Application of GPR for 3-D visualization of geological and structural variation in a limestone formation

Abstract

Ground-penetrating radar (GPR) offers a simple and rapid means of providing valuable information for mapping of geological and structural variations in limestone. Data from closely spaced radar sections were gathered in two areas in Faxe Kalk's limestone quarry on the island of Zealand, Denmark. A `pulseEKKO 100' GPR system with 100 MHz antennas was used for data gathering. In this paper we describe the steps required to obtain three-dimensional (3-D) data. Data were collected in continuous mode with readings every 20 cm. The 3-D cubes were prepared for visualization by using several processing routines. Various data presentations, including chair views, and multiple and single slices, were generated from the 3-D cube to enhance the outline and distribution of flint-free limestone in the surveyed areas. Animation of 3-D data was found to be a very powerful way of visualizing the geological structures in the surveyed areas. The limestone formation in the quarry is of middle Danian age (approx. 63 million years old) and is divided into two main deposition facies—coral limestone and bryozoan limestone. The coral limestone appears as reef structures in the more abundant bryozoan limestone. In the bryozoan limestone frequent flint layers appear often delineating mound-like structures. Coral limestone and areas of bryozoan limestone without flint are quarried selectively and used for high quality products. Division of the limestone formation into areas of coral reefs and bryozoan mounds and separation of flint-free areas is made possible through distinctive reflection patterns and differing penetration depths between the rock units. The 3-D visualization allows estimation of potential volumes of limestone for selective exploitation.