Abstract

The Loudoun Formation of west Maryland consists of conglomerates and phyllites, both of which abound in useful strain and kinematic indicators. Outcrop is sparse, and most of the small-scale structures are seen on the faces of numerous large boulders; thus, strain intensities can be calculated, but stretching and movement directions are scattered. In both the quartzitic and phyllitic members of the formation, cleavage and bedding are clearly decipherable; in outcrop, the dihedral angle between them shows a consistent variation with position along an east-west traverse. We used this angle to assign loose boulders to their correct position in the structural cross section and wrote a computer program to reorient the planes of bedding and cleavage into alignment with those in the chosen outcrop. The rotations necessary to restore data were consistent with structures measured in outcrop in the first place, and they greatly enhance the sparse structural information available from the Loudoun Formation. Our method is applicable to other areas where the intersection of two planar structures provides an internal reference frame for resetting displaced rock.

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