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Genetic divergence along the central Baja California Peninsula, Mexico, has been hypothesized to reflect a Pliocene cross-peninsular seaway that previously isolated northern and southern populations of terrestrial plants and animals. One way to test this hypothesis is through quantitative analysis of relict channels preserved on low-relief paleo-surfaces. Recognition of tidal channels on relict landscapes offers a powerful tool for reconstructing past sea level in tectonically active arid coastal regions where crustal uplift results in relative sea-level fall and preservation of ancient channel networks. This method requires reliable criteria to distinguish fluvial versus tidal channels, which is challenging due to the overlap of standard metrics for the two channel types, and possible inheritance or overprinting of geometries. We improve the utility of existing metrics and explore the potential for identifying paleo-sea-level indicators by analyzing modern and ancient channels to identify unique patterns in planform geometry and to evaluate their applicability for classifying tidal versus fluvial origins. Preliminary measurements of geographically diverse modern systems reveal distinct, quantifiable differences between the two channel types in along-channel curvature, width, and wavelet spectra. Modern tidal channels display a pronounced and systematic down-channel increase in channel width and decrease in curvature. In contrast, modern fluvial channels do not display spatial patterns in channel width and curvature along their lengths. These patterns provide diagnostic criteria that can be paired with wavelet analysis of meander belts to classify the paleoenvironment of ancient channels based on their planform geometry. We apply this approach to evaluate the origin of channels preserved on relict landscapes in the San Ignacio trough in the central Baja California peninsula, a former low-relief embayment of the Pacific Ocean. Early results reveal the presence of ancient tidal channel networks at elevations of ~ 50-300 m above modern sea level on surfaces that are independently dated to be ca. 4-5 Ma. These findings provide evidence for post 4-Ma uplift in the mid-peninsular region and an ancient tidal environment that may have isolated northern and southern terrestrial populations.
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Planform geometric classification of fluvial and tidal channels via machine learning
Abstract Despite forming under different flow conditions, the geometries of tidal and fluvial channel planforms and planform transformations display significant overlap, hindering efforts to differentiate them geometrically. Although studies have demonstrated that globally, tidal and fluvial planforms are statistically distinct based on meander metrics, there are currently no machine‐learning methodologies for classifying channels as tidal or fluvial that do not focus on meander‐specific geometries. In this study, we present a methodology for classifying channel planforms as tidal or fluvial using statistical representations of channel planforms and machine‐learning algorithms. Using a dataset of 4294 tidal and fluvial channel segments (63 channel reaches), we trained three machine‐learning classifiers (Logistic Regression, Multi‐layer Perceptron, and Random Forest) across 69 trials to identify the machine‐learning algorithm and variables that perform best at classifying channel reaches. We evaluated the performance of the classifiers at three thresholds based on the percent of channel segments correctly identified in a given reach (>50%, >66% and >75%). At the >50% classification threshold, all three classifiers attained a 95% reach‐scale accuracy during individual trials. However, at higher classification thresholds, the RF classifier performed best. Feature importances from the RF classifier indicate that measures of the central tendency and minimum/maximum of the normalized radius of curvature convolved with normalized width of channel segments play a key role in differentiating between the planforms, with normalized width also contributing to the difference. This indicates that the relationship between width and radius of curvature is more important than width or measures of curvature on their own. This result likely reflects the downstream funnelling of tidal channels and the limitation on the sharpness of bends associated with increased width. These methods have potential for application in the study of channels preserved on relict geomorphic surfaces and in mixed‐energy settings.
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- Award ID(s):
- 1925560
- PAR ID:
- 10635501
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Earth Surface Processes and Landforms
- Volume:
- 50
- Issue:
- 4
- ISSN:
- 0197-9337
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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