KINEMATICS OF DEFORMATION BAND FORMATION AND REACTIVATION ASSOCIATED WITH A LARAMIDE FAULT PROPAGATION FOLD

The Jurassic Navajo Sandstone exposed in the eastern limb of the San Rafael Swell, Utah, hosts several deformation band sets that provide a record of strain accumulation during fault propagation folding. We group the deformation bands into two broad categories: cementation and cataclastic bands. Both these band categories occur as one of six different deformation band types that are organized into five orientation sets. The deformation band types include bedding and lamination parallel; conjugate shear; shear; en-echelon Riedel shear; ladder structures; and fragmentation bands. Cross-cutting relationships between band sets were used to determine relative timing, while kinematic restoration of the San Rafael Swell monocline was used to ascertain subtle changes in stress throughout folding history to identify the relationships between folding and band formation. The kinematic analysis suggests that most band sets form early during folding (<30° dip) and often take advantage of existing bands to propagate. Oblique-slip on steeply dipping shear bands and en-echelon Riedel shear bands suggest that sinistral shear occurred early during folding (<10° dip). Kink-bands are oriented subparallel to the fold axis and cut the cross--lamination parallel bands taking advantage of these pre-existing bands to propagate. Ladder structures and fragmentation bands are cataclastic in nature and occur in accommodation zones between other bands. The latest deformation band sets are oriented nearly perpendicular to the fold axis and include cementation bands cut by quartz cemented cataclastic bands. The presence of oxides in these cementation bands indicates fluid flow through permeable deformation band pathways prior to a final stage of cataclasis. Understanding the timing of band formation and its relation to the expected band type and location at which the bands will form within the fold structure is important for modeling reservoir compartmentalization in comparable folds for CO₂ storage and oil and gas prospects.