Sequence Stratigraphy

Sequence stratigraphy is the study of sediments and sedimentary rocks in terms of repetitively arranged facies and associated stratal geometry (Vail 1987; Van Wagoner et al 1988, 1990; Christie-Blick 1991). It is a technique that can be traced back to the work of Sloss et al (1949), Sloss (1950, 1963), and Wheeler (1958) on interregional unconformities of the North American craton, but it became systematized only after the advent of seismic stratigraphy, the stratigraphic interpretation of seismic reflection profiles (Vail et al 1977, 1984, 1991; Berg & Woolverton 1985; Cross & Lessenger 1988; Sloss 1988; Christie-Blick et al 1990; Van Wagoner et al 1990; Vail 1992). Sequence stratigraphy makes use of the fact that sedimentary successions are pervaded by physical discontinuities. These are present at a great range of scales and they arise in a number of quite different ways: for example, by fluvial incision and subaerial erosion (above sea level); submergence of nonmarine or shallow-marine sediments during transgression (flooding surfaces and drowning unconformities), in some cases with shoreface erosion (ravinement); shoreface erosion during regression; erosion in the marine environment as a result of storms, currents, or mass-wasting; and through condensation under conditions of diminished sediment supply (intervals of sediment starvation). The main attribute shared by virtually all of these discontinuities, independent of origin and scale, is that to a first approximation they separate older deposits from younger ones. The recognition of discontinuities is therefore useful because they allow sedimentary successions to be divided into geometrical units that have time-stratigraphic and hence genetic significance. Precise correlation has of course long been a goal in sedimentary geology, and the emergence of sequence stratigraphy does not imply that existing techniques or data ought to be discarded. Instead, sequence stratigraphy provides a