![]() ![]() Biostratigraphy in sequence stratigraphy.Traps in a framework of sequence stratigraphy.Fourth- and fifth-order sequences (Parasequences).The slope angle of siliciclastic margins is generally less than carbonate margins. This plus the unique ability of carbonate sedimentation to keep pace with sea level rise is responsible for the diverse morphology of carbonate platforms, i.e., ramps, rimmed platforms, and isolated platforms. Organic and inorganic processes produce carbonate sediment within the basin. Streams and rivers draining areas landward and updip from the basin deliver sediment to the basin. Sediment supply is a greater factor in siliciclastic sequence deposition than carbonate sequence deposition because siliciclastic sediments originate from outside the basin, whereas carbonate sediments originate within the basin. However, if global sea level is falling but more slowly than the basin is subsiding, then new space is created.įigure 1 shows how, at a point on a shelf, for example, global sea level cycles combine with subsidence to produce accommodation. For example, if global sea level is falling at the same rate as subsidence, then no new space is made for sediment accumulation. ![]() Accommodation is equal to the rate of eustatic change minus the rate of subsidence. In most cases, subsidence can be considered as constant. Copyright: Posamentier and Vail courtesy SEPM.Īccommodation is the space made available for the accumulation of sediment that results from global sea level change and subsidence. carbonate), basin type, and differential compaction.įigure 1 Example of global sea level cycles combining with subsidence to produce accommodation. Other factors that influence sequence deposition (although not to the same extent) are crustal loading, dominant sediment type (i.e., siliciclastic vs. This type of analysis, termed sequence stratigraphy, defines a hierarchy of stratal units that range from thousands of meters to millimeters in thickness and that were deposited by events that range from tens of millions of years to days in duration.įour factors control sequence deposition: During the 1980s, a finer resolution of stratigraphic analysis developed when outcrop and well data were applied to seismic stratigraphy. In the late 1970s, seismic data was interpreted stratigraphically to define packages of strata hundreds of meters thick that were deposited between sea level cycles that lasted 0.5–5 m.y. define sequence stratigraphy as “… the study of rock relationships within a chronostratigraphic framework of repetitive, genetically related strata bounded by surfaces of erosion or nondeposition, or their correlative unconformities.” Paleogeographic reconstruction of facies belts at precise moments in time is the goal of the sequence stratigrapher. 3 Factors controlling sequence deposition.Interested readers should review the abundant literature regarding sequence stratigraphy and the role of tectonics and rapid sedimentation in stratigraphic architecture. Basic principles are reviewed below, but many important details, model variations, and examples are not included. Sequence stratigraphic techniques provide (1) a more effective method for evaluating reservoir system continuity and trend directions and (2) improved methods for predicting reservoir system, source, and sealing facies away from well control. Sequence stratigraphic concepts provide a means to classify, correlate, and map sedimentary rocks using time–stratigraphic units. Sequence stratigraphy allows an effective, systematic approach to stratigraphic trap exploration. Predicting the occurrence of oil and gas traps ![]()
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