Mapping of Multiphase Dolomitization Using Ground-Based Spectral Imaging and Lidar Scanning
Spectral imaging is a well developed technique for aerial and satellite remote sensing, which is used for remote mapping of mineralogical and lithological variations. This method is based on the physical interaction of electromagnetic radiation (reflection properties of sunlight) with surface material. The reflection and absorption of certain wavelengths are directly controlled by the chemical composition and the crystal structure of the object. In this study spectral imaging has been introduced to a ground-based application using a new hyperspectral sensor to improve and automate the collection and interpretation of outcrop data. The applied spectral sensor operates in the infrared portion of the electromagnetic spectrum, which makes it suitable for geological applications. To allow analysis of the image processing results in a real-world coordinate system, the spectral images have been integrated with ground-based lidar data to create geologically and mineralogically classified, 3D virtual outcrop models.
This method has been tested on dolomitized limestones. The carbonate absorption band at 2.3 μm shows a clear shift to a lower wavelength between unaltered and dolomitized limestone, and this feature can be used to quantify the degree of dolomitization. Furthermore, differences in chemical composition and textural properties of different dolomite facies result in specific spectral signatures which can be utilized to distinguish between phases of dolomitization. The depths of specific absorption bands allow quantification of chemical variations. Variable porosity values associated with the different dolomite phases are used to estimate the porosity distribution in the outcrop. Essential gain of information is received from weathered surfaces or inaccessible areas, where visible inspections and standard photographs are inconclusive. The relationship between spectral signatures and chemical and textural properties of the dolomite phases has been examined by XRF and thin section analysis of spot samplings. This study demonstrates that spectral imaging of lithology combined with geometrically accurate lidar data has significant implications for the collection of large volumes of quantitative geological outcrop data.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009