Forced regression

Abstract

In this commentary article, architecture, component lithofacies, and bounding surface features of forced-regressive deposits are discussed in terms of a four-fold classification scheme of sequence stratigraphy in siliciclastic successions. Forced-regressive deposits are interpreted to represent a falling-stage systems tract, which develops mainly in a shallow marine environment, and to be equivalent chronostratigraphically to basin-floor-fan and slope-fan deposits in a deep-water environment. The standard sequence-stratigraphic model classifies shelf-margin deltas as a component of the lowstand wedge, which is interpreted to develop over the basin-floor-fan and slope-fan deposits. However, shelf-margin deltas, in general, consist of downstepping forced-regressive and overlying progradational and aggradational deposits, which can be assigned, respectively, to falling-stage and lowstand systems tracts of the four-fold classification scheme. Recognition of forced-regressive deposits depends on appropriate definition of datum for the correlation of stratigraphic successions and on detailed process-oriented lithofacies analysis that is crucial for the identification of depositional events responding to a relative sea-level fall. Thus, practical approaches of facies analysis and sequence-stratigrapy should constantly be upgraded for the better understand of formative processes, 3D geometry, distribution patterns, and heterogeneity of forced-regressive deposits.