Sequence Stratigraphy

The currently accepted definition of “sequence” is that proposed by Vail et al. (1977, p. 53). It is a “stratigraphic unit composed of a relatively conformable succession of genetically related strata ... bounded at its top and base by unconformities or their correlative conformities”. However, the term sequence has had a checkered history. Sloss (1963) defined stratigraphic sequences as “rock-stratigraphic units of higher rank than group, megagroup, or supergroup, traceable over major areas of a continent and bounded by unconformities of interregional scope.” This useage has not received universal acceptance. In some of the literature “sequence” has been used as a synonym for “succession”, and it has been employed for cyclic or unconformity-bounded units of varying dimensions and for time spans ranging from thousands of years to hundreds of millions of years.