1990. "Introduction", Siliciclastic Sequence Stratigraphy in Well Logs, Cores, and Outcrops: Concepts for High-Resolution Correlation of Time and Facies, J. C. Van Wagoner, R. M. Mitchum, K. M. Campion, V. D. Rahmanian
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As the search for oil and gas becomes more sophisticated and producing basins and fields become more intensely developed, geoscientists need correspondingly more accurate techniques for stratigraphic analysis. To achieve this accuracy, companies are shooting higher-resolution seismic lines, acquiring3-D seismic surveys over fields, and coring more to quantify reservoir properties. Exploration and production staff, provided with these more accurate but expensive data, often under-utilize the well log. In basins or fields with a sufficient density of well COntrol, the coupling of conventional well logs and cores with the techniques of sequence stratigraphy results in an ultra-high-resolution chronostratigraphic frame work for subsurface correlation. Where integrated with seismic and biostratigraphic data, well-log cross sections, interpreted using sequence and parasequenceconcepts, provide a state-of-the-art framework for analyzing reservoir, source, and seal distribution, whether on a regional or a field-reservoir scale.
Sequence stratigraphy is the study of genetically related facies within a framework of chronostratigraphically significant surfaces. The sequence is the fundamental stratal unit for sequence-stratigraphic analysis. The sequence is defined as a relatively conformable, genetically related succession of strata bounded by unconformities or their correlative conformities (Mitchum, 1977). Sequence boundaries form in response to relative falls in sea level. Parasequencesand parasequence sets are the building blocks of sequences. A parasequence is defined as a relatively conformable, genetically related succession of' Present address; Sangree, Sneider, and Mitchum, Houston, Texas, U.s.A. beds or bed sets bounded by marine-flooding surfaces or their correlative surfaces (Van Wagoner, 1985; Van Wagoner et al., 1988).
A parasequence set is defined as
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Siliciclastic Sequence Stratigraphy in Well Logs, Cores, and Outcrops: Concepts for High-Resolution Correlation of Time and Facies
Application of sequence-stratigraphic analysis depends on the recognition of a hierarchy of stratal units including beds, bedsets, parasequences, parasequence sets, and sequences bounded by chronostratigraphically significant surfaces of erosion, nondeposition, or their correlative surfaces. This method of stratigraphic analysis contrasts with the use of transgressive and regressive cycles of strata for regional correlation of time and facies. Transgressive and regressive cycles have been used for regional correlation for at least 50 years. Recently, proponents of transgressive and regressive cycles, referred to as T-R units, for regional correlation have included Ryer (1983), Busch and Rollins (1984), Busch et al. (1985), and Galloway (1989a). Galloway (1989a) introduced the “genetic stratigraphic sequence,” which is a regressive depositional unit bounded by transgressive surfaces. Although he did not define it specifically, he described it as “a package of sediments recording a significant episode of basin-margin outbuilding and basin filling, bounded by periods of widespread basin margin flooding.”