on Sequence Stratigraphic and Allostratigraphic Principles and Concepts, Dallas, August 26–29, Program and Abstracts Volume, pp. 26–27.
Hunt, D., Tucker, M.E., 1992, Stranded parasequences and the forced regressive wedge systems tract: deposition during base-level fall. Sedimentary Geology 81, 1–9.
Kolla, V., 1993, Lowstand deep-water siliciclastic depositional systems: characteristics and terminology in sequence stratigraphy and sedimentology. Bulletin of the Center for Research and Exploration–– Production Elf Aquitaine 17, 67–78.
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
Posamentier, H.W., Jervey, M.T., Vail, P.R., 1988, eustatic controls on clastic deposition. I. Conceptual framework. 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. 110– 124.
Vail, P.R., Wornardt, W.W., 1990, Well log-seismic stratigraphy; an integrated tool for the 90s: Gulf Coast Section. In: SEPM Foundation Eleventh Annual Research Conference Program and Extended Abstracts, pp. 379–388.