Assessing thermal maturity through a multi-proxy approach: a case study from the Permian Faraghan Formation (Zagros Basin, Southwest Iran)

This study focuses on the thermal maturity of Permian deposits from the Zagros Basin, Southwest Iran, employing both optical methods (Thermal Alteration Index, Palynomorph Darkness Index, Vitrinite Reflectance, UV Fluorescence) and geochemical analyses of organic matter (Rock Eval Pyrolysis and MicroRaman spectroscopy) applied to the Faraghan Formation along two investigated Darreh Yas and Kuh e Faraghan surface sections. Furthermore, an integrated palynofacies and lithofacies analysis was carried out in order to integrate the few studies on the depositional environment. The Faraghan Formation, which is widely distributed in the Zagros area, generally consists of shale intercalated with sandstones and pebble conglomerates in the lower part, followed by a succession of sandstone, siltstone and shaly intercalations and with carbonate levels at the top. The integrated palynofacies and lithofacies data confirm a coastal depositional setting evolving upwards to a shallow marine carbonate environment upwards. Rock Eval Pyrolysis and Vitrinite Reflectance analysis showed that the organic matter from samples of the Darreh Yas and Kuh e Faraghan sections fall in the mature to postmature range with respect to the oil to gas generation window, restricting the thermal maturity range proposed by previous authors. Similar results were obtained with MicroRaman spectroscopy and optical analysis such as Thermal Alteration Index and UV Fluorescence. Palynomorph Darkness Index values were compared with Rock Eval Pyrolysis and vitrinite reflectance values and discussed for the first time in the late stage of oil generation.This research was funded by PRIN (2017RX9XXXY-CIRILLI), by Fondo Ricerca di Base Department of Physics and Geology, University of Perugia (SPIRICBAS2018-SPINA), by the project “Paleontological Studies and Biozonation of Paleozoic Sediments in Central Iran and Zagros Basins” (coordinator R. Rettori) and MIUR grants-SORCI to PhD School of Science and Technology for Physics and Geology (XXXIV Cycle), University of Perugia; Project “Paleontological Studies and Biozonation of Paleozoic Sediments in Central Iran and Zagros Basins” (RETTORI).info:eu-repo/semantics/publishedVersio

Occurrence of organic matter-rich deposits (Middle Jurassic to Lower Cretaceous) from Qalikuh locality, Zagros Basin, South–West of Iran: A possible oil shale resource

Organic-rich deposits of Qalikuh locality, Zagros Basin, Southwest of Iran are unconventional hydrocarbon resources considered as an oil shale, which is hosted within a carbonate succession with the age range of Middle Jurassic to Lower Cretaceous. Leco carbon, Rock-Eval VI and modified Fischer Assay analysis were performed on some outcrop samples of these resources to investigate the occurrence of oil shale. In the studied samples, mean total organic carbon (TOC) is 17.3 wt.% and the average of petroleum genetic potential (S-1 + S-2) is 98 kg HC/t rock. Furthermore, TOC has direct relationship with petroleum genetic potential. Hydrogen index (HI)-T-max diagram indicates that the organic matter corresponds to Type II kerogen of probable marine origin with high quality of oil generation. According to Rock-Eval data, and bitumen reflectance (BRr), the samples are thermally early mature. Based on the studied samples, oil yield of the Qalikuh oil shales ranges from 6.1 to 7.9 wt.%. Mean oil-gas ratio is 2.7 and mean oil yield is 56.7 l/t rock. According to the observations, the production value of Qalikuh oil shale is more or less similar in the entire studied regions. Whereas the total production is below the expected values, the produced oil is considerably lighter (higher API) than that of most other known oil shales