Sequence Stratigraphy and the Hierarchy of Stratal Units
1990. "Sequence Stratigraphy and the Hierarchy of Stratal Units", 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 already discussed, stratal units from the laminato the sequence can be grouped into a hierarchy. Recognition of these stratal units and their use in correlating time and facies is the essence of sequences tratigraphy. The following discussion builds upward from the smallest unit in the hierarchy, the lamina, to the largest unit considered in this book, the sequence.
Each stratal unit in the hierarchy is defined and identified only by the physical relationships of the strata, including lateral continuity and geometry of the surfaces bounding the units, vertical-stacking patterns, and lateral geometry of the strata within the units. In addition, facies and environmental interpretations of strata on either side of bounding surfaces are critical, especially for parasequence, parasequence set, and sequence-boundary identification. Thickness, time for formation, and interpretation of regional or global ongm are not used to define stratal units or to place them in the hierarchy. In particular, parasequencesand sequences can be identified in well logs, cores, or outcrops and used to construct a stratigraphic framework regardless of their interpreted relationship to changes in eustasy.
Documentation of parasequences, parasequencesets, and sequences in this book is primarily from Tertiary strata in the northern Gulf of Mexico and Cretaceous strata of the basins in the western interior of the United States. Examples are exclusively of siliciclastic rocks; however, many of the concepts documented by these examples can also be applied to carbonate strata (Sarg, 1988).
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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.”