Delta Morphodynamics

Deltas are landforms where the mouth of a river flows into an ocean, sea, estuary, lake, or another river. These landforms, which are home to millions of people, are currently the focus of intense study due to ongoing climate change. They also are of particular interest to my research group due to our location on the Mississippi Delta in New Orleans. Current research interests include quantifying the internal dynamics of deltas through statistics, the influence of tectonics on deltas, including growth faulting and the Pleistocene evolution of the Mississippi delta.

Statistical methods for quantifying autogenic processes in sedimentary basins: with Liz Hajek (Penn State University)
Research assistantship available for this project

Alluvial basins provide important records of climate and tectonic changes on Earth, as well as information about how land surfaces evolve under different boundary conditions. Consequently our ability to reliably interpret and predict stratigraphic patterns is fundamentally important both scientifically and in its bearing on broader society. Recent work has shown that internally-generated (autogenic) dynamics in sedimentary systems can produce stratigraphy that mimics patterns produced by tectonics, climate, and eustatic change. In light of these results, it is clear that new quantitative methods are needed to filter autogenic signals from sedimentary deposits in order fully understand and model stratigraphy.

Using a combination of reduced-scale experiments, numerical modeling, and fieldwork, we are measuring signals of autogenic sedimentation patterns in alluvial basins. Our work is utilizing two recently developed statistical methods to measure stratigraphic patterns: the compensation index and the K function measure of channel clustering. These surface and object based statistics compare observed stratigraphic organization to synthetic patterns produced by statistically defined random processes. By quantifying these patterns, we are extracting information about the underlying autogenic processes that build stratigraphy. This work will improve efforts at recovering meaningful data about autogenic processes from stratigraphic datasets, isolating signals of changing boundary conditions in ancient basins, and modeling and predicting stratigraphy in alluvial basins.

Experiments for this project will take place in our new Delta Basin. This project is supported by the National Science Foundation. The grant includes funds for graduate and undergraduate support (please contact me if you are interested in pursuing research on this topic).
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Reconstructing ancient passive margin dynamics by relating geomorphic and stratigraphic surfaces: with Ben Sheets (U. of Washington)
Research Assistantship available for this project

The primary objective of this project is to improve our ability to invert the stratigraphic record for paleo-surface-dynamics and topography. The architecture of continental margin stratigraphy contains features which resemble bars, channels, and channel networks, yet scientists cannot precisely reconstruct the relationship between these preserved deposits and the geomorphic processes that constructed them. This is unfortunate, as the stratigraphic records of modern systems contain invaluable information that could improve our ability to interpret paleo climatic and tectonic records in active and ancient rift settings.

Due to the large spatial and temporal scales associated with natural systems, we are investigating this through reduced scale experiments, in which surface topography is monitored at high spatial and temporal scales. Coupled with digital images of stratigraphy produced by these experimental systems, we are quantifying the relationship between geomorphic and stratigraphic surfaces. Our range of planned experiments will allow for the targeted investigation of controls on the construction of channelized passive margin stratigraphy, including parameters such as channel mobility, avulsion rate, and flow type.

Data collected from each experiment will be used to construct statistical relationships between morphodynamics and stratigraphic surfaces in one, two, and three dimensions. These data, in turn, will be used to benchmark the development of deterministic cellular models of channelized flow. Finally, we are planning to apply these insights to the inversion of physical stratigraphy from two field sites: 1) the Quaternary stratigraphy of the Mississippi Delta below Breton Sound and the Cretaceous Ferron Sandstone.

Heavy-tailed statistics in depositional systems and implications for stratigraphy: with Vamsi Ganti, Efi Foufoula-Georgiou, and Chris Paola (U. of Minnesota)
In depositional systems, channels migrate from one location to another causing erosion and deposition at any given point in the domain. The duration of depositional and erosional events, as well as their magnitudes controls the structure of the stratigraphic record. In this study, we are using high-resolution temporal surface elevation data from a controlled delta experiment to quantify the probability distributions of the processes that govern the evolution of depositional systems. We have documented heavy-tailed statistics of erosional and depositional events indicating that a small, but significant chance exists for the occurrence of extreme events. We have found that channel depths act as a first order control on the truncation of these heavy-tailed distributions. Further, we have found that the heavy tails in the magnitudes of the erosion and depositional events are not preserved in the stratigraphic record, resulting in an exponential distribution for the distribution of bed thicknesses.
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Compensational stacking of sedimentary deposits: with Chris Paola (U. of Minnesota) & David Mohrig (U. Texas Austin)

The combination of relative subsidence and sediment transport systems in geological basins produce environmental conditions favorable to the construction of stratigraphy. While it is clear that these two conditions are necessary to produce thick stratigraphic packages, we lack a full description of how spatial and temporal patterns of relative subsidence feedback on sediment transport systems or visa-versa. One qualitative feedback model that is widely used when interpreting the stratigraphic record is compensation stacking of sedimentary deposits. Compensational stacking is the tendency of flow event deposits to fill topographic lows and as a result smooth topographic relief. We are currently using data from experimental, and field scale in both deep and shallow water settings to study the tendency of stratigraphy to aggrade through compensational stacking.
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Tectonic steering of channels on delta tops: with Chris Paola (U. of Minnesota), Wonsuck Kim (U. Texas Austin), and Ben Sheets (U. Washington)

Early stratigraphic architecture models developed by Leeder and Allen hypothesized that the density of channel deposits for any given basin was highest at the location of maximum subsidence. However, recent experiments in the XES basin have shown that channels are not always directed to the regional subsidence maximum. We are examining the relationship between the time-scale of autogenic sediment transport field reorganizations and the shape/rate of basin subsidence to determine when channels are or are not steered by tectonics. This work should improve our ability to decipher environmental and or tectonic signals from stratigraphic interpretations.

Influence of growth faults on regional subsidence rates in the Lower Mississippi Delta: with David Mohrig (U. Texas Austin)

Throughout the past century, the Louisiana coastline has been deteriorating at an alarming rate. Fault induced subsidence has been suggested to be one of the likely drivers of this land loss. We are directly addressing the control of faulting on Quaternary delta subsidence using an industry grade 3D seismic survey to evaluate the interaction of complex fault patterns and shallow substrate (<1 s or 1,000 m). We aim to asses the control of normal faults on the present day delta topography and compare the long term fault influenced subsidence rates to short term (1-10 year) GPS derived subsidence rates.