Search

Coal, especially the inertinite in it, is highly sensitive to climate changes, showing an obvious response to paleoclimate conditions, in particular, to paleo-oxygen concentration (pO2). In this study, the inertinite abundance data of typical coal-forming periods in China were systematically collected and analyzed. Its characteristics and control factors were studied, and its evolution was established. Based on inertinite abundance data, pO2 evolution curves of various coal-forming periods in China were established, which fluctuated between 15% and 30% during the entire Phanerozoic. The inertinite abundance in coal deposits during Paleozoic in China was basically consistent with that of other areas of the world, while it was quite different globally from the Mesozoic to the Cenozoic. The results show that the inertinite abundance in coal deposits is controlled by pO2 and other factors including climatic zones, plant differentiation, sedimentary environments, and tectonic activities. The inertinite abundance in coal deposits in China during the Jurassic was high, suggesting dry paleoclimate of inland China.

Inertinite is an important type of organic maceral in coal deposits, and also an important geological information carrier of coal forming environ ments. In the southern section of the Ordos Basin, the No. 4 inertinite-rich coal seam of the Middle Jurassic Yan’an Formation in the Binchang Coal field was selected as an example to study the genetic mechanism of the inertinite. In this study, the results obtained from experimental tests of coal rock, including principal and trace elements, stable carbon isotopes, scanning electron microscopy, inertinite reflectance, sporopollen and free radical retorting methods, were analyzed. Then, the findings were combined with the previous understanding of the oxygen content in the atmosphere and ground fire characteristics, in order to discuss the genesis mechanism of inertinite in the No. 4 coal seam. The obtained research results were as follows: (1) During the coal forming period of the No. 4 coal seam, the overall climate had been relatively dry. There were four relatively dry-wet climate cycles in the No.4 coal seam, which were controlled by the eccentricity astronomical period. The inertinite content were relatively high during the dry periods; (2) The temperature range suitable for microorganism activities during the oxidation processes was between 0 and 80℃ . The simulation results of the free radical concentra tions showed that the maximum temperature of fusain in the No. 4 coal seam during the process of coalification had not exceeded 300℃ , which was significantly higher than the temperature range of microorganism activities. Therefore, these were not conducive to the activities of mi croorganism and formation of inertinite during the coal-forming period; (3) The genesis temperature of the inertinite in the No. 4 coal seam was calculated according to the reflectance of the inertinite, which was lower than 400 ℃ . This result supported the cause of wildfire of the inertinite and reflected that the type of wildfire was mainly ground fire, along with partially surface fire. Moreover, the paleogeographic location, climatic conditions, atmospheric oxygen concentration, etc. of the study area showed that the conditions for wildfire events were in fact available; (4) There were dense and scattered fusinite observed in the No. 4 coal seam, and the thickness of cell walls were found to differ. It was speculated that this was related to the type of wildfire, combustion temperatures, com bustion timeframes, and different initial conditions of the burned objects during the coal forming periods.