ORIGIN OF MINOR STRUCTURES IN THE LOWER PALEOZOIC WILLHITE FORMATION IN THE WESTERN BLUE RIDGE PROVIDENCE, TENNESSE

Well known outcrops of the Lower Paelozoic Willhite Formation are found along the Ocoee River at Madden Branch, Tennesse. The rocks consist of low-grade metasediments composed of thinly interlayered phyllite and micaeous siltstone as well as layers of carbonate-rich siltstone and quartzite (Sutton,1991). Deformation features in these rocks include axial planar “slaty” cleavage in the argillaceous facies and both quartz and calcite “veins” in the sandy facies. Both features appear to have a pressure solution origin.

Carbonate-rich layers consist of elliptical “pods” which are parallel to, and separated by, cleavage in the metasiltstone. The “pods” have a fishhook appearance (Ramsey, 1987)on the limbs of macroscopic (10 meter wavelength) folds, and a true elliptical form in the hinge regions of those folds. Original bedding in carbonate-rich layers had sole markings (such as flute casts) that appear to have nucleated minor folds (Milici et.al., 1978) Thin section study and SEM-EDX analysis indicate that the pods began as minor s, z and m folds (10 centimeter wavelength) and then became separated from one another by pressure solution in which the strained carbonate fraction of the layers was dissolved away by fluids leaving behind insoluble clay material. The insoluble clay material has a slaty cleavage in it that is bent around the “pods” of carbonate-rich material that survived dissolution.

The quartz-rich layers range from 10 centimeters to 30 centimeters thick. Veins in these layers are oriented nearly perpendicular to bedding and are refracted toward axial plane orientation at the top and bottom of the layers where they are in contact with the metasiltstone. Thin sections indicate that the veins were formed initially as pressure solution seams, probably by shortening parallel to layering. As folding began they opened and were first filled with quartz, and as folding continued the seams continued to open and were filled with calcite, that was probably dissolved from the carbonate rich layers.