This research characterized a system of small faults (displacement < 0.3 m) in
seven closely-spaced continuous 2.4 inch (6.1 cm) diameter cores. Cores were obtained
from central Texas, on the western edge of the Llano Uplift. Cores penetrate a dip-slip
dominant, normal fault (Nobles Fault) with 18.3 m (60 ft) of stratigraphic throw. The
spatial, geometric and kinematic attributes of small faults within the Nobles Fault system
were characterized to explore potential cause-and-effect relationships.
To quantify spatial distributions, a "density" measure based on individual small
fault magnitude was utilized. Approximately half of the small faults in the core
possessed no discernible offset markers; thus displacement amount for these faults could
not be measured directly. Using a nonparametric method in which an alternating
conditional expectation determined optimal transformations for the data, a statistically
significant empirical correlation was established for faults with measurable gouge
thickness, displacement, protolith mean grain size and sorting. Gouge thickness of small
faults was found to be dependant upon the displacement amount of the small fault and
the textural characteristics of the host protolith.
The role of protolith lithology, proximity to crystalline basement, and structural
position relative to the Nobles Fault system were examined to explain observed
ubiquitous spatial distribution of small faults. Small faults were found to occur in
clusters and the number of faults per foot only weakly correlates to the cumulative
displacement of the corresponding faults. The amount of mudstone present is the
dominant factor controlling small fault formation. Intervals with only minor quantities of mudstone have the largest number of faults per foot as well as largest associated
cumulative displacement per foot. Frequency of occurrence of small faults near the
basement is greater when compared to similar lithologies higher in the core. Intensity of
small faults do not universally increase with proximity to large faults. To observe an
increase in small faults, it is necessary to use a mean global cumulative displacement
approach. Zones of greater than average cumulative displacement of small faults in
close proximity to large faults were observed in zones that are compatible with faultfault
interaction.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4385 |
| Date | 30 October 2006 |
| Creators | Graff, Mitchell C |
| Contributors | Johnson, Brann |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 52332003 bytes, electronic, application/pdf, born digital |
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