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

Kód výsledku v 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>

Výsledek na webu

<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>

Jazyk výsledku

angličtina

Název v původním jazyce

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

Popis výsledku v původním jazyce

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.

Název v anglickém jazyce

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

Popis výsledku anglicky

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.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10505 - Geology

Projekt

Výsledek vznikl pri realizaci vícero projektů. Více informací v záložce Projekty.

Návaznosti

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Rok uplatnění

2025

Kód důvěrnosti údajů

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

Název periodika

International Journal of Coal Geology

ISSN

0166-5162

e-ISSN

1872-7840

Svazek periodika

310

Číslo periodika v rámci svazku

5 November

Stát vydavatele periodika

NL - Nizozemsko

Počet stran výsledku

13

Strana od-do

104883

Kód UT WoS článku

001582930200001

EID výsledku v databázi Scopus

2-s2.0-105016306938