downlap

onlap

terminations

A term describing terminations of strata along the lower boundary of a depositional sequence, used only where discrimination between onlap and downlap is difficult or impossible.

References
Mitchum Jr., R.M., 1977. Seismic stratigraphy and global changes of sea level. Part 11: glossary of terms used in seismic stratigraphy. In: Payton, C.E. (Ed.), Seismic Stratigraphy––Applications to Hydrocarbon Exploration, vol. 26. A.A.P.G. Memoir, pp. 205–212.