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Numerical Simulations of the Formation and Destruction of Fluvial Terraces: Implications for Fluvial Sediment Inputs to Continental-Margin Depositional Basins

Limaye, Ajay B.*1; Lamb, Michael P.1
(1) Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA.

Fill-cut and strath terraces flank the margins of many river channels, and offer unique subaerial archives of river history. The information held by terraces may also aid in decoding connections between terrestrial sediment sources and marine sinks. Terrace formation and abandonment is commonly interpreted to record a climate-induced pulse of vertical incision. Conversely, terraces may also form from lateral migration and continuous incision, or from pulses of incision caused by intrinsic river dynamics (e.g., neck cutoffs). Few tools currently exist to distinguish terraces that record intrinsic stream dynamics from those that record events with significance for the depositional record. Moreover, the role of lateral erosion in destroying terraces is poorly understood. To address these knowledge gaps, we constructed a numerical model to simulate terrace formation of a meandering single-thread river under a variety vertical and lateral erosion rates. Sediment and bedrock surfaces are tracked during each simulation, allowing the lateral erosion rate to respond to heterogeneous bank composition. The model also includes a novel, fully automated algorithm to detect river terraces and extract their ages, dimensions, and spatial orientations. We examine how channel dimensions and incision rates control these terrace metrics with the aim of developing reliable tools for identifying the mode of terrace formation. We compare modeled terraces to those at field sites including the Colorado River, Texas, that have been argued to record regional climate change and a pulse of sediment flux to marine depocenters. Simulations suggest that, in addition to forming terraces, lateral erosion imposes a residence time on terraces in river valleys. This residence time can be used to assess the likelihood of terrace preservation over various timescales, with implications for identifying tectonic, climatic, or higher-frequency terrace formation mechanisms.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California