Using HySpex SWIR-320m hyperspectral data for the identification and mapping of minerals in hand specimens of carbonate rocks from the Ankloute Formation (Agadir Basin, Western Morocco)

摘要

Nowadays the development of sensors for acquiring hyperspectral images has contributed greatly to the identification of different constituents of the earth's surface and therefore to the improvement of cartographic products. Carbonate rocks are often altered by physical and chemical processes. The natural tendency in most carbonate sediments is that primary porosity is substantially reduced by cementation and compaction during post-depositional. For example the subaerial meteoric diagenetic (freshwater) was promoted as a means of explaining porosity evolution in carbonates. These processes lead to the formation of new carbonate minerals with highly variable phase crystallization. Frequently, with the optical microscope, the precise identification and discrimination of these phases are beyond the resolving power of the eye, which makes mapping mineralogical microfacies difficult. It requires, first, the use of staining techniques. This work proposes to study hand specimens of the carbonate facies of Jurassic age in the Agadir Basin, using hyperspectral imagery provided by the camera HySpex SWIR-320m, at wavelengths ranging from 1300 to 2500 nm. These images offer the possibility to identify with precision the different carbonate minerals and to allow diagenetic facies characterization. The approach is to calculate an index of carbonate, called the Normalized Difference Carbonate Index or NDCI, to study the deepening of the main absorption band of carbonates and a supervised classification method based on the Spectral Angle Mapper (SAM) to study the overall shape of reflection spectra of carbonates and to map other accessory minerals. This method has allowed the development of mineralogical maps supplemented by their degrees of diagenesis.