CLSM (Spectral fluorescence) to derive thermal maturity in marine siltstone and claystone

Country / Region: Germany / Selected Regions

Begin of project: March 1, 2020

End of project: March 1, 2024

Status of project: March 1, 2021

CLSM images of Tasmanites (fossil, unicellular algae). Micrometer-scale punctiform shaped pores with maximum emission intensity at the edge Source: BGR

In vitrinite-lean sediments or sedimentary strata devoid of vitrinite, the normed standard procedure of vitrinite reflectance measurements according to DIN 22020-5 (2005) has considerable limitations, when applied to determine thermal maturity. Vitrinite macerals are microscopically recognizable, individual organic constituents of fossilized plant material (humous substances), which originate in course of biochemical and geochemical transformation processes and as a result of burial in sedimentary basins or depocenters. Vitrinite macerals belong to the so-called vitrinite maceral group. In addition to vitrinite maceral group, macerals of inertinite and liptinite groups are often being observed in vitrinite-lean sediments or sedimentary strata lacking vitrinite.
Within the framework of CLSM-based method development, thermal maturity data are to be derived with aid of different spectral fluorescence parameters. Such thermal maturity data are relevant for the following BGR topics: Energy resources, Final disposal of radioactive waste, Subsurface use, as well as Polar research. Aim of the investigations is based upon former spectral fluorescence measurements performed on varied macerals of the liptinite group under conventional incident light microscopy (e.g.: Teichmüller and Durand, 1983; Araujo et al., 2014), and CLSM (Kus et al., 2012; Hackley et al., 2013; Hackley and Kus, 2015; Kus, 2015; Kus et al., 2016). The CLSM method is established at the BGR Laboratory for Geochemistry and Organic Petrography since several years.
With aid of CLSM-based method, spectral fluorescence examinations are to be performed on selected marine fine-grained clastic sedimentary rock samples (siltstone and claystone). A comparison between the existing vitrinite reflectance measurements and the CLSM-associated spectral fluorescence parameters will enable to improve the understanding on the correspondence between both parameters. Further, a CLSM-based investigation of thermal maturity in vitrinite-lean sediments or sedimentary strata lacking vitrinite will be performed.
With the increase of thermal maturity, changes in spectral fluorescence properties of macerals of liptinite group can be detected and observed from thermally immature to overmature stages of dispersed organic matter.
The development of CLSM-based method to derive thermal maturity in vitrinite-poor sediments or sedimentary strata lacking vitrinite is conducted in a tight cooperation with organic petrographers at USGS (USA) and at the State Key Laboratory in Guangzhou (China). In addition, a cooperation with the International Committee for Coal and Organic Petrology (ICCP) in the field of standardization of spectral fluorescence measurements is to be further continued.

Literature:

• Araujo, C. V., Borrego, A. G., Cardott, B., das Chagas, R. B. A., Flores, D., Gonçalves, P., et al. (2014). Petrographic maturity parameters of a Devonian shale maturation series, Appalachian Basin, USA. ICCP Thermal Indices Working Group interlaboratory exercise. International Journal of Coal Geology 130, 89-101.
• DIN 22020-5:2005-02, 2005. Rohstoffuntersuchungen im Steinkohlenbergbau - Mikroskopische Untersuchungen an Steinkohle, Koks und Briketts - Teil 5: Reflexionsmessungen an Vitriniten. DIN Deutsches Institut für Normung e.V. Beuth Verlag GmbH, p. 1-21.
• Hackley et al., 2013. Application of excitation-emission fluorescence microscopy to thermal maturity of geological samples. Geological Society of America [abs.], 45(7), p. 650.
• Hackley and Kus, 2015. Thermal maturity of Tasmanites microfossils from confocal laser scanning fluorescence microscopy. Fuel 143, 343-350.
• Kus et al., 2012. Confocal laser scanning microscopy (CLSM) applied to microstructural analysis of Tasmanites in the Huron Member of the Ohio Shale, Appalachian Basin, USA. Schriftenreihe der Deutschen Gesellschaft für Geowissenschaften, [abs.], 80, p. 432.
• Kus, J. 2015. Application of confocal laser-scanning microscopy (CLSM) to autofluorescent organic and mineral matter in peat, coals and siliciclastic sedimentary rocks — A qualitative approach. International Journal of Coal Geology 137, 1-18.
• Kus et al. 2016. Solid bitumen, bituminite and thermal maturity of the Upper Jurassic-Lower Cretaceous Chia Gara Formation, Kirkuk Oil Field, Zagros Fold Belt, Kurdistan, Iraq. International Journal of Coal Geology 165, 28-48.
• Teichmüller. M., Durand B., 1983. Fluorescence microscopical rank studies on liptinites and vitrinites in peat and coals, and comparison with results of the Rock-Eval pyrolysis. International Journal of Coal Geology 2, 197-230.