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To date this project has supported 12 undergraduate students in conducting undergraduate research on the origin of chalcedony vein and clastic dike arrays in the Tertiary White River Group of South Dakota and Nebraska, with a focus on the role that structural diagenesis played. Students have been involved in an array of field work, GIS database construction, and structural, petrographic (thin sections) and XRD analysis. Field work has developed information for 6 new sites. In the summer of 2010, we visited three field areas with our students. These included Scotts Bluff, NE, Toadstool, NE, and Badlands National Park. All students have contributed to team reports. One senior thesis is near completion and three others are in progress. Two related presentations have been made at professional meetings, and a third has been accepted for this fall. An internal web site with reports generated by previous students, reference articles, an array of data collected, an image bank , along with sample and thin section suites, will help to support continued undergraduate research. The project has and will continue to provide invaluable support to our geology program through expanding our undergraduate research efforts and involving the students in a research team that genuinely is contributing to the understanding of structural diagenesis. Such undergraduate research experiences help attract and retrain a higher quality of student, and helps provide them with experience and credentials that aid their continued career development. We have done this by including students of all levels of geologic experience in our teams of students. There have been seniors to freshmen participating in this project and our retention rate is 10 of12 students are still in the program or have graduated (one student is too far along in his course of studies - Math Education - to switch, although he remains very active in the project). This support also comes at a particularly opportune time as interest in and prospects for geoscience careers grows.

The following describes some of the scientific findings to date. In the northern part of Sheep Mountain Table in the south unit of the Badlands National Park five different levels of stratiform chalcedony vein arrays have been identified from several meters to several tens of meters in individual vertical extent. Two very widely developed layers occur at the Chadron-Brule contact, and at the Heck Table marker. Stratigraphically higher vein arrays are less developed (thinner), suggesting a vertical gradient in the degree of local silica mobilization. Vein strike orientations from different sites vary from statistically random to highly patterned. At one site east of Toadstool Nebraska, an array of well developed veins about 1 m in vertical extent is clearly centered on a greenish, clay rich horizon. Preliminary XRD analysis show strikingly variable clay signatures stratigraphically, and also suggests the chalcedony vein host layers are richer in smectite, which may be driving structural diagenesis and vein formation. In addition, stratiform gypsum vein arrays have been found, mapped and sampled in Brule Formation strata at Scotts Bluff (the focus of a senior thesis).

At Sheep Mountain Table chalcedony veins are aligned with and locally intruded into clastic dikes, and mobilized sediment appears to occur in some chalcedony veins. Thin section textures suggest vein formation within the dike occurred while the sediment was still mobile, and unlithified. These relations indicate vein and dike formation was roughly coeval. Clastic dikes also show strongly varying degrees of preferred orientation from site to site. Clastic dikes taper downward into the Brule Formation, but some reach down to the very top of the Chadron formation. Most dikes are composite, with geometries clearly indicating multiple injection events, often mobilizing different sediment sources for the same dike. Enough lithification of the pre-existing dike fill must have occurred in order to allow for brittle fracture geometries to develop. Internal flow structures clearly indicate upward flow for some of the dikes, and an injection origin. Other internal structures are consistent with downward propagation and injection. The sediment source has yet to be identified. Significant post-dike modification of dikes occurs. A GIS database of clastic dikes was created for the Cedar Creek Pass area in the Badlands National Park with over 850 individual stations. Two preferred orientation sets exist, but clearly overlap significantly in time. A significant percentage of the readings are not accounted for in the two orientations sets. A subset of dikes here exhibit significant wall rock discoloration with greenish tinted zones 10s of centimeters wide. Uranium mineralization also occurs within the dikes. Both suggest that at times reducing fluids migrated along the dikes. Results to date are consistent with structural diagenesis playing a role in both chalcedony vein and clastic dike formation in these volcanic ash rich, terrestrial, Tertiary sediments. Continued work will focus on identifying the specific agents of structural diagenesis, working out the history of diagenesis, and considering the interplay between local diagenetic and more far field, tectonic forces in developing the orientation patterns of these fracture systems. In addition to smectite cation exchange, silica phase changes and possibly clinoptolite cation exchanges are being considered as possible mechanisms that drive deformation.

We would like to acknowledge the following: Dr. Rachel Benton for help in understanding the Badlands National Park geology and for oversight of the research permit; Dr. Evan Evanoff for sharing his wealth of knowledge on the stratigraphy; and Dr. Mary Ann Holmes for helping our students conduct the XRD work and sharing her expertise in clay mineralogy. Of course, all errors are ours. Finally we would like to thank the very enthusiastic and motivating students who chose to engage in this project.