Sequence stratigraphy: hierarchy of sequences
Global sea level changes (eustacy) are cyclic phenomena. Six orders of sea level cycles are recognized from stratigraphic evidence.[1] Third-, fourth-, and fifth-order sea level cycles model sequence deposition for petroleum exploration. A third-order sequence is a composite of fourth- and fifth-order sequences.
The table below shows sea level cycle frequencies, thickness ranges, and stratigraphic names for third-, fourth-, and fifth-order sequences.
| Sequence order | Cycle frequency, m.y. | Thickness, m | Stratigraphic name |
|---|---|---|---|
| Third | 0.5–5 | 100–1000 | Sequence |
| Fourth | 0.1–0.5 | 1–10 | Parasequence |
| Fifth | 0.01–0.1 | 1–10 | Parasequence |
Superimposition of cycles
Several frequencies, representing different orders of sea level cycles, are superimposed on one another to make a composite sea level cycle curve. For stratigraphic trap exploration, cycles that impact trap location are usually third-, fourth-, and fifth-order sea level cycles. Figure 1 shows how adding third-, fourth-, and fifth-order cycles together will produce a composite curve.
See also
References
- ↑ Van Wagoner, J., C., Mitchum, R., M., Campion, K., M., Rahmanian, V., D., 1990, Siliciclastic Sequence stratigraphy in Well Logs, Cores and Outcrops: Concepts for High-Resolution Correlation of Time and Facies: AAPG Methods in Exploration Series No. 7, 55 p.
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