Abstract:

Discoveries of cataclysmic glacial lake outburst floods have expanded the scale and frequency of known mass transport events on Earth and other planets. It has been realized that sedimentary deposits related to high-energy freshwater floods are widespread across continents and these deposits share some commonalities when compared carefully. However, the identification and sophisticated reconstruction of these high-energy flood events require well-conditioned stratigraphic models of depositional successions, yet such models are still lacking. Thus, the primary purpose of this paper is to examine and condense the published stratigraphic and sedimentological evidence to identify the key signatures of megaflood successions. The deposits are often the only record of a flood; therefore, the secondary purpose is to interpret the sedimentary sequences in order to reconstruct the behavior and dynamics of a single and multiple flood events. The deposits of high-energy floods are usually massive and extensive, exhibiting sedimentary structures such as amalgamation, rhythmicity, outsized clasts, intraclasts, and obstacle marks. Typical sedimentary successions of high-energy floods include basal coarse parallel-bedded units, large-scale clinoforms, horizontally bedded thin laminated units, ripple and dune cross-beds, silt beds, and debris flow deposits. Such a succession is usually dominated by high concentration suspension rain-outs, representing a single cycle of waxing and waning flood flow. Clay and silt are generally sparse or absent and are transported further down the system. At the scale of the hydrograph, the successions indicate that flows initially accelerate and then decelerate, with significantly shorter periods of flow pulses also evident in the sedimentary signatures.

Key words: high-energy flood, hydrologic characteristics, sedimentological characteristics, typical succession