SPACED CLEAVAGE DEVELOPMENT AT McCartney MOUNTAIN, MONTANA

At the McCartney Mountain salient in southwest Montana, spaced cleavage is exposed exclusively in two thin silty orange brittle dolostone layers in the lower gastropod member of the Kootenai formation. Characterization and classification of cleavage morphology, orientation, and domain spacing is used to assess the attributes of the strain field in terms of minimum elongation direction and homogeneity of deformation distribution. Controls on spaced cleavage development are explored, including lithology, structural proximity, and insoluble content. Results from stereonet analysis show that our initial field hypothesis that spaced cleavage reflected early bedding parallel shortening, with minimum elongation trending east-west, is not supported by the observations, which show shortening trending north-south. Structural analysis, chemical dissolution, and microscopic observations are used to build a descriptive and kinematic history of spaced cleavage development.