Presentation Title

Analysis of Smectite-Illite within the White River Group

Advisor Information

Robert Shuster

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 last summer work on fractures and fracture systems within the Miocene (23-5.3 million year old) age White River Group strata was focused on two locations in northwestern Nebraska. These were Monroe Creek (near Harrison, NE) and Toadstool Geologic State Park (near Crawford, NE). These fractures may have formed by chemically driven volume changes as the sediments were buried, an understudied phenomena. Fracture types include clastic dikes, which are sediment filled fractures, and chalcedony veins. Samples were collected, spanning the White River Group and including the very base of the overlying Arikaree Group. Prepared samples were sent out to be analyzed by x-ray diffraction (XRD) for their mineralogy, including the clay minerals, smectite and illite. These two minerals are of particular interest. Swelling clays like smectite can change during geologic burial into nonswelling illite. Change from smectite to illite causes a volume loss and release of water within the rocks, which may produce fractures. The results of the XRD analysis indicate that there were distinct changes in smectite, illite, and mixed smectite-illite content with sample ascent through the White River Group. At Toadstool Geologic State Park mixed smectite-illite vanishes at the very top of the Chadron Formation, a lower unit in the White River Group. The clastic dikes and chalcedony veins are strongly concentrated in the Chadron Formation. Continued research of fractures and fracture systems will aid in understanding how water and other fluids move through sedimentary rocks.

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

Analysis of Smectite-Illite within the White River Group

Milo Bail Student Center Ballroom

This last summer work on fractures and fracture systems within the Miocene (23-5.3 million year old) age White River Group strata was focused on two locations in northwestern Nebraska. These were Monroe Creek (near Harrison, NE) and Toadstool Geologic State Park (near Crawford, NE). These fractures may have formed by chemically driven volume changes as the sediments were buried, an understudied phenomena. Fracture types include clastic dikes, which are sediment filled fractures, and chalcedony veins. Samples were collected, spanning the White River Group and including the very base of the overlying Arikaree Group. Prepared samples were sent out to be analyzed by x-ray diffraction (XRD) for their mineralogy, including the clay minerals, smectite and illite. These two minerals are of particular interest. Swelling clays like smectite can change during geologic burial into nonswelling illite. Change from smectite to illite causes a volume loss and release of water within the rocks, which may produce fractures. The results of the XRD analysis indicate that there were distinct changes in smectite, illite, and mixed smectite-illite content with sample ascent through the White River Group. At Toadstool Geologic State Park mixed smectite-illite vanishes at the very top of the Chadron Formation, a lower unit in the White River Group. The clastic dikes and chalcedony veins are strongly concentrated in the Chadron Formation. Continued research of fractures and fracture systems will aid in understanding how water and other fluids move through sedimentary rocks.