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Paleogene Stratigraphy, Sedimentation and Volcanism of New Mexico
Paleogene rocks of New Mexico consist of clastic and igneous lithologies that represent a wide range of fluvial, lacustrine, eolian, and volcanic environments. Paleocene-upper Eocene rocks are sediments that were shed from monoclinal and basement-cored/fault-bounded uplifts and deposited in adjoining basins as the result of essentially amagmatic basement deformation (Laramide orogeny). During the Paleocene-late Eocene, three main phases of basin filling can be recognized: Paleocene (San Juan, Raton, and Cutter Sag-Love Ranch basins), early Eocene (San Juan, Galisteo, Raton, and Cutter Sag-Love Ranch basins), and middle-late Eocene (Chuska, Galisteo-El Rito, Baca, Carthage-La Joya, Sierra Blanca, and Love Ranch basins). Deposition in these basins ranges from high energy fluvial (debris flow, alluvial fan, braided stream) facies to meandering stream facies and local lacustrine facies. The initiation of massive eruptions of intermediate to silicic volcanic rocks throughout much of New Mexico just before the end of the Eocene terminated Laramide basinal deposition, and set the stage for pervasive Oligocene volcanism.
In Oligocene time, volcanism was widespread in western New Mexico. The southwestern quarter of the state, in particular, became a volcanic highland, consisting of thousands of meters of calc-alkalic lavas and pyroclastic flows. The landscape was dominated by resurgent domes of ash-flow tuff (ignimbrite) cauldrons and by andesitic stratovolcanoes. Aprons of volcaniclastic sediments were shed around clusters of volcanic centers, such as the Mogollon-Datil volcanic field. Horizontal east-west extension provided room for plutons that fed the volcanoes and caused crustal thinning. The low-angle normal faults that developed during extension arc geometrically distinct from Miocene and younger high-angle faults that characterize modern basins and ranges.
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