Sequences and Systems Tracts—a Sedimentologic View
Stratigraphic sequences and systems tracts as defined in sequence stratigraphy (Figure 4-1) are lithostratigraphic concepts and as such interpretable in sedimentologic terms. We believe that sedimento-logic analysis is the most appropriate way to reveal the primary controls behind a certain feature of sequence stratigraphy. This, in turn, allows one to assess the role of sea level and other factors in building the sequence record.
When sedimentologic analysis is performed, it turns out that very often sea level is not the only process that may generate sequences and systems tracts. The classical interpretation of sequences and systems tracts in terms of sea-level cycles (Figure 4-2) is a possible, but generally not a unique solution. In particular, changes in volume and composition of sediment will often have similar effects as sea-level fluctuations (Figure 4-3). Whether these alternative controls do apply, has to be determined specifically for each instance. Chapter 6 discusses examples of sequences created not by sea level but by other processes. Here, we will examine some pivotal concepts and terms of sequence stratigraphy and seismic stratigraphy to improve our understanding of their genesis.
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Sedimentology and Sequence Stratigraphy of Reefs and Carbonate Platforms: A Short Course
Classical sequence stratigraphy has been developed primarily from siliciclastic systems. Application of the concept to carbonates has not been as straightforward as expected even though the basic tenets of sequence stratigraphy are supposed to be applicable to all depositional systems. Rather than force carbonate platforms into the straightjacket of a concept derived from another sediment family, this publication takes a different tack, starting out from the premise that sequence stratigraphy is a modern and sophisticated version of lithostratigraphy. It reviews sedimentologic principles governing the large-scale anatomy of reefs and platforms; looks at sequences and systems tracts from a sedimentologic point of view; assesses the differences between siliciclastics and carbonates in their response to sea level; evaluates processes that compete with sea level for control on carbonate sequences; and presents a set of guidelines for application of sequence stratigraphy to reefs and carbonate platforms.