HR: 10:20h
AN: T42C-01    [Abstracts]
TI: Power-law Scaling of Fracture Aperture Sizes in Otherwise-Undeformed Foreland Basin Sandstone: An Example From the Cozzette Sandstone, Piceance Basin, Colorado
AU: * Hooker, J N
EM: john.hooker@beg.utexas.edu
AF: University of Texas at Austin, Jackson School of Geosciences, Bureau of Economic Geology, University Station, Box X, Austin, TX 78713-8924, United States
AU: Gale, J F
EM: julia.gale@beg.utexas.edu
AF: University of Texas at Austin, Jackson School of Geosciences, Bureau of Economic Geology, University Station, Box X, Austin, TX 78713-8924, United States
AU: Laubach, S E
EM: steve.laubach@beg.utexas.edu
AF: University of Texas at Austin, Jackson School of Geosciences, Bureau of Economic Geology, University Station, Box X, Austin, TX 78713-8924, United States
AU: Gomez, L A
EM: leonel.gomez@exxonmobil.com
AF: ExxonMobil Upstream Research Company, 3120 Buffalo Speedway, Houston, TX 77098, United States
AU: Marrett, R
EM: marrett@mail.utexas.edu
AF: Univeristy of Texas at Austin, Jackson School of Geosciences, Department of Geological Sciences, 1 University Station C1100, Austin, TX 78712, United States
AU: Reed, R M
EM: rob.reed@beg.utexas.edu
AF: University of Texas at Austin, Jackson School of Geosciences, Bureau of Economic Geology, University Station, Box X, Austin, TX 78713-8924, United States
AB: Power-law variation of aperture size with cumulative frequency has been documented in vein arrays, but such patterns have not been conclusively demonstrated from open or incompletely mineralized opening-mode fractures (joints) in otherwise-undeformed sedimentary rocks. We used subhorizontal core from the nearly flat- lying Cretaceous Cozzette Sandstone, Piceance Basin, Colorado, to document fracture aperture sizes over five orders of magnitude. We measured microfractures (0.0004-0.1164 mm in aperture) along a 276-mm-long scanline using scanning electron microscope-based cathodoluminescence; we measured macrofractures (0.5- 2.15 mm in aperture) in 35 m of approximately horizontal core cut normal to fracture strike. Microfractures are typically filled with quartz. Macrofractures are mostly open and resemble non-mineralized joints, except for thin veneers of quartz cement lining their walls. Micro- and macrofractures share both a common orientation and the same timing with respect to diagenetic sequence, only differing in size and the degree to which they are filled with quartz cement. Power-law scaling equations were derived by fitting trendlines to aperture vs. cumulative frequency data for the microfractures. These equations successfully predicted the cumulative frequencies of the macrofractures, accurate to within a factor of four in each test and within a factor of two in 75 percent of tests. Our results show that tectonic deformation is not prerequisite for power-law scaling of fractures, but instead suggest that scaling emerges from fracture interaction during propagation.
DE: 8010 Fractures and faults
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8030 Microstructures
DE: 8109 Continental tectonics: extensional (0905)
DE: 8169 Sedimentary basin processes
SC: Tectonophysics [T]
MN: 2007 Fall Meeting