| Abstract |
- The Cedar Creek area, consisting of about 30 square miles, is
located on the west flank of the central Madison Range in Madison
County, Montana.
The rocks of the area include carbonates, sandstones, mudstones,
cherts, phosphorite, metamorphic rocks, intrusive igneous
rocks, and unconsolidated sediments and have been divided into 16
mapped units.
An undetermined thickness of Precambrian metamorphic basement
rocks, approximately 7,000 feet of sedimentary rocks, and an
undetermined thickness of Tertiary intrusive igneous rocks are
exposed in the area. In addition, surficial deposits of unconsolidated
alluvium and landslide debris are present in the area.
Sedimentary rocks in the area are correlated with the Devonian
Jefferson and Three Forks Formations, the Mississippian Lodgepole and Mission Canyon Formations, the Mississippian-Pennsylvanian
Amsden Formation, the Pennsylvanian Quadrant Formation, the
Permian Park City, Shedhorn, and Phosphoria Formations, the
Triassic Dinwoody Formation, the Jurassic Sawtooth, Rierdon, and
Morrison Formations, and the Cretaceous Kootenai Formation and
Colorado Group.
The area has undergone two major episodes of deformation.
The first occurred in latest Cretaceous to Early Tertiary time when
compressive forces produced thrust-faulting and folding in the area.
During the second episode, tensional forces, probably related to
epeirrogenic uplift, initiated normal faulting in the area.
Stream erosion and several cycles of glaciation have modified
the topography of the area to its present form.
No stratigraphic or structural conditions in the area are
favorable for the accumulation of oil and gas, Beds of furnace-grade
phosphorite are present in the area, but at this time the cost of
mining the phosphorite beds is far greater than the value of the phosphorite.
|
|---|