Reconciling Sinuosity Changes in Ancient Mississippi River Meanders in the Context of Late-Pleistocene and Holocene Active Faults
Abstract
Numerous studies have documented changes in the sinuosity of alluvial streams in response to crustal deformation; however, there are few examples that quantitatively link sinuosity amplitude and wavelength with fault slip rate. The Fisk (1944) maps recording the Holocene channel planforms of the lower Mississippi River along with recently-acquired high-resolution seismic reflection imaging of faults that offset late Pleistocene and Holocene alluvium beneath the Mississippi floodplain provide a unique opportunity to quantitatively explore functional relationships between fault slip and meander sinuosity. Here we present a python-based jupyter notebook code that objectively and systematically quantifies the sinuosity of a river, based on a time-series analysis approach. We digitized ten Mississippi River thalwegs from the Fisk maps spanning the last 8,000 years, and applied our code to measure how the sinuosity of the channel has changed throughout time. First, we geometrically transformed the river to mimic a continuously increasing time function and evenly sampled the river planform along the thalweg to extract spatial data. Next, we applied a Fast Fourier Transform (FFT) to identify the dominant frequencies at which the river meanders. Our hypothesis is that we expect to see a sinuosity 'signature' with a spectral peak (significant power) at a specific frequency in regions where long-term crustal deformation has caused a local change in slope. The FFT data is displayed on an 'evolutionary spectrogram' to spatially locate the frequencies at which spectral power (color-contoured) occurs along the river channel. By analyzing a long-term record of Holocene channel planforms, we can also reconstruct the temporal evolution of river sinuosity. Our results show that two regions of significant power in the evolutionary spectrograms co-locate with two neotectonic faults (White River fault zone and Meeman Shelby Fault) imaged by high-resolution seismic reflection data. Additionally, reconstructed Holocene channel planforms show significant power in these same regions, suggesting a long-term influence of crustal deformation related to the neotectonics faults. Our ultimate goal is to quantify the change in river meander sinuosity to constrain Quaternary fault slip in the Mississippi Floodplain.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T33D0431C
- Keywords:
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- 8155 Plate motions: general;
- TECTONOPHYSICSDE: 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS