RESTORATION OF SERIAL SECTIONS FOR PALEOGEOGRAPHIC RECONSTRUCTIONS: EXAMPLE FROM THE SAN LUIS VALLEY IN SOUTH-CENTRAL COLORADO

The northern San Luis Basin, in south-central Colorado is part of the Rio Grande Rift that extends the crust from southern New Mexico to central Colorado. Seismic, well and surface data permit the construction of cross sections of the present-day geology. Restoration of these sections provides view through the Cenozoic rift-related deformation to provide locations and geometries of the earlier Laramide (Late Cretaceous to mid-Eocene) and Ancestral Rocky Mountain (middle Pennsylvanian) structures. These restored cross sections are then used to construct paleogeographic maps for the end of the Laramide deformation and the end of the Pennsylvanian deformation.

The restoration suggests that the thrust-related structures in the present-day Sangre de Cristo Range are the eastern part of a basement-involved uplift with approximately 20 km of eastward shortening. The core of this uplift has been cut by the rift normal faults and is now below the San Luis Basin. The restoration of the Laramide structures suggests that the Laramide shortening telescoped a Late Paleozoic Ancestral Rocky Mountain basin and adjacent uplift. The area of the San Luis Basin and Sangre de Cristo Range was a Pennsylvanian basin, was later telescoped and inverted as a Laramide uplift and is presently extended and subsided (reinverted) as part of the Rio Grande Rift.