Sequence stratigraphy

Abstract

Stratal stacking patterns provide the key to the definition of all units and surfaces of sequence stratigraphy, in a manner that is independent of the interpretation of the underlying controls. The construction of a sequence stratigraphic framework follows a standard workflow guided by the observation of stratal stacking patterns at scales defined by the purpose of study or by the resolution of the data available. Beyond the purpose of the methodological workflow, the modelling and testing of the possible controls on sequence development can continue indefinitely after the construction of a sequence stratigraphic framework. Scale is a key topic in sequence stratigraphy, with implications for methodology, nomenclature, and the classification of stratigraphic cycles that develop at different scales. Stratigraphic cyclicity is basin-specific in terms of timing and scales, reflecting the importance of local controls on accommodation and sedimentation. The scale of the smallest stratigraphic cycle that can be identified at any location depends on the resolution of the data available. In the context of seismic stratigraphy, the smallest identifiable 'sequence' is typically not the smallest stratigraphic cycle within the study area, but the smallest stratigraphic cycle that is above the resolution of the seismic data. The inability to identify the smallest sequence in every study indicates that the classification of stratigraphic cycles is best approached from the 'first-order' basin fill as the anchor for the definition of hierarchical ranks. The scale of the lowest rank systems tracts at any location defines the highest resolution that can be achieved with a stratigraphic study. A scale-independent approach to methodology and nomenclature is key to a consistent application of sequence stratigraphy across the entire range of geological settings, stratigraphic scales, and types of data available.