Wiktionary
onlap
n. (context geology English) The phenomenon of successively younger rock stratum extending progressively further across an erosion surface cut in older rocks. vb. (context geology English) (rfdef: English)
Wikipedia
Onlap
Onlap or overlap is the geologic phenomenon of successively wedge-shaped younger rock strata extending progressively further across an erosion surface cut in older rocks. It is generally associated with a marine transgression. It is a more general term than overstep, in which the younger beds overlap onto successively older beds. The opposite is offlap.
Category:Stratigraphy