Document Type

Thesis

Abstract

The Rockfish Conglomerate is a Neoprotorozoic metasedimentary rock in the Blue Ridge of central Virginia, and a member of the Lynchburg Group. (Fig. 1) This rock is likely a glacial deposit, as evidenced by the presence of glacial dropstones (Wehr, 1986)—clasts within a unit that have deformed the surrounding matrix by being dropped into it by a melting glacier. While its depositional environment and contact with other members of the Lynchburg Group is fairly well researched and understood (Wehr, 1986; Jonas and Stose, 1939; Fullagar and Dietrich, 1976), the Rockfish Conglomerate has not yet undergone strain analysis, which can reveal new information regarding the unit’s original shape and orientation, based on the current shape and orientation of deformed clasts within the unit. The Rockfish Conglomerate has experienced strain, as shown by the distinctly ellipsoid shape of many of its cobble-sized clasts, as well as penetrative foliation. Because the Rockfish Conglomerate contains abundant, rounded, pebble to cobble clasts, it is a prime candidate for strain analysis. However, in order to fully understand strain undergone by the Rockfish Conglomerate, we cannot rely wholly on the deformed clasts, as the clasts may have been deformed before they were deposited into the matrix. We must also analyze the Rockfish Conglomerate on the thin section scale, in order to determine if the strain we believe we see represented by the large clasts has also affected the sand-sized grains of the matrix (Fig. 2). For this analysis, we used the Rf/ф method of strain analysis, which quantifies the current shape (Rf) and orientation (ф) of clasts. By quantifying strain in the Rockfish Conglomerate, I plan to determine how much shortening and elongation the Rockfish Conglomerate has experienced and use that information to understand the original shape of the deposit (Fig. 3).

Date Awarded

2014

Department

Geology

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