Geospatial Characterization of Clastic Dikes in Badlands National Park: A General Model for Fracture System Analysis

Michael P. Madison and Mark P. Fischer
Northern Illinois University, Department of Geology and Environmental Geosciences DeKalb, IL 60115-2854, [email protected], [email protected]

Abundant exposures of clastic dikes in Badlands National Park, SD, provide an excellent opportunity to use modern GIS techniques as a tool for characterizing fracture networks. Over 150 dikes were mapped with high resolution GPS as well as in 1-2m resolution air photos and satellite images. During mapping we simultaneously collected data on attributes such as dike aperture, internal structures, grain size of dike material, and cross-cutting relations. We analyzed the spatial distribution of all of these attributes, as well as dike length, orientation, and distribution of dikes throughout the roughly 2 square kilometer study area.

Average dike aperture for dikes measured was roughly 10cm, with relatively little variation along strike. Dike material was very angular and poorly sorted with grains ranging from fine sand to clay. Dike length data displayed multifractal distributions with fractal dimensions of -1.047 and -2.631. Average dike densities throughout the study area were 0.028m/m². Network volume estimates were made using the collected data, and assuming a depth based on stratigraphy. Dike azimuths were acquired using GIS, with data weighted by length. Orientations can be organized into four subperpendicular groups with two in the east, and two in the west of the study area. Mapping cross-cutting relations revealed a complex, chaotic history of dike growth with no clear chronology of dike formation.

Using these data, geologists can constrain important variables necessary to construct quality reservoir models for clastic injectite complexes. These techniques can also be adapted for fracture network analysis where dikes are not present.

AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009