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The AAPG/Datapages Combined Publications Database
Approximately 26,000 ft (7,930 m) of Paleozoic carbonate and subordinate clastic sedimentary rocks is exposed in the central Grant Range. Cambrian quartzite, shale, and minor limestone are the oldest exposed rocks in the area. The overlying 11,200 ft (3,416 m) consists of limestone, dolomite, shale, and minor quartzite and sandstone; this sequence begins with the Ordovician Pogonip Group and ends with the Mississippian Joana Limestone. The overlying strata are Upper Mississippian and Pennsylvanian shale, and minor sandstone and limestone. The Paleozoic sequence is overlain unconformably by Cenozoic sedimentary and volcanic rocks.
Three major low-angle faults that separate younger rocks from older are exposed in the area. They are, in ascending order, the Grant Canyon, Heath Canyon, and Beaty Canyon faults. The Grant Canyon fault emplaces gently dipping Middle Cambrian limestone and shale over steeply dipping Lower Cambrian Prospect Mountain Quartzite. Rocks considered to be Lower Ordovician are separated from overlying Cambrian units by the Heath Canyon fault. The Beaty Canyon fault generally carries concordant Silurian through Pennsylvanian strata over Lower Ordovician rocks. Relative eastward movement of the upper plate rocks is demonstrated by folds in the lower plates, which are overturned to the east. In addition, five subordinate low-angle faults are recognized.
Synorogenic regional metamorphism, predating the faulting, converted part of the Cambrian and Lower Ordovician strata into tectonically banded marbles, and chlorite-muscovite and biotite phyllites. Postmetamorphic low-angle faulting resulted in superposed local mylonitization. Medium- to high-grade calc-silicate rocks are associated with a granitic intrusion. Folding within the range is locally intense, and high-angle faulting, with the exception of the range front fault or faults, is mostly of small displacement. A Mesozoic age of metamorphism and thrusting is inferred from regional evidence.
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