Sequence stratigraphic analysis is based on the identification of depositional sequences, which are stratigraphic units composed of a relatively conformable succession of genetically related strata bounded by two major unconformities (Mitchum, 1977). This method is usually used to reconstruct the effects of sea level rise and fall on the history of deposition on continental margins. Seismic stratigraphic analysis of SHR strata differs from traditional sequence stratigraphy in that the stratal succession was not significantly influenced by sea level changes. SHR is located on the continental slope at 800 m depth (Fig. F1), and the sediments composing the core of the ridge originated from accretion of abyssal plain sediment originally deposited at ~2900 m depth. Deposition of the overlying slope basin sediments was controlled by the formation and evolution of the accretionary wedge fold-thrust belt system. In spite of the difference between the processes controlling changes in sediment deposition patterns, similar types of angular unconformities can be distinguished based on the geometry of the strata and their termination (Fig. F3). The unconformities bound sets of relatively concordant strata. Each of these sets is interpreted to represent one depositional sequence. Each seismic unit is subdivided into a few depositional sequences. Characteristics of the sequences are controlled by syn- and postdepositional tectonic activity.
Seismic sequence analysis of the depositional sequences mapped at SHR was used to reconstruct the sedimentary and tectonic events that deformed the sediments in the SHR fold and thrust system and the concomitant active basins and to derive a relative time-correlation of these events. The method included evaluating the relationship between the synsedimentary thrust and fold systems responsible for the formation of the ridge and the migration of the intervening slope basins. The primary tectonic processes observed on SHR are thrust-related folding of the strata and migration of the thrust system. These processes control the location and growth of sediment depocenters and result in tilting of the strata on the limbs of folds and/or along the flanks of subsiding depocenters.