The organic petrology of graptolites in sections parallel and perpendicular to the bedding: Implication for thermal maturity evaluation

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F61389005%3A_____%2F25%3A00640542" target="_blank" >RIV/61389005:_____/25:00640542 - isvavai.cz</a>

Result on the web

<a href="https://www.sciencedirect.com/science/article/pii/S0166516225002009" target="_blank" >https://www.sciencedirect.com/science/article/pii/S0166516225002009</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1016/j.coal.2025.104883" target="_blank" >10.1016/j.coal.2025.104883</a>

Result language

angličtina

Original language name

The organic petrology of graptolites in sections parallel and perpendicular to the bedding: Implication for thermal maturity evaluation

Original language description

Graptolites are widely presented in the Ordovician-Silurian Wufeng-Longmaxi Formations and other Lower Paleozoic marine shales throughout the world, and their reflectance is regarded as an effective index for the thermal maturity assessment of the graptolite-bearing shales devoid of vitrinite. Graptolites display distinct optically biaxial features, and the optical characteristics and reflectance of graptolites reveal significant differences depending on orientation of respective graptolite fragments relative to the bedding planes. However, specific studies on these optical discrepancies remains limited, resulting in confusion and/or substantial errors in thermal maturity assessment of graptolite-bearing shales. In this study, the organic petrological method was employed to compare the optical characteristics of graptolites in sections parallel and perpendicular to the bedding. Graptolites and in-source solid bitumen (SB) are the dominant organic components in the Alum and Wufeng-Longmaxi graptolite-bearing shales, and the liptinites are only detected in low maturity samples. In the studied sediments, both non-granular and granular graptolites were identified in abundance, but non-granular graptolites, which exhibit higher reflectance and stronger anisotropy than granular graptolites, were the predominant species. The intense positive correlations between the mean random reflectance (GRo) and true maximum reflectance (Rmax) and bireflectance of non-granular graptolites indicate their increasing anisotropy with maturation. Rmax values in sections parallel to the bedding are slightly lower than or equal to those in sections perpendicular to the bedding, and the mean maximum reflectance (Rmax), the intermediate reflectance (Rint), and bireflectance are lower than those in sections perpendicular to the bedding. GRo values in sections parallel to the bedding display a strong positive correlation with GRo in sections perpendicular to the bedding, and the former are higher than the latter. GRo exhibits stronger positive correlations with Rmax, Rmax, and bireflectance in sections perpendicular to the bedding than those in sections parallel to the bedding, revealing the stronger anisotropy of non-granular graptolites in sections perpendicular to the bedding. According to the reflectance discrepancies of non-granular graptolites in sections parallel and perpendicular to the bedding, several equivalent equations are proposed to evaluate the thermal maturity of Ordovician-Silurian graptolitesbearing sediments.

Czech name

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Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

—

OECD FORD branch

10505 - Geology

Project

Result was created during the realization of more than one project. More information in the Projects tab.

Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2025

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Name of the periodical

International Journal of Coal Geology

ISSN

0166-5162

e-ISSN

1872-7840

Volume of the periodical

310

Issue of the periodical within the volume

5 November

Country of publishing house

NL - THE KINGDOM OF THE NETHERLANDS

Number of pages

13

Pages from-to

104883

UT code for WoS article

001582930200001

EID of the result in the Scopus database

2-s2.0-105016306938