Presentation Title

Fracture Evolution in the Niobrara Chalks of the Castle Rock Area, west-central Kansas

Advisor Information

Harmon Maher

Location

Dr. C.C. and Mabel L. Criss Library

Presentation Type

Poster

Start Date

7-3-2014 9:00 AM

End Date

7-3-2014 12:00 PM

Abstract

Castle Rock is a predominantly north-south exposure of the Cretaceous age of Niobrara Chalks. At this location, multiple structural features are visible for analysis and interpretation, including normal faults, veins (opening fracture with mineralization), and joints (unmineralized opening fracture), from which a history of deformation can be constructed. In the middle of the continent, such deformations are uncommon and faults can suggest a potential seismic risk. The faults cut through both the lower and upper chalk units, are filled with calcite slickensides, and are oriented mostly east-west, but with significant variability. All faults were normal faults, which are associated with local extension. Vertical fault offsets varied from centimeters to meters. Two joint sets were mapped in the study area: longitudinal joints striking SE-NW, and cross joints striking SW-NE. A cross cutting relationship suggests that joints are more recent than faults. The veins are predominantly found in the lower part of the exposed stratigraphy, are typically dish/bowl shaped in cross section with sub-horizontal bases, and have a preferred orientation. We conclude that there were at least three distinct periods of deformation each forming the different types of fractures. The different episodes of deformations and orientations may be due to changes in the stress field associated with North American plate tectonics. There is also a possibility that fracturing occurred during sediment burial and due to compaction, de-watering and mineralogical changes. The veins may be due to modern weathering and topography.

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COinS
 
Mar 7th, 9:00 AM Mar 7th, 12:00 PM

Fracture Evolution in the Niobrara Chalks of the Castle Rock Area, west-central Kansas

Dr. C.C. and Mabel L. Criss Library

Castle Rock is a predominantly north-south exposure of the Cretaceous age of Niobrara Chalks. At this location, multiple structural features are visible for analysis and interpretation, including normal faults, veins (opening fracture with mineralization), and joints (unmineralized opening fracture), from which a history of deformation can be constructed. In the middle of the continent, such deformations are uncommon and faults can suggest a potential seismic risk. The faults cut through both the lower and upper chalk units, are filled with calcite slickensides, and are oriented mostly east-west, but with significant variability. All faults were normal faults, which are associated with local extension. Vertical fault offsets varied from centimeters to meters. Two joint sets were mapped in the study area: longitudinal joints striking SE-NW, and cross joints striking SW-NE. A cross cutting relationship suggests that joints are more recent than faults. The veins are predominantly found in the lower part of the exposed stratigraphy, are typically dish/bowl shaped in cross section with sub-horizontal bases, and have a preferred orientation. We conclude that there were at least three distinct periods of deformation each forming the different types of fractures. The different episodes of deformations and orientations may be due to changes in the stress field associated with North American plate tectonics. There is also a possibility that fracturing occurred during sediment burial and due to compaction, de-watering and mineralogical changes. The veins may be due to modern weathering and topography.