Chapter 6 - Stratigraphic surfaces

Abstract

This chapter explains the difference between sequence stratigraphic surfaces and other types of stratigraphic contacts, and provides the criteria that afford the identification of all surfaces with relevance to sequence stratigraphy. A sequence stratigraphic surface is a type of stratigraphic contact that invariably serves, at least in part, as a systems tract boundary. As systems tract boundaries, sequence stratigraphic surfaces mark changes in stacking patterns between the strata below and above the contact. This defining attribute separates a sequence stratigraphic surface from any other type of stratigraphic contact, and provides the basis for sequence stratigraphic correlation. Sequence stratigraphic surfaces define the framework of sequences and component systems tracts. Within this framework, lithological changes inside systems tracts define “within-trend” facies contacts, which have physical expression (i.e., they are surfaces of lithostratigraphy or allostratigraphy) but do not mark a change in stratal stacking pattern. All types of stratigraphic surfaces are important in stratigraphic studies. However, the workflow of sequence stratigraphy requires the identification of sequence stratigraphic surfaces first, followed by the placement and rationalization of facies contacts in the context of systems tracts. The same types of stratigraphic surfaces can be observed at different stratigraphic scales (hierarchical levels). The physical expression of all types of sequence stratigraphic surfaces and within-trend facies contacts is exemplified in this chapter with outcrop images and subsurface (borehole and seismic) data.