Dictionary:Sequence boundary

A type-1 sequence boundary (or unconformity) is characterized by subaerial erosion, stream rejuvination, a basinward shift of facies, a downward shift in coastal onlap, and onlap of overlying strata. A type-2 sequence boundary lacks the subaerial erosion associated with stream rejuvenation and the abrupt basinward shift of facies. It forms when the rate of eustatic fall is less than the rate of basin subsidence at the depositional shoreline break. See Figure S-32.