sgr ms thesis - University of Maine

outline of the clast, with a dark backbone directly over the border that brightens
up with distance from the outline. The brightness of the pixel is directly
proportional to the distance to the clast border, and an outline of known width is
made by setting a threshold to that value of brightness. D r can be calculated by
plotting the log of ribbon area A versus the grayscale number W and is obtained
by
(5.6)
with S as the slope subtracted from the Euclidean dimension of 2 to yield D r . The
Euclidean dimension 2 signifies that the clast exists on a two-dimensional
surface (Berube and Jebrak 1999, Lorilleux et al. 2002).
5.3.4. The Fractal Dimension-Brecciation Mechanism Link for Clast
Boundary Shape (CBS)
The most complex boundary shapes come from chemical breccias (D r
≥1.25), while the simplest are found in hydraulic or magmatic breccias (D r ≤ 1.1)
(Jebrak, 1997; Barnett, 2004). Explosive and abrasive breccias initially produce
angular clasts that may show relative complexity, but D r would still be relatively
low (≤ 1.25). CBS would tend to be low in a physically brecciated material
because fractures tend to align themselves with the direction of the maximum
principal stress. Because the direction of fracture would tend not to change, the
surface pattern of the fracture is defined by the paths of relatively straight cracks
(Berube and Jebrak, 1999). Modification processes that involve clast rounding
and corner break-off would also effectively reduce D r . It is unlikely that chemical
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