Geology Reports⌕ Search

Geology topics

Research about Montana, Wyoming

Source-linked reports with geographic coverage including Montana, Wyoming.

At least 145 records · Page 8Linked to original sources
USGS1975

Linkage effects between deposit discovery and postdiscovery exploratory drilling

For the 1950-71 period of petroleum exploration in the Powder River Basin, northeastern Wyoming and southeastern Montana, three specific topics were investigated. First, the wildcat wells drilled during the ambient phases of exploration are estimated to have discovered 2.80 times as much petroleum per well as the wildcat wells drilled during the cyclical phases of exploration, periods when exploration plays were active. Second, the hypothesis was tested and verified that during ambient phases of exploration the discovery of deposits could be anticipated by a small but statistically significant rise in the ambient drilling rate during the year prior to the year of discovery. Closer examination of the data suggests that this anticipation effect decreases through time. Third, a regression model utilizing the two independent variables of (1) the volume of petroleum contained in each deposit discovered in a cell and the directly adjacent cells and (2) the respective depths of these deposits was constructed to predict the expected yearly cyclical wildcat drilling rate in four 30 by 30 min (approximately 860 mi 2 ) sized cells. In two of these cells relatively large volumes of petroleum were discovered, whereas in the other two cells smaller volumes were discovered. The predicted and actual rates of wildcat drilling which occurred in each cell agreed rather closely.

Montana, Wyoming↗
USGS1975

Cylindrical jointing in mafic dikes, central Beartooth Mountains, Montana

Cylindrical joints are well displayed in two Precambrian mafic dikes that cut granitic gneiss in the central Beartooth Mountains, Mont. The dikes are vertical and about 23 m (75 ft) and 23 to 46 m (75-150 ft) thick, respectively. The cylindrical joints are perpendicular to the dike walls, and the cylinders defined by the joints are as much as 5 m (16 ft) in diameter. No petrographic, textural, or other features related to or possibly responsible for the joints are recognized. The dikes are chemically and petrographically similar to quartz dolerite dikes found throughout the Beartooth Mountains. Some of these dikes show typical polygonal columnar joints; a few others have cylindrical jointing, but in most dikes neither kind of jointing was observed. The orientation of the cylindrical joints normal to the walls of the dikes indicates that they probably formed by thermal contraction during post-crystallization cooling of the dikes and are thus genetically related to the much more common polygonal jointing. However, the model proposed to explain the cylindrical joints suggests that their origin is partly dependent on the geometric relation between the orientation of the dikes and that of the predike fracture pattern in the host rock.

Montana, Wyoming↗
USGS1974

New evidence on the age of the top of the Madison Limestone (Mississippian), Bighorn Mountains, Wyoming and Montana

The youngest strata recognized in the Madison Limestone arc dated by foraminifers and corals at two localities on the west flank of the Bighorn Mountains in Wyoming and Montana. Fossils collected in situ from the Madison at Shell Canyon represent Zone 12 of Mamet and Skipp of late Salem age (middle Visean), previously thought to be unrepresented by strata in the northern Cordilleran region of the United States. A block of residual chert found at Devils Canyon contains fossils with a possible age range of microfaunal Zones 12 15 (late Salem to Ste. Genevieve, middle to late Visean), providing further evidence of an extended age range for Madison strata prior to post-Madison, pre-Amsden erosion.

Montana, Wyoming↗
USGS1956

Bentonite deposits in marine Cretaceous formations, Hardin district, Montana and Wyoming

The bentonite deposits described in this report, which are roughly and tentatively estimated to include a minable reserve of 110 million short tons of montmorillonitic clay, are shown on a geologic map covering approximately 1,280 square miles, mostly in the Crow Indian Reservation, Big Horn County, Mont., but extending a short distance southward into Sheridan County, Wyo. Bentonite has been mined in recent years from two small workings in Sheridan County, one of which is north of Gay Creek and the other near West Pass Oreek; the clay has been processed within the district in a plant at Aberdeen Siding, Mont., a shilJping point on the Chicago, Burlington and Quincy Railroad. The bentonite beds of minable thickness are interspersed among strata belonging to Cretaceous formations ranging from the Thermopolis shale to the Bearpaw shale. Two beds in the Cody shale and two other beds in the Bearpaw shale are extremely thick locally; these, and a number of other beds, are favorably situated for mining along some parts of their outcrops. Primarily, the beds are described with reference to their location, stratigraphic positions, thicknesses, geologic structural relations, accessibility and content of material that might be suitable for industrial use. Also outlined are the laboratory procedures employed in testing samples of the bentonite as molding-sand bonding materials for use by foundries and as ingredients of rotary oil well drilling muds.

Montana, Wyoming↗