At the onset of Laramide orogeny in Late Cretaceous time, most of the buried mountain ranges were re-elevated, and adjoining Laramide basins, in part inherited from the late Paleozoic basins, began to subside and receive orogenic sediments.
In addition, two anticlines of mountain-range proportions—the Sawatch and Uinta—rose from the sites of late Paleozoic basins. Orogeny began in the southwest part of the province before marine deposition ended in the northeast. The late Paleozoic San Luis highland of southwestern Colorado and northern New Mexico was re-elevated in late Campanian or middle Montana Cretaceous time, as indicated by orogenic sediments in the San Juan basin to the south and the Raton basin to the east.
The Sawatch anticline, which diverges northward from the rejuvenated San Luis highland, rose at about the same time, as indicated by the age 72 to 70 m. Uplift and erosion were rapid. Once started, uplift of mountain units continued through Paleocene and into Eocene time, as indicated by nearly continuous Upper Cretaceous to Eocene sedimentary sequences in the interiors of bordering basins. Uplifts grew laterally as they rose vertically.
Consequently, the major uplifts of today are areally larger than those that supplied the first orogenic sediments, and their border structures are younger than those sediments. The crystalline rock body of the interior of the Laramide San Luis highland supplied sediments to adjoining basins in Cretaceous time, but the sedimentary rock flank of the uplift at the site of the Sangre de Cristo Range was not uplifted and deformed until Paleocene and early Eocene time. Similarly, an interior part of the Front Range supplied Precambrian rock detritus to bordering basins very late in Cretaceous time, but the flank structures of the range, which involve the early orogenic sediments, developed in Paleocene and Eocene time.
The Laramie Range prong of the northern Front Range probably did not begin to rise until Paleocene time. The White River Plateau, the last major Laramide uplift unit to appear in the province, began to rise in early Eocene time, but it did not attain its present outline and flank structure until late Eocene time.
The primary objectives of this task will be to improve knowledge on the timing, geometry, and structural controls of surface uplift, sedimentation, and synorogenic basin evolution during the Cenozoic across the Southern Rocky Mountains.
Comparison of the timing, style, and magnitude of events recorded in this area with that of other basins and uplifts in the southern Rocky Mountains will allow for a regional scale assessment and revision of current tectonic models of basin evolution. Comparison of new details of the sedimentary record west of the Front Range, for example, with that of the previously studied Denver Basin east of the Front Range during the Late Cretaceous through Paleocene will place limits on the wavelength and geometry of the Laramide Front Range uplift.
New or revised paradigms will be tested across other basins and refined accordingly. Generalized composite stratigraphic section of exposed rocks in the North and Middle Park basins compiled by project member Marieke Dechesne based upon measured sections and drill logs throughout the study area.
Timing of deposition of Laramide strata in the Colorado Headwaters Basin vs. From Dechesne and others, Correlations of sandy units of the Upper Cretaceous Pierre Shale within, and east and west of the Kremmling Middle Park area showing degree of incision and subsequent deposition during Laramide basin evolution.
Figure modified from Izett and others, The youngest clast collected from this unit produced an Ar-Ar age of Public domain. Study the topographic map below and also click on geographic map to find their location and the locations of other mountain ranges described below.
The Laramide uplifts also include the frontal Rockies of Colorado, the primitive Beartooth Mountains, the Wind River and Uinta mountains, the Bighorns, and numerous other small and large mountain ranges. These uplifts reach heights that exceed 13, feet and have classic alpine features that include mountain glaciers, U-shaped valleys, high mountain lakes, and glacially carved topography. Despite their height, some of the ranges such as the Beartooths have extensive relatively flat expanses near or at their tops.
These are relicts of the once lower and flat land surface that was uplifted by as much as 40, feet in some areas with respect to basement in the adjacent basins. The Laramide uplifts are amongst the most beautiful mountain ranges in the country. Following the graphics below, there is a list of geographic features for which aerial photos are available. Please click on each feature and study the photos.
Click here for map that shows names of major mountain ranges in the maps above. Black Hills, South Dakota. Laramide-period volcanic features , South Dakota. User Tools.
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