1990. "Sequence", 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
Download citation file:
Sequence: A relatively conformable succession of genetically related strata bounded by unconformities or their correlative conformities (Mitchum, 1977).Parasequences and parasequence sets are the stratal building blocks of the sequence. Sequence characteristics are summarized in Table 1.
Unconformity: A surface separating younger from older strata along which there is evidence of subaerialerosional truncation and, in some areas, correlative submarine erosion, or subaerial exposure, with a significanthiatus indicated (Van Wagoner et al., 1988).This definition restricts the usage of unconformity to subaerial surfaces and their correlative submarine erosional surfaces and is somewhat more restrictive than the definition of unconformity used by Mitchum (1977). Local, contemporaneous erosion and deposition associated with geological processes such as point-bar development or aeolian-dune migration are excluded from the definition of unconformity used in this book.
Conformity: A surface separating younger from olderstrata along which there is no evidence of erosion (neithersubaerial nor submarine) or nond eposition, and along which no significant hiatus is indicated. It includes surfaces onto which there is very slow deposition or low rates of sediment accumulation, with long periods of geologic time being represented by very thin deposits
Sequences can be subdivided into systems tracts(Van Wagoner et al., 1988; Posamentier et al., 1988)based on objective criteria including types of bounding surfaces, parasequence set distribution, and position within the sequence. Systems tracts also can be characterized by geometry and facies associations. Systems tracts are defined as a linkage of contemporaneous depositional systems (Brown and Fisher, 1977);depositional systems are defined as three-dimensional assemblages of lithofacies (Fisher
Figures & Tables
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.”