stratigraphic boundary  search
NTK-T boundary
 Permian-Triassic boundary
UFboundaries, stratigraphic
RTallostratigraphy
 stratigraphy
 stratigraphic columns
 stratotypes
SNBefore 1993, also search boundary which was used for this concept from 1978-1992. Use in combination with appropriate age terms (list E). Added to Thesaurus in 1993.