Abstract
Jurassic and Triassic coals and organic matter-rich shales of the Tabas Basin, Iran, were investigated with respect to their thermal maturation and petrographic composition. The Triassic coals of the Parvadeh coal field range in vitrinite reflectance between 1.17% and 1.37% and the Jurassic coals of the Mazino coal field between 2.08% and 2.29% VRr. Maceral analysis revealed a predominance of vitrinite in all samples, with slightly higher percentages of inertinite in the Jurassic samples. Rock–Eval analyses confirm the presence of type III kerogen in the Triassic coals, while the Jurassic coals contain strongly carbonized residual kerogen. The range of sulfur contents for coals from the Parvadeh coal field (0.37% to 4.64%) and Mazino coal field (0.45% to 2.92%) is related to the effect of marine water in peat. The studied samples are characterized by the predominance of short- over long-chained n-alkanes. The relatively high Pr/Ph ratios indicate predominance of terrestrial organic matter whereas Pr/n-C17 and Ph/n-C18 ratios prove oxic conditions during deposition. In addition, the DBT/Phen ratio shows that these coals formed in fluvial/deltaic environments. Molecular geochemical parameters such as carbon preference index (CPI, 0.99–1.04), methyl phenanthrene index (MPI, 1.20–1.60), methyl naphthalene ratio (MNR, 1.61–3.45), and ethyl naphthalene ratio (ENR, 4–6.78) confirm the high maturity of the samples. Burial and thermal history reconstruction indicates necessity of an erosional thickness of about 4000 m in the Parvadeh area. Towards the Mazino area, a higher basal heat flow up to 80 mW m−2 is assumed for the Paleogene leading to higher maturities.
Highlights
Coal deposits of Iran are mainly located in the northern (e.g. Alborz Basin) and central part of the country (Tabas and Kerman Basins; Fig. 1)
We focus on the three layers exploitable within the Chahrekhneh mine (K1, K2, and K3)
The microscopic analyses showed that the major maceral group in the samples from both, the Parvadeh and Mazino deposits is vitrinite (V) the samples from the Mazino deposit show a slight enrichment in inertinite (I)
Summary
Coal deposits of Iran are mainly located in the northern (e.g. Alborz Basin) and central part of the country (Tabas and Kerman Basins; Fig. 1). The Tabas Basin, located in the southern Khorasan province in northeastern Iran holds more than 60% of the country’s coal reserves, and is the most important coal mining area. This study deals with the organic geochemical and organic petrological characteristics of bituminous coals from the Parvadeh field as well as semianthracites from the Mazino coalfield (Fig. 1). The Parvadeh coalfield has an area of about 1200 km and is divided into six sections based on fault structures (Parvadeh 1–4, and northern-, and southeastern Parvadeh). We discuss some petrological and geochemical parameters of the B1, B2, C1, and D seams, sampled in the Parvadeh sections 1–4.
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