Semester of Graduation

Spring 2019

Degree

Master of Science (MS)

Department

Geology & Geophysics

Document Type

Thesis

Abstract

Various studies of ancient point bars have noted that a relationship can be observed between the dip angle and grain size of point bar lateral accretion deposits, with the most mud-rich deposits tending to exhibit the greatest dip. No analysis and only cursory explanations for this relationship have been provided. Additionally, buried mid-channel bars are absent from typical models of point bar architecture.

We successfully image the architecture of late-stage point bar deposits with a near surface 2D seismic SH-wave reflection survey and generate an SH-wave velocity model of the subsurface in the study area in order to interpret the history of its development. The presence of inclined reflectors with uniform dip directions toward the paleochannel confirms a typical model of point bar architecture, but the observation of coherent reflectors dipping away from the paleochannel complicates the ideal model by suggesting the burial of a mid-channel bar by the migrating point bar.

Spatial trends in reflector dip magnitude calculated via the analysis of dip-affected reflectors. Dips trend toward an increase both upwards and laterally in the paleochannel direction. The SH-wave velocity model and well-logs from previous studies demonstrate a lateral fining trend in the paleochannel direction but fail to support upwards fining. The failure to confirm upwards fining in the presence of a ubiquitous upwards increase in reflector dip suggests that sediment cohesion is an incomplete explanation for the relationship between dip angle and grain size in point bar lateral accretion deposits. As a whole, this study provides an example of the ability of seismic SH-wave reflection methods to image and characterize the shallow subsurface.

Committee Chair

Lorenzo, Juan

DOI

10.31390/gradschool_theses.4851

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