CLARIFYING 50 YEARS OF DEFINITIONS ASCRIBED TO THE MAXIMUM FLOODING SURFACE WITH FUZZY IF-THEN CLASSIFIERS AND INFERENCE SYSTEMS

Since the middle of the 20th century, one of the best temporal markers for correlations across sedimentary sections has been what is now commonly identified as the “maximum flooding surface.” However, multiple definitions for this term have appeared through the years founded on various sedimentary processes and events. Three primary definitions for the maximum flooding surface have been published: 1) a surface formed during the time of deepest water, 2) a surface marking the time of the maximum landward position of the basinward pinchouts of shelfal units, and 3) a surface representing time of maximum starvation formed during low depositional rates associated with the condensed section and maximum rate of sea-level rise. It is often assumed that all three events occur simultaneously and define a synchronous surface. Recognition of the maximum flooding surface is complicated by the fact that the surface is classified by ambiguous characteristics, different identification techniques for various datasets, and various genetic interpretations attributed to descriptive definitions.

Infinite-valued (fuzzy) logic methods have been used to address some of these problems. Fuzzy logic, a branch of mathematical logic, has been shown to provide sedimentary and stratigraphic modelers with a method that formalizes qualitative information. Fuzzy methods quantify subjective data so that geologic observations are repeatable, accept context dependency, and effectively integrate much of the qualitative and quantitative data available. These qualities are used to 1) quantify sedimentary characteristics through fuzzy classifier design to reduce subjective identification and to facilitate repeated recognition of the maximum flooding surface in rock descriptions and to 2) develop a fuzzy inference system to elucidate the genetic significance of the surface. The model argues that the time of maximum sediment starvation and maximum flooding are discrete events. The surface of maximum starvation, as recognized in outcrop, is recorded as a synchronous horizon, whereas the maximum flooding event is complicated by the interplay of rates of sediment accumulation and accommodation space.