Comparison of different methods of
strain analysis within the Tamaqua Syncline, central Pennsylvania
Stickler, Brandon, and
Tindall, Sarah,
2014, Comparison of different methods of strain analysis within
the Tamaqua Syncline, central Pennsylvania: Geological Society of
America Abstracts with Programs, Northeastern Section - 49th
Annual Meeting Lancaster, PA, (23–25 March), v. 46, no. 2.
The Indian Run Member of the Mississippian Mauch Chunk Formation
crops out on the north and south limbs of the Tamaqua Syncline on
route 309 outside of Tamaqua, Pennsylvania. The sandstone and
mudstone redbeds preserve strained mud cracks, raindrop impressions,
and mud rip-up clasts, as well as outcrop-scale thrust faults and
cleavage, each providing an independent measure of strain direction
and /or magnitude. We determined the principle direction and
magnitude of strain using different methods to evaluate the
consistency of results revealed by using various features and
techniques, and to identify discrepancies in shortening direction or
strain magnitude that might indicate multiple phases in the
Alleghanian Orogeny. The fold axis of the Tamaqua Syncline trends
73° giving a shortening azimuth of 163°. Map-scale thrust faults
strike 67°, perpendicular to a shortening direction of 157°, and
slickenlines on outcrop-scale, low-displacement (1-3m) thrust faults
indicate a shortening direction of 155°. Cleavage formed before
significant folding occurred, and its orientation is consistent with
a shortening direction of 159°. The direction of shortening derived
from elliptical strained raindrop impressions is 161°. Fry
center-to-center method on a bedding surface containing hundreds of
strained raindrop impressions provided an ellipticity (R) of 1.6.
Calculations of ellipticity based on measurements from 40 individual
raindrop impressions also yielded an average R of 1.6 with values
ranging from 1.2 to 2.0 and a standard deviation of 0.17. Individual
raindrops in the Mauch Chunk Formation vary in ellipticity, possibly
indicating that some impressions were not initially circular, but
the average ellipticity of a large population gives R similar to
that derived by the Fry method. Post-deformation clustering of
initially distributed mud crack trends yields a shortening direction
of 160°. The various methods and deformed features used in this
study reveal very similar shortening directions, between 155° to
163°, and R values of 1.6, indicating that only one phase of
Alleghanian deformation was responsible for producing these features
in the Tamaqua Syncline. Using different methods on different strain
markers also verifies that these methods, in this locality, yield
compatible results.
Comparison of different methods of
strain analysis within the Tamaqua Syncline, central Pennsylvania