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Program Manager: Grant C. Willis (UGS)
Project Manager: Douglas A. Sprinkel (UGS)
GIS and Cartography: Basia Matyjasik , Jay C. Hill (UGS)
Geology review: Grant C. Willis, Douglas A. Sprinkel, Robert Ressetar, and Michael D. Hylland (all with the UGS), and Tim Lawton (Emeritus, New Mexico State University)
Cartography and GIS review: Kent D. Brown (UGS)
Funding: Utah Geological Survey and the U.S. Geological Survey, National Cooperative Geologic Mapping Program, through USGS STATEMAP award numbers 08HQAG0096, G09AC00152, G10AC00386, and G11AC20249. |
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This digital dataset represents the geology of the Panguitch 30' x 60' quadrangle at 1:62,500 scale. The quadrangle spans the southernmost High Plateaus in southwest Utah, a structural and stratigraphic transition zone between the highly extended Basin and Range Province on the west and the colorful, mostly flat-lying strata of the Colorado Plateau to the east. The structural grain of the map area is dominated by north- to northeast-trending normal faults that bound relatively unfaulted blocks represented by the Markagunt and Paunsaugunt-Sevier Plateaus. That grain is imprinted on the leading edge of the Sevier orogenic belt, whose thrust faults and folds are dramatically displayed in the Red Hills and in Cedar Canyon at the west edge of the map area, and whose subtle effects are documented eastward to the Paunsaugunt fault zone.The map area also includes the southern margin of the Marysvale volcanic field. Gravitational spreading of the southern sector of the volcanic field created unusual, east-trending, south-vergent thrust faults and folds of the Rubys Inn thrust fault zone, which is much younger than and trends nearly at a right angle to Sevier-age structures. Our mapping suggests that the Rubys Inn thrust fault continues westward into the Markagunt Plateau as a blind thrust fault roughly coincident with the southern margin of the Markagunt gravity slide. The Markagunt gravity slide, which apparently covers at least 1600 mi2(4160 km2) of the central and northern Markagunt Plateau and adjacent area, resulted from catastrophic collapse of the southwestern sector of the Marysvale volcanic field in the early Miocene, 21 to 22 million years ago. It is thus considerably larger than the famous Heart Mountain detachment of northwestern Wyoming, long known as the largest subaerial gravity slide in the world. We remain uncertain of what caused the collapse, but suggest that it may be related to pre-caldera inflation of the 20-18 Ma Mount Belknap caldera.The oldest rocks exposed in the map area, at Parowan Gap, belong to the Lower Jurassic Navajo Sandstone. Middle Jurassic strata are also exposed there, as well as in Cedar Canyon and south of Tropic. But it is Upper Cretaceous, Paleocene, and Eocene strata for which the quadrangle is most noteworthy. Our mapping documents correlation of Upper Cretaceous strata at the west edge of the Markagunt Plateau with better exposed and more thoroughly studied strata of the Kaiparowits basin east of the map area. Our mapping also constrains the evolution and demise of the Claron depositional basin, whose colorful strata are famously known at Cedar Breaks National Monument and Bryce Canyon National Park. For those interested in volcanic rocks, we report new late Eocene ages for the inception of volcanism in this part of southwest Utah, we map the distribution of regional ash-flow tuffs that erupted from Oligocene and Miocene calderas near the Utah-Nevada border (documenting paleotopography of the region and constraining the inception of basin-range faulting), and we map 38 relatively young basaltic lava flows and cinder cones, the most recent phase in the volcanic legacy of the southernmost High Plateaus. Because the map area contains such a wide range of young and old lava flows and ash-flow tuffs, it is adorned with inverted valleys representing each stage in the evolution of these enigmatic features. Several of these lava flows cross and are offset by faults associated with Basin and Range extension and so serve as markers for long-term slip rates on major normal faults in the area.This CD contains geographic information system (GIS) files in ESRI file geodatabase and shapefile formats. Also included are three plates the geologic map at 1:62,500 and two explanation sheets both in PDF format. The latest version of Adobe Reader is required to view the PDF files and can be downloaded at www.adobe.com. Specialized GIS software is required to use the GIS files. |