2007 GSA Denver Annual Meeting (2831 October 2007)
Paper No. 118-10
Presentation Time: 1:30 PM-5:30 PM

ELECTRON MICROPROBE ANALYSIS OF FRACTURE FILLING CEMENTS IN THE WOODFORD SHALE, SE OKLAHOMA

BERRYMAN, Robert R., Boone Pickens School of Geology, Oklahoma State University, 105 Noble Research Center, Stillwater, OK 74075, riter.berryman@okstate.edu, BLYTHE, Joseph W., School of Geology, Oklahoma State University, 105 Noble Research Center, Stillwater, OK 74075, PUCKETTE, Jim, School of Geology, Oklahoma State University, 105 NRC, OSU, Stillwater, OK 74078, and CATLOS, Elizabeth J., School of Geology, Oklahoma State Univ, Stillwater, OK 74078

In this undergraduate research project, we investigated the composition of fracture-filling cement within the Woodford Shale located in southeastern Oklahoma. Our goal was to gain an understanding of the composition of the fracture filling cements and determine how the cementation occurred.

The Woodford Shale is a late Devonian/early Mississippian unit that is located below carbonates and shale of the "Mississippi Limestone" and above limestone/dolostone of the Hunton Group. This shale is typically comprised of three separate sections. The beds in these sections all have low permeability, and porosity is seemingly dependent on fractures. Core samples of over one hundred feet of highly fractured shale were taken from a recently drilled well in southeastern Oklahoma. Fractures within the shale are mineralized. As part of a course at OSU, we used an Electron Microprobe to analyze the fracture fill and adjacent host shale. An Energy Dispersive Spectrometer obtained qualitative compositional information and a Wavelength Dispersive Spectrometer was used for element mapping.

Fractures in the uppermost section of the Woodford Shale are filled with calcite. However, the middle section fractures contain dolomite with minor amounts of pyrite. Many fractures in the lower section are filled with pyrite and minor amounts of dolomite. The upper and middle sections contain pyrite in the matrix of the rock, however, fracture-filling pyrite is rare.

We suggest that the adjacent carbonates may be one source for calcite present in fractures in the uppermost and lowermost Woodford Shale. Another source is hydrothermal fluids, which could precipitate calcite throughout the formation. Hydrothermal fluids rich in magnesium entered the middle section, leading to dolomitization. The lowermost section contains fracture-filling pyrite that may be the result of depositional geochemisty or diagenesis.

2007 GSA Denver Annual Meeting (2831 October 2007)
General Information for this Meeting
Session No. 118--Booth# 183
Involvement in Geological Research: Close Collaboration among the Faculty and Undergraduate and K12 Students (Posters)
Colorado Convention Center: Exhibit Hall E/F
1:30 PM-5:30 PM, Monday, 29 October 2007

Geological Society of America Abstracts with Programs, Vol. 39, No. 6, p. 328

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