A second orogenic event took place in the Ridge and Valley region of central Alabama which is also known as the Fold and Thrust zone. Structural deformation is widespread and this second event is totally out of character with the original Appalachian mountain-building episode.
The original mountains' sequence of thrusting is generally from the southeast to the northwest (break-forward sequence) but in this area it is dramatically reversed (break-back sequence).
Basement rocks of dolomite, limestone and shale are affected to the point that they are sometimes void of fossils, or have very few and some carry only broken pieces. The mountains are covered with deep layers of sandstone that form anticlines and synclines, some of which has become so hot it melted to the point that individual grains of sand are no longer visible. Huge ejecta rocks line the peaks that include limestone blasted from the impact site.
Without knowledge of the presence of such a large astrobleme in the area, geologists have noted that deformation is fully developed in the Pottsville Formation, which are the youngest rocks to be found in the Appalachian fold-thrust belt in Alabama. This has been interpreted as being an indication that the late, large scale structural deformation is post early Pennsylvanian, or about 290 mya. Since the astrobleme is much younger than any of these rock formations, it is understandable how deformation is present in the youngest.
Since some of the thrust sheets suggest a more complex thrusting history that has never been understood and the structural deformation mimics those found along the walls of other astroblemes, it cannot be ruled out until it is thoroughly investigated.
A separate orogenic event seems likely to have occurred in east Alabama from tectonic material moving beneath the Piedmont from the Atlantic Ocean. Although these mountains are named individually, they comprise the eastern region of the Talladega National Forest. The highest point in Alabama the 2,0407 ft. Cheaha Mountain is located here. They tend to run north to south, rather than southwest to northwest as the other mountains do.
Alabama's Piedmont region begins in central Alabama with the astrobleme and extends eastward through Georgia to the Atlantic ocean. It is felt that this unusual metamorphic area may have been one of two routes molten material flowed from beneath the oceanic crust into the void created by the massive impact.
There are several reasons for this:
A.)Commonality in the loss of fossils.
B.)The Fall Line runs along the bottom of both areas through both Georgia and Alabama until it exits the northwest corner of the state.
C.)The Fall Line Hills, a collection of sandy hills that average 750 ft. high run parallel to the Fall Line through both states, separating from it only around the perimeters of the astrobleme east of Montgomery and reconnecting to the north and west of Clanton, AL.
D.)Rare earth minerals and metals, especailly gold, were brought to the surface in both states.
E.)Geologically, the section has been considered as one unit not belonging to the original continent.
F.)Such an event, when coupled with similar situations along the Gulf of Mexico would certainly provide enough material reduction from beneath the ocean's floor to have the dramatic effect necessary for the Cretaceous tragedy.
It is entirely possible that it was during this time frame the Piedmont Uplift area was raised. Shaped like a giant sock, it covers about 3,500 sq. miles in seven counties and includes most of the gold producing areas in Alabama. Granite is found at Hog Mountain and the granitite Almond Trondhjemite forms a giant slab of rock in western Randolph County, AL, which highly suggests an orogenic event on a major scale.
| Introduction/Main | The Sylacauga Astrobleme | Photographs | Conclusion |
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