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Paul C. Hackley, Jolanta Kus, João Graciano Mendonça Filho, Andrew D. Czaja, Angeles G. Borrego, Dragana Životić, Brett J. Valentine, Javin J. Hatcherian

Characterization of bituminite in Kimmeridge Clay by confocal laser scanning and atomic force microscopy

International Journal of Coal Geology

Elsevier BV

2022

This work investigates bituminite (amorphous sedimentary organic matter) in Upper Jurassic Kimmeridge Clay
source rock via confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM). These petrographic
tools were used to provide better understanding of the nature of bituminite, which has been historically
difficult to identify and differentiate from similar organic matter types in source rocks. As part of an International
Committee for Coal and Organic Petrology (ICCP) working group, an immature (0.42% vitrinite reflectance),
organic-rich (44.1 wt% total organic carbon content) sample of Kimmeridge Clay was distributed to multiple
laboratories for CLSM characterization. The primary observations from CLSM imaging and spectroscopy include:
1) the interpreted presence of Botryococcus algae as a contributor to bituminite precursors; 2) color red-shift of
sulfide reflectance and bituminite auto-fluorescence from below the sample surface; 3) positive alteration of
bituminite from laser-induced photo-oxidation of the sample surface, including fluorescence blue-shift; 4)
fluorescence blue-shift associated to higher fluorescence intensity regions in bituminite indicative of compositional
(fluorophore) differences; 5) the need for fluorescence spectroscopy standardization as applied via CLSM;
and 6) the suitability of CLSM fluorescence spectroscopy to predict solid bitumen reflectance from bituminite
spectral emission via calibration to an extant dataset. Secondary CLSM observations include detection of reflected
laser light from highly reflective inclusions in bituminite, including sulfides and fusinite, and radiolytic
alteration of bituminite caused by substitution of U for Fe in sulfides. Findings from AFM include the observation
that surface roughening or surface flattening of bituminite are induced by differential broad ion beam (BIB)
milling and are dependent on the location and scale of AFM topology measurement. This result highlights our
still limited understanding of the effects of BIB milling on sedimentary organic matter and indicates the need for
further research before this technique can be advanced as a standard practice in petrographic sample preparation.
Collectively, the results of this study illustrate the general applicability and versatility of AFM and CLSM as
tools for organic petrology research, specifically for better understanding of the nature and properties of the
bituminite maceral.

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10.1016/j.coal.2022.103927

0166-5162

Битуминит, Kонфокална ласерска скенирајућа микроскопија, Mикроскопија атомских сила, Органска петрологија, Термичка зрелост

Bituminite, Confocal laser scanning microscopy, Atomic force microscopy, Organic petrology, Thermal maturity

https://api.elsevier.com/content/article/PII:S0166516222000039?httpAccept=text/xml

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OI176007 - Геохемијска испитивања седиментних стена - фосилна горива и загађивачи животне средине

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