Sequence Stratigraphic Concepts
Modern sequence stratigraphy is a direct outgrowth of the concept of unconformity bound stratigraphic units as proposed by Sloss (1963), with some very important variations. In simplest terms, Sloss’s (1963) sequence stratigraphy was a tool to identify major unconformity-bound packages (e.g., Sauk, Kaskaskia) for the purpose of correlation across large areas of the craton (Fig. 1.1). We now call these 2nd order sequences.
The second major evolutionary step in the conceptual evolution to modern sequence stratigraphy was seismic stratigraphy. AAPG Memoir 26 (Payton et al. 1977) captures, in a series of manuscripts by Exxon geologists, a methodology for identifying Slossian type unconformity-bound sequences using reflection seismic data. The emphasis of this methodology was the use of seismic geometry and termination styles to delineate unconformity-bound seismic sequences (Fig. 1.2; Mitchum et al. 1977a, b), derivation of eustatic curves using coastal onlap (Vail et al. 1977a), and global sequence correlation based on biostratigraphic control (Vail et al. 1977b). Another key aspect of this research (Vail et al. 1977c), which was also echoed by Brown and Fisher (1977) among others, was the chronostratigraphic significance of seismic reflectors. The observation that a single shelf-to-basin reflector mimicked a depositional time-line opened the door for sedimentologic analysis of the internal make-up of seismic sequences (Fig. 1.3). This seismic chronostratigraphy led to the third key development, which was concept of sequence stratigraphy.
The transition from seismic stratigraphy to sequence stratigraphy represents a major conceptual jump. Focus shifted from global mapping of unconformity-bound packages to the interpretation of