Stratigraphy of the Rio Grande Rift

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        Under the Colorado Plateau there is a sequence of Paleozoic to Mesozoic (Cretaceous) rocks. Precambrian basement rocks (granite, gneiss, schist and quartzite) underlies the Colorado Plateau by more 1,800 feet of overlying sedimentary rocks. Rift sediments include pre- and synrift units. This stratigraphic section is generalized from the Abiquiu area in the Espanola basin New Mexico.
         Above the precambrian basement, are the Arroyo Penasco and Log Springs Formation (dolomite, siltstone, sandstone and shale), the Madera Group (cherty limestone, minor sandstone and conglomerate), the Cutler Formation (Arkose sandstone, pebble conglomerate with interbedded shale), the Chinle Formation (shale, sandstone, siltstone and pebble conglomerate), the Entrada Sandstone (eolian sandstone), Todilto Formation (shale limestone and gypsum), the Morrison formation (sandstone, siltstone and shale) and the Dakota formation (sandstone, pebble conglomerate, siltstone and shale).
        In the Rio Grande Rift, the rocks of the Colorado Plateau are beneath Tertiary Rift sediments of the Santa Fe Group (conglomerates, sandstone, mudstone, evaporites, minor limestone, and volcanic tuff), Abiquiu Formation (Tuffaceuos and volcaniclastic conglomerate) and the El Rito Formation (sandstone, shale, freshwater limestone)
        During a SAGE experiment the western edge of the rift where it comes in contact with the Colorado Plateau, was imaged using seismic reflection. Most of these formation were resolved from the data. A gravity profile was conducted along the seismic line and can be compared to the seismic data to resolve individual units.
(Figure from Baldridge et al 1994)  Back to Index