From Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.

AAPG Annual Convention, Houston, Texas, April 9–12, 2006

Calcite-Dolomite Delineation Using Airborne Hyperspectral Data for Ordovician Paleokarst Mapping

Jerome A. Bellian, Charles Kerans, Richard A. Beck, Yolanda Price, and
Kumar Nedunuri

Abstract:

The El Paso Group outcrops in the Franklin Mountains of west Texas, contains world-class Ordovician paleocave systems developed beneath the Sauk supersequence boundary. This paleokarst system is widely used as an analog for Ellenburger Group and other. complex paleokarst reservoir systems where fracture and intra-breccia clast porosity developed during cave collapse. A central unresolved issue for our work here in the Franklin Mountains is developing an understanding of the three-dimensional extents and connectivity of these deep phreatic and water-table-associated caves and their related cave-roof and cave-fill facies.

Quantitative digital mapping techniques including GPS (global positioning systems), airborne LIDAR, and conventionally available DEM (digital elevation model) data, has been used in concert with hyperspectral AVIRIS (Visible InfraRed Imaging Spectrometer) and hand-held full-range (350-2,500 nanometers) spectroradiometer data to reveal spectral patterns of calcite-dolomite transitions associated with paleocave deposits. Together, these datasets enable accurate reconstruction of the size, shape, connectivity, and lithologic characteristics of the El Paso paleokarst system.

Of particular interest is a novel approach to mineralogic mapping developed during the field mapping phase of the project. Atmospherically corrected and georeferenced airborne hyperspectral AVIRIS data were analyzed over the field area at 20 meter spectral resolution and found to correspond extremely well with variations in lithology keyed to measured stratigraphic sections. Field mapping has revealed that late-phase dolomitization correlates with collapse paleokarst breccia deposits just below the Sauk second order supersequence surface.