Integrated Laser-Induced Breakdown Spectroscopy (LIBS) and Multivariate Wavelet Tessellation: A New, Rapid Approach for Lithogeochemical Analysis and Interpretation

Abstract

This paper demonstrates a novel approach that uses wavelet tessellation in rapid analysis of raw geochemical data produced by laser-induced breakdown spectroscopy (LIBS) to produce pseudologs that are representative of stratigraphy. Single-line LIBS spectral data for seven major rock-forming elements (Al, Ca, Fe, Mg, Si, Na and K) were collected from a synthetic 22-sample rock-block comprising two distinct lithological groups based on mineralogy, chemistry and texture: plutonic rocks and marble. Seven sublithologies are identified within the rock-block from traditional laboratory whole-rock geochemical analysis: marble, Mg-marble, granite, quartz monzonite, foidolite, granodiorite and gabbroic diorite. Two-domain clustering (k = 2) on raw spectral LIBS data combined with wavelet tessellation was applied to generate a simplified lithological stratigraphy of marble and plutonic rocks and generate a pseudolog identical to the rock-block stratigraphy. A pseudolog generated from seven-domain clustering (k = 7) and wavelet tessellation successfully discriminated most sublithologies within the rock-block slabs, especially marble slabs. Small-scale units were identified within the more mineralogically and geochemically complex plutonic slabs. The spatial resolution of the LIBS analysis, with a measurement spacing of ~0.35 mm, allowed for assessment of individual mineral compositions and rock textures, and small-scale units within the plutonic rocks can be correlated to specific coarse-grained minerals or mineralogical associations. The application of the wavelet tessellation method to raw LIBS geochemical data offers the possibility of rapid and objective lithogeochemical analysis and interpretations which can predate further analysis (quantitative) and supplement geological logging.

Thickness Variation Characteristics of Tidal Rhythmites—An Example From the Pinghu Formation, Xihu Sag, East China Sea Shelf Basin

“…Its basic principle is to decompose the composite wave system into several simple harmonics with different amplitudes and phases through data transformation and then calculate the period value according to the main frequency of the wavelet (Zhao et al, 2009). First, the spectrum analysis program RedFit3.8 was used to calculate the fast Fourier transform (FFT) (Li et al, 2006;Santos et al, 2020;Fontana et al, 2021) for each lamina thickness data sequence under the background of red noise, and the characteristic period distribution of lamina thickness was explained. Second, on this basis, through AnalySeries 2.08 software of low pass filtering function to remove the high-frequency factor such as wave abnormalities, the coring grain layer thickness of lithofacies association cycle information was extracted, and analysis of the periodicity of the couplet, the sandy laminae, and the argillaceous lamina thickness was carried out.…”

“…Wavelet analysis not only retains the advantages of the Fourier transform but also makes up for the deficiency that the Fourier transform cannot reflect signal characteristics in local time (space). Many scholars have introduced this method into a high-precision sequence unit division to amplify the information in logging signals and to identify sequence cycles of different levels (Zhu et al, 2010;Chen et al, 2018;He, 2020;Fontana et al, 2021). Through frequency division processing on the data on variation in the thickness of sandy laminae, argillaceous laminae, and couplets, the frequency division signal was extracted and compared with the sedimentary facies divided by core observations, and the corresponding relationship between the frequency signal and sedimentary facies was summarized.…”

Current State of Laser-Induced Fluorescence Spectroscopy for Designing Biochemical Sensors

“…Femtosecond LIBS for in situ ammonia (NH 3 ) measurements was demonstrated when a femtosecond laser beam (λ = 800 nm) was focused at NH 3 molecules, photolysis generated electronic-excited NH fragments with subsequent fluorescence detection at 336 nm to attain a lower limit of 205 ppm [148]. Data from single-line LIBS for seven major rock-forming elements (Al, Ca, Fe, Mg, Si, Na and K) were collected to produce pseudo-logs of geochemical data that are representative of stratigraphy [149]. The optimal LIF excitation locations were the center of the plasma for Fe, but the periphery for Cr and Ni.…”