Morphodynamic Hierarchy and the Fabric of the Sedimentary Record. Issue 14 (15th July 2020)

• Record Type: Journal Article
• Authors: Ganti, Vamsi; Hajek, Elizabeth A.; Leary, Kate; Straub, Kyle M.; Paola, Chris
• Is Part Of: Geophysical research letters. Volume 47:Issue 14(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-07-15
• Subjects: alluvial stratigraphy -- channel bars -- preservation -- river kinematics -- avulsions -- hierarchy; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL087921
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The low temporal completeness of fluvial strata could indicate that recorded events represent unusual and extreme conditions. However, field observations suggest that preserved strata predominantly record relatively common transport conditions—a paradox termed the strange ordinariness of fluvial strata. We theorize that the self‐organization of fluvial systems into a morphodynamic hierarchy that spans bed to basin scales facilitates the preservation of ordinary events in fluvial strata. Using a new probabilistic model and existing field and experimental data sets across these scales, we show that fluvial morphodynamic hierarchy enhances the stratigraphic preservation of medial topography—ordinary events. We show that lower‐order landforms have a higher likelihood of complete preservation when the kinematic rates of evolution of successive levels in the morphodynamic hierarchy are comparable. We highlight how relative changes in kinematic rates of evolution of successive levels in the morphodynamic hierarchy can manifest as major shifts in stratigraphic architecture through Earth history. Plain Language Summary: Earth's ability to archive its evolution in sedimentary rocks forms the basis of our knowledge of past environments and life. The fraction of time preserved, however, is vanishingly small, which could indicate that preserved strata preferentially record the catastrophic and extreme events of the geologic past. Contrary to this expectation, field evidence across a range of scales suggests that fluvial strata predominantly record the mundane and relatively common transport conditions—a paradox termed the strange ordinariness of fluvial strata. Using a new probabilistic modeling framework and existing experimental and field data, we suggest that the strange ordinariness of fluvial strata is a result of the propensity of rivers to organize themselves into hierarchical elements (e.g., river dunes, bars, channels, and channel belts) that each have their representative timescale of evolution. We show that the presence of this hierarchy reconciles the paradox between the rarity of event preservation and the familiarity of the preserved events in stratigraphy at all scales. We also find that when successive hierarchical elements evolve at comparable rates, ordinary events are more likely to be preserved in stratigraphy. The story written in rocks is thus mostly of the common and mundane, not the rare and spectacular. Key Points: Fluvial morphodynamic hierarchy can explain how common, rather than extreme, transport conditions are routinely preserved in strata The presence of morphodynamic hierarchy in a fluvial network increases the preservation of all lower‐order hierarchical elements Preservation of a given morphodynamic level is highest when its evolution timescale is comparable to that of the next highest level