Semester of Graduation

Fall 2018

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

The development of ridge-and-swale scroll bar topography of meandering river point bars is not well understood. We hypothesize that scroll bars formed during lateral accretion by the landward migration of transverse bars. To explore this, we relate the scroll bar topography to the internal sedimentary structure. We acquire, invert, and interpolate three pseudo-2D shear wave velocity profiles in two regions of the False River point bar, a Mississippi river oxbow lake in Pointe Coupee Parish Louisiana. Prior studies provide electrical conductivity well logs and cores as well as SH seismic reflection images along the same seismic surveys. LiDAR elevation data provide maps of the ridge-and-swale topography bisected by the seismic surveys. The uppermost 10-15 meters of point bar sediments cannot be well-imaged by reflection seismic processing techniques. From the same seismic data acquired for reflection processing, we extract surface wave signals for dispersion interpretation. The dispersion data are then inverted using a direct-search nearest neighbor algorithm. We then interpolate the inversion results to create pseudo-2D shear wave velocity profiles that image the uppermost 12 meters of sediment. Well log and core data are then correlated with these velocity profiles during interpretation. This study finds that velocity layers dip in two directions away from the crests of scroll bar ridges, parallel to the ridge and swale topography in both overbank sediments and the underlying IHS zone. We interpret this finding as evidence attributing False River scroll bar development to the landward migration of transverse bars, as this parallel sedimentary architecture suggests a stratigraphic link between the IHS and surface topography. A competing model for scroll bar development that attributes individual scrolls to single low-frequency high-discharge flooding events does not suggest this stratigraphic link.

Date

10-29-2018

Committee Chair

Lorenzo, Juan

DOI

10.31390/gradschool_theses.4812

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