THREE-DIMENSIONAL GPR ANALYSIS OF TRIASSIC CARBONATE SEDIMENTATION, VIRGIN LIMESTONE, SOUTHERN UTAH

In order to assess the suitability of high-resolution ground-penetrating radar (GPR) for revealing fine-scale sedimentary structures and fabrics within limestone, we performed a detailed survey of a 100 x 100 inch area of the Early Triassic Virgin Limestone Member of the Moenkopi Formation in southern Utah. A 400-MHz antenna was used to survey an orthogonal grid of profiles spaced two inches apart. A bare, flat bedding surface that abutted a vertical outcrop was chosen for the GPR survey. The adjacent outcrop along with thin-section petrography furnished detailed control on the interpretation of the GPR data. The survey grid enabled a 3D volume of waveform data from vertical (cross section) and horizontal (map) views that could be extracted using state-of-the-art visualization computer software. The radar results furnished fine-scale images of the clinoform fabric that clearly dominates the adjacent outcrop. The 3D visualization was also able to image subtle variations in this fabric and identify "domains" of sedimentary structure that delimit regions of distinct versus less coherent fabric development. Such observations will likely have applications in studying reservoir compartmentalization in oil and gas extraction in carbonate rocks. Future work will include applying advanced volume-based filtering algorithms derived from seismic attribute programs normally used in petroleum exploration. Especially useful will be waveform classification and coherency-based volume filtering.