Current point-bar complex models do not include subsurface unit bars as a normal feature. This study provides evidence for a potential buried unit bar amongst point-bar sediments of the large-scale, modern-day False River point-bar complex of the Mississippi River. We collect, process and interpret a two-dimensional, 150-m-long CMP seismic reflection profile that cuts perpendicularly across a major discontinuity surface in the False River point bar complex. The seismic source consists of a ground recoil device that fires a shotgun shell horizontally, producing shear waves. Multiple field experiments demonstrated which type of source and receiver provided the least amount of noise, with the most coherent incoming signal from reflections. LiDAR data allow the ridge-swale topography that exists above the point bar deposits to be readily mapped; this ridge-swale topography gives clues to the relative history of the meander bend. Seismic methods allow us to map the internal structure of the deposit, something that LiDAR cannot do. Gamma-ray and electrical conductivity data have previously been collected in a well located along our seismic line. These are correlated with the seismic data in order to assist with the interpretation. We find a seismic boundary dipping in the opposite direction that we anticipate in a point-bar complex. This may be a unit bar buried beneath many meters of point bar sediment, or may be the result of an erosive event. Unit bars add to the complexity of a point bar complex; they can lead to opposite-dipping boundaries than those caused by IHS layers. Two different models are created that could have resulted in the subsurface geometry seen in the seismic data. This study provides valuable insight into the evolution of fine-grained river systems, both modern and ancient.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-03312017-154201 |
| Date | 18 April 2017 |
| Creators | Morrison, Martial James |
| Contributors | Lorenzo, Juan M, Clift, Peter D, Konsoer, Kory M |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-03312017-154201/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached herein a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to LSU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below and in appropriate University policies, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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