1. Terminations: Base of a Sequence
Older
Beds
Older
Beds
SLIDE 17
Vail & Mitchum gave us a set of terms to use when marking seismic unconformities
There are two types of terminations we might observe at the base of a depositional package, a sequence
If the reflections that terminate are at a lower dip than the surface against which they terminate, then we call these onlap terminations
If the reflections that terminate are at a higher dip than the surface against which they terminate, then we call these downlap terminations
NOTE: These definitions are based on observed geometric relationships, not on inferred depositional processes
Onlap
Downlap
A base-discordant relationship in which younger strata terminate progressively against a surface of greater inclination
A base-discordant relationship in which younger inclined strata terminate progressively against a surface of lower inclination
NOTE: These definitions are based on observed geometric relationships, not on inferred depositional processes
Courtesy of ExxonMobil
L 11 – Stratigraphic Analysis