| The East China Sea continental margin is characterized by abundant sediment supply, high energy, and a unique shelf physiography---a fairly shallow shelf with a low gradient, extreme width, and deep shelf-slope break. Three sequences are chronologically constrained by core data in the shallow strata from the late Pleistocene to present. Regional seismic surveys, collected as part of a broader investigation, provide unique observations unavailable to previous studies. A revised stratigraphy is presented that provides an alternate stratigraphic framework and, in the process, clarifies existing ECS stratigraphic nomenclature. In these strata, the lowstand fluvial systems, prior to oxygen isotope stage 4 do not incise the East China Sea continental margin. Instead, they comprise laterally (>400 km) and vertically (>40 m) extensive sand sheets interpreted as low-energy and low-sinuosity fluvial braidplains dominated by bed load. It is suggested in this paper that the rare nature of lowstand unincised fluvial systems (LUFS) are related to the rare nature of the extreme depositional boundary conditions forming the LUFS on continental margins (i.e., low gradient, deep shelf-slope break, abundant sediment supply). Extensive (>100 km), unincised fluvial sheet sands resembling the LUFS from the ECS margin are preserved in foreland basins throughout the Phanerozoic. Because this stratal architecture is similar to the LUFS preserved on the ECS margin, it may have been created under similar depositional conditions. In order to better understand stratal sensitivity under these conditions, a three-dimensional, forward simulator (fuzzyPEACH) was developed. In this investigation, numerous scenarios of eustasy, tectonic subsidence, and sediment influx were simulated. The various rates and magnitudes of eustatic fluctuations may also be used as a proxy for the effect of margin physiography on stratal geometry, although fuzzyPEACH allows the geometry to be user defined. Fuzzy PEACH simulations collectively uses only five FISs containing a total of 21 separate rules. These rules incorporate 15 variables and are defined by 47 fuzzy sets. Fuzzy logic was chosen for its ability to quantify subjectivity, by capturing the vagueness of linguistic terms, and assemble a robust fuzzy logic inference system, in relatively short order, that can describe complex, nonlinear relationships. |
