Lessons from large lake systems— Thresholds, nonlinearity, and strange attractors

Lake systems are the largest integrated depositional complexes in the continental realm: modern lakes have areas up to 374,000 km2, and ancient lake strata extend up to 300,000 km2 in the Cretaceous systems of the south Atlantic and eastern China and the Permian system of western China. The largest lakes do not appear to form a significantly different population in many of their attributes. Their area, maximum depth, and volume closely follow power-law distributions with fractional exponents (–1.20, –1.67, –2.37 respectively), with minimal breaks between the largest lakes and the majority of lakes. Controls on lake size and stratigraphic extent are not straightforward and intuitively obvious. For example, there is little relation of modern lake area, depth, and volume, with origin, climatic conditions, mixis, or water chemistry. Indeed, two-thirds of the largest-area lakes occur in relatively dry climates (precipitation-evaporation ratio [P/E] <1.6). In ancient lake strata, deposits of largest areal extent and thickness tended to form mostly under relatively shallow-water, evaporitic conditions in both convergent and divergent tectonic settings. Geometric and dynamical thresholds appear to govern lake systems as complex, sensitive, nonlinear dynamical systems. Phanerozic examples worldwide indicate that the existence, character, and stacking patterns of lake strata are a function of the interaction of rates of supply of sediment + water and potential accommodation change. Lake-system behavior reflects interactions of four main state variables: sediment supply, water supply, sill height, and basin-floor depth. The stratal record ultimately records five main modes of behavior indicating that nonmarine basin dynamical systems are governed by two fundamental bifurcations and five strange attractors in the sediment + water supply – potential accommodation phase plane: fluvial, overfilled lake, balanced filled lake, underfilled lake, and aeolian/playa. Thus, extremely large lakes are highly dependent on intricate convolutions of climatic and tectonic influences and occur in a variety of settings and climates.