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Integration of seismic stratigraphic concepts with detailed field studies and geohistory analysis provides powerful interpretation leverage for deciphering the complex geologic history of carbonate platform-basin areas. Changes in carbonate productivity as well as platform growth and the resultant facies distribution are controlled most importantly by changes in relative sea level.
The structural history of the Permian basin during the Permian shows two subsidence cycles of 10-20 m.y. duration. These subsidence cycles were major factors in the long-term (106 - 107 m.y.) development of the Permian carbonate platforms. During periods of relatively rapid subsidence, aggradation was dominant; during periods of slow subsidence, major platform progradation occurred.
Superimposed on the long-term tectonic cycles is a series of third-order eustatic cycles (0.5-3 m.y.), which controlled development of 27 depositional sequences. Each sequence is composed of three depositional systems tracts: (1) a lower basin-restricted wedge interpreted to have been deposited during a relative fall and lowstand of sea level, (2) a transgressive systems tract of variable thickness, and (3) an upper, relatively thick, aggradational-to-progradational carbonate platform system, which includes significant allochthonous deposition in the basin and is interpreted to have been deposited during a relative highstand in sea level. The lowstand systems tracts are composed dominantly of quartz sandstone, commonly intercalated with carbonate debris beds at the toe of the slope. S quence boundaries display erosional truncation (subaerial on platform or at platform margin, subaqueous on slope) and/or subaerial exposure. Erosion and debris deposition occurs both within and outside submarine-canyon feeder systems.
Two highstand depositional styles are differentiated here: (1) a keep-up system, which represents a relatively rapid rate of accumulation able to keep pace with periodic rises in sea level and displays a mounded-oblique stratal geometry at the platform margin, and (2) a catch-up system, which represents a relatively slow rate of accumulation and displays a sigmoid profile at the platform margin. Individual strata units of the platform margin and slope area of the catch-up carbonate system have a much longer sea-floor residence time and display significantly greater amounts of early submarine cement. The underlying transgressive systems tract tends to have a keep-up or give-up (i.e., thin, drowned) depositional style.
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