Recognition of eustatic versus tectonic signatures in the carbonate sequence stratigraphic record
- Chevron U.S.A. Production Co., Midland, TX (United States)
In the process of building sequence stratigraphic models it has become apparent that both eustatic and tectonic signatures can be recognized in the sequence stratigraphic record. Tectonics, active during deposition, modify the shelf to basin profile to leave a signature of increased or decreased rates of subsidence or uplift, or by quiescence. Subsidence or uplift may increase, decrease, or stop, and start again in short amounts of time. Tectonics can dramatically control the positioning of high to low quality reservoir rock. Eustatic sea level rise and fall may be synchronous or out of phase with tectonic events on the cycle, set, or sequence scale. On the sequence scale, if subsidence rates increased dramatically eustatic sea level rise and fall would deposit less complete shallowing-upward cycles in a transgressive systems tract. As subsidence slowed eustatic sea level would deposit complete cycles, containing exposure surfaces, in a highstand systems tract. If the basement is broken into discrete blocks, individual blocks may adjust differentially. One block may subside while an adjacent block may be quiescent or slowly uplifting. If one block abruptly subsides adjacent to a block that did not, cycles in the subsiding block thicken to form a wedge. As subsidence slowed and became more uniform, cycles across the same area will be of equal thickness. If subsidence stopped entirely, subaerial exposure would create an unconformity. Blocks slowly uplifting during deposition would receive thinner cycles across that block or the cycles would onlap onto it, and appear as a bulge in the shelf to basin profile.
- OSTI ID:
- 425689
- Report Number(s):
- CONF-960527--
- Country of Publication:
- United States
- Language:
- English
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