Presentation Title

Fracture analysis of Cretaceous Rocks, Francis Case Lake, South Dakota

Advisor Information

Harmon Maher

Location

Milo Bail Student Center Ballroom

Presentation Type

Poster

Start Date

8-3-2013 1:00 PM

End Date

8-3-2013 4:00 PM

Abstract

This project was carried out by students in a Structural Geology Field Methods class, as a larger ongoing project looking at fracture generation in the Great Plains. The focus is fractures in the Niobrara chalk and Pierre shale at two sites in the area of Francis Case Reservoir, South Dakota. The first site visited was the dam spillway of the reservoir and the second was on the west bank where the highway 44 crosses the reservoir. Orientation data and field observations on joints, veins and faults were collected at both locations. At the bridge 44 site a stratabound and dense network of distinctive veins was the focus of scrutiny. Vein spacing, width and orientation data was measured using both horizontal and vertical traverses. Orientations and observations were also collected from a lower unit, which had more typical joint and vein patterns. Sliding sector circular histograms were constructed for the strike data and then statistically modeled (with up to 4 preferred orientations and a uniform component) for both locations. Comparisons within this study and with other studies, indicates a regionally consistent SE to ESE longitudinal fracture direction exists. Overall the character of the stratabound veins is consistent with deformation, and regional stresses have aligned the veins to their current orientations. Strain measurements indicate a rough estimate of the amount of volume lost in the rock. Because of the complex deformation mechanisms involved, many are still unidentified for this project. These strata show a fracture history worthy of future research.

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COinS
 
Mar 8th, 1:00 PM Mar 8th, 4:00 PM

Fracture analysis of Cretaceous Rocks, Francis Case Lake, South Dakota

Milo Bail Student Center Ballroom

This project was carried out by students in a Structural Geology Field Methods class, as a larger ongoing project looking at fracture generation in the Great Plains. The focus is fractures in the Niobrara chalk and Pierre shale at two sites in the area of Francis Case Reservoir, South Dakota. The first site visited was the dam spillway of the reservoir and the second was on the west bank where the highway 44 crosses the reservoir. Orientation data and field observations on joints, veins and faults were collected at both locations. At the bridge 44 site a stratabound and dense network of distinctive veins was the focus of scrutiny. Vein spacing, width and orientation data was measured using both horizontal and vertical traverses. Orientations and observations were also collected from a lower unit, which had more typical joint and vein patterns. Sliding sector circular histograms were constructed for the strike data and then statistically modeled (with up to 4 preferred orientations and a uniform component) for both locations. Comparisons within this study and with other studies, indicates a regionally consistent SE to ESE longitudinal fracture direction exists. Overall the character of the stratabound veins is consistent with deformation, and regional stresses have aligned the veins to their current orientations. Strain measurements indicate a rough estimate of the amount of volume lost in the rock. Because of the complex deformation mechanisms involved, many are still unidentified for this project. These strata show a fracture history worthy of future research.