Viki Bankey

Geometry, timing, and continuity of the Rock Springs uplift, Wyoming, and Douglas Creek arch, Colorado: Implications for uplift mechanisms in the Rocky Mountain foreland, U.S.A.

The Rock Springs uplift of Wyoming and the Douglas Creek arch of Colorado are intrabasinal, Laramide-age basement uplifts within the Rocky Mountain foreland, and are currently separated by the east–west-trending Uinta Mountains. The geometry, timing, and progressive development of these uplifts were investigated using a combined geophysical and geological approach. New gravity surveys were combined with existing regional data to provide a regional Bouguer gravity anomaly map of these two uplifts and the intervening Uinta uplift. The gravity data show a distinct and continuous north–south-striking gravity high along the trend of the two uplifts that crosses the east–west-trending Uinta uplift. The relatively constant amplitude (∼40 mGal) of the gravity anomaly indicates that the inferred basement relief is similar for both arches (∼4 km). Sedimentation patterns indicate that the Rock Springs uplift and Douglas Creek arch formed simultaneously in the Late Cretaceous. The intrabasinal setting of the uplifts records aspects of foreland deformation that are overprinted or obscured in better-developed uplifts. On the local scale, neither the Rock Springs or Douglas Creek uplift apparently reactivates a pre-existing structure. On a regional scale, there is no change in structural style or timing of the two uplifts, despite their formation in different crustal provinces. The Rock Springs uplift occurs within the Archean Wyoming province north of the Cheyenne belt, whereas the Douglas Creek arch occurs in Proterozoic crust south of this boundary. Timing relations, available from the basinal stratigraphy, indicate the uplifts were initiated as broad arches in the Late Cretaceous before developing into more concentrated uplifts. Thus, large-scale folding, and not reactivation of pre-existing structures, may be the primary control on the initial pattern of north- to northwest-trending foreland deformation.

Principal facts for gravity stations of the Broadwater geothermal area, Montana

Two complete Bouguer anomaly values were calculated for each of the 67 stations assuming average rock densities of 2.67 g/cm/sup 3/ and 2.45 g/cm/sup 3/. The corrections and anomaly values are listed. A hand contoured Bouguer gravity map is included.