offlapn.
/ˈɒflap/, U.S. /ˈɔfˌlæp/, /ˈɑfˌlæp/ Geology.
A progressive diminution in the lateral extent of sedimentary deposits in passing upwards from older to younger strata, so that each stratum leaves a portion of the underlying one exposed; a set of strata exhibiting this, typically as a result of regression of a shoreline. Contrasted with onlap. Cf. overlap n. 2.
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the world > the earth > structure of the earth > structural features > sedimentary formation > [noun] > stratum > position or direction of strata > offlap or onlap
offlap1913
onlap1947
1913 A. W. Grabau Princ. Stratigr. xviii. 734 (caption) Diagram illustrating regressive overlap (off-lap) and the formation of a sandstone of emergence..into which the shore-ends of the successive members of the retreatal series..grade.
1948 Jrnl. Geol. (Chicago) 56 147/1 Marine blanket sands represent the horizontal welding of many parallel prismatic shore lines during a long, continuous period of over-lap or off-lap.
1969 G. M. Bennison & A. E. Wright Geol. Hist. Brit. Isles i. 14 The offlaps of marine sedimentation are accompanied, in this case, by lateral and vertical gradation into beds of continental facies.
1975 Nature 10 Jan. 107/1 The stratigraphic relationship of the Devensian Tills of eastern England is therefore one of offlap..and not of overlap.
1993 P. Kearey Encycl. Solid Earth Sci. 322/1 Global correlation of changes in eustatic sea-level was re-attempted from the seismic stratigraphy of onlap and offlap sequences in a number of sedimentary basins.
This entry has been updated (OED Third Edition, March 2004; most recently modified version published online March 2022).
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n.1913