Petrology, rank and evidence for petroleum generation, Upper Triassic to Middle Jurassic coals, Central Alborz Region, Northern Iran

摘要

Upper Triassic to Middle Jurassic coals from the Alborz region of northern Iran were analyzed by reflected light-fluorescence microscopy and Rock Eval 6~R pyrolysis to evaluate their regional rank variation, degree of hydrothermal alteration, and petroleum generative potential. The coal ranks in the region range from a low of 0.69 percent Ro_R in the Glanddeh-Rud area to a high of 1.02 percent Ro_R in the Gajereh area. T_(max) ( degC) values (Rock Eval 6 pyrolysis) also increase progressively with increasing vitrinite percent Ro values, however T_(max) is suppressed lower than would be expected for each rank ranging from 428 deg C for the Glandeeh coal to 438 deg C for the Gajereh coal. T_(max) suppression may be caused by maceral composition and soluble organics within the coal. Moderately high hydrogen indices, persistent and oily exudations from the coals during UV exposure, and traces of hydrocarbon fluid inclusions suggest that liquid petroleum was likely generated within some of the coals.