Vitrinite and vitrinite like solid bitumen reflectance in thermal maturity studies: Correlations from diagenesis to incipient metamorphism in different geodynamic settings

• Published in: International journal of coal geology 2016-03, Vol.157, p.52-73
• Main Authors: Ferreiro Mählmann, Rafael, Le Bayon, Ronan
• Format: Article
• Language: English
• Subjects: Basins; Bitumen classification; Bitumens; Correlation; Correlation analysis; Diagenesis; Geodynamics; Geology; Incipient metamorphism; Reflectance; Reflectivity; Rocks; Vitrinite like solid bitumen reflectance; Vitrinite reflectance
• ISSN: 0166-5162; 1872-7840
• DOI: 10.1016/j.coal.2015.12.008

Vitrinite reflectance (VR) is a useful and reliable parameter to monitor the level of organic matter maturation from the immature stage to graphite. Additionally, VR is a useful and essential tool in modelling the temperature–maturation time path. Huminite/vitrinite-bearing sedimentary and meta-sedimentary rocks can be used to reconstruct the thermal history of basins or orogenic terranes throughout their geological history. The usefulness of VR evidently depends on the presence of huminite/vitrinite phytoclasts. However, pre-upper Silurian rocks and many organic-rich marine rocks (e.g. sapropelic sediments) lack of huminite/vitrinite particles. Furthermore, vitrinite is sparse in carbonate sediments. However, the presence of bitumen in rocks lacking Type III kerogen provides a valuable aid via its reflectance (vitrinite like solid bitumen reflectance — VlBR, and/or solid bitumen reflectance — BR) to fulfil the above-described tasks that VR enables. This study presents basically a relationship between BR/VlBR and VR for various types of geodynamic settings and over the largest possible range of maturation levels so that VlBR may be used as a substitute for VR. Whereas the effort to correlate VR with BR is not novel, it is the first time that the VR/BR correlation is re-judged, discriminating bitumen from VlB. Moreover for the first time the correlation is established for various geodynamic settings. The investigated geological contexts are:(1)sedimentary basins (e.g., the Saar, Ruhr, Ohio, West Virginia, and Petrosani basins);(2)metasedimentary terranes occurring as inverted basins in orogenic belts (e.g., from the Subalpine-Molasse, Helvetic, Austroalpine and Danubian nappe systems) and having suffered from very low to low grade metamorphism (from anchizone to greenschist facies);(3)metasedimentary terranes (e.g., slates and schists from the Franciscan and Alpine belts) that were subducted at anchizone to blueschist facies conditions; and(4)metasedimentary rocks affected by contact metamorphism. Together, the frequent geological settings are referred and most of the earth geothermal conditions and heat fluxes considered. Despite temperature, pressure, and heating time, also heat flow gradient dependences cannot be ignored. •A subdivision of three solid bitumen types is proposed and characterized in high-grade diagenetic to very low-grade metamorphic rocks.•Reflectance development and optical anisotropy initiation in vitrinite and solid bitumen is shown, d