Subsurface to Surface Correlation of the Tensleep Sandstone in the West Flank of the Pryor Mountains in Carbon County, Montana

The Pennsylvanian Tensleep Sandstone is an eolian and nearshore marine/sabka quartz arenite unit with prominent outcrops along the western Pryor/Bighorn Mountain front east of Red Lodge, MT. Regionally, the formation represents one of the largest ergs in the global geologic record. High permeability makes it an important oil and gas reservoir and aquifer in south central Montana and throughout much of Wyoming. The Tensleep Sandstone’s high percentage of quartz content and grain roundness, due to its eolian origin, makes it a prospective source for natural proppant sand. Three continuous 4-inch cores were obtained during a cooperative project between Montana Tech and industry partners. Using stratigraphic sections, cores, thin sections, and x-ray fluorescence (XRF) analysis, the usefulness and economic feasibility of the Tensleep Sandstone as a minable hydraulic fracture proppant was explored. Usefulness depends on cementation, grain shape, grain size, and depth from surface of the prospective zone. Grain shape and size were determined by thin sections, sieving, and stereomicroscope analysis. Analysis of 20 disaggregated sand samples has shown that as much as 30 percent of the grain sizes fall between 30-50 mesh (medium- to finegrained sand size) and about 45 percent of the grain sizes fall between 70–140 mesh (very fine-grained sand to coarse silt), grain sizes appropriate for some hydraulic fracture operations. Core descriptions and XRF data display the distribution of lithology and cementation. Core descriptions and XRF data display the distribution of lithology and cementation. Elemental (XRF) analyses help to delineate more pure quartz sands from those with grain fractions reflecting fine-grained clastic and evaporitic inputs. The core and nearby stratigraphic sections are used to quantify the amount of overburden and the 3 amount of resource in the area. Initial results show favorable crush strength and useable grain size and shape.

Kibbey Sandstone in Montana

Much attention has recently been given, by geolog­ists, to prolific water bearing horizon and a potent­ial oil horizon, known as the Kibbey sandstone, which lies deeply buried under much of central Montana. In some local­ities the sandstone is dry, and its identification in cut­tings from deep wells has in many cases proved difficult.

The Problem of the Tensleep Sandstone

Sandstone is probably one of the most important groups of rocks in existence today. The economic importance of so insignifi­cant a thing as a mass of sand grains grows with the true reality of the situation. By increasing our knowledge of grains of sand, or particles of sandstone in all their ram­ifications, it would undoubtedly reflect upon our everyday life by increasing commercial possibilities of an undevel­oped natural resource of Montana.

Stratigraphy and Paleontology of the Eagle Formation in Montana and Adjacent Areas

A conspicuous two hundred and fifty foot sandstone of central Montana, known as the Eagle Formation, constitutes part of the some five thousand feet of Cretaceous sediments in the state. It stands out in steep cliffs which stretch for many miles in the outcrop area from Wyoming to Canada.

Sandstones of the Lance and Fort Union Formations

The Fort Union and Lance formations are widespread terrestrial sediments exposed in Montana, North Dakota, South Dakota, Wyoming, and Canada. Their stratigraphic position, especially that of the Lance, has long been in doubt, and has provoked much controversy among geologists.