40 YEARS OF CHANGING VIEWS ON THE SEQUENCE-STRATIGRAPHIC PARADIGM

Modern Sequence stratigraphy emerged on the scene 40 years ago with the publication of the 1977 AAPG Memoir 26. The sequence-stratigraphic paradigm was crystalized over the following few years. Sequence stratigraphy produced two principle products, a framework for genetically subdividing the stratigraphic record (the slug diagram), and a record of eustatic sea-level change (the Vail curves). The Vail curves were an early victim of critical examination. The core of this framework survives as a foundational means of stratigraphic interpretation these 40 years later.

Testing though field techniques, experimentation, and modeling modified sequence stratigraphy over the past 40 years. Much of this change has come either in the interpretation of the key bounding surfaces, or in the understanding of sediment supply and accommodation on sequence accumulation. Early models assumed sediment bypass across the sequence bounding unconformity. This justified the assumption that this surface was a time line that everywhere separated younger and older strata. Field testing and experimentation showed that this surface was in fact a composite surface that recorded continuous erosion and deposition and was neither a time boundary, synchronous, nor even an unconformity. While the other principle surfaces (i.e., the correlative conformity, the maximum flooding surface, and the maximum regressive surface) have survived conceptually, their tangible definition in the rocks has seen a range of interpretations. Many close proxies for these surfaces are well defined, but precise and definitive matches for these surfaces in rock are still atypical. In short, the original promise of sequence stratigraphic surfaces as time lines has faltered or been proven approximate. The original assertion of these surfaces as defining genetic breaks in the stratigraphic record remains robust. Original assumptions regarding sediment supply and accommodation have also seen modification. Assumptions for timing and duration of sediment routing to each of the systems tracts were based on early bypass assumptions that were not accurate. Numerous models and field tests have corrected these oversights.

Be it older and wiser from its many bends and morphs, sequence stratigraphy remains alive and well on its 40^th birthday.