Stratigraphy is the science of rock strata (layers of sedimentary rocks), and it deals specifically with the character and attributes of strata. Sequence stratigraphy is the study of genetically related strata bounded by unconformities or their correlative conformities (Sheriff, 1991). Seismic stratigraphy is the study and interpretation of information obtained by seismic-reflection profiling to construct subsurface stratigraphic cross sections (Allaby and Allaby, 1999). Sheriff (1991) describes seismic stratigraphy as methods to determine from seismic evidence the nature and geologic history of sedimentary rocks and their depositional environment. Figure 1 shows an example of the stratigraphic boundaries that are defined by seismic data. Before looking at seismic interpretations, we shall visit sequence stratigraphy.
Sequence stratigraphy refers to sediment deposition controlled by four factors:
subsidence of the crust as a result of tectonic and/or isostatic forces
eustasy (the rise and fall of sea level)
sediment influx from rivers and streams
climate, especially as it relates to the development of carbonate reefs in tropical environments
In other words, we could view sequence stratigraphy as an attempt to relate sedimentation to sea levels, tectonics, sediment flow, and climate change.
But what is a sequence? We can think of a sequence as a relatively conformable section between sequence boundaries, which we describe below. A parasequence is a subunit of a sequence (Sheriff, 1991). A sechron is the time interval between the top and bottom boundaries. The boundaries and erosional surfaces are determined
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Fundamentals of Geophysical Interpretation
Fundamentals of Geophysical Interpretation, SEG Geophysical Monograph Series No. 13, is a practical handbook for the petroleum geophysicist. Fundamental concepts are explained using heuristic descriptions of seismic modeling, deconvolution, depth migration, and tomography. Pitfalls in processing and contouring are described briefly. Applications include petroleum exploration of carbonate reefs, salt intrusions, and overthrust faults. The book includes past, present, and possible future developments in time-lapse seismology, borehole geophysics, multicomponent seismology, and integrated reservoir characterization.