baselap

downlap

onlap

Termination of strata against an overlying surface mainly as a result of nondposition (sedimentary bypassing) with perhaps only minor erosion.

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.