The role of discharge variability in determining alluvial stratigraphy

NICHOLAS, ANDREW P.; SAMBROOK SMITH, GREGORY H.; AMSLER, MARIO L.; ASHWORTH, PHILIP J.; BEST, JAMES; HARDY, RICHARD J.; LANE, STUART N.; ORFEO, OSCAR; PARSONS, DANIELS; REESINK, ARNOLD J.H.; SANDBACH, STEVEN D.; SIMPSON, CHRISTOPHER J; SZUPIANY, RICARDO N.

GEOLOGY

GEOLOGICAL SOC AMER, INC

Lugar: Boulder; Año: 2015 vol. 44 p. 3 - 6

0091-7613

We illustrate the potential for using physics-based modelingto link alluvial stratigraphy to large river morphology and dynamics. Modelsimulations, validated using ground penetrating radar data from the Río Paraná,Argentina, demonstrate a strong relationship between bar-scale set thicknessand channel depth, which applies across a wide range of river patterns and bartypes. We show that hydrologic regime, indexed by discharge variability andflood duration, exerts a first-order influence on morphodynamics and hence bar setthickness, and that planform morphology alone may be a misleading variable forinterpreting deposits. Indeed, our results illustrate that rivers evolvingunder contrasting hydrologic regimes may have very similar morphology, yet becharacterized by marked differencesin stratigraphy. This realization representsan important limitation on the application of established theory that links rivertopography to alluvial deposits, and highlights the need to obtain fieldevidence of discharge variability when developing paleoenvironmentalreconstructions. Model simulations demonstrate the potential for deriving suchevidence using metrics of paleocurrent variance.