Autostratigraphy: A Framework Norm for Genetic Stratigraphy

Abstract

Abstract Autostratigraphy is the stratigraphy generated by large-scale autogenic processes, and needs to be heeded because of a current overreliance on allogenic controls in sequence stratigraphy. Key principles of autostratigraphy, emerging from the theory of autoretreat and a new understanding of alluvial grade, derive from the non-equilibrium stratigraphic response, i.e., the general lack of equilibrium configuration of depositional systems. The non-equilibrium behavior of fluvial deltas during times (T) of steady dynamic forcing leads to variable stratigraphic response that is the inevitable result of length (D) and time (τ) scaling particular to the depositional system, rather than necessarily reflecting any sudden or unsteady change in the rate of allogenic forcing. Some abrupt breaks in the stratigraphic record are not necessarily associated with changes in allogenic conditions but can result from purely autogenic processes of the system. When T is comparable to or longer than τ, (1) the depositional system takes the non-equilibrium, large-scale autogenic response, (2) the superposition of autogenic and allogenic components of the forcing is prominently nonlinear, and thus (3) sequence stratigraphic models that have been built on the assumption of equilibrium response are incorrect. Autostratigraphic analysis makes it possible to detect and identify complex autogenic responses and unsteady allogenic events in the stratigraphic record by quantifying a temporal change in the magnitude of D. Autostratigraphy thus functions as a norm for genetic stratigraphy.