Understanding the kinematic development of basement-involved compressive structures that form at low temperature is dependent, in part, on gaining a better factual understanding of their deformational behavior. Results presented here show that the response of crystalline basement to deformation is incongruous among different structures in Colorado and Wyoming. At Big Thompson anticline and Rattlesnake Mountain anticline, Precambrian basement was not rotated in the anticlinal hinge during Tertiary folding. At both Banner Mountain and at a minor fold on Casper Mountain the basement has been rotated near the anticlinal hinge by as much as 26°. In the steep limb of all four of these monoclinal structures the basement is in fault contact with the stratified cover. At two sites, the Five Springs Creek area of the Bighorn Mountains and Casper Mountain, evidence for greater rotation of basement is clear. Precambrian dikes at Five Springs exhibit rotation of as much as 85° across the Laramide anticlinal hinge. Although the anticline at Casper Mountain shows minor folding, in the footwall a depositional contact on basement is rotated 50° from regional dip. These structures (Big Thompson anticline, Casper Mountain, and Five Springs) show minor fractures in the basement that apparently do not control the kinematics of basement deformation, but do indicate the stress field orientation. Typically σ 1 is nearly horizontal and normal to the fold axis, σ 2 is parallel to the fold axis, and σ 3 is very steep. This is the stress field normally associated with thrust faulting.

Abstract The Mississippian rocks of Mount Head area in the southern foothills of Alberta are included in the standard formations of the Alberta Rocky Mountains—the Banff, Rundle, and Rocky Mountain formations. The succession differs in several respects from that of the type region at Banff, these variations being, in part, of economic interest. The Banff formation is Kinderhookian in age. The Rundle formation is raised to group status to include three formations, the Livingstone, Mount Head, and Etherington. The Livingstone formation, of Osagean age, is divided into two members, Pekisko and Turner Valley, and the latter into the following groups of beds—Banner, Dark Limestone, Lower Porous, Middle Hard, and Upper Porous beds. The Mount Head formation of Meramecian age contains the following members—Wileman, Baril, Salter, Loomis, Marston, and Carnarvon. The Etherington formation, Chesterian in age, is divided into three parts. Only a few feet of strata are assigned to the Rocky Mountain formation which may be of Pennsylvanian or Permian age. The Mississippian succession throughout the southern foothills of Alberta resembles that of the Mount Head area. Its division into several formations and members permits detailed correlation and study of the lateral variations of the beds.